Couple -IS fuse assembly questions

[Brantel]

So for those that have done this before, which direction should the flange on this little triangular gusset face? In toward the occupants or to the outside toward the skin and vertical brace? Seems to make sense to have it point outboard so nothing can catch on it but the drawings seem to have it pointed inward but it is very hard to tell since the drawings are small. I think this ends up right under the instrument panel.

Next question is on the aft end of the longerons, the side skins have this temporary extension so you can match drill the tailcone mating holes. Well it appears that when Van’s pre bends the aft end, it bends the longeron down a little. The side skin while flush with the vertex before the bend, it is not aft of the bend. What did you do? Did you just drill the holes at an angle or did you attempt to bend the longeron back up? Both sides are virtually the same.

 

[Bob Y]

You have the flange oriented correctly in the photo - flange pointing outboard. And I don’t recall having to bend the end of my longerons, but someone who’s performed this step more recently could give you more current information.

 

[BryanStearns]

Just did my longerons in the last month or so, and both of mine came bent like yours. I wrote to Van’s and asked about the bend in the trailing sections, and they said not to try to straighten them. Since the droop is downward, the holes you’ll drill will be a little closer to the apex of the angle than the center of the flange(but not too close!), so edge distance won’t be an issue.

 

[rvbuilder2002]

Just did my longerons in the last month or so, and both of mine came bent like yours. I wrote to Van’s and asked about the bend in the trailing sections, and they said not to try to straighten them. Since the droop is downward, the holes you’ll drill will be a little closer to the apex of the angle than the center of the flange(but not too close!), so edge distance won’t be an issue.

Yup

The bend angle in the lateral direction is the important one.

A slight bend in the vertical direction has no baring on proper fit.
If you attempt to straighten it, it would most surely change the angle for the lateral direction.

 

[Brantel]

You have the flange oriented correctly in the photo - flange pointing outboard. And I don’t recall having to bend the end of my longerons, but someone who’s performed this step more recently could give you more current information.

Thanks for the confirmation on the flange!

Just did my longerons in the last month or so, and both of mine came bent like yours. I wrote to Van’s and asked about the bend in the trailing sections, and they said not to try to straighten them. Since the droop is downward, the holes you’ll drill will be a little closer to the apex of the angle than the center of the flange(but not too close!), so edge distance won’t be an issue.

Thanks for the reply and for passing along the advice from Van's!

Yup

The bend angle in the lateral direction is the important one.

A slight bend in the vertical direction has no baring on proper fit.
If you attempt to straighten it, it would most surely change the angle for the lateral direction.

Thanks Scott! My mind went to the same place but I did not want to screw this up now and find a mess for myself down the road when the big join happens. I definitely was not looking forward to attempting to straighten the downward angle!

Thanks for continuing to support the VAF family!

 

[N8DAV8R]

Just did my longerons in the last month or so, and both of mine came bent like yours. I wrote to Van’s and asked about the bend in the trailing sections, and they said not to try to straighten them. Since the droop is downward, the holes you’ll drill will be a little closer to the apex of the angle than the center of the flange(but not too close!), so edge distance won’t be an issue.

Interesting guidance. I followed the KIA here and aligned the vertex of the longeron with the upper edge of the skin. It took a little bit of force to clamp but nothing major, and the all of the tail parts went together fine.

 

[Brantel]

Interesting guidance. I followed the KIA here and aligned the vertex of the longeron with the upper edge of the skin. It took a little bit of force to clamp but nothing major, and the all of the tail parts went together fine.

I too have aligned the top of the side skin appropriately to the vertex of the longeron fwd of the factory bend in the aft end of the longerons. The issue I have is aft of that bend. There is no way my longerons are going to give enough to align with the temporary skin extension without the skin being distorted and stressed.

 

[N8DAV8R]

I too have aligned the top of the side skin appropriately to the vertex of the longeron fwd of the factory bend in the aft end of the longerons. The issue I have is aft of that bend. There is no way my longerons are going to give enough to align with the temporary skin extension without the skin being distorted and stressed.

Don't want to seem argumentative, if anything what I'm getting at is that an adjustment to the KAI may be appropriate. The KAI doesn't mention the limitations that you are using here, 'fwd of the factory bend', it says to align and clamp. The extension is temporary, but it's there until after the drilling when relative dimensions are set. The implication of an instruction to align those edges and clamp, at least to me, is that there may be some amount of force required to accomplish the alignment that is described. Van's uses the term 'stressed skin' in describing their airframes, further describing localized points of attachment on the longerons. It just didn't seem that out of place to have a bit of tension as a result of making things line up as they say.

Scott's comment seems to fall somewhere in the middle. Lateral alignment is more important than vertical. If I were doing it again I would probably follow that guidance, it's easier. Van's support at the time I was finishing up responded to me with some wild guesses at stuff they clearly didn't understand so I have less confidence that a phone call gets the right answer any more.

If the right thing to do is to let the longeron run wild as long as you have appropriate edge distance, that would be an easy clarification.

Anyway, it will go together fine. I think people will find that this alignment has more effect on the fit of the baggage bulkheads as you tie in the rollover structure than it does the attachment of the tail.