Pilot – June 2018

pilotweb.aero | Pilot June 2018 | 63

Feature | The slow-build Wot

insist on the owner doing at least
51 per cent of the work, so a great
deal can be farmed out, but if you
pay others to do the specialist
stuff you will end up with an
aeroplane worth a fraction of
what it cost to build.
I intend to do as much as
possible myself, and that
includes making all the metal
fittings, the covering in fabric
and painting, but even I will still
be farming out a huge amount.
I could−but won’t−make my
own turnbuckles, for instance.
Or instruments. Or−taking it to
extremes−turn my own bolts,
weave my own cloth and make my
own dope, paint and glue. And I
could, but I won’t, make my own
propeller. It’s all relative.
There are no kits for the Wot,
but the LAA will sell you a set of
plans for eighty quid. The design
started life in the 1930s as a
scaled-down de Havilland DH60
Moth with simplified construction
and a single cockpit. Over the
decades the plans have been
copied, updated and altered. For
instance, Dr John Urmston came
up with a list of modifications to
allow aerobatics, and these were
included in the package sent to
me by the LAA.
I decided to begin the
construction of my Super Wot (a
clipped-wing variant) with the tail
surfaces, and drew up a cutting
list from the plans. I sent this to
SkySport who accepted the order
and delivered the wood cut to
size around six months later, with
a bill for £750, which sounded
rather steep, until I stopped to
consider what exactly I was paying
for. And that, in a word, is labour.
It takes a long time to saw and
plane wood to size and my first
tip is don’t pay someone else to
do it, do it yourself. I did later
on, with the wing rib stock, and
it isn’t difficult. In fact, it’s quite
satisfying. (Perhaps making my
own turnbuckles isn’t such a crazy
idea.) The stripwood and more
bulky items, such as the tailplane
spars all have to conform to fairly
strict rules. The grain must run
straight and have a reasonable
density of grain lines. Obviously
you can’t have any knots or
wood discolouration. SkySport’s
wood was perfect in every way,
possibly rather more so than
strictly necessary.

I began by making the tailplane

ribs. These are built up from strip

wood in a lattice shape, with

plywood ‘biscuits’ glued over each

junction. The Wot’s tailplane has a

fairly thick, but flat cross-section

and the curved leading edge

is covered with thin plywood.

The ribs are directly under this

plywood, supporting it.

My first job was to devise

a means of steaming the rib

‘booms’−they run continuously

from trailing edge to trailing

edge with a sharp curve in the

middle at the tailplane leading

edge. I drilled a hole in each

side of an electric kettle to make

the steamer. The next task was

to devise some kind of former

to produce the bend. Using my

bandsaw I cut a suitable curve in

a piece of thick plywood, splitting

it in two. Clamping the two halves

together with the steamed rib

boom in between them ought

to produce the desired shape. I

tried first with scrap wood. I gave

it two minutes in the steamer,

then placed it between the two

halves of the former, clamped in

a vice, and carefully forced the

two halves together. The scrap

wood snapped long before it had

anything like enough curve.

I experimented with different

steaming durations and style, and

with more closely grained wood

(which helped), but couldn’t

get anything like the required

bend. Could I have mis-read the

plans? No, they did call for one

continuous rib boom. Both sides

of the rib had plywood glued on

at the nose, so that must be the

main source of strength, not the

rib boom. It was tempting to cheat

by substituting a block spacer,

but I decided to persevere. In the

end, the solution was to steam

a modest bend in one former

and allow it to set; then after

more steaming, a tighter bend

in a second former; finally the

tight bend called for in the plans.

Three sets of steaming, allowing

an overnight set between each.

Fortunately I had over-ordered

the rib stock because, despite

this cautious approach and the

excellent quality of the wood, two

booms snapped before the third

in the series of formers could be

clamped shut.

So now I had a set of shaped rib

booms. The next job was to make

a jig to form the ribs. I stapled

greaseproof paper on to a sheet

of thick plywood, then drew on

it an outline of the latticework−

dimensions are in the plans.

Next, I screwed on a dozen pairs

of plywood blocks, one pair for

each component of the lattice (i.e.

length of stripwood). This ensures

that each rib exactly matches the

others. The idea is to cut lengths

of stripwood to make the lattice

so that each strip abuts neatly

with its neighbours and the rib

boom, ready to be glued in place.

Finally, I cut a lot of small squares

and triangles from thin plywood

to make the biscuits and ‘D’

TOP TO BOTTOM:

improvised electric

kettle steamer; rib boom

former clamped in vice;

and the set of formers

required to produce the

tight leading edge curve

of the tailplane ribs

It was

tempting to

cheat but I

decided to

persevere