Okay, so I am getting a little concerned now. If what I hear is
correct, the inflight loads on the tail planes is not enough force to
cause the the elongation of the holes in the TP12. That would make
sense. So the primary cause is probably the fact the tail planes are
not balanced with relation to the tube position (hence the large mass
balance), and as a result, the vibration of running over rough ground
and engine/prop inbalance causes the tail planes to shake up and down.
This would cause large forces on the pin hole positions on TP12
causing elongation.
Would the act if decreasing the weight in the mass balance, and
inserting lead into the leading edge of the tail planes to retain the
balance not cure this problem. If the tail plane was more balanced
within itself, the forces on the pins would surely be decreased. I
know that this would add overall weight as the moment arm within the
limits of the tail plane is shorter than the mass balance but
hopefully it would improve the situation. Perhaps?
Any thoughts
Eddie
Quoting Fred Fillinger <fillinger@ameritech.net>:
> 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.
>
> The Europa List is supported by Aviators Network UK -
info@avnet.co.uk
>
/////Eddie Hatcher Bill Lams Nick Crisp///////
///SouthEastLondonFlyingGroup/////////////////
www.crispsite.flyer.co.uk/newropa.htm
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