Hi Ed, Don
You're right, of course. I spoke with reference to comparing a NEW
rubber donut installation with a NEW
Belleville installation because the specific complaint was that seven
years back NEW donuts and the spacer
package was still 1" shy of a "recommended height" that may have been
incorrect for this particular airframe.
Now, some seven years later, I would not be at all surprised if even
with the weight off the stack that it were
permanently "set" 1/4" shorter. Once the rubber donuts becomes hard
with age and compression, the "set"
taken does not expand much when weight is removed. It never occurred
to me that anyone would measure
that stack with the old ones in it since it is obviously well beyond
time to replace them. The "yearly height
loss is likely higher in hot climates than in cold ones and thus
difficult to quantify as an average.
What is of importance at present is the comparison of your "stack" with
NEW donuts to the one in the other coupe,
and my point was that regardless of whether donuts or Bellevilles were
installed the height of the "stack" going back
on the bird should be the same.
If a "tail height" problem still exists it must be corrected with
greater spacer height or returning to the 4" nose
wheel/tire arrangement. I continue to presume that Don has the Forney
nose fork with the 5" wheel and tire and
that is the actual "cause" of his "tail height" problem.
Any "permanent solution" should not be in the "stack" once it is back
"to spec.", and I would personally replace
donuts or shim Bellevilles at any annual that the tail is found to be
1" below LEVEL. That would probably be more
on the order of 2-3 years with the rubber units. Bellevilles should
last indefinitely unless operating off of an uneven
or deteriorated surface or in a flight training environment.
It sounds like 1/8" difference in "stack" or spacer thickness changes
your tail height 1".
Regards,
WRB
--
On Feb 27, 2009, at 22:44, Ed Burkhead wrote:
Bill,
I think you are right on all points, except . . .
If the mechanic measured the height of the donut stack while the
weight of the aircraft is on it, then a stack of tired donuts might
measure shorter than a stack of better donuts. The weight of the
aircraft would be compressing the stack.
Don,
Please go to Skyport’s website and page down to near the bottom.
Click on the link for information about the tail low and spacers.
Print out that information and it’ll help you calculate the thickness
of the spacer needed to fix the problem. This is the most up-to-date
version of the guidelines.
http://skyportservices.net/
Ed
