Having received the Mod 73 instructions on Friday afternoon, I have spent
the weekend working on 3 sets of tailplanes with the following results;
Adrian Lloyd, my inspector, has been around all weekend, and has inspected
at the relevant stages, and the owners have helped:
1 The aircraft are UK no's 10, 76, and 265; 76 and 265 are on the
airfield here at Shobdon, the tailplanes for 10 came by car.
2 Opening up all 6, ready for lay-up, was completed in 3 hours. We
were surprised by the differences inside - apparently early classic models
had TP6 positioned with the centre of the tube on the centreline of the ply
bulkhead, so the pip pin holes are not half way along TP6.
3 All 6 tailplanes had strong flox bonds attaching them to the ply
bulkhead, and none showed any sign of dis-bonding.
4 After opening up in the workshop, we moved down to the airfield
and positioned the tailpanes for 76 and 265 onto the TP4's of those aircraft
as instructed.
5 I did not consider that grease alone would be sufficient release
agent, and therefore on top of the grease I positioned a triangle of very
thin polythene sheet - sheet that I had been using throughout my build to
wet out lay-ups on, and then transfer the lay-up onto wherever it was
required. In the context of Mod 73, this sheet is so thin that it does not
increase the thickness of the grease - in fact, the opposite - and therefore
the flox "lip" is not compromised.
6 Because of the shorter than expected length of TP4 showing
through the dug-out hole on no's 10 and 76, because of the factor referred
to in 2 above, there was quite a gap between the bottom of the foam and the
TP4 itself; this needs either a very stiff flox mix, ("outside" the runny
flox mix on the TP4 itself) or an added fillet of foam, or both, because of
the fairly severe stippling required to get the BID layers into place
without any creases or air bubbles.
7 I worked on all 4 tailplanes at the same time yesterday; in
retrospect, I would do 2 at a time in future.
8 Around the dug-out hole, we have to stipple down the 2 BID layers
onto the sanded off skin; it was very hard work getting a satisfactory
lay-up, and I support the thoughts of those who have commented that a flox
joint would be better.
9 Today we returned the tailplanes for 76 and 265 to the workshop
for inspection and then (tomorrow?) covering. We then found that 10's
tailplanes would not fit onto either 76 or 265's TP4.
10 I have a short length of plastic pipe - almost the correct size -
around which I had previously wrapped masking tape to give a good fit into
my TP5 and TP6. We therefore wrapped one layer of the very thin plastic
sheet around what would be the TP6's band of masking tape and laid up one
tailplane; this was successful, and after 4 hours I turned the plastic pipe,
which immediately freed itself from the flox lay-up. I have now laid up the
second tailplane for 10.
11 On all 6 tailplanes, the two layers of BID stippled down onto the
sanded down 1" width of tailplane skin around the hole are already proud of
the painted surface outside them; there are another two layers to be added
when the holes are covered after final inspection, so there is going to be
more sanding off of paint required (another 1" at least all round), and then
lots of filler to blend the raised area into the existing tailplane surface.
How lucky that this mod is on the under side!
12 So this is definitely not a "one day to cosmetic finish" job!
Provided that I can get the last two tailplanes inspected tomorrow, I should
get all 6 covered by the end of the day - some of the foam plugs are already
prepared. Then the sanding and finishing has to be done.
I am lucky, because I had the aircraft, the materials, the workshop, and my
inspector all on site. We have discovered that the job can be done away from
the aircraft, but it is essential to be sure that whatever "insert" you use
is a good fit, and is properly fitted with a good release agent.
I hope this helps, and does not frighten anyone off!
David
G-BZAM - UK 265
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