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-7 Flap Lip too Close to Upper Wing Skin

mfleming

Well Known Member
Patron
I have my flaps installed for the first time. Cut the flap push rod holes and trimmed the flap skins as needed. In the up position they line up pretty good with a neutral aileron and the bottom flap skins fit nicely against the bottom of the fuselage.

I measured the flap down angle at 45° which section 15 says is the max.

The concern is, the flap lip is very close to to the top wing skin. I understand that if the flap lip pops over on top of the upper wing skin and the flap is retracted much damage ensues :eek:

My question is...how do I limit the flap travel like Mel suggest to 38°?

It seem that once the flap up adjustment has been made...the down is what it is.

A lot of people say they limited the down adjustment but don't say how the did it :confused:

If the answers really simple, my apologies ahead of time ;)

Here's a video of the flaps in action just for fun...doesn't really show the lip issue
 
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If you use the stock setup and adjust as you have mentioned, there should be no issue. Many many 7?s out there running full stock travel....
 
Michael,
I am glad you are aware of this possible issue. This happened to a good friend of mine and the result was UGLY.
The flap as it is fully down, if pushed by accident or some minor force, it deflects enough that the leading skin could pop out.
In my friends case, he believes, people had leaned over to look at his panel and inadvertently pushed the retracted flap just enough that it had popped out. when he retracted it, it bent the top skin of the wing 90 degrees upward. The repair was not easy, specially in a painted plane.

One way to limit the travel, maybe even just a couple of degree or so, is to install a limit switch. Many have done this and using a micro switch is an easy way to accomplish this. Alternatively, you could shorten the push rod if the rod end bearings are fully in.
I have seen one damaged wing and heard of another individual with this issue. It is well worth the effort to ensure it could not happen
 
I forgot to mention, I am using the PH Aviation flap actuator instead of the Van's stock unit.

Here's a link to when I installed it.

This flap actuator has internal sensing and internal electrical stops. I'm not sure if I can set the down limit from the avionics or not?
 
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Ph aviation flap, me too

I am also running the PH aviation flap actuator. I am not flying but my intent is not to rely on the internal flap limit switch to set the down position, but rather the Garmin G3x system. Since the PH aviation actuator also has a position sensing potentiometer built in, the G3x system can use that to set down and up stops electronically. The limit switches inside the actuator will only come into play if there is a runaway condition. I guess the control rod length can be adjusted so that one stop relies on the limit switch.
 
....inadvertently pushed the retracted flap just enough that it had popped out. when he retracted it, it bent the top skin of the wing...

This happened to me on my -6. I leaned against the extended flap without realizing it. For now, I have a line marked on my left flap with a sharpie about 5 degrees up from fully extended that I use when on the ground. I don't believe it is really ever an issue in flight. It only occurs when the fully extended flap is "bumped" on the ground.
 
I am also running the PH aviation flap actuator. I am not flying but my intent is not to rely on the internal flap limit switch to set the down position, but rather the Garmin G3x system. Since the PH aviation actuator also has a position sensing potentiometer built in, the G3x system can use that to set down and up stops electronically. The limit switches inside the actuator will only come into play if there is a runaway condition. I guess the control rod length can be adjusted so that one stop relies on the limit switch.

This sounds like a good idea.
I'm also planning on using the Garmin system. I like the idea of setting the down limit via the G3X system instead of using the internal stop.
 
I'd like to make one other point to add to this discussion. Limiting the stroke of the actuator will not necessarily solve this problem. Unless you severely limit the stroke, the leading edge can still pop out. This is a design quirk of certain RVs, but with a little care should not be a problem.

There are thousands of RVs flying around that are susceptible to this but have not encountered a problem. Can it happen? Yes, and if does, but my solution is to always, and I mean always, check the leading edge of the flaps prior to raising the flaps. I always glance out both sides of the cockpit at the flap leading edges prior to raising them. Some folks always keep the flaps retracted on the ground so that this can't happen.

However, most folks keep their flaps full down after landing and leave them there until the next takeoff. I'm in that camp, but I also assume someone might have leaned on them and popped them out. In 17 years in my -6 it has never happened, but I've seen it more than once happen to others.

I just don't think this is a big problem--if care is exercised.
 
I've been messing around with my flaps in regards to the curved lip that fits under the upper wing skin.

When I disconnect my flaps from the flap push rod, there is no tendency for the curved flap lip to try and ride over the top wing skin. The curved flap lip doesn't touch the wing at all. So there's no propensity for the flap lip to do anything if pushed down.

Maybe my flaps are not rigged correctly but I've met all the parameters laid out in the manual and drawings.

Here's a short video of the flap fit.
 
I rigged my flap linkage so that it cannot happen. On my 6 I set 40 degrees as my full down.
 
I've been messing around with my flaps in regards to the curved lip that fits under the upper wing skin.

When I disconnect my flaps from the flap push rod, there is no tendency for the curved flap lip to try and ride over the top wing skin. The curved flap lip doesn't touch the wing at all. So there's no propensity for the flap lip to do anything if pushed down.

Maybe my flaps are not rigged correctly but I've met all the parameters laid out in the manual and drawings.

Here's a short video of the flap fit.

Michael,

I would say your gap is a little greater than most. I believe the desired situation is no gap. As a matter of fact, most folks have seen the need to place some PTFE tape on the underside of the trailing edge wing skin to keep from scoring the flap skins. You can work the flaps' leading edge skins to decrease this gap by increasing the radius of the bend.
 
How?
When the linkage is set for full up, there?s no adjustment for the down.
Please share your method.

I set the flap push rod length so that when the actuator is at the full down position, the flap angle is 40 degrees. The only way that my flap top skin will come over the top of the wing skin is if I have the linkage removed. I rely on the limits and the inside edge of the flap against the bottom of the fuselage to control the up flap position.
 
I also adjust flap to extend max 40 degrees, no limit switches or linkage modifications. On some planes I have to bend lower inboard skin extension to conform to belly skin contour. This may affect aileron & tip alignment a bit, just adjust them to conform. A slight bit of up trailing edge deflection shouldn't affect flight characteristics, might even add a quarter knot of speed...
 
Michael,

I would say your gap is a little greater than most. I believe the desired situation is no gap. As a matter of fact, most folks have seen the need to place some PTFE tape on the underside of the trailing edge wing skin to keep from scoring the flap skins. You can work the flaps' leading edge skins to decrease this gap by increasing the radius of the bend.

Thanks for the advice Pat.

I just talked to Van's tech support. He asked me if my wing top skin trailing edge was flat with the wing or had a bit of a ski jump to it...they have a special tool if it does.

My wing top skins are flat.

Tech support didn't think there would be any problem with a bit of a gap between the wing skin and the curved upper flap skin. But he mentioned I might slightly massage the wing upper skin down a bit to meet the flap.

It would be interesting to know if it mattered aerodynamically. To me it looks like a cosmetic thing.
 
I set the flap push rod length so that when the actuator is at the full down position, the flap angle is 40 degrees. The only way that my flap top skin will come over the top of the wing skin is if I have the linkage removed. I rely on the limits and the inside edge of the flap against the bottom of the fuselage to control the up flap position.

Duh! :p

OK, I see now. The stock flap actuator has a clutch that just slips when the flap if up and you use the linkage to set the down...
 
Thanks for the advice Pat.

I just talked to Van's tech support. He asked me if my wing top skin trailing edge was flat with the wing or had a bit of a ski jump to it...they have a special tool if it does.

My wing top skins are flat.

Tech support didn't think there would be any problem with a bit of a gap between the wing skin and the curved upper flap skin. But he mentioned I might slightly massage the wing upper skin down a bit to meet the flap.

It would be interesting to know if it mattered aerodynamically. To me it looks like a cosmetic thing.

Agreed, mostly a cosmetic thing and in your case probably helps prevent your flap skins from popping out. You could try to intentionally pop them out by leaning on the trailing edge of the flaps when they're full down but I think you'll find that in your case they won't pop out. Just a guess.
 
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