There seems still to be some controversy over just how wings provide
lift. I personally have had several people disagree when I explained
that a flat wing provides nearly as much lift as a cambered wing,
without as much drag. One gentleman explained that he was a pilot, and
that without a cambered wing a real airplane could not produce enough
lift to fly. Another critic stated that the aerodynamics of flight were
totally different for a toothpick sized aircraft, and that different
laws applied to real airplanes, and real (cambered) wings.
Both of these gentlemen were partially correct, but both were wrong in
the absoluteness of their arguments. My intent here is not to be
controversial, but only to illustrate a point.
Wing shape (camber) causes effects that change the amount of lift a wing
can generate, but the principles involved are the same no matter whether
the aircraft is a modern airliner in size, or a toothpick glider.
Likewise, the lift and control surfaces of toothpick sized aircraft have
the same functions as wings, ailerons, elevators, and rudders on the
real aircraft, for the same reasons.
A flat rigid wing (like a paper wing), large and strong enough to
provide the lift necessary to get man off the ground, would be very
difficult to build with today's best technology. In the Wright brothers
day, it would not have been possible at all. This is a technical
difference.
The fact is still the same, camber can increase lift, but it is not
required for lift. Lift is primarily a function of the angle of attack.
For more discussion on how wings work, see "Why We Go Up", Robert
Kunzig, DISCOVER Magazine, April 2001.
The wing cross-section below shows how chord and camber are measured.
 The chord of a wing is the measure of an imaginary line stretching from the leading edge to the trailing edge. |
 |
 The camber of a wing is its measure from the top curved surface to that imaginary chord line. Most modern wings have both upper and lower camber. |
The wing cross section above has under-camber. It is open on the
bottom. A cambered wing produces more lift, and is stronger. In TA
aircraft, flat paper wings can be made stronger, and more like the
original aircraft, by adding camber. While making TA wings with no
under-camber is possible, the resulting wings are heavier, tend to have
worse warping problems, and can be difficult to assemble. A whole
different book.
Leaving the lower surface of the wing open, however, causes a phenomenon
known as under-camber. Most of the first airplanes were deliberately
built with under-camber. Popular theory of the time held that while
lift was generated by camber, increased lift or speed was possible from
under-camber. For further discussion of under-camber in early aircraft,
see "Undercambered Airfoils" by Caroll F. Gray, W.W.I Aero No. 170,
November, 2000.
The main reason to resort to a cambered wing in TA aircraft is the
increased rigidity of the paper wing. Especially in large TA aircraft,
wings tend to sag as they get older. The Wright brothers' biplane
designs help counter this effect also. An added benefit of the
cambered wing for TA aircraft is realism. Many of the stability
problems you will encounter will be recognizable when you read and
explore accounts of the original pioneers and their aircraft flight.
How To Add Camber
| |
Bend the leading edge of your wing down. Your airplane will fly slower,
glide farther. |
Grasp the first wing between your thumb and fore-finger beginning at one
side, about one sixteenth of an inch from the leading edge. Place the
printed or traced side down, or away from you, just the way it will be
mounted on the Wright aircraft. Press the leading edge of the wing
down, bending it to the same shape along the entire width of the wing.
Repeat this procedure for the second wing.
This simple modification changes the way your TA glider flies. Because
of the wing's changed shape, the camber (and under camber) creates more
lift and drag! Your aircraft may fly more slowly, but will probably
fly farther with less thrust. Experiment by moving the cambering fold
farther back on the wing, or making a second, shallower fold behind the
first.
From the author of BUILD AND FLY THE WRIGHT FLYERS:
My purpose in writing and publishing THE TOOTHPICK AIRFORCE series is to
share a concept I have enjoyed since I was very young. My children
enjoyed building toothpick gliders, and I eventually had to show nearly
every youngster in the neighborhood how to build them. I wrote the
first book, REAL GLIDER REPLICAS (ISBN 0-9650751-1-7) when various
parents asked for the instructions to send to their out of state
relations. The TA Wright 1900, and 1901 gliders were designed
especially for the Centennial of Flight, while the 1902 Wright glider
and the Kitty Hawk Flyer are redesigned for simpler assembly and fewer
parts. Both of those TA aeroplanes first appeared in BUILD AND FLY THE
FIRST FLYERS (ISBN 0-9650751-2-5).
I worked out most of the bugs in building and flying toothpick airplanes
when I was between 11 and 13 years old (1960 to 1963), growing up in
Lakewood and Georgetown, Colorado. It all started in Georgetown, with
an issue of Boy's Life. The magazine had an article and drawings
describing a miniature rocket engine using a length of small soda straw,
glued to a second section of straw. One end of the straw was to be
glued shut, then packed full of match heads. We had an old coal stove,
so kitchen matches were available. The second piece of straw was to be
placed on a string, to act as a guide when the match heads were ignited.
I remember it did not work very well.
I knew I could do better. The string was causing too much friction, I
thought. First I attached wings, and tail empennage. I had great
difficulty making the wings on both sides equal dimension-wise. My
mother asked me if I had never made paper dolls, and I said I had not,
somewhat annoyed (I was #7 of 8 children) so she really did not know
which ones she had shown that particular trick to. She folded a piece
of paper in half and had me cut out my wings and tail planes and I was
very impressed.
My rocket powered airplanes burned up before they could get airborne,
but I had a whole pile of stripped kitchen matches. Thus was borne the
Matchstick Air Force. My mother wanted me to sell the idea to Boy's
Life. Unfortunately their standard offer of the time was something like
$35. Again, I thought I could do better.
It seemed that there was a continuing shortage of wooden matches to
start the fire in the mornings, and in the mountains it could get very
cold at night. My mother bought me a box of flat toothpicks, and the
rest is history.
|
