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  #1  
Old 06-27-2013, 05:41 PM
kritsher kritsher is offline
 
Join Date: Feb 2007
Location: Stow MA
Posts: 165
Default pulls to the left when taxiing

My relatively new (6 hrs) RV-12 seems to pull to the left quite a bit during taxiing.

First, I thought it was weathervaning from the wind until I realized it was always in the same direction.

Then I thought the left brake pad was catching, but I can roll that wheel by hand no problem. The brake assembly has a little play and I can see daylight between the disk and the pads.

Then I thought one of the brake cylinders wasn't free to rotate where it's attached to the pedal, causing it to maybe stick occasionally in the engaged position, so I loosened the bolts there by one or two castellations.

I'm running out of ideas. Any thoughts on how to troubleshoot this?

Thanks!
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RV-12 #359
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6B6 - Minuteman Field, Stow, MA
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  #2  
Old 06-27-2013, 07:00 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,957
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Quote:
Originally Posted by kritsher View Post
My relatively new (6 hrs) RV-12 seems to pull to the left quite a bit during taxiing.

First, I thought it was weathervaning from the wind until I realized it was always in the same direction.

Then I thought the left brake pad was catching, but I can roll that wheel by hand no problem. The brake assembly has a little play and I can see daylight between the disk and the pads.

Then I thought one of the brake cylinders wasn't free to rotate where it's attached to the pedal, causing it to maybe stick occasionally in the engaged position, so I loosened the bolts there by one or two castellations.

I'm running out of ideas. Any thoughts on how to troubleshoot this?

Thanks!
Since it sounds like you checked everything related to a possibly dragging brake or wheel friction... did you check axle alignment and shim if needed, when installing the gear legs and axles?
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  #3  
Old 06-27-2013, 07:47 PM
JAT JAT is offline
 
Join Date: Feb 2007
Location: Durango, CO
Posts: 126
Default

Ken,

Check out today's thread titled, RV12 Rudder Pedal Extensions by RV12Roger. My RV-8A would come to a stop when I tried to do a 180 and back taxi. I found out that my clodhoppers were applying the brakes. I made extensions out of alum. angles and bolted them to the bottom of my pedals and it worked. It is something to look at. Good hunting. If you would like to see a picture of my setup send your email address to jpthornton at frontier.net.

Jim
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  #4  
Old 06-27-2013, 08:16 PM
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Jesse Jesse is offline
 
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Location: X35 - Ocala, FL
Posts: 3,648
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I assume you have already checked tire pressure. That would do it.
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  #5  
Old 06-27-2013, 08:19 PM
kritsher kritsher is offline
 
Join Date: Feb 2007
Location: Stow MA
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Default

Thanks for the suggestions, guys.

Scott, I did check the axle alignment during the build, but it feels like I should re-check it. Are there any tricks out there for checking axle alignment without jacking up the plane and taking off the wheels?
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  #6  
Old 06-27-2013, 08:36 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
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Mine sometime pulls right or left. I attribute it to friction in the nose wheel castor because I can usually stop it by tapping the brakes until it centers
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  #7  
Old 06-27-2013, 09:21 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Quote:
Originally Posted by kritsher View Post
Thanks for the suggestions, guys.

Scott, I did check the axle alignment during the build, but it feels like I should re-check it. Are there any tricks out there for checking axle alignment without jacking up the plane and taking off the wheels?
Not a trick really, but you could get a good idea of the situation with a couple of straight edges (4 ft carpenters levels). Lightly clamp one to the outside of each tire with them parallel to the ground. Drop a couple plumb lines from the belly center line and measure front and back to see if the values are all close to the same. Checking 2 ft for and aft of the axle should be more than enough distance to detect if things are off very far.

Your next question would likely be how much is acceptable. I don't know the answer to that. You could calculate the value based on what the KAI suggests, but I think the best thing to start with would be just verifying if there is a difference between left and right.
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  #8  
Old 06-30-2013, 05:56 PM
kritsher kritsher is offline
 
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Location: Stow MA
Posts: 165
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Using Scott's technique, it appears that the right wheel is about 1/4 degree toe-out and the left wheel is about 1/4 degree toe-in. One quarter degree does not seem like a lot (given that the smallest shim is 1/2 degree). On the other hand, if both main wheels are angled off to the right, it makes sense that the nose would want to go left.

So, two questions:
1. Does anyone think that 1/4 degree could cause a significant tracking problem? and if so:
2. Is it better to shim the left wheel 1/2 degree so that both wheels are a tiny bit toe out, or is it better to shim the right wheel 1/2 degree to that both wheels are a tiny bit toe-in?
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  #9  
Old 06-30-2013, 06:36 PM
JBPILOT JBPILOT is offline
 
Join Date: Nov 2007
Location: Jesup, Iowa
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Default Hey Ken - -

what speed are you using to judge it turning during taxi ?
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  #10  
Old 06-30-2013, 07:06 PM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,754
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It seems to me that no matter how many degrees the main wheels are out of alignment, the nose wheel has much more affect. For instance, if the main wheel is pointed 1 degree to the left and the nose wheel is pointed 15 degrees to the right, the plane is not going to pull to the left. The direction that the nose wheel is pointed needs to be known before looking for other causes.
A GoPro camera would come in handy for this situation.
Joe Gores
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