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Flap hits trailing edge wing skin!

:mad: After a pleasant flight we started up to depart, raised the flaps, started to taxi, and our friend began waving us to a stop. We got out to see what the problem was and saw some ugly damage to the right flap and top wing skin.

The airplane has 150 hours with no problems. In this instance the leading edge of the right flap slightly overlapped the trailing edge of the upper wing skin. When the flap was driven up by the flap motor it severely pushed the top wing skin up and bent the flap leading edge down. The motor stopped when the fuse blew.

The only reason that I can think of for this to happen on this occasion is, my passenger may have stepped on the trailing edge of the wing skin and bent it down past the leading edge of the flap. Can't prove that.

At first I thought I would have to take the wings off and trailer it home. Fortunately a very good mechanic (Hood River Airport) took an interest and managed to manipulate the flap leading edge back under the wing skin. With the flap retracted he deemed it safe to fly home. I flew the RV-7 on the one hour flight home and the flight was perfectly normal, in spite of the wing skin that was still bent up at the trailing edge.

I would like to make recommendations so that no one else has this experience, but I really don't know what caused it.

Don Owens
[email protected]
 
You are not the first. A friend just bought a 7 with the same type of damage. Sorry I also don't have any bright ideas to avoid this. It sucks.
 
Don, I have finished three RV-7A's. One was at a local airport and had some guys looking inside and leaning against the right flap. There is enough slop in the flap drive system to allow the skin to pop up and lodge against the wing skin. Needless to say when the owner retracted the flaps the skins collided and bent things. For some reason there seems to be more slop/flex in the right side and more opportunity for this to occur on that side. I have modified four '7A's now by removing the flap drive torque tube assembly and having 1/2" removed from each arm that connects to the flap drive rods. That limits the flap travel by 5 degrees and will NOT allow the skin overlap damage to occur. The loss of 5 degrees of flap travel isn't even noticeable. I have leaned really hard on the flaps after this mod and have not been able to dislodge the flap skin. I'm sorry you have that damage to deal with. The little flap drive motor is really powerful and will not stop for anything that gets in it's way. "My bright idea"

Rex
 
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This is one of the main reasons that I have always adjusted my full flap travel to 37°-38° instead of 40°.

This gives enough overlap to prevent this happening.
 
check the wing walk doubler

Another way the flap can be jammed is if the leading edge (or even the anti-chaff tape) catches the doubler beneath the wing walk. It is a good idea to trim the doubler back flush with the spar so the flap can't snag it. This might happen if the trailing edge of the wing walk is distorted by someone stepping on it. The wing skin springs back into position but the doubler beneath remains bent and ready to snag the flap.
 
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This is one of the main reasons that I have always adjusted my full flap travel to 37?-38? instead of 40?.

This gives enough overlap to prevent this happening.

Yup... what Mel said... and geez, 20-30 is all you need. :)
 
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The airplane has 150 hours with no problems. In this instance the leading edge of the right flap slightly overlapped the trailing edge of the upper wing skin. When the flap was driven up by the flap motor it severely pushed the top wing skin up and bent the flap leading edge down. The motor stopped when the fuse blew.

Don Owens
[email protected]

This has been a recurring problem for many years. Quite a number of threads on this one. Many builders have been caught. And the damage that can occur can be severe requiring serious repairs including the replacement of the upper wing skin and a repaint. :eek:

The obvious cause of it is too much down flap angle thus reducing the overlap between the leading edge of the flap and the trailing edge of the upper wing skin.

Interestingly enough, I did a final TC inspection of an RV7 not long back and when I was checking on the control surface deflections I discovered that the builder had 45 degrees of down flap. I suggested that Vans specifications called for max 40 degrees but the builder showed me his construction manual and, sure enough, it called for maximum "40 to 45" degrees. So some time between the issue of my RV7A manual in 2004 (which called for max 40 degrees) and today Vans upped the max flap deflection on the RV7(A) from 40to 45 degrees.

For the life of me I cannot understand why Vans did this considering that so many builders had already mangled their electric flaps at 40 degrees.

Many builders have also had failure of the RV7(A) extruded aluminium flap pushrod and many (including me) have swapped over to the beefier RV9A pushrod. Once again you would have to ask yourself why Vans would increase the max flap deflection in light of this problem.

And finally, one might like to ponder whether flap deflection in excess of 40 degrees could possible be warranted. When I throw out 40 degrees of flap it's like a parachute. I honestly believe that anything beyond 40 degrees must entail a lot of strain for virtually no gain. ;)

The problem with Vans upping the deflection is that inevitably builders will always attempt to opt for the max deflection. That's what I've found on my TC inspections. Everyone wants to be at the upper limit of all deflections on all control surfaces. They're frightened that they might be missing out on something if they opt for less than max deflection. :D
 
A non slotted flap has almost certainly separated (aerodynamically speaking) at anything more than 35 deg. I suppose there might be a tiny bit more drag at 40 but hardly worth risking re-skinning a wing for.
 
Top skin replacement

I bought 7 with flap to skin damage and as I am not a builder would like to talk to some one about repair.
If some one who had this damage and replaced top skin could contact me by PM I would really appreciate it

Thanks
Julian
 
Yup... what Mel said... and geez, 20-30 is all you need
I would not 100% agree with this - for short strip work max drag is desired and every degree of flap helps. RV-4 drivers point out how much better the 3/4 is in this regard to the 7/8...

The key, IMO, to preventing this issue is not leaving the flaps fully down when parked. Raise them a small amount from full down is what I was told, and pass on / teach to others - for exactly this reason.

Clearly if you do not need the aerodynamic benefits of full flap, then set the limit higher - but this is not possible (?) if you just use the Vans system - the flap rods are adjusted so the internal motor "up limit" is with flaps up, and the down limit is just where it ends up :eek:
 
Down limit switch

Plenty of room in the housing where the flap motor & push rod are to put a simple limit switch & diode. Then you can adjust the down limit to exactly where you want it.

Almost saw my wing get bent but luckily it was in the hangar so I could hear the electric motor start to load up.

Andy
 
Has this ever happened on the 8?

I'm sure it has. The -3, -4, -6, -7, and -8 all have the same flap system.

The true solution......manual flaps! With manual flaps, you can set the stops wherever you want them. Mine are set at 0-13-26-38°.
 
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The key, IMO, to preventing this issue is not leaving the flaps fully down when parked. Raise them a small amount from full down is what I was told, and pass on / teach to others - for exactly this reason.
Someone beat me to it. This is the best solution, IMHO. You can have full deflection for flying, but when parked bring them up a bit. On my manual-flapped -6, I leave them one notch up from full travel when parked away from the hangar.
 
I have searched the threads and cannot find any case where the 8 did this. I found one article that said the 8 flap overhang was longer. Any inputs to this?
 
No real mechanical adjustments possible ...

I had the same, during installation I recognized, that I hat more than 40° down travel. I tryed to adjust this by screwing in here and out there ... but after a while I give up.

There is no possibility to correct the with the original Vans setup.

- The motor is moving from end to end.
- The lenght of the arm from the motor to the main tube is fix.
- The lenght of the two tubes from the main bearing tube is fix.

With any adjustment you make you affect both positions, and not only the fully extended one.

I have done this many 100 times, especially in the time when you had simple RC controlls without computers. You need to adjust the by the lenght of the arm. At the actuator if you where reducing the lenght, then the travel was less and the force was higher. At the driven part, closer to the pivot point made more travel with less force. If you played the game right, you got the correct travel.

Interestingly I contacted Vans and got the answer: Airfow will push it back enough, it does not matter :eek:

I limit my flaps by the use of a positioning system (VPX) and the use of a Ray Allen position-unit. But these can fail ... and I end up in the same thread ...

The only real adjustment is like Rex Daniels http://www.vansairforce.com/community/showpost.php?p=985186&postcount=3 has done it.

It would be interesting how Mel has adjustded his flaptravel?
 
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Mel's flaps are manual, and travel is controlled by the location cut into the flap position locator plate.
 
I have posed this before. I never have understood this.
I have slightly more than the full 40 deg. and my skins have at least 3/4 - 1" of overlap. There is no way they could ever be pushed or prodded to the point of catching.
I do not understand why some have this issue and others, like me, couldn't make them catch with 50 deg. down or more.
Weird.
 
Flap Actuator Mod

I modified the actuator as follows:

1. Remove motor (2 screws)
2. Clamp actuator "Block" in vise and unscrew outer tube with pipe wrench.
3. The roll pin in the jackscrew is what engages the clutch mechanism and
limits flap down travel. Drill hole further down jackscrew and relocate
the roll pin to this hole.
4. Reassemble.

NOTES: The actuator "Block" was lightly staked to the outer tube and one
could use Locktite on the threads as well.
In my case I moved the roll pin about .5" and decreased flap travel
from 44 deg to 40 deg
IMG_20150628_223238336_HDR_zpscfwrhvkm.jpg.html
 
My RV-8 has 40 deg of flaps with an electric actuator. It has 5/8" over lap along the entire span of the flaps. I did convert to the hex shaped flap rods from Avery (purpose built length for the 8) after finding my original rods had developed a slight bow in them after 50 hrs.
 
Have to agree with JohJay
I too have the same overlap and do not believe it would ever catch the trailing edge of my wing

I have 44 degrees of travel. I think we should install lift / dump flaps like our hawker has, could you imagine the descend if they could be used in the air....yeahaw.

Or how bout that Waco with the cj610. You know he is having too much fun.

Wonder what a couple sonex jet engines would be like under the wings
YEAHAW!!!!!!
oh Just dreaming..........
 
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