Aileron Heim bearings

[0TreeLemur]

4 minutes ago, EricJ said:

I tend to agree.   The center of pressure and center of lift are well forward of the ailerons.    Deflecting a surface into an airstream creates a pretty big delta-P by changing the pressure on both sides of the surface, which is usually the desired outcome of deflecting the surface.   The zero-force-applied position would be expected to be in trail where the pressure on both sides is equalized.   I wouldn't expect that to be at the up stop in level flight, especially with any significant airspeed. 

I was thinking it'd be great if Blue On Top were around to comment, but it turns out he did:
 

 

Good find!

[Ragsf15e]

20 minutes ago, EricJ said:

I tend to agree.   The center of pressure and center of lift are well forward of the ailerons.    Deflecting a surface into an airstream creates a pretty big delta-P by changing the pressure on both sides of the surface, which is usually the desired outcome of deflecting the surface.   The zero-force-applied position would be expected to be in trail where the pressure on both sides is equalized.   I wouldn't expect that to be at the up stop in level flight, especially with any significant airspeed. 

I was thinking it'd be great if Blue On Top were around to comment, but it turns out he did:
 

 

My dad’s got a whole bunch of rc airplanes of questionable design and maintenance.  He likes to put cameras all over them to make pretty videos and help with the crash investigations.  If he doesn’t already have video of an aileron disconnected in flight, I bet i could persuade him to try it…

[PT20J]

6 hours ago, N201MKTurbo said:

Doesn’t happen. There is about 120 Lbs of force between the two ailerons. It varies a bit as you move the controls through the range of motion, but it never goes to zero.

As others have noted, the lift is not evenly distributed over the wing surface area. Most of the lift is generated near the leading edge. It is common to assume that it is concentrated at the quarter chord line as predicted by thin airfoil theory. The pressure differential between the top and bottom surface of the aileron is relatively small.

5 hours ago, N201MKTurbo said:

These charts are assuming zero angle of attack. Our wings have a positive angle of attack. The text says the hinge moment is highly influenced by angle of attack. In all cases the wing has a positive angle of attack and the tail has a negative angle of attack.

True, but AOA has a small effect for small angles. I’ve Included the following two pages from the text previously cited. I’ll leave it as an exercise for someone to compute the angle of attack at cruise in a Mooney 

[MikeOH]

42 minutes ago, EricJ said:

I tend to agree.   The center of pressure and center of lift are well forward of the ailerons.    Deflecting a surface into an airstream creates a pretty big delta-P by changing the pressure on both sides of the surface, which is usually the desired outcome of deflecting the surface.   The zero-force-applied position would be expected to be in trail where the pressure on both sides is equalized.   I wouldn't expect that to be at the up stop in level flight, especially with any significant airspeed. 

I was thinking it'd be great if Blue On Top were around to comment, but it turns out he did:
 

 

Nice pull!

Salient/pertinent quote, "BUT, in reality, there is a pressure distribution on the wing (the highest pressure differential is ~30% chord and very low at the trailing edge.  So, long story short, if the aileron pushrod were disconnected in flight, the aileron would float up some but not up vertically.  It will float up a little from "trail".  Bonus note: your airplane will fly fine with only one aileron … don't try this at home … or the airport."

 

[0TreeLemur]

23 minutes ago, PT20J said:

I’ll leave it as an exercise for someone to compute the angle if attack at cruise in a Mooney

I did that once using the drag polars that you posted a while back.   Here are the calcs.   For the assumed conditions (low altitude, 165 mph), the angle of attack is less than 1 degree up to gross weight.

 

Edited February 8 by 0TreeLemur
de

[Pinecone]

My gut call is that if disconnected, it will trail up, but nowhere near the stop.

Just like the elevator trails to the trimmed position.

[N201MKTurbo]

Ok, ok, my theory has been debunked. I will change my thinking. 

[1980Mooney]

3 hours ago, Pinecone said:

My gut call is that if disconnected, it will trail up, but nowhere near the stop.

Just like the elevator trails to the trimmed position.

 

2 hours ago, N201MKTurbo said:

Ok, ok, my theory has been debunked. I will change my thinking. 

This discussion went off the rails with @N201MKTurbo's comment about a disconnected aileron rising to "the stop".  OK that was too extreme, but his theory is otherwise basically correct.  (BTW - per the Service Manual - Down stop limit is 8 degrees and Up stop limit is 12.5-17 degrees for Serial No. 0001 through 1037 and 12.5-14.5 degrees after.)

Back to the OP's @0TreeLemur's question about slop and dead spots.

As @N201MKTurbo pointed out there are 2 separate sources of bearing slop/ excess clearance which affect the feel/handling differently.

• If there is slop/looseness in the hinge on the yoke or the heim linkages attached to the yoke under the panel (4, 10, 8, 12,14) anywhere up to where the L&R aileron control rods (15) are connected together at (16), then you will get slop/looseness in the yoke (dead spots) while the ailerons are completely stable and not moving.
• If there is slop/looseness in the bellcrank joint/hinge and heim lingages (push/pull tubes and bellcranks) outboard on the wings connected to the ailerons (17, 19, 28, 30), then the slop will be taken up due to the lift on the ailerons in stable flight
  • As pointed out in the post on the prior page "Ailerons high in trail" from 2018, several Mooney owners (presumably with a lot of slop in the outboard heim linkages) report seeing the ailerons rise as much as 1 inch above the flap in flight.  Assuming the chord on the aileron is about 12 inches that is about 5 degree upward deflection.  Obviously they are still attached and they still have upward lift holding them up so it remains to be seen what the maximum deflection would be. 
    • Also none of the posters with "high trailing ailerons" said that they experienced any "dead zones"
      • I think this is because even when with an 1 inch (5 degree) upward deflection due to "slop" there was still lift (we can review all the theory and analysis but the real world "acid test" is that there is still material lift on the ailerons.)
      • As a result one aileron will always have the slop pulled out tight as you deflect the ailerons in opposite directions (one aileron control tube is pushing while the other is pulling.
      • I think this covers up any feeling of a dead zone in the opposite aileron as the push-pull tube reverses direction
        • All the heim and other bearings remain pulled tight in one wing while the bearings in the other wing are momentarily not touching either side of the bearing.  Once the "momentarily loose" push/pull tube moves so that the linkages touch the other side of the bearing, then the slack has been taken up in that direction.
      • I think that this is also a matter of degree - minor slop in the outboard heims will never be felt.  Major looseness at some point might be noticeable.
• About 10 years ago I replaced one of the linkages (29) to the aileron hinge due to looseness.  The heim bearings were welded on so I had to get it from a Mooney MSC.  I can't remember the price I recall that I thought it outrageous back then.  I bet it is more so now.

This diagram is typical of most Mooney's but not exactly the same as your J:

 

 

Edited February 8 by 1980Mooney

[1980Mooney]

On 2/7/2024 at 10:01 AM, 0TreeLemur said:

For estimation purposes, if they need replacement, how many hours would it take an A&P to remove, replace the bearings, and reinstall one side?  Looks like a pretty tough job.

 

[0TreeLemur]

6 minutes ago, 1980Mooney said:

 

Thanks.   A couple of hours.  

Anyone else miss Clarence?  I sure do.

[Fly Boomer]

16 hours ago, 0TreeLemur said:

Lift is predominantly a by-product of streamline curvature.  That's why lift generation mostly happens near the leading edge where the airfoil is most curved.   At a cruising angle of attack with the ailerons in trail the streamlines in their vicinity are pretty much straight.  They will therefore produce no lift for that reason. 

I agree with @MikeOH that at the trailing edge of the wing or aileron the pressure is single-valued but there is a little pressure difference on average between the top and bottom, which will push the aileron up a little until its deflection creates and equal but opposite downward force.  If appropriately balanced it shouldn't oscillate.

I just convinced myself that if a Heim bearing on one aileron failed, there would likely not be dire consequences.  Provided that the linkage to the other aileron remained intact a pilot would still have about 1/2 the normal roll authority. 

Thanks for the entertaining discussion!

 

 

 

[PT20J]

It is true, that control surfaces tend to float up. But the float is not unbounded until the control reaches the stop. As soon as the surface floats up, the pressure distribution changes creating a counteracting moment and there will be an equilibrium point where the two moments cancel and the surface will stabilize at some angle. Usually designers try to minimize this tendency. It appears that Mooney didn't do a great job at this. The hinge line for the ailerons is not set back far enough to provide good aerodynamic balance to counteract this tendency. Also the hinge moment is a function of the distance from the center of pressure on the surface to the hinge line and the Mooney ailerons, being of relatively short span and thus necessarily greater chord to get the necessary area, will have a greater hinge moment compared to say a Bonanza. Both these factors contribute to the "heaviness" of the Mooney ailerons.

So, with zero aileron control deflection, I believe that the float would take most of the "slop" out of the control system. However, as soon as we deflect the ailerons, the forces change. And it is only when maneuvering (and thus deflecting ailerons) that we care about any dead zone. The change in moments with deflection arises because the down aileron has increased upward pressure and the up aileron has increased downward pressure. In fact, one of the reasons for having an aileron deflect up on one wing is to reduce the control force because of the reversal of moment direction. We are not talking about a lot of dead zone (unless the rod ends are dangerously loose) and a pilot might not even notice it because we quickly adapt to minor control system deficiencies.

Anyway, an interesting experiment would be to block both ailerons in trail so that they cannot move and measure the amount of rotation of the control wheel permitted by any lost motion in the linkages on the ground. Then this could be repeated in the air in level flight and also during left and right rolls.

 

 

[0TreeLemur]

I like this set of figures that show the effect of airfoil curvature, which is a proxy for streamline curvature near the wing surface, on the distribution of pressure for  0, 5, and 10- degree angle of attack.   The arrows show the deviation of the pressure from static.  Arrows pointing away from the surface denote pressure less than static, while arrows pointing towards the surface denote pressure greater than static.   The length of the arrow denotes the magnitude of the deviation from static.   Pressure always acts normal (perpendicular) to the surface.

Notice that minimal pressure deviation is produced where the streamlines are straight.  The curvature of the streamlines creates a pressure gradient by Newton's 2nd law written normal to the streamlines.

At the highest angle of attack (10-degrees) where the stagnation streamline terminates well below the leading edge, there is radical streamline curvature and a lot of pressure deviation where that happens.  It looks like this creates a lot of forward thrust.  In reality it doesn't because the area that this large negative pressure deviation acts on is small.  Incidentally, it does provide a tiny bit of thrust that is offset by the increased drag due to separation further down the airfoil. This simulation does not show that separation realistically for high angle of attack.

At the trailing edge, there is a net upward force on an aileron if present, but as previously mentioned a small upward deflection would balance that force.  The lift is the integrated effect around the airfoil.

 

Edited February 9 by 0TreeLemur
make it better

[PT20J]

I've been rethinking this. @N201MKTurbo and @1980Mooney made good arguments about the effect of suction on the upper aileron surfaces.

So, I enlisted Ed Kolano (aeronautical engineer and test pilot). He hadn't really thought about it before, so we went back and forth and here is what we concluded:

In cruise, with the control wheel neutral, both ailerons tend to drift up and take out the control slack on both sides by putting the push pull tubes in compression. Now suppose we begin to deflect the control wheel to the left. The left aileron will begin to move up immediately because it has no slack. However, the right aileron will not move down until the control wheel moves far enough to take up the slack. So what does the pilot feel? There would be an immediate force on the wheel when the left aileron moves and the force would increase when the right aileron begins to move. This might be noticeable if there was a LOT of slop or if you rapidly reverse the roll direction. But, because the roll will begin immediately with control wheel movement it will not cause a dead zone. Any apparent dead zone would have to be due to looseness in the part of the control system that is common to both ailerons as @N201MKTurbo pointed out. While it is true that the hinge moments are in opposite directions, I neglected the fact that one side will always be in compression and thus one aileron will have no slack and will move immediately when the control wheel is moved.

To @0TreeLemur's original concern: The rod ends are captive between the U-shaped ends of their attach points, so they are pretty fail safe. The only way I can see that they could fail and cause a serious control issue is if the bolt came out or the ball froze solid. By the way, I had some slop in one of mine that turned out to be that the bolt through the rod end that attached to the aileron was under torqued and allowed the ball to move on the bolt. I replaced the bolt and torqued it properly and it is much improved.

[Ragsf15e]

7 hours ago, PT20J said:

I've been rethinking this. @N201MKTurbo and @1980Mooney made good arguments about the effect of suction on the upper aileron surfaces.

So, I enlisted Ed Kolano (aeronautical engineer and test pilot). He hadn't really thought about it before, so we went back and forth and here is what we concluded:

In cruise, with the control wheel neutral, both ailerons tend to drift up and take out the control slack on both sides by putting the push pull tubes in compression. Now suppose we begin to deflect the control wheel to the left. The left aileron will begin to move up immediately because it has no slack. However, the right aileron will not move down until the control wheel moves far enough to take up the slack. So what does the pilot feel? There would be an immediate force on the wheel when the left aileron moves and the force would increase when the right aileron begins to move. This might be noticeable if there was a LOT of slop or if you rapidly reverse the roll direction. But, because the roll will begin immediately with control wheel movement it will not cause a dead zone. Any apparent dead zone would have to be due to looseness in the part of the control system that is common to both ailerons as @N201MKTurbo pointed out. While it is true that the hinge moments are in opposite directions, I neglected the fact that one side will always be in compression and thus one aileron will have no slack and will move immediately when the control wheel is moved.

To @0TreeLemur's original concern: The rod ends are captive between the U-shaped ends of their attach points, so they are pretty fail safe. The only way I can see that they could fail and cause a serious control issue is if the bolt came out or the ball froze solid. By the way, I had some slop in one of mine that turned out to be that the bolt through the rod end that attached to the aileron was under torqued and allowed the ball to move on the bolt. I replaced the bolt and torqued it properly and it is much improved.

Ha! So part of @N201MKTurbo ‘s theory lives on!

[EricJ]

On 2/7/2024 at 9:01 AM, 0TreeLemur said:

For estimation purposes, if they need replacement, how many hours would it take an A&P to remove, replace the bearings, and reinstall one side?  Looks like a pretty tough job.

I had the same issue in that the rod end that attached to the aileron had a fair amount of slop and it was slowly getting worse.    Since that rod end was the unthreaded roll-pin type, I bought a couple used pushrod assemblies from BAS, and one of them was in great shape and had threaded rod ends on each end, so no unthreaded ends.   Yesterday I removed the old one and replaced it with the new one, and today I replaced the tail-most rod end on the rudder and then rerigged everything.

You're right, replacing that rod is not trivial.   All told it probably took me three hours, but I'm slow and wasn't in a hurry and had never done it before.   If I was doing it again on the clock it'd probably be half that or so.   Because it is all part of the control system, all of the fasteners have interference with something for removal.   The bolt for the rod end at the aileron requires removing the flap hinge cover to get it out.   There isn't enough space to remove the bolt on the other end at the belcrank because the bracket interferes.   I could only get that bolt out by removing the bolt for the belcrank hinge (which is normally captive by the inspection plate), and then wiggling everything around until I could get the pushrod bolt out of the belcrank.   Getting it all back together was even trickier.   It might be easier to remove the bolt from the long, actuating pushrod and take the whole assembly out, but that fastener is also pretty difficult to get to and is mostly blind, so I didn't want to have to deal with that, too.

But now the slop is pretty much gone in the aileron and mostly so in the rudder, so that's nice.

And look!   When you disconnect the aileron it does go up!   (I stuck a screwdriver in there to keep it out of the way, but couldn't resist the pic.  ) 

[0TreeLemur]

2 hours ago, EricJ said:

I had the same issue in that the rod end that attached to the aileron had a fair amount of slop and it was slowly getting worse.    Since that rod end was the unthreaded roll-pin type, I bought a couple used pushrod assemblies from BAS, and one of them was in great shape and had threaded rod ends on each end, so no unthreaded ends.   Yesterday I removed the old one and replaced it with the new one, and today I replaced the tail-most rod end on the rudder and then rerigged everything.

You're right, replacing that rod is not trivial.   All told it probably took me three hours, but I'm slow and wasn't in a hurry and had never done it before.   If I was doing it again on the clock it'd probably be half that or so.   Because it is all part of the control system, all of the fasteners have interference with something for removal.   The bolt for the rod end at the aileron requires removing the flap hinge cover to get it out.   There isn't enough space to remove the bolt on the other end at the belcrank because the bracket interferes.   I could only get that bolt out by removing the bolt for the belcrank hinge (which is normally captive by the inspection plate), and then wiggling everything around until I could get the pushrod bolt out of the belcrank.   Getting it all back together was even trickier.   It might be easier to remove the bolt from the long, actuating pushrod and take the whole assembly out, but that fastener is also pretty difficult to get to and is mostly blind, so I didn't want to have to deal with that, too.

But now the slop is pretty much gone in the aileron and mostly so in the rudder, so that's nice.

 

Wow. Thanks for the description.  I'm kind of surprised it only took you three hours. 

The flap hinge cover on our J is pop riveted on.  Removing that sounds like it would be tricky to not damage that plastic cover?

[Hector]

I had the same issue in that the rod end that attached to the aileron had a fair amount of slop and it was slowly getting worse.    Since that rod end was the unthreaded roll-pin type, I bought a couple used pushrod assemblies from BAS, and one of them was in great shape and had threaded rod ends on each end, so no unthreaded ends.   Yesterday I removed the old one and replaced it with the new one, and today I replaced the tail-most rod end on the rudder and then rerigged everything.

You're right, replacing that rod is not trivial.   All told it probably took me three hours, but I'm slow and wasn't in a hurry and had never done it before.   If I was doing it again on the clock it'd probably be half that or so.   Because it is all part of the control system, all of the fasteners have interference with something for removal.   The bolt for the rod end at the aileron requires removing the flap hinge cover to get it out.   There isn't enough space to remove the bolt on the other end at the belcrank because the bracket interferes.   I could only get that bolt out by removing the bolt for the belcrank hinge (which is normally captive by the inspection plate), and then wiggling everything around until I could get the pushrod bolt out of the belcrank.   Getting it all back together was even trickier.   It might be easier to remove the bolt from the long, actuating pushrod and take the whole assembly out, but that fastener is also pretty difficult to get to and is mostly blind, so I didn't want to have to deal with that, too.

But now the slop is pretty much gone in the aileron and mostly so in the rudder, so that's nice.

And look!   When you disconnect the aileron it does go up!   (I stuck a screwdriver in there to keep it out of the way, but couldn't resist the pic.  ) 

Nice job. I tried to do this myself and after one hour and bloodied knuckles I decided I would let the pros handle it. I had Maxwell replace the control rods on both sides this past December. My old C was showing quite a bit of slop. I had the roll-pin rod ends so I ordered the complete threaded rods from he factory a couple of years ago. Access to disconnect the rod end inside the wing is a challenge and I didn’t have the patience. Sold my C shortly thereafter and purchased an F of the same age (and flight time) but no wear in the aileron rod ends. Have not looked through the logbooks yet to see if they were replaced at some point


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[skykrawler]

Good motivation to keep those spherical bearings regularly lubed.

[N201MKTurbo]

2 hours ago, skykrawler said:

Good motivation to keep those spherical bearings regularly lubed.

Couldn’t agree more. If lubed according to the maintenance manual, they should last forever. Even if you don’t use the proper lube, any lube is better than no lube. It still amazes me when I work on a Mooney I’ve never seen before and how many dry rusty rod ends I can find.

Of course it isn’t just a Mooney thing. I have worked on brand C, B and P with cable pulleys that haven’t seen a drop of oil in decades.

[EricJ]

9 hours ago, 0TreeLemur said:

Wow. Thanks for the description.  I'm kind of surprised it only took you three hours. 

The flap hinge cover on our J is pop riveted on.  Removing that sounds like it would be tricky to not damage that plastic cover?

Removing the cover is not a big deal.   The pop rivets drill out easily.

[N201MKTurbo]

1 hour ago, EricJ said:

Removing the cover is not a big deal.   The pop rivets drill out easily.

Just don’t replace them with CherryMax rivets, they are a royal pain to drill out.