Hello Fred
"Ron...a picture's worth 1000 words...thanks, and I need a few more words:
I take it the shoulder of the screws is what penetrates the TT and
bushes, and both the CF tube and the embedded and threaded "base" you
turned help to keep the outer bush bonded in place."
The shoulder of the screw acts like a pin, instead of 2 balls to hold pin
in place I used threads (need a wrench for prying hands to remove). The
inner and outer bushings are glassed to plywood ribs. The CF tube is
glassed to each bushing and fillet that is holding bushing to rib. The
lower insert does not really help with bushing bond, it is glassed to CF
tube and rib fillet (perhaps helps a mini tad but not much). The top
receptical does not help bushing bond, it is bonded to recess and a bit of
CF tube on the bottom, and a flox ring on top bonds it to outer 2 UNI.
Sorry, not much in the way of more pictures, will try to describe:
1) First it is absolute imperative TP9 and two TP12s are well stuck to TT
TP4. You can search Archives "Ron Parigoris Torque Tube" for a description
how I made the fit right. Slop between TP4 TT and TP12 stabilator drive
arm, if enough will allow the pip pin, or in my case the shoulder screw to
begin to allow torque to be applied the the outer bushing. If built to
plans, the bond on the outer bushing is not tremendous robust, and if you
apply torque to it, it could easily debond where if no torque was applied,
it could have lived a happy life. Read the PFA procedure careful
describing wiggle of pip pins, they are trying to determine if torque is
being applied to outer bushing. Again if there was no motion between TP4
and TP12, the pip pins could not drive, only motion can allow the
undesirable drive. It is possible that there is motion but within
allowable limits. If this is the case it is possible you could debond the
outer bushing as described if the fit in the TT and outer bushing and pip
pin is tight. As described the only reason for the Pip Pin is to keep the
stabilator on the TT, and the TP12 drive arms engaged to the TP13 driven
bushings that are bonded into the root plywood rib. Just a side note my TP
13 bushings were bonded in place with rapid epoxy and only 50 % coverage
and also in the wrong position where the angle of attack was not the same
on both stabilators. Oval holes, well scuffed washer under the step on the
bushing and redux/Flox repaired. OK I hope not confusing too much, but the
pip pin only needs to contact to prevent any outboard movement. The fit to
the outer bushing can be fairly close and round, but the TT if radially
elongated (I did mine ~.020" each way) still will hold the Stabilator
inboard, but if motion developed between TP4TT and TP12 stabilator drive
arm, the TT elongated pip pin hole could not drive the pip pin (if less
than max. recommended motion) before the pin hit the side of the oval.
2) My "Mutilation" was done after my accelerated tailplanes were built.
The Redux used on metal first pass bonds a bit better than Aeropoxy. A bit
of flexibility that can allow things to load just a tad more even before
joint lets go. Idea is to make sure inner and outer bushings are well
stuck to plywood insert ribs. The club mod is a good one (although I still
like redux first pass on metal.) Connecting the bushings helps prevent
twisting forces from debonding. When only the inner bushing is taking the
full load when sliding on the stabilator to TT, there is a lot of force
due to leverage that can be applied to that lone bushing. The CF Rowing
skull oar has a very slight taper. The second the TT enters the CF it is
held from allowing this undesirable torque upon assembly, and it guides
the tip into the outer bushing.
3) OK so my inner and outer bushings are stuck to stabilator and each
other pretty good. If they stay stuck then the outer bushing is a fine
means to pin the stabilator to the TT. 006 pip pin recess dilemma is
trying to make sure that if the outer bushing debonded that the stabilator
was not allowed to move outboard and have TP12 drive arm pins, disengage
---From the stabilator driven TP13 bushings by ensuring that the pip pin
recess is strong enough to take outboard forces. I am not certain about
the minimum base requirements if plans not followed exact, but I suspect
it is to help hold the outer bushing a bit better. I was able to contact
with my glass reinforcement/filled a little more than 1/2 the
circumferance of the bushing from the bottom, and my CF tube had half of
it sneak around by twisting it so it was reduxed to the top of the
bushing! On a new build following the Club Mod is pretty easy, on
completed stabilators it took a bit more creativity.
Even though my outer bushing is stuck pretty well, I made sure my bottom
threaded insert is stuck well to the outer plywood rib. My top receptacle
is stuck on the bottom pretty well on the BID of the pip pin recess, then
I filled with foam and left a space for a flox fillet to the top 2 UNI
plies that completed the top and left it flat except for a perhaps 3/8"
hole.
4) One more time, my shoulder screw goes through top receptacle, top of
outer bushing, through top of TT that is elongated .020" each side,
through the bottom of the TT that is elongated .020" each side, through
the bottom of the outer bushing, through CF tube and glass, and into
threaded bottom insert.
First means to hold stabilator on TT is shoulder screw to outer bushing
top and bottom and TT top and bottom.
If Outer bushing debonded second means is shoulder screw to upper
receptacle to both sides of TT and on bottom CF tube, glass and insert.
Hope this is clearer than mud?
Ron Parigoris
|