Proper Cruise Settings

[Capt. Manuvar]

Good of you to bring up the idea of leaning. I don't think that instructors in the UK don't teach it becase of lack of time. Instructors in other countries aren't better paid but still teach leaning. There is a myth going around the UK ppl training world : PPL+leaning=cracked cylinders.
I totally disagree with those who don't bother using the POH due to inaccurate guages/old engines. It is totally irresponsible for any pilot to take off without knowing how much fuel there is. There is the lazy method of filling the tanks but not everyone has that option as any "four seat" aircarft pilot will tell you. Nowadays ther are £10 dip-thingies that you can use to check how much fuel you have, i wonder why all aircraft owners/clubs dont have one of those in the glove compartment, even 737s have them.
As for fuel burn, why not calculate the POH figure and then add 10% for pilot error and 10% for the cr@p engine. I agree that when it comes to local training sorties or jollies, calculating accurate fuel flow is pointless, but it would be a good idea to know what the max fuel consumpton is and to kno the you will be able to divert should the need arise. The problem i have is with people flying a particular airspeed or rpm regardless of OAT or altitude. 2400rpm or 110KIAS could be 60%/6gph in the winter or 90%/12gph on a hot day. Luckily a lot of crosscountries during training rarely exceed 2hrs, so we can get away with "fill the tanks". But when PPLs decide to 'spread their wings' or 'expand their horizons' then there is the potential for trouble, especially since most GA magazines are on a crusade to hae us flying as far as possible into the continent.

Capt. M (who doesn't know how to lean)

[High Wing Drifter]

In my honest opinion the notion that PPLs don't know how to lean and that instructors don't teach it, is one confined to internet forums.

[IO540]

CM

The problem, as someone finds out when they have a high perf plane with a flowmeter and they start leaning for LOP operation, is that the difference between

a) leaning until the engine goes rough and then going rich a bit, then applying carb heat and if the rpm drops you haven't leaned too much (this is the method normally taught in spamcans), and

b) leaning for peak-EGT or LOP operation, likely to work only on an engine which just happens to have a reasonably well balanced air/fuel flow, and perhaps more likely to work with a pilot who is used to cr@p planes and doesn't notice excessive vibration

is perhaps 20-30% on fuel flow.

With the sort of weight/range tradeoffs one is making on the average PA28 with three average adults in it (never mind four; most of those cases are overweight no matter what), a 20-30% error on the fuel flow is all it can take to run out.

I am not offering a solution; just pointing out that attempting to lean and assuming that the fuel flow will be X GPH, is no more accurate than flying full rich at a specific RPM and assuming the fuel flow will be Y GPH. In fact the latter is likely to be more accurate - assuming that somebody has actually gone up for a flight and measured it. A POH is the official reference but a POH for some 30 year old plane isn't likely to be accurate enough for this very safety critical department.

Somebody owning such a plane could establish the actual flow rates but I don't think it is ever done in the training environment.

HWD

I am sure PP posters are not a representative sample of the PPL population but I can assure you that leaning wasn't taught to me as a standard procedure. I was shown once.

[tyro]

I learned leaning last month. Before that, I was under the misapprehension, having never asked, that leaning was something that only happened during high altitude cruises.

I had planned a 340nm round trip in a Warrior to a private strip with no fuel. Having never flown so far before, I was getting a bit twitchy about the fuel planning. So I met my former instructor for a drink to discuss it. It was a surprise when he suggested that, even at 2000', leaning would be worthwhile and might save 1 or 2 GPH.

For good measure, he also commented that fuel gauges in a Warrior aren't quite as bad their reputation and I would know if and when it was time to land and refuel.

So I went with brimming tanks, leaned and arrived back 3.5 log hours later with apparently in excess of 7USG in each wing. I still have no real idea what actual difference fiddling with the red knob made.

[Flyin'Dutch']

HWD,

I notice from your location that you are heading up Norf. Are we talking about the same planet though.

When you write:

In my honest opinion the notion that PPLs don't know how to lean and that instructors don't teach it, is one confined to internet forums.

You have to be kidding!

That this may seem to you to be only a subject raised here on the internet has probably more to do with the fact that people do talk about their uncertainties/questions in the comfort of a bit of anonimity rather than in full gaze at the 'Hangar Talk Inn'

If you were taught all about fuel management and leaning during your PPL syllabus and were made comfortable with that, great and credit to your instructor/training outfit.

A lot of people are under the misapprehension that what happens to them is what happens to everyone else (not just in aviation) and you only have to look at the threads which come up time and time again on these two essentials issues to realise that they are not well taught.

FD

[GroundBound]

During my training I was never shown a POH (I did however spend some time looking through one in a non-flying aircraft). I was given a photocopy with the target approach speeds and checks.

I have flown in the last couple of years in two clubs, and a POH was never available, even on request. One has been taken over, and they now have a photocopy of the POH which can be bought, "if you really want to".

During my training I was told lean above 3000ft ("pull the red knob back a bit").

My knowledge of leaning comes only from reading Thom (lean until loss of power then advance a bit), or the rants and raves on Pelican's Perch.

Some while ago I made a cross border trip and decided to go to FL60 in cruise (PA28/181) (lovely weather and some rising ground). I leaned until the EGT needle reached the red line. I left it on standard cruise power 2300RPM. The IAS fell back to 95kts.

I have no idea what 65%, 75% power means. I have no idea how to interpret the power graphs. I filled up before departure and before returning (2 hour flight, 4.5 hours of fuel approx.)

I don't know what I did wrong. I don't know what I did right.

Do I have any idea about engine management? Doesn't look like it!

Am I typical? Wouldn't surprise me, at all.

Do the people who rent me their planes care? I don't think so.

GB

[BigEndBob]

Leaning would also probably reduce the risk of carb. icing.
Less fuel evaporating in throat of carb. and hotter exhaust for carb heat.


And cleaner plugs.

At FL60 probably only see 2300rpm at full throttle 95kt ias but 105 tas typical.

Dont mix up throttle posn with actual power output.

[BEagle]

Flew with a chap once who suddenly yanked the mixture lever back at 1000ft. Predictably, the engine started running rather roughly. After about half a minute I aked him whather this was his normal way of operation...."Yes, always lean it off. Saves the club fuel" was his answer! "Well, please richen it again and save the club money on replacing burnt pistons and pots!" quoth I.

We've had a few cooked engines due to over-leaning over the years. I'd sooner waste money on burning a little too much gas at 85p per litre than have to fork out hundreds of pounds for engine repairs YET AGAIN!

Leaning off is really only safe if you've got the appropriate EGT and CHT gauges to assess how hot the engine is getting.

[Capt. Manuvar]

Pressure altitude

A quick question regarding the use of POH graphs:
The graphs I deal with have density altitude calculations based on Pressure Alt and Temp. Does pressure altitude mean Pressure altitude on 1013 or on QNH? (don't be too hard on me, I'm just another product of the system )
Beagle
I agree that there will be a tiny minority who will abuse the controls, but if instructors teach it properly in the first place it shouldn't be a problem. It's normal practice in other countries.

[tyro]

Beagle,

I can imagine that CHT and EGT meters would make leaning an exact science. However in club planes with neither, how good an approximation is the "lean until it starts to run rough and back off" method? If it's done right will it significantly alter fuel consumption or the life of the pistons and "pots"?

BTW: Is a pot the cylinder or its head or something else?

[Final 3 Greens]

BEagle

Is this the "lean it until you can't read the shaking dashboard and then enrich it a bit" method?

Seriously, how do you think our Yank cousins manage out of 7000ft airfields in basic kit? Without leaning, the engine won't develop rated power and without that power it won't make the grade at 8-10,000ft density altitudes.

I agree that 1,000 ft is a bit aggressive for a PA28, but is there really a prob leaning by instantly enriching at the very first tremor of rough running?

[High Wing Drifter]

FD,

I notice from your location that you are heading up Norf. Are we talking about the same planet though.

Now, now. Be nice!

A lot of people are under the misapprehension that what happens to them is what happens to everyone else...

Oh really! Well I never.

[Dale Harris]

OK, just so I have this straight....... You guys pay 85p ($2.20 oz) per litre........ And you don't get taught to lean the mixture?? Are you fair dinkum? Even in the biggest POS I've ever flown in, the fuel burn I've got has always been within 2 or 3 % of the figures shown in the POH, more usually 1% in the aircraft i currently fly. What is with this "Can't trust the book thing"? Our aircraft are as old, if not older than yours, and as far as engine life goes, pretty much any warrior, 150/2, 172 et al, makes tbo. I just don't understand what is really going on here. Never trust fuel gauges, sure, that is what dipsticks are for, or visual checks. Gauges are a backup to fuel in/out. I really find it hard to believe that PPL's haven't been taught to lean an engine properly. Engine management is just as important as any other skill associated with aviation.

[IO540]

The explanation for the poor training is, I think, that here in the UK only a very small % of PPL students are doing it to go places.

Just hang around some airfield for a year, and look around. Most are doing it as a one-off challenge, or to impress the mates down the pub, or to pull birds (a complete waste of time for that), or because they got some money for Xmas to do a PPL. Some 90% don't bother to renew their PPL after 2 years.

Some are doing it to gain an ATPL but for most of those that seems to be a long haul too. A lot of people spend say 5 years as PPL instructors, on peanut pay, before they can get a job.

Also, most people that are attracted to PPL training don't have enough money to fly afterwards, or even at the time in many cases. There are plenty of people about with money; they just spend it elsewhere, presumably buying into some activity with a more exciting social scene.

If more people did it for some long term purpose, and more of them had more money, then there would be the demand for better training, better instructors, and untimately the aircraft available for self fly hire would improve in quality and condition.

In the end, we get what we deserve.

However I think there may be a particular problem with N European weather. The basic PPL really isn't very useful for going somewhere; instrument flight capability is more or less essential (even if, on the day, the weather is actually VMC). But nobody is willing to admit it, and if you turn up to do a PPL here, you won't be told that on any given year you will end up cancelling most of your planned flights. Also in flying clubs there are a lot of retired men, with plenty of time on their hands, who say "you can go everywhere VFR".

It is going to be very different in Australia.

This is all off-topic I know but unless one asks basic questions, the debate about what is unavoidably training standards can go on for ever.

[Gertrude the Wombat]

You guys pay 85p ($2.20 oz) per litre........

Er, no, not all of us. Very many of us rent wet, and pay by the hour. Unless all hirers aren't leaning to start with and then start leaning the operator won't see enough of a drop in fuel burn to lower the hourly rate.

[englishal]

I can hand on heart say that I do the fuel calculations for every single flight test (about 5 or so).

I learned to fly in California, where it is hot, and you get up high often, so you had to lean properly. The instructors were good, and taught leaning from the word go.

Often you have to lean in the climb, which is not a big deal, even though many people will no doubt scoff.

EA

[IO540]

It is fine to lean in the climb provided the airfield altitude is such that the engine never develops the power above which one isn't allowed to lean.

For example the IO-540-C4D5D is allowed to run at peak EGT (the hottest condition!) at any power of 75% of max HP (75% of 250HP). I don't know off hand how to work this out (the Lyco engine manual doesn't have a graph of HP versus density altitude; one would have to estimate the MP from the DA and look up the HP for a given MP) but 75% is probably reached at about 5000ft elevation (ISA). So, when departing from 5000ft or higher, one would lean for peak EGT on the runway.

But below that elevation, one would use full-rich because that's what the engine manual says.

It is unlikely that one would be authorised to lean at sea level, at full throttle. I suppose some engines may allow it. But it takes one into the detonation area.

OTOH there is no law against taking off at cruise power, 75% or less, from sea level, and leaning for peak EGT then. Just needs a lot more runway, and most would regard it as a stupid thing to do.

[dirkdj]

Sorry IO540 but I can't let this pass..

Quote: For example the IO-540-C4D5D is allowed to run at peak EGT (the hottest condition!) at any power of 75% of max HP (75% of 250HP).

There is truth in that statement but "(the hottest condition!)" should be left out completely.

The hottest place to run an engine (as seen on the EGT) is at 40-50 ROP, where the highest CHT will be found. The EGT reading is just a navigation landmark on the power curve and the EGT temperatures bear no relationship to the real temperatures of the exhaust valves.

Best power mixture is at the 80°F ROP EGT point, but at high power (take-off) more fuel is needed to make the mixture richer in order to give a wider detonation margin.

Given good instrumentation an engine can be run full thottle, at sea level , but very lean at about 80°F LOP EGT. This is in fact the FAA approved way to run the TATurbo.

Running it ROP at this power level would be asking for trouble.

Take-off should be done at maximum power, full rich with sufficient margin for detonation, leaning is necessary in high altitude or high temp situations in non-turbo engines only.

There is no better detonation protection than to be well lean of peak at high power, temperatures are well down, because the bulk of the combustion event occurs later in the downgoing power cycle: less compressed ergo lower temperatures.

Of course if a given engine will run smoothly lean of peak depends on several factors, mainly how well the horsepower of the 4 or 6 individual cylinders is matched. If some are still ROP while others are LOP then a power mismatch will give a rough running engine.

I have flown a Mooney 231 that was so well balanced it could be leaned until the engine died from lack of fuel without any roughness.

Dirk

[IO540]

Peak EGT is the highest EGT, by definition. That is also the stochiometric point, where all fuel is being burnt with just the right amount of air. This isn't the max power point, which as you say occurs slightly rich of peak. But it is a lot more economical point.

I think the #1 problem is that any specific statements should be limited to specific engines.

Lyco certainly don't allow leaning above 75% power for the one I referred to. Whether leaning to LOP at full throttle does any actualy damage is another matter. Most likely not, but of course if you are at full throttle at sea level and then lean it LOP, you won't be developing the rated HP anyway; that happens at the setting on the fuel metering unit where all 3 levers are fully forward which on the engine in question is about 125F ROP.

The rest of what you say I agree with; one needs balanced injectors (probably GAMI), decent multi-cylinder instrumentation, and knowledge. This makes it irrelevant to probably 99% of UK GA operations.

If PPL training included advanced engine management, the "45 hrs" would have to be 60-70hrs, a lot of people who manage to get through the exams would never understand it, and the planes don't have the instruments... so we have what we have. In the typical spamcan flown at 2000ft, it doesn't matter.

[High Wing Drifter]

Those interested in this thread maybe interested in this link from Lycoming: http://www.lycoming.textron.com/main...ips/index.html