RV-9 flap twist?

[intothinair]

I am in the process of building the left flap and now ready to match drill the skins to the FL-905 ribs. Before drilling, I noticed that all of the ribs and bottom skin lay flat on the table except for at the inboard end.

The FL-905 on the inboard trailing edge lifts up the skin by 1/4". I have adjusted the inboard FL-905 rib root flange, but the problem still persists.

Shouldn't the inboard trailing edge lay flat on the table before match drilling? Will I introduce twist in to the flap even if I weigh down skin/ribs and match drill?

The table has been checked to be flat.

http://pages.sbcglobal.net/knsinc/rv9/IMG_0965.JPG
http://pages.sbcglobal.net/knsinc/rv9/IMG_0963.JPG

 

[vlittle]

I am in the process of building the left flap and now ready to match drill the skins to the FL-905 ribs. Before drilling, I noticed that all of the ribs and bottom skin lay flat on the table except for at the inboard end.

The FL-905 on the inboard trailing edge lifts up the skin by 1/4". I have adjusted the inboard FL-905 rib root flange, but the problem still persists.

Shouldn't the inboard trailing edge lay flat on the table before match drilling? Will I introduce twist in to the flap even if I weigh down skin/ribs and match drill?

The table has been checked to be flat.

http://pages.sbcglobal.net/knsinc/rv9/IMG_0965.JPG
http://pages.sbcglobal.net/knsinc/rv9/IMG_0963.JPG

Check for a twist in the spar, ensure that the holes in the skin are correctly punched, and ditto for the rib. Try swapping the rib temporarily to see if it the problem goes away. Do not assume that Van's parts are perfect... verify! I had a slightly mispunched main spar, and another part that picasso must have punched!

If just a little bit of weight on the skin flattens everything out, you are probably ok, but if not, find the problem.

Good Luck,
Vern

 

[FredMagare]

I had a similar problem. Just make sure it's weighted down prior to drilling. I used a 1x6 (or 8) across the entire length of the flap with something like SEVENTY-FIVE pounds of weight spread across the board. (I used individual flat five pound weights.) My flaps (and ailerons) look very straight!

 

[intothinair]

RV9 flaps

Fred,

Thanks for the tip. I weighed down the flaps prior to drilling and they came out very straight.

John

 

[Robert M]

Flat table

Everyone I talked to told me to build a super lat table to build the flaps and ailerons on. I clecoed the flap skin to the table as I drilled it. I used the holes from drilling the trailing edge to keep the skin flat and twist free for riveting - worked great - no twists.