This is why we do runups

"Rick Durden" wrote in message
...
Jim,

Yes, but that statement should be further qualified by saying that
descents
should be made at less than 75% power or else EGT and CHT could exceed
operating limits. 65% power sounds like a good number. Some carbed
engines
with good fuel distribution will run smooth when too lean (close to
peak,
either rich or lean of peak).

Actually, that doesn't make sense. I think you may mean
"inappropriately" lean, rather than too lean. The worst spot is about
50 degrees rich of peak when at high power as that is generally max
for CHT and BMEP. So long as you are richer or leaner than that, you
aren't going to hurt the engine. Leaner is generally better in terms
of keeping temps down and plugs from fouling, so long as the engine
runs smoothly.

Yup. I did not explain it very well.

On 20 Aug 2003 12:24:20 -0700, Rick Durden wrote:
park. If you make a go around, push the mixture to rich, carb heat to
cold and apply full throttle. Some folks don't like the extra work
with the mixture at that time, so they go to full rich on downwind,

Depends on the aircraft. On many aircraft, you can push prop, mixture
and throttle forward at the same time with one hand which makes it easier
to follow that practise.

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

(Rick Durden) writes:

It doesn't hurt
to lean it when taxiing as well, but do so very aggressively, so that
if you forget to go to full rich before takeoff it will quit on you
rather than make a takeoff with the mixture other than at full rich.

Rick, I had a talk with my mechanic a couple of months ago about
leaning when idling. He says for my carburator and C-90 engine, and I
suppose many other aircraft engines, leaning at idle doesn't do
anything unless it is nearly at idle cutoff. It is only when the RPMs
are well above idle that the mixture control begins to really control.
So does leaning on the ground--during idle--do anything unless it is
leaned nearly to idle cutoff?

The idea is in fact to lean aggressively on the ground. I lean mine till
it stumbles then turn the vernier in just till it is smooth. That works
out to pretty close to idle cutoff. Leaning this aggressively, the engine
will quit if you advance the throttle, making it impossible to take off
with it still leaned.

Bob Fry wrote:

(Rick Durden) writes:

It doesn't hurt
to lean it when taxiing as well, but do so very aggressively, so that
if you forget to go to full rich before takeoff it will quit on you
rather than make a takeoff with the mixture other than at full rich.

Rick, I had a talk with my mechanic a couple of months ago about
leaning when idling. He says for my carburator and C-90 engine, and I
suppose many other aircraft engines, leaning at idle doesn't do
anything unless it is nearly at idle cutoff. It is only when the RPMs
are well above idle that the mixture control begins to really control.
So does leaning on the ground--during idle--do anything unless it is
leaned nearly to idle cutoff?

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

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