Mooney tail aerodynamics - not backwards

[PT20J]

22 minutes ago, Aerodon said:

My 2c.    I don't think it has much to do with aerodynamics, but all to do with structure and weight.  It starts with the decision to have an all moving vertical and horizontal stabilizer.  Then to keep the loads on the hinge as low as possible, one needs to have the horizontal and vertical aerodynamic forces as close to the hinge as possible.  Best way to do this is keep most of the structural weight and aerodynamic forces as far forward as possible = straight leading edge.

Aerodon

Well, let's think that through. The horizontal stabilizer has a spar located at it's approximate aerodynamic center. The hinge is attached to this spar and thus the aerodynamic force of the tail acts at or very near the hinge line. From a structural perspective, the shape of the horizontal stabilizer doesn't matter much since it is the spar that carries the load to the structure. The vertical stabilizer is a little more complicated because it has to have a low aspect ratio (it needs greater chord at the bottom than the top) in order to prevent it from stalling at high yaw angles. The 25 degree forward slant of the trailing edge provides most of the necessary aspect ratio with the dorsal fin providing the rest.

In all likelihood, the vertical stabilizer was designed to meet stability and control requirements at the low speed range and the horizontal stabilizer, which has fewer constraints, was designed to match the shape for aesthetics.

Skip

[1964-M20E]

Sounds lie we need to convince some aerodynamic engineer working on his doctorate degree to take this on as his thesis and once and for all using computer simulations, wind tunnels and math to prove which is more efficient.  However, we all know the real answer already and that is the Mooney design is more efficient and better.

 

 

[Shadrach]

On 4/28/2019 at 7:57 AM, Alan Fox said:

Too add insult to injury.....https://en.wikipedia.org/wiki/Category:V-tail_aircraft

Insult? Have you been drinking?  The discussion centers around straight vs swept vertical airfoil.  If you take a look at most low speed V-tail designs (most V-tail piston recips) they tend towards the vertical, not the swept.  I can surmise that the added efficiency of the straight configuration is desirable with one less control surface to work with.  There are many...many...many modern "straight" slightly forward swept rudder designs.

 

With regard to the Bonanza's design (not so modern), the leading edge sweeps back slightly but it appears the trailing edge sweeps forward slightly.   I think the biggest reason not to make an airplane with a tail like a Mooney is because it is very much recognizable from a branding stand point.   Carry on with your sad attempt to be contentious! I expect more from you...

 

 

On 4/28/2019 at 7:54 AM, Alan Fox said:

Funny , I see LOTS of modern Vee Tail designs flying , but not a single modern design with a straight vertical tail..... Wonder why....

 

See above, you don't seem to understand whats being discussed.  Many V-tails are indeed straight tails...

Edited April 30, 2019 by Shadrach

[EricJ]

6 hours ago, Aerodon said:

My 2c.    I don't think it has much to do with aerodynamics, but all to do with structure and weight.  It starts with the decision to have an all moving vertical and horizontal stabilizer.  Then to keep the loads on the hinge as low as possible, one needs to have the horizontal and vertical aerodynamic forces as close to the hinge as possible.  Best way to do this is keep most of the structural weight and aerodynamic forces as far forward as possible = straight leading edge.

Aerodon

Usually a big, sometimes driving, factor in control surface design is flutter mitigation.   I don't know how much that drove the Mooney tail engineering (other than both the rudder and elevator have pretty substantial balance weights), but Al Mooney had a few decades to think about tail design before they made the M18.   My recollection of his biography was that he indicated that style was a significant consideration.   So it was a neat way to combine a bit of function and some style.   Clearly there are other effective ways to do it, because nearly everybody does another way, but I think he hit it out of the park on combining style with some pragmatic functionality.

He wasn't doing any aerodynamic FEA simulations, I'm pretty sure. 

[0TreeLemur]

On 8/24/2013 at 8:07 PM, Robert C. said:

"Everybody knows that aircraft handling tends to go critical at a high angle of attack. So I gave the vertical fin the straight up-and-down lines it still has today. Few people realize this was not a style gimmick."
-- Al Mooney, quoted by Gordon Baxter in the MAPA Log, March 1997

 

I knew I had read that somewhere and finally found it

 

Source: http://www.mooneyevents.com/quotes.htm

 

Robert

Does anyone have a copy of this article that they can scan and send me?   I'm having a raging battle with a self-appointed editorial troll on the M20 Wikipedia page about this issue.   Really pissing me off.   I'd love to have a scanned copy of this article so I can cite it.  Thanks.

[Robert C.]

I don't, but you could email or call the MAPA Office. I imagine that they have files of the old issues.

Robert

http://mooneypilots.com

[phik]

The Internet Archive gets to be the hero once again:

http://web.archive.org/web/20120321094130/https://www.mooney.org.au/files/Up_to_Speed_Mooney.pdf

[A64Pilot]

On 8/19/2013 at 11:16 PM, yvesg said:

My guess is that it was easier to build it this way....

 

Yves

People are interesting, they try to find the mystery in anything they don’t understand. For instance if you look at the tail rotor of an AH-64, it’s not an X, the blades are not 90 apart, this has led to all kinds of theories by smart people about noise and vortice propogation and all kinds of scientific theories.

What it really is that the tail rotor is simply a scaled up Hughes 500 rotor and to have four blades they had to be offset so you could simply stack another one on top and be able to connect the PC links. Simply stacking a second pair on top meant no redesign.

‘My personal belief is that the Mooney tail has straight leading edges because back in the day they were plywood skinned, and it’s a whole lot easier to wrap plywood over a straight edge, so back to what Yves said, it’s easier to build.

it’s really that simple, but I can’t prove it of course, but as has been said over and over, and they are correct, if it was in fact “better” there would be many copies, but it’s not, so there isn’t.

‘On edit, now a swept back tail at the airspeeds we fly at is simply a styling gimmick. the original straight tail Cessna’s were more efficient as in less weight and stronger etc, but styling won out of course.

The wing tips on later model Mooney’s are more styling gimmick than anything, I’m surprised that they were added, because they do increase wing length, and if you do that, it’s real common for the FAA to make you re pull the wing, so I assume it wasn’t hard through analysis to show that the Mooney wing was plenty strong. Point being is that marketing and styling often win out 

Edited March 30, 2021 by A64Pilot

[spistora]

1 hour ago, A64Pilot said:

‘My personal belief is that the Mooney tail has straight leading edges because back in the day they were plywood skinned, and it’s a whole lot easier to wrap plywood over a straight edge, so back to what Yves said, it’s easier to build.

My guess was the three tail stabilizers were essentially the same design, two horizontal and one vertical. Simplifying the manufacturing process. I'm only speculating though.

[A64Pilot]

5 minutes ago, spistora said:

My guess was the three tail stabilizers were essentially the same design, two horizontal and one vertical. Simplifying the manufacturing process. I'm only speculating though.

The original Cheetah or whatever it was called had one fight control, flaps, ailerons, elevator and rudder were the same, it was a home built and that simplified things. I think there was also one wing no left and right

Just looked it up, it was the BD-1 and later became the AA-1 Yankee

[201Steve]

Paging @Blue on Top for his missing contribution here. 

[0TreeLemur]

9 hours ago, phik said:

The Internet Archive gets to be the hero once again:

http://web.archive.org/web/20120321094130/https://www.mooney.org.au/files/Up_to_Speed_Mooney.pdf

Thanks.  I appreciated the read.   Sadly "the theory is" regarding straight tails is just that.  I was hoping for some definitive statement.

While a forward leaning rudder is going to present a larger windward projection at high angle of attack (e.g. landing), it is just as likely that this is an unintended consequence of the ease of manufacture that the orthogonal leading edge of the vertical stab provides...

[Blue on Top]

On 3/30/2021 at 10:13 PM, 201Steve said:

Paging @Blue on Top for his missing contribution here. 

I'll get back to all y'all this weekend.  I had to post something to be able to follow the topic   This is soooooo exciting!

Sun-N-Fun is just around the corner, too! 

[steingar]

On 8/20/2013 at 1:04 PM, David Mazer said:

Noone seems to be answering the obvious remaining question.  In this high cost fuel environment, if the Mooney tail is more efficient, why haven't other manufacturers copied it.  If it is a safety benefit (better rudder control at high AOA), why haven't others copied it?

Why do Cessnas still have struts?

 

[PT20J]

2 minutes ago, steingar said:

Why do Cessnas still have struts?

 

Weight. A strut-braced structure is lighter than a cantilever structure for equal strength. The high wing has aerodynamic advantages (less interference drag and less geometric dihedral required) and shelters you from the rain 

Why low wing airplanes were generally designed with only one door (until recently) is a mystery to me.

Skip

[Hank]

17 minutes ago, PT20J said:

Weight. A strut-braced structure is lighter than a cantilever structure for equal strength. The high wing has aerodynamic advantages (less interference drag and less geometric dihedral required) and shelters you from the rain 

Don't forget the propensity to dimple pilot's foreheads!

[PT20J]

15 minutes ago, Hank said:

Don't forget the propensity to dimple pilot's foreheads!

A line of forehead diamonds is the mark of an experienced Cessna driver.

[A64Pilot]

46 minutes ago, PT20J said:

 

Why low wing airplanes were generally designed with only one door (until recently) is a mystery to me.

Skip

Again weight, cut a hole in the cabin and you have to reinforce it, also the door of course weighs more just skin, maybe a better question why do high wings have two or more doors? My Maule had four, one baggage but it was as big as a regular door.

Edited April 2, 2021 by A64Pilot

[A64Pilot]

I had forgotten I had this picture, notice the tail on one of them, anyone know it’s name?

[MikeOH]

On a lark, I'd say Aero Commander Lark

[MikeOH]

24 minutes ago, PT20J said:

A line of forehead diamonds is the mark of an experienced Cessna driver.

Or, a slow learner

[amillet]

Lark

[PT20J]

4 hours ago, A64Pilot said:

Again weight, cut a hole in the cabin and you have to reinforce it, also the door of course weighs more just skin, maybe a better question why do high wings have two or more doors? My Maule had four, one baggage but it was as big as a regular door.

Maybe, but a DHC-2 will carry a ton and has FOUR doors.

[carusoam]

Jimmy Peace recently posted a pic on a lark....

 

[Blue on Top]

Wow!  It's the only word I can say after reading this whole thread.  Everyone is close, but ... that only works for horseshoes and hand grenades (like we used to say in grade school).  All y'all nailed the strutted, high wing Cessnas and the Lark, so let's get to the Mooney tail.  Note: The Mooney tail aerodynamics visualized my be my last "The Mooney Flyer" article for a while ... hopefully in the May issue.  Let's go ...

Rule #1 - EVERYTHING in design is a tradeoff.

Forget the leading and trailing edge sweep angles as they really don't matter.  What really matters (aerodynamically) is the 25% chord line.  Since Mooney surfaces are all straight tapered, measure 25% aft from the leading edge at the root and at the tip and connect those points.  This is the sweep that the airflow cares about.  ALL 3 Mooney surfaces (wing, horizontal and vertical) are forward swept.

Now we'll look at the stabilizing surfaces.  The horizontal doesn't change sweep with a change in aircraft AOA, but it does change local AOA.  As the wing (aircraft) AOA increases, so does the local horizontal AOA due to an increase in the wing downwash.  This AOA on the tail is further increased with flaps.  A couple notes here: 1) downwash increases as wing lift increases and 2) remember that the horizontal is an upside down airfoil that creates a down force.  Now to the main topic.

The Mooney vertical surface is more effective as aircraft AOA increases because the 25% chord line is getting closer to perpendicular to the airflow (noting that downwash lessens this effect).  This allows the tail to be relatively smaller.  Tails are designed for the low airspeed conditions ... there's lots of yawing moment available at higher speeds.  And now the kicker ...

The rudder hinge line is actually more forward swept than the 25% chord line.  Why does this matter?  Mother Nature (airflow) wants to take the easiest path possible.  If the vertical surface is aft swept (most modern airplanes), when the rudder is deflected, the air has a tendency to travel up the hinge line (easier) than going around the deflected surface (harder).  With a Mooney, the air can't do this as easily.  In other words (let's look at the left side of the vertical surface with a left rudder deflection - aero people call this the pressure side).  Air doesn't want to go up the hinge line because it also has to go forward at the same time.  Nor does it want to go down the hinge line as this is INTO a higher pressure area.  As a result, it has a tendency to travel straight backwards around the deflected rudder.  This is also why gap seals are more important in Mooney aircraft.

,,, and now you know the rest of the story.

Blue on Top, Ron

PS.  Questions are welcome ... I'll learn, too.