ArVeeNiner

ArVeeNiner

Well Known Member
OK, I've adjusted my ailerons then, I lined up my flaps to those. I installed wing tips and everything look peachy.

I look at the inboard side of the flaps and worse case, I see about a 3/4" gap between the flap skin and the bottom of the fuselage when the flaps are completely sucked up. The left side is a little less.

Then, I go to the airport to look at a friends RV-9A and he's got no gap!

So, I do a search and everybody says this gap varies a lot and it's not abnormal. I confirmed this with Van's. What I can't get my head wrapped around is how can there be so much variance here? The kit is prepunched. I doubt if the incidence varies much because you don't have much wiggle room when drilling the rear spar. Yea, I'm sure there is some sort of tolerance build up but I'm having a hard time buying that much build up.

Any ideas?

What kind of gaps are others seeing with the 9?
 
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poll?

obviously I'm not laying under my plane, but I'm gonna say 1/4 to 3/8", pretty uniform side to side. I wonder how NO gap is achieved; would the flap motor like bottoming out like that?...or perhaps it's no different than full extension?
 
You might post a picture or two... but you've probably got a bit of warp in one of your flaps, Kelly. That is not at all unusual given the 8'+ length of them. It's pretty hard to build a perfectly flat flap. One of my flaps has about 1/4"-3/8" twist, making the flaps and ailerons not line up exactly when the flap is in the full up position (bottom skin of flap tucked up tightly to bottom of fuselage). Ken Scott indicated to me that this is common and that the plane probably won't notice it, but that only flight would tell. The only options are to either rebuild the flap or, at a minimum, try to separate the trailing edge of the flap and re-rivet. If you used proseal or some other adhesive on the trailing edge, however, the latter is probably not a good option.
 
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alpinelakespilot2000 said:
You might post a picture or two... but you've probably got a bit of warp in one of your flaps, Kelly. That is not at all unusual given the 8'+ length of them. It's pretty hard to build a perfectly flat flap. One of my flaps has about 1/4"-3/8" twist, making the flaps and ailerons not line up exactly when the flap is in the full up position (bottom skin of flap tucked up tightly to bottom of fuselage). Ken Scott indicated to me that this is common and that the plane probably won't notice it, but that only flight would tell. The only options are to either rebuild the flap or, at a minimum, try to separate the trailing edge of the flap and re-rivet. If you used proseal or some other adhesive on the trailing edge, however, the latter is probably not a good option.
Click to expand...

Nope, flaps are straight. I remember marvelling at how straight they came out. Of course, I haven't checked them since they've been installed. I'll do that.

I'll post some pictures.
 
ArVeeNiner said:
Nope, flaps are straight. I remember marvelling at how straight they came out.
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Well, if so, cross my explanation off the list. However, remember that a control surface can be perfectly straight (have no wave) in its trailing edge and yet be warped, or have twist. Initially, I thought mine turned out perfectly as well b/c the trailing edge was straight as an arrow. The problem was that the trailing edge and rest of the flap, both straight, were going different directions. The best test is to lay the flap down (upside down) on a known perfectly flat surface and see if either the inboard or outboard side of the trailing edge sticks up a bit from the flat surface. Anyway, good luck with your investigations.
 
I had so much difference in that gap that I had to cut one of those overlapping flap skins off to get full retraction on the left. I perseverated over this, but ultimately, I saw no other option. My plane flies straight as an arrow-it just looks a little catawhompy if you crawl underneath.

Steve Johnson
RV-9A, 175 hours
 
The gap

Even though every thing is pre punched there is still "slop" in the way things fit. Our RV 7 came out the same way. If you were able to mount the wings in the exact position they are suppose to be in permanently (the angle of incidence) then rivet the flap hinges it would have come out flush with the bottom of the wing.
 
IMHO even with a pre-punched kit it is possible to build a twist in the wing, the flap and the aileron and all could conspire to cause a gap between the lower flap surface and the fuselage. See this thread post #21 for my further comments.

Fin
9A
 
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I got another data point tonight after our EAA meeting. I looked at another 9 and he had the same issue. He just bent up the inboard end of the flap which closed the gap. Weird. I'm sure it will fly just fine!

Steve, I'm am curious though if my perfectly straight flap is really straight. I'll put a straight edge on it the next time I'm out there.

Thanks guys!
 
Nope.

Kelly, the way to check for warpage is NOT with a straight edge.

Back away from the airplane/flap and sit down, looking at the trailing edge of the flap from a few feet away.
Position yourself vertically, until there is as much flap above the trailing edge as below it. If it's warped, it will be evident.

Best,
 
Flap clearance

My flaps came out to be flush with the bottom of the fuselage in the retracted position. I spent a lot of time on the wing angle of incidence before drilling and a lot more time geting a straight flap trailing edge. When set according to Vans I barely got 30 degrees of flap travel which I understand is also common. If you are confident on the wing incidence angle, aileron & flap relationship according to Vans then look closely at the straightness of your flaps.

Pete :cool:
 
Errors need to hide some where. Just ask anyone that has built a house.
Installing the wing is the most important. The ailerons are next on the important list. Then the wing tips. And last, the flaps closest to the fuselage with less effect on roll.

Bend and form the tab to fit flush and cover the push rod hole, this is done all the time. You really got to get down to see this adjustment. This is the best place to hide this minor build adjustment.
 
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