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Is there something seriously wrong with UK PPL training?

Surely "best power" on any petrol engine is about 100-150F ROP, not 50F ROP.

This was a quote from 1979, it really says 50°F rich. Interestingly the 1976 C172M manual recommends flying lean of peak as much as possible -- that's with a carbureted O-320! They keep learning. The Lycoming engine manuals from that time were already much more detailed and up to date. I guess airframe makers didn't really have a thorough understanding back then -- at least the department that wrote the POHs. Fuel was cheap anyway.

This is the old misconception of Cessna saying "don't lean below x thousand feet in the climb" and "don't lean below x thousand feet in cuise...

I have heard this many times but so far nobody has shown me an actual Cessna POH where statements like this are made.

I think a FI that teaches students to not lean in cruise is simply not qualified to instruct.

Remind me what leaning is again....I have already started to forget.........isn't that something to do with reciprocating engines?

EGTK Oxford

Leaning is what you do when you pull the throttle(s) aft. It automatically makes the aircraft slow down, so it is best avoided, except for landing in which case it is highly desirable.

ESSB, Stockholm Bromma

Remind me what leaning is again....I have already started to forget.........isn't that something to do with reciprocating engines?

You can't misadjust the mixture of a Lycoming/Conti badly enough to even come close to the awful SFC of a small turbine with the PT6 being the least efficient of all!

You can't misadjust the mixture of a Lycoming/Conti badly enough to even come close to the awful SFC of a small turbine with the PT6 being the least efficient of all!

You are certainly right. But I feel I am helping the environment by removing lead from my aircraft! The tradeoff is using a little more fuel

EGTK Oxford

... with the PT6 being the least efficient of all!

Mind you, it was originally designed to power agricultural machinery (that was what we "Garrett drivers" used to say about it - the truth is that the Garrett engine delivers the same power with less than 3/4 of the fuel consumption but twice as much noise ;-) )

You can't misadjust the mixture of a Lycoming/Conti badly enough to even come close...

The GTSIO engines of the Cessna 421 (and similar) that I had the pleasure to fly for over 1000h are cooled with excess fuel at maximum power. Full-rich full-power results in a fuel flow of approx. 250lb/hr (per engine!) which is not far away from some turboprops. The manual therefore gives quite some information about leaning, otherwise the range figures will be off by more than a factor of two. The recommended setting is "best power", as this increases TAS by 2kt and significantly reduces thermal stress on the exhaust system and turbochargers compared to peak EGT.

BTW: If any Cessna manual really does not contain information on leaning that it will certainly be in the engine manual that comes with every aeroplane!

EDDS - Stuttgart

I have heard this many times but so far nobody has shown me an actual Cessna POH where statements like this are made.

From a 1975 C172M POH that I happened to have to hand.

CLIMB SPEEDS

Normal climbs are performed at 80 to 90 MPH with flaps up and full throttle for best engine cooling. The mixture should be full rich below 3000ft and may be leaned above 3000ft for smoother engine operation or to obtain maximum RPM for maximum performance climb.
(then some stuff about airspeeds).

You're quite right that it says nothing about mixture in the cruise.

Checking a couple of other manuals to hand.

  • C182P: advice about leaning in cruise and climb, but no mention of altitude.

  • C182Q:

    The mixture should be full rich during climb at altitudes up to 5000 feet. Above 5000 feet, the mixure may be leaned for smooth engine operation and increased power. (then various discussion about power and mixture in the cruise, but no mention concerning altitude.)

  • Reims Rocket

    For maximum engine power, the mixture should be adjusted during the initial take-off roll to the fuel flow corresponding to the field elevation. (Refer to fuel flow placard located on the right side of the instrument panel). The power increase is significant above 3000 feet and this procedure always should be employed for field elevations greater than 5000 feet above sea level. (similar discussion about leaning in the climb). Normal cruising is done between 65% and 75% power with the mixture leaned at all altitudes. the power settings required to obtain these powers at various altitudes and standard outside air temperatures can be determined using the Cruise Performance charts in section V.

And finally a C152 POH...

Prior to takeoff from fields above 300 feet elevation, the mixture should be leaned to give maximum RPM in a full-throttle static runup.

ENROUTE CLIMB Normal climbs are performed with the flaps up and full throttle and at speeds 5 to 10 knots higher than best rate-of-climb speeds for the best combination of performance, visibility and engine cooling. The mixture should be full rich below 3000 feet and may be leaned above 3000 feet for smoother operation or to obtain maximum RPM.

And in the cruise

To achieve the recommended lean mixture fuel consumption figures shown in Section 5, the mixture should be leaned until engine RPM peaks and drops 25-50RPM. At lower powers it may be necessary to enrichen the mixture slightly to obtain smooth operation.

So yes, it appears that Cessna consistently give advice that you should lean at all altitudes in the cruise, and in most aeroplanes in the take-off and climb; a few with caveats not to lean IN THE CLIMB at lower heights.

Interesting. Something new to beat flying instructors over the head with.

G

Boffin at large
Various, southern UK.

I think a FI that teaches students to not lean in cruise is simply not qualified to instruct.

Of course, you are right. When I was instructing on a more regular basis, I used to show my primary students the very few basic things about leaning right in the first lesson.

Again: the POHs mandate correct leaning every time the aircraft in in cruise flight, at cruise power. It is not an "optional" thing that you can "defer" just because there are other, arguably more important things to focus on in the very first few lessons. Sure, a C152 will run just fine at 2000 feet, 2200 RPM and full rich mixture, but it's not in compliance with the POH, nor is it good airmanhip.

The problems lie deeper, though. I used to work at a flight school where primary students changed instructors frequently (whether this is a good thing or a bad thing is for another thread...). Inevitably, it did happen that a student came to me and said that he got his hand slapped by another instructor when he started to lean the mixture during the cruise portion of his flight...:-(

These things grossly confuse student pilots, and confusion is very bad for a primary student. Anyway, as long as we have instructors like the one above, teaching leaning is going to remain a difficult chore. Just have a look at this thread!

But it's worth it. One good reason for teaching primary students proper leaning right from the start is that it develops a better understanding why the mixture needs to be full rich for landings. If students never lean, they will sooner or later start to consider the "full rich" item on their landing checklist as a "moot point", which in turn causes future complacency in this regard.

Obviously, what should be avoided is dedicating too much time to leaning in the very first few lessons, as the student will indeed be sufficiently "loaded" with all the other "new stuff". So: just a few words and a few basic guidelines and instructions. No more... but no less, either!

Mainz (EDFZ) & Egelsbach (EDFE), Germany

Genghis thank you for your offer. Not been to Cranfield yet so will let you know when I am planning to.

I hadn't realised the can of worms when I posted....but it has been really interesting and informative reading, thank you everyone.

EGBJ, EGBP, EGTW, EGVN, EGBS
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