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  #1  
Old 05-24-2021, 11:00 AM
rcarsey's Avatar
rcarsey rcarsey is offline
 
Join Date: Jul 2012
Location: North Brunswick, NJ
Posts: 236
Default dragging brake

I finally got around to troubleshooting a dragging brake problem I've had from the beginning. This was an interesting one..

The symptom was that the plane would pull to one side pretty hard regardless of how much engine torque was applied. I got the plane up on two horses. One wheel would rotate relatively freely (like 1 or two fingers on the wheel could provide enough force to make it rotate), while the other would have a dragging brake (you need your entire hand on the wheel to give it enough force to rotate). The problem existed for only half of the rotation.. NOT throughout the entire rotation of the wheel.

I dug out my runout gauge and found that the good wheel/rotor had 0.005" runout, while the "bad" wheel/rotor had 0.030" of runout. I disassembled the wheel halves thinking perhaps I had a bit of debris that got sandwiched between something during assembly. Everything was clean.

I mounted the wheel's center hub/bearings and its rotor to the plane's axle. The problem still existed. I swapped rotors between the two wheels (attempt to confirm or rule out the rotor itself). The problem followed the wheel, not the rotor. I examined the wheel's center hub.. and found the issue. Apparently one of the three "spokes" of the center hub was machined down exactly 0.020" too much. I sandwiched a feeler gauge between the hub and rotor and re-measured the runout.. which was now 0.004". (see photo)

I usually attack problems as "what did I do wrong this time?" rather than a manufacturing problem.. so it took me a long time to get down to the root cause of the issue. I have a call out to Matco, but for now, the shim is working very good with greatly improved ground handling. The next time I put the plane up on horses, I'll most likely replace the hub (about $50 new from Matco)
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Rob Carsey, North Brunswick NJ
RV-12iS (N713) / Completed 12/2020
ASEL, Glider, AGI/IGI, LSRM-I, FCC GROL
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  #2  
Old 05-24-2021, 12:48 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,136
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Quote:
Originally Posted by rcarsey View Post
I finally got around to troubleshooting a dragging brake problem I've had from the beginning. This was an interesting one..

The symptom was that the plane would pull to one side pretty hard regardless of how much engine torque was applied. I got the plane up on two horses. One wheel would rotate relatively freely (like 1 or two fingers on the wheel could provide enough force to make it rotate), while the other would have a dragging brake (you need your entire hand on the wheel to give it enough force to rotate). The problem existed for only half of the rotation.. NOT throughout the entire rotation of the wheel.

I dug out my runout gauge and found that the good wheel/rotor had 0.005" runout, while the "bad" wheel/rotor had 0.030" of runout. I disassembled the wheel halves thinking perhaps I had a bit of debris that got sandwiched between something during assembly. Everything was clean.

I mounted the wheel's center hub/bearings and its rotor to the plane's axle. The problem still existed. I swapped rotors between the two wheels (attempt to confirm or rule out the rotor itself). The problem followed the wheel, not the rotor. I examined the wheel's center hub.. and found the issue. Apparently one of the three "spokes" of the center hub was machined down exactly 0.020" too much. I sandwiched a feeler gauge between the hub and rotor and re-measured the runout.. which was now 0.004". (see photo)

I usually attack problems as "what did I do wrong this time?" rather than a manufacturing problem.. so it took me a long time to get down to the root cause of the issue. I have a call out to Matco, but for now, the shim is working very good with greatly improved ground handling. The next time I put the plane up on horses, I'll most likely replace the hub (about $50 new from Matco)
I would assume that hub was machined on a lathe and therefore hard to get one spoke low u less the operator got the assembly cocked a bit on setup. I would press out the bearing races and look for a burr or debris that caused the race to be canted. That would better explain the run out.

Disregard. On further look it was probably done on a cnc mill.

Larry
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Last edited by lr172 : 05-24-2021 at 12:55 PM.
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  #3  
Old 05-24-2021, 03:59 PM
funflying funflying is offline
 
Join Date: Oct 2006
Location: arvada, co
Posts: 484
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Thanks for the post and doing the runout checking. Ive been chasing a left turning issue while taxiing for years and cant seem to determine the cause. Your work will give me something else to look at with my Matco setup.
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RV12, #401, Flying 2013, N612PC
RV6, 1996-2010 sold
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  #4  
Old 05-24-2021, 09:11 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 3,068
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The first homebuilt I did was a plans built WAR FW-190 with Cleveland brakes. When I put everything together both brakes dragged badly. I solved the problem with a .01 shim plate between the calipers.

Fast forward a few years when I sold it to my German cousin, a Sierra Hotel Bundesmarine Tornado fighter pilot. He had just retired and reassembled the aircraft after shipping. He flew it into his old airfield, Eggebeck for an air show. He let it roll out for awhile and then applied the non existent brakes. Fortunately the runway was very long. When he got to parking he could hear the brake fluid boiling. He had taken out the shims!

Incidentally it was the first FW-190 since 1945 that had landed there.😁
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