Testing On The Cheap

Peter, Brian,

thanks for the bright thoughts. Think I know what caused the problem. Per
the plans my engine requires about 1.5" long spacers between the mount's
attach points and the engine itself. This creates an extra bending moment
which may have triggered the failure.

The mount is made of 3/4" 4130 tube with 0.035" wall thickness.

My current idea of repair is to weld a short round bar into the remaining
tube and so rebuilding the attach points. Maybe I'll shorten the spacers a
bit and bring some ballast further forward instead (battery).

rattlesnake wrote:
Peter, Brian,

thanks for the bright thoughts. Think I know what caused the problem. Per
the plans my engine requires about 1.5" long spacers between the mount's
attach points and the engine itself. This creates an extra bending moment
which may have triggered the failure.

The mount is made of 3/4" 4130 tube with 0.035" wall thickness.

My current idea of repair is to weld a short round bar into the remaining
tube and so rebuilding the attach points. Maybe I'll shorten the spacers a
bit and bring some ballast further forward instead (battery).


See if you can find some tube that will fit inside or outside the failed
tube. perhaps 50 thou wall. fish mouth the ends. Rossette and end weld.
Take a look at CAM18. It gives specific instructions on repairing tubes.

Brian W

hmmm....

found a tube which fits inside the faild tube, but how can I weld it in
then - just asking


"Brian Whatcott" schrieb im Newsbeitrag
...
rattlesnake wrote:
Peter, Brian,

thanks for the bright thoughts. Think I know what caused the problem. Per
the plans my engine requires about 1.5" long spacers between the mount's
attach points and the engine itself. This creates an extra bending moment
which may have triggered the failure.

The mount is made of 3/4" 4130 tube with 0.035" wall thickness.

My current idea of repair is to weld a short round bar into the remaining
tube and so rebuilding the attach points. Maybe I'll shorten the spacers
a bit and bring some ballast further forward instead (battery).


See if you can find some tube that will fit inside or outside the failed
tube. perhaps 50 thou wall. fish mouth the ends. Rossette and end weld.
Take a look at CAM18. It gives specific instructions on repairing tubes.

Brian W

rattlesnake wrote:
hmmm....

found a tube which fits inside the failed tube, but how can I weld it in
then - just asking


....
The ends of the insert are tapered. Holes are drilled in the failed tube
to allow rosette welds of the interior tube, which have much the same
effect as through bolts, but rather lighter and stronger, if well done.

Brian W

hmmm.....

my idea was to take out about 1" of the failed tube and fishmouth(spelling?)
both open ends. Inserted tube (with about twice wall thickness) is visible
and can be welded in. How's about this?

"Brian Whatcott" schrieb im Newsbeitrag
...
rattlesnake wrote:
hmmm....

found a tube which fits inside the failed tube, but how can I weld it in
then - just asking


...
The ends of the insert are tapered. Holes are drilled in the failed tube
to allow rosette welds of the interior tube, which have much the same
effect as through bolts, but rather lighter and stronger, if well done.

Brian W

rattlesnake wrote:
hmmm.....

my idea was to take out about 1" of the failed tube and fishmouth(spelling?)
both open ends. Inserted tube (with about twice wall thickness) is visible
and can be welded in. How's about this?



I wouldn't even consider it, snake.

This mount BROKE.

It's either too light, or has a stress riser at the break - or both.
(I'm guessing both from the pic)

Consider yourself lucky (you dodged a big bad bullet) and build it again.

Better this time.




Richard

PS: Read Bob's Jesus Factor post again.
And take it to heart...

cavelamb wrote:
rattlesnake wrote:
hmmm.....

my idea was to take out about 1" of the failed tube and
fishmouth(spelling?) both open ends. Inserted tube (with about twice
wall thickness) is visible and can be welded in. How's about this?



I wouldn't even consider it, snake.

This mount BROKE.

It's either too light, or has a stress riser at the break - or both.
(I'm guessing both from the pic)

Consider yourself lucky (you dodged a big bad bullet) and build it again.

Better this time.




Richard

PS: Read Bob's Jesus Factor post again.
And take it to heart...


It would be helpful to know if there are any more samples of this
airplane design flying, and in particular, are there any more examples
of this engine mount in existence?
If there ARE, then that would focus the debate onto material defect or
construction defect or test rig defect.
Richard reminds us that you didn't see a permanent distortion of the
mount - which is the desired failure mode (supposing that any failure is
desirable) but a clean break - presumably two clean breaks. That should
not happen, ever on a test.

Brian W

oh, think I got it now with rossettes and fishmouths :-))


"Brian Whatcott" schrieb im Newsbeitrag
...
rattlesnake wrote:
Peter, Brian,

thanks for the bright thoughts. Think I know what caused the problem. Per
the plans my engine requires about 1.5" long spacers between the mount's
attach points and the engine itself. This creates an extra bending moment
which may have triggered the failure.

The mount is made of 3/4" 4130 tube with 0.035" wall thickness.

My current idea of repair is to weld a short round bar into the remaining
tube and so rebuilding the attach points. Maybe I'll shorten the spacers
a bit and bring some ballast further forward instead (battery).


See if you can find some tube that will fit inside or outside the failed
tube. perhaps 50 thou wall. fish mouth the ends. Rossette and end weld.
Take a look at CAM18. It gives specific instructions on repairing tubes.

Brian W