Thorp Air Command - T18.net

This thread seemed like the right place to ask this question:
Is there any way to tell, by inspection, if a particular gear set is a Brock gear?

D

Not to my knowledge. Why?
Cubes

Why? My gear on N886Y came to me with cracks in all four places. I found a new assembly. It would be nice to know if it was a Brock before I buy, since the legend is that Brock gear don't crack.

D

That sounds like a question for Dan Eggleston, Dan you out there?

Ken Brock made a excellent gear. I have had two on my S-18. The second gear leg while installing the engine mount on it, one of the tabs that holds the lower mount attachment literally fell off and I had it welded back on. Tig welds are only as good as the welder.

All of my gear (3) have cracked. One was Jenkins and two were Brock. Ken Brock once told me they all came from the same place in the old days. As Bill Williams said, some of the TIG welds were mighty small.

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Bob Highley
N711SH
SN 835
KLAL

Brock gear were very good at least the ones I have seen. I have seen some gear legs that did have some welds that were a little skimpy, I have always prefered to have a good Fillet instead of just a fuse weld and I do believe most of the Brock gear I have seen had some pretty good Fillets. Cracket gear can be repaired, the cracks can be welded up providing the gear can be held in such a way that it has alignment. I have always used 4130 Tig rod on the landing gear, I know there are different alloys of rod that are compatible but I myself prefer the 4130 Tig rod for welding Landing Gear. Dan

Way back in the dinosaur days when gas welding was the norm and TIG was trying to get a foot hold, TIG got a bad rap because folks were using 4130 rod and it cracked. The reason the TIG welds were cracking and the gas welds were not was because there is a lot more heat in gas welding and the 4130 tubing, as well as the 4130 filler would pretty much get annealed in the process, thereby defeating the benefit of using Cro-Moly tubing in the first place.

I'm not sure when TIG welding made the scene, but I do know that Piper was still making Super Cub fuse's out of 1018 mild steel tubing as late as the 50s. If Cro-Moly *and* TIG came to the party around the same time I can see were the cornfusion could occur. Back in the day I imagine the ole boys were using coat hanger for rod but the mix of 4130 tube and rod and TIG and TOO MUCH heat made brittle welds.

Today, the current thinking for not only aircraft, but anything including Cro-Moly tubing weldments, including NHRA top fuel as well as NASCAR is: Filler rod, ER70s-2 or slightly better ER80s-D2 mild steel TIG rod, and the use of the absolute least amount of heat needed to form a puddle. The rule of thumb is blue/yellow weld, if it's grey it's too hot. A minimum of 70 deg. F ambient temp. and dead still air. And no post weld heating, none. Old plans that call out 4130 rod get ignored.

As Dan pointed out, 4130 filler rod used in a part that will be heat treated after welding, like our gear, is fine. I think our gear takes a lot of abuse, some more than others, eventually it stands a chance that it's going to crack.

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http://www.dixiefriedfabrication.com/

Cracked landing gear have as much to do with welding as how the pilot lands and what surface you taxi on. The Brock gear are no different
Cubes

So, Dan/Lou, are we saying that the modern miracle of TIG with ER70s-2 filler, and good welding technique, can lead to a successful repair without having to heat treat the entire gear set? I'd be willing to try that!

I wonder how many gear sets there are out there already flying that were repaired this way. (TIG)

d

I have repaired Gear with The Tig, even completely replaced gear legs that were bent too bad to cold streighten, without troubles. In each case I used 4130 filler Rod, no troubles. There are other fillers that are very compatible with 4130 that will do the same job. Clean all surfaces that will be welded, scale and such. I haven't welded on Gear in awhile, I have been welding quite a bit of mild steel and have been using ER70S-2, this is also compatible with 4130, and is used on Chromoly car frames it's pretty good stuff. My headers on my Bird are mild steel, but I welded them with 3/32 4130 chromoly filler Rod, 300 hrs ago. I have no problem at all welding on the A frame part of the gear for repairs, however I would not weld on the leg itself except right at the very top where it is mounted. I f I had to weld on the leg itself say for instance down at the axle mount, I would think seriously about have it a treated back up to 180,000 PSI, when It gets good and red,4130 will normalize. Dan

OOPS forgot to say , I agree with Lou, I always like to see a nice yellow fillet and sometimes it will have a little blue marbled in it, these are what we call perty welds......And yes, I did beat the crap out of my gear during training, sometimes it was pitiful, embarrassing and even sometimes scary.....Dan

I think it's a case by case bassist. If we are talking about a bend that does not kink the tube and a small crack like the 3/4 inch weld that crosses the tube on the bottom edge of the bottom mount then fine. the welder isn't going to put enough heat in the heat treated tubing re-welding that crack to hurt anything. There are a lot of guys that think that weld shouldn't be there in the first place. If the gear is more torn up than tha,t it might be time to rethink things.

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http://www.dixiefriedfabrication.com/

Thx. Agreed. Repair of gross damage to landing gear is a different problem for another discussion.

I'm just talking about the fatigue cracks that develop in the welds along the bottom edge of gusset that ties the cross tube to the outer leg tubes; a chronic problem for the aging fleet. If nicely TIG'd repairs are holding out well without HT, then we have a solution.

I have TIG welded several gears with these small cracks on these weldments and been quite successful over the years, even to the point where I have straightened the tube and welded the crack. I agree there is a time and place to scrap the gear and start over.