There is a slight misunderstanding regarding where the wear in the
"torque tube assembly" occurrs. The torque tube itself is a hardened
(possibly crome moly) steel.
Having just implemented Mod 62 we found that there was no noticeable
wear in the torque tube itself. All the wear occurred in the TP9 and
TP12 components as these do not appear to be hardened steel (or as hard
as the torque tube itself).
You are right about the reaming needing to be done accurately and it is
advisable to drill each hole from the outside and not through the tube.
The reaming should also be done from the outside and not through the
opposing holes. The factory specified drill size and reamer is crucial
(23/64 drill and 3/8 reamer) - dont be tempted to use a 3/8 or 9.5mm
drill - it will ruin the job. Incidentally we measured the factory
supplied pins and found them to be a couple of thou oversize which is
probably a good thing.
The factory instructions say you should ream through the whole assembly
but our experience was that this opened the holes out too much with a
slightly looser fit. We practiced on a spare piece of mild steel tube
before risking our engineering skills on the real thing. The purists
among you will say this leads to misalignment of the holes however under
the circumstances we found this simply made for a tighter fit.
We drilled and reamed all the holes individually making sure the
opposing hole had a TP14 pin inserted half way. We then assembled the
whole assembly once on the workbench and it was necessary to lightly
hammer all the pins into place.
We thought it prudent to assemble at least once in case of a possible
misalignment even though this process will have started to wear the pin
holes. The risk of discovering the misalignment down the back end of the
tailplane and the attendant possibility of being unable to remove the
pins was not an option we wanted to contemplate. In the final event a
fair amount of tapping with a hammer was needed to fully drive the pins
home but has resulted in an excellent solid fit. Only time will tell how
good a job this makes.
Carl Pattinson
G-LABS
PS: Im not sure the bolted option will prevent wear/ elongation of the
holes. I had a Shadow pre the Europa and a lot of the tubular
components were held together using bolts - in time the holes still
elongated.
I did suggest to Andy that perhaps building the counterweights into the
leading edge of the tailplanes would eliminate the need for the
counterbalance arm but he was quick to point out this would require a
substantial increase in the weight needed due to the relatively short
distance between the torque tube and leading edges. Ultimately this may
not be as big a problem as it seems since many Europas with heavy VP
props have additional weight in the rear anyway. If this could be used
to counterbalance the tailplane it would be likking two birds with one
stone.
Still I am not a design engineer and I havent done the sums - and
wouldnt know how to.
----- Original Message -----
From: William Harrison
To: europa-list@matronics.com
Sent: Sunday, June 24, 2007 12:07 PM
Subject: Re: Europa-List: Tailplane flutter
Thanks Ian
The bolted option sounds like good engineering if done properly.
One other idea I have heard suggested, (by Tony Kay) is that a snug
fitting inner tube is assembled, eg with Bearing Fit /retainer grade
Loctite, into the torque tube, basically to make the whole thing
thicker-walled and therefore to reduce the contact stress of the
pin/tube contact areas. I think it would be a machine shop job to get
the drilling and reaming done accurately so obviously the torque tube
would have to come out.
The other option might be simply to junk the existing torque tube and
substitute something beefier (thicker walled and or harder). Not sure
how the CofG works out for a mono but most trigears seem to have a hefty
lump of lead in the tail so they could presumably take the extra weight
of a reinforced or beefier torque tube with a corresponding reduction in
the ballast weight.
By the way, I think it is highly enlightened of Francis to invite
ideas from owner/builders. Most of us know from uncomfortable experience
what practical implications are put on any solution by the access
issue, to say nothing of being "stakeholders" in the success of the
outcome.
Thanks for your good work.
Willie Harrison
On 24 Jun 2007, at 11:13, G-IANI wrote:
William
The idea of the bolt option is that it does two things. a) It
clamps the two parts together. b) to ensure the tubes stay round a cross
drilled spacer is fitted inside the TP4 tube. This is Loctited in. So
you have both clamping and a glue joint but retain the ability to
dismantle.
This is not PFA approved at present but has been discussed with Andy
Draper in 2005.
Francis Donaldson asked me on Friday to pool any ideas we have on
eliminating slop in this area. He wants to address this as part of any
solution to the present problems. I will have a document ready for him,
by tonight, summarising all the options (existing pins, big pins, taper
pins, Bobs blocks and bolts). If anyone can think of anything else I
will be glad to hear from them.
If the PFA decides that bolts is the way to go, then we will have it
documented and approved very quickly.
Ian Rickard #505 G-IANI XS Trigear
Europa Club Mods Rep (Trigear)
e-mail mods@europaclub.org.uk
or direct g-iani@ntlworld.com
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