REFLECTOR:Nose Gear Shimmy

[John Dibble]

Well, Chuck, it works like a charm!  I reduced the nose pressure from 40 to 18 psig
and no shimmy at high speeds.  Of course, as life goes, my test flight was a perfect
landing, touching down on the numbers at 70 kn, so I didn't give it the acid test.
However the following day after 6 hours in the air, it seemed that the Franklin was
not running smoothly at any prop pitch setting (it was probably just that I was
fatigued, or does the engine get fatigued too?), so I had an unplanned, and
less-than-perfect landing at 80+kn at Punxsutawney (3000 ft, and, no, I didn't see the
woodchuck).  Again, no shimmy at the maximum braking a Matco can offer.  I do get some
shimmy at ~ 15 kn, so ultimately I will balance the wheel, but the higher speed is
most important.  I haven't loosened the nut yet, but will do that soon for better
steering.
BTW, my flying club is having a fly-in breakfast on 9/1 (Labor Day).  We have a 3000
ft grass strip in the middle of the Finger Lakes (NY).  Dundee - D48.  If anyone is
interested I will provide more info.

John

Chuck Jensen wrote:

> Well, in answer to John's query about the pressure I carry in the nose tire,
> and contrary to Steve's experience, I found the softer-the-better, at least
> to the point that the tire is "squishy" when pilot/copilot is loaded.  On my
> first post, I was going to put in the pressures, then I thought that I might
> just be showing/confirming my ignorance.
>
> At that risk, the initial pressure was 16.5#, which was a shock when I took
> the reading because usually a smaller tire will have a higher pressure and I
> run my mains at 40#.  So, I pressured the nose to 35#, which resulted in the
> shimmy.  When I reduced it back to 15.0#, the shimmy was gone.  I then
> tightened the washers 1/3 turn to cinch them up a bit.  I haven't tried
> increasing the air pressure since tightening the washers.  I'm going to
> locate a good grass strip by my home base before I do that!
>
> Previously, I had the washers really tightened down and got tired of having
> to "punch" the brakes to get the nose to break loose for steering.  I
> disassembled the nose gear (it was pretty dry and grabby), cleaned, buffed
> and regreased everything.  When I put it back together, I tightened it to be
> somewhat less (though not measured) than the 15-20# recommended break-away
> force.  This worked great, easy to steer, until I increased the tire
> pressure and made the tire hard.  My theory is the slightly softer tire may
> incur greater friction and less bounce which reduces shimmy tendency, though
> Scott's experience is directly contrary.
>
> A possible side benefit of the soft tire is less stress on the nose gear
> during landing, particularly a hard one.  (I've never done one, you
> understand, but I hear stories about others with lesser piloting skills.)
> The slight compression of the front tire would seem likely to reduce the
> impact-shock if your nose drops on the runway instead of greasing it on like
> I always do.
>
> Chuck
> With ocean property in Arizona.