Percent power for a given MP/RPM (Chart discrepancy)

[skykrawler]

So the Aircraft Power app is not installed power.

 

[testwest]

@skykrawler, you are correct. The Aircraft Power app uses the Lycoming charts for its calculations. And the IO-360-A**** are all on the same chart. Here is a screen shot from the app for @mkrakoff 's conditions of standard day, 22"/2200 and 4000 feet pressure altitude:

As stated before, this is not the "as-installed" power in a stock Mooney M20J. This power setting and atmospheric conditions is 55% power in a J. More below!

Mooney was very accurate in its engine power data gathering for the M20J effort. In particular, the airborne engine torque meter, fuel flow instrumentation and air data instrumentation were the best obtainable for a GA airplane in 1975-76, and the flight test engineers, Roy Lopresti, and Fen and Dorothy Taylor, were without peer.

I modeled the M20J IO-360-A3B6D "as-installed" power in Benchmark. Here is a chart under the same conditions as before:

This chart shows 55% in the J, right on the money. And of course, Benchmark allows any combination of every possible MP/RPM/Temp/ALT, just like the OP, @mkrakoff wanted!

So, let's find the lowest altitude where WOT and, say, 2400 RPM gives exactly 65% power, and what the book fuel flow would be at best economy (which in this case is 25 degrees rich of peak EGT, that's how Mooney did it):

So, for @mkrakoff , fly your airplane to 9000 feet density altitude (note for here it is a standard day, so 29.92" altimeter and -3 deg C in the chart is 9000 ft pressure altitude as well as density altitude). Go wide open throttle and 2400 RPM (hopefully your tachometer has been recently calibrated). Slowly lean back to 9.3 to 9.2 gallons per hour. Ideally, you should see 22.5" MP under these conditions, and none of the cylinders has passed peak EGT yet. Manage your cowl flaps to keep the hottest cylinder below 380 deg F. At cruise you "should" not have to worry and you should be able to run cowl flaps closed. Let the engine stabilize, then slowly lean some more. Your first EGT should peak about 25 degrees higher and the fuel flow should be about 8.7 gph. If your first cylinder peaked at 8.8 gph and the last at 8.6 gph you have a really good baseline and your airplane is pretty close to the type design, and you are pretty much exact at 65%! And you could probably run LOP very nicely without GAMIs. Many Lycomings can do this.

On the other hand, under these same conditions, if you get a first peak at "something like" 9 gph and a last at 8.2, you have a high GAMI spread and GAMIs would help. If it's really bad you engine might feel a little rough before the last cylinder peaks. Or, at WOT if you are getting significantly less than 22.5 inches MAP you may have a restriction in the induction system somewhere. A 1" loss under these conditions (21.5" at WOT) equals a 3% power loss, so your peaks would be around 8.3 gph instead of 8.7. I got this answer instantly "flying" the Benchmark power chart just like flying the airplane.

Now then. I would like you to please go fly these numbers and report back your data. And we will go from here.

Hint, we will look at cruise performance next. You should see about 138-139 KCAS, or about 2 knots higher indicated (which computes to ~158 KTAS) in the stated conditions above and around 2600 lb GW. Draggy stuff on the airplane will knock that down some, so the common wisdom is that the J is a 155 knot true airspeed flyer under every day 65% power conditions.

[carusoam]

Norman are you working on a PhD thesis?   

Great pirep regarding the work of Lopresti, Fen, and Taylor...  ( @Speed Merchant may like to see that...)

Thanks for sharing all of this great detail!   They are Slightly more than just the ordinary PP thoughts...

Best regards,

-a-

[testwest]

Bump, hoping for @mkrakoff to reply back here!

[mkrakoff]

On 11/1/2020 at 1:03 AM, testwest said:

@skykrawler, you are correct. The Aircraft Power app uses the Lycoming charts for its calculations. And the IO-360-A**** are all on the same chart. Here is a screen shot from the app for @mkrakoff 's conditions of standard day, 22"/2200 and 4000 feet pressure altitude:

As stated before, this is not the "as-installed" power in a stock Mooney M20J. This power setting and atmospheric conditions is 55% power in a J. More below!

Mooney was very accurate in its engine power data gathering for the M20J effort. In particular, the airborne engine torque meter, fuel flow instrumentation and air data instrumentation were the best obtainable for a GA airplane in 1975-76, and the flight test engineers, Roy Lopresti, and Fen and Dorothy Taylor, were without peer.

I modeled the M20J IO-360-A3B6D "as-installed" power in Benchmark. Here is a chart under the same conditions as before:

This chart shows 55% in the J, right on the money. And of course, Benchmark allows any combination of every possible MP/RPM/Temp/ALT, just like the OP, @mkrakoff wanted!

So, let's find the lowest altitude where WOT and, say, 2400 RPM gives exactly 65% power, and what the book fuel flow would be at best economy (which in this case is 25 degrees rich of peak EGT, that's how Mooney did it):

So, for @mkrakoff , fly your airplane to 9000 feet density altitude (note for here it is a standard day, so 29.92" altimeter and -3 deg C in the chart is 9000 ft pressure altitude as well as density altitude). Go wide open throttle and 2400 RPM (hopefully your tachometer has been recently calibrated). Slowly lean back to 9.3 to 9.2 gallons per hour. Ideally, you should see 22.5" MP under these conditions, and none of the cylinders has passed peak EGT yet. Manage your cowl flaps to keep the hottest cylinder below 380 deg F. At cruise you "should" not have to worry and you should be able to run cowl flaps closed. Let the engine stabilize, then slowly lean some more. Your first EGT should peak about 25 degrees higher and the fuel flow should be about 8.7 gph. If your first cylinder peaked at 8.8 gph and the last at 8.6 gph you have a really good baseline and your airplane is pretty close to the type design, and you are pretty much exact at 65%! And you could probably run LOP very nicely without GAMIs. Many Lycomings can do this.

On the other hand, under these same conditions, if you get a first peak at "something like" 9 gph and a last at 8.2, you have a high GAMI spread and GAMIs would help. If it's really bad you engine might feel a little rough before the last cylinder peaks. Or, at WOT if you are getting significantly less than 22.5 inches MAP you may have a restriction in the induction system somewhere. A 1" loss under these conditions (21.5" at WOT) equals a 3% power loss, so your peaks would be around 8.3 gph instead of 8.7. I got this answer instantly "flying" the Benchmark power chart just like flying the airplane.

Now then. I would like you to please go fly these numbers and report back your data. And we will go from here.

Hint, we will look at cruise performance next. You should see about 138-139 KCAS, or about 2 knots higher indicated (which computes to ~158 KTAS) in the stated conditions above and around 2600 lb GW. Draggy stuff on the airplane will knock that down some, so the common wisdom is that the J is a 155 knot true airspeed flyer under every day 65% power conditions.

Amazing. Thank you so much for the detailed and thoughtful post. I’m headed out to fly tomorrow and will let you know how it goes. 

[mkrakoff]

1 hour ago, testwest said:

Bump, hoping for @mkrakoff to reply back here!

Just out of curiosity, is that benchmark model publicly available or are you working on a Future project with the data right now. 

[mkrakoff]

13 minutes ago, bluehighwayflyer said:

It is available in the Mac App Store.  Here is the developer’s website, which includes a link to it ...

Jim

http://www.seqair.com/benchmark/

Thanks, downloaded!

[testwest]

Anytime! Looking forward to the data. What kind of engine analyzer do you have?

[testwest]

Oh yes, the M20J airplane model, "as installed" engine model and several M20J props are on the Seqair site, so you can download those two and start right in.

[mkrakoff]

17 hours ago, testwest said:

Oh yes, the M20J airplane model, "as installed" engine model and several M20J props are on the Seqair site, so you can download those two and start right in.

Got it thanks. I went flying today but wasn’t able to run the test due to workload. I’ll run a flight dedicated to just this shortly. Also I may wait, as I have an EDM upgrade scheduled next week to a 730/830 from a 700. Right now I don’t have FF connected to the 700 but will after upgrade, so it makes it much more difficult to pull an accurate gami spread. I’ll post as soon as I get good data for you. 

Edited November 4, 2020 by mkrakoff

[testwest]

Excellent, you will like that 730/830 upgrade. Be sure to look at the setup menus and record data at the highest possible rate, I think it is once every two seconds is the highest rate choice.

[testwest]

Bump, how is that upgrade to the 730/830, @mkrakoff?

[mkrakoff]

A great upgrade! I just flew it to a shop for it's big tank reseal so when I fly it back I'll get the flight test data off of it. I tried with a USB I had in my bag, but it wasn't being recognized. I'll bring a fresh formatted USB next time. 

[Tim Jodice]

On 10/28/2020 at 7:22 PM, takair said:

I use an app called “Aircraft Power” where you can enter your engine and parameters to get various power combinations.  Have not fully validated its accuracy, but it seems reasonably correct.

I can't find the app. I searched simply "aircraft power". What am I missing?

[carusoam]

13 minutes ago, Tim Jodice said:

I can't find the app. I searched simply "aircraft power". What am I missing?

Tim,

Not what you are missing... it’s what you have too many of....

looks like you got an extra space in the middle... aircraftpower 

Go MS!

-a-