testwest

So, for Jetdriven, Benchmark nailed your performance, under those same conditions it shows 155.2 KTAS. Within a knot using 55% power. At the POH "Economy Cruise" you would have been using a little over 8 gph and around 19 NMPG. LOP is good.

There is a pretty good summary of Deakin's work on the Vans Air Force web site: Understanding LOP Operations - A Summary of John Deakin's Knowledge http://www.vansairforce.com/community/showthread.php?t=75132 But you may want to read through all of the articles in depth as CLRB suggested too. You're flying an Ovation, right?

So, for Jetdriven, Benchmark nailed your performance, under those same conditions it shows 155.2 KTAS. Within a knot using 55% power. At the POH "Economy Cruise" you would have been using a little over 8 gph and around 19 NMPG. LOP is good. Curious how you calculated TAS, under your atmospheric conditions you have 123 KIAS. Assuming no instrument correction, the position correction is -2 knots, so you get 121 KCAS. Running the density corrections to TAS on the "MyE6B" iPad app gives 146 KTAS. Assuming your reported TAS is accurate (GPS Speed Course?) I'll bet you dollars to donuts your airspeed indicator is reading about 6 knots lower than it should. Also, your MP seems to be reading a mite low, it should be a little closer to 20 inches to make the power. For Cruiser, 8.6 gph LOP is 130 hp from the Power Wheel app on iPad. That is 65% power. Benchmark says you should be indicating 146 knots, less 2 for position error correction, giving 144 KCAS, and assuming zero instrument correction. The density correction to TAS from 144 KCAS gives 158 KTAS. Again, how are you calculating TAS? If your numbers are accurate, there is something slowing you down, like cowl flaps open or landing gear not fully retracting.

You are welcome!

And for Cruiser, hoo boy, I am not sure what to say. Your FF should be getting you 70% power if you are LOP. Benchmark says 161 KTAS...and you are saying 150 KTAS? Hmm. I still have a bit of work to do! The model does use Best Economy at peak. It is still a work in progress. I may go get a much later version of the POH and model it. Maybe the drag and Oswald's E will be closer. The thought of hand entering another couple hundred data points is a bit daunting though.

So, for Jetdriven, I get 159 KTAS at 70% power under those condtions, where you "should" be getting 154 KTAS. If I drag the Cdo down (so to speak) to .1875 instead of .165 or so I get your 152KTAS...I think maybe those doors are more costly than 2 knots? Roy Loresti always said the J had a Cdo of .1599, but the aggregate data tell me a higher number is more likely.

JimR, thank for the kind words!

Here is 201ers model, it is about 5 knots optimistic, assuming max gross weight. It is a work in progress, and I really can't model LOP well at all at this point.

And for George, you said "A more realistic number, and what I’ve seen, is 67% power would yield 156-162 KTAS at 10.2-10.8 GPH ROP." Benchmark gives me 157.8 KTAS at 67% power, box stock airplane. So I think the drag, prop and power models are good. I can't make it do Best Power at 67%, it defaults to Best Economy for fuel flow. And LOP is really a WAG at this point. This tells me I need to focus on the fuel part of the thing. And thanks! I am gonna have to defend this thesis some day soon in front of a bunch of professors, without a teleprompter. So keep me on my toes.

Wow! Such great response!! OK here we go, one at a time. See the attached for Jeff S, this is modeled with the Hartzell three blade. IAS is ~138 or so, but I am doing a wild ass guess on your conditions.

Ok, check it out, apples to apples comparison of the Hartzell Top Prop BA (Blended Airfoil) prop versus the standard C212 McCauley in Benchmark. About 2 knot speed gain at a representative cruise condition.....matches very close what I found in flight test.

OK guys!! I think I have a pretty darn good model of the M20J in Benchmark. I could use some help validating the model. If anyone has some good cruise data numbers I could throw 'em into Benchmark, and compare. Attached is a Benchmark screenshot....fudged for a 25 degree LOP cruise at 8000'. So, for example, at 2600# gross weight, standard day, WOT/2500RPM/25degLOP, you are actually making about 67% power at the engine, and should have a fuel flow of 8.8 gph, IAS of 143 knots, TAS of 159 knots. The equivalent Best Economy per the POH under the same conditions would be a MAP of ~22.5 inches instead of WOT, and a FF of 9.5 gph. Same speed, 18 nmpg versus 16.5. I am using a combination of Benchmark and the iPad app called "Power Wheel" to come up with LOP data. If there is enough interest, I can make a little test card to fill in the data. The program inputs are RPM MAP Airplane Gross Weight Pressure Altitude OAT Best Power, Best Economy, or LOP. I can estimate other than 25 deg LOP with some work..... Any nonstandard configuration? I can handle most of the props now except an MT, but don't have an IO-390 or a Missile modeled yet. Looking forward to some interesting discoveries with this.

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........

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?

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.

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.

I have one, but it is at home and I am in Korea right now. Came out of a twin Mooney, uh, I mean Aerostar. Will be back home after Thanksgiving. If you need a hot spare I'm willing to sell it cheap. It probably does need an overhaul but would probably work for a while, as in to solve an AOG issue......

Bump, again. There is a lot more coming on this subject...stand by, y'all.

Bumping this thread, I have made huge progress in modeling the Mooney M20J in Benchmark. I think I'll be able to publish some charts before too long. Had to get used to this new MacBook Air laptop.....wow. Starting to think I've crossed the river and ain't going back....

You are welcome, sir. And thank you again for taking time to make thoughtful, factual posts.....everyone wins.

KSMooniac is *exactly* correct, as he nearly always is. We have the siamese mag as well, and almost has a problem, the case of ours broke at the interface to the engine (due to a loose clamp, natch), luckily the mag is so tight to the firewall it did not fall out. It was only a 15 minute flight, I was ferrying the airplane to our AMT for annual time. Overhaul every 500 hours, and check those clamps. We have the Lopresti cowl which has large inspection doors on the upper surface. I reach in to the engine compartment through those doors on preflight, grab the mag and give it a shake to make sure it is tight, before every flight.

+1 for Dan and Ross. Ross's explainations are dead nuts on. Also +1 for Ross on inflight diagnosis of the bad mag. It has been said many times, but bears repeating for casual readers of this post....an all-cylinder engine analyzer is the best money you will ever spend on your plane. When you pull the plugs on the #4 cylinder, check the center electrode resistance. The nominal new value is 1000ish ohms. More than 5000 ohms, think seriously about replacing them even if all other checks look OK. Tempest plugs have a far better design in this regard, and they are slightly less expensive for massives than brand C.

OK, I got a nice email from Les Doud at Hartzell: The blade activity factors for the various blades are: 7497 - AF=95 (This is the blended airfoil or "scimitar" Hartzell prop) 7282 - AF=81 (This is the 3-blade non scimitar prop, the activity factor is lower per blade, as expected) 7666-2 - AF=106 (This is a standard Hartzell 2-blade, don't know how many of these are out there, most Js have McCauleys) 7666-3Q - AF=110 (This is the 2-blade Q-tip prop, if anyone has one of those). Anyone get any McCauley measurements over the weekend? Thanks!