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  #1  
Old 07-15-2007, 06:57 PM
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kens_cockpit kens_cockpit is offline
 
Join Date: Jan 2005
Location: Launceston, Tasmania, Australia
Posts: 79
Default Bending brake lines

I've been making the brake lines to run from the centre and then down inside the landing gear legs on my RV8QB.

I made the LHS beauthifully if I do say so myself (on the third go!). I thought I would use the LHS as a template for the RHS and just do the required bends in the opposite directions.

You know what happens next. I bent RHS one the wrong way at the first 90 degree turn. I decided I would just bend it back the other way using my tube bender. I figured if it cracked I could still use it to get the fit just right and make up another one.

Problem is I've run out of tube and it didn't crack and I finally got the bends just right and installed and after bruising my forearms inside the landing gear box I'm reluctant to take it out and redo it if I don't have to.

Will bending the 1/4" tube 90 degrees one way and then back 90 degrees the other way make it so weak it will split at the first sign of vibration? Or if it didn't crack during the bending will it be OK?

I'm inclined to replace it if there is any doubt.

Thanks for your thoughts.

Ken Stanton
RV8QB
Fuse plumbing and wiring
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  #2  
Old 07-15-2007, 07:31 PM
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airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,145
Default

I'm assuming your using stainless tubing here? I've done close to what you describe with 1/4" OD 316 stainless, .035" wall thickness. I've had pieces bent in 2" radius 90's that I later straightened out by pressing in a vise inch-by-inch to remove the bend, and then later bent that same area again in a different configuration. I've done this many times, have had no failures to date, and I pressure test all my tubing pieces to 10,000 psi before putting in service at 6,000 psi. Granted, most of my installs are low vibration with static pressures.

I recently had an pressure switch malfunction that took one of those bent-again pieces over 14,000 psi. The pump stalled, the tube held.

My 2 cents....
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid
N16GN flying 700 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, 430W
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.

Last edited by airguy : 07-15-2007 at 07:38 PM.
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  #3  
Old 07-15-2007, 08:05 PM
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Mel Mel is offline
 
Join Date: Mar 2005
Location: Dallas area
Posts: 10,768
Default These brake lines are aluminum not stainless steel

I would not reuse this aluminum tubing after 2 opposite 90 degree bends. The brakes carry quite a bit of pressure.
Make a new one and be comfortable.
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Mel Asberry, DAR since the last century.
EAA Flight Advisor/Tech Counselor, Friend of the RV-1
Recipient of Tony Bingelis Award and Wright Brothers Master Pilot Award
USAF Vet, High School E-LSA Project Mentor.
RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>
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  #4  
Old 07-15-2007, 08:27 PM
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kens_cockpit kens_cockpit is offline
 
Join Date: Jan 2005
Location: Launceston, Tasmania, Australia
Posts: 79
Default

I will do it again. I suspect I would have done it again anyway. I will be happier with the next one.

And if I can say Mel, though we have never met, due in large part I suspect to the fact we live on the opposite sides of the world, I have found your advice on these forums to be exceedingly helpful.

Cheers

Ken Stanton
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  #5  
Old 07-15-2007, 10:30 PM
Ted Farmin Ted Farmin is offline
 
Join Date: Mar 2005
Location: Sandpoint, Idaho
Posts: 104
Default brake lines

I made a pattern with welding rod first to get the exact pattern for both sides so as to not make a mistake for the second side.

test flew our 4 Fri. 13th
hands off no trim needed.
Ted and Tim Farmin
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