KB3 owners

dabkb2

Dave Bacon
Joined
Sep 26, 2005
Messages
2,494
Location
Vista, Ca
Aircraft
Sport Copter Vortex 582, 2 KB2 90Mac KB3 582
Total Flight Time
529 hours
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.
 

BEN S

Super Member
Joined
Nov 15, 2007
Messages
2,750
Location
Guam
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Sportcopter Vortex
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300+
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

Senior Member
Joined
Feb 17, 2007
Messages
3,018
Location
DICKSON, TN
Aircraft
Grumman AA5
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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

Gold Supporter
Joined
Oct 30, 2003
Messages
1,091
Location
Avondale, Arizona
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

Super Member
Joined
Nov 15, 2007
Messages
2,750
Location
Guam
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Sportcopter Vortex
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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

Gold Supporter
Joined
Oct 30, 2003
Messages
1,091
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Avondale, Arizona
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.
 
Last edited:

BEN S

Super Member
Joined
Nov 15, 2007
Messages
2,750
Location
Guam
Aircraft
Sportcopter Vortex
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300+
I only ask as Dave still has his KB3 and
I know next to nothing about welding.
 

dabkb2

Dave Bacon
Joined
Sep 26, 2005
Messages
2,494
Location
Vista, Ca
Aircraft
Sport Copter Vortex 582, 2 KB2 90Mac KB3 582
Total Flight Time
529 hours
After seeing this I will be keeping a microscope on the motor mount until I can get it changed.
 

JEFF TIPTON

Senior Member
Joined
Feb 17, 2007
Messages
3,018
Location
DICKSON, TN
Aircraft
Grumman AA5
Total Flight Time
1350
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

Platinum Member
Joined
Jan 11, 2004
Messages
6,752
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

Dave Bacon
Joined
Sep 26, 2005
Messages
2,494
Location
Vista, Ca
Aircraft
Sport Copter Vortex 582, 2 KB2 90Mac KB3 582
Total Flight Time
529 hours
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.
 
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