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]

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]

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]

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]

Flap travel and actuator travel

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]

Do the -9s have this problem?

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]

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.

 

[Danny7]

I am building an RV-7A. ......
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.

I'd be interested.

note - looks like Mel says this isn't a problem for the 9s

 

[Kevin Horton]

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.

I must be extra thick today, because this statement has me very puzzled.

I thought the flap actuator had a fixed amount of travel. If you drill everything so that the flaps are lined up with the airfoil when the actuator is fully retracted, then the full flap angle is whatever it will be when the actuator is fully extended. If you set things up so that full flap is at a lessor angle, then the fully retracted position would have the flap trailing edge too high.

I think the only way to reduce the full flap angle without changing the flap retracted angle is to move the flap rod hole further from the flap hinge line. Is that what you do Mel?

 

[L.Adamson]

I must be extra thick today, because this statement has me very puzzled.

I thought the flap actuator had a fixed amount of travel. If you drill everything so that the flaps are lined up with the airfoil when the actuator is fully retracted, then the full flap angle is whatever it will be when the actuator is fully extended. If you set things up so that full flap is at a lessor angle, then the fully retracted position would have the flap trailing edge too high.

I think the only way to reduce the full flap angle without changing the flap retracted angle is to move the flap rod hole further from the flap hinge line. Is that what you do Mel?

I just figured that Mel raised the flaps with the switch a bit, when the plane is not in motion. ----- edit ---- nevermind

edit: but re-reading his post, I see what you mean. On my flaps, they'd have to be pushed rather hard to release from under the wing. I don't really know how my doubler was bent for sure.


L.Adamson --- RV6A

 

[Mel]

Sorry for the misunderstanding. My flap switch is 66 years old and doesn't require an electrical system. To reduce the max flap extension I just cut the last notch slightly lower on the ratchet arm.
As far as the doubler goes, I cut that even with the rear spar while building back in the very early '90s.

 

[Dave Cole]

Adjust for 40 degrees at the extended travel limit

I thought the flap actuator had a fixed amount of travel. If you drill everything so that the flaps are lined up with the airfoil when the actuator is fully retracted, then the full flap angle is whatever it will be when the actuator is fully extended. If you set things up so that full flap is at a lessor angle, then the fully retracted position would have the flap trailing edge too high.

On my RV-7, I found that the flap actuator provided more travel than required for 40 degrees of flap extension. One solution is to adjust the linkage so that the flaps are at 0 degrees with the actuator at the flap retracted travel stop, and then deal with the flap extended overtravel with an electrical control, like a limit switch.

Alternately, you can adjust the linkage so that the flaps are at 40 degrees with the actuator at the flap extended travel stop, and then deal with the flap retracted overtravel. I chose this route, and installed a flap retracted limit switch to set the flap retracted position. This arrangement has the advantage of eliminating the flap over travel problem.

There are a variety of schemes that could be used for wiring the limit switch, but I chose the one suggested by Vern Little in this post.

http://www.vansairforce.com/community/showpost.php?p=77444&postcount=7

 

[Kevin Horton]

On my RV-7, I found that the flap actuator provided more travel than required for 40 degrees of flap extension. One solution is to adjust the linkage so that the flaps are at 0 degrees with the actuator at the flap retracted travel stop, and then deal with the flap extended overtravel with an electrical control, like a limit switch.

Alternately, you can adjust the linkage so that the flaps are at 40 degrees with the actuator at the flap extended travel stop, and then deal with the flap retracted overtravel. I chose this route, and installed a flap retracted limit switch to set the flap retracted position. This arrangement has the advantage of eliminating the flap over travel problem.

What are the predicted consequences if the limit switch fails? If the flaps are like those on my RV-8, I think there might be damage to the inboard end of the flap if the actuator attempted to pull them up too far.

It might be better to use the limit switch to limit the flap extended end of things, as the failure mode is more palatable. Even if the limit switch were to fail, and the actuator continued to full travel, someone needs to push against the trailing edge of the flap to push them far enough to have a problem.

 

[Andy_RR]

epoxy?

Would it be worth getting the expoxy out and laminate them together during construction?

Any reason why this wouldn't be a good idea, allowing that surfaces would be primed etc for corrosion resistance?

A

 

[JRFlyer]

Wing skin fix?

Hello everyone,

So I just had this same problem occur on my RV-6?the flap sandwiched itself on retraction between the doubler and the trailing edge of the upper wing skin. Unfortunately I didn't catch it in time to avoid slightly bending the upper wing skin so now it slightly flares up. It is a slight but noticeable bend about 2 feet long without any creasing of the metal itself, leaving about 3/4 inch of space between the flap and wing skin. I was wondering if anyone had any advice as to how best straighten/flatten slightly flared up sheet metal without removing/replacing that portion of the wing skin?