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

Bruce King has a really nice flying design based on an upgraded Hummel.

It started of off as a $5K, but increases in the cost of aluminum have
run the build cost up a bit. $7K would be pretty close.

The bubble canopy does too, but it flies so much better it's worth it.

The prototype was a little weak kneed, the gear almost retracted on a
hard landing. But that seems to be corrected now.

It performs very well on an 1835.



http://www.bkfliers.com/

BK1 a new design to carry up to 6' 4" 250lb pilot, 30 lbs of baggage 130
mph for 400 miles with an hour reserve. Can be built from scratch for
under $10K. Pre-made components are in the future plans
Tri-Gear and Electric Start coming on Production Plans Model
Flown 1200 miles to Oshkosh 2005-10 flight hours-2 fuel stops-33 MPG,
also flown to Sun-N-Fun 2006 and Oshkosh 2006

On Sep 26, 1:01*pm, " wrote:

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. * -R.S.Hoover

Pictures and some more words of yours truly bending such a flange:

http://users.lmi.net/~ryoung/2006/11...ilders-of.html

I find the use of a scrap of 1/4" softwood ply to be very, very
helpful in distributing the blows - NOT door skin, and NOT anything
any thicker - if it's too thick it'll form a hard spot at the edge of
the ply, and put kinks in.

I learned this technigue from a video of Dave Thatcher of CX-4 fame
demonstrating this with a folding table, 2 ea 2X4s and a rubber mallet
at Sun and Fun a few years ago.

Regarding all metal VW powered single place designs, the BK1 is
looking really nice, but plans aren't available yet. Bruce has done so
much of his own design and engineering that it's not fair, IMHO to
call it "an upgraded Hummel".

Plans for the CX-4 and the Hummelbird Ultracruiser Plus ARE available,
and there are several builder completed airplanes flying for each. I
have plans for the Teenie Two...and that's one of the reasons I'm
building an Ultracruiser Plus. The Ultracruiser Plus has the added
benefit of easily accomodating a flywheel drive prop hub without any
airframe changes due to it's bed mount for the engine, but it's a low
and slow, fat winged ultralight on steroids, and doesn't suit every
mission profile.

On Sep 26, 2:43*pm, flybynightkarmarepair wrote:

http://users.lmi.net/~ryoung/2006/11...atch-builders-...

I find the use of a scrap of 1/4" softwood ply to be very, very
helpful in distributing the blows - NOT door skin, and NOT anything
any thicker - if it's too thick it'll form a hard spot at the edge of
the ply, and put kinks in.
------------------------------------------------------------------------------------------


To All:

I'm remiss for failing to mention this technique which is often
referred to as 'dressing' the flange. As Ryan mentions -- and shows
in the photo -- dressing can produce a beautifully accurate flange and
is the standard method when an accurate flange -- of any length -- is
required. A good example of this would be the flanges on the aft
belly skin of the Teenie Two. But there are many cases where
dressing, while desirable, is NOT required, such as for the spar
flanges. Subsequent steps in which the wing skins are attached to the
flanges, will cause the uneveness of the flange to disappear,
submerged beneath the wing skins.

Some may think EVERY flange should be dressed but that is true for
every case. Dressing will produce a neat flange of uniform width but
it will also give you a bend that exactly matches the edge of whatever
you are using as your clamp. In the case of the Teenie Two spars, the
RADIUS of that bend should be at least an eighth of an inch or about
3T (T being the thickkness of the metal). This is because extrusions
will be nested INTO that bend. In order for the extruded angles to
nest properly their outside corner must be rounded off to match the
radius of the bend. If the radius of the bend is too large you will
remove too much metal from the extruded angles. Indeed, a bend radius
of 3T is pretty much the norm when forming a flange and for the Teenie
Two's spars that degree of precision is achieved by sanding or filing
the edge of your hold-down and then 'dressing' the metal against it.
But the hold-down used to produce a 3T flange in the 0.040" spar stock
would be inappropriate for the flanges on the aft-lower fuselage skin,
which is only 0.020" ...giving you a bend radius of 6T. For the .020"
skins you would need a different hold-down.

Metal hold-downs work best but forming the radius'd edge takes quite a
bit of work. Wood is much easier to work but is usually too soft to
form an accurate bend in heavy gauge aluminum. A good compromise is
to use DOOR SILL STOCK. This is usually made of Red Oak and comes in
lengths up to six feet.

An advantage of the Teenie Two over other metal airframes is that it
uses only TWO thicknesses of metal, .020 and .040. Some will argue
that this is inefficient, that using a variety of metal thicknesses
saves weight. And it does. About THREE POUNDS. The performance of
the Teenie Two and the number of them flying makes it clear that a
three pound penalty is acceptable.

-R.S.Hoover

On Fri, 26 Sep 2008 13:01:50 -0700 (PDT), "
wrote:








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

Having had experience with both of those aircraft, I would have to say
that after you built it you would have to fly the sucker. The VP
handles like a toad and the Teenie two is damn twitchy and has the
sink rate of a greased fire hydrant.

Ed Sullivan, the curmudge