F-917 lower longeron twist

[Ron]

Can't seem to get the hang of this twist...any thoughts out there or good pics...
Thanks
Ron

[Steve]

Dan C. has useful pics on his site. The twist is very slight and may vary from plane to plane.
www.rvproject.com

Steve

[LettersFromFlyoverCountry]

When you way you can't quite get it....can you say a bit more about what you're experiencing? In other words, have you acdtually tried to twist it and it's not working out? Or you haven't figured out how to accomplish the twist yet and haven't tried? The answers depend on which.

I'm assuming you've already formed the longerons to the curvature of the fuselage as directed by the plans so you already know two important things (1) if you try to form aluminum angle one way, it will try to pop out and change shape 90 degrees later and (2) longerons, when you throw them across the garage and they hit the concrete floor... make a really spectacular sound.

I believe the next is step is the downward bend at the front of each longeron.

On a 7 this is on DWG 18; I'm not sure what it's on on a 9...

Remember, all the distances on the callout are BEFORE you bend the angle at all. So hopefully all these marks have been measaured and indicated already.

Place your angle in a sturdy vice at the indicated mark.... might be 28 1/.4... I forget. Take a crescent wrench or pipe wrench or whatever you want to use with LOTS of padding (you don't want to put ANY marks on the metal). Attach it near the end...make sure the vice is holding the angle firmly and begin to TWIST in a small manner INBOARD.

Give it a little bit of pressure but don't try to accomplish this all at once.

Take it out of the vice ....put a straightedge (one of those long Stanley Levels works here....along the top face of the longeron, line it up flush with the inboard edge... extending aft of that 28 1/4 mark, forward TO the very forward end of the angle....and measure the distance between that straight edge and the very forward corner of the angle (whic of course will be lower than the straight edge because you just twisted it . When the distance is 7/32", that's a 17 degree bend and -- at least on a 7 -- that's what you want there.

Now...check to see of the twist changed your downward bend or pulled the angle inboard or outboard. If it did....put it in the vice...take a rubber mallet and give it a few whacks to get it back.

Repeat....repeat.....repeat...until you're there.

AFter you do this...check everything again. Put the angle back on the bottom skin edge to make sure it follows the contour....fix it if it doesn't... check the downward bend again..... check the twist again.

Just like when you're flying and you have to adjust trim when you change power....you have to do the same thing with aluminum angle. If you change something on it....you probably have to change something else too.

This is a maddeningly frustrated point of the project -- or can be -- but tkae your time and invest the frustration now....because if you get those longerons perfect....you're eliminating a lot of it later and guaranteeing a beautiful job on the fuselage.

Holler if this doesn't make sense.

[Ron]

Thanks Bob, The main longerons came out fiine, no problem, fit good. These lower ones, I put the forward end into the vise 3 7/8 I think, then twist with the cresent wrench a little at a time. I want to ensure, put the wrench on the verticle side, the 1 1/4 flange, and push toward the inside? or pull to the outside. If that makes sense..And then just work my way down to the other end gently? I'm sure it's a nutty question, but it's sure hangin me up... Doesn't look like it's going to take much.. I saw Dan's pics, but still need some clarification..
Thanks again
Ron

[Radomir]

put it in place and see how it fits.. that will immediately clarify what needs to be done. it'll turn out to be really, really simple. Just a slight twist so it sits flat in the back..

[LettersFromFlyoverCountry]

Originally Posted by Ron

I'm sure it's a nutty question, but it's sure hangin me up... Doesn't look like it's going to take much.. I saw Dan's pics, but still need some clarification..
Thanks again
Ron

It's not nutty at all. Visualize what's going to happen to these longerons and it'll be easier. They are going to "surround" the top corner gusset on the firewall, which -- if you've already done this part of the firewall --you'll notice twist inboard and down (I'm referring to as it actually sits i the plane, not as when everything is upside down).

So each longeron twist is INBOARD.

[Ron]

Finally, it made sense, no problem, just making it harder than I should have,
Thanks for replies
RB