Hi! Shaun.
Sorry but it IS confusing if I (and probably Graham!) keep messing up on
the numbers !.
The TP6 bushes tend to take rotational load from the PIP pins and become
loose in the tailplane IF the tailplane rotational driving forces are not
completely taken by the offending drive pins, which elongate the holes in
the TP12 plates. Therefore it is recommended that the holes in the TP4 at
the PIP pins are slightly slotted (rotationally) since they are only there
to retain the tailplanes from sliding OFF the TP4 torque tube. This saves
the TP6's becoming loose, but also ensures that all the rotational driving
load is transmitted by the pins through the drive plates TP12's BUT they
elongate the TP12 holes being a softer material than the torque tube TP4.
Since the trailing edge is so far behind the centreline a minute amount of
wear at this place allows the trailing edge to move about 35 times as much!
I believe the limit between the two tail planes is 3/8ths" before you need
to take some corrective action. However it seems that in spite of
considerable care drilling /reeming the holes and in one of mine needing to
drive the pin into place with a hammer it still wears/tears the TP12 holes.
Our proposed clamp arrangement fixes the TP12's to the tube, TP4, and the
central drive TP9 (one each side) so the whole lot is locked up without any
change to the original design, leaving it all still dismantleable and
coincidentally stiffens the torque tube T4 in bending stresses.
Hopefully this enables you to come to grips with it all?
I strongly recommend some action to be taken before the top of the fuselage
is put on because it is a "BASTARD" job retrospectively especially if the
access hole is less than 5 inches diameter. It's bad enough at 5" diameter
with only one hand and pearing through the small inspection hole above.
Watch this space!
Regards
Bob Harrison. G-PTAG
-----Original Message-----
From: owner-europa@post.aviators.net
Subject: Re: tailplane torque tube reinforcing
O.K., now I'm REALLY confused.
1. Bob, just HOW are your tailplanes loose? fore/aft? side/side?
rotationally?
2. Graham, it seems to me that the TP14 pins in both TP9 and TP12 serve to
transfer the
torques from the pitch pushrod to the tailplanes, so they both have to
be precisely
fit. And therefore additional bearing surface would help. Unless
there's a bit of slop
between TP12's I.D. and the tailplane torque tube's O.D.
Am I missing something?
Shaun
A207
----- Original Message -----
From: "Graham Singleton" <grasingleton@avnet.co.uk>
Subject: Re: tailplane torque tube reinforcing
> >hi guys i`m at the point of drilling my tailplane torque tubes and was
> >thinking of bonding in a small section of aluminise bar inside the tube
> >directly inline with the pip pins,
> >would this be a practical idea to increase the surface area of the pins,
any
> >thought`s on the above would be appreciated
> >ivor phillips
> >XS486 trike
>
> No. These pins are supposed to allow a little fore and aft play, (but not
> spanwise) so that torque cannot be transmitted by the pip pins. This would
> put too much load on the bonded in TP12s
>
> Graham
>
>
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