Mooney tail aerodynamics - not backwards

[Blue on Top]

PS2 Swept tails are heavier.

PS3 Remember I said everything in design is a tradeoff?  The aerodynamic center of Mooney surfaces are closer to the CG (shorter arm) than airplanes that have swept (aft) tail surfaces.

PS4 Yes, the straight leading edges were an ART Mooney input for easier manufacturing (and less wasted material). 

[Andy95W]

Considering Al Mooney’s lack of formal education, do you think he learned these concepts (such as the importance of the 25% chord line, etc.) over his decades of experience, or do you think he just had a natural and innate feel for efficiency and aerodynamic design?

[cliffy]

Why do high wing airplanes have a strut?

BECAUSE they have a weaker wing than we do  !!!!     :-) :-)

Now to another aerodynamic anomaly on Mooneys-

Why up to 68 did the short body have elevator deflection angles of UP 24 and DOWN 10 1/2 degrees BUT 

the next year and on they went to 22 degrees each way

With NO other changes to the airplane that I can see.

I have an old memory but I'll hold off until I see some postings

Check the TCDS

 

[ArtVandelay]

Why do high wing airplanes have a strut?
BECAUSE they have a weaker wing than we do  !!!!     :-) :-)
Now to another aerodynamic anomaly on Mooneys-
Why up to 68 did the short body have elevator deflection angles of UP 24 and DOWN 10 1/2 degrees BUT 
the next year and on they went to 22 degrees each way
With NO other changes to the airplane that I can see.
I have an old memory but I'll hold off until I see some postings
Check the TCDS
 

Didn’t they move the battery at that time? Less nose heavy, better balanced.

[Raymond J1]

On an airfield, one day, my wife says: The others do not have the same tail as you, I could recognize you... So for me, the explanation is that Al thought about pilot women.

[Will.iam]

5 hours ago, cliffy said:

Why do high wing airplanes have a strut?

BECAUSE they have a weaker wing than we do  !!!!     :-) :-)

Now to another aerodynamic anomaly on Mooneys-

Why up to 68 did the short body have elevator deflection angles of UP 24 and DOWN 10 1/2 degrees BUT 

the next year and on they went to 22 degrees each way

With NO other changes to the airplane that I can see.

I have an old memory but I'll hold off until I see some postings

Check the TCDS

 

Would it be that further aircraft flight testing revealed they needed more down trim travel and not as much up trim as was originally calculated? 

[Blue on Top]

6 hours ago, Andy95W said:

Considering Al Mooney’s lack of formal education, do you think he learned these concepts (such as the importance of the 25% chord line, etc.) over his decades of experience, or do you think he just had a natural and innate feel for efficiency and aerodynamic design?

@Andy95W  I would estimate both.  Al was an avid reader/learner and designed his first airplane professionally at the age of 19.  All of his work at Culver with elliptical wings and leading edge slots culminated in the M20 wing design.  Of course this is with his brother Art adding in the manufacturing portion.  The Al Mooney M20 wing (the wood wing) development is documented in a very interesting Mooney document.  The wing has a very close to perfect elliptical lift distribution.  Preliminary design of the M20 was actually completed in Wichita.  Al and Art knew their stuff  

[Cyril Gibb]

32 minutes ago, Blue on Top said:

The Al Mooney M20 wing (the wood wing) development is documented in a very interesting Mooney document. 

Sounds interesting.  Available somewhere?

[cliffy]

2 hours ago, Will.iam said:

Would it be that further aircraft flight testing revealed they needed more down trim travel and not as much up trim as was originally calculated? 

I want to invite "blueontop" but don't know how

The above is very close to what I remember-

IIRC Mooney was cited in some FAA investigation as not being in full compliance in stall/spin recovery at the very end of the envelope and the FAA did some testing on it and the change to these throws in 69 was the result. 

I can't find the reference to being "out of the box' BY THE FAA anywhere now and when I inquired about same back at Mooney headquarters (when Bill Wheat was still alive)  no one including him would comment. All I got was "we don't remember" ? 

My question remains that if this is all that was changed for "better response at the end of the box" why not make it retroactive to all S/Ns and/or what would the ramifications be to resetting the early short bodies to these parameters? 

I've cogitated over this conundrum for decades now.

Someone please throw some meat in the cage here, will you? 

BTW-  I haven't considered the battery relocation yet but IF so and it was the cause to change what about those who have relocated early models to the rear location? Do they have to change their elevator throws? Just thinking out loud right now.

But on second thought the total CG limits didn't change that I know of so the ends of the box remained the same BUT maybe  the total force available to recover from high angles was weak even though it recovered? Just guessing right now pending further investigation.

Edited April 3, 2021 by cliffy
add

[Andy95W]

Cliffy- you use the “@“ and then start typing their name, then select the individual.  Example:

@Blue on Top

Cliffy has a question about elevator deflections, above.

[A64Pilot]

If elevator deflections changed, I’d expect to see an allowable CG range change.

‘If they were changed to correct some kind of lack of control response, I’d expect to see an AD requiring the change on other similar models.

‘In  practice increasing negative elevator throw isn’t going to change anything, when was the last time you hit the down elevator stops in flight?

The breaking a stall / spin is logical as of course to break a spin down elevator is used as is opposite rudder.

‘My guess why it’s not required of other models is that it was only found in this one model, you would expect the FAA to test every model if they find a discrepancy in one, but that often doesn’t happen.

‘What does drive the FAA is complaints and or accidents, and that actually makes some sense, if on a mature design, there are no complaints and no accidents, maybe there isn’t a problem?

Edited April 3, 2021 by A64Pilot

[PT20J]

8 hours ago, cliffy said:

Why do high wing airplanes have a strut?

BECAUSE they have a weaker wing than we do  !!!!     :-) :-)

Now to another aerodynamic anomaly on Mooneys-

Why up to 68 did the short body have elevator deflection angles of UP 24 and DOWN 10 1/2 degrees BUT 

the next year and on they went to 22 degrees each way

With NO other changes to the airplane that I can see.

I have an old memory but I'll hold off until I see some postings

Check the TCDS

 

When was the rudder extended? Was it at the same time?

[PT20J]

@Blue on Top here’s a puzzle about tail airfoils:

First it seems obvious that the fin would have a symmetrical airfoil since it must produce “lift” in either direction.

But, the stabilizer generates a tail down force, yet many airplanes (including Mooney) use a symmetrical airfoil for the stabilizer also. Perhaps, the choice is for structural considerations for the same reason that many helicopter rotor blades utilize symmetrical airfoils, but that’s only a guess.

And, the Stearman has a positively cambered airfoil which seems upside down. I don’t understand that at all. Do biplanes need a tail up force?

Skip

[cliffy]

1 hour ago, A64Pilot said:

In  practice increasing negative elevator throw isn’t going to change anything, when was the last time you hit the down elevator stops in flight?

The breaking a stall / spin is logical as of course to break a spin down elevator is used as is opposite rudder.

There had to be a reason to DOUBLE the down elevator throw

My foggy memory of it was an FAA investigation as to recovery from the back corner of the envelope was weak.

Are these kinds of things investigable in FAA records in some way?

AND why not make it applicable to the earlier same models?

[A64Pilot]

1 hour ago, PT20J said:

@Blue on Top here’s a puzzle about tail airfoils:

First it seems obvious that the fin would have a symmetrical airfoil since it must produce “lift” in either direction.

But, the stabilizer generates a tail down force, yet many airplanes (including Mooney) use a symmetrical airfoil for the stabilizer also. Perhaps, the choice is for structural considerations for the same reason that many helicopter rotor blades utilize symmetrical airfoils, but that’s only a guess.

And, the Stearman has a positively cambered airfoil which seems upside down. I don’t understand that at all. Do biplanes need a tail up force?

Skip

Fully symmetrical airfoils are often chosen because their center of pressure doesn’t change much with increasing angles of attack, where on asymmetrical airfoils it does.

‘Only older helicopter designs use fully symmetrical designs, newer ones use asymmetrical airfoils as they provide more lift for the same power

In search of more (free) carrying capacity the Army in its infinite wisdom put asymmetrical blades on the AH-1, (Kaman 747 blades) the center of pressure moved with angle of attack and it fed forces back into the swash plate that it wasn’t designed to handle and some failed of course killing the occupants.

As I didn’t fly Cobra’s, I don’t know what other than increased swash plate inspections was done.

‘There have been aircraft designed with flying tails as they would be more efficient, but almost always they end up with the name widomaker, if a tail is providing lift, what’s the corrective action if it stalls?

Canards are more efficient largely because both wings provide lift, and of course a normal aircraft is faster and more efficient with aft CG, but more unstable, I believe modern airliners fly with so far an aft CG that they are very unstable, but the flight control computer provides artificial stability.

[bfreelove]

2 hours ago, PT20J said:

And, the Stearman has a positively cambered airfoil which seems upside down. I don’t understand that at all. Do biplanes need a tail up force?

 

Contrary to common belief, a conventional tailed aircraft can be stable in pitch with either an upload or a download on the tail.  To find out you must calculate all the pitching moments on the aircraft for a given condition.  Aerobatic airplanes with symmetrical airfoils would almost always require a lifting force on the tail (I've done a stability analysis on most of the current unlimited level monoplanes, and some aerobatic biplanes).  I don't know about the Stearman specifically, but it could require a lifting force on the tail due to low wing loading and long fuselage (fuselage is destabilizing in pitch) depending on how much pitching moment the airfoil has.  

[A64Pilot]

An aircraft with a “flying tail” can be stable, instability usually comes when the tail is at or near zero lift as it can easily go either way at that point, this usually corresponds to the stick force neutral point which is what it sounds like, no or very low forces are required to move the stick or yoke and no or little increasing effort with amplitude so not only is a aircraft unstable, its very easy to overstress one with little stick force.

‘Usually the prohibition of a flying or lifting tail is how does one recover from a tail stall? In a normal aircraft its self correcting, the nose drops, speed increases and the stall breaks, same for a canard.

I don’t play with aerobatic airplanes but would be very surprised if any had tails that in normal level flight produced lift, I wouldn't be surprised if they fly close to the stick force neutral point, I’d expect them to, I’d be surprised if they didn’t.

 

Maybe aerobatic airplanes have so much elevator authority that they can break a tail stall that way, the elevator simply overpowers the stall?

Edited April 3, 2021 by A64Pilot

[Blue on Top]

6 hours ago, Cyril Gibb said:

Sounds interesting.  Available somewhere?

@Cyril Gibb Probably not publicly, but you can ask Mooney.  I wish I could tell you more.

[Blue on Top]

6 hours ago, cliffy said:

IIRC Mooney was cited in some FAA investigation as not being in full compliance in stall/spin recovery at the very end of the envelope and the FAA did some testing on it and the change to these throws in 69 was the result. 

My question remains that if this is all that was changed for "better response at the end of the box" why not make it retroactive to all S/Ns and/or what would the ramifications be to resetting the early short bodies to these parameters? 

I've cogitated over this conundrum for decades now.  Oh my!  Stop that!  It hurts after a while.

But on second thought the total CG limits didn't change ...

I'll do my best, but this might take further explanations.  

So increasing down elevator travel very much supports stall/spin recovery.  And @cliffywas going down the right path ... until he cogitated a little too much.  Here's an aspect of CG where many people falter.  After several unrecoverable spins (and fatalities) aerobatic pilots are beginning to understand this, too.  CG is not just CG when discussing spin recovery.  I'll try to put this into a good example (which I am not good at).

The M20C and M20E have the same CG envelope, so what could be different?  Mass (or weight) distribution is different.  I'll go further with the example than the real airplanes.  In other words, I'm making up numbers here.  Say an owner installed a new engine that was 100 lbs. heavier than the old one, and it was 4' in front of the CG.  To keep the CG in the same position, he adds a 25 lbs. lead weight in the tail, 16' aft of the CG.  Both CG moments are 400 ft.*lbs., and they offset each other.  CG is in the same location.  BUT ...

Izz (the moment of inertia about the vertical axis) has gone up dramatically.  In other words, in a spin, the airplane will want to spin faster AND flatter, but the aerodynamic recovery forces have not changed.  Spin dynamics and aerodynamics are very, very, very complicated.

Hope this helps ... as a beginning. 

[carusoam]

There is a certain time order to various changes...

... and some marketing assumptions that fall to the wayside over time...

 

1) Some companies like to make improvements to their plane over time to compete better against the competition...

2) Some companies like to make those changes not apply to the older model...  to induce people into moving up to the newer version...

3) There is always going to be a backlash and hard feelings that come with buying the latest and greatest... and have a newer latest and greatest model get announced a few months later....

4) Over the decades...   we have seen very few people or companies swapping to newer planes, unless there is a significant improvement to the newer one... or the older one is very worn out...  infant mortality still has a strong driving force...

5) Bill Wheat was the king of knowing all the facts... and having a way of saying... you are right with your assumption... if I told you more, I would need a new job... 

6) Once every decade...  all the stars align... and we can’t get enough Mooneys... new or used...

7) Somedays jobs are more plentiful, interest rates are low, fuel costs are contained... and money is flowing more freely...

8) Updating tail feathers doesn’t occur very often...  But, there are Many M20Bs that have updated their rudder throw to match the later M20Cs...

9) There was one company that recognized these opportunities very well... and turned M20Fs into something similar to an M20J...  and 231s into 262s... find the Mod Squad...

10) What got lost in translation... how expensive it is to make these changes... using new machinery prices...

11) If you make enough changes at new machinery prices... you have essentially paid the full price of buying a new machine...

12) What could possibly change...  is the method updates for some models can be technically discussed, mass produced, and pre-sold, at realistic prices for existing owners... find the discussion on user produced down lock blocks...

13) Some updates are simple bolt ons...  others require what is being bolted onto to be updated first...

14) A cool business model would be reviving The Mod Squad type of updates... with a focus on lower cost, ‘mass’ production, automated machining...

15) How much can you update an older M20C over the years to become Bob’s M20E if you wanted it too?

16) John’s M20F looks very similar to a brand new M20J...

17) I can only think of one mod people would have liked undone... the twisted wing...

18) this covers staying within the envelope of existing designs... with known performance envelopes...

Having a basic Mooney forever-plane is a great way to start... 

Best regards,

-a-

[Blue on Top]

4 hours ago, PT20J said:

@Blue on Top here’s a puzzle about tail airfoils:

1) First it seems obvious that the fin would have a symmetrical airfoil since it must produce “lift” in either direction.

2) But, the stabilizer generates a tail down force, yet many airplanes (including Mooney) use a symmetrical airfoil for the stabilizer also. Perhaps, the choice is for structural considerations for the same reason that many helicopter rotor blades utilize symmetrical airfoils, but that’s only a guess.

3) And, the Stearman has a positively cambered airfoil which seems upside down. I don’t understand that at all. Do biplanes need a tail up force?

Skip

1) Not all airplanes have a symmetrical vertical fin airfoil.  Some even have the fin offset to counter torque.

2) Symmetric horizontal stabilizers are to lower part count; they can be left or right (same with elevators).  Even if the stabilizers have camber, the elevators may not (again to save part count/tooling).

3) The Stearman tail is VERY heavy (probably in the range of 400 lbs. on the tail wheel (it needs lift to offset its weight).

Ron

[Blue on Top]

3 hours ago, A64Pilot said:

Canards are more efficient largely because both wings provide lift, and of course a normal aircraft is faster and more efficient with aft CG, but more unstable, I believe modern airliners fly with so far an aft CG that they are very unstable, but the flight control computer provides artificial stability.

Canards are much LESS efficient than conventional tails.  The Beech Starship/King Air is a great example.  Why?  Downwash off the canard changes the wing local angle of attack ... and is different for every flight condition.  The main wing angle of incidence would need to be variable ... but that would mess up the outboard wing outside of the canard downwash.  With a conventional airplane the whole tail is the the downwash of the wing and can be changed accordingly.

In addition, a canard maximizes efficiency of a small surface (the canard) at the expense of the efficiency of the much, larger main wing.  In cruise of the Starship, the inboard main wing is pushing DOWN with a force of ~1000 lbs.  In addition, the pusher propellers of the Starship need 5 sectors of different blade pitch to be more efficient ... hence the weed wacker sound when they fly over ... with exhaust going through them.

[Blue on Top]

17 minutes ago, carusoam said:

17) I can only think of one mod people would have liked undone... the twisted wing...

Best regards,

-a-

@carusoam  Please tell me more.  I thought the wing was twisted through the M20G and the M20J wing was "untwisted" to gain speed.

Warning!  WARNING!!  Selfless plug coming ... I, "Blue on Top LLC", is here to be your mod/STC/improvement shop  

[carusoam]

As I understand it...

The mid bodies got the twisted wing for a couple of years...

The intent was to have the wing begin stalling by section of the wing more...  

Leaving the section of the wing with the ailerons still flying deeper into the stall situation...

The trained/experienced pilots didn’t notice the value as much as they noticed the slower cruise speed...

Some people have good rudder skills...   they eventually become Mooney owners... 

The twisted wing is probably a precursor to cuffed wing designs...

They give Giant signs that a full stall is coming, with more controllability, available to keep things from turning disastrous in an instant...

Lots of focus on stall awareness works pretty well... until it doesn’t.

 

Best regards,

-a-

[cliffy]

1 hour ago, Blue on Top said:

The M20C and M20E have the same CG envelope, so what could be different?  Mass (or weight) distribution is different.  I'll go further with the example than the real airplanes.  In other words, I'm making up numbers here.  Say an owner installed a new engine that was 100 lbs. heavier than the old one, and it was 4' in front of the CG.  To keep the CG in the same position, he adds a 25 lbs. lead weight in the tail, 16' aft of the CG.  Both CG moments are 400 ft.*lbs., and they offset each other.  CG is in the same location.  BUT ...

@Blue on Top

Polar Moments in airplanes are understood and I can go along with that theory for spin recovery BUT in this instance my thoughts are not on spin recovery per se 

Both the E model and the C model show the change in elevator down deflection (at the same production point)  AND both show that the elevator bungee deflection changes with the down angle change.

I'm only looking for a definitive answer as to why Mooney found it necessary to change the angles from 69 on and not make them retro active to the other short bodied that came before.  

All are virtually identical.

There had to be a reason

Also I wonder what the affect in handling was when the change occurred or was it not felt at all? Could it have had some affect on cruise speed with the lower bungee force with its lower angle set (trim drag?)?

What would happen if we reset an older Mooney to the new settings? How would it fly? No different than the more recent models? 

There has to be a reason why it was done. AND its somewhere in the in flight handling!         I'll bet $50 bucks. :-)