I Can't find my flap/fuselage problem

Hi everyone,

Yesterday I put the wings on the fuselage for the first time. After checking a tenth of time, I drilled the rear spar to set the incidence angle. Everything went good (zero sweep, squaring within a 1/32" 0.0 degree checked with numeric level and laser). Today I put the ailerons to set the neutral position and the flaps. I ground the fuselage side skin to let the pushrod go freely through the fuselage and seat floor. But here is my problem :
The flaps don't kiss the fuselage at the wing root. I checked the flap and aileron twist, it doesn't exist. I checked the wind incidence, it is good. The ailerons neutral position is ok.
On the photo below you will see the problem.

Am I missing something or is that normal?



thanks a lot

Mine did the exact same thing so I am curious as to what the answer is.

-david

This is a common problem. Do a search on Flap Alignment, and start reading. I have not heard of a common theory on why this occurs. I suspect it is build variance in the fuselage, wing, or both. Even the QB's seem to suffer, although you would think on a matched drilled and machined product it shouldn't happen, small tolerances still add up quickly.
Don't fret over it too much if you can not locate what is causing this. As long as both flaps have the same drop it should fly straght and be a non-issue.
I have seen much worse.

Bend the lower skins upward to meet the fuselage, and build new flap fairings to match.

First thing to do is...

check for a twisted flap.

Put a digital level, cord wise on each end of the flap and see if it reads the same value at each location.

I am a little bit less anxious since it seems that I'm not the only one who have this problem. I just recheck the flaps twist with a numeric level and the value I read along the cord is the same.
The fuselage and wings are from the prepunched kit and seems to have not twist in either direction.
I will bend a little the flap bottom skin and maybe do some little epoxy work to have something looking better than it actually do.
I really appreciate all the answers I get in less than an 1:30 hr. I would have wait more time phoning directly to Van's Aircraft .

Mine were the about the same, maybe a smidge less. Also, my wings lined up with very little fuss and almost no tension to get the rear spars aligned for drilling.
I'm going to guess that this is pretty normal, and if you want a perfect fit, you will need to find a way to get the inboard end of the flap to curve upward to meet the fuselage, like an ideal fillet.
Then show all of us how you did it, and what your speed gain is.
You will be a local hero, and get you 15 minutes of fame too.
But for now, play on through. Once you are flying and have base line performance numbers, you can measure the effect of your mods.

Normal.

I believe this is totally normal. I have yet to see an RV-8 that did not have this neutral flap position. Mine was a quickbuild and it looks just like yours. My wing incidence is perfect.

So -- I believe it is actually an error in the design -- the wing just sits a bit lower than they thought.

Eventually I will cut the flaps off square at the side of the fuselage and make a fiberglass root fairing that will mate to the flap and make a nice transition. If you are going to race, I would advise doing this.

Otherwise, once you start flying, its out of sight, out of mind. Build on.

The fairing helps

When you attach the flap fairing to the fuselage a lot of this can be easily streamlined, along with a slight bit of bending upward up the flap end. I forget the fairing part number, bu dig it out and hold it in place and you will get the idea.
Don't worry about it. This is pretty normal.

Steve, and Steve are absolutely right on! Actually, if I didn't see what we are seeing on your flap Bastien, I would suspect you did something wrong!!!!!
Bend the overhanging flap skin up with a very slight "pre load" on it against the fuselage bottom skin. After paint put some "anti-chafe UHMW" tape on the flap skin and you'll be good to go. You won't have to make a new flap fairing at all. The stock one can be bent and adjusted to "mate" with the flap skin.

Mod is done

Hi everyone,
I made a mod to solve the cosmetic problem I explained above. Some bending and fiberglassing were necessary to have something I expect to look good. I will post some photos tomorrow once the epoxy fully cures and the sanding job complete.

It's quite "funny", a friend of mine told me yesterday that I might have a incidence problem when I drilled the rear spar as he didn't have this flap/fuselage problem. Tomorrow I will phone him to tell him that he maybe have a problem as everything went good on his Van's...

Bastien said:

Hi everyone,
I made a mod to solve the cosmetic problem I explained above. Some bending and fiberglassing were necessary to have something I expect to look good. I will post some photos tomorrow once the epoxy fully cures and the sanding job complete.

It's quite "funny", a friend of mine told me yesterday that I might have a incidence problem when I drilled the rear spar as he didn't have this flap/fuselage problem. Tomorrow I will phone him to tell him that he maybe have a problem as everything went good on his Van's...

Click to expand...

This guys website is what I used for mine and what I modeled my flaps after. My fairings didnt come out as wellas his, but my flap/fuse fit is very nice. My flaps looked exactly like yours before they were cut and fit. Check out his pictures on this page under "Flap/fuselage Interface"

http://www.romeolima.com/RV8/Wings.htm

Matt, That solution looks pretty good but its hard to depict exactly what is going on just by those 3 pictures, do you have any of the way you did yours that you can link us too?

Thanks
-david

Matt, the way I did the mod is very close to Romeo lima's one.

I began by separating the trailing edge of the flap on about 1", I stop the cut with a #30 hole. Then I bend the flap bottom skin to close the gap there was between the flap and the fuselage. It was almost good but had to rivet the top part of the flap to the bottom part of the flap to maintain the angle I made in the previous step. To make something looking better, I did some epoxy that I put on the flap and on the fuselage and let everything cure protecting the fuselage with tape. I put the flaps down today to start sanding but I realize that a little piece of tape was under the epoxy so I had to redo the job and so it isn't nice for the moment (and the photo below is not well taken).
I put the wings off this evening and so you won't see the final result in assembly but in parts when it will be done (I still have some sanding to do by the end of the week so I will report the finish job photos later).