It's curious also that Jim Thursby's post said only one tailplane was
real sloppy, so that would rule out service loads. I looked back at
the manual's method re TP12 where you drill the plastic collars. I
remember doing the plastic all on the bench, and fitting it to TP12
and pins on same bench, not in the airplane. A rat-tail file don't
ream nylon quick at all, I remember, but it kept my titanium drills
that are sharp enough for nasty razor cuts just handling them, out of
those metal holes to preserve tight fit of the pins. .001" of
accidental reaming is trailing-edge play already, and maybe the
increasing slop with flight time is first elongation of the holes in
the nylon spacer?
Can't challenge your calcs for sure, but maybe pulling G's makes the
balance weight heavier, making stick force lighter, so more
aerodynamic load must be built in to counteract - more load on the
pins. The calc I thus did was crude and potentially questionable, but
reflected this, and put the 3.8G load on the pins at more then you,
but seemingly OK.
Cheers,
Fred F.
McFadyean wrote:
>
> The "few" is actually the "many"!
>
> 13 ft.lbs times inertial load factor (3.8g)* = 593 ins.lbs
>
> Times 1.5* = 889 ins.lbs ultimate
>
> Times 1.5* = 1334 ins.lbs ultimate with nominal factor for non-interference
> fit/potential for light hammering.
>
> 2no. 1/4" pins bearing on 0.063" wall of 1.5" dia tube generates a
> bearing pressure of 27,587 psi.
>
> This should be well within the bearing strength of 4130 N.
> Hence, in my very first contribution to this thread I caveated my response
> that I could not get the tube to fail by means of calculation.
>
> Nevertheless, they do fail and, as Bob Harrison has pointed out, it is not
> the 4130 tube that fails. Rather, the stainless tube instead. All we need
> to do now is find out what grade it is.
>
> (* Ref. Bruhn "The Analysis of Flight Vehicle Structures", JAR-VLA and
> others).
>
> Duncan mcFadyean
>
> On Saturday, January 19, 2002 4:30 AM, Fred Fillinger wrote:
> > Indeed true, and I see where I made it sound like the mass balance has
> > no effect, but I measured it. It takes only about 13 foot-pounds to
> > lift the balance weight. That's about 1/20th of that required to
> > elongate
> > two 1/4" holes in 4130 at least, to the point of noticeable play, in
> > my test. Maybe 13, reflecting inflation, is still a "few?" :-)
> >
> > Best,
> > Fred F.
> >
> > > The "few pounds of rotational force" is the weight of the
> counterbalance
> > > times the length of the arm it sits on. Same difference in trimmed
> flight
> > > where any air-load eccentricity is reacted by the effect of the trim
> tabs.
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