VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.

  #31  
Old 11-29-2017, 05:52 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,080
Default

I read somewhere on VAF that adding balance weight to the wheel fairing nose helped a lot. Don't remember where I saw that, though.

Dave
RV-3B, skinning fuselage
Reply With Quote
  #32  
Old 12-03-2017, 07:32 PM
13brv3's Avatar
13brv3 13brv3 is offline
 
Join Date: Nov 2005
Location: Tellico Plains, TN
Posts: 566
Default

For anyone playing along, I ended up replacing the tires and tubes. I got a cheap balancer, and found that the left tire was significantly out of round, and would have required 2.5 oz of weight to balance. The right tire was fairly round, but still would have needed about 1.25 oz of weight.

The new 6 ply rated Desser Monster retreads with Airstop tubes are nice and round, and spot on balance. I literally couldn't identify a heavy spot on either tire/wheel combo. I had to open up the wheel pants a bit more to fit the monster tread, but it's back together now.

I decided to remove the left stiffener too, even though it wasn't loose like the right one was. I figure I'll have them both be the same when I install new stiffeners. For today's test, I had the wheel pants on, but no gear leg fairings or stiffeners. I'm going to leave the tires at 30 psi since the goal is to fix the problem with the stiffeners.

I didn't note the groundspeed for the original test in the video, but it was way faster than I hit shimmy today. Today, I could feel them starting around 7-8 kts, and by 10-12kts they were both going wild. The good news is that this is exactly what I would have expected, so it seems predictable. The tires are heavier, so I effectively added weight to the end of the "spring", and also made the spring less stiff. Both of those changes would reduce the resonant frequency, and that's just what happened.

Next step will be to install stiffeners as close to Van's drawings as possible. They allow for mounting these in front or rear of the gear leg, and I'm going to mount them on the front side since that's less in the way of my brake lines. With cold weather and a distant hangar, it might be a while before that happens.

Rusty
__________________
RV-8, SN-80587, built, flown, sold.
RV-3B, SN-10751, rotary engine, built, flown, sold
RV-8, SN-82470, built, flown, sold.
RV-3B, SN-11351, purchased, , flown, sold
A&P - 2018
Reply With Quote
  #33  
Old 12-05-2017, 02:06 PM
woodmanrog's Avatar
woodmanrog woodmanrog is offline
 
Join Date: May 2005
Location: Florida
Posts: 781
Default

When it's time to mount the stiffeners, be sure to TAPE them in place and make sure the fairings fit before permanent attachment.
Reply With Quote
  #34  
Old 12-05-2017, 07:26 PM
13brv3's Avatar
13brv3 13brv3 is offline
 
Join Date: Nov 2005
Location: Tellico Plains, TN
Posts: 566
Default

Quote:
Originally Posted by woodmanrog View Post
When it's time to mount the stiffeners, be sure to TAPE them in place and make sure the fairings fit before permanent attachment.
Thanks for the thought, but I'm way ahead of you worrying about the fairings

Rusty
__________________
RV-8, SN-80587, built, flown, sold.
RV-3B, SN-10751, rotary engine, built, flown, sold
RV-8, SN-82470, built, flown, sold.
RV-3B, SN-11351, purchased, , flown, sold
A&P - 2018
Reply With Quote
  #35  
Old 12-06-2017, 10:10 AM
13brv3's Avatar
13brv3 13brv3 is offline
 
Join Date: Nov 2005
Location: Tellico Plains, TN
Posts: 566
Default

Has anyone had success attaching a stiffener without the fiberglass? I've seen pictures of people using Ty-wraps, though there wasn't a report of how well it worked. I also know there's some really heavy duty reinforced packing tape that would probably work a lot better. You would probably have to replace it periodically, but it might be at least a temporary option.

The reason for asking is the sudden realization that it's too cold to apply the fiberglass. It's not impossible, but it would take a lot of extra effort to try to heat the epoxy and work surface. It would also be really interesting to be able to easily test different types of stiffeners, though I realize the fiberglass cloth does become part of the stiffener.

I need to make a 3 hour round trip to the cold (by my standards) hangar today, and since I need to remove the wheel pants again to increase the opening a bit more, I might do a taxi test without them. I'd expect that to increase the taxi speed where the shimmy occurs, and if it helps, I can easily see putting this whole stiffener project off until Spring when hopefully I'll have a hangar closer to home.

Cheers,
Rusty (I hate cold, and fiberglass)
__________________
RV-8, SN-80587, built, flown, sold.
RV-3B, SN-10751, rotary engine, built, flown, sold
RV-8, SN-82470, built, flown, sold.
RV-3B, SN-11351, purchased, , flown, sold
A&P - 2018
Reply With Quote
  #36  
Old 12-08-2017, 01:46 PM
Larco's Avatar
Larco Larco is offline
 
Join Date: Mar 2005
Location: DVT Phoenix
Posts: 1,254
Default Stiffener report

My 7 had, regardless what I did a shake right at taxi speed so I finally decided to install stiffeners. I read where tape worked well so I tried it and it did improve the shaking but not to my satisfaction. I just this week removed the tape and did the fiberglass attachment, It worked very very well, NO shaking and what a pleasure to taxi now. I wish I had done it a long time ago.
As someone earlier said tape stiffeners on first to get proper alignment with current fairings. Lots of work to glass them on but IMO well worth the effort.
__________________
Larry
Reply With Quote
  #37  
Old 12-08-2017, 02:36 PM
13brv3's Avatar
13brv3 13brv3 is offline
 
Join Date: Nov 2005
Location: Tellico Plains, TN
Posts: 566
Default

Thanks for the comments Larry. When you added the stiffeners with tape, did the speed of the vibration increase? If so, I'm assuming the speed increased even more with the fiberglass, probably to a point faster than you normally maintain a steady ground speed.

Rusty (snowing...)
__________________
RV-8, SN-80587, built, flown, sold.
RV-3B, SN-10751, rotary engine, built, flown, sold
RV-8, SN-82470, built, flown, sold.
RV-3B, SN-11351, purchased, , flown, sold
A&P - 2018
Reply With Quote
  #38  
Old 12-08-2017, 06:04 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,647
Default Alternative

For many years the standard attach method for Wittman Tailwind was the steel strapping bands used in packaging. Maybe four straps in the length of the gear leg. You would need to find someone to loan you a tool as I believe they are quite expensive.
Another separate issue I have not seen addressed is the fit of the gear in the lower end of the socket. It has become common on the Tailwinds to weld a bushing across the socket and cut a slot thru the center of the bushing and the end of the socket. AN5 bolt in the bushing, tighten to remove any play between the gear and socket.
Reply With Quote
  #39  
Old 02-08-2018, 09:41 AM
jliltd's Avatar
jliltd jliltd is offline
 
Join Date: Sep 2013
Location: Rancho San Lorenzo
Posts: 1,218
Default Success ridding RV-3B of shimmy

I just had great success eliminating my main gear shimmy in my RV-3B. My shimmy issue was primarily on taxi and exacerbated by concrete taxiways with expansion joints.

So after reading through this thread and others on the subject I ordered two Goodyear Flight Custom III 6-ply 5.00-5 tires and Michelin AirStop tubes. I went for the 6-ply for the stiffer sidewall to minimize flexing of the tire (i.e. shifting the natural frequency and reducing elastic perturbation). Load capacity rating was of no consideration. I went with the Michelin tubes after multiple failures of "leak guard" brand in various aircraft.

I filled the new tires to 45psi. Now things are smooth and nice on taxi like they should have always been. I am very satisfied.

My gear legs don't have the stiffeners (although I have a set of wooden ones in a box I had procured). Also, my wheel pants now ride higher allowing more clearance over hangar door angles. The ground stance looks better too.

So now the one and only thing that bothered me about my RV-3B has gone away. For now anyway. I fly it much more often which is super great.

Jim
__________________
Jim Ivey
RV-8
(and a few more airplanes)
Reply With Quote
  #40  
Old 02-08-2018, 01:07 PM
13brv3's Avatar
13brv3 13brv3 is offline
 
Join Date: Nov 2005
Location: Tellico Plains, TN
Posts: 566
Default

That's great new Jim. My plane might as well be in storage since the combination of work and weather have kept me away from the airport. I did manage one flight with a new set of dampers clamped to the gear legs, and there was no shimmy at all. I've since rotated the stiffeners to the front of the leg instead of the back, and await confirmation that it still works. Way too cold for epoxy, so it will stay temporarily clamped until later.

BTW, I never tried higher than 30 psi. Maybe I'll try that without the stiffeners before committing to epoxy.

Rusty
__________________
RV-8, SN-80587, built, flown, sold.
RV-3B, SN-10751, rotary engine, built, flown, sold
RV-8, SN-82470, built, flown, sold.
RV-3B, SN-11351, purchased, , flown, sold
A&P - 2018
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 04:56 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.