M20F Speed Checks... Comparison Please?

[Ragsf15e]

Ok folks, we all fly Mooney's to go fast.  My 1968 F model goes a few knots less than book (I know book was optimistic), but I'd like to get a few comparisons to see if it's about the same as others or if my 16 year old engine overhaul is starting to catch up with me.

 

So here's what I did, I flew a speed test at 10,500 and 7,500 and I'm putting the results below.  If anyone else has a chance, I'd like to know how your bird comes out on a similar test.

 

The only speed mods I've got are the sloped windshield and the Lasar cowl closure (which cools nice, but I doubt it goes any faster)

 

The speed check is very accurate and you only need 3 legs, 90 degree off - like North, East, South.  You just write down the GPS groundspeed on each leg.  It's actually more accurate than doing all 4 directions and averaging because it uses math to take out the crosswinds you'll have.  The calculator is at http://www.csgnetwork.com/tasgpscalc.html.   If you note the temp and altimeter setting it'll also give you the density altitude and the actual winds.

 

I used 100' ROP for the test (although I normally run LOP which is ~6 knots slower).

 

I used WOT, 2500 RPM, RAM air on for both runs.  Weight was about 2400 lbs.

 

My 7500' TAS was 142.6 Knots and the density altitude was 9465'.

 

My 10,500 TAS was 139.9 Knots and the density altitude was 11,951'.

 

Thanks for anyone that wants to use this as an excuse to go fly and report back!

 

Rags

[N601RX]

Here is one data point. It would be interesting to see others.

http://www.mooneypilots.com/mapalog/M20F%20Evaluation/M20F_Evaluation_Report.html

[Ragsf15e]

Yeah, that's a good one.  I read all those several times before choosing my M20F.  He got pretty good speed out of that F model - around 150KTAS at 7000' with no speed mods.

 

I think that might be a bit more than most of them are capable of (mine included) and I'd like to see some other data points too.

 

Interestingly, my IAS was almost exactly what his was (123KTS at 10,500 and 129 KTS at 7,500) but if you use the temp and pressure to turn IAS into TAS, I find that my airspeed indicator is showing about 6KTS too fast - calibration error maybe?  Anyway, the 3 way groundspeed test is very accurate.  

 

I used the pilot report above, put 3 of his directions into the 3 way test and get about 1 knot slower, so they aren't far off of each other.

[carusoam]

I know Byron was a proponent of a three leg method.

IIRC he used 120° of separation and math to balance the approach.

90° seems like it is missing something.

Now I will read the thread suggested....

Best regards,

-a-

So now I have read the MAPA article, but it mentions level cruise performance data in four directions...W,S,E,N.

I read the TAS calculator and put in some data.

I would think there is an error related to the speed of the wind using an unbalanced method.

I would prefer the four course method. It is logical if an error is being induced, it will be easier to recognize.

How much am I saving by doing a 3 course method every couple of years? Then I would have to explain it to every one I shared the data with.

[Bob_Belville]

Old E model (probably 350# below gross)

 

9500' OAT 5C

21.6/2540 70% ROP  10.2 GPH

136 KIAS

158 KTAS 

 

 

8500' OAT 7C

21.5/2360 65% LOP 8.2 GPH

128 KIAS

146 KTAS

[scottfromiowa]

Bob, is the second number supposed to be MPH?

[garytex]

100 Rop mine has shown 150 Kts or very slightly above 3 or 4 times on the 4 way GPS ground speed average at 7500 on cool (for Texas) days. I also think my airspeed indicator over reports maybe 6 or 8 kts.  Plane has full boat of SWTA mods.  Runs 5 - 8 kt slower 30 LOP around 8 GPH   

[Bob_Belville]

Bob, is the second number supposed to be MPH?

All knots. KIAS is indicated air speed in knots, KTAS is true air speed in knots.

 

Both are displayed on the Aspen.

 

(My "old" E has about every mod available. I would expect performance should be about as good as a J. Perhaps better since power to weight ratio is higher.)

[M20F-1968]

1968 M20F - highly modified

Turbo Normalized

J model cowling and windshield, aileron/flap/elevator gap seals and hinge covers

long range tanks, manual gear and hydraulic flaps

100 deg ROP

 

9,500 ft -  160 kts true air speed

17,000 ft - 170-175 kts true air speed - still collecting data here

[FloridaMan]

I have collected a ton of data flying my 67F. I will go do your test and report back, but if you want to look at my flight data, you can view it here: http://airwaysandrunways.com/Flights/Default.aspx

 

I'm Alan on the site. If the numbers on a particular flight seem way off, it might be one of the handful of flights when I was in something other than the Mooney. The average speeds include averaging from climbout. Clicking within the flight path will show you the speed at that data point. Click the date to select the flight. Map overlay data is current data and not data at the time of flight. 

[Bob_Belville]

I have collected a ton of data flying my 67F. I will go do your test and report back, but if you want to look at my flight data, you can view it here: http://airwaysandrunways.com/Flights/Default.aspx

 

I'm Alan on the site. If the numbers on a particular flight seem way off, it might be one of the handful of flights when I was in something other than the Mooney. The average speeds include averaging from climbout. Clicking within the flight path will show you the speed at that data point. Click the date to select the flight. Map overlay data is current data and not data at the time of flight. 

All ground speed? Without knowing winds, TAS could be anything?

[FloridaMan]

All ground speed? Without knowing winds, TAS could be anything?

 

That is correct. But we do know what ground speeds we're used to seeing in our airplanes. A leg I flew in October a couple years ago in New Mexico I think I averaged just over 100kts, and over 200 on the return trip, but in general, we know that in level cruise what we expect to see. In my airplane, it's 150-165kts over the ground in most cases. Maybe today I'll go up and try the experiment. I'm kindof scared to do it because I might find my plane to be slower than I keep telling myself

[Super Dave]

'76 F here with sloped windshield and cowl closures. Also have aileron, elevator, and flap-gap seals, but I don't remember if those are aftermarket mods or factory. Roller tappet engine timed to 20˚ BTDC. Engine and prop at about 600hrs. 

 

I've used the three-turn calculator to verify the accuracy of the Aspen TAS readout and found it to be within 3%. 

 

I'm almost always flying with wife, kids and luggage, so near MGTOW. Anywhere rom a 9000'-12,000' I can count on 148-150 KTAS. 9.3 GPH LOP.

 

As a side note, with the instantaneous TAS readout on the Aspen, I've experimented with different RPMs at 9.3 GPH, and I don't see one knot of difference between 2350-2650RPM. 2500RPM seems to be the best balance of noise/vibration so that's usually where I run.

[Bob_Belville]

That is correct. But we do know what ground speeds we're used to seeing in our airplanes. A leg I flew in October a couple years ago in New Mexico I think I averaged just over 100kts, and over 200 on the return trip, but in general, we know that in level cruise what we expect to see. In my airplane, it's 150-165kts over the ground in most cases. Maybe today I'll go up and try the experiment. I'm kindof scared to do it because I might find my plane to be slower than I keep telling myself

Yeah, I suspect the 180 knots flights stick in your mind longer that those in the 130 range. 

[Ragsf15e]

That's some good data and you guys have some fast airplanes!

 

Super Dave, I'm glad you've checked the TAS on the Aspen vs TAS derived from a ground speed check because I found that TAS indicators or TAS computed on your GPS can easily be corrupted by your pitot system.  The real data we have has to take the calibration error from the airspeed indicator out of the equation.

 

The only good way to really do it is the 3 way (or maybe 4 way) test.

 

Thanks for the feedback!

 

Rags 

[Bob_Belville]

I've used the three-turn calculator to verify the accuracy of the Aspen TAS readout and found it to be within 3%. .

I suppose the Aspen which "sees" the IAS, OAT, and PALT can calculate TAS (think E6B) as accurately as the precision of your ASI, the OAT sensor, and the Pressure sensor.   

[Ragsf15e]

Bob - 

 

First, that's a beautiful panel on your E model!

 

I have to say though, I don't think your Aspen displayed TAS is too accurate.  First, you got a higher TAS at 9500' than you did at 8500'.  7-8000' D.A. should be right in the sweet spot for our max speeds (not for the turbo crowd).  Higher should be slower according to data and the book numbers.

 

My real problem with the Aspen TAS is that it's using your 50 year old pitot system for the IAS input.  As I found on mine, it's off by about 6 knots at cruise.  I'd recommend doing the GS test and verifying the accuracy of your TAS like Super Dave.  Also, the pitot system error is most likely off different amounts at different speeds - so maybe 1 knot at 80 knots on final, but 6 knots at cruise.

 

I do drool over your panel though...

 

Rags

[Ragsf15e]

Yep, Bob, you posted just as I was writing... I agree, the Aspen data is only as good as the inputs whereas the ground speed test is much more accurate.

[Awful_Charlie]

I know Byron was a proponent of a three leg method.

IIRC he used 120° of separation and math to balance the approach.

90° seems like it is missing something.

Now I will read the thread suggested....

Best regards,

-a-

So now I have read the MAPA article, but it mentions level cruise performance data in four directions...W,S,E,N.

I read the TAS calculator and put in some data.

I would think there is an error related to the speed of the wind using an unbalanced method.

I would prefer the four course method. It is logical if an error is being induced, it will be easier to recognize.

How much am I saving by doing a 3 course method every couple of years? Then I would have to explain it to every one I shared the data with.

 

I prefer the three course method too. Hopefully our resident mathematician can chime in the the error margins, but if you consider the four heading N,E,S,W test:

 

Say the wind is blowing a hooley from the north, Your ground speed on a northerly heading is reduced by the wind speed, and on the southerly course it is increased by as much. (If you had the wind *exactly* on the nose or tail here, you could stop at this point and average the figure), On the east and west headings though, your ground speed is actually higher than your TAS, as you are making the TAS along your heading, but also making progress to the south thanks to the wind. The higher the wind, the more significant the error

[Marauder]

Bob -

First, that's a beautiful panel on your E model!

I do drool over your panel though...

Rags

Since you are drooling over panels... here is my F panel to drool on...

It's interesting you are bring up your concerns over engine performance. I have owned my F for 23 years and over the last several flights have perceived a loss of airspeed as well on my 900 hour factory rebuild. I wonder if there is something in the air?

I haven't done a recent KTAS a calculation but will do one the next time I am up. In the past, my KTAS was consistently at 150 KTAS give or take a knot. If I bumped the RPM to 2600, I would see 154.

The Aspen will typically show around 2 KTAS higher than the calculated KTAS. I attributed this to errors in the pitot side (leaks?). Since my 3 airspeed indicators are all fed off of the same pitot source, the error should be the same for each, provided they are all reading correctly. When I fly with both Aspens showing airspeed, they are within 1 KIAS of each other and match the indicated airspeed of the mechanical ASI.

[Raygun15E]

Rags,

I get similar KTAS numbers as you, just a few kts slowe with a N,E,S,W method. I'll have to try the three leg method at your altitudes to compare. In addition, I rarely get my KIAS over 128kts in cruise. I think I may have a few knots of error in my IAS as well.

Let me know if you want to get together some weekend to go up and compare numbers.

- Raygun

[Ragsf15e]

Marauder - that's one heck of a nice panel!  However, I do like my "older model" engine controls and the removal of my "steam gauges"!!

 

Rags

 

[Marauder]

I have adapted to the "airline" style quadrant despite preferring the verniers. Speaking of engine controls, this is what I did to the factory RPM, FP & MP gauges:

[Lood]

@ Rags and Raygun,

 

My '67 F matches yours almost to the number. Before the engine and prop overhaul, I got 138kts and afterwards, 142kts - WOT, 100 deg ROP, 2500rpm. We have an annual air race here in SA, during which the pilots try their utmost to get every last knot out of the airplanes. I've worked through the end results of quite a few years and with the odd 146kt exception here and there, most South African M20F's are 140 - 142kt airplanes.

[Bob_Belville]

Bob - 

 

First, that's a beautiful panel on your E model

I have to say though, I don't think your Aspen displayed TAS is too accurate.  First, you got a higher TAS at 9500' than you did at 8500'.  7-8000' D.A. should be right in the sweet spot for our max speeds (not for the turbo crowd).  Higher should be slower according to data and the book numbers.

 

My real problem with the Aspen TAS is that it's using your 50 year old pitot system for the IAS input.  As I found on mine, it's off by about 6 knots at cruise.  I'd recommend doing the GS test and verifying the accuracy of your TAS like Super Dave.  Also, the pitot system error is most likely off different amounts at different speeds - so maybe 1 knot at 80 knots on final, but 6 knots at cruise.

 

I do drool over your panel though...

 

Rags

Rags, thanks!.

 

You need to study the details more carefully.

The 9500' flight is @ 70% power rich of peak. The 8500' flight is 65% power, lean of peak.

The RAM air is open @ 9500 and closed @ 8500, and

the RPM is 2540 @ 9500 and 2350 @ 8500.

Apples and oranges.

I suppose I would have been over 160 KTAS @ 8500 at a higher power setting & ROP. But I don't have a pic of that to share.