Avia Economia, Part 1

In the early days of Aviation it was fostered by government and civic
agencies. The Boy Scouts were encouraged to build Primary Gliders, as
were the Aviation Class at the local High School. A Progressive
Nation was an Air-Minded Nation and our National Pride was embodied in
Flights of Discovery, many funded by corporations such as Johnson's
Wax and even by private individuals.

Every town of any size had its Flying Club, organized on the European
model with the basic Flying Machine being a Primary Glider built and
maintained by the club's members. Most of the primaries followed the
design of the School Glider developed in Germany (and described in my
Blog).

SAE 4130 was uncommon stuff in those days, still designated as X4130,
difficult to obtain and expensive. But the Primary Glider had few
metal fittings and Mild Steel served well enough, it's thickness
doubled where greater strength was needed. Each Flying Club had its
Glider Committee, broken down according to machines already finished
and those under construction, further divided according to Tail Group,
Wings, Fuselage, Trailer Group and so forth. Metal Fittings usually
had its own Group. where the fittings were hack-sawed from flat stock,
bent to shape, holes drilled, edges polished then finished with anti-
corrosion paint. .

We no longer have Flying Clubs but we do have EAA Chapters.

There was no aircraft-grade turn-buckles back then but the same thing
was used on a variety of small, high performance sailboats, iceboats
and even three-wheeled landboats, some capable of speeds up to 70
miles per hour. The turn-buckles were inexpensive, according to the
economics of that era and lent themselves to use in a two-spar, truss-
braced wing in which the drag- and anti-drag wires were tensioned by
turn-buckles, a design used on the NYP and still with us in the 'Fly
Baby' wing and others. Alas, the aviation-grade turn-buckles of today
have become so expensive that a Primary Glider has become a luxury
item... BUT ONLY IF we follow the plans of those early-day Primarys.

Today we have the Ison-type wing which follows the same two-spar
design but with the drag- and anti-drag members made of solid wood.
Or we may elect to use Curtiss Pitts' design in which the drag- and
anti-drag members were mild steel rod, about 1/8" dia. threaded on
each end, passing through the intersection of the compression ribs and
the spars. With a fixed T-nut on the aft spar, tension was adjusted
by a coupling nut on the forward face of the front spar, secured with
an elastic stop-nut and a dob of lacquer. The leading edge was
usually provided with a fabric-covered inspection port to allow period
inspection of the tensioning nuts, the ports covered by a simple patch
(a feature you can see on the NYP).

Thanks to their lighter weight, these modern methods are MORE SUITABLE
for a primary glider. These latter methods are inexpensive and their
use eliminates the need for metal fittings, turn-buckles, flexible
cable and Nicopress sleeves. What's 'inexpensive'? In the 1980's a
spool of 1/8" solid mild-steel wire sufficient for a primary glider
cost $7.00. It's bound to be more today but back then I was able to
buy the nuts, wire and washers for a Pitt's-type wing for less than
$20.00. Surely some Chapters could do the same today.

In a similar vein, the drag- and anti-drag wires for an early primary
glider were made from music wire, still available from a variety of
sources (I use McMaster-Carr). Alas, here again we run into the high
cost of turn-buckles... as well as the lack of experience in forming
music-wire fittings. But nowadays steel tubing is commonly
available, making a STRUT-BRACED wing a practical alternative for the
bird's-nest of wire found on early primaries. Indeed, given the light
loading of the primary's wing and suitable jury struts, the steel
tubing used as the top-piece in wire-mesh FENCING works perfectly well
as strut material. There is no adjustment as such with a strut-braced
wing. The lower fitting is welded but the outer fitting is BOLTED,
the holes drilled ON ASSEMBLY once the wing(s) have been jigged into
position. After some period of service, should adjustment be
required, you simply re-manufacture the strut-to-wing fitting, re-
drilling the strut-to-fitting bolt hole to accommodate the required
change. This is a relatively trivial task since the fitting may be of
mild steel or aluminum plate.

Another stumbling block for the building of a primary glider in
today's high-priced world is the plywood used for the leading edge,
often costing $300.00 or more... and often that much for the
SHIPPING. There are several practical alternatives here, the most
common being to form the leading edge of scrap STYROFOAM then cutting
it to shape using a hot-wire knife. The surface is then covered with
COTTON FABRIC saturated with Weldwood 'Plastic Resin' glue. And if
you don't think such a surface is strong enough it simply means you've
never built one. So try it. Styrofoam is ubiquitous as a packing
material and you only need about an inch of it to provide the basis
for your lamination. Real, 100% cotton works best but an old bed
sheet, typically 35% cotton and 65% polyester, works well enough for a
test. As to finding 100% cotton material, simply turn off your
blinders -- the fabric does not have to be white. Indeed, it can
patterned and there's nothing that says the same pattern must be used
for the entire wing :-)

To get a dead-smooth surface for your leading edge simply lay the
fabric out atop a sheet of Mylar or other heavy plastic and saturate
it with the glue. Once fully saturated, lift the panel BY THE PLASTIC
and smooth it into place atop the styrofoam. If working alone you'll
be limited to sections about two feet in length but with more hands on
the job you can do four feet at a time. Weldwood 'Plastic Resin' is
not the best choice for this task, it is merely the cheapest. Indeed,
'Plastic Resin' trapped between Mylar and syrofoam will resist curing
since it must DRY in order to cure. That means you'll need to peel
away the plastic before the glue is fully cured. Your experiments
will show that any number of other glues will do a better job.. but at
a higher price, with Titebond III being first among them. Avoid
epoxies and polyester resins. They all contain enough solvents to
destroy your styrofoam. (But if epoxy is all you have... seal the
styrofoam with light-weight dry-wall spackle and sand it smooth. The
spackle will seal the surface and prevent the resin from dissolving
the styrofoam.)

I'll write more on the fabrication of a primary glider and will
include drawings right down to the structural fittings and controls.
For best coverage I'll post the material here (for plain text), on my
Blog and in the FILES archive of the chuggers Group on Yahoo.

The purpose of this post is to make you aware of the similarity
between EAA Chapters of today and the Flying Clubs of yesterday. But
today we have just one organization that claims to speak for grass-
roots aviation. Unfortunately, the definition of 'grass-roots' has
been prostituted to mean $100,000.00 imported airplanes. The
advantage of Primary Gliders is that they have no Easy Virtue. You
roll up your sleeves, divide the tasks amongst your Chapter members,
and get busy. Leave the bean-counters to waste their time discussing
Insurance, Registration and Aviation-Approved materials. Multiple
voices will always be heard and if loud enough, exceptions will be
granted. Indeed, many exceptions already exist when it comes to
PRIMARY gliders, such as Catch-22 and Primary 101. Read the regs,
especially those which establish the Experimental, Amateur-Built
license category. Then go build yourself an airplane.

-R.S.Hoover