The CAFE Measure of Efficiency - Mooney Style!

[testwest]

OK, folks, I am sufficiently happy with the M20J in Benchmark to be able to share some screen shots.

The first is the result of inputting the entire "Best Power" cruise tables from the M20J POH for our airplane (s/n 24-0042), that is manual #1220 Revision G, original issue date 9-27-1976, revised 3-7-1984. For each altitude and weight, Benchmark calculates a Cdo drag coefficient and an airplane efficiency factor called Oswald's e. The first shot shows the line fit to the 6000' Best Power cruise table, at 2740# gross weight. This table seems to fit the aggregate data best, while neglecting some data that is clearly "out to lunch"......

And that is the second screen shot..[ignore the captions on this and the next one, the board has some technical issues]..the 14000' Best Power data at 2300# clearly has some problems....the pink "pluses" are the data points for that condition (the greyed points are all the rest of the reduced data), they are kind of all over the place and the resulting Cdo and e don't jive with the rest of the airplane. I'll probably drop that run as the work progresses.

Now here is the neat screen....the modeled performance of the M20J at 8000', Best Economy power per the POH, 2700 lb, standard day. Power is WOT/2400, resulting in about 159 knots TAS...and that is darn close to the book. The left side of the screen is the power side, starts from the bottom where the "throttle" slider is, up to the prop CPx (power factor) then feeds right into the performance chart. The right side is the rotational side, starts from the bottom where the "propeller" slider is, up to the prop advance ratio, then feeds left into the performance chart.

What the model does not do, yet, is show a 25 degree LOP cruise power choice. I am working with Alfred Scott at Sequoia to implement that choice as well as a bunch of other enhancements.

Another really cool thing this could do (doesn't do it yet) is to show a "before and after" snapshot of a prop change. The prop installation in this case is as easy as dragging and dropping the new prop model on top of the old one. Can't wait to drop the Hartzell 7497 BA on top of the McCauley 212 model.

More later.

[testwest]

And here is another thing, take a look at the two charts below, ignore the fuel flow models for now, they should both be full rich (or Target EGT, future enhancement). The first is a WOT/2700 RPM climb through 2000' at max GW standard day. This power setting is what I do (and this is what Bob Kromer advocated)....and the second is the OWT climb at "25 square".....

Look at the lines of predicted best rates of climb on both charts.

~1100 fpm versus ~750 fpm?? And to even get that you need to go 5 knots slower!!

YGBSM. I had no idea the performance penalty was this high.

Guys, don't even fly this way! It's like starting a horse race atop a thoroughbred, then hauling back on the bit as hard as you can out of the gate for a third of the race!

Jeez, if you have to take a BFR with a CFI who still believes the 25 square stuff, and I am anywhere around, I'll fly with you and sign off a BFR for FREE to spare you the intellectual indignity.

[Steve Dawson]

Quite a lot of information. Have you every thought of starting a course on effeciencies of flight?

Thanks Norman

[schule]

Great discussion.  I am looking at doing my ERAU project on the newly certified electronic ignitions by ElectroAir.  There is a very nice section on thier website under Technical Support - Reports where the CAFE test data from their Mooney with electronic ignition was tested.  There are some very technical data for several power settings, altitudes, ROP and LOP with several different ignition configurations including dual Bendix mags.

-Mark

[testwest]

For Fastbyk....thanks, I am glad you appreciate it. I am fully employed by Boeing, but if this paper I am working on pans out, I can see maybe doing a webinar or two, or perhaps a presentation at some convention like MAPA, AOPA or EAA.....

For schule, good luck on your ERAU project.

Anyone else like this discussion? Shall I continue posting to it as I make more discoveries with Benchmark?

[KSMooniac]

I'm still interested, but haven't made time to digest it or measure my MT prop.  

[jetdriven]

I am all for it.  We are looking to get the real 201 MPH from the M20J.  SO far, it has gone from 183 to 186.

[testwest]

You got it. What I need to do is go fly some drag points and input those into Benchmark. I am very happy with the 6000' Best Power data from the POH (as shown in the first image a few posts back) being the "truth" for a baseline M20J.

And while I was typing this, I realized something. I can drop the model of the Hartzell BA prop on the baseline M20J, and then put in my data. The difference between my performance and the baseline/BA modded model would effectively separate out the drag reduction changes (from the Lopresti cowl and everything else) from the new prop......and I could do that vice versa by dropping a C212 model on my data to separate out the prop effects.

Holy.... spumoni........

[jetdriven]

EDIT:  Our mag timing was et to 20 degrees BTDC.   We reset it to 25 degrees and man, what a difference.   It used ot fall down completely at 50 LOP, now it still retains much more power while LOP evidenced by the higher IAS at the same degrees LOP numbers.  We can also run more FF up to about 10.0 GPH at least until 3000-4000 feet.  However, the EGT peaks at a higher GPH so we can run the higher GPH  (9.2) while 15 LOP and take the quite higher TAS, or lean to the original 8.7 GPH with a little more TAS than before.   Initial data suggests about a 3-5 knot higher TAS.  just from mag timing.  Its worth looking at.

Quote: jetdriven

 

[danb35]

Make sure you're legal with the different mag timing--if it doesn't conform to the engine's data plate, it isn't a legal timing setting.

[jetdriven]

Actually 20 degrees was not allowed on the Io-360-a3b6d.     Funny though it is ok on the -a3b6!   

[danb35]

Interesting--the -A1A started at 25 BTDC, but some time ago Lycoming decided it ought to be 20 instead.  Any engine that went back to Lyc for overhaul since then has had the timing changed, and the data plate changed, so it's now illegal to run it at the original timing.

[jetdriven]

On page 2 of the 1E10 type  certificate it says that all models 20 degrees is optional except -A3B6D.  Strange isn't it?     

http://rgl.faa.gov/Regulatory_and_Guidance_library/rgMakeModel.nsf/0/450619753f0fec87862575e6004f3dac/$FILE/1E10.pdf

[alfredscott]

I'd like to announce a new version of Benchmark which is available now.  It includes climb charts that Norman Howell requested and also dramatically different and improved Fuel Efficiency charts.  MPG and CAFE scores are now combined in a single, highly interactive chart, and you are able to 'fly' your airplane in any of the CAFE competitions and see how your airplane compares to the other aircraft that were entered. 

Find information on the new charts at

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

and download the latest Benchmark from

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

Alfred Scott

Sequoia Aircraft Corporation

 

[jetdriven]

Jim and I must be twins separated at birth, although he is taller than me.

 

I recently completed a 780 NM flight in our M20J and burned 43.8 gallons. Taxi, runup, and takeoff took 1 gallon. I went 11.0 GPH LOP at 500 feet.   Thats 18.22 NMPG average.  

 

GTOW was 2,650#, and it was flown at 2,500 feet, 21.5" MP, 2450 RPM, 128 KTAS, and 25 LOP on #2 (#1,3,and 4 were 80 LOP).   Average tailwind was 2 knots.  FF was 7.0-7.2 GPH on average (53% power) and the trip took 6:02 flight time.

 

I could have busted 20 NMPG at 6 or 7K feet, but headwinds kept us down low.

[testwest]

Thank you for the kind words! I completed my Master's Thesis and use the Vz climb profile and predicted CAFE scores from fltplan.com (the winds matrix page off the navlog) for all my flight planning now. I still need to tweak the M20J advanced profile in fltplan, but my Aerostar profile is dead nuts on.

[hoot777]

Got any data for a G model???

[Pinecone]

Cool thread.

I ran the CAFE numbers on my 252 and am doing a happy dance.  175 KTAS, 10.1 GPH = 14277.  WOOHOO>