J model POH performance change over years

[OZMOONEYMAN]

Hi,

Any performance specialists?  I'm interested to understand the takeoff performance differences in the J model.  Apart form some aerodynamic improvements the sizeable disparity between the attached 1977 and 1996 issued POH in takeoff performance I attribute to A) regulator imposing increased factoring / buffer inbuilt as time went on and/or the 'speed at 50ft'.  I note the stall speeds in both books listed as 57kt in takeoff config (Flap 15 deg), yet the speed at 50ft in the 1977 book only 71kts and in the 1996 book 76kts .  The lower margin above stall speed will achieve better numbers for takeoff distance I understand but I'm not certain its the only factor at play here in the differences.  71 kts is 24.56% margin above stall and 76 kts is 33.33% margin above 1G stall.  Takeoff Safety speed for light aircraft I believe has to be at least 20 percent above stall speed??

Was there an FAA change at some stage on this?  Are the 1977 figures allowed to be used... certainly not providing as much margin as later book data in the real world.

[ArtVandelay]

You’re not comparing apples to apples since MGW is different.

[Ragsf15e]

Totally agree with the weight being the majority of the issue.

[carusoam]

Same 200hp

Same wings

Different MGTW

Expect to see a corresponding change in the climb rates as well for the same reason…

 

You should be able to calculate identical performance if you lessen the load on the higher MGTW plane….

Everyone prefers the higher MGTW… but not everyone gets more…. (Structural changes that go with that…)

 

Then compare to reality…. Each plane will be different but should be comparable to the POH…

To get real numbers… Consider using an app like CloudAhoy, and a portable WAAS source….

PP thoughts only,

-a-

[OZMOONEYMAN]

3 hours ago, ArtVandelay said:

You’re not comparing apples to apples since MGW is different.

Charts have a weight adjustment area

[OZMOONEYMAN]

1 hour ago, Ragsf15e said:

Totally agree with the weight being the majority of the issue.

Charts have a weight adjustment area

[PT20J]

There is another thread on this. Somewhere mid-thread I showed that the POH charted takeoff performance at the same gross weights  is considerably better for a 1978 M20J compared to a 1994 M20J. None of the Mooney instructors could account for it. Bob Kromer also had no explanation.

 

[OZMOONEYMAN]

7 minutes ago, carusoam said:

Same 200hp

Same wings

Different MGTW

Expect to see a corresponding change in the climb rates as well for the same reason…

 

You should be able to calculate identical performance if you lessen the load on the higher MGTW plane….

Everyone prefers the higher MGTW… but not everyone gets more…. (Structural changes that go with that…)

 

Then compare to reality…. Each plane will be different but should be comparable to the POH…

To get real numbers… Consider using an app like CloudAhoy, and a portable WAAS source….

PP thoughts only,

-a-

Thanks yes I calculated both scenarios and both aircraft charts using a MTOW of 2740 pounds.  Certainly not the same output from what I can see.

[OZMOONEYMAN]

2 minutes ago, PT20J said:

There is another thread on this. Somewhere mid-thread I showed that the POH charted takeoff performance at the same gross weights  is considerably better for a 1978 M20J compared to a 1994 M20J. None of the Mooney instructors could account for it. Bob Kromer also had mo explanation.

 

Thanks for reply.  Yes this is my findings also.  Interesting

[carusoam]

Beware of old POH data…

The older the POHs are… the less data is actually in them…

Often the data that is in them doesn’t pass a typical quality test we would see today…

In the 60s… the POH was called an owners manual and was about 30 pages long including the welcoming statement and how smart you are for buying a Mooney…. 

In the 70s… the POH resembles a real POH but it only has about 100 pages of info in it…

For comparison… a 90s POH is about 300 pages long and is written to a much higher standard…

 

Some of the most obvious errors are in the power setting charts… for things that couldn’t be measured by the average pilot…

With today’s instrumentation… we know a calibrated MP to the closest 0.1”….

Fun details…

 

When getting my engine OH’d…

We had a choice… 

One price for the 280hp version, and another for the 310hp version….

The marketing numbers for performance data was unbelievable….

There was no way I could afford to pay for something like that…. Then be disappointed if the real numbers didn’t really match expectations….

 

So…. A fellow MSer invited me to go on a flight in his 310hp Screamin’ Eagle….  I brought my iPad and my SkyRadar/WAAS… and measured the T/O roll…. And initial climb rate…. Accuracy to the foot…

Holy cow the performance numbers matched the sales brochure….

Data generated in 2012 is much better than data generated before the digital age…

PP thoughts only,

-a-

[A64Pilot]

The FAA issued an AC and one of the things covered in the AC was takeoff performance, the old way was for a pilot to horse the thing off of the ground and get it to 50 ft as quickly as possible, the new way has the pilot takeing off and climbing normally, actually the FAR didn’t specify a method.

Being an AC it’s “advisory” not regulatory, but I’ve been told recently thet you can’t win that argument anymore.

This came up recently on an aircraft I built with a GE turbine, it’s now being Certified with a Pratt&Whitney under the theory it’s the same, but takeoff performance numbers are greatly different due to how the methods used in obtaining them, so the current owner called me all upset thinking he wouldn’t get Certification.

[PT20J]

I agree that a change in procedure is the only reasonable explanation.

[OZMOONEYMAN]

12 hours ago, A64Pilot said:

The FAA issued an AC and one of the things covered in the AC was takeoff performance, the old way was for a pilot to horse the thing off of the ground and get it to 50 ft as quickly as possible, the new way has the pilot takeing off and climbing normally, actually the FAR didn’t specify a method.

Being an AC it’s “advisory” not regulatory, but I’ve been told recently thet you can’t win that argument anymore.

This came up recently on an aircraft I built with a GE turbine, it’s now being Certified with a Pratt&Whitney under the theory it’s the same, but takeoff performance numbers are greatly different due to how the methods used in obtaining them, so the current owner called me all upset thinking he wouldn’t get Certification.

Copy thanks.  Yes hard rotation and over rotation giving up acceleration to a more prudent margin above stall speed and achieving a 'on the slow side' speed at 50ft rather than achieving a better safety margin over stall may well have been very good for marketing in the 70's and explain the large differences.  

[1980Mooney]

6 hours ago, PT20J said:

I agree that a change in procedure is the only reasonable explanation.

No one has mentioned the addition of winglets/wingtips which appeared in 1981. The 1977 model has squared off wing tips. The 1977 wingspan is 35 feet. The 1994 wingspan is 36‘1“. If you subtract the width of the fuselage from the wingspan that results in a 3.4% increase in lifting wingspan. More importantly the curved shape of the winglet modifies how the vortex rolls off the wing tip during flight.

Edited January 21, 2022 by 1980Mooney

[1980Mooney]

23 hours ago, carusoam said:

Same 200hp

Same wings

The aluminum wing structure is the same however the later models came from the factory with the addition of winglet/wingtips that increase the wingspan by 1’1”. They also changed how the vortex rolls off the end of the wing. 

My M20 J had the squared off wingtips however during the Missile conversion winglets had to be added per STC in order to enhance performance for the added weight of the 300 hp Continental. 

Edited January 21, 2022 by 1980Mooney

[PT20J]

Perhaps @Blue on Top could comment on wing tip treatments. My understanding is that while some have benefit for specific applications (e.g., winglets, raked) sculpted tips like on the Mooney are primarily aesthetic. It’s such a simple mod that it’s hard to believe LoPresti would have overlooked them. Manufacturing is certainly less expensive with the squared off tips.

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[carusoam]

The squared off tips allow the high pressure to move to the low pressure side…

Thus generating the vortexes….

This challenge essentially lops Off the lift characteristics of the last foot or so of wing…

And leaves us with the full drag all the way out to the tip…

The wing tips were reported to cut this loss of lift length in half…

Maybe they extended the wing a bit while cutting the effect some…

It would be great if I could remember a reference for that… 

Best regards,

-a-

[PT20J]

If the wingtips improved the aerodynamics, why are the takeoff performance numbers worse for the newer models than the older ones with squared off tips?

The goal of wingtip devices is to reduce induced drag. Recalling that a longer span wing has less induced drag than a wing of lesser span, it is seen that the devices are clever aerodynamic means of increasing the effective wingspan with minimal increases in the geometric wingspan. 

The idea that a wingtip device can reduce drag by altering only the tip vortex originates in the misunderstanding that the induced drag is solely a function of the tip vortex. For this to be true would require an unrealizable spanwise lift distribution. In fact, the wingtip vortices are an integral part of a much larger 3D flow pattern and it is not possible to alter one part of it without affecting the whole. McLean, Understanding Aerodynamics, 2013, has a good discussion of this in Chapter 8.

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[carusoam]

Hmmmmm…..

Is Vr the same for all years of M20J?

Does it have a weight based range?

How much do people stick to the script on this during ordinary flights? (Not performance testing flights…)

Best regards,

-a-

[A64Pilot]

Wing tips on the average general aviation airplane are purely decorative, they are pretty much functionless, but they do add ramp appeal and I’m sure may help sell airplanes.

I Seem to remember that Lopresti in a interview was asked about the performance increase of the upswept tips, and he skillfully shifted it to they reminded him of someone  named Stacy and she has such a pretty nose or something, this is memory from long ago so I may have it wrong.

I’ve also read somewhere the someone at Mooney claimed they reduced turbulent flow over the outer aileron and they improved aileron response.

But I’ve not heard that they increased cruise by X kts or climb rate by X FPM.

Winglets for example are only effective at high angles of attack, and general aviation airplanes simply spend very little time at high AOA, now airliners cruise at high AOA so they are very effective on an airliner.

By the way, my J has the upswept tips.

 

On edit, there has been some work with winglets on Ag airplanes trying to reduce wing tip vortices with mixed results. When an Ag plane is spraying its possible that the spray can be caught up in those vortices and cause drift, or off target application, both bad things.

Second edit, I think I found that article,and it was Stancie not Stacy?

https://airfactsjournal.com/2020/06/the-magical-mooney/

Edited January 22, 2022 by A64Pilot

[A64Pilot]

I’m surprised the FAA didn’t require Mooney to re-pull the wing when they increased the wingspan with the tips. 

Maule with the M-6 needed to increase the aileron size, they wouldn’t give up flap length and if they added a foot of wingspan to get 6” more aileron, the FAA would require them to re-test the wing, so they changed the wing tip from a swept down tip to a Horner tip and got the 6” longer aileron without an increase in wingspan.

There are quite a few that will argue that a Horner tip is lower drag than any other, and may be on paper.

[Hank]

12 hours ago, A64Pilot said:

I’m surprised the FAA didn’t require Mooney to re-pull the wing when they increased the wingspan with the tips. 

Maule with the M-6 needed to increase the aileron size, they wouldn’t give up flap length and if they added a foot of wingspan to get 6” more aileron, the FAA would require them to re-test the wing, so they changed the wing tip from a swept down tip to a Horner tip and got the 6” longer aileron without an increase in wingspan.

There are quite a few that will argue that a Horner tip is lower drag than any other, and may be on paper.

The Mooney wingtip aren't structural and don't affect aileron length. That's probably why.

My C has the wingtip, they're simple fiberglass parts that screw to the flat wingtip. I remember being told when I bought the plane (with the tips installed) that they were purely cosmetic. 

[PT20J]

2 hours ago, Hank said:

The Mooney wingtip aren't structural and don't affect aileron length. That's probably why.

My C has the wingtip, they're simple fiberglass parts that screw to the flat wingtip. I remember being told when I bought the plane (with the tips installed) that they were purely cosmetic. 

One thing that the tips should do aerodynamically is reduce the roll stick force because they move the tip vortex away from the aileron. 

[Blue on Top]

I'm asking for flames, but that's my job    Honestly, though, there are people on both sides of this on this thread, so here goes ...

1) I'll ask a few questions first.  Was there a propeller change between these years?  Yes, I know they are all constant speed.  Even constant speed propellers will be twisted differently for climb (slow speed) and cruise (high speed).  In addition, propellers can be twisted and shaped inboard quite differently for cooling reasons.  Did the cowl change?  Was there a propeller aspect ratio change?  Two-blade versus three?

2) At the same weight and conditions, all "J"s should perform the same.  But, it was mentioned above that the speed at 50' was raised significantly in the later airplanes.  This will definitely increase takeoff distances.  Those speeds are typically not changed with less than gross weight takeoff data.  As a result, the apples-to-apples comparison at 2740 lbs. is really not apples-to-apples as the newer airplanes still need to accelerate to the higher climb speed.

3) With that said, someone mentioned that the ground roll is also longer in the newer airplanes (but Vs and Vr are the same).  This screams of a different propeller to me.  If Mooney elected to give up takeoff performance for a little higher cruise speed, that would not surprise me at all.

4) As for wing tip treatments, squared off tips are actually fairly effective as it causes cleaner vortex separations from the wing.  Additional span is ALWAYS good.  My apologies to @PT20J (I love you, man), but ANY span outboard of the aileron (Mooney geometry) will increase the aileron control forces and their effectiveness.  With the additional span (though minor) will cause less wingtip loss ... especially locally at the aileron itself.

[PT20J]

My 1978 M20J and 1994 M20J both had the same prop and engine. The only differences I note are the 1994 has the sculpted wingtips and the one piece belly panel.

From the POH charts:

Common conditions: 20 deg C, sea level, 2740 lbs, 15 deg flaps, paved, level, dry runway, full power before brake release, landing gear extended until obstacle cleared, cowl flaps open.

1994: Lift off speed 59 KIAS, ground roll 1480'; 50' speed 76 KIAS, 50' distance 2200'

1978: Lift off speed 63 KIAS, ground roll 965'; 50' speed 71 KIAS, 50' distance 1831'

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