Cruise power setting for higher altitudes

pmh wrote:

I’ve seen some here that cruise at levels close to service ceiling of the aircraft.

I think we know who that is This is however probably not good to your engine, and particularly your piston and oil control rings.

pmh wrote:

Is it then full throttle all the way in the climb and then continue full throttle in the cruise?

In the DA40 I used to climb at 2400 RPM and WOT. In the SR22 (NA) I limited the RPM to 2500 below FL100. In both aircraft I would increase the RPM above FL100

pmh wrote:

Do you lean in the climb?

Yes. I use the constant EGT method. After the initial power reduction after take-off I note the EGT and maintain that EGT throughout the climb. As I reach FL75 I can lean a little more agressively but take care not to get the CHTs above 360°F.

Aviathor wrote:

In the SR22 (NA) I limited the RPM to 2500 below FL100. In both aircraft I would increase the RPM above FL100

Same here, except I don’t increase RPM at altitude. What is the rationale behind that?

@pmh What type of aircraft? Turbo or non-turbo? (Edit: crossed posts.)

pmh wrote:

I just find it a bit hard to continue the climb and then the cruise flat out as it feels I’m stressing the engine.

In the 172, I set fuel flow and manifold pressure according to the tables in the POH. No, you’re not stressing the engine just because RPM goes up at altitude. And since the air density decreases as you climb, climbing is really the same thing as closing the throttle as far as manifold pressure is concerned. If you closed the throttle further, you would achieve the same effect as if you were flying with a clogged air filter (to quote John Deakin).

Rwy20 is your 172 an RG or does it have a glass cockpit ? Unusual for a fixed pitch aircraft to have a MP gauge?

These engines shouldn’t be babied they are designed to be happiest at 65-75% power.

RobertL18C wrote:

These engines shouldn’t be babied they are designed to be happiest at 65-75% power.

Yes, but at high altitude (as is the question that was asked here, if I understand correctly) they won’t achieve those 65% even at full throttle. Personally, I don’t like to operate any machinery at full throttle for extended periods of time, be it aircraft, car or even lawnmower, so I always throttle back a little even if the manual would allow otherwise.

RobertL18C wrote:

Rwy20 is your 172 an RG or does it have a glass cockpit ? Unusual for a fixed pitch aircraft to have a MP gauge?

Oops, the fact checkers got me here. I checked back the table which I had in mind, and in fact I set RPM (with the throttle) and fuel flow. It is a C172S with classical instruments and fuel injection.

what_next wrote:

I don’t like to operate any machinery at full throttle for extended periods of time

One of the points John Deakin makes very clearly is that this sympathetic reduction in power (with the exception of engines with a time limit on maximum take-off power) is actually potentially harmful to an aviation engine with fixed ignition timing. It actually increases the peak cylinder pressure causing more heat to be transferred to the cylinder head.

Whether you accept the evidence he presents as gospel is another question.

LondonMike I always operated the Lycoming -540s at wide open throttle altitude which gave me around 65% in typical airways FL. They would make TBO plus 20% and in the USA no doubt would have gone well beyond that.

The Super Cub C-90 feels allergic to flying at full throttle altitudes but one day will go over the Alps and report back – the 66 year old Conti does not like to be flown at anything below top of the green on the, possibly not very accurate, RPM.