MATCO Tail wheel shimmy

44 posts in this topic

Posted

Problem with not enough "resistive damping" could be caused by missing "silentblock" or sort of flexible material inside U-strap in my case I think.

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Posted (edited)

Spiit lock washers are not the sameSpring Washer as bellville washers.  Here are some pictures of each.  JImChukImage result for belleville washers

Edited by 1avidflyer

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Posted

I was taxing with a 275 lb guy in the other seat.


 

275? Wow did you have hopes of getting off the ground?

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Posted

Not really just then.  just taxied him around in it.  The friend of mine that passed away a year ago did fly with me  a few times though, and he was about 6' 1" and weighed about 240.  We filled up the space for sure.  Maybe that's why I like the idea of widening the fuselage.  JImChuk

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Posted

No, Belleville spring and split lockwasher are two different things.  Belleville spring, if laid on a flat surface, is raised on the inside relative to the outside.  It's like a shallow cone, with elevation varying with radius only.  When compressed, the outer edge is in tension, and the inner edge is in compression.  It's a nonlinear "softening" spring; spring rate decreases with deflection towards flat.

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Posted (edited)

Jenki,

Belleville washers are washers that are not flat, they are cupped, and if not made of spring steel, have some spring to them so they keep pressure on the bolt/nut when they are torqued down correctly.  The amount of pressure can be varied by changing how much torque is applied to the bolt.

Mark

 

 

Jenki,

Belleville washers are washers that are not flat, they are cupped, and if not made of spring steel, have some spring to them so they keep pressure on the bolt/nut when they are torqued down correctly.  The amount of pressure can be varied by changing how much torque is applied to the bolt.

Mark

 

Oh, thank you, we call this spring washer, split lock washer ... now I understand

No Jenki, not a split lock washer, these are belleville washers. Nested stack increases the pressure available, inverted stack increases the range of operation. Nested and inverted increase both. They are not designed to be tightened down flat. Do an internet search on them.

https://www.mcmaster.com/belleville-disc-springs

P.S. I missed that others had already answered... had an image added too but it didn't make it.

 

 

Edited by marcusofcotton

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Posted

Spiit lock washers are not the sameSpring Washer as bellville washers.  Here are some pictures of each.  JImChukImage result for belleville washers

Thought this showed up the first time I posted it.  :-)  JImChuk

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Posted

Thank you very much. Better to have more answers than not know what is exactly going on.

I need to check it, better say, I will ask manufacturer as I am reaching 200 hours for inspection. I will ask for both, check of caster angle and U-strap settings (resistive damping).

It will be the last mandatory inspection (2 years since manufacture date) so they will do complete check. I didn't fly Bristell since 9th September till 5th December now (nearly 3 months) due to starter clutch repair (I am using old ROTAX 912) so I missed good or at least suitable weather here to fly to manufacture. Till the inspection it is still under warranty period and I need to be ready to bring all findings to solve.

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Posted (edited)

KSpiit lock washers are not the sameSpring Washer as bellville washers.  Here are some pictures h each.  JImChukImage result for belleville washers

Spiit lock washers are not the sameSpring Washer as bellville washers.  Here are some pictures of each.  JImChukImage result for belleville washers

Thought this showed up the first time I posted it.  :-)  JImChuk

 

this showed up the first time I posted it.  :-)  JImChuk

Hey Jim that second picture looks more like nord-locks than Belleville washers.:) Probably just the picture, here is a different one.

https://en.m.wikipedia.org/wiki/File:Belleville_washer.jpg

Edited by wypaul

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Posted

Jenki, not the same as split lock or spring.  both of those are to keep the fastener from becoming loose.  Belleville washers are to keep the connection from coming loose, or to keep constant, predictable pressure on a connection.  One use of them is when fastening a wooden propeller, so as the wood expands and contracts with humidity the connection to the hub stays tight.

Mark

 

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Posted

My high speed shimmy stopped when I tightened up the pivot nut enough to damp the wheel pivot, but at that happy place where the TW still castored and allowed me to turn. Took a little experimenting.

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Posted

Over kill for an Avid Flyer or Kitfox but worthy of mention is the solution used to fix the tail on Draco. Link here: https://youtu.be/j2WKyra8HBc

A small air cylinder with adjustable flow ports on the intake and exhaust could be used to dampen the Avid or Kitfox wheel similar to how the Draco was tamed. We had many hydraulic cylinder designs that used this idea to control flow under various load conditions. Those smaller air cylinders are made of aluminum and are very light and the flow restriction idea works for air just as well as hydraulic fluid. The gas block on an AR-15 is another example of a port being used to control gas flow rate. Many applications use needle valves to make the flow rate adjustable.

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Posted

Murphy aircraft and others have used fiberglass tailwheel springs.  I also made one for an Avid, but it cracked when I was taxing with a 275 lb guy in the other seat.  Picture is not of mine, but one I pulled off the web.  JImChuk

Image result for fiberglass tailwheel spring
 

Was it under built for the load or maybe the cloth needed to be run in a different direction? Did it totally fail or de laminate? Have you thought about building another?

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Posted

With the fiberglass spring, I think I got a couple of dry spots between the layers of fiberglass and that's where the crack started.  I never got around to building another, but I'm sure it could be done.   A friend of mine has been building a Murph Rebel, and he got a fiberglass tailspring from Murphy with the kit.  I used to have a main landing gear on my Himax that was all fiberglass.  Built by a guy out in Pennsilvania.  He has an interesting website describing how he built fiberglass parts.   Look at the fourth bullet point up from the bottom. Also he has a lot of other good info, including how to run a 2 stroke engine without cooking it. JImChuk

www.curedcomposites.com/
 

 

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Posted

1avidflyer, what did the fiberglass spring weigh? Seems like a good way to cut a pound or two.

 

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Posted

Not sure on the weight, but it has to be less then a steel tail wheel spring.  On the other hand, being that Avids are usually nose heavy, maybe that's not such a good thing after all.  JImChuk

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Posted

Hey Guys 

I have been successfully operating a fibreglass spring on my Catalina. It saved me more than 2 Lbs of weight compared to the double steel setup and it does not sag as much/a bit stiffer which prevents my rudder to be hit (remember the Catalina is extremely tail heavy compared to the other Avids ....static, wings unfolded I have about 110Lbs weight but when I fold the wings the weight goes up to about 220Lbs!!!)

I was going to make a spring but did not have the equipment to prevent air bubbles between the layup ( oven and bagging technique). I found the easy way to by a 84-96 Chevrolet corvette rear fibreglass rear mono leaf spring. like this one on ebay 

https://www.ebay.com/itm/Corvette-rear-fiberglass-leaf-spring-84-85-86-87-88-89-90-91-92-93-94-95-96-NYU/372502247525?hash=item56badd3865:g:OcgAAOSw8PJb7Jlq:rk:8:pf:0

With it I cut 4 different length to make the perfect one having good strength, rigidity and rebound. I tested mine to over 2000Lbs no problem

See the picture of my tail assy below. Last picture is the before..

 

P1100140.jpg

P1100141.jpg

P1100142.jpg

P1100145.jpg

P6230013.jpg

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Posted

With the fiberglass spring, I think I got a couple of dry spots between the layers of fiberglass and that's where the crack started.  I never got around to building another, but I'm sure it could be done.   A friend of mine has been building a Murph Rebel, and he got a fiberglass tailspring from Murphy with the kit.  I used to have a main landing gear on my Himax that was all fiberglass.  Built by a guy out in Pennsilvania.  He has an interesting website describing how he built fiberglass parts.   Look at the fourth bullet point up from the bottom. Also he has a lot of other good info, including how to run a 2 stroke engine without cooking it. JImChuk

www.curedcomposites.com/
 

 

Thanks for the link, that took me down a rabbit hole with some great information.

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Posted

There are enough opinions to go around on tail wheel shimmy.

MATCO sent me a couple bellville washers to put under the top nut.

John M

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