F-704

[AltonD]

on the bottom flange of the forward, center section, spar carry through, F-704:
My impression from reading the instrustions is that I dimple this flange with the exception of the the floor stiffner locations. This sure looks to thick to dimple, and that I should machine countersink. I looked at Dan's site and couldn't tell that level of detail.

Anybody been down this road?

 

[Gsuit]

Alton,

I have a pneumatic squeezer from Cleveland, and it dimpled these with no problem. But, if you do this and the rib dimple doesn't seem to lay down flat in the flange dimple, you can use a deburring tool with a countersink installed, and give it a turn or two to "freshen up" the dimple. Don't take out much material, though.

This technique is used on the wing aft spar and works well plus maintains the structural intergrity. Squeezing is our friend!

 

[alpinelakespilot2000]

Agreed that dimpled is the way to go except on those four holes. If I remember correctly that flange is only .040. I used a DRDT2 to do most of the holes and then got the tricky ones with the hand squeezer. Worked great. Good luck.

 

[Flying Scotsman]

I see that this thread is a couple of years old, but it's relevant as I'm right at the point of match-drilling the bottom skins to the 704/705/etc....so, everyone still concurs that drimpling the bottom flange of the center section spar (except for the 4 noted) is still the way to go? Just checking, since the plans were pretty explicit on the *wing* spar about *not* dimpling the flange...

 

[mcencula]

Read Van's answer...

...Here

They describe the situation quite well.

Happy building!

 

[IowaRV9Dreamer]

Vans was wrong on the wing instructions about not dimpling - especially in the aileron main spars. Following those instructions cost me a set of ailerons - now I dimple everything 0.040 or under. Results are cosmetically great (using pneumatic squeezer BTW) and stronger joint with no material removed.

I dimpled the F-704 flanges you described with good results. Of course special rules apply to those outboard 5 rivets that you will set double flush.

Good luck,