Balsa Glider Design

Balsa Glider Design

Otto Lilienthal, a German pioneer of aviation also known as flying man quoted “To invent an airplane is nothing. To build one is something. But to fly is everything”. Building your own plane from pieces with bare hands and then seeing it soar in the sky can be the most satisfying personal experience. Balsa Glider Design (basically of wood) is an inexpensive vehicle for students to gain this experience while learning the basics of aerodynamics.

This article aims to provide you with all the concepts, workings and designing principles associated with balsa glider design. So that you can not only build but design your own glider according to your needs and preferences.

A glider is a heavier-than-air aircraft that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose free flight does not depend on an engine. It is designed to glide after being towed aloft or launched from a catapult. In flight, a glider has three forces acting on it as compared to the four forces that act on a powered aircraft. Both types of aircraft are subjected to the forces of lift, drag, and weight. The powered aircraft has an engine that generates thrust, while the glider has no thrust. For a glider to fly, it must generate lift to oppose its weight. To generate lift, a glider must move through the air. The motion of a glider through the air also generates drag. In a powered aircraft, the thrust from the engine opposes drag, but a glider has no engine to generate thrust. With the drag unopposed, a glider quickly slows down until it can no longer generate enough lift to oppose the weight, and it then falls to earth.

How does glider achieve the velocity needed for flight?

For balsa gliders, the aircraft is given an initial velocity by throwing the aircraft. Some larger balsa gliders employ a catapult made from rubber bands and a tow line to provide velocity and some initial altitude. Pulling the glider aloft gives the glider a certain amount of potential energy. The glider can trade the potential energy difference from a higher altitude to a lower altitude to produce kinetic energy, which means velocity. Gliders are always descending relative to the air in which they are flying.

How does the Balsa Glider Design work?

parts of balsa glider

  1. Fuselage links all the components together and supports most of the load when glider is on the ground.
  2. Wings  create the lift, allowing the aircraft to fly. But how do they create this lift? aerofoil                                                                                                      A cross section of a typical airplane wing will show the top surface to be more curved than the bottom surface. This shaped profile is called an ‘airfoil’ (or ‘aerofoil’).  As the fluid elements approach the wing, they split at the leading edge and meets again at the trailing edge. As a result, the air must go faster over the top of the wing since this distance traveled is larger. Bernoulli’s equation implies that pressure will be lower on the upper surface. This net pressure difference causes lift. Learn more about concepts of flying in our drone building course.
  3. The horizontal stabilizer helps to make the glider stable in the nose-to-tail direction (pitch), preventing it tipping nose up or nose down.
  4. The vertical stabilizer prevents the glider twisting side to side (yaw), so it continues in a straight line.
  5. The winglets help to make the glider stable in the wing-tip to wing-tip direction, preventing it rolling side to side.
  6. Nose weight helps to move the center of gravity forward. This works with the horizontal stabilizer to make the glider stable in the nose-to-tail direction.

Equipment

A small glider can be built with cheap and easily accessible material. Materials selected should be lightweight and tough because of obvious reasons. Balsa wood is mostly preferred because weight of the model is to be kept as minimum as possible. The special quality of this wood is that it is very light and hence adequate for our purpose along with the fact that it has good enough strength to not to breakdown away in wind. Other required materials may include Metal ruler, suitable surface to cut onto, such as cutting mat, hot glue, glue stick, large elastic band, sticky tack.

Some useful tips!

  • Try to streamline the body as far as possible, in order to reduce drag.
  • All the ends are rounded, again to minimize the effect of drag.
  • Dihedral: the purpose of building dihedral on a wing is to improve the lateral (roll) stability of an airplane. The dihedral angle is the angle that each wing of an airplane makes with the horizontal
  • Wing Taper: compared to a simple rectangular wing, using a wing with taper on your glider can decrease the amount of induced drag that develops at its wingtips. The total amount of taper angle should not exceed 10 degrees.
  • Aspect Ratio: the aspect ratio (AR) of a wing is defined to be the square of the span, divided by the wing area. Aspect ratio is a measure of how long and slender a wing is from tip to tip. For a rectangular wing, this reduces to the ratio of the span to the chord length. Gliders have a high aspect ratio because the drag of the aircraft depends on this parameter. A higher aspect ratio gives a lower drag, a higher lift to drag ratio, and a better glide angle.
  • You can design a prototype of your glider in Solidworks or any other CAD software and carry out simulations and studies of it. This will help you to predict and rate the performance of design. Further, static analysis can be used to determine deflections and stresses in different parts of the glider to improve the design. Want to learn Solidworks?

Dimensions for reference

  • Aspect Ratio =9-10
  • Wing span = 50-60 cm
  • Angle of attack = 3-4 deg
  • Horizontal Stabilizer = 20-25% of wing area
  • Vertical Stabilizer = 40% to 50% of Horizontal Stabilizer area
  • Length of fuselage = 65%-75% of span
  • Dihedral = 2-3 deg

These glider models which seem to be toys at first glance, were once used by Wright brothers to unravel the mysteries of flight. Even today NASA uses such model airplanes to develop new concepts, create new designs and test ideas in aviation. Now you are ready to design and build your own balsa glider using the provided information. Who knows it can be the next breakthrough design for aviation industry?  We also, have some more cool projects and courses for you.

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