Turkey Buzzard (oz15972)

About this Plan

Turkey Buzzard. Free flight model.

Quote: "Experimental Tailless Free Flight. Turkey Buzzard, by Roy Clough.

Ever since the airplane was invented people have been looking at it and telling themselves that its performance could be improved if they could eliminate the weight and drag of the tail.

As a result, quite a number of tailless planes have been built down through the years. Some of them were pretty good. (A tailless plane has to be pretty good to fly at all as we'll explain shortly.) But, none of them managed to crowd out conventional designs.

Why? The answer is complex and touches upon many factors from simple mechanical leverage to pilot psychology. Strangely enough, it is some of the disadvantages of the tailless design that make it a good bet for a flying miniature.

Early flight experiments were made with flat surfaces, that is where we got the term "plane". Some of them flew fairly well, with and without tails. Then it was discovered that curved surfaces, copied from bird wings, produced more lift. This was a major discovery but it introduced a problem: A cambered wing tended to 'tuck under' or perform the first half of an outside loop as soon as it picked up a little speed. To prevent this it was necessary to add a boom and stabilizing surface either behind, or ahead of the wing.

The first planes to fly had this stabilizer in front. Later, mechanical and aerodynamic expediencies moved it around to the rear with the rudders and it became known as the 'tail'.

When designers first tried to do away with the tail they had to substitute some other steadying influence. One of the first tricks they learned was to break the wing in the middle, bend it sharply backward, and twist the tips downward. This eliminated the need for a tail but it was rather begging the question because such planes really had two tails - the swept back tips of the wings located far behind the center of lift. Wings of this type could be quite efficient, but 'sweepback' put a terrific leverage on the wing roots. This faced the designer with the choice of building his wings weak - or taking the structural weight he - saved in the tail and using it to beef up the wings. The sharp angle of the wings could also play nasty tricks on pilots who lost too much flying speed near the ground. Nevertheless, a number of fairly successful machines of this type were built. One of the earliest and most noteworthy was the Burgess-Dunne, a swept wing biplane which was a marvel of inherent stability for its time (1912).

Designers then tried to find wing cambers that would not require auxiliary supporting stabilizing surfaces or sweep-back. Two general areas of choice were open, symmetrical sections with the same curve top and bottom and reflex airfoils which were like a regular wing with the trailing edge turned up.

The symmetrical wing had nothing to make it pitch up or down (neutral stability) because it was the same on both sides. The reflex wing had a tendency to pitch up balancing off its tendency to tuck under. There were disadvantages to both types. The symmetrical wing section had no built-in 'recovery' and the reflex wing tended to pitch up higher and higher with an increase in speed. Designers, however, refined these wing sections and arrived at compromise sections that dealt with these problems fairly well. Then they were able to build tailless planes with straight, lightweight wings of high lifting and structural efficiency.

But that wasn't the entire story. It is easier to move something with a long lever than a short one. Airplanes with control surfaces located a short distance from their centers of mass must have somewhat sluggish control response - or very large control surfaces. Sluggish response, really a form of excessive stability, is fine in a performing model but it is a great disadvantage to a pilot - say if a gust hits him when he's landing. If the control surfaces are enlarged enough to provide fairly fast response in the medium speed ranges the tailless plane may be very touchy at high speed. Then, when it is slowed down, the excessive surface gives no guarantee of control: large control deflections at low speeds can produce great drag and further loss of speed and control.

Another tailless plane disadvantage is that stalls, without the balancing inertia of a long tail boom, can be quick and nasty. But this is no concern to a free flight model because the surfaces are not moved in flight and it actually makes a model easier to adjust - one can tell right away where to set it.

A short overall length can mean poor directional stability, it can be very annoying to a pilot when the nose of his plane tends to 'hunt' all over the sky. But for a model this is a good thing - it lets it fly longer within a small area and is not likely to bee-line over the hills and far away.

There are advantages to the tailless configuration that are shared by both models and big ones alike. Not the least of these is a big saving in storage space. Simplicity of construction and light weight - which allows the use of less material and lower powered engines is another advantage.

Our model, although very simple to build, is quite refined in concept. It uses a stable wing section that borrows characteristics of both the reflex and symmetrical airfoil. It has slots which permit it to climb at a higher angle without stalling and a thrust line location and angle that produces an excellent climb... "

Direct submission to Outerzone.

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