RV-10 takeoff Power settings

[vic syracuse]

Here?s a simple way to think about it. If you had a fixed pitch prop on the front of the RV-10 you probably wouldn?t pull the power back. So, noise considerations aside (and temps of course), why pull it back with the constant speed?

The engine is rated for 2700 rpm?s all day long. As a matter of fact, during certification they run them at full rated power, with all of the temps maxed for 150 hours straight!

Especially when breaking the engine in, keep the manifold pressure high if you must pull the prop back. It seats the rings better and faster.

Vic

[rvbuilder2002]

Since there is obviously a lot of passion regarding correct power settings for climb I won't get mixed up in that, but hopefully people will at least keep noise signature in the back of there mind. It is a much bigger problem than most of us are willing to admit. Particularly on RV's without mufflers.

[AviatorJ]

I appreciate all the responses.

I took off yesterday kept it all forward up to around 2000 AGL before the engine temps started getting a bit high. I'm going to keep testing it out to see what works best, but I'm going to stop being paranoid about the squaring of the engine.

[RV10inOz]

Originally Posted by AviatorJ

I appreciate all the responses.

I took off yesterday kept it all forward up to around 2000 AGL before the engine temps started getting a bit high. I'm going to keep testing it out to see what works best, but I'm going to stop being paranoid about the squaring of the engine.

High? If you climb at 125KIAS it should not get high. Or is it a new engine?

[DanH]

Originally Posted by AviatorJ

I took off yesterday kept it all forward up to around 2000 AGL before the engine temps started getting a bit high.

Go back to the NACA research on air cooling, and you'll find a little gem...cooling requirement is proportional to mass flow. For those of us not wearing lab coats, it translates to cooling requirement is proportional to RPM, because our engines are volumetric air pumps.

Now take a look at the 540 power charts. Over on the left you'll find a limit line for manifold pressure vs RPM. The whole chart assumes best power mixture. I've taken the liberty of highlighting the limit line in red, and the notations in green. You can pull RPM back to 2500 at full throttle (>29") with no danger at all, while leaned to best power. 2300 would be the absolute limit at sea level manifold pressure....and this is the chart for a K-model, generally assumed to be among the most detonation prone of the Lycomings.

Originally Posted by RV10inOz

Bruce, Why do you reduce to 2500 RPM at 1500' ? You probably know it but that is reducing your available power for climb. It is also harder on the engine, by a small amount.

No, it is not harder on the engine. Inertia stress goes with the square of piston speed, so here reducing RPM from 2700 to 2500 reduces that stress by 14%. At the same time, power is reduced by approximately 7.5%.

So Justin, if a bit lower CHT is your goal, I'd recommend the approach Bruce mapped out. I do pretty much the same, although with the lower typical CHT of the angle valve I begin leaning to maintain constant EGT much earlier than 5000. You want to try 2500/WOT and target EGT for climb. If I assume fixed timing, I'd guess Bruce's "lean to best speed" is just a little rich of peak.

[RV10inOz]

Dan, you are taking only one element.

ICP increases with 2500/2700.

I would say however, both elements are in real terms not that serious.

No, it is not harder on the engine. Inertia stress goes with the square of piston speed, so here reducing RPM from 2700 to 2500 reduces that stress by 14%. At the same time, power is reduced by approximately 7.5%.

Dan, the power is reduced by 7.5%, but the ICP increases by (rough guess) 4%, while the inertial change affects some items, they are not the items that suffer relative to their ability.

Pick ya poison. But this is a futile argument.

What is not futile is that if you assume a desire to climb to a height in a given time or at a given IAS, the longer you subject the engine to higher ICP and with reduced cooling airflow this is harder on the engine.

Smarter people than us have proven this.

[bizpilot]

Dave, I agree, except I reduce the RPM to 2500 at 500 agl, for noise. Significant sound reduction from 2700 to 2500. Otherwise same as you. I use this for our IO390 powered RV14A or my D95A Travel Air.

[DanH]

Originally Posted by RV10inOz

Dan, you are taking only one element.

First three paragraphs, in order, are cooling demand, cylinder pressure, and inertia.

ICP increases with 2500/2700.

Yes Dave. The big chart says the dreaded high ICP is well within limits...not that it matters, because it is rapidly decreasing with every additional foot above sea level. Inertia, on the other hand, does not.

Returning to cooling demand, which seems to be the OP's interest...

Smarter people than us have proven this.

Cooling demand is proportional to mass flow, i.e. RPM in the case of a normally aspirated 540. I'll show you mine. You show me yours

[RV10inOz]

Dan,

We can agree on what you posted, that is not in dispute at all.

However, climbing to altitude, at reduced rpm (power) if you wish to have climb time as a constant, involves higher angle of attack and lower airspeed.

Yes the peak pressure reduces with lowering MAP (except in a turbo of course), but it is always going to be higher for all given altitudes, so you subject the engine to higher forces for longer all the while having less cooling air.

At the end of the day the effects are subtle and not of significant margin, but when you get your cooling together (as you so eloquently do and advise) you are better off using 2700 and getting to TOC sooner and with more cooling airflow.

[DanH]

Originally Posted by RV10inOz

However, climbing to altitude, at reduced rpm (power) if you wish to have climb time as a constant, involves higher angle of attack and lower airspeed.

Straw man argument. Nobody does it.

Fly your usual cruise climb IAS at WOT after a pull to 2500. Lean in the climb, target EGT method, rather than full rich "for cooling". Report back.