Shock Cooling - Myth Busted!!

[Jabawocky]

Here is a little story I thought I would share with you.


One of the great Old Wives Tales, Shock Cooling!

Well I am not sure how easy it would be to do this, apart from spear into a lake, that would do it for sure, but even in an extreme descent with 2000FPM plus ROD I can't seem to do it.

So here is the story, last Saturday returning from St George Qld to Caboolture (Brisbane) I climbed to FL130 and was enjoying 45 knots on the tail, so a GS of 210 knots. As I was about 20 minutes out, I advised BNE CEN that my TOD point was 46 miles from YCAB and that was 13 minutes, to allow for a 12000' descent to circuit area altitude. I do this so it helps them with all the crossing traffic I have going against the flow. My tracks are often a pain I am sure.

Anyway 13 minutes comes and goes, and I think any second now........10 minutes, hmmm I wonder if my mate is on BNE APP this afternoon. Anyway they are busy with jet traffic and RFDS etc into YBBN, so I figure I can fit in with whatever keeps everyone happy. At 6.5 minutes to run, 22NM to destination.....the following occurs;
BNE CEN: Lima November Lima, Descend 6000 and contact BNE APP on 124.7 , I do the read back and over I go to 124.7,
LNL: Brisbane Approach, Lima November Lima FL130 cleared 6000 and Visual.
BNE APP: Lima November Lima, cleared to leave on descent, Brisbane QNH 1014, good afternoon Brownie!
LNL: Cleared to leave on descent, 1014 LNL....and gooday to you NP and did you have something to do with the late descent?
BNE APP: I have NO Idea what you are talking about <laughing>
LNL: WATHCH THIS <laughing>

Now 6 minutes and 20 miles

Now not exceeding VNE (by TAS), and then as the bumpy bits over the mountains (ok hills) staying out of the yellow arc and not wanting to lose the game, I had a job to do. At times the ROD was around and over 2000 FPM, and I watched happily the CHT's very slowly decline. The Throttle was pulled right back and the RPM about half way down was increased to 2550 to help the cause. Pitch went from +1 in cruise to -8.5 at times and mostly -5 to -7 and this was a very different view of the Brisbane region.

So I have downloaded the data, and done a Delta T on CHT and the graph shows a flat line. The cumulative Delta T shows a greater ramp for the taxi and take off than at any point in the descent. Unfortunately the Delta T will not upload to the SAVVY site, however you can see the slope on the curves.

I have uploaded the file to the Savvy site, you can click on the extra displayed data to show Vert Speed or other things.

https://my.savvyanalysis.com/public/9e2cc04c-e1f4-41da-b401-b50788c2095a

No doubt some flat earthers will tell me that the cylinders will fall apart due cracks in a few hundred hours.

It is pretty hard to shock cool and engine that is already cool!

Shock Cooling - BUSTED! :}

[Frank Arouet]

Oh goodness what have you done?

[NIK320]

Awesome graph..

If you zoom in on the descent you can see the CHT is steadily dropping at 10*/min
If only the data continued after shut down.. How long does it take the remaining 270* to dissipate??

[Shagpile]

I've got another one - is it the rate of cooling/heating, or the actual temp.

My understanding is that hotter temps, above 190-200degC result in significant cylinder wear.

But if you slowly cool the engine to 100-110 deg and then glide descend at high rates of descent, and the CHT remains stable, does the fact that the engine is turning over cooler (and tighter seals I guess?) result in significantly more wear, even at minimal power & RPM?

[I realise a go-around at low CHT will be where a lot of wear occurs, but like the op, I'm more interested in if running at low CHT in a glide actually does any damage]

[VH-XXX]

Would like to see the same level of analysis on a parachuting aircraft Jabba.

[adsyj]

Oh goodness what have you done?

Haha should be good.

Hope you have not jinxed yourself Jaba;)

[Weheka]

I would have to agree, after probably 12000+ descents from 12000ft to SL in the Cessna 180/185, I have never experienced a cracked cylinder. I would always leave RPM at 2200 or 2300 and pin the MP at that as well when it caught up. Descent rate would be around 3000fpm and airspeed quite high in smooth air. In later years I had an engine monitor etc.
http://i303.photobucket.com/albums/nn137/jskerr-photos/DSC01500.jpg

http://i303.photobucket.com/albums/nn137/jskerr-photos/IMG_6836.jpg

[Jack Ranga]

What happened at 14:10 Jabba? (you didn't fart did you?)

Doggies \\ //

[Jabawocky]

hehehhehehe :}

yeah I deliberately did all the bad things, throttle closed, increased RPM to increase ROD, left the mixture alone from what was 37-38 LPH in the cruise.

Ohh yes the graph after shut down!

Taxi in the temps went from 256 to 276 and then after shut down they went up! Then they went down at 1Deg F every 6 seconds, then the monitor was shut down.

So shut down is just as nasty! :} And maybe worse! No oils moving around :}:eek::} :E

Ohhh dear me...... seems those rednecks Braly Deakin and Atkinson were not talking out their data ports after all! :D

[Jabawocky]

Jack you trouble maker!! Doggies!! \\ // from Jnr Jaba to ya!:ok: And happy fathers day for next Sunday!:ok:

I was just doing some experiments on how far LOP I could go and see what the speeds did.

Lucky I did not include a high altitude WOTLOP mag check in that lot! :E

hey whatever you do, do not post a link to this in the Private Flying Forum, you may start a war......and besides, I may want to save this little gem for a later posting!

A kiwi or two might know what I mean :E

[prospector]

It is pretty hard to shock cool and engine that is already cool!

Do you think that perhaps you have answered your own query??

Shock cooling can and will damage a piston engine very rapidly under the right conditions, or wrong conditions.

Try carting a ton of fertiliser for a climb of maybe 2,000ft, max continuous power, relatively slow speed, sow the load, pull the pwer and descend rapidly back to the strip. Do this maybe 10 times an hour, for maybe 10 hour flight time day and you will soon find that shock cooling is not an old wives tale.

When I first started in Aerial Ag work, as loader driver, heard an FU24 with 300hp flat six coming up the strip sounding like an old chaff cutter,
Stopped the ops till the cowls were lifted and engine inspected, three blown plug inserts, big cracks, engineers put it down to shock cooling.

This was fifty years ago, no where near the engine instrumentation available then as is now, but if there was it would no doubt have shown just how hard these engines were worked, and would have shown, as most of us learned quite rapidly, leave a bit of power on during the descent.

[remoak]

Stopped the ops till the cowls were lifted and engine inspected, three blown plug inserts, big cracks, engineers put it down to shock cooling.

This was fifty years ago, no where near the engine instrumentation available then as is now

So my question would be... sure, the engineers may have put it down to shock cooling... but what ACTUALLY caused it?

Back in the day, with no hard data, it was pretty normal to blame failures on mis-handling, whether it actually was or not. Many engine shops would blame any failure of one of their engines on the pilot, and "shock-cooling" was a pretty common charge.

Back when I was younger I used to race motocross bikes, and it always used to make me wonder why my two stroke motor, operating pretty much on the edge of seizing for most of the race, could endure being occasionally dunked in freezing water without ill effect... because that really IS shock-cooling...

[Ixixly]

Would be pretty interesting to see something like this done on a C206 or C182 doing parachute ops, only obvious difference I can see if on a real hot day with the engine struggling to take a full load all the way to say 14,000ft then dropping and descending say 2,500 - 3,000 fpm, i'd imagine this would be somewhat different!! Not to mention, as prospector said, doing it up to a dozen times a day.

BUT, IMHO, you're probably right about it being hard to shock cool an already cool engine!! Most of the decent drop pilots i've known had taught me the real trick is to start letting those temps come down as soon as you're at top of climb before you start descending, that means getting the power back to just above what you need, start getting a bit of extra mixture in, cowl flaps open etc...etc...

If memory serves me right, we were told to never exceed -13 on descent (Thats 13degrees per minute on the CHT, determined using a JPI Gauge), but my memory on those numbers is a little fuzzy now!!

[prospector]

sure, the engineers may have put it down to shock cooling... but what ACTUALLY caused it?

Shock cooling caused it, from a hard climb with temps on top limit, to a high speed descent with no power does cause shock cooling.

Engineers who were responsible for fleets of up to 20 aircraft or more sould see a pattern Th aircxraft operating in locations with a long hard climb to sowing area and then a high speed descent saw a lot more cracked cylinders, plug inserts than those aircraft operating in kinder country.

, operating pretty much on the edge of seizing for most of the race, could endure being occasionally dunked in freezing water without ill effect... because that really IS shock-cooling...

Perhaps because they are two entirely different engine types, different metal masses etc.

[Arnold E]

Hmmm \, interesting one this, there is no doubt (is there?) that if you heated a cylinder to, say 350- 400 degrees and shoved it in a bucket of cold water, cracking would be possible, if not likely, however, if you shove it into air, what then? My experience leads me to believe that not much will happen except the cylinder will get cool at a fairly even rate. On the other hand, I have heard of many glider tugs that have cracked cylinders from descending too rapidly, or indeed, is this the reason that glider tugs seem to suffer an unusually high incidence of cracked cylinders? Hmmmm?:confused:

Actually Jabba what you have shown us with your graph is that your cylinders were not shock cooled, had you done that let me assure you that they would have cracked.

[remoak]

Perhaps because they are two entirely different engine types, different metal masses etc

They are... the two-stroke engine being far more powerful for a given displacement, and, when in racing tune, running on the ragged edge of destruction every race... with very tight tolerances when operating like that. Throw less than perfect lubrication into the mix... you would have thought that the racing engine, particularly with it's low mass and therefore greater susceptibility to temperature change by sudden immersion in cold water, would be far more prone to failure... but they aren't.

Anyway, hard to argue with traditional wisdom... lol

[Jack Ranga]

And happy fathers day for next Sunday

And back at ya :ok:

Say hello to the bigger Jnr!

[WannaBeBiggles]

Quite an interesting bit of data from some pretty nifty monitoring gear (gotta love technology!), but to play a bit of devils advocate here, statistically speaking the data means nothing as it isn't repeated and we have only one sample. One could easily say that the engine held up well because it was handled properly over time so held up well with a little bit of "tough love".

I would really like to see how this graph (sample 1 if you may) holds up if you repeat this over a period of time.

I'd also love to see how the graphs would compare to super or turbocharged engines.

I'm by no means discounting (or rubbishing your theory for that matter), your monitoring equipment provides some some fantastic insights in to what is happening inside the engine and gives us possible insights in to debunking a wives tale, but lets not get ahead of ourselves, I'm sure you would not get a great reception from any of your mates who own a radial engined plane if you pulled the throttle back to the stops and pointed the nose down at the ground with the assurance of "I tried this once and the graph showed it was fine" :E

Again, just playing devils advocate.

[Super Cecil]

Lots of old wives tales in aviation. Continental's seem more prone to cracking and warming up issues than Lycoming.
The more lives a cylinder has the more chance of cracking. Cylinder cracks seem less prevalent these days, people tend to put new cylinders on and I think that is part of it. The old days it wasn't unusual to have 4 or 5 lives of a cylinder before it was junked. The days Prospector was talking about the Flitchers used to have Continentals in and they had to run flat stick to get anywhere. I'm sure it was put down to shock cooling when a cylinder finally gave up the ghost after 5 or 6 thousand hours.
To talk radial folklore you have to be a deaf, dried up old fart with piles. Plenty on here like that so lets hear the old wives tales about radials. :8

[peterc005]

I have a bit of experience with this.

At my last 100 hourly check on my plane with a Lycoming O-320-E1A engine three of the cylinders had fine cracks near the exhaust valve.

The fourth cylinder had a crack aluminium welded about 400 hours ago.

As I do a lot of aerobatics in the plane I thought the problem was shock cooling

When I checked the maintenance documentation I found that the cylinders manufactured in 1971) had 3,100 hours on them, including a 10 thou overbore at 2,000 hours done about 20 years ago.

Interestingly, the Lycoming documentation said the cylinders are good for 3,000, which means they made their estimated service life.

The most economical fix was to buy four new complete Lycoming cylinder kits, which include new cylinders, pistons, valves etc. It cost the same to switch to higher compression pistons, so these were installed under an Engineering Order and I picked up an extra 10 HP. Each cylinder kit cost about $1,300.

Bottom line is that cylinders do fail, but think that it is possibly people worry too much about shock cooling and that the problem is over stated.

[Jabawocky]

prospector
Quote:
It is pretty hard to shock cool and engine that is already cool!
Do you think that perhaps you have answered your own query??


No, not really, I never had the question. However you read all sorts of threads on prune, some not in D&G which are less well informed, and folk spruik on with all manner of old wives tales, and the punters reading believe it. So facts and data are pretty good to see, and very few actually get to see it. I am fortunate, not just in what I see on my own EMS but from other sources, so it is only fair to share good facts and data when they come along.

I sent this data file complete to Mr Deakin and co as well, JD was delighted with all the other data that you just don't get from a JPI. So why not share it here. His reply started with "we're convinced :)" so I figure that was good enough!

Getting onto your anecdotal story, and I do not mean that in a derogatory manner, as I believe you when you say what you saw and was told. However as remoak has pointed out already that has always been the "claim from the mechanics".

I did refer to John Deakins articles of years gone by, and while he rightly says that getting an engine REALLY Hot, and then diving at the ground, may have some negative effect, and possibly the ag ops you refer to could be less than optimal for an nine, the vast majority of flying does not involve this.

Lets look at the scenario you describe.
> Ag plane, rough and ready, but perhaps with poor baffles and maybe fuel delivery. Without proper instrumentation you would never know.
>Climb out temps, and operating temps. Again you would never know, and it is my opinion only that this is where the damage was done. It is the opinion of others as well. but again, no data to prove one way for sure.

If the cycles of shock cooling were real, why do so many flying school aircraft not suffer from it? And they are all operated sub optimal.

I think it was most likely, given the vast data and knowledge that we have today, that the genuine observations of your ag engineers of yesteryear while valid were misguided into believing the descent was to blame. Knowing what we know now, and seeing lots of good data, it is most likely what you describe was the takeoff and delivery phase.

So maybe it involves a rethink to dropping/glider ops in order to extend life.

It is a bit like the exhaust valve failures of TCM's for the last 10-15 years, all blamed on LOP operations, even when some engines never ever went LOP. It was never about mixture and all about the reaming of the valve guides and accuracy of the fit of valve to seat.

nitey nite! :)

[Jabawocky]

prospector

SHOW ME THE DATA

Wannabe biggles..... some radials have different issues, nothing to do with cooling so please do not confuse the issues :ok:

facts and data........Wannabebiggles aid about repeated data.......come on mate, John Deakin has been writing about this stuff for 10-15 years. His data has come from not just an amazing career in pitons (flat and radial) and jets but also from being involved as an unpaid test customer of GAMI/TAT and involved in the only decent pilot education program on the planet.

So this i just Jaba proving many many many years of other proven science, by those approved to test and those who do FAA approved testing. This is no way a java revelation. Just proving known facts, and those still surrounded in folklore myths (OWT's).

Hey ranga

DOGIES!!!!!!!!! \\\\ ////

Anecdotal evidence...but from a reliable source

I was chief pilot of a busy skydiving operation with 3 Cessna 185s which have TCM 520s. I was involved with the operation in various capacities for 25 years.

We would climb at gross mostly on hot days, always at Vy, to 11,500. Descend empty as fast as we could for the next load.

Always had good experience with cylinders, mostly because we flew alot.

Shock cooling is obviously a myth.


This was from the USA, and in response to my data, just saying...... :ok:

[A37575]

big cracks, engineers put it down to shock cooling.


From reading John Deakin's articles on engine handling and so called shock cooling, I realise he has done a great deal of high class research on the subject. On the other hand almost all the LAME's I have met over many years have a huge variety of personal opinions on engine handling invariably gleaned from their apprentice days from their teachers - who passed it on from their teachers who were LAME's and so on.

LAME's and their ilk may know how to tear down and build up engines and fix things but the majority do not conduct further in-depth reading once they have their licence. Therefore to say "engineers put it down to shock cooling" means nothing since they are personal opinions and not hard measured data.
While I listen what an LAME has to say, I also treat his opinion on engine handling with great reservations knowing it is a personal opinion only.

[Ixixly]

Jabawocky, could it not also be that in that Quote you posted, its as I was saying, its hard to do if you're taking care of the engine and doing the right things?

Obviously I think everyone can agree that Shock Cooling is a real possibility, but it seems (Keep in mind this is based on my own relatively low experience and the data from your graph) that it would mostly be caused by poorly managed engines and perhaps those with higher T/Os and LDGs cycles operated in hotter climates?

I've always wondered somewhat about the relationship between Dropships going up to say 10,000ft or more and the positives that the cooler air up there have on the engine in respect to Shock Cooling. Wouldn't it be fair to say that as you get higher that the cooler temperatures can help the engine from getting as hot as one operated lower and then, when on Jump Run, as the power is brought back, with the cowls open and the nose brought down the effects of being nice and high would allow the engine to cool somewhat before you even begin your descent?

I always remembered the worst part of any hot day was the first 5,000ft or so with the aircraft at gross and watching all the temps get waaayy waaaayyyy waaaaaayyyyyy up the dials, after that though you were usually free and clear!

[jas24zzk]

I think its operation type dependant. Having a a gliding background, i've seen plenty of cracked cylinders.

Tug ops would have to be the worst environment. its full noise to TOC (normally 2000') normally at 60 knots. then power off and nose down for a stuka descent.

Looking at jaba's data and thinking about the other ops, most of them have a period where they are running at a lower power level.

Even meatbombers run for a period that full power is not being used. Looking at Jaba's data, the run into the drop appears to be enough time to drop the CHT's back to cruise levels.

Someone mentioned training aircraft doing laps. Same would apply as PJ ops. The run on downwind at less than full power, is enough to lower the temps to an acceptable range. And if you think about it truly, in a warrior, turning base you drop the power to 1700 rpm, which means you are still generating power/heat. Rethinking it a lil, it might not be as critical as PJ ops, as the climb is shorter so the chance of reaching max CHT lowers.


I relate this whole thread back to the one we had about turbo charger cool down.
In this case, for most operation types, it's an old OWT, however in an operation like glider tugging, it is a very real threat, and one that needs carefull management.

[jas24zzk]

I've always wondered somewhat about the relationship between Dropships going up to say 10,000ft or more and the positives that the cooler air up there have on the engine in respect to Shock Cooling. Wouldn't it be fair to say that as you get higher that the cooler temperatures can help the engine from getting as hot as one operated lower and then, when on Jump Run, as the power is brought back, with the cowls open and the nose brought down the effects of being nice and high would allow the engine to cool somewhat before you even begin your descent?

You are on the right path here.

And this next bit taken as a whole only applies to naturally aspirated,
The thing to remember, is that the by product of power production, is heat. So as you climb past Full throttle height, the amount of heat you are capable of generating lessens. Then you add in the fact you pointed out the air is cooler. So heading towards the top of climb, things are working in your favour (except climb rate). Even the best jump pilots will have 30-60 seconds of run into the drop at a reduced power level. Yes its cooling, but not at a prodigous rate, as 1. the engine is still producing power, slowing the cooling rate, and 2, still at a slow airspeed, so cold air is not being rammed through the baffles. Using jaba's graph as a guide, i wouldn't expect a jump engine to be much hotter than normal cruise once he points the nose at the ground, and CLOSES the cowl flaps to keep the heat in.

I always remembered the worst part of any hot day was the first 5,000ft or so with the aircraft at gross and watching all the temps get waaayy waaaayyyy waaaaaayyyyyy up the dials, after that though you were usually free and clear!

That might be where you need to use your head, lower the nose a lil, gain an extra 5 knots to make the owner a lil happier.

[Jabawocky]

IXILY and Jaz

I think if you mean getting an engine up to 475F or something stupid, and then doing a dive, it may be possible. However I doubt from basic engineering understanding that the Delta T can still exceed something reasonable. I have not tried it, but I can assure you a few of the known "guru" folk do not see it being reasonable. You will have to trust me on that one.

If you dive at twice the rate, say 4-5K FPM will you double the cooling rate? how about square the rate? It is still bugger all. It is still less than the heat up rate, or the after shut down rate.

It is like the turbo cooling debate, everyone with an pinion has never stuck multiple thermocouples to a turbo and done it. The one group who have have a bunch of data that proves the old myths are full of BS. Unless you have data to prove the other data wrong, well its just an opinion.

Meat bombers do have a period of transition, even they can't do engine suicide, otherwise the grass darts would not get out!

[jas24zzk]

i'm with you jaba,

was on the turbo debate also.........

Of i was to put my position down, i'd say in short.

1) in general operations, operating within the manufacturers guidlines, shock cooling is pretty much impossible.

2) operations like glider towing do present a risk of shock cooling. No manufacturer offers guidlines on engine management for this type of operation, so everything done, is based on OWT's, and the very real and frequent cylinder cracking that occurs.

[Weheka]

I always used 380 dgrs as a top limit in the climb and did not usually lean below around 5000ft depending on the day. Regardless until level on jump run it was not below 18 gph at 12000 ft, I would lean it more before descent, close cowl flaps etc temps now in low 300s dgrs.

Also at WOT and full rich at the start of the climb I liked the fuel flow on the red line, to me this was minimum, not maximum. The only trouble I ever had with cylinders was sometimes having to relap exhaust valves. I always had factory remans rather than rebuilds, mainly to save time.

I did use LOP on any cruise flights, going to maintenance etc, and it worked very well, just as advertised.

[Tankengine]

You guys all seem to believe the wives tale that your fancy gauges have their probes in exactly the right position for all enviroments and that cylinders have equal temps across them.:ugh:
With a bit of intelligent operation shock cooling should not happen, but nothing is fool-proof.:E

[mcgrath50]

Interesting as always Jaba, thanks.

the only decent pilot education program on the planet

Yours isn't bad either :ok:

[prospector]

SHOW ME THE DATA

Sorry cannot do that, the technology was not available at that time. What was known was that some pilots were very good at cracking cylinders and some never did. It had to do with the operating environment ie Some area's had an hourly charge out rate, and some charged ton/mile. Some had long hard climb at max temps followed by power off descent.

On the hourly rate the farmer was often cracking the whip for the fastest job, on the ton mile rate the Company kept a very close eye on times, so the power off high speed descent was an easy way to save a few minutes, but was hard on cylinders.

As has been stated by Glider tug and parachute operators the problem was much alleviated when a trickle of power was left on for the descent.

Perhaps if the problem of cracking cylinders in these type operations was referred to as thermal cycling rather than shock cooling it would be more accurate.

A good example would be the Lycoming IO720 when used in the agricultural role had a TBO of around 1,500 hrs.

The same engine used in a Queenair regularly flying 2:30 legs we got the TBO up to 2,400 hrs.

[hiwaytohell]

Perhaps if the problem of cracking cylinders in these type operations was referred to as thermal cycling rather than shock cooling it would be more accurate.

Yes I think this is closer.

Some years ago I spent some time with a technical representative from Teledyne Continental in respect to a court case that involved cracked cylinders on a couple of TSIO-520s. The matter involved a dispute where one party was arguing the cylinder cracking was caused by the operator and the other party was arguing the cracking was caused by fatigue (despite the engines only having about 300 hours time since new).

The cylinders are made up of a number of different metals with different expansion rates, (aluminium alloy heads, steel barrels, steel valves, steel spark plugs, steel studs & inserts, bronze valve guides and stainless or inconel exhausts etc).... these all expand and contract at different rates as a result experience considerable stress during rapid temperature changes.

If you rapidly apply full power to a cold engine or cut the power to hot engine and allow it to rapidly cool as would occur after TOD before a high speed descent the amount of stress over a period of time will cause the cylinders to crack.

On the IO-520 and TSIO-520s one of the weakest points is between the upper spark plug insert and the fuel injector port. If repeated rapid engine cooling occurs, the alloy cylinder head will cool much quicker as a result of the cylinder cooling fins dissipating the heat much more quickly than other parts of the head such as the steel spark plugs... as a result the hotter plug causes considerable stress on the now cooler (and shrinking) plug hole... over time the stress is released by cracking from the plug hole (often towards the injector)

A similar thing occurs on the 360 Lycomings where you will get cracking in the exhaust port emanating from stress around the valve guide and seat.

Another example was on the TSIO-520s, in aircraft like the C402, where repeated rapidly applying full power on take off without warming up the engines properly would likely manifest itself by the alloy cylinder head separating from the steel cylinder barrel. This is because the alloy head and combustion chamber heat up far more quickly that the barrel... the end result is cracking and eventual separation between the head and barrel.

Good engine warm up, smooth application of power, smooth reduction of power and good temperature management will result in far fewer engine problems including cracked cylinders and wear, particularly older manufactured engines where the manufacturing process resulted in metal that is not quite a strong.

As for parachute & glider ops, we worked out years ago by slowly pulling of the power prior to drop or release, and carrying some power on descent until slowed up on final approach, exerted far less stress on the engines.

I wish I still had the Continental report from the court case, but it was a beautifully written technical document that said the operator was a hamfisted mug!!

[Ultralights]

i have heated quite complex aluminium/steel/titanium aircraft fittings/casting and forgings to well over 500degC for quite a few hrs, then dunked them in room temperature water..

never had one crack.. (shock cooling in manufacture tends to create a part thats more resistant to cracking)


is it possible that cylinder cracking might be caused by incorrect torque down procedures? ill fitting/re-used gaskets?.

[Fred Gassit]

Uniform heating shouldn't introduce unwanted internal stresses in a properly designed component.
The thermal gradient (and number of cycles) within the cylinder itself are the primary causes of thermal fatigue problems, at least as I was taught.
Using reworked cylinders seems to set one up for these sort of problems.

[Trent 972]

Jaba, really interesting data in the graphs. Thank you for posting. Probably the most interesting stuff I've seen on here for ages.
Just a couple of questions if I may be so bold.
In accordance with your statement Throttle was pulled right backCan you confirm that
One minute after TOD as you passed 11,000 ft with a MAP of 15.3 inches and a Fuel Flow of 32 Litres/Hour the throttle was at Idle?
The MAP increases to 16.4 inches over the next 3 minutes as you approach 9,000 ft at which time the MAP drops to 13.6 inches.
The MAP then increases once again to 14.2 inches over the next minute as you pass through 8,000 ft and it seems that an idle MAP (MAP drops to 8.5 inches) is indicated as you passed 6,400 ft @14.37 (MAP drops to 8.5 inches) until you reach 2,800ft at 14.39, indicating that twice or (perhaps only once with the RPM increase) that the throttle was reduced again.
The delta T from 13k down to 6,400 ft on cylinder #1 was a modest 26 Degree F. However the Delta T from 6,400ft to 2,800ft on that cylinder was 39 degrees F. coinciding with the 8.5 inch MAP.
It seems to me that the data shows (by the step increases in MAP as air density increases on descent, that the engine wasn't fully at idle until passing 6,400ft).
I'm just a poor layman trying to interpret that awesome data graph.
I find the info you provided fascinating. Well done.

[diddly squat]

Do note this is a Lycoming, and not a Cuntinental who seem to have much bigger issues with this.

Anyone like to comment on using TAS not IAS for VNE ?

In cruise, roughly what % power you using? Something like 65%
I noticed 18.5 MP / 2450 RPM in cruise. Why use climb RPM? just curious, not saying it is bad, just trying to learn other reasoning?

What is "Pitch" on the graph?

Fantastic graph by the way.

[nomorecatering]

It seems that they build engines better these days. I have long suspected that many of the failures of the past have been down to the fact that while the basic design was right, the manufacturing of the engine was so poor.

From FLYING APR 2012
Improvements in modern reciprocating engine production all start with the switch-over to more modern machining, which can cut metal to incredibly close tolerances. This means that a Continental, Lycoming or Rotax engine built today is a physically better aircraft engine than has ever been mass-produced. You might recall that Continental at one point offered a Platinum-series engine that cost more to buy but had tighter tolerances and therefore a longer warranty. With improvements in machining — including a change to automated manufacturing processes — all the engines Continental builds today meet or exceed the Platinum specifications, and so the special line has been discontinued.

[Big Pistons Forever]

The shock cooling debate has been a fixture of operating piston engines for a good long time. I think care has to be taken in out and out rubbishing "old wives" tales. Many reflect opinions that are reflective of a lot of practical experience as well as the innate conservatism of an endeavor where the penalty for getting it wrong can be unforgiving.

That been said my 02 cents are as follows

1) Understanding the effect the mixture has on engine temps is IMO generally rather poor for GA operations. In particular I just cringe when I see the mixture jammed full rich prior to the start of the descent, particularly on cool days.

2) Flying the airplane comes first. Ya do what Ya gotta do. If that means a rapid power reduction because you got held up close and high well then that is what you do.

3) Despite point 2 in general my feeling is that piston engines have a lot of hot parts moving at high speed. It would seem to me that "gentle" handling of the engine, that is slow and smooth power changes and in particular a slow reduction in power as the airplane descends will make life easier for the engine

4) I think care must be taken in interpreting EMS data. The only temperature that is measured is that at the probe. I am not sure you can automatically assume you have the entire picture of what is happening at every part of the cylinder. That been said EMS data is still extremely useful particularly in diagnosing engine faults earlier enough to prevent damage.

[remoak]

Well, one thing is for sure... this thread is a very good reason why the ancient design of most common aircraft engines should be dumped in favour of a good, reliable turbine! Try shock-cooling that sucker... it will just laugh in your face and carry on regardless... :ok:

[Jabawocky]

Trent,

How ya doing :ok:

When I was patiently awaiting my clearance to drop.....me that is not meat bombs, I had no idea I would collect the data and start this thread, so I must admit, it was not planned, initially I reset the Assigned Altitude, changed frequency, pushed the nose over and had some cheeky banter with BNE APP, and wait till I see him next :}

So I did not pay much attention to the exact throttle position, and as altiude varies so does the available MP, and as RPM changes so does MP, so you can see variations all the way down. At some point I did start making a really concerted effort to get down and join the circuit at 1000', which on the day meant a join closer to me than the other side of the field. So between that and watching TAS, and then as that became less an issue watching yellow arc over the hills, the actual MP was not a concern.

I did not consider it at all until in the circuit area. I was packed up and home before I contemplated the data and its interest to others, so I downloaded the data a week later.

It is what it is, but even if I look back at other data files where I have done descents rapidly, it just proves that the Delta T is never remarkable no matter what.

It was an awesome view of Brisbane that I have never had before though! :ok:

Night all!

[Capt Fathom]

Jaba, can I ask? Why did you wait so long for a clearance to descend! After all, you PAY for the service!

[Jabawocky]

Fathom, ask away!

I do have a path that is at times difficult with crossing traffic, especially at night or in IMC and can't descend visual. So I find the ATC guys appreciate or at least make noises such that I can give them a TOD that I would like well in advance, and also be flexible to go over or under the others.

I have had this discussion with said ATC at various school rugby games and so on, and on this occasion when the busy traffic level was apparent, I was prepared to go with the flow. But then it dawned on me who might be on BNE APP. He got me :}

It was all sport, and I could have reminded them, but I figured there was a game on, so I played the hand that was dealt.

Forkie will tell you similar things in TL.

There was no real problem and it was a good exercise in meeting a target from a great distance without the aid of an FMC, just my mental maths.

I was prepared for a clearance overhead the field, but that too cuts across the MLY-BN track and they want you out of the way of morno and tkfs coming through there at a great rate of knots! :E

cheers,
Jaba:ok:

[Chimbu chuckles]

Prospector et al 'shock cooling' IS a myth.

What damaged those hard worked Flitcher engines was the heat put into them on climb NOT the rate of cooling on the descent.

This graph shows residual tensile strength vs heat in PW radial engines - identical metal/combustion etc to a modern flat engine. You will notice the tensile strength of aluminium is approximately half at the temperature that was/is considered 'redline' on our engines - 460F. The most likely cause of the damage you recall was repeatedly heating the cylinders up around 450F - which over time weakens the metal - and then you get a blown jug/cracks because that weakened metal can no longer withstand the internal pressures of the normal combustion event.

http://www.fototime.com/{29F899BC-F354-4D48-B2E3-7EC5954D9D32}/origpict/pp18n.jpg

[prospector]

We never had a John Deakin, or an internet to get this information from. One cylinder head gauge, no way of knowing EGT, working engines a lot harder than they were ever designed for. Only time mixture was ever used was to shut down engine. Not suprising that not all engines made it to the official TBO. perhaps using cylinders till they eventually died, on second third or even fourth life explains why some appeared to have more trouble than others with cylinders cracking.

It was called Shock Cooling by our engineers, wrongly it would appear, but in the advice to young pilots it certainly made you more aware of engine handling procedures. ie, dont pull power from full throttle to nothing as you stuff the nose down in a race back to the strip.

What is suprising looking back is that the engines survived so many hours of such extremes of temperature changes for up to 1,200 hours. and sometimes more between overhauls.

On a good day 120 or more take offs could be carried out, with no way of knowing what was happening to Temps apart from the one cylinder head gauge, that may not have been on the hottest cylinder.

[Mr.Buzzy]

I know a fella that smoked a pack of Malboro cigarettes last week and he doesn't have lung cancer..........

Bbbbzbzbzbzbzbzbzbzbzbzbzbzb

[Ixixly]

Well, next time you see him Mr Buzzy, do us all a favour and stick some probes inside of him and get some data posted for us to discuss :D

[Shagpile]

And make sure it's 4 probes. No use sticking just one probe inside of him - the cancer could be in a different spot.

[Checkboard]

Jaba, I remember reading the Deakin articles when they were first written, and one of the things which sticks in my memory is the difficulty (impossibility?) of operating Lean Of Peak with the standard engines of the day as the mixtures were so unmatched in each cylinder. Deakin "fixed" this by using tuned Gami injectors to tweak the fuel flow to each cylinder, using his individual CHT information from his JPI engine gage.

So - question - do you run a standard original engine (ie. are engines that much better today?), or do you use after-market matched injectors?

edit: second question - you were at FL140? Were you on Oxygen or in a pressurised aircraft? If you were on O2, I'm sure you've also read Deakin's articles on using welder's oxygen and nasal cannulas with pulse oxymeters - is this what you were doing at FL140?

[Jabawocky]

Gooday Checkers,

Regards to Reddo :ok:

Many years ago, say mid 90's and beyond nobody really bothered, until GAMI who with George Braly and Tim Roehl decided enough was enough.

John Deakin bought and I mean paid for set No1, Walter Atkinson paid for set No3. and George (&Tim) paid a heap for set No. 2, Mind you they own the business.

Prior to that engines had run LOP for 50 + years, Lindburgh and the Doolittle raiders would not be household names without it. FACT :ok:

Problem was TCM had poor induction and fuel delivery ratios, but they were at least uniform and consistent. Lycoming on the other hand had worse inductions, and worse still were not consistent or repeatable.

So GAMI solved this and they did it very cleverly by not just getting the fuel PPH (pounds per hour) correct to match the airflow, but they improved the back pressure at the injector tip and also the shape and a few other things of the nozzle to get a better spray. This is most important as you slow the flow rate down.

I think JD had more than a single point CHT, the eary JPI's had multi EGT and CHT. But thats a minor point.

My Lycoming, out of the box was to be honest a pig, a basket case. I have flown other identical genuine factory engines, straight out of the box that fly LOP even better than mine does today. Such is Lycomings ability to variation.

So with our engine I had to do a rough tune, just to get the thing to peak.....t would not even run smooth approaching peak as the spreads were so bad one stopped long before the others got close.

With much patience of my good friend Andrew Denyer at Riverina Airmotive we sent injectors back and forth and eventually got it about right. Even today I have what I consider just good enough. Too lazy to tweak one.....but I might if JD or others want some data logged that might need me more on spec.

So to answer your question I have tunned them however Andrew did the tiny reaming of the restrictors. For anyone thinking of doing this somehow themselves....DON'T BE STUPID......this is not a DIY job.

So in my case it has tuned injectors, yet some engines out of the box are fine. TCM(CMI) or Lycoming. Even George and Tim will not sell you GAMI's unless you need them.

As for FL's.....Trent is far more astute.....:= FL130 my friend and I do use a Mountain High O2 setup, 4 place Oxymisers and it is awesome. Above 5000 at night(every time due LSALT) and when at or above 8K for longer than 2.5 hours, or always above 10K :ok: It is a major safety benefit! Glider guys swear by it and I can see why. I monitor with a pulse oximeter regularly both me and passengers.

So back to George.....I have the privilege of calling these guys my friends these days and I must say if I ever know as much as George Braly has forgotten, I will be the smartest bloke in GA in Australia. I kid you not, behind the scenes what this guy has done and is doing even today is mind blowing. Not all of it I can share here. But I can tell you that I have smelled tasted and seen all the data and test reports, even know what is the chemical makeup of the likely only replacement for leaded AVGAS. Only a month or two now from FAA certification, and it is going to make anyone with big radials like on conies, T28's or other big HP things who wish they had 100/145 but less the lead and the down sides, VERRRRY HAPPPPY indeed.

G100UL, is something that will be the biggest boost to GA in Australia. Period!. And USA and Europe. He should be knighted for his work. Some of you will scoff, but watch this space. george is a modest quiet man, and if you think the GAMI's were a big deal, TAT TN systems are good, or the Beech T34 wing box mod was something special, well hang on to your hats.

So this is major thread drift, but I feel it is important enough that in the next year or so it is likely all refineries in Australia will be able to produce G100UL, using existing gear, without special tank and transport, and there being no reason for a price rise, maybe even less. Heck I can brew my own! And be in spec. The good news is that G100UL, no matter how much 100LL is mixed with it, is still within spec. So changeover is a non issue. Cirrus have already written the approval for the Sr range and the POH amendments. That is confidence with a Capital G :)

So a lot has come from the humble tuned injector............more than most appreciate, especially T34 owners!

Want to know more come see Andrew Denyer or myself at Ausfly.

Clinton will be lurking here, what you say? Agreed?:ok:

Sorry Checkers for the thread drift......I got carried away. :ok:

[Jamair]

SIT, Ubu SIT........Good dog!

While being carried away (quite rightly) by excitement (or maybe too much O2), Jaba may not have quite got across the key points that Checky was chasing. (or maybe he did & I just wanna wax lyrical)

If you want to go LoP, you first install a multipoint engine monitor which these days are pretty cheap (mine cost $14K fitted in 2002).

Then you get onto GAMI and they will email you a Lean Test protocol. This involves taking off and climbing to a nominal altitude (IIRC it was 7000'), whereupon you set up the power as per the instructions then incrementally decrease the mixture over a period of several minutes, recording the resulting data as you go (pushing the EVENT button works fine).

Once you have got to the point where the engine is no longer producing power, you quit the test, go home, download the data and send it to GAMI. They make up a set of GAMIJECTORS each individually tailored for each cylinder for your engine and send them to you (after you pay of course). You bung them in and do the lean test again. Same deal, download the data and send it to GAMI, they send you any revised injectors you need, you do the test again and all should be good, but they will continue to fine tune your injectors as required until the optimum result for your engine is achieved. Alternatively you can have a local guru like AD sort it, but GAMI worked fine for me.

Contis do respond a bit better than Lycos in general terms, but I was very happy with my IO540 results. They ran cool, clean and happy LoP with no CHT ever above 400.

And two years of JPI data downloads, taken every 20 seconds for some 600 hours of ops, across all EGTs, CHTs, FF, yada yada, demonstrated conclusively that shock cooling is bollocks. Shock heating, on the other hand (ie overtemping through mismanagement or other issues like preignition ) is a sure engine killer.

So Jaba me old, when you coming here for a play?:E:E We can talk SERIOUS descent profiles:eek:

[Jabawocky]

Jamair.......... I need the world I spin around on to slow down a few radians per second...........you know, the pace you are used to :}

I really do need to get up there, a mate of mine, one has a really nice RV7A that he purchased recently, IFR, GNS 530, lits of round dials and a D10A, tip tanks with more than 6.5 hours in the FL's 130-150, and TAS155 or a bit faster lower and a bit more fuel, and he does YBAF-YBMA and other ports up there quite a bit for business.

VH-ORF if you see it on the ramp. Go say gooday!

Will need to work out how to get the GSX1250FA into the plane.....so we can do some road rides. How about we get the bike in one of yours.... :}

Your profiles would shock cool me :eek:




Speaking of DATA, DATA is the real deal. But this is quite clever and funny!
http://www.youtube.com/watch?v=l0ue8r9L4As&feature=player_embedded

[Jamair]

You BUGGER, you owe me a keyboard and a screen cleaner; I near ferkin CHOKED on my coffee with that clip.........:=:D:ok:

[RVDT]

TCM (http://www.insightavionics.com/pdf%20files/Continental.pdf) don't seem to be aware of it either.

Crap baffle seals is possibly the biggest cause of bad cooling.

The other one to avoid is increasing the mixture to rich rapidly when in the circuit.

[Jabawocky]

Jamair........ you know you deserve it :ok::E

VK2....damned that is one thing I can measure. The system logs everything, and I mean everything. It doesn't (coz i have no sensors) measure aileron, elevator and rudder position, but it could. there are spare inputs. no I will not be bothering either. Then you could really see how sloppy I am. But flap and trim it does as it displays these on the EMS, so a flap over speed is detectable :ouch:

RVDT, Baffles and their seals is a biggie indeed. More than most realise :ok:

As for mixture, you are spot on again, in the circuit or at TOD:ugh:. Why would you jam the mixture in on descent. The fuel will not shock cool either (popular myth) but it is very wasteful and harmful to the engine. All those nice clean plugs and cylinders from good ground leaning, in flight operation, all messed up coming down. That would be stupid.

A point to note here for those folk who do not fully understand their fuel systems. TCM and Lycoming use different suppliers for fuel delivery (IO) and the Lycoming, which has the Precission or Bendix system looks after the F/A mix as you get into denser air on the way down. Any slight errors, usually gum/dye buildup makes it less accurate so you just tweek the mixture a bee's ...err whisker if it gets a bit rumbly on the way down.

On a TCM (CMI) you have a fuel pump that is coupled to the engine (as is the lyc) but the fuel delivery is proportional to RPM. So you lean against the flow by RPM, so as you descend into denser air, the mass airflow is not affecting the fuel flow, so it needs slightly more tweaking. on the other hand, the TCM with better airflow in the engine will run generally speaking much further LOP on descent anyway, so the problem is off set a little.

Lastly, Carby engines behave like the Bendix / Precission intake, metering against mass airflow, so only tweeks required if necessary.:ok:

[Jamair]

So that explains why the Retard Vehicle was farting like a trooper in the circuit when we last went for a jolly.......it was you playing with your red knob.:E

[currawong]

I would be much obliged if someone would post their engine performance graphs for
1/ a max continuous power climb at best angle to say 8000, followed by
2/ cutting the power to idle, followed by
3/ a descent at vne to landing

:ok:

any takers?

[Trent 972]

Clinton saidThe data show that the highest rate of cooling, and (therefore presumably) the greatest risk of ‘shock cooling’, occurs at shut down. If anyone’s got data to show a greater rate of cooling at any other phase of any other kind of flight, post it please.
Looking at Jaba's data, that is not the case at all.
The greatest rate of cooling shown is Jaba's idle descent from 6,400ft to circuit height at about 17deg/min (as the oat increased by 19 deg).
What I also found very interesting was the 45 deg CHT decrease at TOC as the RPM was reduced from 2630rpm to 2450rpm with no other changes. Significantly greater rates of cooling (x3) than after shutdown.
It's all in that amazing data presentation.
ps Jaba, is the donk meant to put out 2700rpm at take-off. It looks like you're 40rpm short of perfection if so.

[Jabawocky]

Give me a break, you mean best rate at least, after all that is what a tug/grass dart plane is asked to do. But if I get a chance one day I will do a best rate and see what I get. The issue is really all about Delta T/min. So if my CHT is 475 not 375 which is normal, well it wont matter what I do at 8000' will it. Besides the ICP's are so low pulling the power, half the problem has gone away!

The point is a conforming engine, with conforming baffles etc, should not be seeing 475-500F anyway. As GB would say, it is hard to shock cool an engine that is already cool.

I did a series of climb tests to gather data for a bunch of interested fellows yesterday none of which were like the ones you mentioned, but using a steady IAS and comparing WOT/MAX RPM/Target EGT Vs doing a WOT/MAX/Full Rich and a 25/25/FR climb like the old wives tails suggest.

Each descent was power pulled and back to 700AGL for a go around and do the next run. CHT's never went below 235-250 on the way down.

Best bit was the climb performance, time to climb and temps, which is what the logging was about. All favoured which method do you think? (Hint: Braly who wanted the data will not be changing his course material :ok:)

[Jabawocky]

Trent, I think if I pulled out all the stops and tweaked the little screw, it would but that is hard work, involves lock wire and such.

I like your eye for detail!

[A37575]

With the first air cooled cylinders visible through the front of the engine cowls in Chieftains and their ilk, I often wonder why flying through heavy rain does apparently not cause shock cooling as the rain hits the cylinders.

Of course, radial engines such as those in the DC3, Sea Fury, Beaver, DC4 and similar would also be affected by rain impinging on the first row of cylinders causing significant cooling and quickly at that. Would that be termed `shock cooling`? Were cylinders cracking after flights in wet weather or large water droplets found in towering Cu?

[Jabawocky]

A37575

It does do things to the F/A ratio a bit.

You would also be surprised as to where the air entering the cowls actually goes, and does not.

Hard to describe in words but the bulk air travels in around the edge of the inlet, travels down the back and returns to the front, trying to escape behind the spinner. One of the reasons why a small amount of oil spilled soon ends evenly spread across your windscreen.

Basically, what you think would happen doesn't and in fact quite the opposite. Of course airframe to airframe variances apply so get some tufts of wool out and a tiny camera or 4 and video away!:ok:

[Jabawocky]

CM

I think your point was missed indeed.

I will have to search through a pile of data to find some better examples.

Thermal inertia is hard to overcome and hence why shock cooling is very hard to achieve, if in fact it exists.

The point to cylinder cracking is all about pressure and temperature. So it should be considered that all the damage reffered to is when the pressure pulses are high and temperature is high.

This issue of temperature difference is rather funny. The temperature at the tip of a fin is way less than that at the base, but the fins do ot all fall off on the first engine start do they?

So the worst things are high temp and high ICP. I have seen this on George Braly's dyno and lets just say, we made jokes about hiding behind not just the wall, but the Control Console as well! :eek:

So when do you think the slightly less abusive instances of high pressure and temperature happen? When the ag guys are taking the load OUT, when the grass darts are being taken up.

Most pilots flying most planes do not do this. And that is why they do not have the problems.

I was sent recently pictures of a G36....yes G36 bonanza engine with 800 hours on it. Lots of cracks, all around the plugs, and while the early guess is plug torque, it is most likely a manufacturing defect in all of them.

My bet is if I get my boroscope onto this beast some time soon, the LAME's and the owner will be shocked.....not shock cooled, but shock heated into new cylinders! And not the cracks, the likely crappy valve guide fitting! Just a hunch, but I bet a carton on it.:ok:

Anyway...as clinton points out, the data after shut down is not often considered. I have data which varies from 12F/min to a lot less. This will depend on ambient, airflow, the airframe etc. Some will be higher, some not so much, but of course these are at nil ICP ;)

The bottom line is a start up the Delta T is often at 60F/min and there is mild ICP. So perhaps that is worse by far, but I never hear anyone get bent out of shape over SHOCK WARMING :eek:

I have hours and hours of really cool data, and I can assure you that folk like John Deakin love it. Why you ask? no not because it comes from a land upside down, but it backs up all they have been saying for years. It also combines flight data not just engine data. And that further proves what John Deakin, George Braly and Walter Atkinson have been teaching for the last 12-13 years.

So lets not get bogged down in Jaba's data files, lets learn from the guys who have been teaching this stuff for years. My data is just icing on the cake :ok:

Any sensible questions greatly appreciated.:)

[Tinstaafl]

I tend to think fast cooling, rather than fast warming, is an issue due to the mix of metals used in the cylinders ie aluminium vs steel. Different metals expand & contract at different rates. Is it not the case that aluminium's rate is greater than steel's? A typical cylinder has aluminum surrounding a steel liner and also the steel spark plugs (valve seats too? Can't remember what they're made from). Warming the engine has the aluminum structure expand faster than the steel, leaving the steel to 'catch up' into the minute gap. Cooling, however, has the aluminium contract around the slower shrinking steel structure. Over many cycles it seems reasonable to me that the stress will lead to fatigue & cracking.

Reduce the rate of cooling (and possibly the starting temp ie very hot vs hot vs warm vs cool) and the difference in shrinkage would be reduced.

[Jabawocky]

Tinstaafl

You need to remember that as all these items expand and contract, they are sinking heat from one to the other, they are not acting independently. So what you might think is happening is not.

Sure things change at different rates, however the mass and shape of the object affect the rate of expansion. A piston is aluminium, the cylinder is steel, the head aluminium. The cylinder is thin, the piston and head not.

There are folk who for some strange reason have done many tests, like multi probing turbochargers and cylinders to see what is actually happening. I am sure you can guess which mad engineer/lawyer this guy is? Whats more he has no axe to grind, just education.

The fruits of his labours can be found at Advanced Pilot (http://www.advancedpilot.com)

Need I say more. :ok:

[T28D]

Thereason why you never hear about these issues with radial engines, at least the single row and double row engines ( no comment about the corn cob radials), is in engine handling.

Big engines deserve and get respect, no rapid throttle movements, if you can see your hand moving it is too damn fast.

It is about thermal cycles and keeping the changes in thermal states nice and slow so the engine metal bits can keep up with the power developed.

Also radial engines are NEVER allowed to be windmilled by the propellor this is an engine killing practice and most large radials are geared so positive manifold pressure is always applied with the one exception in the landing roll out

[Super Cecil]

Also radial engines are NEVER allowed to be windmilled by the propellor this is an engine killing practice and most large radials are geared so positive manifold pressure is always applied with the one exception in the landing roll out
Got any examples?

[T28D]

Wright 1820-86A propellor geared to .666 engine speed, P & W 1830 same,

Wright 3350 same

[Super Cecil]

Yip, got a rough idea what a geared radial is. I should have asked do you have any examples of radials self destructing from such handling?

[T28D]

It is aself evident fact that those of us priveliged enough to own one of these today are very careful with them, the evidence on which we rely came from the WW 2 veterans who flew aircraft with these into battle.

The RAN had a run of failures in theTrackers which had an up rated version of the Wright 1820.

[Super Cecil]

So no hard evidence then? Were the RAN failures gearboxes? I have heard the mention of the prop pushing the engine being bad.
From the geared and direct drive radials I've worked I can't remember (Could be bad memory) any mention of special proceedures in flight manuals apart from standard temps and pressure stuff. As I said I could be wrong, it strikes me as being one of those tails.

[Volumex]

In the late 80's/early 90's I believe that the geared R-1340 in VH-WIR had the prop driving the engine, as it needed a gearbox rebuild fairly early. 50/100 hours-ish?? The bloke who flew it the most had no skin in the game and was generally abusive to equipment.
Once that fella was off the scene, the poor old girl also had a main bearing failure around the mid-90's. I have no idea what triggered that though.

[Trent 972]

Jaba, the link you provided to Advanced Pilot says in part And because it saves gas and emits fewer unburned hydrocarbons, it's also greener.
You and Clinton and Jas told me in the 'Oversquare/LOP' thread, that was not possible. (said with tongue planted firmly in cheek)

[T28D]

Cecil as long as you don't come near my 1820 life will be good.

[A37575]

Back in the Sixties, the RAAF had a Dakota stationed at Butterworth. Over a period of time (don't know how long because this is going from memory but I was in the RAAF when it happened), there was a marked increase in the number of engine changes when previously the serviceability was good. The problem was tracked down to the engine handling technique of a new captain who had recently arrived at the unit.

I think he was the qualified flying instructor (QFI) allotted to the unit to conduct training, instrument rating tests and conversions to type. His method of simulated engine failure after take off was to harshly close the throttle and have the pilot drag the Dakota around the circuit with its propeller windmilling.

The result being the propeller was in effect driving the engine by means of very low manifold pressure and high windmilling RPM. This was extremely damaging to the engine in the long run due I think to reversal of bearing loads. In fact I vaguely recall he left the windmilling prop pitch lever at full fine.

In terms of figures, I would guess that at 100 knots IAS with full fine pitch and throttle against the idle stop, it would likely give less than 12 inches manifold pressure and RPM windmilling around 2300 RPM.. I know that take off power in the Dakota was 48"HG and 2700RPM and typical cruise power 30.5"HG and 2050 RPM. Anyway an engineering investigation nailed the engine failures to the habit of this particular pilot because as unit QFI he was doing all the throttle yanking on "training".

He was "counselled" and given a kick up the arse and from then on engine failures were the thing of the past. Note: This interested me at the time because I too was a Dakota QFI although at another squadron and I recall we received a letter from the RAAF detailing what had happened. A slow smooth closure of the throttle to simulate engine failure was used after that and we also pulled back the pitch lever to around 1500 RPM I think to minimise the gap between manifold pressure and RPM. Of course we had to pull back the throttles on base leg to around 15"MP for the landing approach and Pratt& Whitney advised us by letter that it would not cause a problem at the slow IAS on base and final (90 knots slowing to 80 knots over the fence). P&W went on to say that a fully throttled back engine and high IAS such as could happen in a descent from altitude would eventually cause long term engine damage.

[Jabawocky]

I have very little knowledge of the radials construction and design, however they are not designed to carry thrust loads in the reverse direction and the same applies to some geared engines, although not all.

Engine braking is not what the design criteria of a big radial.....it was in fact to look and sound awesome!:)

Trent....They are not combusted or burned in a power producing way.....but they do not remain as fuel drops that one can condense (and reuse) in the exhaust either. They get a little black and crispy, over exposed to heat you might say. George is not interested in them once they have gone into the exhaust aft the turbo.;) Nice try:ok:

[Super Cecil]

Cecil as long as you don't come near my 1820 life will be good.
T28 I'm not saying it's good practice, just saying I have not seen anything written. A37575 the handling proceedure you mention seems the way you treat any aircraft engine, small flat, large flat, large round or kero burner. You should treat all with respect.

[T28D]

I didn't want to hi jack this excellent thread to have a discourse on Planatery gearboxes or the wonders of the geometry of radial engines and the importance of protecting the master rod bearing no matter what is happening to the flight profile.

My point in raising radial enines is/was that they don't suffer from cracking through thermal cycling to anywhere near the degree that the flat engines do, and that is primarily a result of the way radials are managed in flight.

The mid sized radials are generally in the 1500 H.P. area so their thermal loads are significant, but with good disciplined handling they are a really reliable power plant.

the1820 cyl head temp runs 170 celciusin the climb cowls open and 150 celcius in cruise cowls closed, very benign temps.

So lets get back to Thermal Cycles and engine management

[FokkerInYour12]

I'd like to see some figures on descent rates, EGT/CHT and forward slips too.

I'm a big fan of forward slips (when flying solo - pax don't like it too much).

(Beware some aircraft types don't like slips when flaps are out beyond a certain amount. Read the POH.)

[Arnold E]

I'm a big fan of forward slips

I'm not trying to be funny, but what is a forward slip?

[FokkerInYour12]

Pretty much same aerodynamics with cross controls.

Forward slip maintains track (so is used for altitude loss only)

Side slip deviates track and maintains heading (think maintaining centreline when landing with crosswind)

Or we'll just say "slip" and keep everyone happy.

[Jabawocky]

T28D
The mid sized radials are generally in the 1500 H.P. area so their thermal loads are significant, but with good disciplined handling they are a really reliable power plant.

the1820 cyl head temp runs 170 celciusin the climb cowls open and 150 celcius in cruise cowls closed, very benign temps.

I dont think this is thread drift at all. It fits nicely in the thread. Issues of radial handling are for specific reasons, none of which are scientifically based on cooling. Very scientifically based on reverse loads.

The correct handling you refer to is most likely ....careful descents = crank/gearcase and careful climbs = 170 (340F) and cruise = 150 (300-310F) This clearly not shock heating ;)

This is closely aligned with reality and the opinion of some folk i know who are regarded the experts. You can beat engine temps like those you are talking about. :ok:

[jas24zzk]

Keh ??

Pretty much same aerodynamics with cross controls.

Forward slip maintains track (so is used for altitude loss only)

Side slip deviates track and maintains heading (think maintaining centreline when landing with crosswind)

Or we'll just say "slip" and keep everyone happy.

http://www.mustangtech.com.au/images/smiles/popcorn.gif

[T28D]

Or the knife edge of inexperienced calamity

[FokkerInYour12]

what part don't you understand?

[jas24zzk]

I'm interested in your reply to Arnold E

http://www.mustangtech.com.au/images/smiles/popcorn.gifhttp://www.mustangtech.com.au/images/smiles/icon_drink.gif

You haven't thought it through very well have you...in the meantime, risking a hijack of a quality thread

[T28D]

Thebit where inexperienced folk are all "crossed up "and yet still in control, no mention of flap position, manifold pressuer ( power being developed) or what the POH says.

Yup it can be done, but I simply say WHY would you introduce a student to the edge of incipient spin on final, seems a bit silly and full of machismo bravado to me.

What ever happened to the stabilised approach ?????? from which the kiss the ground arrival is possible.

Test pilots all be aware your jobs are being threatened by newby's getting all crossed up on final and hopefully living to tell the tale.

Sheesh.

[Trent 972]

Forward Slip (http://www.aopa.org/asf/publications/inst_reports2.cfm?article=6156)
The forward slip is performed just like the turning slip, but the heading remains constant. Its purpose is to lose altitude without a corresponding increase in airspeed, which would be the case if you simply pushed forward on the yoke.

[FokkerInYour12]

On final, slips are great. Ignoring crosswinds, ever had a short field with obstacles to land in? Ever tried a landing on the keys consistently every time? Munch your popcorn away.

Putting this thread back on topic:

Regarding this thread and forward slips, I am interested in any readings on a prolonged slip to rapidly reduce altitude without yellow arc airspeed increases and what the EGT/CHT/MP changes result. I do not having the sophisticated monitoring equipment to measure this.

I am interested in this approach versus the original poster's "point the nose down and pull the power"@2000FPM descent for 6 minutes.

[Super Cecil]

Continuing on from the radial myths, if you can't rotate the engine with the prop then how do they use reverse on radials without the load being reversed? Albatross have 1820's and reversing props, do they have a different gearbox to cope with the reversed loads? What about R2000's on DC 4's and Caribou's they reverse them, do they have to change gearbox's after every reverse landing?

[T28D]

Yes different Gearbox and the propellor is NOT windmilling the engine the engine is producing power !!!!!!!

[Trent 972]

Shock Cooling - Myth Busted!!
Lycoming Service Instructions (http://www.lycoming.com/support/publications/service-instructions/index.html) link
One of those 'Instructions' is SI-1094D (http://www.lycoming.com/support/publications/service-instructions/pdfs/SI1094D.pdf) Fuel Mixture Leaning Procedures (pdf file) dated March 25, 1994 (still current)Revision "D" to Service Instruction on No. 1094 supersedes all previous recommendations and should be used for engine leaning during normal flight operations. ALL LEANING RECOMMENDATIONS ARE BASED ON CALIBRATED INSTRUMENTATION.
What does Lycoming define as 'Shock Cooling'?At all times, caution must be taken not to shock cool the cylinders. The maximum recommended temperature change should not exceed 50°F. per minute.

Only pointing out the current recommendations of the manufacturer.
Myth Busted?
I don't think so.

[Trent 972]

Jaba, special note to you. In no way do I want you to think I'm having a shot at you. I just don't agree that the myth is busted, by way of that data set.
Not to worry though, according to the data graph you provided in the OP, the max 'cooling' Delta T indicated is 41°F/min, oddly enough, as you reduced the fuel flow after TOC @13.42.39. :)

[Jabawocky]

Trent

that document is from 1994, almost 20 years ago and right in the thick of many OWT's bouncing around the manuals of TCM and LYC. I would be very concerned at believing much that was printed in that document. Some may be good, some not.

I love point 2. Mixture changes should be done slowly! :D:}:}:} You are kidding me right, they say that but do not quantify it :ugh: Let me give you a tip, and I am not sure I know which data point you are referring to but I use the BMP (Big Mixture Pull) and then sneak up from the lean side. Some times I don't, just because I lik observing the data. And I would guess the 42dF/min was from a BMP. Heck that is shock cooling at its best, and it is still 20% less than Lycomings suggested 50F/min.

If that there is not enough proof the myth is busted, I do not know what is.

By the way I just went and looked at the raw data file, 42F/min......not that I can find, I see just after TOC and a massive fuel flow drop, the fastest was 32dF per minute. Maybe there was one cylinder that was closer to 40, but whoopee!

I still maintain, the only shock cooling likely is when you spear into a lake/ocean.

George Braly, who has done more testing than anyone I know, took my data set and graphed it far better...... he was chomping at the bit to get it, and he was not surprised.

Seriously, as John Deakin has written before, maybe you can cook an engine to 475-500F and dive like a rock with no power, and maybe just maybe you can create cooling bad enough. But who actually does that. The data proves that it is climbs that create the bigger Delta T and in combination with high ICP.

If I have to repeat the above again...........clearly I am wasting my time. OK one last time ;) Delta T and ICP.

Shock Cooling = Myth Busted! Even more so! :ok:

[Jabawocky]

I can't help myself.......really have a read of this would you

For cruise powers where best power mixture operation is allowed, slowly lean the mixture from full rich to maximum power. Best power mixture operation provides the most miles per hour for a given power setting. For engines equipped with fixed pitch propellers, gradually lean the mixture until either the tachometer or the airspeed indicator reading peaks. For engines equipped with controllable pitch propellers, lean until a slight increase of airspeed is noted.

Now think about this one carefully folks. You can have 70% power in two ways. And best power is at 75dF ROP, so as they suggest for a given power setting, lets look at this.

Say the given power setting is 70% power. Lycoming correctly state that the best power is where you get the fastest speed. However you can achieve a "Given Setting" in this case 70% power or any other for that matter, by a ROP setting, which 75ROP is, or a 25LOP setting. Or the same power at 150ROP.

Which one of these same power settings, same IAS same performance out the prop has the;
a: Coolest CHT
b: lowest Fuel Flow
c: lower ICP
d: Least engine wear and deposits?

So choose answers 1=75ROP , 2=25LOP or 3=150ROP


And you wonder why I laugh at the tech bulletins written by the "Manufacturers"

So please folks, in all good spirits of education have a crack at answering the above, and in a day or so I will do my best to explain the correct answers. I expect most of the local folk here will know the right stuff, but it is a fun education exercise all the same.

The better manuals are really old, produced by P&W and Curtis Wright. The crap printed by TCM and Lyc in the "dark ages" is pure fiction and often comedy. I have many examples in a folder beside my bed (sad hey), but after many a pprune thread I look them up just to be sure I am criticising them properly.

The problem here is 100% of students never get a chance to reason with this stuff.

You know what makes me mad, my wife has been doing some aviation subjects as part of her business degree. Last exam she received 20% of the marks for the exam by answering with completely wrong answers. Yes she deliberately answered them wrong knowing that is what the text books (CPL) preach. If I posted them here 75% of the prune community would recognise them as BS. But the industry, CASA and FAA etc keep churning this crap out.

Rant Off!!!!!!

[T28D]

The big radials do ( mixture ) automatically, absolutely dependent on altitude, throttle position, Carby Temp, and where the diaphragm puts it !!!!!!!!

Generally bloody accurate, thank god for pressure carburetors ( throttle bodies in moder vernacular ).

After flight look at the exhaust colour soft grey = good black = too rich white = too lean

It is not rocket science.

For once I am with Jabawocky, the most common problem in the weekend warrior ranks is engine handling ,closely followed by bloody big circuit patterns.

See probably thread drift , now we start on Actual "SideSlipping " as opposed to Forward slipping what ever that is ??????

[Trent 972]

You make a claim of "Shock Cooling - Myth Busted" and provide the data that shows, even without trying, your engine operating technique at one point in time on one engine cylinder (#4), cooled momentarily at a rate of 82% of the recommended OEM maximum.
That being the case, I am sure that it would be very easy for a 'Ham Fisted' effort to achieve a Delta T far greater than 50°F/min.
I'm sorry that you think that you are wasting your time.
As far as questioning the value of the OEM recommendations, perhaps a more recent example from a POH of a 2009 PA46 TIO540 AE2A might show that there has been no change since SI-1094DPlan ahead to make a smooth temperature transition between cruise and descent. Start descent early and allow airspeed to increase within aircraft limits. Maintain power and mixture setting as required. Cylinder head temperature change rate is not to exceed 50°F per minute to avoid rapid shock cooling.
OEM says one thing and Jaba says differently, as we have said before, 'each to their own'.... myth busted... I call bullish!t. :E
ps. waiting for Clinton to come on now and tell me all about how the greatest rate of cooling occurs after shutdown (short of using a garden hose to cool it).
I already have the links prepared to show that as blatantly false.

[A37575]

the most common problem in the weekend warrior ranks is engine handling ,closely followed by bloody big circuit patterns.


You forgot to add "picking up a dropped wing with rudder":ugh:

[Trent 972]

Sorry Jaba, I missed your and T28's last post while I was typing.
What was that in your quote box in previous post.... Ah yes ......slowly lean the mixture from full rich to maximum power
How does that fit in with your BMP (Big Mixture Pull)? :O

[Trent 972]

Apologies for being too noisy on this thread but I think Jaba and others might enjoy this from the PA46 POH. operating on the lean side of peak TIT with elevated manifold pressure substantially reduces or may entirely eliminate the detonation margin. It is certainly not a procedure that is operator friendly to be used in today’s environment with high ATC (Aircraft Traffic Control) attention and traffic demands. The cost of replacing a burned valve or piston will more than offset the small savings in fuel burn. If a $5 per hour savings in fuel is necessary for an operator to afford the use of a Mirage at the risk of engine wear or damage, this is not the correct powerplant or aircraft.

[Jabawocky]

Trent, you are getting confused.

I was not trying to prove the myth is busted. I was trying to be a smart arse with BN APP who was trying to be a smart arse with me.

I was trying alright, I was trying to descnd a fast as I could possibly go, believe me, VNE for TAS and VNE once TAS was not an issue and the out of the yellow arc over the hills and bumps.

I WAS TRYING but it was not about a shock cooling effort, I never gave that a thought as I knew it was a myth. Driving home talking to Chimbu Chuckles he or I made the comment about how that busts the myth on shock cooling so I went back and downloaded the data a few days later.

You got that :ok:

Sorry Jaba, I missed your and T28's last post while I was typing.
What was that in your quote box in previous post.... Ah yes
Quote:
......slowly lean the mixture from full rich to maximum power
How does that fit in with your BMP (Big Mixture Pull)?


How does the quote fit in with my BMP.....exactly, I don't fit in with it. The Lycoming quote is laughable. my BMP is the reason for the 32dF delta T.

Am I not making sense, or are you trying to wind me up?:confused: Trouble with debating you smart blokes, even when you are off track its hard to keep up :} Maybe I am fatigued. Should impliment a pprune fatigue management plan! :8

[Jabawocky]

Who wrote this rubbish Trent. What garbage!!

This is fact, bank it. The scope for engine damage as defined by the area under the curve is considerably greater on the Rich side of Peak.

I will repeat that slower, the area under the curve where there is a greater chance of both detonation (especially in a turbo at high MP) and from general high CHT and ICP, is biased heavily on the ROP side of the curve.

The LOP side of the curve is so much better, considerably so, that there is less scope LOP to do long term (hundreds of hours) damage that the statement you quote is scientifically and factually false.

Have you ever watched the detonation index on a fully instrumented dyne with a high HP turbocharged piston engine, while you do all manner of things to it? It really is an education.

Some folk might find it like drinking from a firehose, but it seriously is very educational. The myths and rubbish stories like the one you just posted soon become nothing but laughing stock.

PA46 hey, the TSIO520E where the engine manufacturer actually states how to set up the max cruise HP setting of 75% and 235HP; Set RPM for desired cruise setting (note nothing specific, the smart ones have already worked out why this matters not), and then shock horror, lean to .....no surely not.....OMG LOP!!!! :D

Not sure why they then go on to say 235HP is at 31" and 2400RPM and a 25-50F LOP setting, because when LOP the rpm does not matter but anyway old habits die hard.

So there ya go! Funny hey! :ok:

The burned valves were all Factory Fitted Options, the result was the same despite what the pilot did.:ugh: And in the PA46 case all the accelerated failures, forgetting the valve guide issues, the ones with major problems were from pilots who read this manual, and just as their old CFI or hangar buddies said, a bit richer would be better. So they went from a perfectly happy 50LOP to around typically 25-50 ROP against the manuals advice.

Where do you think the highest CHT/ICP and valve temps live? :D

So these guys blame LOP ops when they were in fact ROP.

I am glad you brought up the PA46 because this actually supports my previous post about where the risky side of the curve lives.

Now back to my Quizz :ok:

[Trent 972]

Who wrote this rubbish Trent. What garbage!!
The Manufacturer!
Not sure about the cruise power settings you quote for the TIO-540 AE2A Jaba, my book says
Lycoming recommends that a cruise setting of 65% power be used for typical flight profiles. This power setting corresponds to 2400 RPM, 29 in. Hg. manifold pressure. Recommended TIT is 1650°F or 100 degrees richer than peak TIT whichever is less.
I do understand that you wish to illuminate what you and others see as the dark ages in aircraft engine handling, but until you get the OEM to put your ideas into the OEM manuals, your'e on the outside looking in.
When I go to my night job I get to play with 4 very big round things from Derby UK and I operate them exactly as per the OEM manual, because IF and WHEN they go BANG, I won't have to pay them off over the next thousand years. If I were to say to the boss "I found a better way on the internet to operate the engine" and it went BANG, I think I would be ringing up TruckMasters looking for a job.

[Jabawocky]

Quote:
Who wrote this rubbish Trent. What garbage!!
The Manufacturer!

http://www.beechtalk.com/forums/images/smilies/rofl02.gif http://www.beechtalk.com/forums/images/smilies/rofl02.gif http://www.beechtalk.com/forums/images/smilies/rofl02.gif

When I go to my night job I get to play with 4 very big round things from Derby UK and I operate them exactly as per the OEM manual, because IF and WHEN they go BANG, I won't have to pay them off over the next thousand years. If I were to say to the boss "I found a better way on the internet to operate the engine" and it went BANG, I think I would be ringing up TruckMasters looking for a job.

Ahhh Trent, chances are the manuals you are operating have decent manuals that are not full of BS generated by marketing and legal departments in conflict with the old and wise engineers.

Do they say things contradictory to other similar manuals?

Do they say things that contradict themselves in their own publications?

Do they have contradictions in the same very manual?

Most likely not. If they do, and any of it contradicts known science, why would you not go see the boss and get him to investigate it with your help and get a change made to the SOP.

I am privilleged to be reading a Curtis Wright troubleshooting manual "Troubleshooting for Optimum Performance" at the moment, very good stuff. Printed in 1957. Why was it these guys back in the 50's had it nailed? Wot Went Wong in the last 40 years? (rhetorical question)

[Trent 972]

I am privilleged to be reading a Curtis Wright troubleshooting manual "Troubleshooting for Optimum Performance" at the moment, very good stuff. Printed in 1957. Why was it these guys back in the 50's had it nailed? Wot Went Wong in the last 40 years? (rhetorical question)Rhetorical answer. My first guess would be that they had 'flying spanners' to look after the engines. Or perhaps as you allude to withWot Went Wong in the last 40 years?Engine parts manufacturing moved to China. :E

[Trent 972]

Morning Clinton, I hope you're well.
If you wish to take the time to check back on any of my previous posts you will see that I have not posted personal opinion, rather I have referenced links from OEM's. If one were to continually discount OEM recommendations as what you say as ...inconsistent and demonstrably unscientific assertions of some manufacturers It would be silly of me to continue.
As Benjamin Franklin saidThe definition of insanity is doing the same thing over and over and expecting different results. I am quite comfortable with my own knowledge on this subject, however I do fear for some who may try some of this 'home brew', without the benefit of previous experience.
Caveat Emptor.

[mcgrath50]

Hi Trent,

Please post that link you have! I am learning a lot from this thread and the guys who are posting real data are doing a lot for my education. I'd really appreciate it!

[Trent 972]

Clinton, therein lies our difference.
I am not prepared to discount the wisdom of the people who built the engine.
I am not prepared to tell you to do other than whatever you wish with your own engine.
I am prepared to say it is wrong to suggest to other people to ignore the wisdom of the people who designed and built the engine.
On Benjamin Franklin's advice I shall retire, because I'm still trying to get to grips with Jaba's statement I will repeat that slower, the area under the curve where there is a greater chance of both detonation (especially in a turbo at high MP) and from general high CHT and ICP, is biased heavily on the ROP side of the curve. Detonation caused by ROP?
Low Octane and Lean Mixtures Advanced Spark and high inlet air temperatures causes detonation. Show me where that is wrong and I'll keep my ear/mind open.
Apologies McGrath, I missed your post while typing. Anything I have posted here is easily found by a google search. ATM I now have to prepare for my next MS flight Sim session. I'll be back in about 16 hours.

[T28D]

the area under the curve where there is a greater chance of both detonation (especially in a turbo at high MP)

And that folks is why on blown engines the compression ratio is lower than normall aspirated engines.

[Tinstaafl]

Interestingly, the factory manual for the 1980 PA31-325 that I operate offers 50 deg LOP as an alternative to ROP. It even goes so far as to give instructions to get to LOP if the EGT limit is reached before obtaining LOP.

[Aussie Bob]

Ok, all very interesting and a great thread BUT:

There is precious little information about best practice. I have a long involvement with a company operating 200 series and 185 Cessna's with O520 and policy has always been: Full power for take off, 25/25 for the climb and 2400/23 for the cruise. Lean to top of green on pressure gauge in climb and to 2 divisions ROP in cruise. Engines have always made TBO + extension, a top is generally done around 1200. This policy works well, but what would work better? The 185's are on floats and despite 1500 odd metre 3 minute takeoffs and 20' sectors the engines still make TBO + 100 with few problems. You guys hint that these are poor practices but offer no alternative suggestions other than to fit multi point digital thingies and LOP

In my Scout (O360 + CSU) my policy is about the same although I sometimes I leave the throttle wide open in the climb and simply reduce RPM to 2500. Leaning to a couple or three divs rich of peak at 2400/23" gives a burn of 30 per taco hour. How can I improve this? I do note with this engine that shock cooling seems impossible, CHT is very stable in all stages of flight at around 330 - 365F regardless of power setting, only have single probes though.

Sadly I am unable to make NATFLY where I think some of you are doing presentations.

And Jabba, I look forward to your answers, unfortunately I don't know http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/infopop/icons/icon11.gif

[mcgrath50]

Leaning to a couple or three divs rich of peak at 2400/23"

Won't this put the CHTs at about their hottest point (50ROP EGT)? (Question more directed at Jaba to check my learning thus far :ok: )

[ForkTailedDrKiller]

I have a few hours sitting behind IO520/550s - so here, for what its worth, is my take on this!

1) If you are paying the maintenance bills on the engine - do whatever you like!

2) If you are not paying the maintenance bills - then do what you are told to do by the person who is!

3) If in doubt - do what the POH says!

Dr :8

[Jabawocky]

Ok Trent, I am quite comfortable with my own knowledge on this subject, however I do fear for some who may try some of this 'home brew', without the benefit of previous experience.

You have just shot yourself in the butt here, there is nothing home cooked about the data and advice given by at least some of us. It is well researched, and documented, going back 60 years. The home brew stuff is mostly what the flying schools dish out as a one size fits all, and they get it wrong.

Fuel and and O2 do not know the difference between your IO550 or the Brigs and stratten mower engine. All air cooled fixed spark 4 stroke petrol engines share 99% of things in common.

Rhetorical answer. My first guess would be that they had 'flying spanners' to look after the engines. No they had pilots and a flight engineer, and good data logs, not the JPI type, more the paper and pencil type, but effective non the less.

because I'm still trying to get to grips with Jaba's statement
Quote:
I will repeat that slower, the area under the curve where there is a greater chance of both detonation (especially in a turbo at high MP) and from general high CHT and ICP, is biased heavily on the ROP side of the curve.
Detonation caused by ROP?
Low Octane and Lean Mixtures Advanced Spark and high inlet air temperatures causes detonation. Show me where that is wrong and I'll keep my ear/mind open.
Apologies McGrath, I missed your post while typing. Anything I have posted here is easily found by a google search. ATM I now have to prepare for my next MS flight Sim session. I'll be back in about 16 hours.

Ok this is not going to be easy here, this sort of stuff is part of a multi day professional training course, and is impossible to easily replicate that on prune, and I am not about to try. However here is a snapshot of the answer.

Detonation potential exists in far greater amounts on the ROP side of the curve, the region on the leans side is fairly narrow even at full MP, so lets say in simple terms 30" up the beach at 500-1000' once on the LOP side of the curve the detonation region is from peak to maybe 20FLOP and the risk is eliminated at anything past 40LOP, the best place to be running here is 60-90LOP. And this is a fairly small movement of the mixture knob.

On the Rich side of the curve, the region is far greater, from peak through 75ROP which is best power and through to maybe 125-150 ROP and once out to a region of 200ROP the problem goes away again.

So tell me ......which side of the curve, has the most potential? And understanding that you do need high HP high temps and high IAT to get it going. And on a Turbo this is much easier to do!
http://www.beechtalk.com/forums/download/file.php?id=25052Courtesy of Advanced Pilot Seminars

So when you say a Lean mixture is what causes detonation, what you really mean is a Rich mixture that is not Rich enough. I am sure I have said this before, technically all mixtures on the curve above to the left of peak EGT are RICH and all the graph to right of peak is a lean mixture.

By definition TOO LEAN would have to be from the RHS and to be too lean over there, the engine stops.

To be TOO RICH, you would be way out the left and drowning the engine, but if you lean the flow and get to a bad zone that would be correctly described as NOT RICH ENOUGH.

Tinstaafl, yes indeed.....they just do not do many manuals, and probably yours any justice with a thorough explanation so hence the reason the pilots who fly them get a wird mix of the manual Vs the CFI..... and that is where the trouble starts.


I have to go to a School function, so Aussie Bob and McGrath, when I get home I will pay particular attention to your questions. :ok:

J:)

And Forkie......that post is the worst of yours I have ever seen := Wait till Chuckles gets a hold of you :}

[Trent 972]

EXPERTS ARE EVERYWHERE TO HELP YOU (http://www.lycoming.com/support/troubleshooting/resources/SSP700A.pdf)
THE “NEW” OLD LEANING TECHNIQUE (smallish pdf)
caution it is another Lycoming link...:p
(OEM keeps getting it wrong.... or do they?)

[Aussie Bob]

And Forkie......that post is the worst of yours I have ever seen := Wait till Chuckles gets a hold of you http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/badteeth.gif

I think it is a gem!

[Jabawocky]

Ahh time to kill while waiting!

Aussie Bob,

You are quite correct, there is little written about best practise by the manufacturers, and it is quite surprising, when back in the radial days it was quite the opposite. The last 40 years has been different, Lycoming have been known to print that they think the process I use every flight, and thousands of others do every day, is too hard for the average pilot to cope with. They said different words, but thats what they meant.

Full power for take off :ok:
25/2500 for the climb :{ This is not nice to engines. Unless there is a limitation in the LIMITATIONS section, you should be climbing WOT/2700RPM and using a target EGT that you had at 1000 AMSL lean back every couple of thousand to that same EGT number. This works even with a single point probe.

Last week I did a batch of takeoff and climb tests with all the data being logged. The 4 flights were the same place the same route the same as I could make them and at the same IAS 120knots. I did this after I mentioned it to George Braly and his reply was Actually - - that would be pretty nice. So, yes. Please!

The data files are quite huge and video massive, and has been given to John for processing to see if there is any useful classroom stuff in it, so I wont try to post it all here, however here is my email to George Walter and John.
1st run = Data 15901 – 16184 Trial run done as a normal lean in the climb WOT/2650/Target EGT
2nd run = Data 16515 – 16820 WOT/2650/full rich all the way to 5500
3rd run = Data 17100 – 17452 WOT full bore till 500 AGL then @1300’ (1000AGL) back to 25/25 and full rich.
4th run = Data 17783 - 18000 a proper WOT/2650/Target EGT

Things I noted already without reviewing the data, just the video.

Noting the RMI as I fly down RWY12 at about 700AGL and the RMI pointer says I have passed the ARP, the power is on and away we go, in both video 3 & 4. So my start is consistent, yet going through 2500’ which is only 1500 of climb, the 25/25 is already almost 15F hotter. The time to 5500’ is 4.5min Vs 3.5 minutes.

I reckon if I climbed slower, apart from a pitch attitude more common to Jay Apt, the temps would have been more noticeable, but just a guess.


So a climb of 4500 feet and the time to TOC was in order of run, 3.5min, 4.0min, 4.5min, 3.5min.

The temps CHT was 15F hotter by 2500 and they started that run about 10-15 cooler.

Here is a photo I snapped with my iphone of the trusty G296.The inner most arc is the first run and the turn being done is the 4th run at the same place, same as the initial control run.http://i849.photobucket.com/albums/ab58/jaba430/photo-6.jpg

Once in the cruise, either an appropriate ROP setting or an appropriate LOP setting is the go.

Now I would really have to question why you think the engine life you are seeing in these engines is normal and acceptable:eek: Why is it acceptable to have engines that are run all the time in commercial ops (the best kind) to have tops at 1200 hours? That is not what I would call optimal. Operators in the USA who changed their training and better understood their engines soon find that their engines are reaching TBO with no or very little work, especially if fitted with cylinders that were built right to begin with. So your observation while you think it is good and normal, is exactly the opposite, but only because you have never known otherwise. TBO of those big cranky difficult radials (Wright & P&W) engines was around 3600, and run LOP!

mcgrath,

You would be correct, that would depending on the scale, be 75ROP which is best power. If it was 50 ROP or near enough some will be either side, but roughly that is near the high point of ICP and CHT, at around 30-40ROP.

This is not ideal, there are better places to be, but getting to the bottom of that in this one post is not possible. Bob's 2400/23" is at a power where there is not any real danger, it is not optimal, but it is not deadly.

If you guys want to talk about this some time get in contact with me, happy to help, but there is no simple post, no simple 30 minute phone call and definately no cookbook recipe that can be given. This is what the TCM and LYC manuals give you, a couple of samples recipe's they do not teach you about the engine. It really takes a 2-3 day APS course that is extremely well constructed, in a step by step building block approach. I have never heard anyone say they wanted their money back. Thats testimony in itself.

Unfortunately Ada Ok is a long way away, but I reckon there may be some classes in Oz in 2013, so hang in there, read the John Deakin articles until then. When I get a whisper I will make sure you gus are the first to know :ok:

[Jabawocky]

Trent

Yes you found one of Lycomings real Gems.

I dare you, pick up the phone and call George Braly and ask him what he thinks of that cracker.I know what he thinks, and why they wrote it too. i would love to see what you write back with.:E

You obviously will not believe me and all you are doing is ruining a constructive sequence of posts.

But at the same time, for the rest of the readers read that publication with a careful and critical eye.

They own graphs, their own comments, and their own contradictions. This is also the one where they say 98% of pilots are too dumb to do it safely.

And you wonder why I and many others are so critical of the TCM and Lycoming publications.:rolleyes:

Keep throwing them up, you are helpng my cause, especially for the astute reader.:ok::ok::ok:

[Trent 972]

Jaba, I'm sorry that you think I am "ruining a constructive sequence of posts". All I have offered to the readers of this thread is links to Lycoming's position.
You and I both know who Lycoming targeted with the previous link I put up.
As he could, he had his own shot back.
I'd like you to offer your thoughts on whether 'Detonation' can be heard in the typical GA engine in flight. I'm sure that, like me, you know that it is a much deeper sound and unless you know exactly what to listen for, it is almost impossible to hear. (unlike a car engine).
For those who didn't bother to read the link, here is the important bitLycoming is in complete agreement that it is possible to
operate an engine on the lean side of peak TIT. It is done on
engines in our well-instrumented Experimental Test laboratory
every day. There is nothing detrimental in operating an engine in
this manner. However, we can attest to the fact that things that
work well in the test laboratory have not always proven
successful in service. In the sales literature provided for this
“new” technique, it is stated that Lycoming recommended this
operational procedure in an owner’s manual that dates back to the
late ‘60’s. No mention is made why it is no longer recommended
on our present engines. The fact is that the technique of operating
lean of peak and power recovery was discontinued due to the
resulting increase in service issues.I have no doubt that you and your friends fit the first sentence, but the vast majority fit the last sentence. I wish you all the luck in educating the pilot fraternity, and hope that you have better success than Lycoming, who after years of preaching the same, gave up and now recommend the conservative alternative.

[Obidiah]

Somewhere in one of the Baron series POH's there is a statement that goes something like this;

When operating the engine at between 65% to 75% do not set mixtures between 25c LOP and 25c ROP.

This is a fairly broad range and I am certain that it is broad so as to accommodate the scatter of peak points on a standard engine. It moves you away from the narrow area of margin for detonation.

Trent

I am not prepared to discount the wisdom of the people who built the engine.


I doubt very much that when you read the POH you are reading the wisdom of those that built the engine. But the wording of the marketing/legal team. Many of the Lycoming Flyer articles are a great resource but the Flyer responding to LOP operations was little more than a hurt response from a company being exposed for not doing enough to accurately tune their engines. Humans are fairly predictable.

About a year or so ago I was speaking to one of Lycomings senior tech reps, he fully acknowledged the short comings of the old 50F ROP recommendation and much preferred running at peak. LOP was not on the menu as it was unlikely that smooth running could be achieved. Solve the smooth running issue and no problems.

Shock cooling is and is not a myth in much the same way as shock heating is and is not a myth.

If the cylinders are old, + 3000 hours they are reasonably fatigued if you subject an old cylinder to rapid cooling, say greater than 50F/minute and you commence this process from a high temperature were the tensile yield values are low you will probably enhance the risk of cracking in areas around steel components, such as valve seat inserts, the cylinder barrel itself and the spark plugs.

Those who have spent some time flying the small PW series radials (985/1340) will know all too well that the cylinders could have been in service since the mid 50's. They fail all the time, cracking ears and around the cylinder barrel, this happens regardless of how the engine is managed but those that boost them hard seem to have more failures than those that don't, (observation only).

I don't hear anywhere near as much carry on these days about shock cooling as was around 25 years ago. I think most have grasped the subject.

[Jabawocky]

Trent, don't take the ruining the thread too personally, it just interrupts a flow of good education.

But at the same time, it actually helps show the point being made. :ok:

I hope I did not offend, even though I was taking a swipe ;)

I have no doubt that you and your friends fit the first sentence, but the vast majority fit the last sentence.

The reason service costs went up was clearly demonstrated by the Mirage and the TIO540, and as I mentioned previously pilots thinking just a tad richer would be safer. WRONG. The old wives tales were the very reason they had this problem. It is well known and documented.

hope that you have better success than Lycoming, who after years of preaching the same, gave up and now recommend the conservative alternative.

The reason they keep giving up s even they can't teach it in a POH, just like a series of posts here, and they don't have the tools, people and they simply can't accept this.

TCM produce a poorly balanced engine but do it consistently. Lycoming produce worse F/A balanced engines but can't do it consistently. I have proven this myself. Huge variation.

If they can't sell well balanced engines they can't recommend using the efficient end of its performance spectrum. Funny how others in the industry can. Companies like GAMI lead the way, but others such as Airflow Performance have followed, engine builders in the USA such as Zepher, Barrett and many others, Aerosport Power for example. They can do it.

In Australia, we have Riverina Airmotive, anyone ever wanting good engine building, fuel system and injector tuning, be it GAMI or their own adjusted nozzles, and call Andrew Denyer, he has the gear, and he knows his stuff, if I have to find an answer for myself or others Andrew is one of 4 people I know who are the best to ask. Funny enough, they say the same about him :ok:

Get down to Brissy one day.......we can go play. Anything the airframe can take, you can do to the engine;)

Obidiah, funny how the old engineers who know their stuff will tell the truth.:ok::ok:

Clinton.....:D :D :D surely not, a legally endorsed document full of :mad: how is this possible. I wonder how far you have to look to find another one?

[Tinstaafl]

I had the owner of the PA31 install a JPI EDM760 when I took over managing the aircraft. Even though it's manual approved LOP, I wasn't prepared to do it with only a single point EGT. Or rather, do it only once or twice to show the owner the change in fuel flow and then back to ROP. Instead of automatically installing GAMIs, I suggested we suck it & see. As it turned out, both engines run smoothly at 50 LOP. That's 50 LOP for the richest cylinder so the rest are even leaner. Glad I had the EDM though - the richest cylinder wasn't the one that had the factory single point probe! Had I run LOP on the factory EGT then one or two cylinders would have been significantly richer than the measured cylinder.

As manuals go, this one is reasonably thorough in it's procedures for LOP. As I alluded to before, it includes instructions on what to do if the EGT limit is reached before LOP is achieved (reduce MP, continue leaning to achieve 50 LOP, then increase MP). Part of that includes a warning that MP will need to be reduced before enrichening the mixture again.

And this is the original factory flight manual/POH, not some after market product's sales material.

[Aussie Bob]

Whenever you guys do or recommend a course I am coming, until then ...

Once in the cruise, either an appropriate ROP setting or an appropriate LOP setting is the go.

WOT and 2700 is great advice and I will start and begin recording data (according to what I can), but cruise in an 0360? I can occasionally achieve LOP but not consistently and am hesitant to leave it there. Lycoming recommend cruising at peak ... This too doesn't "feel" that good, so in the absence of any hard data devices I have settled into a few divisions ROP where then engine "feels" happy. A few more perhaps?

I do tend to agree, a top at 1200 should not be necessary in an 0520, but these are not my engines.

My engine seems best at around 2400 - 2500 RPM, 2300 is "lumpy" 21 - 2300 is a red arc and ops below 2100 don't feel that good although I would love to experiment.

So what is the starting point for these settings?

Great thread and info from all participants http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/infopop/icons/icon14.gif

[Jabawocky]

Whenever you guys do or recommend a course I am coming, until then ...

Quote:
Once in the cruise, either an appropriate ROP setting or an appropriate LOP setting is the go.
WOT and 2700 is great advice and I will start and begin recording data (according to what I can), but cruise in an 0360? I can occasionally achieve LOP but not consistently and am hesitant to leave it there. Lycoming recommend cruising at peak ... This too doesn't "feel" that good, so in the absence of any hard data devices I have settled into a few divisions ROP where then engine "feels" happy. A few more perhaps?

I do tend to agree, a top at 1200 should not be necessary in an 0520, but these are not my engines.

My engine seems best at around 2400 - 2500 RPM, 2300 is "lumpy" 21 - 2300 is a red arc and ops below 2100 don't feel that good although I would love to experiment.

So what is the starting point for these settings?

Great thread and info from all participants

Carby engines are quite capable of running LOP, however the following needs consideration. The flat TCM/LYC engines are not real good in their F/A ratio's to begin with. The TCM is more consistent, the LYC not so much. So lets work through some things.

1. A conforming engine is one where, there are NO induction leaks, one of the things you learn in an APS seminar is about being able to fault find from the cockpit, and this is one of them. So all intake gaskets, couplings etc must be in tip top shape. I bet the majority of the fleet have one or more that are not.

2. Spark plugs: Gapped correctly, 0.016" to 0.018" and electrodes in spec. If they are Champions in particular, check the resistance, should be under 2.5k ohms and if 5K or more bin them. Tempest do not seem to suffer from this. If you drop one even from a small height......hit with big hammer, destroy threads and then bin them.

3. Harness and connection points all clean and in good order. Many I see are terrible, how people expect these things o work for 30+ years is beyond me.

4. Timing, go to great lengths to ensure this is correct. You would be surprised how many folk think their timing is set right and it is not. I recently had Andrew Denyer check ours, just for the heck of it, he could not believe how deadly accurate both were. He rarely sees that. Understanding that it is not hard to do, and that it must checked in the direction of rotation of the engine, which seems obvious when I say it, but is not to some folk apparently. If you are not qualified to change it, under Schedule 8 pilot maintenance you can remove a spark plug, and nothing stops you from getting a timing device and learning how to use it, you should be allowed to at least check yours. - Clinton may be able to offer an expert legal opinion here, but I do not see any act there that is outside Schedule 8.

5. Air cleaner is actually clean. Carby heat actually works! If you have a carby temp probe, this along with 6 eggs will come in real handy!

So when you think about fuel drops, mist and anywhere in between coming out of the carboy, around several bends, the heavy stuff wants to keep going the light stuff stays more or less in the flow. How do you think temperature affects this? There is going to be an optimum temperate through the induction system that achieves the best atomisation, and the best delivery to the head. Use the EGT's (all of them) and apply carby heat to determine at a constant cruise setting, a Delta EGT that is the lowest you can find. The actual numbers mean nothing just want the point where the difference is the least. You may also benefit from cocking the throttle plate a bit, not enough to make a big MP change, but just enough to stir up the airflow a bit more. Maybe do this first then apply carby heat. A few experiments are needed.

If you have a carboy temp gauge, once you have found this optimum, take careful note of the carboy temp. This is now the optimum. Every time you fly, set the same WOT(or cocked slightly) and the same carby temp, and go leaning.

Carby engines will vary a lot, so there is a chance you will struggle, but most of them given the above will play nice.

So Bob, in your case, in the cruise at say 5500-9500 there is a target of around 10-20LOP for the cleanest most efficient running, peak EGT under these circumstances is not bad, understanding that peak EGT is actually better than slight richer. Even in the safe zones, the temps and ICP's are lower at peak EGT.

The APS graph above needs to be studied and thoroughly understood to really get your head around things, and even when you think you have it nailed.....there is more. I don't know what I don't know, and this education process must be treated this way.

Lastly, if you are LOP RPM makes no difference but as a general rule find a smooth RPM for your engine., this may be 2437, or 2508, or 2600 or anywhere in-between. Prop efficiency plays a part so think about that too. but anywhere from 2400 -2600 should be fine, avoid the LIMITATIONS as you have some.

To finish off, as soon as I know when the APS guys (or any number of them) are coming down under, I dare say the news will spread pretty quick. So standby.

If you want some good reading material send me a PM with your email details.:ok:

[Jabawocky]

Clinton, great pickup!:ok:
I always find this one in the same POH amusingly circular:
Quote:
Changes in … power settings require the peak EGT to be rechecked and the mixture reset.
The implication is that ‘power settings’ are independent of mixture: you set ‘power’ then check the mixture.

I’m confident that power is, in fact, a function of, among other factors, the mixture setting …


You are indeed correct, on the Rich side of peak, in other words with Rich Mixtures, the HP developed is a function of MASS AIRFLOW, and once on the lean side it is about FUEL FLOW.

Now Brake HP caries a bit of variation from other factors and the Theta PP has an effect on this along with the frictional and compression losses so this is why the 1/BSFC can vary a bit. But for all intents the above concept is near enough, and if you look at the curves above you can see why the things APS teach are based around dat backed facts.

Onto the concept of rechecking the peak EGT, so long as you are LOP all you need is fuel flow to set power, and if using a Lycoming the Fuel Injection system will follow pretty accurately the changes in mass airflow, this is why the descent works so well. On a TCM the fuel delivery is pump RPM related so that is different, but if you vary the RPM both the mass airflow and fuel flow will change together.

[Trent 972]

Dear Sirs, What advice can you offer to the legions of young guys and gals busting their asses off in GA in the 'long grass ' operating aircraft that are more often than not, 20 years older than themselves and usually fitted with only the most basic of engine gauges? Can you tailor that advice bearing in mind that these young guys and gals change aircraft types throughout the working day, you know what I mean? A C207 in the morning or a 210 if they're luckier, a C310 later on towards lunchtime, a local scenic in the C172 in the afternoon and cross chartered C310 for afternoon delights.
The vast majority of these aircraft have been around the block quite a few times and I'm pretty sure that the EGT probe may not be on the appropriate cylinder and the last time the CHT gauges were calibrated is unknown.
I read that even a 1/16th inch gap in the engine baffles can make a huge difference to the airflow through the engine compartment. I only ask this because I can stick my arm through some of the gaps in the baffles on some of these old timers.
I read here that LoP operations is the way to go, but my companies ops manual just gives the engine manufacturers advice.
Please if you could, make your advice 'one size fits all' because as I said we don't have the luxury of getting to fly the same machine every day.
So far, because I am changing engine types and models throughout the day, I have been ultra conservative and running around RoP to be sure to be sure.
I see there is only one dissenter to your advice so far, that Trent goose, so I thought you might be the real deal.
We are almost to a person quite bright and intelligent and are more than capable of absorbing information or should we just keep being conservative. Please advise.
signed
The great many young CPL pilots flogging their asses off in the Great Australian Fark All!

[FokkerInYour12]

For aircraft without CHT running "somewhat" ROP is always risky because you don't really know what power level you are at. Running at best power means max CHTs.

For such aircraft, best to run at "best economy" which is simply:
Lean until slight rough running encountered, enrichen until it stops running rough, check periodically. Works for me and keeps the aircraft going to TBO in my experience (limited sample size though).

[Jabawocky]

Trent,

That is a RIPPER of a post :D:ok:

One of the best I have seen asking a really great question. And I am sure we all know what you mean about planes 20 years older etc.

Two answers for you.

A: There is no one size fits all COOKBOOK approach to this. I can't sit here and say just do this. even though fuel air and the combustion process is a constant, there are a few things you need. A bit like saying flying involves take off, fly straight and level, and land. There is a little more to flight training than that. So a one shot piece of advice acn only be found in answer B.

B: Advanced Pilot (http://www.advancedpilot.com)

I can't make any promises, and certainly not yet but there are a few people on both sides of the pacific working on getting some APS action down here next year. Time will tell, but they have done it before, so just hang in there for now.

Awesome post......awesome...:ok:

[Jabawocky]

Fokker, the problem with even that approach is at some times that is fine at others it is not, so when is and when isn't is not a judgement call you can make without really knowing stuff.

Often the scenario is fine, but is it the optimal solution.

Maybe your engine maintenance bill is fine, but as Aussie Bob showed us earlier, what he thought was a good run was actually far from optimal.

I am sure in a Boeing jet there are infinite numbers of ways to get from Sydney to Melbourne, and I could walk up and let her rip and arrive, but when a pilot who really knows his stuff does it, the fuel bill is going to be way less, and a whole heap of other stuff is going to be far oops...closer to optimal.

That help?:ok:

[ForkTailedDrKiller]

but when a pilot who really knows his stuff does it, the fuel bill is going to be way less, and a whole heap of other stuff is going to be far from optimal.????

Jaba, does that statement actually make sense to you?

Here's some more ForkWisdom for you to tear your hair out over!

For those you don't have an all cyclinder engine monitor and tuned gammis etc:

1) if in doubt leave it full rich in the climb or lean it only to keep it running smoothly
2) alternatetively, look at the EGT reading on TO and only lean to that during the climb
3) in the cruise, if you are confident that your power setting/ altitude has you below 75% HP, lean till it just starts to run rough then richen just till running smoothly

:O :O :O

Dr :8

[Aussie Bob]

Trent: These young guys and gals you are talking about will one day fly something for someone that is really nice. If they stay in GA it may just be something simple like a 182 that the owner is fastidious about, an owner who will listen. I meet lots of these folk, they let me fly their aeroplanes and they listen and are open to new stuff ....

In the interim, just follow the good Doctors advice back at #123

[Jabawocky]

Quote:
but when a pilot who really knows his stuff does it, the fuel bill is going to be way less, and a whole heap of other stuff is going to be far from optimal.
????

Jaba, does that statement actually make sense to you?


ooops I just fixed that......too many distractions


Yeah Forkie that will work fine, but it is sub optimal ;) And in aviation we always strive for excellence don't we. :ok:

No hair removal required.


Hey when is that TN, IO550, tip tanked FTDK going to be a reality?

[Obidiah]

Trent 972

For better or worse you are obliged to set what your boss asked you to set. SOP's do have merit.

However, a good one size fits all might be something like 75 ROP a power setting of 65% and the smoothest RPM that is within the parameters. Not grossly under or over square.

Treat your engines gently, typically maintenance and owners don’t

Hope that helps

[Jabawocky]

However, a good one size fits all might be something like 75 ROP a power setting of 65% and the smoothest RPM that is within the parameters. Not grossly under or over square.

Why would that be a good one size fits all? The very reason a one size fits all in a cook book like a POH is the very reason half this thread exists.

And if I run my engine at 980mb and 251 rad/s is that over square? I am sure there has been enough education on this forum already. Ohh and I do that about 60-80F LOP too.;)

[Trent 972]

And if I run my engine at 980mb and 251 rad/s is that over square?
HA! Trick Question!
The only time the mighty RV-10 could make 29in/2400rpm is below 1000 feet amsl (on an average day) and running 60 - 80 LoP at that stage is just showing off. :D

[Obidiah]

Jabawocky

The reason why it is a one size fits all is simply because it is.

Even John Deakin points this out in his writings.

65% power is not so high as to put you above some TCM recommendations on leaning and not so low as to result in low ICP leading to ring float and poor sealing. It also gets you from A to B at a reasonable speed in a naturally aspirated twin, and this is usually of financial benefit as maintenance costs out way fuel burn costs.

At 65% you can’t hurt anything.

75 ROP moves you away from the hot CHT values of ~40 ROP and as you are not striving for all out speed at 75% power, then little reason to run the richer mixture of 100 – 125 ROP best power mixture setting. So 75 ROP is a reasonable compromise mixture setting.

RPM set to wherever the engine runs smoothest. That should be a no brainer. Grossly under square can lead to the first point and is inefficient. Grossly over square will frighten the boss and when ROP the effective timing is too advanced.

Your bite on the metric v US instrumentation values is as meaningless as the OWT that states one shouldn’t run over square. The reality is all reading this understand what is meant by under or over square, it is a handy measuring tool. Having spent some time flying behind metric instrumented 1820 radials I find it not as intuitive as the US system.

There are not too many aircraft I know of particularly in reference to Trent 972’s question that will not be perfectly happy to run with this type of power setting. Sure there is better but that was not the question.

You won’t convert me to the APS way of running an engine, I was already there 14 years ago. As you convert to your new (?) religion try not to become too rabid and one eyed. WOT LOP is a great thing in the right place with a correctly set up aircraft, instrumentation and properly educated pilot. Remove one of these elements and you’re better off back with something like the one size fits all set up.

[Jabawocky]

The problem with a one size fits all is some poor chap is going to apply it wrong one day. Everyone who fears running LOP fears running it wrong.

My point is if you know what you are doing, there is a lot less to fear. I am glad you are one of them :ok:

Ahhh trent...... that little gem was for you, a thinking mans gag! :ok:

[Kharon]

Jabba #149 – "My point is if you know what you are doing". Now, there is the rub. Jabba, half don't understand (and won't admit to) suck, push, bang, blow; and, are not remotely interested. Bit like my Pa's beer analogy – he says - the young 'uns, never tasted good beer, so they will drink whatever; crook or not. Because they think it' a good beer, they know no better.

Those with the 'nowse', savvy or basic interest will come; there will always be those who slam car doors or simply wish to be seen as experts. Then of course, there is the dreaded 'legal eagle' angle. Take care mate, take good care and tailwinds.

[Obidiah]

half don't understand (and won't admit to) suck, push, bang, blow


Suck, squeeze, bang, blow. :E

[Kharon]

Obidiah: Maestro; mea culpa. I have read and appreciated (even agreed). Speaking as 'old school ' one who has operated (the engineers), normal, round, super charged and turbo charged engines (hell even the odd jet), without anything more than a couple of crook plugs, stuck valve and one (secret and private) fright.

The real issue (IMO) is that engineers are 'qualified' people, pilots ain't. The exponential increase in arrogance, is only matched by a lack of knowledge, i.e. the modern (non interested pilots) cannot and will not talk to the "Ginger beers'. Sad, but very true. It takes a lot more folk than a half educated pilot to get from 'push – to squeeze'.

Otto - over and out.

[Kharon]

There are some pilots who can, both bang and blow. Not rocket science, simple matter of engage brain, before opening throttle. Like that.....