On 30 Oct 2006 08:36:26 -0800, wrote:


Orval Fairbairn wrote:

Actually, filament winding would be a poor choice for spars, as the
filaments should run primarily parallel to the spar and be concentrated
at the top and bottom. You do need some in the webs, to handle shear
loads, but an "I" section is the most efficient. A tubular spar for a
wing is also a poor choice, as it concentrates a lot of its tensile
strength at its center, where it doesn't get much loading.

A mast is a different story, as it is expected to take similar bending
loads in all directions; a spar does not.

The spar in my Jodel is a one-piece box spar and is the only
spar in the wing. It takes the lifting and landing loads, the drag
loads, and the torsion loads. The washout is built into it. It's about

I have a section of the main spar out in the shop for Barracuda. It is
a box about 2 1/4 X 10 1/4 " at the inboard edge of the main gear
attach point. The sides appear to be about 3 /32" plywood (not the
big box kind) and the spar caps are three 2" X 3/4" internal, making
each cap 2" X 3". There are internal risers spaced along the length of
the spar. I don't have a rear spar and don't remember its dimensions.
That spar had thousands of hours on it.

I measured the Cuda spar, I'm going by memory on the G-III.

The main spar for the Glasair III is a monster. The web is a foam
core covered with BID on the 45 degree bias that is of a very heavy
weave. I don't know how many layers as it comes from the factory
bonded to the bottom wing skin. The caps are about 4 inches wide by
3/4 inch thick are basically a lot of parallel fibers running length
wise. It looks like a fiberglass I-beam. The rear spar caps are
molded into the trailing edges of the top and bottom skins and are
about 1/4" thick. The fibers are quite easy to see and are arranged
like those in the main spar caps. The web is 1/2" foam (forget the
weight) and several layers of BID on the 45 degree bias. They don't
even give you a template for the rear spar. Just a set of dimensions
and you sand to fit. The wash out is set into the wing fixture and
you just "twist to fit" at closing time.

The Cozy and I believe the LongEZ both use the same kind of spar.
Using the lay-up over foam type of construction they simply cut a slot
into the foam for the wing, pour in a bunch of epoxy and lay in a
fiberglass rope. They work the resin into the rope until it is
saturated. They keep doing this until the slot is filled with
saturated fiberglass rope. So you again end up with a very strong
spar that has the fibers laid out lengthwise (more or less)

Comparing the wing loading of the SR-22, the G-III is just shy of 30#
per sq ft. A power off descent to the runway in that is a real eye
opener. As I recall best glide produced a rate of descent in the
neighborhood of 2200 fpm. Rate of climb solo is close to 4,000 fpm. A
descent at best glide to the runway gives a roll out of only 700 to
800 feet with the round out being quite rapid and using little space
(If your nerves can handle it):-)) This procedure results in a
rather *firm* arrival. :-))

snip
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com