Metal vs Wood (T2 vs VP)

Recent threads on RAH have caused an increase in private posts. When
three or more people ask the same question -- or substantially the
same -- I feel it justifies a public response. In this case the
question(s) had to do with wood versus metal with regard to ease (or
difficulty) of construction, costs, especially of tools, and storing
an airplane outside. At first glance these things do not appear to be
related but the body of the messages voiced identical concerns, their
only difference being which factor they considered most important.
For example, all three mentioned the lack of hangar space, either
because it was simply not available or was too expensive. One man saw
this as a major difficulty, the others gave it less emphasis but it
was mentioned by all three. Materials, costs and skills were other
common factors and if isolated, would raise the number of questioners
to about half a dozen.

As to why so many people would seek information via a PRIVATE message,
I assume it's because so many subscribers to the RAH Newsgroup have a
habit of attacking the messenger instead of addressing the question.

The 'BEST' airplane.

The interesting thing about this topic is that is has very little to
do with airplanes. What this topic actually addresses is the factors
needed to BUILD an airplane, in the sense that if you can't build it,
it can't possibly be 'best.' But when all of the factors needed to
build the plane are satisfied, the question becomes valid. Since the
use of a Volkswagen engine, lowest possible cost and minimum
construction time were included as foundation factors, the question
virtually answers itself: The VP-1 is the 'best' airplane in this
case, largely because he is allowed to share hangar space with a King
Air.

Clearly, the VP-1 would be a poor choice if the fellow could not store
it inside -- or even under a 'Sun Shed.' If the bird must live out
of doors then metal would be the wiser choice. Apply those foundation
factors and don't be surprised when 'best' turns out to be the Teenie
Two.

Cost

This is another factor the answer of which is not immediately evident
because any question of 'cost' is usually taken to mean the cost of
materials. It comes as quite a shock to the novice to discover that
their major expense MAY be for TOOLS rather than materials. This can
be a bit tricky because all of the tools needed to build the Teenie
Two will fit in a small toolbox, whereas building a VP-1 may require a
table saw, joiner, router, drill-press and so on -- a hefty bill if
you buy those tools specifically for this construction project.
However, tools may be sold after the project is finished, allowing you
to recover much of their cost.

Skills

Having built a bird-house or gun-rack, the typical American is
comfortable around wood and considers themselves qualified to tackle
something like a VP-1, whereas most Americans are not familiar with
sheet-metal work. This may come as a surprise but there are actually
FEWER skills needed to build a Teenie Two than to build a VP-1. This
is not intuitively evident; you may need to build one of each before
you can appreciate the fact that while sheet-metal appears to use
hundreds of techniques, you need only half a dozen or so to produce a
simple airframe such as the VP-1. By comparison, with woodworking you
must master a dozen or more skills just to use the table-saw. If you
are an accomplished woodworker you probably don't even notice setting-
up a zero-clearance shoe or rigging a scarfing jig. But for the
novice, these are procedures that must be mastered before he can build
even a simple airframe such as the VP-1.

As a point of interest, the novice builder typically approaches sheet-
metal work with trepidation due to the need to create long bends,
ASSUMING that such work REQUIRES a bending brake. On the VP-1 (for
example) one of the first steps is to fabricate three spars out of .
040 2024-T3. In fact any STRAIGHT bend can be produced with a
straight-edge, such as a piece of angle iron, something to serve as a
clamp, and a rubber mallet to form the bend. The reason novices find
this difficult is because they generally don't know HOW to form an
accurate bend using only a mallet. So I'll tell you:

Take any malleable material, hit it with the round end of a ball peen
hammer and you'll leave a little bulls-eye surrounded by an area of
deformation. The force of the blow has deformed the material in a
distinctive circular pattern reflecting the shape of the hammer's
head, the difference in hardness between the hammer and the material,
the force of the blow, and the material's freedom to move when
struck. If the material is perfectly free to move in all directions
you'll get the classic 'bulls-eye' pattern. What's happened here is
that the metal directly under the head of the hammer has been
STRETCHED, pushing away the metal around it. To bend a flange we
simply take advantage of the properties of the material and the
hardness of the hammer's head. By restraining the material -- by
clamping it down -- the stretching will be asymmetrical; the metal
will be pushed to the front and sides whilst the material under the
clamp will not be moved at all. To obtain a nice EVEN bend, we use a
LIGHT hammer with a head that is SOFTER than the material to be bent.
This could be rawhide, plastic or even rubber. And when we hit the
material we use only a modest amount of force -- the stuff doesn't
even bend for the first half dozen or so hits. Subsequent hits are
off-set by some small amount relative to the diameter of hammer's
head. Do that half a dozen times and the material will develop a very
modest bend. So we keep doing it, always working from one end to the
other, always using light blows.

The metal is still being stretched -- we can't prevent that from
happening. So we take ADVANTAGE of that. The series of light, over-
lapping blows and the restraint imposed by whatever is clamping the
material, causes the material to stretch along the line of the bend
and outward, toward the free edge of the material.

Do that enough times and you will form a nice flange. The free edge
will not be perfectly straight and the newly formed flange may have
some waviness but neither of those things will prevent the piece from
serving as a wing spar. The edge may be cleaned up with a vixen file
or left as-is, while the waviness in the flange will vanish when the
skins are riveted to it.

The typical novice picks up this procedure in a few minutes, after
which it's just a matter of practice.

The Teenie Two uses three self-bent spars. After the flanges are
formed and fitted with doublers, the three spars are arranged on the
bench so as to lay-out the dihedral, allowing the spars to be drilled
for taper pins. Once drilled, the outer spars are put aside and the
center-section spar is used as a jig for fabrication of the cockpit
and center-section. Since the Teenie Two is assembled using pop-
rivets, construction goes very quickly.

The point here is that while bending a flange may have to be learned,
it is a skill that is used over and over again for ANY flange. The
same applies to riveting, which entails laying-out and drilling..
While the drilling may appear complicated it is actually the same
procedure, repeated as many times as needed. When the airframe is
finishing you will see that while it required dozens of bends and
flanges, as well as thousands of rivets, you've actually used only TWO
procedures, modifying them a little or a lot, as needed for a
particular application.

-R.S.Hoover