That is correct matey , One shouldnt just be leaning based on height . Aircraft use fuel at all altitudes and power settings ,your paying for that fuel so you really want to to use as little as possible . As I said I lean as soon as I am in the cruise , even if that is 1000ft leaving the zone . As part of your checks prior to a climb or descent or a change in power setting always select micxture fully rich . This is vital becaue if you put full throttle in with the engine leaned you run the risk of detonation(I thinkit is ) and possible engine damage. Im afraid d I am notgreat at putting down facts and figures and I dont have abook to hand , Im sure someone will clarify but imho lean lean lean like I say your paying for it . I gave the example of the g1000 172 that cruises at 11-12gph lean it at 1000ft to 8 gph if you on a nav trip of several hours then that is a significant saving and like your instructor said , more fuel if it all goes wrong. Flying schools in my experience dont lean , that fuel cost is put down on your bill .
This is the leaning protocol from my aircraft group it may help
A few common myths about leaning are detailed and countered as follows:-
Myth:- You shouldn't lean below 3000ft
Answer:- The aircraft flight manual clearly states that you should lean at any altitude when using less than 75 percent power. It then goes on to say that you can even lean off when using full power if you are above 3000ft. So the 3000ft thing is only applicable to full power operation, not cruise power.
Myth:- If you forget to richen up in the descent it will damage your engine
Answer:- No it won't if you are not using more than 75 percent power which you wouldn't be using in the descent anyway. All that might happen is that if you have the mixture leaned for optimum power at high altitude and forget to richen as you descend, you may not get the power you want as you level off because the mixture will be too lean to provide enough power. Simple remedy, when you notice this lack of power, richen up.
Myth:- If you lean too much by mistake your engine will stop
Answer:- Richen up again and guess what, it will start again. The engine never fully stops, it windmills, as soon as you richen up it starts again right away. I'll demo this to anyone who wants to see it!
So in summary a few too many bar room flyers over the years have made the whole populus of real pilots afraid of the big red knob. Result, club aircraft that cost you £150+ per hour to fly.
We have aircraft which cost you £45, £60 and £65 per hour to fly because we lean off and save £14 per hour in fuel, all have a healthier and happier engine and bank balance. (We charge our hourly rates based on the flight manual published fuel burn for each aircraft which is for optimum mixtures. We only charge cost price so if it costs us more it ends up having to cost you more)
Now to the main point of this training post, how we do it!
As a slightly over cautious approach we have a little policy to only lean when in the cruise. We don't complicate the issue by saying that you can lean off in the climb above 3000 ft and you don't need to fully richen in the descent etc. So:-
1:- Lean off only when established in the cruise at cruise RPM (which is less than 75 percent power so you can lean at all levels)
2:- When climbing or descending, always remember to go full rich. (Never forget this, one time only can damage an engine)
3:- After changing levels, re-lean for the new altitude
4:- Circuit details or manoeuvres such as stalls or steep turns etc, always use full rich
In aircraft without a fuel flow gauge, use the rpm fall away method of leaning which is as follows:-
Set cruise power, maintain level flight and lean off until a noticeable drop in RPM occurrs. (RPM will fluctuate slightly on fixed pitch propellers as you fly along through up and down drafts or turbulence so you are looking for a definite leaning related drop)
Once the drop has occurred, advance the mixture towards rich until the cruise RPM is restored
Thats it!
It's as simple as that
8 Gallons per hour is a good fuel flow at low levels typical of which we usually fly around at. You can use the RPM fall away method described above if you prefer and if you go higher, (5000ft plus) you are better off using that method because 8 GPH will be too rich. You will get a lower fuel burn the higher you go.
It wouldn't be uncommon that as you go to these higher levels and try to maintain power as you climb, that you would get more power if you do lean off a little even under full power and of course once you level off you may find you need full throttle to maintain your cruise power. If that is the case, full thottle does not mean full power so you can still lean off using the RPM fall away method.
Full throttle is what you are asking for. Full power is what you get only if the air pressure permits, so as you get higher, full throttle can't give you full power even though you are asking for it which is why you can lean at high throttle settings when you get to high altitude.
The main point to keep it simple is ALWAYS remember to richen up when climbing or descending and always lean off in the cruise
I hope you have found this informative and useful. If we all adopt good leaning procedures we can all help to keep it low cost for all.
Last edited by maxdrypower; 17th Jun 2007 at 12:56.
Reason: typos