Rubber Discs for Shock Strut

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karmarepair

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So, its off to make a stack of aluminum washers, I am!
The aluminum washers provide a lot of frictional damping, as the rubber scrubs against the aluminum as it compresses. In most installations I've seen of this particular type, the washers are a good bit bigger in diameter than the uncompressed rubber, to maintain that damping action longer in the "stroke" and to keep the rubber from squishing right over the aluminum washers. One example in "Landing Gear Design For Light Aircraft" uses rubbers of OD 3.5" and washers of OD 4.75"

SOME gear of this type BOND the rubber to the washers.
 

Vigilant1

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A person could learn a lot about the damping and where it happens by dropping about 500 lbs on various stacks and see how far the load rebounds.
1) Existing metal spring
2) Appropriate height stack of bare rubber doughnuts
3) Same height as above, but with metal washers
4) As number 2, but with metal rod inside and a friction fit
5) As number 3, but with metal rod inside.

If trying to eliminate pogo effect, the rebound is more significant than the degree of deflection of the stack/spring.
 
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challenger_II

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Rebound: Hence, the use of what the Original Designer specified. :)
If correctly fitted, the rubber puck has X amount of rebound snubbing. As the rubber pucks become loaded, the rebound snubbing increases.

When you state "steel washers", are you referring to flat washers, or Belleville Spring Washers?
 

Vigilant1

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When you state "steel washers", are you referring to flat washers, or Belleville Spring Washers?
Flat ones (of AL, steel, whatever) that the rubber pucks scrub against during the "squish" and the subsequent "return to unsquished state".
The systems that have the compressed rubber pucks scrubbing against a metal cylinder that is around them work well, and the outer cylinder keeps grime and UV off the rubber. But, it is harder to inspect.
 

challenger_II

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Ok, so, after slaving away in the 100 degree heat, I have my aluminum spacer discs... coming! :)
Found an outfit that will laser-cut them, to specification! Inexpensively, too! Look, Ma! No cuts, and no aluminum chips on my clothes!
Awaiting parts arrival, with great anticipation! I should have a field report in about a week.
 

challenger_II

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Let me see the quality of their work before I post the link.

As for links, the link I posted for the rubber pucks is an outfit in Houston, and their product was spot-on.
The link another forum member posted, the initial order wasn't up to spec, however they were more than happy to make the pucks over, to a closer tolerance.
 

PTAirco

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The way it looks it needs a taller stack of rubber. The wheels are already splayed out at 1G with nobody nobody in it.
 

challenger_II

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That would not change the gear geometry. The lower section of the shock strut has a slot in the upper part of the tube, to limit travel. It is extended to the limit, whether with the original die spring, or the rubber disc column. I had to slightly compress the rubber disc column to get the cross bolt installed.
 

cluttonfred

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Hmmm...well, I agree with PTAirco that the pronounced negative camber seems like a bad idea. Ideally you want a little positive camber for the empty aircraft at rest so with the pilot aboard the wheels are completely vertical at rest.
 

Pops

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I preloaded my die spring for the normal flying weight, and for fine adjustment I used a large rod end on the upper end of the shock strut for adjustment of shock strut length.
Same rod I had left over from the 4 seat Bearhawk LG.
Not good pictures , but the rod end is on the upper end of the shock strut above the die spring streamline covering.
 

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challenger_II

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Well, while I agree with the premise the camber should be more positive, the Original Builder set the geometry when constructed, the plane has been in service for 29 years, and handles very well on the ground. My modification only addresses the deficiencies of the previous die spring installation ( if you didn't hold your mouth right, when landing, you found yourself galumphing down the runway) by using the rubber spring discs.
As previously stated, I do not wish to construct a new set of shock strut assemblies.
 
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