What do Cirrus pilots think of getting the RPM lever back?

This firm


has an STC for an interesting modification which I am sure many will have heard of.


Welcome around here. Good to See you again. Most Cirrus owners consider it a waste of money, it seems from the discussions in the forum. There’s just no benefit one could think of - apart from running the engine in RPM regimes it isn’t meant to be run per the POH. Not having an rpm lever is generally considered a good thing around here.

It would be more interesting to lose mixture lever.

A step backwards in my opinion. Not that a power control would be a problem if that’s the way the airplane was built. But spending money for it? I don’t see the point. It adds no practical utility IMHO.


You get more MPG if the engine runs at a lower RPM. Not a lot, but a few percent.

Not nearly enough to pay for the thing in a sensible amount of time. Also, if you consider the turbo and turbo normalized, most people in the US run it at 85 percent. They would loose power with less rpm since they are already at max continuous MP. Some with the TN choose to run it at even more than 2500 rpm to improve cooling.

Perhaps you were unaware that many, if not most, Cirrus pilots fly LOP and get quite decent efficiency. Typical cruise numbers for SR22 aircraft without turbos are 160-165 knots at 12.5 to 13.5 gph. With modest winds aloft, that’s typically about 12-15 mpg, better than many SUVs.

So, adding the blue knob may get a few percent, but how much beyond those numbers?

Given the efficiency of LOP and the operational ease of the Cirrus integrated throttle-prop control, I’m not highly motivated to go backwards.


I agree, but it brings a question. If I am low enough (say 5000 in NA) and LOP, I can pull the throttle a bit (which in fact reduces RPM, without changing MP) and adjust fuel flow to get the same power, right?
For example , I get less vibration and it is a bit more quiet if I set it up at 2600 rpm at 5000.

Paging Gordon F. White courtesy phone please.

Any mitigation for those posting in a second language?

If I posted corrections to all of the “lose vs loose” instances I would have 25,000 posts instead of 14,000. Yes, exemptions for international posters are appropriate.

Apologies. One of the few things I seem to be too lazy to get the hang of in your language. So let me invoke Borchert’s law :wink:

You do much better than most Americans, so don’t sweat it!

Wasn’t the Continental RPM band restriction controversial i.e. they were unable to come up with any engineering data to support it?

I will do a flight test when I next go up but dropping down to say 2300, or even 2200 at higher altitudes for a non-turbo engine, is well worth doing and reduces cockpit noise substantially.

Last I flew in an SR22 (don’t recal the type but it was Avidyne) it was suprisingly noisy, with Bose X headsets.

The RPM limits are really an engine-prop thing, one of those odd harmonic problems. Thus many of the limits are based on the prop mfg’s vibration testing (engine power pulse in combination with the crankshaft-propeller hub-blade natural freq.) that they are required to test during the certification.

Finally I got around to doing an interesting test

All was done at peak EGT i.e. best economy.

There are worthwhile economy gains at lower RPM.

I used just 20" MP because the engine doesn’t like running at 23" at 2200rpm or less, but at Eurocontrol altitudes (FL100+ generally) one flies at wide open throttle and the MP is low enough.

Peak EGT <> best economy.

Curious why you would peak at such varied fuel flows when the MP was the same. Assuming all other variables were the same, I would have expected fuel flow to remain the same, right? Or what am I missing? I would be more curious to see this test with constant fuel flow and the only variable being the RPM, since the economy gains here seem related to the reduced fuel flows (and would yield results like that even if RPM had been held constant).


  1. “Peak EGT” is meaningless unless your GAMI-spread is zero or close to it. What is you engine’s GAMI-spread?

  2. “Peak EGT” is slightly off from best HP and best economy (see graph posted by Gordon).

  3. Running a the engine at “peak EGT” puts it awfully close to peak ICP and peak CHT - not necessarily a good place to operate as it may result in cylinder overheating (see graph posted by Gordon).

Do you by any chance work for or in any other way represent the manufacturer of the RPM-lever STC?

Did you not misspell your name Peter?

Best SFC is approx 20F LOP but it is barely measurably different to peak EGT. It’s a reasonable point to work at.

The highest CHT is about 50F ROP - Deakin’s famous “red box” :slight_smile:

My post-GAMI data is here

The fuel flow at which peak EGT is reached varies with the RPM. I don’t know for sure why.

I must admit I was suprised at the extent of the savings in this test, though I have noted substantial savings on many long flights where the wx was good enough to enable flight at altitudes low enough (e.g. FL100) to enable the use of low RPM (say 2200) with wide open throttle.

The reason for constant MP and near-constant IAS is to keep engine pumping losses and airframe drag constant. It’s trivial to show huge fuel savings by flying LOP, when actually you have lost a lot of IAS so the fuel saving is due to flying closer to Vbg :slight_smile:

No I have no aviation business interests etc.