[rebel-builders] New issue FUS-30 thickness and FUS-30 doubler
Posted: Sun Feb 19, 2012 5:24 pm
With a reference plane of the center of the wheel, you correctly did not
show a moment at the center of the wheel which I will call point D.
After all a thin wheel would fall over if it had to depend on ground
contact to resist a moment. There would be shear in the axle at that
point but not a moment.
Similarly you should not expect a moment at A. I assure you that there
is no twist on my spring no matter how much I bounce the tail up and
down. So remove the statement "then at A, then at the moment point above
A." and your description then makes sense to me.
Alternately try working it from the perspective of moments acting on the
vertical part of the fork ie the solid section B-C There is a moment at
point B and C which cancel. No moment at A or D.
Or turn your diagram upside down and see if it makes sense. The forces
and moments will be the same. The fact that the weight vector passes
vertically through the mountpoint is what causes the magnitude of the
moments to exactly cancel. If it did not pass through the center there
would indeed be a moment and a resultant twist on the tailspring.
|
A|__ B
|
__|C
D|
|
Ken
Garry Wright wrote:
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show a moment at the center of the wheel which I will call point D.
After all a thin wheel would fall over if it had to depend on ground
contact to resist a moment. There would be shear in the axle at that
point but not a moment.
Similarly you should not expect a moment at A. I assure you that there
is no twist on my spring no matter how much I bounce the tail up and
down. So remove the statement "then at A, then at the moment point above
A." and your description then makes sense to me.
Alternately try working it from the perspective of moments acting on the
vertical part of the fork ie the solid section B-C There is a moment at
point B and C which cancel. No moment at A or D.
Or turn your diagram upside down and see if it makes sense. The forces
and moments will be the same. The fact that the weight vector passes
vertically through the mountpoint is what causes the magnitude of the
moments to exactly cancel. If it did not pass through the center there
would indeed be a moment and a resultant twist on the tailspring.
|
A|__ B
|
__|C
D|
|
Ken
Garry Wright wrote:
The concept seems rather simple actually. Looking at the tailwheel from
the rear in ascii form below we see various points of reference
|
|
A |______ B
|
| | One armed tail wheel assembly.
|_____ | C
|
|
The wheel is just a line - sorry my ascii art leaves a lot to be
desired. : )
The wheel creates a cw moment at C of weight x distanceAB in inch lbs or
whatever units you like. This must be countered by a moment provided in
an anti-cw direction at C by the member BC. This in turn is countered by
a moment at B, then at A, then at the mount point above A. If anyone can
adjust my understanding of the statics involved here I would appreciate
being un-misconceived. The fact that the weight vector does indeed pass
vertically thru the mountpoint is not relevant to the resolution of moments.
Garry
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