Best power settings..

[N8632Y]

Coming home, flying my twinco at 11,500 eastbound, my settings were MP 19" RPM 2400 OAT: a warm 8C
FF: 7.3/side

My CHT's were warmer than usual avg: 400 which is warm for her, of course I don't usually fly at 11.5, but i was catching a tailwind. I imagined the thinner air had less density to help cool the cylinders.

Mixture was set by a lean find, followed by enrichen till smoothess setting, just ROP.

When I came back, I was talking to a fellow pilot who said, some planes will fly same speed, but use less fuel, by pulling the power back, but enrichen mixture to best power setting, or 100 ROP, and have cooler temps too!!

In otherwords, if i set up my pwr settings at 65%, mixture to PEAK, I will have FF of "X" and IAS of "M"

If I reduce pwr to say 55%(guessing) and mixture to 100 ROP, i might have FF of "X - 0.3 GPH" and hold same IAS (M).. and have cooler CHT's......


Anyone experiment w/ this?
I might go out and test fly this tomorrow....i'll post if i do
steve d.

[SLIMDREDGER]

I have a Robertson PA30, counter rotated, with Lopresti cowls, and some of the Knots 2U fairing mods.

After flying for years at 65% power settings per the Lycoming power chart with adjustments for altitude and temperature at 2300 rpm, I tried flying at 2100 rpm because someone suggested there would be less stress on the engine prop extension and engine mounts in rough air.

Was surprised to find that at the slower rpm, burning the same fuel quantity, the airplane was 4 to 5 mph faster at the slower RPM> Quieter, too.

It's worth a try. A. H. Powers

[Zach Grant L1011jock]

Steve,
Go play with your airplane using the mpg display on your JPI. As Al says, you will find that horsepower has only a loose connection to thrust and performance. Every one is different as there are variences in engines and props, as well as airframes. There are no straight lines of deviation in this, some of just is and is really hard to show mathmatically.
-Zach

[Tony Scarpelli]

I have a Turbo Single.

For us it is the highest altitude that you can still maintain enought MP to get 75% power (or your preferred power %). For fuel efficiency it is the highest MP and enough rpm's to get that power within the range of your prop.

Some run at 80%, I would only consider that during the winter when the temps are really cold. The turbo puts out a bunch of heat which is not good for long term life.

My preferred settings are 22/2300 RPM with MP of 24-26. Above 12,000' I have to run 2400 or 2500 rpm to get enough MP to run 75%. So I run 24 squared or 25 squared if I am in a big hurry.

[N8632Y]

I ran some tests: in my twinco, 5500 agl about 60% pwr
MP 21" 2300 peak find at 6.4 gph 131 kt IAS
Now lean to 50 deg LOP, my speed slowed to 118 IAS
Fuel flow down to 5.5 gph/side

So the test is to go 100 deg ROP, and pull MP to get to 118 kts, which i did, MP 17" 6.5/side

Therefore this test shows, LOP is more fuel efficient, no i was not hot on any cylinders,

This came from a mooney guy, but obviously doesn't work for the twinco.
steve

[Tony Scarpelli]

There is a really interesting article posted on aopa by Dr. Bruce Chien about max range cruise (which is also best fuel usage).

I remember for my 250 and two other models I looked at it worked out to be about 15% faster than Vy. I think it worked out to 120 knots on my Comanche. All speeds faster than that will insure a fuel premium relative to gain in speed. Rich of peak or lean of peak is another matter. At such low power settings you can use peak.

[Zach Grant L1011jock]