Fwd Fuse Gusset Fit

skelrad · #1 09-06-2023, 06:30 PM

My F-695 Fwd Fuse Gusset doesn't seem to fit all that well. On the left side, my longeron twist looks to be really close to what it's supposed to be (sits snugly into the angle of the upper engine mount bracket), but because of how the top firewall stiffener fits against the longeron, the gusset doesn't nest against the stiffener where the stiffener and longeron meet. Am I good to bend the gusset to match, or do I need to address something else so I don't back myself into a corner with another part down the road?

The left side isn't horrible, but on the right side, it looks like my longeron is under twisted a bit (maybe between 1/32-1/16" gap between it and the engine mount bracket - although with a little pressure that gap closes up pretty well), causing the gusset to have a bigger gap. I'm trying to figure out how I deal with that given everything that is riveted together at this point.

idubrov · #2 09-06-2023, 08:14 PM

I slightly bent the gusset to fit the key points (where the rivets are) as good as I could.

I think, I also had a small gap between the longeron and the engine mount -- it all went away once I riveted everything. I haven't fitted nor riveted the top skin, however, so I might still get into trouble in the future.

Also, among all the edge distances to watch for (edge of the longeron, the inner / outer edges of the engine mount tabs), one non-obvious was the spacing for the shop head of the 4th aft rivet (4th counting from the aft).

On my first try, I located all 14 longitudinal rivets equispaced and that 4th rivet hole got located exactly at the edge of the engine mount "tab" under the longeron -- wouldn't be possible to buck the rivet.

(I'm building RV-7, but I think the fuselage is very similar to RV-9.)

nohoflyer · #3 09-07-2023, 10:45 AM

You want the gusset to be even with the edge of the longeron and firewall. Bend as needed. Make sure you drill the holes along the longeron side iaw the plans. The rivets need to have edge distance on all three layers on the longeron side.

Along the firewall side is where I used a few of my cherry-maxes due to bucking bar accessibility.

I just finished this section awhile ago and there are no future gotchas.

GeoffP · #4 09-07-2023, 02:36 PM

I just checked my photos from when I riveted these parts on about a year ago. The fit was just fine, across both the main longerons and the firewall angle, but it looks like I just increased the bend in F-695 a little towards the firewall end.

Girraf · #5 09-07-2023, 03:11 PM

Mine didn't fit very well. I had to increase the bend angles to get it to sit nicely. Thinking back, I spent a fair amount of time on these between laying out the rivet patterns, figuring out that the fwd edge of the doesn't wind up parallel to the firewall when its also parallel to the longeron, and adjusting the bend angles.

Karetaker aero on youtube had a nice detailed discussion about this specific task.

nohoflyer · #6 09-08-2023, 08:59 AM

Btw my right side did not sit well either. Big gap between the longeron the weldement. I added a fat shim.

skelrad · #7 09-08-2023, 09:24 AM

I was able to get both sides to fit better after some time bending at the vice. I added a new bend line about 1/4" inside the existing bends on the longeron side to make the vertex sit in the actual spot where the angle changes (the existing bend is just at the edge of the longeron, which isn't actually where the firewall stiffener needs the change in bend). I also added a slight bend on the short leg of the gusset so that it would lay flat on the stiffener. With those two changes, it all fits nicely.

idubrov · #8 09-08-2023, 05:55 PM

How much overlap do you have between the engine mount "tab" and the longeron? I had about 1/2", which gives 0.250" edge distance on both the longeron and the engine mount bracket, if everything is perfect. I think, I biased towards edge distance on the longeron and got what seems like 7/32" on the engine mount bracket.

Can you push longeron inside, so it overlaps more with the top engine mount "tab"?

This is what mine looks like. I think, I have less "spread" between the side and the top "tabs"?

Click image for larger version

Name: IMG_7766.jpeg
Views: 69
Size: 467.9 KB
ID: 47688

skelrad · #9 09-08-2023, 07:17 PM

Quote:

Originally Posted by idubrov

How much overlap do you have between the engine mount "tab" and the longeron? I had about 1/2", which gives 0.250" edge distance on both the longeron and the engine mount bracket, if everything is perfect. I think, I biased towards edge distance on the longeron and got what seems like 7/32" on the engine mount bracket.

Can you push longeron inside, so it overlaps more with the top engine mount "tab"?

This is what mine looks like. I think, I have less "spread" between the side and the top "tabs"?

Attachment 47688

On the right side I have what you have in terms of overlap - about 1/2", so I was able to cheat the edge distance of the longeron over and get 3/16" edge distance on the bracket. I've seen other references from people who have checked with Van's and have said 3/16" is ok for the steel. So that side I'm comfortable with. The left side is another story. I only have 3/8" overlap of the longeron and bracket (my bracket opens up a bit more than yours at the aft end - I tried squeezing it in, but no luck since that's how it's welded), so edge distance is going to be slim. I have emailed Van's about it. I have a few holes drilled in the fore end of the bracket already, but I think those will be okay in terms of edge distance since the bracket wedge is almost closed at that point. I think if I make a new gusset and cheat all of the other holes over a bit, I might just sneak by. I'll have a few of the original rivets that aren't in the same line, but as long as Van's blesses the locations, I'll just call that hidden "character" for the plane.