F450 forward attachment

[Derek]

I was wondering if there is anyone else out there that's experienced the same as what ive shown in the picture. It's looking like that to make the forward weldments fit correctly to F450 I'll need to cut them and re weld to the correct angle. Just curious to hear if anyone else has experienced the same issue.

http://i1118.photobucket.com/albums/...achmentgap.jpg

Here is a link to a clearer picture.

[joeboisselle]

Vans weld those in a jig, so something else isn't right.

[Russ McCutcheon]

Originally Posted by joeboisselle

Vans weld those in a jig, so something else isn't right.

Well not exactly. We weld those for Van?s but yes they are welded in a jig. Same jig for the past 30 years!

Where?s the problem exactly I don?t know. We installed these in my Dad?s old flying -4 a year or two ago and ran into the same problem, I did mention it to Van?s but we had no way of knowing how fare off the airplane is so nothing was done.

You?re in a good spot while building new, triple check everything then cut them up and make them fit or shim them, I would prefer to cut them along the break and bend the remaining ears out to fit then weld them back up about half way, you?ll have it fixed up in an hour.

[Derek]

All, Thanks for your responses. Even though the error is only minor, I will more than likely cut the weldment to suit and reweld to the "correct" angle. All good.

[foka4]

Derek,

I recently retrofit these brackets into an older airframe, and had the same issues with fit as you. In my case, one bracket was so far out of alignment that I suspected it was defective. I ordered a second one and it fit much better. Between fixturing variation and weld warpage, I measured more than 1/8" difference between one bracket and the other! From your photos, it looks like your situation is very similar.

These brackets are critical structural elements, so it's worth the extra effort to achieve a perfect, shim-free fit.

While you're working on that part of the airframe, you might also consider adding some gussets between the bracket and the 3/4" angle vertical firewall support. Opinions vary on whether this is necessary, but RV3s and 4s are classically weak in this area, and later models have the gussets. More info in this thread: http://www.vansairforce.com/communit...ad.php?t=50838

m

[Master Designs]

Unfortunately Photobucket has dropped Derek's photo due to it being posted 2 years ago, but without seeing the photo, I think I might be in the same boat. Since the new one-piece weldments don't have the play the original weldments had, I'm having a issues with clamping in the new weldments without any gaps.

Option A) As the weldment sits in place, there is a 3/16" gap between the weldment and the lower longhorns due to the side angle of the weldment being different. The weldment is 101 degrees (like the plans show), and my -4 must have been built to something closer to 95 degrees. I can fill the gap with a shim, but then it would require bolts instead of rivets, and I don't want to go this route.

Option B) When I use a large C-Clamp and draw the weldment and side longerons together, it is drawing the sides together perfectly, however, the 1/8" kick down on the front of the weldment (bottom front edge of the weldment is not totally flat) forcing the horizontal 3/4" angle the weldment sits on downward 1/8"??creating an 1/8" gap in my lower mitered corners where the engine mount bolt will be drilled, and increased the distance of the top and bottom horizontal angles from the required 21-1/2" to 21-5/8"

Option C) Cut one weld on each gusset, bend it to fit (bring the sides back 6 degrees) and have it re-welded?

Thoughts?

[Derek]

I ended up cutting the weldment, adjusting it to fit, then welded it back together again.

[chris mitchell]

I've just seen this thread and have another one about this problem on the go.

However, As far as I can determine, my build is dimensionally correct but the weldments do not fit properly. Simple geometry indicates that the weldments need to be angled - the firewall and F-404 are not the same width or height. SO either there is some variation in the weldments and some folks get lucky, or most folk are just clamping it all up and carrying on.

Ross - you indicate that you have been doing these parts the same way for years - the Vans plans suggest that the weldments are "straight" - is that how they actually get made or are they in fact slightly angled?

Thanks

Chris

[Russ McCutcheon]

Originally Posted by chris mitchell

I've just seen this thread and have another one about this problem on the go.

However, As far as I can determine, my build is dimensionally correct but the weldments do not fit properly. Simple geometry indicates that the weldments need to be angled - the firewall and F-404 are not the same width or height. SO either there is some variation in the weldments and some folks get lucky, or most folk are just clamping it all up and carrying on.

Ross - you indicate that you have been doing these parts the same way for years - the Vans plans suggest that the weldments are "straight" - is that how they actually get made or are they in fact slightly angled?

Thanks

Chris

Hi Chris,

Lee built these fixtures 30 odd years ago, I came along in 91 and started welding for him as instructed, I would say they are welded straight, not angled out, as for the plans, I have never seen any, Lee probably built the first ones off a drawing Van brought him , then Van checked the parts and said build more. As I said before I would and did just cut them along the bend/break and tweak them into position and re weld them an inch or two back up.