Wheel pants vibration

[round_peg]

We've been noticing that our main gear wheel farings are vibrating in cruise. We are not sure when this started (we've owned the airplane since June) or if it has always been present. Since buying the airplane we have removed the rubber tubing spacers and replaced them with washers (per advice here) and notched a semicircle into the bottom edge for access to the valve stems. Could the pants have become crooked or distorted during any of these modifications? Or is some vibration normal? We've got tundra tires, if that makes any difference. Thanks!

[Jim]

I have tundra tires, 300 hours and mine vibrate, right side more than left.

[Roger Lee]

Hi Mitch,

 

This is normal for the tundra wheel pants. Not as noticeable for the smaller wheel pants. Removing the rubber spacer and replacing it with the metal fender washer will reduce this. Make sure the screw is tight. Think how bad it see saws with that loose rubber spacer, you can't really tighten it well. At least the two washers sandwich it together and keep the hole from getting enlarged or broken out and then it would need to be re-enforced. When I repair these I usually put 6 layers of a 2" fiberglass patch there to strengthen the hole area.

[round_peg]

We will check the connection points and see if they need to be tightened. Are these vibrations typically something that can be felt inside the airplane?

[Roger Lee]

If they get bad enough, yes.

[Runtoeat]

Just a FWIW here. I used 3/4" stainless washers and cupped these to fit the contour of the depression for the attaching bolts. One cupped washer on the inside and a second one on the outside. Also smoothed and rounded off the edges of these washers. This was done so the bolts could be snuggly tightened (and locktited) to sandwich the wheel pant material without allowing the washers to cut into it. I did this at all three fasteners on the main gear wheel pants and the two fasteners on the front pant. I have a CTSW with tundra gear. Note: I had to repair both main gear pants due to the old rubber washers allowing the axles to finally eat thru the pants. Throw out the old rubber washers and just use steel washers as Roger suggests.

[Roger Lee]

The rubber spacer ( a piece of fuel line) was not a good idea. I have replaced everyone's with metal fender washers on the mains and solid plastic or metal spacers on the front and that allows you to tighten the pants front or rear to help keep them from eating the screw holes out. I find some wheel pant screws loose during inspections so make sure once in a while that you put a wrench on these and check them. If you torque them down well they usually won't come loose.

[Jim Meade]

I have a couple of buckets of bin washers left over from assembling grain bins. Maybe I'll try one of them. they are a washer with a piece of rubber cemented to it. For the bins, the idea is that they provide an air seal so if you run an aeration fan the air goes up through the grain not out a zillion bolt holes and that water does not wick in through the same holes and cause spoilage. Of course, mine is an ELSA.

 

 

 

 

 

 

 

 

[round_peg]

We've already done the washer modification, but perhaps not to the spec that Dick has suggested. I will have to ask my partner, who did the actual work. Perhaps some bolt tightening is in order.

[Roger Lee]

So long as the washer on the outside is small enough to fit inside the depression you are good to go. The washer on the back can be flat.

[cdarza]

Old topic revisited -  for the CTSW Tundra Wheel Pants ;   are your wheels pants rock solid in flight or do you get a little shudder?   I estimate mine shudder at least a few mm and usually it is not that noticeable but am curious if i should be trying something to get them to not shudder at all.  (noted as Roger mentioned that it is normal for them to move a bit - but does anyone have rock solid wheel pants?)

 

[Ed Cesnalis]

Mine shudder a bit but I can't feel it.  On take off I need to use the brake to make them quiet.

[Roger Lee]

If your brakes stop the vibration then your wheels need to be balanced. Put a 1" fender washer on the underside of the axle screw so you can tighten that screw down tight and stop the vibration. The washer will also help stop the screw hole from becoming larger from moving around on the bolt threads.

[sandpiper]

Bought my 2007 CTSW with Tundra gear when new. I am the only pilot. It has about 530 hours now. Replaced the rubber washers immediately after purchase. The wheel pants have vibrated slightly since day one. Also stick bump since day one. Back when Roger Heller was alive and lived just up the road I asked to fly his 2007 CTSW to compare. His was the same. My brain pretty much tuned this out since then.

[Tom Baker]

The wheel pant shake is likely due to the air not flowing smoothly around the pant. One way to find out would be to tuft the pant and video it in flight to see what is going on. My guess is the airflow is not staying attached to the rear 25 to 30% of the fairing and burbling off the trailing edge.

[FlyingMonkey]

I have the smaller, non-tundra wheels.  Mine vibrate quite a bit, and always have.  Enough that a friend noticed it in flight and said "ah, that's where that slight shake is coming from.  I rarely notice it, but occasionally I can feel it, especially in high cruise settings.  It has never caused a problem.  

It's possible that adding some weight inside the wheel pants might help this by giving more inertia to resist the movement, but it's also possible it might get worse because you have more weight to move around.  I meant to experiment with this a while back, but never got around to it.  I suggest if anybody tries weighting the pants to keep the weights near the center of the pants, around the center point of the wheels; weights far to the front or back will probably increase the motion due to the longer moment arm.  

[Roger Lee]

People have tried that and it took a lot of weight and didn't work that well. Put a 1" - 1.25" fender washer behind the axle bolt and tighten that screw nice and tight. That should keep the wheel pant from moving. make sure all tires are balanced.

'

[Anticept]

The vibration is probably from turbulent air currents coming off the prop. Not really an easy way to solve that problem except by Roger's method. Adding structure might help but again, weight.

[ct9000]

I had this problem on my sw on one side only. It was not properly aligned with the airflow so I loosened all the screws then re-tightened whilst holding the thing straight. I also had to slightly bend the bracket a bit. It appears that it does not need to be out much to cause this flutter.

[JLang]

So we are hopefully done with significant snow after this week here in the midwest, which means putting the main wheel pants back on.

Or not.  With them on I, too, usually get a noticeable vibration/flutter at cruise.  Checking tire pressure is a pain.  I figure it's only a matter of time before I neglect to warn a passenger and they use the fairing as a step.  Sure, there is a speed benefit: maaaybe a knot.  Admittedly, the plane simply looks better with them on, and this may rule the day, but for now I'm going to leave them off.  Am I missing something?

[FredG]

I took my wheel pants off years ago and I don't miss them.  I'm a knot or two slower.  I like not worrying about damaging them and I like having easy access to the tires and valve stems.   Personal choice.  

2006 CTsw (E-LSA)

[Roger Lee]

Always balance tires.

Wheel pants will vibrate, but you can fix that. Remove any rubber piece on the backside of the wheel pant. Place a large fender washer on the backside between the wheel pant rod and the outside of the wheel pant. This will sandwich the wheel pant and keep it from moving and vibrating and letting the threads on the screw eat the hole out larger. Tighten that wheel pant screw tight. The pant should not be able to move. I have done this on every single CT that has come through the shop.

Do the same for the front wheel pant. Place a large fender washer on the left side and the right side, but on the right side add a plastic or metal bushing about 3/8" long because there is a space there and you don't want to squeeze down the pant in an un-natural position. The spacer goes between the wheel pants and the spacer and the spacer is against the front wheel axle. Make sure these screws are tight. I find these screws too loose way to often. This will cause vibration, but more importantly cause the holes to wear out and cause the hole up inside the front wheel pant that sits over the positioning pint to wear out. With washers on both sides of the wheel pants and NO rubber make sure all these screws are tight.

 

Between the tire balance and the fender washers on the inside of the pants the problem will go away.

[FlyingMonkey]

Just a heads up, some CT wheel/tire combos are devilishly hard to get to balance without a ton of weight.  This is especially true of the smaller non-tundra wheels like I have, they are not factory balanced and do not have a mark to align with the valve stem.  I have had mine on some pretty fancy professional airplane wheel balancers, and could not get them to balance with 4 ounces of weights on each wheel.  I essentially ran out of space to attach weights.  I now get them "close enough" that they don't shake the plane on landing roll out and call it good.

BTW, my pants always shake in cruise (small pants).  I can sometimes feel it a little if I'm at higher altitude and cruising fast.

[Anticept]

Try checking the balance of the assembly without tire and tube. Then put your index marks on. Make sure that's in balance or reasonably close first.

[sandpiper]

Some say to put put some wheel weights on the rear "wall" of the pant just behind the tire and that this will help reduce the vibration. I tried it several years ago and didn't see a noticeable improvement. Probably didn't have the patience to do it right.

This problem is not unique to the FD. I've had about 6 Cessnas over the years and they all did it. Lived in Alaska so no pants. The worst was probably a C-180 with 8:50's.

What I'd really like to reduce is stick bump. Am tempted to put a plastic piece inboard of the flaps like on the CTLS to see if that will help my CTSW. Anybody messed around with a cure for stick bump?