Mooney tail

[PT20J]

There have been  numerous threads speculating about the reason for the Mooney "backwards" vertical tail. Some speculations have been thoughtful and some fantastical. In one, I believe we showed that a straight fin is the most efficient (swept back being less efficient) which explains the vertical leading edge, but the rudder hinge line being swept forward is still interesting. Someone found a quote from an interview with Al Mooney where he said something about low speed handling. At a high angle of attack, the forward canted hinge line would provide less spanwise airflow over the rudder improving it's efficiency, but it always seemed to me that not nearly so much forward cant would be required to achieve this in normal flight regimes. I ran across this old April 1995 Flying magazine article by Peter Garrison that provides a plausible explanation. Check out page 55.

https://books.google.bs/books/about/Flying_Magazine.html?id=Ob0MdPxhd4wC&hl=en&output=html_text

Skip

[Hank]

Good read! Interesting, too. Thanks!

[Ragsf15e]

2 hours ago, PT20J said:

There have been  numerous threads speculating about the reason for the Mooney "backwards" vertical tail. Some speculations have been thoughtful and some fantastical. In one, I believe we showed that a straight fin is the most efficient (swept back being less efficient) which explains the vertical leading edge, but the rudder hinge line being swept forward is still interesting. Someone found a quote from an interview with Al Mooney where he said something about low speed handling. At a high angle of attack, the forward canted hinge line would provide less spanwise airflow over the rudder improving it's efficiency, but it always seemed to me that not nearly so much forward cant would be required to achieve this in normal flight regimes. I ran across this old April 1995 Flying magazine article by Peter Garrison that provides a plausible explanation. Check out page 55.

https://books.google.bs/books/about/Flying_Magazine.html?id=Ob0MdPxhd4wC&hl=en&output=html_text

Skip

Awesome article.  However, @M20Doc isn’t gonna like this from page 59....

[PT20J]

According to legend, Piper wanted to buy the Mooney design to quickly launch a product to compete with the Bonanza. Supposedly Mooney flew a plane to Lock Haven and while he and Piper had lunch, Piper engineers descended on the ramp with cameras and tape measures. A business deal was not struck and Piper developed the copycat Comanche but with a Thorpe stabilator. I have no idea if this is true or just an interesting fable. But, if you lay the Comanche planform on top of a Mooney it's almost an exact match.

Skip

[Hank]

6 minutes ago, PT20J said:

According to legend, Piper wanted to buy the Mooney design to quickly launch a product to compete with the Bonanza. Supposedly Mooney flew a plane to Lock Haven and while he and Piper had lunch, Piper engineers descended on the ramp with cameras and tape measures. A business deal was not struck and Piper developed the copycat Comanche but with a Thorpe stabilator. I have no idea if this is true or just an interesting fable. But, if you lay the Comanche planform on top of a Mooney it's almost an exact match.

Skip

Sure looks that way, except for different windows and a funny tail. Maybe that's why Clarence likes his'n so much! Well, that plus the extra 200 hp . . . . .

Edited November 28, 2019 by Hank

[Floyd]

Al Mooney designed the Comanche according to the book "The Al Mooney Story"

[Guest]

23 minutes ago, PT20J said:

According to legend, Piper wanted to buy the Mooney design to quickly launch a product to compete with the Bonanza. Supposedly Mooney flew a plane to Lock Haven and while he and Piper had lunch, Piper engineers descended on the ramp with cameras and tape measures. A business deal was not struck and Piper developed the copycat Comanche but with a Thorpe stabilator. I have no idea if this is true or just an interesting fable. But, if you lay the Comanche planform on top of a Mooney it's almost an exact match.

Skip

If they copied a Mooney, the Piper engineers missed a few things.  They left out the steel cage, the leaky fuel tanks, Lord shock discs, the wooden structures, and the small cabin. 

Clarence

[PT20J]

39 minutes ago, M20Doc said:

If they copied a Mooney, the Piper engineers missed a few things.  They left out the steel cage, the leaky fuel tanks, Lord shock discs, the wooden structures, and the small cabin. 

Clarence

And leaky access panels over the avionics, the doghouse engine cowl and the low roll rate with heavy aileron forces. But both airplanes are too complex to manufacture cost effectively. I still marvel at the Cherokee series for its simplicity and utility. 

Skip

[0TreeLemur]

 

16 hours ago, PT20J said:

Check out page 55.

https://books.google.bs/books/about/Flying_Magazine.html?id=Ob0MdPxhd4wC&hl=en&output=html_text

Skip

Thanks for including the link, great read!  Despite what the article says, I think the real reason for the vertical tail on the M20 series stems from the fact that it would be much easier to make with plywood.   The aerodynamic argument that in a stall or spin, the forward swept tail will have a larger windward projected area is undoubtedly true.  Yet M20s are not noted for having excellent spin recovery characteristics.

[MooneyMitch]

This is gonna be a fun thread!

Your horizontal stabilizers are just a Mooney tail (vertical stabilizer) on the horizontal! 

[Igor_U]

On 11/27/2019 at 6:54 PM, PT20J said:

 But, if you lay the Comanche planform on top of a Mooney it's almost an exact match.

Skip

Skip, not quite. Piper has a straight wings while Mooney has forward swept wings (albeit small angle) in order to have "signature" straight leading edge. That gives Mooney spar a kink forward at the center section. 

[PT20J]

25 minutes ago, Igor_U said:

Skip, not quite. Piper has a straight wings while Mooney has forward swept wings (albeit small angle) in order to have "signature" straight leading edge. That gives Mooney spar a kink forward at the center section. 

Uh, no. The original PA28 (Cherokee) had a rectangular planform, but the PA24 has a forward sweep just like the Mooney. The Mooney and Comanche use slightly different but similar airfoils (maybe Piper didn’t measure carefully ). Later PA28s have a semi-tapered wing increasing the span and improving climb and altitude performance somewhat. 

Skip

[Igor_U]

46 minutes ago, PT20J said:

Uh, no. The original PA28 (Cherokee) had a rectangular planform, but the PA24 has a forward sweep just like the Mooney. The Mooney and Comanche use slightly different but similar airfoils (maybe Piper didn’t measure carefully ). Later PA28s have a semi-tapered wing increasing the span and improving climb and altitude performance somewhat. 

Skip

 

I had to look some pictures and must admit never really noticed that. Even the one below is not that clear - ideally it would be the best to have top view from POH. Empennage is clearly not with straight LE. 

 

 

Years ago when buying my plane, I was considering getting PA24 but FF with bigger 6 cylinder engine with not much of speed increase put me back into Mooney camp.

 

[N201MKTurbo]

I always thought the Mooney tail (and wing) are the way they are because they are easy to manufacture.

the straight leading edges allow a sheet of aluminum to be bent around it with minimum waste.

[Blue on Top]

On 11/29/2019 at 11:02 AM, N201MKTurbo said:

I always thought the Mooney tail (and wing) are the way they are because they are easy to manufacture.

the straight leading edges allow a sheet of aluminum to be bent around it with minimum waste.

Although true; not aluminum.  Al only designed the wood wing and tail airplanes.  Ralph Harmon (Bonanza designer) did the aluminum Mooney.  Which is probably why it's so overbuilt.

On the original point, the vertical tail is swept forward so the 1/4 chord becomes closer to perpendicular at higher angles of attack (lower speeds) where more trail is required.  As a direct result, the Mooney tail is smaller than others (less drag in cruise).  In addition and with the rudder hinge line being forward swept, the air must travel down the surface … something it doesn't want to do (which is good in this case).  On an aft swept tail, the airflow goes up the vertical, losing effectiveness.

[Guest]

On 11/29/2019 at 10:46 AM, PT20J said:

Uh, no. The original PA28 (Cherokee) had a rectangular planform, but the PA24 has a forward sweep just like the Mooney. The Mooney and Comanche use slightly different but similar airfoils (maybe Piper didn’t measure carefully ). Later PA28s have a semi-tapered wing increasing the span and improving climb and altitude performance somewhat. 

Skip

This might show it better.

[cliffy]

The metal wing on the Mooney was designed by Harmon after he designed the Bonanza wing and he told Mooney he would only do it if they did it his way as he didn't want another wing to come apart in flight like the early Bonanzas.

John Thrope designed the first Cherokee "Hershey bar" wing in the late 50s along with the Wing Derringer (always wanted one of those) and he designed the Navy's P2V Neptune which, for a time, held the long distance record until beaten by a B-52. 

[MooneyMitch]

19 minutes ago, cliffy said:

The metal wing on the Mooney was designed by Harmon after he designed the Bonanza wing and he told Mooney he would only do it if they did it his way as he didn't want another wing to come apart in flight like the early Bonanzas.

John Thrope designed the first Cherokee "Hershey bar" wing in the late 50s along with the Wing Derringer (always wanted one of those) and he designed the Navy's P2V Neptune which, for a time, held the long distance record until beaten by a B-52. 

Agree regarding Ralph Harmon comment.

During my interview of Ken Harmon, son of Ralph Harmon, Ken did confirm this.

The Ralph Harmon story is a great read, by the way.  He began his aviation career as a youth, by building a Pietenpol from  a Readers Digest kit !

[Andy95W]

1 hour ago, cliffy said:

The metal wing on the Mooney was designed by Harmon after he designed the Bonanza wing and he told Mooney he would only do it if they did it his way as he didn't want another wing to come apart in flight like the early Bonanzas.

John Thrope designed the first Cherokee "Hershey bar" wing in the late 50s along with the Wing Derringer (always wanted one of those) and he designed the Navy's P2V Neptune which, for a time, held the long distance record until beaten by a B-52. 

This is one of the reasons I'm hopeful Mooney can start manufacturing composite wings and tail for the M20 series.  

Our type certificate includes everything from the M20 through the M20V, which includes wood wings and tail all the way through metal everything with a dual turbo'ed 550.  If they changed the wing and tail to glass composite, it shouldn't be any more involved than in 1961 when they made the M20B using the same type certificate!

Imagine how fast our airplanes would be with a totally smooth wing and tail.  And no corrosion to boot!

[Parker_Woodruff]

Awhile back there was an experimental aircraft for sale on eBay.  It had the parts of a Piper Comanche and a Mooney put together into one package.  Maybe some other airframes were involved as well.

I tried finding a pic but could not.

[bonal]

The Mooney tail makes it easier to find your airplane in a crowded parking ramp. Al probably finished Christmas shopping one day and couldn't remember where he parked so wanted his airplane to stand out in a crowd. Merry Christmas every body.

[PT20J]

5 hours ago, Andy95W said:

This is one of the reasons I'm hopeful Mooney can start manufacturing composite wings and tail for the M20 series.  

Our type certificate includes everything from the M20 through the M20V, which includes wood wings and tail all the way through metal everything with a dual turbo'ed 550.  If they changed the wing and tail to glass composite, it shouldn't be any more involved than in 1961 when they made the M20B using the same type certificate!

Imagine how fast our airplanes would be with a totally smooth wing and tail.  And no corrosion to boot!

Might be a bit faster, because if you look at all the irregularities in the metal wing, it’s doubtful if there is any significant laminar flow. North American couldn’t get laminar flow on the P51 wing unless they bondo-ed it, and a P-51 wing has a lot less surface irregularity than the Mooney wing. The PA28 series utilizes a laminar flow airfoil, and no one claims them to be a speedsters. It turns out that true laminar flow requires a smoothness unobtainable with standard metal wing manufacturing processes. Al’s original wood wing may have been smooth enough, but clearly Harmon was concerned more with strength. 

The Mooney airfoils are decades old from the NACA catalog whereas I believe the Cirrus uses a modern custom airfoil designed by airfoil guru John Roncz. So, maybe a new wing could be better designed and thick enough to enclose the main wheels too.

But the big problem would be weight. Composite structures are usually heavier than corresponding structures built of aluminum. 

Skip

[Blue on Top]

1 minute ago, PT20J said:

But the big problem would be weight. Composite structures are usually heavier than corresponding structures built of aluminum. -Skip

And the people say "AMEN, Brother!"  Thank you, thank you, thank you!  (also for the comments on laminar flow.  You are absolutely right on.

Ironically, the rumor is that the M20/M20As are 5-6 mph faster than the metalized airplanes.  Those wings are fabric covered (little laminar flow … except in very negative pressure gradient areas at the front of the wing).  If I were to make a (very educated) guess, The wood wing, due to the stiffness of the plywood, maintains shape better than the aluminum wing.  There's probably little to no "pillowing" between the ribs and stringers. 

 

[Andy95W]

2 hours ago, Blue on Top said:

And the people say "AMEN, Brother!"  Thank you, thank you, thank you!  (also for the comments on laminar flow.  You are absolutely right on.

Ironically, the rumor is that the M20/M20As are 5-6 mph faster than the metalized airplanes.  Those wings are fabric covered (little laminar flow … except in very negative pressure gradient areas at the front of the wing).  If I were to make a (very educated) guess, The wood wing, due to the stiffness of the plywood, maintains shape better than the aluminum wing.  There's probably little to no "pillowing" between the ribs and stringers. 

 

I didn't realize the composite structure was so much heavier than the metal.  It ought to reduce man hours, at least- but what a waste of useful load.

My thoughts on speed had nothing to do with laminar flow, which is really nonexistent at the speeds our airplanes fly.  It was all about how fast the wood wings were, which I would assume was because of the smoothness.

[PT20J]

22 hours ago, Blue on Top said:

On the original point, the vertical tail is swept forward so the 1/4 chord becomes closer to perpendicular at higher angles of attack (lower speeds) where more trail is required.  As a direct result, the Mooney tail is smaller than others (less drag in cruise). 

Ron, This makes sense. I was thinking about the hinge line, but the mean chord line is more apropos. If I did the calculation correctly, a 2900 lb Mooney at 70 knots would need a C_L of about 1.0 which looks to be about 7.5 deg AOA for a 63₂215 airfoil which might be close to the sweep of the mean chord line. (I’m making a first order assumption here that the nose up trim incidence at the tail approximately matches the wing incidence and neglecting downwash and other airflow disturbances at the vertical stabilizer location)

22 hours ago, Blue on Top said:

In addition and with the rudder hinge line being forward swept, the air must travel down the surface … something it doesn't want to do (which is good in this case).  On an aft swept tail, the airflow goes up the vertical, losing effectiveness.

Not clear about this -- wouldn't a spanwise flow component on the control surface reduce effectiveness either way?

Skip

Edited December 5, 2019 by PT20J