<VV> Mixture - and airplanes

[Roger Gault]

Well, not EVERY piston engine pilot.  This one doesn't know that - but then
airport altitude at Corpus Christi is approximately 40 feet MSL.  I suspect
it depends on the particular engine/carb, how the cable is adjusted, etc.
I'm SURE it depends on altitude.  The main purpose of the mixture control on
small piston driven aircraft is to allow the mixture to be brought back to a
reasonable point as the altitude is increased.  Certainly, if the airport is
high enough (say, Ruidoso, NM), leaning the mixture will increase power, but
I don't think that's generally true near sea level.

I will say that the Piper Cherokees I used to fly out of Corpus Christi did
not smoke or give any other indication of running overly rich when they were
flown with the mixture knob pushed all the way in (rich).  Nor did the plugs
or cylinder walls or exhaust systems show excessive carbon buildup
indicating a rich condition.  The majority of the hours on these (flight
school) engines was done within a couple thousand feet of sea level, and we
did not teach our students to lean them out on those local flights, so I'm
sure the mixture setting was almost always full rich.

Roger Gault

----- Original Message ----- 
From: <corvair at mts.net>
To: <virtualvairs at corvair.org>
Sent: Wednesday, September 21, 2005 10:22 AM
Subject: <VV> Mixture - and airplanes


> Sorry guys, every piston engine pilot knows that max power is NOT found at
full rich. You use full rich at takeoff at low altitude to cool the engine
at high angle of attack/low airspeed/low cooling air flow takeoff
conditions. It also prevents any tendency to detonate (ping) or lean sag
(power drops off rapidly when the mixture is too lean). Takeoff mixture is
too rich for max power. You get cooling because unburned fuel is going out
the exhaust, taking heat with it.
>
> If you're taking off at high altitude you can lean the mixture for more
RPM, but watch engine temps!
>
> At altitude you lean til RPM drops off then enrichen a bit, adjusting
mixture for max RPM or just to the rich side of that. If you're lucky enough
to have EGT gauges there's more scientific methods using EGT to set mixture.
>
> Les
>