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Main gear shake starting around 45kt


ejb_64CT

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I have a 2007 CTLS with 550 hours on it. And I'm getting a very bad vibration that sets in around 45kt.

I replaced the brake rotor, pads and tires recently. I have what's called the Italian design. The new tires I uses are the 'Air Trac 6.00-6-6 ply'

The brake system I replaced was were very, very worn down. Frankly, I'm surprised it wasn't reported on at the 500 hour maintenance inspection.

The holes in the original rotors were elongated into an eliptical shape. The mounting pin contact areas had become egg shaped. You could actually hear the rotors clanking at slow taxi speeds.

I balanced the new tire/wheels on a dual cone motorcycle wheel balancer similar to this one at Harbor Freight
http://www.harborfreight.com/motorcycle-wheel-balancing-stand-98488.html

One tire comes out 'spot on' balanced and the other is out a very small amount.

The plane still shakes.

Does anyone have any suggestions as to what else I can check?

thanks
 

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One thought is whether the shaking is from the nose gear.  Has the pin/slot been checked for wear (if the LS uses the same system for maintaining steering alignment while also allowing vertical wheel travel)?  I have experienced a vibration from the nose gear when that system was worn (2006 CTsw).

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1) If one main is "out a very small amount", why not balance it so it's not? A tiny stick-on wheel weight at the right spot is an easy fix.

 

2) I assume you've spun each wheel to see if the tire itself may be out-of-round?

 

Finally, to avoid the "ovalling" rotor holes, I clean and then apply a tiny bit of disc brake lube to those pins monthly. This was after having one bind due to corrosion. Marc Ignegno, if that's what you have, now with 400 hours.

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I'd use a suction mount GoPro and take a look.  Under each wing, about out at the tie-down, you should be able to get a good shot of the nose and main gear.

My 2006 CT had the shake, and we always attributed it to cheap, unbalanced, Euro tires on the main gear.  'Turned out to be the front end.  If the pin or slots get worn, there is ample looseness to create quite a shimmy.  If you have one of the units that had unintended soft metal (not properly hardened), it could be easily the problem.  Have someone push the tail down and get the nose gear off the ground.  Then check the side-to-side and rotational tightness.

Back in the Day, FD replaced the part under warranty. 

Even the properly hardened part does wear, and if you don't get it quickly, it can cause plenty of additional wear quickly.  I've heard of over-size pins being fabricated to fix the slack.

Tim.

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One thought is whether the shaking is from the nose gear.  Has the pin/slot been checked for wear (if the LS uses the same system for maintaining steering alignment while also allowing vertical wheel travel)?  I have experienced a vibration from the nose gear when that system was worn (2006 CTsw).

 

 

 

Fred,

When you experienced that nose gear shaking, how many hours did your CTSW have on it?

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Start with these things first.

 

If it is the front end,

 

A nose gear on a CT can shake from day one. It is either an out of balance tire and or and very loose front suspension. Push the tail down an inch or so and see if the front wheel moves left to right or up and down. The nose wheel also turns constantly while flying. It should be most notable as you lift off for just out of balance and the loose front end shows up during landing and high speed taxi.

 

If it is at the main tire area it may just be the wheel pants. The wheel pants should have the piece of rubber hose spacer found on the CT wheel thrown away. Put a spacer and or a large fender washer behind the wheel pant so you can tighten the wheel pant screw down to prevent the wheel pant shaking. Same with the front end. Get rid of the rubber spacer and put a solid spacer between the wheel pant and the axle so you can tighten it down to prevent the shakes. Leaving any of these wheel pants loose will only eat the mounting screw hole out until it needs repair.

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You can easily tell if it is the maingear by pulling the brakes immediately after takeoff. If the shaking stops then it's the main wheels. As FastEddieB said, you need to lubricate the rotor pins regularly or they will wear abnormally.

 

The rotor pins may need to be replaced as well. If they are not straight, and look like they have a divot, then they need replacing.

 

The brake pads on the Italian marc ingegno wheels can be worn all the way down to 1 mm. This is because they are epoxied on and not riveted.

 

Stick on weights are dirt cheap. Any tiny amount of out of balance can cause shake.

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Thanks for all of the suggestions.

 

I didn't think to check the nose gear. I'll do that next. I can even try taxing/landing holding the nose off the ground.

 

My plane has a nose gear wheel-pant. The mains do not.

 

I did check the tires for out-of-round when they were on the wheel balancer. That checked out OK.

 

I'll also take the wheels off again and balance them to a 'T'

 

much appreciated

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ejb-64CT, Believe I met you during my trip to FD USA @ Woodstock this summer? A few additional thoughts:

My 2006 CTSW was recently repaired to fix a "shimmy" that developed @ about 650 hours. The front strut developed some play due to wear of the alignment pin. The pin is a round rod which is flatted in the sides. My 2006 has a pin with dimensions of 11mm x 8mm. The only pin now released by FD is a 12mm x 8mm pin. Installation of the new pin solved my shimmy. There is the possibility of both the pin and the slot the pin runs in being worn. Repair of the slot has been discussed elsewhere on the forum. New front struts are in the $3,000+ range and this does not include R&R costs so wear of the slot is a serious financial problem if this cannot be rectified. One might also be aware that a "wheel hop" condition can occur which is caused by a combination or one of the following: a flat spotted front tire, the front wheel is out of balance, worn out spring (older CT's) or urethane elastomers. One might ask "how could the front tire become flat spotted?". The flat spot developed from my poor landing technique during high cross wind landings in the first few hours I owned my plane. I allowed cross wind to push me sideways while only having the front tire planted on the runway. Not my best landings!

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Thanks, Dick.

I did have a flat spot on one of the main gear tires. But, I didn't check the front tire or its struts. I'll do that this week.

We haven't been able to fly, or even taxi, up here for several days. The winds have been over 20mph with gusts to 40.

I usually fly with my wife and she's going to try hitting the brakes immediately after I lift off. I want to see if the shake stops immediately.

Thanks for your suggestions. I hope I see you at Woodstock again sometime.

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Hello all,

 

I've found the source of my vibration problem. It isn't the tires.

 

The main gear itself has too much play in it. I had Dave Armando from Flight Design examine the plane, that's how I know.

 

Dave says there are some bushing in the main gear that probably need replacing. I don't know the details of what the main gear looks like inside the plane, so I can't describe it very well.

 

The CTLS parts and maintenance manual doesn't provide much in the way of an illustration ... it's funny because they have a full, exploded view of the wheel and brake assembly :-)

 

Anyway, it's beyond what I'm authorized to do, so I'm turning it over to Flight Design on the week of Nov 17.

 

thanks to all, for their suggestions.

 

ejb_64CT

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Hello all,

 

I've found the source of my vibration problem. It isn't the tires.

 

The main gear itself has too much play in it. I had Dave Armando from Flight Design examine the plane, that's how I know.

 

Dave says there are some bushing in the main gear that probably need replacing. I don't know the details of what the main gear looks like inside the plane, so I can't describe it very well.

 

The CTLS parts and maintenance manual doesn't provide much in the way of an illustration ... it's funny because they have a full, exploded view of the wheel and brake assembly :-)

 

Anyway, it's beyond what I'm authorized to do, so I'm turning it over to Flight Design on the week of Nov 17.

 

thanks to all, for their suggestions.

 

ejb_64CT

Are you referring to the sealed bearings in the wheel, or gear leg padding and bushings in the mount in the fuselage?

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