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fritzke -> RE: Roy L. Clough, Jr (7/8/2004 5:27:08 AM)
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Here it is:
Dave
1968 Popular Mechanics do-it-yourself Encyclopedia,
p46, Roy Clough Jr.
TROT THIS MODEL out on the field at your next
meet and watch the eyes bug. If anybody snickers,
put 'em in their place by reminding them that the
annular wing is a very old aeronautical principle.
Then launch your Hoopskirt. If its tradition hasn't
impressed them, its performance is certain to!
At least a half-dozen full-scale planes (plus
innumerable kites and gliders) have been built on the
"flying barrel" design. One of the initial aircraft made
by Ellehammer---the first Dane to fly---took this form.
Louis Blerriot, the daring Frenchman who was the
first to fly the English Channel, perched one on
floats and tried, with indifferent success, to get it off
the water. The French are still at it; their latest
attempt at annular-winged aircraft is a tail sitting jet.
One of the big advantages of this design is its
propulsive efficiency. Efficiency in a flying system is
highest when the velocity of the discharged air is
almost as great as the forward speed of the plane.
This means that it's better to
move a lot of air relatively slowly than a small
amount at high speed. (It's rather like matching
impedances.) The annular wing with a propeller
ahead of it functions as an effective aspirator to
increase the amount of air thrust backward.
Such a wing has more lift than you might think.
The closed-circuit nature of the airfoil eliminates
wing-tip vortices. Theoretically, a hoop-wing plane
shouldn't have to bank in order to turn. This model
does, however, because of the vertical stabilizing fin
at the top of the wing. This was added to produce
an effect comparable to dihedral.
The Hoopskirt is an extremely stable flying
machine. It'll teach you a lot about this off-beat
configuration. Don't let the circular wing scare you---
it's quite easy to build. Any cylinder with a diameter
of about 10 in. (a half inch either way won't hurt)
can serve as a mold for the two spars. I used a
straight-sided layer-cake pan. The spars can be of
any light wood that bends easily when soaked in
hot water. Bind these
around the mold with a strip of rag. When dry, trim
the ends in long, matching bevels to form the lap
shown in the sketch; cement and bind with sewing
thread.
You can trace the wing-rib pattern directly onto
your balsa, stacking blanks to cut as many at once
as you can manage. The slots in each end are 3/32 in.
wide and 1/4 in. deep. The width should provide a
snug fit over the spars. When these hoops are
seated in the notches, their outer edges will
protrude 1/16 in. for rounding off.
An easy way to space the ribs accurately is to set
the spar-mold cylinder on a piece of cardboard and
scribe around it to produce a circle the same
diameter as the spars. Mark off sixteen rib positions
by means of radius lines and assemble the wing
vertically over this pattern.
Cover the frame one section at a time with light
model-plane tissue. Sections into which the strut,
fin or booms will pass can be left uncovered until
assembly is completed---or you can cover the entire
wing and then slit the paper
of these sections when you install parts that must be
cemented to the ribs. Water-shrink the paper; when
dry, give it a coat of clear dope.
Careful alignment of all balsa parts pays off in
good performance. Don't diminish the strength of
the rock-hard-balsa booms by sanding off the
corners---leave them square.
The tail plane has a deeply-notched trailing edge,
backed up with parallel pieces of soft wire cemented
to the wood. These wires---which can be snipped
from a paper clip---will hold any flight-adjustment
bends you may give the two elevator sections after
trial runs. An annular wing operates at zero
incidence, so you'll have to bend the elevators up
two or three degrees to get an angle of attack for
climb. Bending one elevator up more than the other
makes the model turn in that direction. The rudders
have no adjustments, and are simply cemented to the
sides of the booms after the tail plane is in place.
The engine-pilot nacelle is given a coat of
pigmented dope after the motor is fastened on its
plywood mount. The color scheme of the model
shown is: red nacelle, rudders and fin: natural white
wing; silver booms, strut and tail plane— a highly
visible combination against a blue sky.
For best performance, be sure the model balances
at a point about 1 1/4-in. ahead of the trailing edge of
the wing. An easy way to balance the plane is to
stick straight pins into both booms 1 1/4-in. ahead of
the trailing edges. Support the plane on these pins
between two stacks of books, and add weight---in
the form of bits of clay, small pieces of lead, etc.---to
either the nose or the tail until the plane is
suspended between the books in a level flight
position.
Hand launch the model over tall grass until, by
bending the elevators up a little at a time, you get a
flat glide. As a check on these adjustments try a
flight with the motor running rich, then lean it out
and watch your model zoom.
This is a free-flying model, and has not been
adapted for control-line operation. It is a stable flyer,
and when out of fuel, it will glide gracefully to a
landing if you balanced it carefully.
If you're flying it in a limited space, it's a good
idea to burn off some of the fuel before turning it
loose, because the model travels at a good clip.
In any event, you'll draw a good many curious
glances---and perhaps a few snorts of derision
when you take Hoopskirt out for its first flight.
Any snickers in your direction, though, will quickly
change to whistles of admiration when onlookers see
the stability of the "flying barrel," one of the earliest
of all aircraft designs.
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