Why Paper Airplanes Look Different Than Real Planes?

Why Paper Airplanes Look Different Than Real Planes?

Most full size planes have wings, a tail, and a fuselage (body) that holds the pilot and passengers. Most paper airplanes have just a wing and fold of paper on the bottom that you hold when you throw the plane.

There are several reasons for the differences.

1 Folding time
The main reason why paper airplanes look different than real planes is to allow the paper airplane constructor to make a plane as easily and quickly as possible. Adding a tail and any other pieces to a paper airplane would require more folds, and probably scissors, tape and glue. The simplest airplane is the flying wing, and that’s what most paper airplanes are.

2 The Tail Is Not Needed
The horizontal tails on full size planes have an elevator (control surface across the back edge of the horizontal tail) which the pilot rotates (back edge) up to make the plane nose up and fly slower, or down to nose the plane down and speed up. Paper airplanes accomplish the same thing by bending the back edge of the wing up to fly slower, of down to fly faster. Several full size airplanes have been flown successfully without tails.

The Northrop XB-35 and B-2, and the sailplanes of the Horton brothers were all stable, good flying airplanes. Many people assume a tail is needed for stability – but the above mentioned planes, and millions of paper airplanes prove different! B-2 Flying wing bomber The horizontal tail of a plane allows the weight to move forward and aft more while remaining stable and controllable.

fun-projects-working-paper-airplanes

Where a plane balances if it were supported at only one point is called the Center of Gravity (CG). The CG can move further forward or aft due to different passenger and cargo loadings, and due to fuel burn (most jets carry about half their empty weight in fuel). All airplanes become unstable if the CG moves aft of a point called the Neutral Point. As the CG moves forward of the neutral point, the plane gets progressively more stable, and progressively needs more up elevator.

Elevators on tails can be more effective than elevators on the back of wings, so planes with tails can have a greater CG range than planes without tails. With paper airplanes their CG does not move, so they are fine without a tail. A tail is also needed to balance the pitching moment (tendency to make the plane rotate nose up or down) caused by flaps. Flaps are the control surfaces on the back edge of the wing which are deflected down to allow the plane to takeoff and land slower.

Paper airplanes do not need to fly any slower, so they do not need flaps, or the tail needed to balance the flaps. The tail of a real plane usually also has a vertical tail. The vertical tail acts like the fins of an arrow to keep the nose of the plane pointed in the direction its headed, this is called positive directional stability. The Fuselage (center body of a plane, on paper airplanes its the part you hold for throwing) acts like the vertical stabilizer of real airplanes. Sometimes bending the wingtips up on paper airplanes also helps to add directional stability. The combination of the fuselage and wingtips on paper airplanes allows them to have positive directional stability without a vertical tail.

3 Wing Shape
Paper airplanes usually have short “stubby” wings, called “low aspect ratio” wings. The distance from wing tip to wing tip is called wing span, and the distance from the front to the back of the wing is called the chord. The ratio of wing span to average chord is called “aspect ratio”, and is an important characteristic of wings. For subsonic (less than the speed of sound) airplanes wing drag is reduced by increasing wing span and decreasing wing chord, both increase the aspect ratio.

For that reason aspect ratio is a good indicator of overall wing drag. Notice that sailplane(glider) designers are extremely concerned with wing drag, and use high aspect ratio (big wing span, narrow chord) wings. Getting back to paper airplanes, or more correctly paper gliders, notice their wing shape is much different from real gliders because they have low aspect ratio wings. There are several good reasons for this difference. Paper is a lousy building material. There is a reason why real airplanes are not made of paper.

Although high aspect ratio wings reduce drag, they also require better building materials. The low strength of paper does not allow the use of high aspect ratio wings. Low aspect ratio wings are easier to fold. One of the reasons we make paper airplanes is because they are fast and easy to build (gee, is that two reasons?). Paper airplane gliding performance is not usually very important. We usually want a plane that does a good job of flying across the room, and aren’t too concerned if another paper airplane design (which would be more difficult to build) could have made the same flight more gracefully.

Notice that for my world record paper airplane gliding performance is extremely important, but a low aspect ratio wing is needed to withstand the high launch speed (more on the specifics of the world record plane later). Low aspect ratio wings look faster, especially if they are swept back. People associate low aspect ratio, swept back wings with low drag, high speed fighters. In reality if an airplane is flying less than 500 miles per hour it will have lower drag with a straight, high aspect ratio wing.

This seems confusing to many. Think of it this way, if low aspect ratio swept back wings had the lowest drag for all planes, all planes would have them. Airplanes flying from 500-600 mph have the lowest drag with fairly high aspect ratio swept back wings. That is why jet airliners have that kind of wing. Airplanes that fly over 600 mph, like jet fighters and the Concorde, really do have the lowest drag with low aspect ratio swept back wings. However the truth doesn’t change the fact that low aspect ratio swept wings look fast, and that’s OK. LS-6 Sailplane

4 Exotic Shapes
Real airplanes have to be optimized to perform some mission. Since its tough to beat the basic wing/fuselage/tail configuration for aerodynamic efficiency, most planes look that way. The mission of a paper airplane is to provide a good time for the pilot. Sometimes that means the amazement of seeing something radical fly through the air. The combinations of wings, tails, fuselages, and other parts that can be made to fly is endless. Beyond the traditional paper airplane designs there are many exotic shapes that don’t look like they should fly.

One of these is the “hoop shape”, known as the Vortex in my original book. Another exotic shape is in my 1997 calendar called the X-Plane. It is basically two wings attached in the middle and at different angles to form an “X” shape. Other more familiar shapes, but not thought of as airplanes, can also be made to fly. One of these is the Starship from my 1997 calendar, which looks like a futuristic space craft, but it actually flies. With paper airplanes its easy to make airplanes that don’t look like real airplanes.

Originally posted 2012-05-19 13:50:58. Republished by Blog Post Promoter

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