KB3 owners

[dabkb2]

We had a KB3 go down yesterday at Corona. Surprisingly no injuries other than the gyro.

The motor mount broke!!!
The motor dropped about 6" and the prop cut the rudder cable. With the all flying tail it turned and made what should have been a non event into a spiral to the ground.

KB3 owners check your motor mounts on preflight. Ken made it lite to make ultralight weight.

 

[dabkb2]

Small helicopter-like aircraft crashes near Corona Municipal Airport – Press Enterprise

Small helicopter-like aircraft crashes near Corona Municipal Airport

First responders were called just before 1 p.m. to a construction yard near Rincon Street and Smith Avenue where the small aircraft had crashed.

www.pe.com

 

[BEN S]

IIRC when yours broke it was welded tubing?
How do you check for internal damage on something like that?
If theres no obvious signs like cracked paint on the outside?
He sure was lucky to walk away from that!

 

[JEFF TIPTON]

An old trick for testing steel tubing is to use an ice pick.

If you can penetrate the steel tube by pushing the ice pick into the tube, it fails the test.

 

[Mayfield]

Someone else may remember this better. Many years ago, Ken Brock and I had a discussion of hydrogen embrittlement in his 4130 tube structures. My memory says he would post weld bake his products at a pretty low temperature (<400F) for 3 or 4 hours. I don't remember the details, but I suspect Abid and/or Brian Rodgers is familiar with the process.

I remember Ken was disturbed enough that he was offering to take back, and send out for processing, his motor mounts

 

[BEN S]

So this is a known issue with KB type engine mounts?
Daves mount broke because we strapped it wrong for a highway trip to spanish forks, at least thats what we thought at the time, maybe it was already weakened?

 

[Mayfield]

So this is a known issue with KB type engine mounts?

Sorry Ben,
I'm trying to start up the "way back machine" and jump start my memory. I was at Ken's shop in Stanton, probably buying stuff. Ken was concerned about hydrogen embrittlement in a batch of welded and/or plated engine frames. I truly don't know if it is an endemic problem.

I "think" if I had an engine frame of this vintage, I might at least consult a good welder to see if he could recommend any curative steps. Another person on the forum that knows a lot about welded structures is Vance.

 

[BEN S]

I only ask as Dave still has his KB3 and
I know next to nothing about welding.

 

[dabkb2]

After seeing this I will be keeping a microscope on the motor mount until I can get it changed.

 

[JEFF TIPTON]

Sorry Ben,
I'm trying to start up the "way back machine" and jump start my memory. I was at Ken's shop (Anaheim?) probably buying stuff. Ken was concerned about hydrogen embrittlement in a batch of welded and/or plated engine frames. I truly don't know if it is an endemic problem.

I "think" if I had an engine frame of this vintage, I might at least consult a good welder to see if he could recommend any curative steps. Another person on the forum that knows a lot about welded structures is Vance.

 

[Doug Riley]

To my knowledge, hydrogen embrittlement is caused by plating, not by the welding process itself.

Weldments can have various problems of their own, some related to changes in the chemical composition of the metal brought on by heating and gases used -- e.g. absorption of carbon or oxygen.

IMHO, it's best to paint, not plate, engine mounts and other important welded pieces.

I use light colors on welded structures, as any cracks will then show up as dark lines.

 

[dabkb2]

To my knowledge, hydrogen embrittlement is caused by plating, not by the welding process itself.

Weldments can have various problems of their own, some related to changes in the chemical composition of the metal brought on by heating and gases used -- e.g. absorption of carbon or oxygen.

IMHO, it's best to paint, not plate, engine mounts and other important welded pieces.

I use light colors on welded structures, as any cracks will then show up as dark lines.

I think the motor mount is powder coated, it had a crack by the mast mount and when we cleaned it off to weld it didn't smell like paint.

 

['cycleflyer]

I'm REAL curios . Where did the weld crack ?

 

[dabkb2]

I'm REAL curios . Where did the weld crack ?

It broke on the rear cross bar right next to the motor bolt on the carburetor side.