Flap damage repair

[Frank Smidler]

Well it finally happened. The flap top skin popped out and caused damage to the wing walk doubler under the top wing skin.

First some background. I always park with my flaps down to prevent stepping on them and causing a lot of damage. As part of my preflight I always look at the flap top skin to make sure it is under the rear edge of the wing top skin, knowing that there has been occasions that others have reported persons leaning on them and having it pop out. If not caught, when you raise the flaps it can cause damage to the flap or the wing top skin. After reading some accounts on VAF after the fact, I now know I should retract the flaps up 5 or 10 degrees to keep this from happening (slow learner).

Up until last weekend, I always unbuckled and helped my passenger get in, giving instructions on how to climb in. With several family members going for short rides I decided to stay buckled in (I did of course shut down) and let my dad help my passengers get up on the wing. My second passenger was my niece and my dad must have inadvertently leaned on the flap when he reached into the back to get the step stool my wife uses to step up onto the wing. Before I started up, per my checklist, I raised the flaps and heard a crunching sound....OH NO... I immediately knew what had happened, lowered the flaps and got out to inspect.

I guess I can count myself as lucky, the only damage was to the wing walk doubler sheet that extends behind the rear spar. I think the flap skin and wing skin must have been just barely caught, tee-peed up and then popped out and caught on the inner doubler. I was able to continue with rides by only using 10 degrees of flaps or less. Well today I fixed the problem and thought I would share what I did.

I could not straighten out the doubler skin without bending the top wing skin so I decided to cut it off. I used a thing strip of steel between the top skin and doubler and used a dremel cutoff wheel to cut off the skin.

As you can see the to skin is just barely deformed on the inboard end.


Only scrapped a little paint on the flap which is not normally visible.


This shows how the doubler skin extends behind the rear spar and has been bent down. The wing skin is only slightly bowed up and can easily be bent back down a small amount after the doubler is cut off.


Here is the steel sheet in place and masking tape marking were to cut. Notice the plate-nut inboard for the wing root fairing, even though it sticks down, it never interferes with the flap.


Here is the piece cut off.


...and the wing were it was cut from.


I hope you do not have to go through this.

[Mel]

To prevent this, I always adjust flaps so that they are at 37-38 degrees when full down (Not 40). This give a little extra safety margin.

[L.Adamson]

Originally Posted by Frank Smidler

I could not straighten out the doubler skin without bending the top wing skin so I decided to cut it off. I used a thing strip of steel between the top skin and doubler and used a dremel cutoff wheel to cut off the skin.

Exactly what I did! And for the same reason..

L.Adamson --- RV6A

[Geico266]

Sorry Frank. I feel you pain. Looks like your fix will be a simple one as damage was minimal. Thanks for posting your misfortune so others may learn and prevent it like Mel suggests.

[L.Adamson]

Originally Posted by Mel

To prevent this, I always adjust flaps so that they are at 37-38 degrees when full down (Not 40). This give a little extra safety margin.

Excellent advice. I'll start doing that as of tomorrow, as I keep the flaps full down while parked. And I stuck an additional "no step" decal on that section too.

L.Adamson --- RV6A

[WingsOnWheels]

Since I am at that point of my build right now; I wonder if it would be a good idea to cut the doubler down to a little bit shorter and give the lower surface a taper...any thoughts?

[Rick6a]

Originally Posted by WingsOnWheels

Since I am at that point of my build right now; I wonder if it would be a good idea to cut the doubler down to a little bit shorter and give the lower surface a taper...any thoughts?

I do seem to vaguely recall a wing drawing showing the wing walk doubler as long as yours. Yet seeing no mechanical advantage having all that excess and unsupported wingwalk doubler length extend well beyond the rear spar, during early construction I went ahead and trimmed it to about 1/8" or so beyond the aft edge of the rear spar flange as you eventually did:

In addition, located near the inboard leading edge of my (2000 kit) flap skins there is a factory cut notch. When the flaps are in the full down position, you should NOT see that notch as it will be hidden underneath the upper wing skin. If you do see that notch, the flaps are almost certainly exceeding the maximum 40° of deflection. As long as that notch is not visible, there is next to no chance the flap skin can pop out.

[Pmerems]

I am building an RV-7A. The flap actuator travel is more then the required travel for 0-40 degrees. At the end of the actuator travel there is a built in bypass that allows the motor to spin but the ram doesn't move. This prevents the actuator from binding up (hard stop) at then of the travel.

If you set the the flap to the retracted position (0 position) such that the actuator is in it's full down travel when fully retracted the actuator will hit it's down limit and go into "bypass mode", motor will spin but flap won't move. However this now means that the flap will travel more then 40 degrees when extended due to the extra actuator travel. This puts the flap skin forward edge very close to the wing skin aft edge and creating this potential issue.

The flap controller available isn't what I want and it is rather expensive.

I am looking into designing a add on flap limiter that will work with the two power wires (no additional wire required) most use to control the flaps. Are there RV'ers out there who would be interested?
This would be something that could be installed easily on existing RV-7/RV-7A/RV-9/RV-9A and possibly RV-6's.

[IowaRV9Dreamer]

The leading edge of the -9 flap is a single piece - it does not have a seam at the leading edge. Does this mean that there is nothing to "catch" the wing skins with?

I've been working on my flap controls a bit and was planning an "up" limit switch to keep the motor from running (as suggested by other posters). If I have a good/working up limit switch, it was my assumption that I could set up the system such that the "down" limit was set by when the jackscrew stops moving down and the motor just goes into free spin mode.

My thought was that since the lower position will be controlled by a momentary switch, the motor won't ever run on very much.

Am I right about how the jackscrew works?

[Mel]

Originally Posted by IowaRV9Dreamer

The leading edge of the -9 flap is a single piece - it does not have a seam at the leading edge. Does this mean that there is nothing to "catch" the wing skins with?

The flaps on the -9 are totally different. No gap seal.
RV9 does not have the problem.