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1969+ M20F speeds


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Folks with a '69 or newer M20F (fixed step, etc), what sorts of speeds are you seeing? I cannot seem to true out past the high 130s / low 140s, for the most part. Frustrating. (The rigging was checked not too long ago by LASAR. It has the LASAR 201 windshield and a bunch of the other LASAR clean-ups (flap gap seals, aileron seals, tail hinge covers, dorsal fin kit mod, brake reversal, wheel well enclosure, cowl closure, oil cooler relocation). I haven't done a "cardinal directions" GPS groundspeed check, but I calculate my true airspeed often - I fly long cross-country flights a lot - did ~900 nm on Monday - and get bored easily ;).

I'm typically WOT and 2550 or 2500 RPM, and leaned <60% HP (I have an EDM-830) for best power. (Still chasing down GAMI spread issues before I can fly LOP comfortably, which I know will shave a few knots.) Usual cruising altitudes are in the 9,000-12,000' range (SoCal, almost all the MEAs around here are 10,000+), but even lower the highest I've ever seen was 148 ktas (about 6,000' IIRC).

At the end of the day, it's not that big of a deal. From GYR to LPC yesterday, even 10 knots would have only shaved 18 minutes total off my ~3 hour trip time. I'm just curious, since everyone says a Mooney "should be" a 150 knot airplane (~160+ ktas for the 201)... And psychologically, IDK, 150 just seems like a good goal. :) 

What true airspeeds are folks seeing in their later, "cost-cutting" Fs, at what altitudes and power settings (RPM/MP/fuel flow)? Thanks!

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9500 feet, WOT, 8.9 gph, 2500 rpm, 3 blade prop, mostly stock airframe, usually close to gross:  139 knots

Go read http://www.mooneypilots.com/mapalog/M20F Evaluation/M20F_Evaluation_Report.html

He is running 50 ROP and likely burning 10.5 or more gph.   If you want 150 knots go lower and burn more fuel.  

I consider 150 knots at 9 gph my dream, to get there I need a new windshield and cowl, otherwise the 20F at about 9 gph is a 140 knot airplane. 

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Mine is very similar to yours but with a 3 blade speedbrake.  I’m usually 142-148kts ROP between 7-10,000’ density altitude.  Depending on density altitude and weight.   If you’re cruising at 10,000’ in socal, what’s the da?  You’re losing some speed up that high.

Also, take the 5 minutes to do a 4 way gps test.  You’re using your indicated airspeed to compute TAS and the IAS is likely off by a few knots.

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2 minutes ago, Ragsf15e said:

Mine is very similar to yours but with a 3 blade speedbrake.  I’m usually 142-148kts ROP between 7-10,000’ density altitude.  Depending on density altitude and weight.   If you’re cruising at 10,000’ in socal, what’s the da?  You’re losing some speed up that high.

Also, take the 5 minutes to do a 4 way gps test.  You’re using your indicated airspeed to compute TAS and the IAS is likely off by a few knots.

Actually, I'm using the calibrated airspeed, but yeah, it's based on the IAS. :)  I'm using the GNS430W to calculate TAS, which factors in the barometer and OAT (i.e., accounts for density altitude). I'm definitely faster in the winter (by several knots).

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When travelling, I'm always WOT and LOP, usually 7-10k feet depending on headwinds.  There's always a headwind. :wacko:  I have gap seals and caliper reversal etc, but no 201 windshield and just the guppy mouth enclosure.  I spent a lot of time with Clarences rigging boards and his help.  It gave me about 10knots over when I first bought it.

I get 150-154KTS TAS, usually near the upper of that range.  I vary RPM and GPH according to the density altitude.  At a higher density altitude I run higher RPM and closer to peak (9.5-10 GPH) to keep the optimum pressure peak where I want it.  Lower DA, of course, is leaner (9 GPH+/-) and lower RPM.

eg.

https://uk.flightaware.com/live/flight/CGNPP/history/20190421/1700Z/KBUF/KPHF

https://www.savvyanalysis.com/flight/3140768/b56a5a32-eedd-4e4b-ba11-c56c72236bf5

 

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9 minutes ago, chrixxer said:

I have, I'm surprised he was getting 145 ktas at 10,000'. But that's a '67 (but also almost completely stock; no 201 mods, just the cowling closure)...

I agree, but he was light in all those tests.  1 person, no bags.  I can notice several knots when light.

Honestly I use the 430w TAS to compare to my own 4 way tests and it’s usually off by several knots.  My IAS is 5 knots higher than it should be.  The correction to CAS takes out about 2 knots of that error.

Best altitude for me is around 6,500’ DA. Ill be pushing 149-150ish.  Mpg suffers down low though.

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8 minutes ago, Cyril Gibb said:

When travelling, I'm always WOT and LOP, usually 7-10k feet depending on headwinds.  There's always a headwind. :wacko:  I have gap seals and caliper reversal etc, but no 201 windshield and just the guppy mouth enclosure.  I spent a lot of time with Clarences rigging boards and his help.  It gave me about 10knots over when I first bought it.

I get 150-154KTS TAS, usually near the upper of that range.  I vary RPM and GPH according to the density altitude.  At a higher density altitude I run higher RPM and closer to peak (9.5-10 GPH) to keep the optimum pressure peak where I want it.  Lower DA, of course, is leaner (9 GPH+/-) and lower RPM.

eg.

https://uk.flightaware.com/live/flight/CGNPP/history/20190421/1700Z/KBUF/KPHF

https://www.savvyanalysis.com/flight/3140768/b56a5a32-eedd-4e4b-ba11-c56c72236bf5

 

Thats a fast one.  Is that with 4 way tests or computed with your indicated as, altitude, temp, etc?

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42 minutes ago, Ragsf15e said:

Thats a fast one.  Is that with 4 way tests or computed with your indicated as, altitude, temp, etc?

Both 4 way and 430W calc.  That flightaware track was about 6-10 kt headwind component.  Next one on May 2 was right on the nose about 10-15kts and a wild ride in the clouds.  We've been out west a few times.  Headwind going west and headwind coming back east. sigh.  One thing I didn't mention.  That 150-154 is with ram air open.  For me, it's worth about 2 kts.

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My bird is a box stock 67F. I am closer to 150Kts or a tad over. Here’s a morning round trip done ~3hrs apart in opposite directions. KHGR>KCHO and then KCHO>KHGR. I put the cruise data into a spreadsheet and came up with 152.74kts. Not a perfect deduction of speed, but one can clearly see that my bird will top 140kts into a headwind. I ran 100ROP into the headwind and peak on the return with the tailwind. My bird indicates anywhere from 135kts to 155kts in level flight below 7000.

KHGR>KCHO

3E7FC088-EBE7-4C63-ABAB-8075BB8E081D.thumb.png.45ef92dc3d7ab1d4af09b7afdbf57a1e.png

 

KCHO>KHGR

AD2C28B1-9A4E-404C-959B-CFD7D1081579.thumb.png.01856833ad82ef7a530824e55ecc377a.png

Edited by Shadrach
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Chrixxer you need to make a gps speed run as described above before you conclude your speed is down. We did ours at 8000 feet with my wife and I on board. I bet you find yourself going faster than you think plus it's fun.

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23 hours ago, chrixxer said:

 

I'm typically WOT and 2550 or 2500 RPM, and leaned <60% HP (I have an EDM-830) for best power. (Still chasing down GAMI spread issues before I can fly LOP comfortably, which I know will shave a few knots.) Usual cruising altitudes are in the 9,000-12,000' range (SoCal, almost all the MEAs around here are 10,000+), but even lower the highest I've ever seen was 148 ktas (about 6,000' IIRC).

if you are truly <60% you are doing well!

My 67F can touch 150 KTAS but at 65%, 9gph. Years ago I would do 4 track GPS runs ROP that would net 155-157 KAS but that was more like 75% (I didn't have FF at the time).

Math seems to confirm that..

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I'm shocked at the low speeds some of these Fs are making! A friend used to have a 75 F with no step, and he walked away from my C; but I would walk away from some of these Fs while some I would run away from.

My C gets ~147-148 KTAS at altitude (7500-10,000 msl], WOT- / 2500. And I have a 3-blade Hartzell speed brake on the nose, guppy mouth closure and 201 windshield. AND a fixed step.

I generally indicate ~145mph like this, with groundspeed envelope of 68-186 knots. When I get it back from the shop, hopefully next week, I will do a 3-leg GPS groundspeed check.

Can't believe I'm that much faster than so many F models . . . . .

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It mostly comes down to altitude and fuel flow.  Most of what you see here is apples to oranges.  Unless they are reporting fuel flow it is pretty meaningless.

Unless you are running more than 100 ROP,  horsepower is pretty much a function of fuel flow (above that you are just using fuel to cool the engine).  For a Lycoming the thermal efficiency number is pretty close to 0.46 lbs/hr/hp.

So at 9 gph or 9 gph * 6.01 lbs/gal = 54.09 lbs/hr.

This gives about 117.6 hp or 59% power for an IO-360 or 65% power for a O-360.

At 10.5 gph you get 137.2 hp or 69% power for an IO-360 or 76% power for a O-360.

For that extra 20 hp and 1.5 gph most will get 5 to 7 knots increase in speed.  Most Mooney pilots are CB's so the number that is import is what can you cruise at efficiently, not just throwing fuel away.  You can cruise at Carson speeds, but in general the hourly operating costs make this less efficient, plus total time of flight gets pretty long.  The optimal  curve is usually about 60% power for the IO-360 aircraft.  It is hard to get the O-360 under about 69% power with WOT.

My 0$0.02 worth

 

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2 hours ago, TTaylor said:

It mostly comes down to altitude and fuel flow.  Most of what you see here is apples to oranges.  Unless they are reporting fuel flow it is pretty meaningless.

Unless you are running more than 100 ROP,  horsepower is pretty much a function of fuel flow (above that you are just using fuel to cool the engine).  For a Lycoming the thermal efficiency number is pretty close to 0.46 lbs/hr/hp.

So at 9 gph or 9 gph * 6.01 lbs/gal = 54.09 lbs/hr.

This gives about 117.6 hp or 59% power for an IO-360 or 65% power for a O-360.

At 10.5 gph you get 137.2 hp or 69% power for an IO-360 or 76% power for a O-360.

For that extra 20 hp and 1.5 gph most will get 5 to 7 knots increase in speed.  Most Mooney pilots are CB's so the number that is import is what can you cruise at efficiently, not just throwing fuel away.  You can cruise at Carson speeds, but in general the hourly operating costs make this less efficient, plus total time of flight gets pretty long.  The optimal  curve is usually about 60% power for the IO-360 aircraft.  It is hard to get the O-360 under about 69% power with WOT.

My 0$0.02 worth

 

Definitely agree with your analysis of horsepower, but I think the huge variability shown here is from differences in drag.  Especially from misrigging, gear not tucked, franken-antennas, etc.  at our cruise speed, drag is at least as important as thrust... maybe they’re equally important?

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3 hours ago, Igor_U said:

if you are truly <60% you are doing well!

My 67F can touch 150 KTAS but at 65%, 9gph. Years ago I would do 4 track GPS runs ROP that would net 155-157 KAS but that was more like 75% (I didn't have FF at the time).

Math seems to confirm that..

4 way runs are optimistic.  The most recent I did yielded an average of 156kts at 6500ft.  I don't think my bird will actually do that at 6500.  I think  Dr. Rogers's 3 way run does a better job of minimizing error.

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3 hours ago, Hank said:

I'm shocked at the low speeds some of these Fs are making! A friend used to have a 75 F with no step, and he walked away from my C; but I would walk away from some of these Fs while some I would run away from.

My C gets ~147-148 KTAS at altitude (7500-10,000 msl], WOT- / 2500. And I have a 3-blade Hartzell speed brake on the nose, guppy mouth closure and 201 windshield. AND a fixed step.

I generally indicate ~145mph like this, with groundspeed envelope of 68-186 knots. When I get it back from the shop, hopefully next week, I will do a 3-leg GPS groundspeed check.

Can't believe I'm that much faster than so many F models . . . . .

You're not, you're just faster than a few that need to be properly sorted.

Edited by Shadrach
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1 hour ago, Ragsf15e said:

Definitely agree with your analysis of horsepower, but I think the huge variability shown here is from differences in drag.  Especially from misrigging, gear not tucked, franken-antennas, etc.  at our cruise speed, drag is at least as important as thrust... maybe they’re equally important?

Actually I agree with you. I am just trying to say that comparing speeds at different fuel flows does not identify how all the things that you point out have helped.  I agree that rigging, modifications, clean-up, etc. all make a difference, but someone saying that they can fly at 150 knots without saying what the fuel flow was does not help us understand if the plane is well set-up or they are just burning lots of fuel to get the speed.  I know the the 201 windshield helps a great deal. I would love to know if there is consensus on the best set-up for rigging. Is there a good aerodynamic fairing we can use on fixed steps to help with them? I look forward to seeing real world numbers at fuel flows around 9.0 gph for close to stock air-frames.

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28 minutes ago, TTaylor said:

I would love to know if there is consensus on the best set-up for rigging. Is there a good aerodynamic fairing we can use on fixed steps to help with them?

There's a range of in-spec values for rigging, +/- a few degrees.  Experimentation can let you know (for your specific airframe) if top of range or bottom of range reaps some benefit. As I mentioned before, rigging including gear door correction got me 10kts.  It was a mess when I bought the plane.

For our fixed step strut, the cylindrical shape is almost the worst shape for aerodynamic drag.  Measure a 201 step fairing and build one.

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