Engine mount weldments - to split or not to split....?

[chris mitchell]

This (not very good) photo shows there gap between the lower forward longeron and the weldment. There is about a 1/4 inch gap unless I clamp it, which then induces a bit of a curve in the longeron - I have the same problem altho' to a lesser degree with the top weldments.

Longeron is running from the top of the photo to th e mount. The clamp is loose. There is an extra bit of angle on th eleft which is jigging the firewall and F-404.



I'm wondering if I should split the weldments to make two ears which would then more easily conform to the required angles.....?? I think this is the arrangement on the RV-3

Both sides are the same and I have (again) rechecked all measurements and angles. The problem is with horizontal alignment - vertical seems more or less OK.

Sorry about the quality of the photo.

Chris

[Derek]

I cut the weldment, corrected the angle and then welded it back together.

[chris mitchell]

Thanks - where abouts on the weldment did you cut?

Its a shame that Vans makes the weldments straight (per the drawings) - when casual inspection of the plans and some simple maths indicates that they really ought to be made with some angulation both laterally and vertically - around 2 degrees up and out would fix it!

Is cutting and rewelding a common fix or do most folk just clamp up and build on?

Chris

[Derek]

It worked for me....

[Russ McCutcheon]

I also like what Derek did on his, good job Derek! Either Derek?s method or what I did, cutting along the bend and tweaking I?m sure would be fine.

[chris mitchell]

My worry about cutting and rewelding - as I understand how you guys have done it and how the weldment is built in the first place - is that now you will have a welded joint in tension rather than in shear. Isn't that structurally less sound?

Right now I am contemplating cutting off the ear, grinding out the original joint and repositioning the ear, to get the joint back in shear. I know nothing about material strength etc so perhaps its not necessary but this is not a joint to have fail! Actually, if I decide to go this route I might bend up an new ear and incorporate the gusset. But I'm guessing that 4130 steel will be a bear to bend, never mind to bend accurately?

An alternative I guess would be to make a small wedge from 6160 aluminum to fill the 1/8 gap Not wild about that.

Moreover, I am still interested to know how many RV-4 builders have this problem and what most folk to to resolve it...?

Chris

[Ironflight]

While it is true that the Van's support team were mostly kids when the RV-3 and -4 were designed, getting an engineering opinion from the guys at the homeship might not be a bad idea when you start talking about loading in shear vs. tension and the like. After all - these four weldments hold your engine to the rest of the plane. Not somethign to casually mess with.

On the RV-3, the wledments are split, and that made the fitting easier.

[smokyray]

Originally Posted by Ironflight

While it is true that the Van's support team were mostly kids when the RV-3 and -4 were designed, getting an engineering opinion from the guys at the homeship might not be a bad idea when you start talking about loading in shear vs. tension and the like. After all - these four weldments hold your engine to the rest of the plane. Not somethign to casually mess with.

On the RV-3, the wledments are split, and that made the fitting easier.

Interestingly enough, the original RV4 and RV3 kits had no weldments whatsoever. My late friend Arvil Porter pointed this out to Van back in the mid 1980's after building his 6th RV4. After seeing the inherent weakness in the nose of the RV4, Arvil designed (and shared with Van's at no cost) his weldment additions he installed on all RV4's he built or assisted with (including my 89' kit). Van's never made any comments to Arvil pro or con, however later RV4 kits would include weldments that looked strikingly similar to Arvil's design with the exception of being straight as mentioned above...Arvil's original's looked much like yours.

What goes around, comes around...

V/R
Smokey

[chris mitchell]

To hear from Vans.

Paul, I already emailed Vans - waiting to hear.

I was really just airing my concern about the cut and weld.

Interesting that the -3 weldments are not the same design.

Smoky -interesting bit of history there.

Chris

[Derek]

I very, very, carefully and patiently......

1. Ground down the welds and separated the weldment into 2 parts, all the while being extremely careful to not grind or cut into the weldment itself.
2. I then adjusted the weldment angles to suit my aircraft.
3. I then re-assembled the weldment as per the original design, then welded the weldment back together, welding in the exact same location as when originally made.

After all this I believe that the structural integrity of the part has not been compromised.