Twisted Wing - What’s the deal?

[gwav8or]

Looking at and trying to buy a ‘67 M20F. It feels like “The One”.

 

However, what’s the deal with the twisted wing? What was the theory behind it?

 

 

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[Browncbr1]

The washout helps improve control as the wing stalls, beginning at the root.  The ailerons are the last part of the wing to stall.  It could be seen as beneficial if flying too slow and get into an accelerated stall turning base to final, but I think the real world benefit wasn't really there.  Some argue it costs a couple ktas.  It's the only thing on my 67F that I don't care for, (for aesthetics), but not a big deal... don't worry about it.

[gwav8or]

Oh it’s not going to affect my decision to buy. I already told the owner I want to buy it. He’s taking it to OshKosh and said he’ll call me after he gets back to let me know if he decides 100% to sell.


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[DCarlton]

I fly a '67F.  65-67 was a great period in Mooney production.  Not sure, but I believe I was told years ago that is was the same wing used on the M22 Mustang (potentially one factor in the brief change).  Again I haven't discussed the issue in years but it may climb better with a slight speed penalty.  Regardless, with all the speed mods, my airplane is consistently a 153 kt airplane in cruise at 8500-9500 feet.  I'm very satisfied.  Would be nice if a Mooney authority could verify the history accurately.  Looks like we have a couple of votes for improved stall performance; if that's true, I'll take it.  If it also helps with climb performance, I'll take that over a few extra knots of speed.  

[M20F]

67 is the last F with flush rivets, hydraulic flaps, and manual gear.  I purposely sought one out when I was looking to acquire.  

[Ragsf15e]

My ‘68 had manual gear, hydraulic flaps and the rivets look the same.  It got electric gear as a mod after leaving the factory.  It doesn’t have the twisted wing though.  Could that have been more costly to build?

[A64Pilot]

The deal with wing wing washout is as was said to help ensure the stall progresses from the root to the tip, a stall at the root is controllable and gives you very good warning to back off before you get into trouble.

The crop duster I built for years had a 1.5 degree washout and was known to have good stall characteristics. Crop dusters operate very close to the stall in most every turn and an airplane that telegraphs an impending full stall is a safer airplane.

You do give up some slight efficiency with washout, it simply works because the outboard part of the wing has 1.5 degree less angle of attack or whatever was built in, it helps prevent a tip stall, stall the tip and your very likely to go over on your back.

I won’t say a Mooney has evil stall characteristics because I’ve not gone out and done any stall work ups but airplanes with benign characteristics don’t have stall strips.

It’s likely you will give up a kt or two, but a washed out wing is generally considered to be safer

[A64Pilot]

1 minute ago, Ragsf15e said:

My ‘68 had manual gear, hydraulic flaps and the rivets look the same.  It got electric gear as a mod after leaving the factory.  It doesn’t have the twisted wing though.  Could that have been more costly to build?

It shouldn’t be, the washout is in the jig, there should be no real difference build time or difficulty wise, if I had to hazard a guess it was decided to not be necessary and it will decrease speed slightly. 

 

[gwav8or]

Awesome. Good luck!  I hope you get it.  

I’m hoping, praying, crossing my fingers and toes, tossing salt over my shoulder…. Anything I can think of.

This F is the cleanest one I’ve found. Been looking since December.

Owner said he’d decide after he gets back from OshKosh.




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[M20F-1968]

35 minutes ago, M20F said:

67 is the last F with flush rivets, hydraulic flaps, and manual gear.  I purposely sought one out when I was looking to acquire.  

My 68 F has flush rivets, twisted wing, hydraulic flaps and manual gear.  I think it was actually made in 1967 however and called a 68.

John Breda

[MBDiagMan]

Aerodynamically, my ‘67 F is a J except for the twisted wing.  It is a 150 knot plus airplane.

[Ragsf15e]

2 hours ago, bluehighwayflyer said:

We shared a community hangar with the 68C model for many years so I became pretty familiar with it; especially since I could compare it directly to our 65C. It had manual gear and hydraulic flaps but did not have a twisted wing.  It’s flush riveting was the same as our 65 model.

Separate and apart from the twisted wing issue, in 1968 Mooney went through a cost cutting process by eliminating the dorsal fin, the adjustable cowl flaps, the retractable step, and some of the flush inspection panels.  Also some of the flush screws.  Around the windows, for instance.  I don’t remember anything else.  I think that is what he was referring to.

I think the E/F still had the moveable cowl flaps.  My ‘68 F does anyway.

[MikeOH]

3 hours ago, Ragsf15e said:

I think the E/F still had the moveable cowl flaps.  My ‘68 F does anyway.

As does my '70 F

[M20F]

11 hours ago, M20F-1968 said:

My 68 F has flush rivets, twisted wing, hydraulic flaps and manual gear.  I think it was actually made in 1967 however and called a 68.

John Breda

I suspect you are correct.  My 67 details came from Maxwell, he and thus I could be wrong as well. 
 
I will say though your F is like no other!

[Browncbr1]

18 hours ago, M20F said:

67 is the last F with flush rivets, hydraulic flaps, and manual gear.  I purposely sought one out when I was looking to acquire.  

+1

[jaylw314]

On 7/4/2022 at 11:29 AM, Browncbr1 said:

The washout helps improve control as the wing stalls, beginning at the root.  The ailerons are the last part of the wing to stall.  It could be seen as beneficial if flying too slow and get into an accelerated stall turning base to final, but I think the real world benefit wasn't really there.  Some argue it costs a couple ktas.  It's the only thing on my 67F that I don't care for, (for aesthetics), but not a big deal... don't worry about it.

Does anybody know if Mooney added the stall strips when they got rid of the twisted wing?

[M20F]

19 minutes ago, jaylw314 said:

Does anybody know if Mooney added the stall strips when they got rid of the twisted wing?

My 67 has stall strips so been around for awhile.  I could probably make a wing drop if I wanted to but the outcome of that maneuver is more then my tighty whites could handle.  
 
Very docile in the stall.  

[Shadrach]

26 minutes ago, jaylw314 said:

Does anybody know if Mooney added the stall strips when they got rid of the twisted wing?

They all have stall strips installed at the factory to enhance the uniformity of the stall. Rigged correctly with the ball centered, power off stalls are benign. 

[Greg Ellis]

We should ask Ron Blum about this, @Ron Blum. He gives a talk about this at Oshkosh.

[KSMooniac]

To my knowledge, all of the metal wing M20's have stall strips... they were tuned to each individual airplane to provide a consistent, even stall break.  This is to correct any minor deviations in the wing and control surface or flap construction, and perhaps rigging.

I like the theory that the M22 might have needed some geometric washout to behave nicely, and perhaps it was propagated to the M20 line as well.  As fast as they were building during the heyday, it would make sense to have a single wing jig (or multiple copies of the same).

There is also another way to accomplish the washout...called aerodynamic washout.  This is done by changing the airfoil at the wing tip, relative to the wing root.  The tip airfoil might stall at a higher angle of attack than the root, even though the leading edge appears straight/un-twisted.  The M20 has different root and tip airfoils, but I've never bothered to do the homework to see where each one nominally stalls.

Ron Blum has a great presentation of this sort of thing that he usually gives at Oshkosh.  I co-star since we used my plane as a demo for his talk.    He took the time to tuft one wing, and then we went up to fly a stall series and record the tuft behavior so he can show exactly how it happens.

[M20F-1968]

16 hours ago, jaylw314 said:

Does anybody know if Mooney added the stall strips when they got rid of the twisted wing?

My 68 with twisted wing has one stall strip on each side installed by the factory.

John Breda