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As a basis for this question, take the following catapult glider:

http://www.guillow.com/spaceshuttle.aspx

This model has low aspect ratio wings, a thick wing section and a relatively wide fuselage, however the surface of the glider is smooth. Is this an optimum design for distance or is there a better design possible?

How will the following parameters affect how well the glider fulfils its requirements?

  • Weight
  • Wing area
  • Wing planform
  • Fuselage width
  • Surface roughness
  • Aspect ratio

(covered here How does chord length affect wing design?)

At least what areas should a designer experiment with in order to achieve long flights?

stackex555
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  • It will all be a function of drag to lift and stability. I would make the assertion that a "flying wing" type design would probably be the best here, but i have nothing to back up that claim. I'm not sure this is even a valid question in this format, as I dont believe it is truely "answerable" – James T Apr 26 '17 at 08:33
  • The question if the model shown is the optimum is answerable, I would think, some ways in which it could be improved, for example streamlined and given a higher aspect ratio wing might be some of the answers. There is a related answer here: https://aviation.stackexchange.com/questions/13609/how-can-you-calculate-the-gliding-distance-for-a-remote-controlled-jet?rq=1 – stackex555 Apr 26 '17 at 11:07

1 Answers1

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Two parameters are important to arrive at a good answer, but not covered in your question:

  • What is the size of the glider? The Shuttle model will fly at Reynolds numbers in the order of a few ten thousands, which puts it in a flight regime quite different from that of large, man-carrying aircraft.
  • How much kinetic energy will be provided at launch? One advantage of the Shuttle model is its large volume relative to surface area. This allows it to start the glide with more kinetic energy when compared to the model of, say, a glider. In the end, it is more ballistics than aerodynamics which can explain the gliding distance.

The optimum configuration will change with the absolute size. Aspect ratio will grow with size, and a high ratio of mass to surface area will yield better results. The Shuttle model has a weak spot, however: Its large base area will result in flow separation and high base drag. A streamlined body should be better at all sizes.

Peter Kämpf
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  • I decided not to edit the question since the meaning will be lost. In order to avoid being put on hold I really need to head for the help section, write and edit the question about 10 times and then ask. One rule should be 1 question only. – stackex555 Apr 27 '17 at 04:16
  • Peter, I am sorry the model size is not given I expect it to be of 20 cm wingspan or so. Catapult launched models in level, slowing flight is an interesting problem but I am not sure how to ask the right question here. Isn't there a trade off between mass and flight distance? Again a complex question. And you are right of course about the shuttle tail - the real shuttle has a large streamlined cover that is used when it is transported (shuttled?) back to base on a suitably modified 747. – stackex555 Apr 27 '17 at 04:21
  • @stackex555: A delta wing is stable in pitch; with a higher aspect ratio and less sweep you need a separate tail. An important point is whether the kinetic energy at launch is limited, or if you can make the model as heavy as you like and only the launch speed is prescribed. Too heavy and lift-induced drag will down the model, but too light and friction will stop it too soon, so there is an optimum. With 20 cm wingspan, a shuttle-like geometry can be made much bigger and heavier than the model of a regular plane, so are you free regarding length and mass? – Peter Kämpf Apr 27 '17 at 07:17
  • The delta wing model I used, actually a semi scale model of a Mirage 111, would fly a short distance, pitch up (probably stall) and then continue in a downward soft of a glide. It weighed about 20 g. Lighter similar models do not have this problem, however I am wondering whether it is due to lack of elevator effectiveness or lack of lift I really find it difficult to think how I could tell the difference. – stackex555 Apr 28 '17 at 11:52
  • Peter, to answer your questions - kinetic energy is limited, using 2 rubber bands on a catapult and I do not intend to increase this, I am actually trying to develop a plan for a child's toy. I think I can decrease the weigh down to 10g and it will fly better, durability requirements make a lighter model unlikely. My final aim is 1:50 scale models of actual jet fighters, so my options are limited.. so much to discuss can this be moved to a discussion? – stackex555 Apr 28 '17 at 11:55
  • @stackex555: Your problem is the location of the center of gravity. Add some mass to the tip of the model until the flight path is straight over the full distance. What you observe is the phygoid motion of the model. – Peter Kämpf Apr 30 '17 at 14:04
  • I have since built successful model gliders that can fly 20 metres or more, which is more than enough for the small space I have. These use thin wings of cardboard from a cereal box for example and weigh between 15 and 20 grammes. A cylindrical fuselage with a nose cone is used, and the correct cg which requires slight up elevator is best. The model is a semiscale model of a Mirage 3, 1: 48 scale.ll – stackex555 Jun 02 '19 at 09:40