Wing spar failure?

[A64Pilot]

23 minutes ago, PT20J said:

Some sources say that the Stearman has a lifting tail. I don’t know if that is true or not, and my aerodynamics guru friend Dave Lednicer didn’t know either. But we both observed that the horizontal stabilizer is positively cambered, and there wouldn’t seem to be another good explanation for that. Maybe @Blue on Top knows.

Skip

I have heard that the fleet biplane also did, but can’t confirm that.

A bunch of older guys usually meet every Fri morning for coffee, a few have Stearman’s I’ll try to remember to ask.
From memory as long as CG is forward of neutral point an aircraft will be positively stable, whether it  has a lifting tail or not, but I still think if they exist, they are as rare as Unicorns.

Edited August 17, 2021 by A64Pilot

[PT20J]

The important thing for stability is a negative slope for the curve of airplane pitching moment as a function of C_L. There are various ways to achieve that for different configurations as in canards and flying wings. 

[Raymond J1]

On 8/11/2021 at 5:30 PM, PT20J said:

The procedures for balancing control surfaces on a M20J are in section 27-93 of the Service and Maintenance Manual. Note that all Mooney control surfaces are underbalanced — that is they are trailing edge heavy.

Skip

Even older models are that way and I've observed that a few have had the addition of static depertitors that increase the underbalance. Have some of you taken this balancing from the factory until you get the perfect ballast?

[A64Pilot]

17 hours ago, Raymond J said:

Even older models are that way and I've observed that a few have had the addition of static depertitors that increase the underbalance. Have some of you taken this balancing from the factory until you get the perfect ballast?

The further nose heavy a flight control is, the more resistant it will be from flutter, I believe that there is an upper weight limit that you can install that’s a function of structure.

Add to that, their is nothing I can think of that you can do to a flight control while in service  that will make it more nose heavy, I’d recommend if your rebalancing to balance towards being nose heavy. 

Any painting or repair or static dissipaters or an ADSB beacon etc will move a controls balance point rearward most likely

Place I worked at we built two types if your will of aircraft, they were (HG) or high gross versions and standard, the HG aircraft had significantly higher VNE, the primary difference in the two was the flight controls balance.

‘It’s unlikely but possible that rebalancing flight controls could cause a CG shift of the entire aircraft, so it’s worth doing the math to make sure.

[PT20J]

Since the wing was metalized, the gross weight has been increased several times. Except for fuel, that weight is on the fuselage which increases the wing bending moment at the spar splice. This is not to say that the wing on later models is weak, but it’s not as strong as the original design.

Skip

[DCarlton]

On 8/10/2021 at 6:50 PM, carusoam said:

If I read that correctly…

All of the parts of the M20J were found at the accident site…. Except the counterbalances for the elevator…

A subtle sign of control flutter prior to arriving at the final resting site…. Where the lead weights don’t want to move as fast as the associated control surface wants to move…

 

PP thoughts only, not an accident investigator…

Best regards,

-a-

I haven't looked at the drawings.  Any idea what holds those weights on?  They look like big rivets of some sort.  I'm seeing a little corrosion on the heads of the fasteners. 

[Blue on Top]

On 8/17/2021 at 10:19 AM, PT20J said:

Some sources say that the Stearman has a lifting tail. I don’t know if that is true or not, and my aerodynamics guru friend Dave Lednicer didn’t know either. But we both observed that the horizontal stabilizer is positively cambered, and there wouldn’t seem to be another good explanation for that. Maybe @Blue on Top knows.

Skip

Yes, the Stearman does have positive camber (similar to the wings and opposite to most other aircraft).  The reason is that the tail is VERY statically heavy.  I have heard one owner state that the tail weighs 600 lbs. on the ground.  The Wright 1911 glider was that way (pictured below) for the same reason ... and many model airplanes, too.

[Will.iam]

if a canard design is inefficient because of the smaller wing in front disrupting the airflow over the back and the conventional design is inefficient because of the down force of horizontal stab/elevator.  Why not make 2 big wings same size for one in the front and one in the back. i.e. take the picture above and just remove the top bi-wing and stick it on the back where the horizontal stab was maybe put it as a T tail so the forward wing would not affect the airflow over the back wing.  wouldn't the wing loading on the one closer to CG be greater thus making that wing stall first which would supply the stability needed due to an upset?  I'm sure if there was viability someone would have already designed one.  I'm just wondering what I'm overlooking that keeps it from being efficient.  

[carusoam]

3 hours ago, DCarlton said:

I haven't looked at the drawings.  Any idea what holds those weights on?  They look like big rivets of some sort.  I'm seeing a little corrosion on the heads of the fasteners. 

On the elevator, I believe the fasteners are visible as the lead weights are visible…

I have the Long Body, so my memory of other Mooneys is pretty limited at that level of detail…

Fuzzy old PP memories only…

Best regards,

-a-

[Nippernaper]

1 hour ago, Will.iam said:

if a canard design is inefficient because of the smaller wing in front disrupting the airflow over the back and the conventional design is inefficient because of the down force of horizontal stab/elevator.  Why not make 2 big wings same size for one in the front and one in the back. i.e. take the picture above and just remove the top bi-wing and stick it on the back where the horizontal stab was maybe put it as a T tail so the forward wing would not affect the airflow over the back wing.  wouldn't the wing loading on the one closer to CG be greater thus making that wing stall first which would supply the stability needed due to an upset?  I'm sure if there was viability someone would have already designed one.  I'm just wondering what I'm overlooking that keeps it from being efficient.  

 As you say, if you keep the wings the same size, one will be more lightly loaded, which means it's not being used efficiently, and all the advantages go away.  If you reduce the lighter loaded one so that the lift/area are the same, you have the problem of a potential stall of the back wing, which would likely be unrecoverable.  Further, I think you would have an unstable arrangement when it comes to dynamic effects.  When the plane encounters a gust, it should pitch up.  Similarly, if a sudden drop in headwind, it should pitch down.  Odd ball planforms can behave in the opposite manner.  There seems to be good discussion here:

What Are Canards, And Why Don't More Aircraft Have Them? | Boldmethod

[Blue on Top]

2 hours ago, Will.iam said:

if a canard design is inefficient because of the smaller wing in front disrupting the airflow over the back and the conventional design is inefficient because of the down force of horizontal stab/elevator.  Why not make 2 big wings same size for one in the front and one in the back. i.e. take the picture above and just remove the top bi-wing and stick it on the back where the horizontal stab was maybe put it as a T tail so the forward wing would not affect the airflow over the back wing.  wouldn't the wing loading on the one closer to CG be greater thus making that wing stall first which would supply the stability needed due to an upset?  I'm sure if there was viability someone would have already designed one.  I'm just wondering what I'm overlooking that keeps it from being efficient.  

These configuration iterations have been done many, many times before ... especially now with CFD being able to run multiple configurations in minutes.  There is a good reason why airplanes are configured "conventionally" - big wing up front and small stabilizer in back.  It's the most efficient configuration.

IF a surface stalls (it needs to be the forward one to make the recovery stable - the most forward wing of a biplane (normally the upper ... except in the case of the Beech "Staggerwing"), a canard, or the main wing of a conventional configuration.  I say "IF a surface stalls" because most conventional configured airplanes don't aerodynamically stall at forward CGs.  In a Mooney, it may be possible to run the trim nose UP far enough, but a C180/182 will not aerodynamically stall at forward CG.

The tail (horizontal stabilizer) should never stall.  The results will be a violent nose down pitching moment.  These cases are typically only in Flight Test (and very, very rare) and often end with fatal results (and often the aircraft coming apart structurally).  This is why tailplane icing is such a huge issue/problem if it happens.  The tailplane also accrues ice significantly faster than the wing (smaller leading edge diameters collect ice quickly).  In other words, if you see a little ice on your winds, there is more on your tail.   

PS. Although Boldmethod has pretty pictures and cool, moving, graphics, ...  

[Blue on Top]

All:  Please remember that the Mooney wing is structurally different than almost all other small, GA, wings ... until one gets into more modern, small, business jets.  The Mooney wing does not transmit wing bending loads into the fuselage.  The attach bolts take only (double) shear loads of pure lift loading.  They are not like a Beech, Piper, etc. that attach at side of body.

[Mooney in Oz]

1 hour ago, Blue on Top said:

The tailplane also accrues ice significantly faster than the wing (smaller leading edge diameters collect ice quickly).

Stall recovery from ice on the tail is opposite to a wing stall recovery. Recognition of a pending stall is sloppy elevator controls.

I hope no one ever gets themselves into this situation.

[Raymond J1]

6 hours ago, Will.iam said:

if a canard design is inefficient because of the smaller wing in front disrupting the airflow over the back and the conventional design is inefficient because of the down force of horizontal stab/elevator.  Why not make 2 big wings same size for one in the front and one in the back. i.e. take the picture above and just remove the top bi-wing and stick it on the back where the horizontal stab was maybe put it as a T tail so the forward wing would not affect the airflow over the back wing.  wouldn't the wing loading on the one closer to CG be greater thus making that wing stall first which would supply the stability needed due to an upset?  I'm sure if there was viability someone would have already designed one.  I'm just wondering what I'm overlooking that keeps it from being efficient.  

Idea of Monsieur Mignet in the 30's : 2 wings in tandem, the first forward and up ensures deep steering. The second at the back is smaller, but that's only because it takes advantage of the split effect. The plane does not stall, it evolves in parachutal descent. Mignets have no Vne... But a limited centering range.

 https://fr.wikipedia.org/wiki/Henri_Mig net

Edited August 19, 2021 by Raymond J

[A64Pilot]

Several aircraft won’t stall in a level flight slowly decreasing speed type of approach stall. The S2R-H80 doesn’t stall even at max aft CG, it simply runs out of elevator authority and just “mushes” at a pretty high descent rate, but you still have full aileron control etc. From memory a Piper 140 is the same way, they just mush, the wing never fully stalls.

But it and I’d bet all aircraft can be made to stall if the entry is aggressive enough.

Not that I have stalled all that many aircraft, but the most violent stall I’ve had was a Cessna 210 at a low cruise power. You knew the stall was going to be ugly because prior to the stall you had run completely out of rudder and the ball was slipping further out as speed decreased, and sure enough when she stalled it went completely over on its back and would have developed a spin I’m sure if allowed.

Cessna’s have as a general rule a reputation of very benign stalls, but a 210 under even low power will get ugly fast, it’s not hard all to see that a real departure stall would be unsurvivable no matter how good you are.

I’ve never stalled a Mooney under power and don’t intend to, ever.

From my limited experience, the more modern the design, often the more difficult the stall / spin recovery, largely due to smaller less effective rudders. All the old aircraft, especially the ones with the little wheel in the back had large. powerful rudders.

There is an old saying, “easy in, easy out” meaning be darn careful spinning an aircraft that's spin resistant, they have a tendency to very difficult to recover.

Edited August 19, 2021 by A64Pilot

[Blue on Top]

4 hours ago, A64Pilot said:

1. Several aircraft won’t stall in a level flight slowly decreasing speed type of approach stall. The S2R-H80 doesn’t stall even at max aft CG, it simply runs out of elevator authority and just “mushes” at a pretty high descent rate, but you still have full aileron control etc. From memory a Piper 140 is the same way, they just mush, the wing never fully stalls.

2. the most violent stall I’ve had was a Cessna 210 at a low cruise power. You knew the stall was going to be ugly because prior to the stall you had run completely out of rudder and the ball was slipping further out as speed decreased, and sure enough when she stalled it went completely over on its back and would have developed a spin I’m sure if allowed.

1. The worst stall characteristics (conventional configuration) are at aft CG and LIGHT weight.  This is the configuration/condition where the tail power is the greatest ... and the tail power required is the least.  Flaps have a tendency to make the stall characteristics better, too, as the flaps drive the separation inboard (where the flaps are located).

2. The C210 was bent (or wing(s) was(were) not installed/adjusted properly).  All certificated airplanes must be stalled from level flight and roll must be kept within 15 degrees.  This is true power ON (75%, test pilots aren't high-risk takers) and power at IDLE (highest stalling speed).  Yes, the margins widen a little for accelerated and turning/accelerated stalls.  None are allowed to be violent.  The newest of those airplanes left the factory 36 years ago, though.

As an add on to "2" above, this is an aha moment to those doing "full power" stalls.  Certification for power ON stalls requires only 75% power.  Flight Test is not going to stall an airplane at sea level altitude (only place where full power exists) as there is not enough room to recover if something goes bad.  Those stalls are typically flown at 5,000' where there is room to recover ... most of the time.  We lose test pilots from stalls and spins ... even with an upset recovery parachute installed on the tail.

Fly safe.

[jaylw314]

On 8/18/2021 at 11:56 AM, Will.iam said:

if a canard design is inefficient because of the smaller wing in front disrupting the airflow over the back and the conventional design is inefficient because of the down force of horizontal stab/elevator.  Why not make 2 big wings same size for one in the front and one in the back. i.e. take the picture above and just remove the top bi-wing and stick it on the back where the horizontal stab was maybe put it as a T tail so the forward wing would not affect the airflow over the back wing.  wouldn't the wing loading on the one closer to CG be greater thus making that wing stall first which would supply the stability needed due to an upset?  I'm sure if there was viability someone would have already designed one.  I'm just wondering what I'm overlooking that keeps it from being efficient.  

Isn't that the Quickie?

[A64Pilot]

The 210 wasn't bent, a friend who is a flight test DER,flight analysis etc was doug the flight testing for an STC for a belly camera mount on a different 210 and ran into the same thing.

‘I’ve done quite a bit of Certification flight testing myself and you don’t have to fully stall at 75%, you stop at first break, fully stalled and or accelerated stalls are a whole different animal, the 210 dropping a wing and trying to get over other back was directly related to insufficient rudder to cancel out P factor.

In short, those stall that we all train for when we get our license, and an accelerated stall and or stalls at high power are a completely different animal.

I’ve also had to take an aircraft at minimum weight and 100% power to a stall. in order to determine max possible deck angle so that we could prove we had enough fuel flow

[Will.iam]

My neighbor has 2 of these strange ducks. They are eagle 150 and come to find out he used to be a saleman for the company. Has more time in them than anybody else. Looks neat but a little to slow for my taste.  

[jlunseth]

6 hours ago, A64Pilot said:

‘I’ve done quite a bit of Certification flight testing myself and you don’t have to fully stall at 75%, you stop at first break, fully stalled and or accelerated stalls are a whole different animal, the 210 dropping a wing and trying to get over other back was directly related to insufficient rudder to cancel out P factor.

In short, those stall that we all train for when we get our license, and an accelerated stall and or stalls at high power are a completely different animal.

Totally true. Straight ahead stalls are benign and take some time to develop. Cross controlled and accelerated stalls are immediate, violent and you are upside down in the first turn of a spin faster than I can write that. 

[A64Pilot]

On 8/18/2021 at 5:58 PM, Blue on Top said:

All:  Please remember that the Mooney wing is structurally different than almost all other small, GA, wings ... until one gets into more modern, small, business jets.  The Mooney wing does not transmit wing bending loads into the fuselage.  The attach bolts take only (double) shear loads of pure lift loading.  They are not like a Beech, Piper, etc. that attach at side of body.

Quite a few small aircraft don’t dump wing loads onto the fuselage. It took forever but I found a picture of a Thrush wing splice joint, This was a decade or more ago, to give an idea how massive this thing is, the largest bolts are 3/4” and all bolts are NAS. The spar caps are not aluminum, but 4340 steel.

‘The wing attaches to the fuselage with two 1/4” aluminum angles per side so obviously those little aluminum angles aren’t carrying much load.

‘I’ve been told but don’t know but Van’s RV’s are very similar to the Thrush design and that pretty much all the loads are carried at the slice joint.

Assuming a Mooney is the same, then a Mooney’s wing if it breaks, ought to break at the center and not outboard by the fuselage?

Edited August 20, 2021 by A64Pilot

[Bartman]

Correct me if I am wrong, but the Mooney spar is continuous from end to end. 

[A64Pilot]

2 hours ago, Bartman said:

Correct me if I am wrong, but the Mooney spar is continuous from end to end. 

I’ve never take one apart or even seen one really, but it woud be tough to get the dihedral with one continuous piece.

Spars that I’m familiar with are sort of I beam construction.

 So I assume the wings are spliced , but the work to separate them is excessive.

 

On edit, whether they are spiced or not isn’t the point, I believe the point being made was that the center of the Spar is where most of the forces are concentrated, not out at the fuselage attach point.

‘But I’d still be surprised if it were all one piece.

Edited August 21, 2021 by A64Pilot

[toto]

We had a longish discussion about the Mooney spar here a while back..

 

[Yetti]

6 hours ago, Bartman said:

Correct me if I am wrong, but the Mooney spar is continuous from end to end. 

It's kind of 3 pieces continuous.  Think big I beam.  They have a big ole press to get the proper shape.  

 

 

Edited August 21, 2021 by Yetti