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Permalink Reply by John Austin on January 14, 2023 at 8:02am

Several years ago, Buzz (used to do the Buzz Air flight training) recommended using 3 of the urethane rubber pieces on each side of my 750 STOL's gear - one above and two below.  This provides some additional spacing so  you don't bottom-out the tensioning nuts on the studs, takes up any slop in the pads, and provides a greater range of compressing the rubber so you can more precisely adjust the compression and therefore the cushioning action of the rubber.

Later, due to the relatively rapid deterioration of the orange rubber pads, Jimmy Young suggested switching to pads cut from 60 durometer, 1/2" thick rubber stock from McMaster Carr.  Since this is thicker material, only one pad above and below are necessary.  These seem to be very durable and the rubber stock is very inexpensive!

In both cases, I've had no problems with shimmy on hard surface runways.

BTW, I don't know if it's a problem on the 701, but on my STOL 750 the original upper pads tended to get displaced outboard with use - never fell out, but it was worrisome.  When I cut my new pads, I cut the upper pads an inch wider and put the notches the same distance from the outboard edge so the result was the pads extend an inch further inboard.  This seems to clamp and hold the pads better and they haven't tended to creep outboard as before.

John

N750A

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Permalink Reply by Mark A Phillips on January 14, 2023 at 11:13am

Hi John- thanks for the feedback!  Not sure if the 750 bracket is the same- the SD750 bracket I looked at had a flat contact surface for the upper rubber.  On my 701, the contact surface is angled- basically the strut attach flange extends down to the rubber with a short section bent upward from the contact point on the rubber like a flattened "V".  This leaves a very small contact area that I believe allows for fore/aft motion (shimmy) when braking.  The plates I added simply allow for the upper rubber to have a lot more contact surface.  I also tried the 60 durometer from McMaster (I had spit the rubber out landing one time but used the same thickness as original- thicker sounds like a good option).  At that time I also began gluing the upper rubber to the gear with Goop.  Forgot to mention in original post that I've made maybe 15-20 landings since adding the plates so far without issues- will update if any problems show up.

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Permalink Reply by John Austin on January 14, 2023 at 11:32am

I believe the gear brackets are similar - on the 750 STOL there is also an upward bend outboard from the contact point.  When I removed one of the original upper pads, I noticed that the bend line of the bracket seemed to exert most of the pressure on the upper pad - you could see an indentation and it was very close to the inboard edge of the pad.  I think this pressure on the edge of the pad is why it tended to want to squeeze-out laterally.  That's why I made my new pad go an extra inch inboard so as to more center this bend-line pressure.  Looks like you accomplished the same thing by providing a flat metal surface to bear on the bracket.  As we say around here, "There's more than one way to skin a cat!"  (Sorry, PETA!) LOL!

John

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