Cowl flaps in hot climate

[Bones13]

Hi,

Just wondering what everyone does with the cowl flaps (specifically C206) in a hot climate (30+). Getting differing opinions.

Using open for takeoff/climb, and generally closed for descent (though most flying is fairly low level anyway (3000 and below)).
More interested in cruise position; whether they are open or closed all temps and pressures remain well within limits. The gain in airspeed from closing is pretty minimal over relatively short legs.

Do the rear cylinders receive enough cooling in this climate if cowl flaps are closed?

Cheers.

[Obidiah]

For start, taxi, TO, and climb....open.


If unusually short time to warm up or open cowls drastically retard oil warm up then perhaps nearly closed during initial warm up.


Cruise, set where experience and common sense dictates.


Descent, closed until circuit height.


Circumstances and individual aircraft will dictate slight variances to the above, these principals apply through winter down to ~10 degrees-ish. The biggest variance in winter summer cowl flap operation is the warm up and taxi period, there after the open until TOC applies.


Here is a tip, might be an old Deakinism, but when you cycle the cowl flaps from open to closed (assuming cable operated) you will feel an area of light load on the lever. This is where the cowl flap wants to "fly" and is balanced between pushing against external ram pressure and internal ram/static pressure.


This spot, around half way is not a bad spot to set for cruise if you are not sure where to set, it also gives you a bench mark to a setting that is either restricting cooling or forcing extra cooling. The problem you face is the industry on the whole is not much interested in aircraft engine operation, being such a largely insignificant component to aviating, that likely you're flying a machine with a compromised single CHT probe placement. If you are blessed with an all cylinder setup hopefully you got the training to go with it, judging by your question though this appears not the case.


"Do the rear cylinders receive enough cooling in this climate if cowl flaps are closed?"


It's not that straight forward, the hottest cylinder can move from left to right bank from middle to front to rear cylinder depending on cowl design, speed of flight, angle of attack and amount of power being used. It can help to think of the airflow being more dictated by pressure differential between top and bottom deck (above/below the cylinder line) and hence flowing downward rather than front to back although it does flow front to back as well.




If you want to see a case study of IO-540 abuse in AC50 Shrikes watch the GAM pilots the country over get cowl flap operation drastically and consistently wrong.


Fuse lit, runs for cover.

[RENURPP]

Maybe start with the questions, what should I try and achieve by changing the cowl flap setting?
If you understand why you move them, then asking for opinions will seem as rediculous as it really is.

[Radix]

..........

[Obidiah]

"Maybe start with the questions, what should I try and achieve by changing the cowl flap setting?
If you understand why you move them, then asking for opinions will seem as rediculous as it really is." (Quote thingy won't work)


A very good point.


Although often we will not know when we have achieved what we set out to as the level of engine instrumentation is so crude and basic.


Warm up and taxiing for example, the instrumentation will tell you that the cowls should be closed but hard won engineering knowledge will often point to problems with closed on the ground. In the cruise with one CHT probe, where to from here?

[Bones13]

What I want to achieve:
Well, all the poh says for cowl flap position in cruise is 'as required'. What I want to know is, what is the best for the engine (given available temps and pressures are all well within limits regardless of position).
Inclined to go with closed during cruise, if no other factors. Mostly just wondered if rear cylinders receive enough cooling of closed given high ambient temps.

[Aussie Bob]

You blokes ever heard of cylinder head and oil temperature gauges?

Edit .... Bones seems to have a general idea.

[Eddie Dean]

Could someone with multi cylinder CHT probes please tell old mate which ones run the hottest.? And when?

[Ixixly]

Open for everything but the Cruise and Descent IMHO. Yes the speed gain is small but it is still a gain maybe 3-5kts depending on your Aircraft, if you're flying for an hour that could mean about 1minute off the flight, not much I know but could mean the difference between a 0.95 flight and a 1.00 flight in the Techlog, do that same flight a few hundred times, say over 400hours that would equate to around 20hrs at an operating cost of say $400/hr and that's $8000 you cost the company just by not operating a simple lever. If you have a fleet of 3-4 Aircraft or more it all starts to add up and that could be your wage or your mates wage for the year! It could mean the difference between the Boss being flush enough to spend some money on extra maintenance or fancy toys like a decent GPS, JPI Gauges, an Upgrade to IO-550s etc...etc...

Of course this very much depends on the Aircraft and Climate you're in, I've had some Singles that you just cannot close the Cowls as they'll start to get real hot, real fast, so don't just do it and expect something, do it and make sure everything is working as expected.

Incidentally, it could save your Exhaust one day, I had a guy who had the Exhaust become disconnected and the only thing that stopped it from completely dropping out the bottom of the Aircraft was the fact he had his Cowl Flaps closed!! the sound it created scared the crap out of him, haha.

[5-in-50]

open, open, open and open. This is Australia, not Alaska!

Cowl flaps are made for colder climates like the USA where engines need to be kept WARM, not Australia's conditions.

Leave them open for ALL operations except possibly a long descent on a cold day.

There are a number of approved modifications available that fix cowl flaps in the open position for the Australian temperatures, and this does not effect engine life or operation.

[Big Pistons Forever]

If unusually short time to warm up or open cowls drastically retard oil warm up then perhaps nearly closed during initial warm up.



r.

The Cessna 206 POH does not permit the cowl flaps to be set to anything but open when the aircraft is started, taxied, runup or for takeoff.

[Aussie Bob]

open, open, open and open. This is Australia, not Alaska!

Struth, words fail me.

[LeadSled]

BPF,
At least somebody has the good sense to mention the AFM/POH.
Tootle pip!

[Defenestrator]

In the absence of common sense and experience talk to your chief pilot and familiarize yourself with the POH.

[The Green Goblin]

The silliest thing you can do is open them after long descent at low power settings in the circuit.

Keep them closed until on the ground and tie them into the flap sequence. Flaps retracted cowl flaps open.

The AFM is the best resource, but it's a one size fills all proposition. Watch the ts and ps and act accordingly.

[Bones13]

Problem is the c206 flight manual just says during cruise open 'as required'
What is 'as required'? If ChT And oil temp/pressures green does that mean ok? (Given cht is hottest cylinder?)

[Aussie Bob]

Bones, the CHT in most 206's is a rather rudimentary gauge. If yours is any good, and assuming it is fitted to the hottest cylinder, I would aim to cruise with the CHT's always lower than 380.

So you could try cowl flaps shut under 370, approaching say 375, cowl flaps open or part open. You will need to experiment. Watch the oil temp as well but here I would just monitor the red line. Approaching oil temp red line, cowl flaps open regardless of CHT.

Unfortunately most CHT gauges are not that good. If it was my aeroplane it would have an engine monitoring system that looked at all cylinders.

Opening the cowl flaps after a long descent will do no harm whatsoever, my preference would be to open them on downwind or according to POH.

Closing them will give a few extra knots and may provide more uniform cooling but again without a monitoring system you really have no idea.

[Bones13]

Thanks Aussie Bob.

My CHT reads 340-350 cowl flaps open and 355-365 closed (never seen it exceed 370 in cruise). Oil temp varies between 170 and 185 depending on cowl flap position, so well below 240 red line.

Cheers

[Centaurus]

In the absence of common sense and experience talk to your chief pilotJust because he has risen to the post of chief pilot does not mean he is an expert in engine handling. He will have his own personal ideas on engine handling and is in a position to insist his employees do what he says.
Every pilot has opinions on engine handling usually handed down from who ever checked him out.

The AFM and POH give the manufacturers recommendations. Stick to those publications. Finally, read the advice by John Deakin, the author of the "Pelican's Perch" His advice is gold. Google his name.

[RatsoreA]

What about high powered, high performance machines, like the humble Aerostar, which is completely devoid of cowl flaps?! They seem to get by in hot parts of Australia just fine without them!

[Radix]

..........

[Old Akro]

I think I'd be worrying less about cowl flap etiquette and more about flexible baffle condition, chafe strip condition and holes, gaps in the aluminium baffling to the engine.

Engine cooling depends on about a 4 psi differential between the top of the engine and below it. Cowl flaps serve to reduce the pressure below the engine by virtue of the venturi effect.

Job 1 is to make sure all the elements of the cooling system are in good condition and doing their job.

This goes for the oil cooler too. A significant proportion of the total cooling of the engine is done by engine oil. Make sure the oil coolers are clear with no bent fins and (one again) properly sealed.

[Bones13]

All baffling and the oil cooler look good in my engine. Only concern really is whether the indicated CHT is actually the hottest and that the rear cylinders are actually sufficiently cooled.

Cheers for all the replies!

[rnuts]

Bones13
Old Akro has covered it !!
Good to see some helpful responses as apposed to some of the smart a$$ comments you get on here.
I flew 182s and 206s years ago meat bombing and we always left the cowl flaps open for climb, then closed for jump run and descent. Once on the ground, retract the wing flaps and open cowl flaps.
Never had to replace a cylinder so it seemed to work well.
If you're flying a 206 with a pod they modify the cowl flap range as part of the fitment.
Cheers

[Mick Stuped]

Bones,
Common sence is the rule with cowl flaps. Watch your CHT. Heat is related also to power, more power more heat. So cowl flap settings are linked to power setting. If on one side you are doing a lot of high power low level work on a hot day your CHT will say leave flaps open, if you are at low power settings in the cruise at altitude then your CHT will say close flaps. The POH is right "as required". Don't lock yourself into doing something because some expert says do this or that unless you can see a logical argument to change. Think about what is happening under the cowl what the CHT,s are telling you. Get a EDM that monitors all cylinders as how do you know what the others are doing.
I urge all pilots to understand what's happening under the cowls and how to make your engine happy. That's the best and safest and most economical way to operate. Understand what CHT your engine is happy at, set yourself a mental alarm eg happy at 350-375 ROP but when we start heading to 400 keep an eye on it, over 400 maybe crack cowls a bit to keep under 400. Now that is only an example as every engine type is different. Talk to an engineer for specific or god forbid look up the POH.
I wish EDM,s and how they relate to good operations were taught as part of the flying syllabus.
If not make it a priory and read up on stuff John Deakin, Walter Atikinson and Goerge Braly have been saying for years. First came across their management ideas 15 years ago and started running our aircraft with their management styles and get all our pilots to understand why engine management and understanding of what they are seeing in front of them is so important to a healthy happy engine.
By the way I have nothing to do with APS. But recommend their courses.
MS

[outnabout]

Yes,talk to your chief pilot but also talk to the Head of aircraft maintenance at your organisation. Hopefully they will be on the same page re engine management. (God help you if they are not).

Otherwise Mick Stup is on the money. Maybe try & convince the boss that an APS course is a good idea (because it is). Otherwise try & find some spare coin and do it for yrself. Not sure if it's tax deductible as part of work related self funded education.

Also not related to anyone at APS but do use the knowledge I learned there every time I fly, with the CP / Haamc / Engineers approval.

[Obidiah]

"What about high powered, high performance machines, like the humble Aerostar, which is completely devoid of cowl flaps?! They seem to get by in hot parts of Australia just fine without them!"


If they do then they are simply unnecessarily overcooled in the cruise and suffering from excessive cooling drag.


Talk to any high performance non cowl flapped kit plane owner about spending undue time on the ground with the engine running.


If you want to see what a 540 donk install looks like on an aircraft that spends its time at high power and low speed and lots of ground idling then look at the size of the cooling outlet on a Pawnee. And still you can get them so hot you can actually feel the powering dying.

[Pinky the pilot]

In PNG years ago when flying some rather well used A model C402s the Company policy was cowl flaps open for all ground ops, T/O and climb, closing them about 200' short of cruise altitude.

They remained closed until after landing when opening them was part of the After Landing checks; ie Flap lever located, identified and flaps Up, cowl flaps Open etc

[UnderneathTheRadar]

"What about high powered, high performance machines, like the humble Aerostar, which is completely devoid of cowl flaps?! They seem to get by in hot parts of Australia just fine without them!"


If they do then they are simply unnecessarily overcooled in the cruise and suffering from excessive cooling drag.

Bit oversimplified here. High performance machines generally do a few things differently like:
1. Climb faster (higher TAS - more cooling airflow)
2. Cruise higher (cooler air)
3. Climb quicker (less time to get hot)

My Aerostar, when it's hot, can't climb at anything near best angle or best rate without the CHTs creeping up. Fortunately, I can still climb at >500fpm at Vy + 30kts. Ted Smith has been accused of many things but 'unecessarily overcooled in the cruise' isn't one of them. Never have any problems with CHTs on the ground.

Your Pawnee example is true because they're designed to fly slow and low - and need to compensate for a lack of cold ram air.

UTR

[Obidiah]

"Bit oversimplified here. High performance machines generally do a few things differently like:
1. Climb faster (higher TAS - more cooling airflow)
2. Cruise higher (cooler air)
3. Climb quicker (less time to get hot)

My Aerostar, when it's hot, can't climb at anything near best angle or best rate without the CHTs creeping up."

1. It is not the TAS that cools it is the IAS
2. Higher = less air density which reduces cooling capability, not sure where the cross over of reducing OAT and air density is but suffice to say at FL's (with turbo/super charging) you will struggle with cooling


Your last comment sums it up, it is either overcooled in the cruise or under cooled for low speeds and ground ops, hence why cowl flaps were invented, you can't have it both ways.

[Old Akro]

At the moment the centre 2 cylinders on our TSIO360's are running hottest. However, despite our baffles LOOKING good, you can see an airflow pattern and location of 2 leaks on the inside of the cowl. These can be traced to 2 issues in our case. Firstly, an area where the baffles don't conform around a strengthening rib adequately and secondly where a LAME has taken some shortcuts in fitting new baffles and not running replacement baffle strip far enough forward to seal to the nose bowl.

I expect that when we correct these deficiencies that we will have quite even CHT's

[Jabawocky]

I have just returned from a packed out (above MTOW) APS class this weekend. Boy am I wrecked! Owners, commercial operators and everything from a Jabiru powered U/L to a C421 owner, Chieftan and Airvans……what a great mix!

I am most pleased to see this thread and some good advice in it. I have a few thoughts, first of all to anyone reading it,PM me your details and I will keep you informed when the next class will be.

First of all a little mind game. A previous student reports that after the class and learning the "really old way" of operating his C182 (IO540) he was able to do the following things. Burn way less fuel, have more range, cooler CHT's and actually have a higher IAS/TAS. How is this possible when WOT/2400 and ROP produces more HP than when he was WOT/2400 and appropriately LOP?

The simple answer is he could now contain CHT to a reasonable level with the cowl flaps closed and they remained lower. A win / win I would say.

The secret to all this lies in the following. First of all you need to get your Fuel/Air ratios sorted out. This then balances up the heat IN part of the equation. Then you can work on a level playing field at getting the baffles etc sorted and thus the heat out part of the equation fixed. What is left is the cruise CHT, and if you have the first two sorted the cowl flaps can be closed.

DO NOT go monkeying around with the injectors unless you work for GAMI or your last name is Denyer and you have a flow bench.

SLIGHT CORRECTION FOR A STATEMENT ABOVE
It is a commonly held belief that the higher the power higher the CHT. this is not true. In fact at 500 feet running WOT/2500 and 80dF LOP generating 82-84% power my CHT's are 30 or so degrees cooler than FL130 WOT/2400 and appropriately LOP. Someone above (not radar identified) mentions the air density. :ok:

It is also true that even generating the SAME horsepower at the same altitude but using two different methods of doing so will result in different CHT's. This is all to do with the effective timing of the engine controlled by mixture, resulting in a different placement of ThetaPP, which results in a higher or lower peak pressure. It is the magnitude of the peak pressure that determines the heat into the cylinder head, and not the HP or fuel flow. This is not what we are taught in flying schools.

In the photo on the front cover of the APS class manual you can see if you look closely some interesting data. Besides weather, look at the engine instruments. Both engines were generating the same HP, the pilots feet were flat on the floor and the skid ball in the middle ;)
http://i849.photobucket.com/albums/ab58/jaba430/APS%20front%20cover_zpsku5rplwe.png

Any questions drop me a line!

[Bones13]

Interesting stuff there ^

A bit off topic, but what sort of CHT (if so?) can tend to cause cylinder glazing.. Experienced this and someone brought up cowl flap use (without explanation). My general understanding is that it is caused by light engine load or improper breakin.

[Jabawocky]

You were correct. It is from babying it during break-in. During break in it is important to have high MEAN(average) EFFECTIVE PRESSURES and not necessarily high peaks.

In other words, engine power settings at greater than 75% is generally considered the goal. So lets assume that is 225HP on a 300 HP engine. You want the high MEP rather than a high peak for two reasons, one has a greater sweep of piston ring travel with a highish pressure and you want the one that has the lower CHT.

This is where many LAME's and all but a few engine builders come unhinged, because the best way to achieve the better break in is using a LOP power setting. Of course some engines straight out of the box will not have good F/A ratio's and thus will not run smoothly LOP. If you can get that sorted at the beginning that is the best way. If you can fit a set of GAMIjectors and go for it, even the first cut is usually good enough, and you can tweak them during the break in period. Which by the way is really 5-6 hours and certainly by 10.

If you can't get a smooth engine (good F/A's) then do the break in at say 75-80%, which generally equates to 5000' or 24" and 2600 RPM in most engines and FULL RICH.

Vary the RPM occasionally and don't be afraid of it. Not a good time to baby it.

One method has cooler cylinders, better mean effective pressures over a greater sweep and is by far cleaner on the combustion chamber etc. One is lighter on your wallet too!

[Aussie Bob]

Babying the engine is a false economy. I recently watched a top overhaul on an O-470 at 1000 hours due to glazed bores. The fact that the owner insisted that the plane was warmed on the ground until the oil was "in the green" then insisted on reducing power as soon as the flaps were retracted was considered a contributing cause.

My gauge of when to take off has always been CHT. Once the first cylinder hits 300 I am away regardless of oil temp. In my POH (for an O-360) it clearly states that full power can be applied as soon as the throttle can be advanced without hesitation or rough running.

I recommend a Jabba (APS) course to any piston aircraft owner.

[Radix]

..........

[601]

What about S/E ops in a Chieftian.

Cowl flaps open you will most likely not be able to maintain height.

Cowl flaps closed, you should be able cruise and maybe climb but from my experience doing endorsements and also according to the very experienced pilot who did my endorsement in BK last century, the live engine will most likely over-temp.

[Old Akro]

If I had an engine failure in a Chieftan for real, I don't think I'd be worry to much about high CHT's.

[Pinky the pilot]

I had two genuine engine failures in PNG flying 'Bongo vans' and I can assure you that high CHTs on the remaining live engine were not even a passing consideration, at least for the first few minutes anyway!:eek:

Once I had everything dealt with, and was headed back to base I then considered the state of the remaining operating engine.

Going down in the approximate area of where one initial failure occurred could possibly have resulted in another aircraft missing and never to be seen again.:ugh::hmm:

[Obidiah]

"A bit overstated again. The venerable GA8 Airvan for example has 'smart' cowling that is designed to produce different cooling airflow at low speeds versus high speeds. All because angle of attack will be different. So, have it both ways without those pesky cowl flaps! And it works very well."


Ok I'm in.


How does it work?


Jabawocky,

"It is a commonly held belief that the higher the power higher the CHT. this is not true. In fact at 500 feet running WOT/2500 and 80dF LOP generating 82-84% power my CHT's are 30 or so degrees cooler than FL130 WOT/2400 and appropriately LOP."

That statement is likely trip off a whole new round of incorrect myth and confusion for some low time/experience pilots.


It is imperative to apply sound scientific principals in your above comparison and that means you must have exactly the same configuration bar one change, the power output. Same AoA same mixture same OAT same altitude same IAS same cooling configuration.


If you do that and increase power you will see greater heat loading and therefore a CHT rise. I point this out for the benefit of others as I have no doubt you know all this and it was just a somewhat rushed statement at the end of a long day.


Certainly using the full mixture spread capability you can do many things with temperature including increasing power whilst reducing CHT and EGT, but this is not the same as saying it is not true that the higher the power the higher the CHT.

[Obidiah]

A few years back I decided my aircraft was due a tidy up on the engine baffles, nothing bad just a few cracks here and there, stiff baffle rubbers the odd gap, you know they story. This is an updraft cooled pusher.


So in I went, it took about 3 times longer than I thought but I wanted it the best it could be.


Previously it was not unusual to see the coldest sitting on 310F and the hottest at 375F


I was more than a little pleased to see on the first flight that with mixture and throttle butterfly positioning I could achieve all 4 cylinders within 2F of each other and sitting around the 330 mark.


What really surprised me was the effect it had on the EGT spread, the O-200 is about as crude as they come and the EGT's were generally random but could be manipulated with throttle position, carb heat and mixture setting. Whilst there was a pattern it was complex and fluky to replicate.


Now with tidied up cooling a distinct repeatable pattern emerged, at WOT the front pair carried significantly higher CHT's than the back pair due to the front pair running much leaner. Cock the throttle butterfly a few degrees by coming off WOT and everything starts to even up. So much so it is nearly smooth enough to go over the hump to LOP. Makes me think this might be one engine that could actually see significant benefits from an internal induction flow straightener or at the other end of the spectrum a swirl plate eg. Hyclone device.


All from attention to detail on a engine baffles.

[Jabawocky]

Obi, too many variables here, but you have quoted me well out of context. And yes it is true that to explain things properly in an internet forum post is impossible. Heck we take 2.5 days to get people to the point where they have a good starting point of understanding.

Let me try to clarify things and maybe expand further.

Jabawocky,

"It is a commonly held belief that the higher the power higher the CHT. this is not true. In fact at 500 feet running WOT/2500 and 80dF LOP generating 82-84% power my CHT's are 30 or so degrees cooler than FL130 WOT/2400 and appropriately LOP."

That statement is likely trip off a whole new round of incorrect myth and confusion for some low time/experience pilots. (no more than the myths they get taught at flying schools all over the country ;)


It is imperative to apply sound scientific principals in your above comparison and that means you must have exactly the same configuration bar one change, the power output. Same AoA same mixture same OAT same altitude same IAS same cooling configuration. No, not really. The statement was that I can have higher power being proceed and lower CHT, which given the higher density of cooling air and equally appropriate low ICP's is very real. However I will explain in more details below**


If you do that and increase power you will see greater heat loading and therefore a CHT rise. I point this out for the benefit of others as I have no doubt you know all this and it was just a somewhat rushed statement at the end of a long day. It was the next morning…but I was recovering from a long few days :ouch:


Certainly using the full mixture spread capability you can do many things with temperature including increasing power whilst reducing CHT and EGT, but this is not the same as saying it is not true that the higher the power the higher the CHT.
Help me here, this does not make sense. How can I use mixture to increase power AND reduce CHT under the constant parameters of flight? The EGT absolute value is of no concern and not relevant

** To explain the answer about power settings at the same altitude on the same day, let me copy a small extract from an article I wrote recently that is yet to hint the printers. This might make some sense.
So what did we get for our trouble? Sure we dropped a few knots, maybe 5% but we dropped about 43% in fuel flow. I know what some of you are thinking, but that’s not the same power, and while that is true, it is not much less and the simple test was to reduce the RPM or MP to achieve a few less sucking events per minute to around 26”/2400 rpm and a fuel flow of 78-80 LPH, so HP per HP that is a reduction of 33-35%. Still serious in terms of my wallet.

Interesting question comes to mind, how does this affect the engine stress? We know from science and data collection over the last 65-75 years that the relationship of internal cylinder pressure tracks accurately with CHT, and in fact it is the driving force literally for the CHT. If you are having trouble thinking about this think of your home garage air compressor. Just don’t add any fuel, to the intake, it might not end well.
So at low level and a nice dense air flow, what are the CHT’s typically on the RV10? When run rich of peak at the same 80% power they are typically in the range of 345 to 375 degrees F, and yet when run LOP for the same 80% power they are around 305-335 degrees F. How can this be?


Drop me a line if I am missing the mark or confusing the question. :ok: PM me for my phone number if you want.

[Obidiah]

Jabawocky,


I think we might be getting lost in the translation somewhat, please forgive me the quote function is U/S so I’ll use italics instead.


"That statement is likely trip off a whole new round of incorrect myth and confusion for some low time/experience pilots. (no more than the myths they get taught at flying schools all over the country"

Yeah yeah, but still not good to use others failings to justify yours, but I take the tongue in cheek delivery.


"It is imperative to apply sound scientific principals in your above comparison and that means you must have exactly the same configuration bar one change, the power output. Same AoA same mixture same OAT same altitude same IAS same cooling configuration. No, not really. The statement was that I can have higher power being proceed and lower CHT, which given the higher density of cooling air and equally appropriate low ICP's is very real. However I will explain in more details below**"


Well it certainly read that way, and here it is……….. "It is a commonly held belief that the higher the power higher the CHT. this is not true. I could forgive some newbie for taking that at face value because it is pretty much a standalone statement although later qualified by how you did it.

The point is if no other parameter changes except power is increased then a higher CHT will follow, these engines are after all heat engines by principal. Therefore it IS a correct belief in its purity.


“Certainly using the full mixture spread capability you can do many things with temperature including increasing power whilst reducing CHT and EGT, but this is not the same as saying it is not true that the higher the power the higher the CHT.
Help me here, this does not make sense. How can I use mixture to increase power AND reduce CHT under the constant parameters of flight? The EGT absolute value is of no concern and not relevant”


Perhaps I mislead you, I am not suggesting here that power was increased with mixture alone just that the full ROP/LOP spectrum was available, what I was eluding to was that with a throttle or RPM derived power increase you can then manipulate the mixture setting from a ROP setting to a LOP setting and achieve higher power with a reduced CHT. For example (and telling you nothing here) increase power by say 4” of MaP and from a setting of 25 ROP then reduce mixture to 35 LOP and you will likely be in the paddock of increased power and reduced CHT. The EGT inclusion was for illustrative purpose, of course it is irrelevant unless you are sitting on a highly strung turbo system.


The original point I was making was that yes it is possible to increase power AND see a reduced CHT, but I see this as vastly different to your opening statement claiming it is incorrect to believe that increasing power will increase CHT. It might be obvious to those in the know what the point is you are making but a new mind trying to unlearn and relearn the true principals of combustion needs to be handled carefully.

[Jabawocky]

I reckon we are on the same page then :ok:

[The name is Porter]

In my POH (for an O-360) it clearly states that full power can be applied as soon as the throttle can be advanced without hesitation or rough running.

Who decided that this could be ignored? I don't know how many 30 year pilots I've flown with have decided that oil temp must be in the green before run-ups or take off.

[Aussie Bob]

I dunno Porter, but I can tell you I am over pilots who want to warm up "till the oil is in the green". It is possibly pointless, unnecessary and not in any engine book I have looked at (which is not a huge amount). I guess it could be beneficial for anyone logging or charging on an oil pressure switch though.

[The name is Porter]

Well, Jabba is doing good work. I view nearly everything a pilot says as an OWT. The science and data says otherwise on most things!

[Capt Fathom]

So I guess this wraps up Cowl Flaps then?

[Aussie Bob]

So I guess this wraps up Cowl Flaps then?

Perhaps if we keep going Tailwheel may change the thread title? I am interested in where the OWT "lets glaze up the bores by bringing oil temp into the green" comes from. It's nearly as bad as the less common "let's close the cowl flaps to speed up the warm up" which I hear occasionally.

[Jabawocky]

Are you saying the cowl flaps are closed? :}

[Obidiah]

Just because the POH states you "can" apply full power the moment the engine will do so without hesitation doesn't mean you should. It just said you can, nothing more nothing less.

I am pretty sure, but I am not going to try it, that all the flat engines particularly the fuel injected ones are more than capable of coming off the starter motor dead cold and straight through to full power without hesitation.

The only engines I have operated that will stumble on a cold morning are the 985, 1340 and 1820, (the entirety of my round engine experience) they seem to lean snuff out if you open the throttle to quick when they're cold and the air is really frosty and atomisation is quite poor.

Incidentally the 1340 I operated (Ag) used to be set to idle around 450 rpm from start up on a cold winter morning and there it would sit for up to 20 minutes until the 70w oil would reach 40c then you could open the throttle. Reason being the super charger bearing spinning at 10:1 of crank speed (4500 rpm at 450 rpm) could burn (coke) the oil onto the bearing races in the cold oil.

The hell you say.....but trying to spin a bearing in a thick medium at speed and an enormous amount of friction is created, the result of which is heat.

Well so the overhaul boys would tell me.

We did suffer the odd glazed cylinder from time to time though, no probs, pop it off hone it and good to go. Maybe that's were the notion of glazing cylinders by waiting for the oil to reach the green came from??

For those (Aussie Bob?) that are implying bad things will happen if you close the cowl flaps to assist with a warm up. Care to explain what those bad things might be or do we wish to leave that statement hanging so that those not in the know form their own opinion on what those things might be. I see a little bit of lee way here with regard to cowl flap ops in frosty conditions, but it is important to explain the why's.


My knowledge of the bad things comes from APS and John Schwanner (of the Skyranch Engineering Manual fame) but I'll let you explain to the masses why it can be bad in certain circumstances and the issues it creates.

[Jabawocky]

Obi,

Well saidJust because the POH states you "can" apply full power the moment the engine will do so without hesitation doesn't mean you should.

I have always wondered how you would know….because you don't know until you try it. Yet another silly statement in POH's.

I think Aussie Bob's concern will be that the checklists may not contain a "check cole flap open" when it was previously done elsewhere in a checklist, and thus the pilot does not check because they do everything by rote and takeoff with them closed.

Not that it will kill anything, and if the alarms are set correctly (which all the certified glass is not) then a timely alert will sound or blink long before it becomes a problem. Of course those with the manufacturer alarm thresholds will just have to rely on noticing or wait till they over temp the engine. But they will know about it at least! ;)

[Aussie Bob]

Obi, I agree with everything you say and I add I have no experience with any radial other than the P&W 985.

I do not ever apply full power straight from a start up but I am also sure it could be done without hesitation. My engine book states that I can do it. I don't.

I believe the cowl flap closed to assist warm up is a waste of time and detrimental to flat engines because they are air cooled and closing the cowl flap with no real airflow through the engine (stationary) will result in uneven cooling. No data sorry, my plane only has ground adjustable cowl flaps. The pilots that I see advocating this are doing nothing more than guessing (if it is not in the POH) and if I recall correctly both the 206 and 185 POH's state cowl flaps open for all ground operations.

Here was yesterday courtesy of an engine monitor.

Start up at 10C
1000 RPM for 2 minutes while seat belt is fitted, oil temp 50F, CHT's through 150F
Power up to 1500 to get moving on long grass
Taxi 600 metres. CHT's now approaching 200F oil at 60F
Run up and cycle prop, CHT's now approaching 300, oil at 70F
Check idle then take off with CHT's around 300, oil at 77F (still below green arc)
At 500 feet, CHT's around 340 and oil suddenly at 120F (well into the green)

I suspect my oil temp sender is where the coldest oil is.

Most engine problems that occur before TBO relate to cylinders, induction systems and turbochargers. The bottom end of most aircraft engines is pretty bulletproof apart from the odd lemon like the 320 H2AD which had a propensity to gall camshafts. Other problems are from lack of use like rusted cams or cracked cases due to too many overhauls perhaps. It is my theory that a flat engine is ready for takeoff power once the cylinders are around 300F.

It is my aircraft, if I was operating yours I would do exactly as you wanted as opposed to "Aussie Bob theory" which is all it is. Works for me. I was going for an annual by the way, all cylinders were good and there was no metal in the filter.

[Obidiah]

No worries Bob.


Not sure where your oil temp is picked off from but suffice to say that sudden jump from an oil temp of 77 to 120 at T.O. is likely an indication that your vernatherm is doing its thing and recirculating oil and bypassing the cooler. I would not think the pick off is at the coldest point it is usually at the end point of its journey through the working internals.


For those wondering what this strange worded device the vernatherm is, it essentially a thermostat for your oil circulation system that regulates the flow through the oil cooler. I can't give you much more than that as I am not a mechanic.


Bob you mentioned no real airflow through the engine when the cowl flaps are closed on the ground. I disagree there is still considerable airflow just not enough for proper cooling in most normal conditions on the ground. My personal observation on some types, Shrike is one I recall is that with the cowl flap open on a frosty morning the oil temp can take an age to get to the minimum for take off (75f from memory).


My personal technique on the Shrike was close them up tight for the first 1 or 2 minutes then open to half after that and full open 1 or 2 minutes later. But this is for sub zero OAT starts. All other times open before start, that way I can hear their little electric motors running and get a feel on how they're doing out there. They have a tough life and get little to no attention, cowls were always parked closed after shutdown.


But closed can lead to issues during the warm up if not done with some thought and understanding.


Back in the late 90's early 2000's John Deakin (as I recall) equipped his Bonanza's cylinder barrels with some temp probes at various locations around the circumference. What he discovered, and this was only on his Bonza was that there was poor cooling airflow around the cylinders and a wide range of temps were recorded.


He also stated and again on his Bonza that the under cowl footage showed the cotton tufting flew best when run ups were done bum to wind. I would like to see a lot more on that before I bought in. I would strongly caution against this unless you own shares in a prop company or hate your boss and can blame another pilot for the fact the blade leading edges look like steak knives.


Over to John Schwanner's book The Sacramento Skyranch Engineering Manual which from memory has some photos of cylinder walls with 4 equally spaced vertical scoring marks attributed to strong differential temperatures around the cylinder barrel. The marks are a result of piston to cylinder contact due to warpage attributed to the cylinder base nut configuration under unneven temps. Note no present barrel temp instrumentation for this just one probe per head if your lucky. Once the cylinder/piston reaches operating temps the clearance tolerance fall into place, particularly as the top of the cylinder is choked (smaller). However when still cool the tolerances are tighter.


Have a look at your inter-cylinder baffling on your particular aircraft, on the Shrikes I flew the inlet opening of the wrap around cylinder baffle might be 30mm and the outlet 5 to 10mm. Almost nothing so a strong pressure gradient is required to get anything to pass through here and in light of the only airflow being from a prop creating the high and low pressure and the inherent gaps and design flaws in the baffling system we really are up against. Having said that the first 30 seconds you could near still hold your hand on the barrels so in icy conditions you are pretty safe for a few minutes, in fact the sooner you can get to operating temperature (with in reason) the better and the piston gets a head start on expanding as its alloy and at the coal face, the barrels lag being steel and not at the blast face.


The key to it is to not exacerbate the already crudely designed cooling system with poor cooling air distribution and pressure gradient unless there is good reason. Frosty mornings are the only good reason and it doesn't stay frosty for long under there.


I think it was John Scwanners book that stated you need 6" of water column pressure diferential to adequately cool a 300hp aircooled engine. It takes 160kph of airflow in the front and most importantly around the outlet lip to create that differential. A prop won't come close


As they say warm up fast cool down quick they do.


The above is all from my memory and posted on a forum for aviation nutters by another nutter who likewise likes the sound of our own opinions, seek clarification before adopting.

[Aussie Bob]

As they say warm up fast cool down quick they do

I am a man with a lot of engines, almost embarrassing, there are tractors, cars, motorcycles, chainsaws, vintage stationary engines and more around here, all being used.

But it's the humble air cooled petrol driven aircraft donk that has my greatest respect. So well built, so hard working so well thought through.

[Lumps]

Aussie Bob, were you thinking of the R2800-R3350 etc when you say air cooled aero engine so well thought through, or the flat engines? Obviously they didn't think the induction / injection through on the latter - or did they? Is it true that they never bothered to balance the FA ratios because they had no say on the wide variety of airframes (induction systems) that the motors would be installed on. But then the early Malibu shows what can be done, so why wasn't this done all the time?

I would like to believe the modern flat engine is still a marvel of engineering but I am no engine connoisseur. If BSFC is the measure a TNIO-550 LOP is pretty impressive, but then a diesel is better again...

[Aussie Bob]

Lumps, this has been done to death already, use the following Google search or similar: "pprune lean of peak" and as I said previously, I have no experience on round engines except for the 985 and that was long ago.

Contact Jabawocky to do a great course on engine management, fuel air ratios, LOP ops and more. An eye opener.

[Lumps]

Nah that last post was an opening for something more specific.

S'ok I'm done

[LeadSled]

Folks,
Unless I have missed something in this discussion, I haven't seen any reference to the type of oil engines are using.

Unlike motor oils, few aircraft oils are multi-grade, and when it comes to radials, much the consistency of treacle when cold.

Hence the widespread use of oil tank heaters to bring the oil up to a "flowable" temperature before pre-oiling and starting -- radials.

Likewise, sump or oil tank heaters (and sometimes pre-oilers) are commonly used in colder climates, such as parts of the USA and Canada, or in really cold conditions, heaters for the whole engine --- any type of piston engine.

I can't say I have looked recently (being largely involved with radials) but last time I took much of an interest, I didn't see any multi-grade oils around, and there were certainly none approved for my old IO-470Ms in Australia.

In USA, there are some excellent multi-grade aero engine oils available, but they have not often been approved by the manufacturer (or in the case of Curtis-Wright engines- no manufacturer exists to "approve" them). Of course, FAA being FAA, and not CASA, this is not a problem, the FAA accepts testing by the oil producers.

Bottom line --- how and why you warm up an engine is very dependent on the type and condition of the oil. No way would I use much more than idle rpm until the numbers are "in the green", and where relevant, the oil cooler thermostat is flowing oil through the cooler.

As for "warming up" causing cylinder glazing --- I simply do not believe that is real, and this is the first time I have heard that claim in my operation of piston engines over 50+ years on three continents -- including LOP since the 1960s.

Tootle pip!!

[Big Pistons Forever]

Phillips makes a 25 W 60 multigrade oil for radials. I use it in the 285 hp 9 Cylinder Husoi engine in my Nanchang Cj6A. You get almost instant oil pressure on start up even with cold oil but temps do not get too hot on hot days.

The only downside is it is not recommended for the bigger radials, that is bigger than a 985 because of reports of master rod bearing distress.

[Aussie Bob]

Phillips also make a 20W 50 which I use in winter in an O360.

Bottom line --- how and why you warm up an engine is very dependent on the type and condition of the oil. No way would I use much more than idle rpm until the numbers are "in the green", and where relevant, the oil cooler thermostat is flowing oil through the cooler.

I don't necessarily disagree with you but what damage/wear is going to be caused by running the engine up above idle before the oil is hot? I don't mean take off power, but say 1500 to speed the warmup? And is a radial any different than a flat engine, supercharger aside.

[LeadSled]

------ supercharger aside. AB,
That's a pretty big "aside", loosing the supercharger ( like Guido Zuccoli in the T-6) is a seriously big deal, although cold oil was not, in this case, the reason for the supercharger bearing lack of oil and the subsequent shearing of the drive).

Other Phillips multi-grade oils are used with great success in the US, but CASA has not approved them here for the likes of the R1820- 86A/86B.
Interestingly, as well as obvious faster time to get the oil pressure up (critical to master rod bearing life) generally the oil consumption is reduced, and there is less of a problem maintaining oil pressure on really hot days.

Tootle pip!!

[Centaurus]

Who decided that this could be ignored? I don't know how many 30 year pilots I've flown with have decided that oil temp must be in the green before run-ups or take off.

Agree - I have seen this many times. I recall getting a dual check in a Cessna 152 at a one man band flying school.

I was fairly experienced as a grade one instructor at the time. My instructor, who was also the flying school owner and an LAME, insisted the oil temp be in the green before run up. He wasn't interested in what the manufacture POH said about in colder than normal OAT the oil temp may not register a rise until after take off. There was more to come.

After I leveled at 1000 feet after take off, he insisted on a wide circuit and long downwind leg to "allow the engine to cool after the climb at full throttle". Then he really arced up when I reduced power to idle on base for a practice glide approach as he said that would cause shock cooling. He wanted nothing less than 1500 RPM on base and final "to keep the engine warm" OAT was 20C... No closed throttle approaches permitted he said in his Cessna 152.

[Jabawocky]

And we wonder why there is a battle to kill off old wives tales!

http://i849.photobucket.com/albums/ab58/jaba430/No%20OWT_zpsfisptbez.png

[LeadSled]

Jaba,

Tell me, do you think having the oil at working temperature, as recommended by the producer of the oil is another OWT??

Tootle pip!!

PS: I differentiate between what engine manufacturers and oil producers say about their products, versus the airframe manufacturer's AFM. I will generally go with the first two, versus the AFM when it comes to engine operation.

[Jabawocky]

Leadsled,

Can you give me a specific example.

Fundamentally, the measurement and use of oil temperature is an indicator the rest of the engine is at a "suitable temperature" for high power use.

Think of the modern motor car, very good synthetic oils with viscosity index improvers give 5W-50 or 0W-30 kind of oils where as once they were 20W-50 and before that straight mineral oils. Today the car engine goes from start to out the street and "give it the jandel" so to speak. (young Scotty will never live that down).

So my feeling is that the oil temperature you need for a mag check, is not as high as you want for takeoff, but in both cases the numbers are very fuzzy in reality. This is not my area of speciality, but I can see with the use of say Phillips 20W-50 or Shell 15W-50 you can safely apply full power with the oil temperature lower as the effective viscosity is appropriate from a lubrication and pumping point of view.

The next issue is the upper engine components which is referenced to CHT, and here again there is a bit of variation from many OEM's as their is for MAX CHT as there is Min, but I find it hard to taxi out and go without the CHT being in the range of acceptable to all OEM's. On a cold day the oil takes longer to come up, but it does not take long to get to or over 75dF which is a fairly universally accepted minimum for operation above 1200RPM.


As for what the oil producers say…….never paid attention to that but I may be about to learn something. Remember the oil temperature varies depending at what point in the system it is measured. So who knows what the oil companies are referring to. Could well be they are all in the big fuzzy tolerance band of acceptable ;)

By the way….in the APS class there is one topic that is made clear to be off limits….OIL. We suggest buy the one that comes in a bottle colour your wife/kids/neighbour likes, so long as it is a suitable grade aviation oil.

[LeadSled]

We suggest buy the one that comes in a bottle colour your wife/kids/neighbour likes, so long as it is a suitable grade aviation oil. Jaba,
The two areas in the aviation field where oil characteristics may be different have nothing to do with pretty bottles (or in my case, until recently, 220lt drums) or with viscosity, but are "anti-corrosion additives" and the ability for a film of oil to "stick" to surfaces.

If you have a flat engine with the camshaft above the crankshaft, this will be more significant, re. the "sticking" means the camshaft will still have a measure of surface lubrication until the oil is flowing after start. I am certain we know all the trials and tribulations of Lycoming camshafts and followers.

IN times gone by, a good mate of mine did all the cam regrinds and repairs for several engine overhaulers in the Sydney area ( and many from further afield) and it was rare to see an auto camshaft as badly worn as the "average" Lycoming --- a bump stick with little of the bumps left.

Modern auto oils are, from what I can see, far superior to available aviation oils (even if your engine is "approved" for the few available multi-grades), I guess a matter of market size and demand. We still have plenty of engines around aviation that are not even "theoretically" approved for ash-less dispersant oils.

Further, it still seem to make a difference with aviation oils whether they are a paraffin or olefine base, something that has long since ceased to be an issue with auto oils.

Interestingly, in US, many operators of round engines swear by one of several well known automotive additives, in the hard life of ag. engines, consistently being able to achieve recommended TBO +50% helps keep the cost down.

I better not mention it here, I wouldn't want to encourage criminal behavior amongst those in Australia already committing aviation.

Tootle pip!!

[Jabawocky]

Agreed, some are better than others however in my opinion…..and I mean my opinion, the best corrosion inhibitor is CAMGUARD and according to its maker best used with either the straight Shell/Phillips/Castrols or if you want to use a multigrade, the Phillips 20W-50.

Apparently it does not play as nicely with the Shell 15-50, not that it will kill your engine.

I think you missed the humour, whether you use Phillips 100 or Shell 100….its awash. The 100 Plus would be better than the non plus.

I think none are bad, some are a bit better, depending on your requirements. And when it comes to the engines that need 120 grade the choices change a lot.

[LeadSled]

I think none are bad, some are a bit better, depending on your requirements. And when it comes to the engines that need 120 grade the choices change a lot.

Jaba,
Agreed.
Tootle pip!!

[Eddie Dean]

Oil SOAP sampling will keep you ahead of the curve on engine wear, just saying

[Neville Nobody]

Don't seem to have much choice in mineral oils these days. Mobil used to be good, a very dark rich colour and the 100 was thick. Buy Mobil 100 now and it's lighter in colour and seems to run quicker. Also the newer oil seems to burn more in the same engine.
Synthetic oil I have had no experience with in aircraft, in cars and bikes (Older) it seems to leak more oil when you use synthetic, same in aircraft?


The difference between a flat engine and a radial on a frosty morning was about 15 minutes in warm up time, that's 3 ton on quicker work

[rnuts]

Information from the Manufacturers to consider.
I know its for cold weather operations but look at the warning notes !!
http://www.tcmlink.com/pdf2/sil03-1.pdf
http://www.lycoming.com/Portals/0/techpublications/serviceinstructions/SI%201505%20(07-01-2002)/Cold%20Weather%20Starting.pdf

From the ten biggest lies about Piston Aircraft Engines..
Lie #3:
Modern multi-viscosity oil offers superior lubrication and longer engine life than old-fashioned single-weight oil.

During the 70s and 80s, there was a dramatic shift from single-weight to multi-viscosity oils by operators of general aviation aircraft...due in large measure to very effective advertising campaigns by Shell and Mobil that touted their multi-vis products (Aeroshell 15W50 and Mobil AV 1) as the greatest aeronautical innovation since the nosewheel.

During the same 20-year period, there was a dramatic increase in premature engine problems in the owner-flown G.A. fleet. It was not a coincidence.

In contrast to "working airplanes" that fly almost every day, most owner-flown airplanes spend most of their lives in the chocks. The biggest enemy of their engines is not inadequate lubrication. It's rust.

Multi-vis oil simply does not provide as effective protection against rust as single-weight oil. The defining characteristic of multi-viscosity oil — the fact that it doesn't thicken up at cool temperatures — makes it a lousy corrosion inhibitor. During periods of disuse, multi-vis oil strips off cylinder walls and cam lobes much more readily than does thick single-weight oil, leaving those parts vulnerable to corrosion, followed by spalling and eventually destruction.

But what about the superior lubricating properties of multi-vis oil? Basically bunk!

It turns out that multi-vis oil is not a better lubricant than single-grade oil. It's actually a bit worse. The reason is that multi-vis oil is made by starting with a thin, single-weight oil stock and adding man-made polymers called "Viscosity Index improvers" that increase viscosity as temperature increases. However, such VI improvers are not lubricants, and their addition actually displaces a certain amount of lubricating base stock (on the order of 10%). In other words, there's more "oil" in a quart of single-weight oil than in a quart of multi-vis.

Now this is no big deal, since the lubrication demands of most piston aircraft engines are rather modest (compared to automobile engines, for example). What is a big deal is the fact that single-weight oil does a better job of protecting engines against rust during period of disuse. That's why we've long recommend single-weight oil for any engine that doesn't fly at least once a week.

Fortunately, after two decades of multi-vis mania, it now appears that more and more G.A. operators are starting to recognize the shortcomings of multi-vis oil and are switching back to single-weight. An increasing number of top-rated overhaul shops are now recommending the use of single-weight oil.

[Adsie]

"If you want to see a case study of IO-540 abuse in AC50 Shrikes watch the GAM pilots the country over get cowl flap operation drastically and consistently wrong."

Obidiah

Would you like to explain what exactly you mean by this - just so other pilots do not get cowl flap operation wrong

[Lumps]

Now this is no big deal, since the lubrication demands of most piston aircraft engines are rather modest (compared to automobile engines, for example).

Please explain?

An interesting post, I take some comfort in it as I pour Aeroshell 100 into thirsty radials and take a good 15 minutes in winter for the oil to get to 40dC even with a bit of preheat