Pilot – June 2018

64 | Pilot June 2018 | pilotweb.aero

shapes for both sides of the nose

of each rib. You have to lightly

sand the side of the biscuit that is

to be glued on, or the glue won’t

take−aircraft plywood has a thin

protective coating.

Eventually I was ready to

assemble my first tailplane rib.

The glue I am choosing to use

on my Wot is the kind that isn’t

coloured; Aerolite 306. (The other

kind is red and works in two equal

parts like epoxy resin. It used to

be called Aerodux and is now

called Prefere 4050 Resin and

5750 Hardener. It isn’t acidic, so

I’ll be using it later in the project,

near metal fittings). Aerolite

comes as a powder in a tin and

acid in a bottle. You mix the

powder with water and can either

apply the resulting paste to one

side of the joint and some acid to

the other side, or mix acid and

paste together. If you mix them,

you have very little time in which

to apply the glue and then clamp

both sides of the joint together,

because once the glue starts to

harden it loses its strength. I

learned to use it mixed on the

previous Wot project and others,

and prefer it used in this way for

making lots of small joints.

Preparing the small batch of

Aerolite required for something

like a tailplane rib is quite an art.

I use a small wooden spatula and

the base of a disposable plastic

cup. Delicately dribble in a small

quantity of water, then, using a

plastic spoon, add about a quarter

of a teaspoon of powder. When

mixed it should be about the

consistency of pouring cream−

and you have to make allowances

for adding more thin liquid with

the acid. The quantity of acid,

ideally, is a single drop, which

gives a relatively slow ‘set’. Two

drops won’t weaken the glue, but

does give less time for applying it

before it starts to go off. I make

periodic tests on scrap plywood to

ensure that my gluing techniques

really are working; the test is

(after an overnight set), when

pulled apart, it’s the wood that

fails, not the glue. I made the ribs

in winter, which gives a slower

set, but still needed on average

two successive glue batches

per rib. This wasn’t me running

out of glue, it was the batch

showing signs of setting before

I had finished.

So, having mixed a batch, I’d

spatula glue on to each end of

each piece of lattice, spread glue

under each plywood biscuit and

then assemble everything. Next,

before the glue has a chance

to set, it all has to be stapled

together. I use a hand stapler

from B&Q and it’s quite an art

(again) to get each staple through

the biscuit and squarely into

the stripwood under it. This bit

requires both speed and accuracy.

Tip: paint an arrow on the head of

the stapler to show exactly where

the staple emerges.

Once secured with staples,

you can lift the rib out of the

jig. The glue will have set, but

not set hard, so it isn’t difficult.

After leaving the rib overnight

for the glue to gain full strength,

the next task is to remove the

staples. I do this with a sharpened

spatula eased under one end of

a staple, then long nose pliers to

lever out the rest. Now biscuits

can be glued on the other side

of the rib. I use butterfly clamps

rather than staples for this.

Feature | The slow-build Wot

THIS PAGE, TOP TO BOTTOM:

marking, sawing, sanding and

installing one part of the a wing

rib lattice