Currently we have an ongoing research project to lift a small UAV (glider) to altitudes of about 100,000ft and let it glide back to a predetermined destination. The UAV would weight about 4kg, give or take.
The concept we are exploring looks like the attached image. However, our expertise in aerodynamic design is limited.
We consider using the NACA 23015-il airfoil, with chord of 56.4 mm a wingspan: 1.70mt and S=1.03 ft2. I would like to know any comments on these paremeters.
Regards,
why did you select such airfoil? is it a modified version of the NACA 23015? what does it mean "il"? it is not easy to answer your question because the parameters you mentioned are all connected. Of course, based on the airfoil, the wing surface you need changes. Additionally, also the tail size and distance from the wing will change. This is because of the trim drag and the optimal compromise between tail surface and tail-wing distance to reduce weight and improve performance.
In general, talking about airfoils for UAV I would consider shapes with high L/D and or high endurance (Cl^1.5 / Cd). It depends on what is the UAV mission. Very important then is the actual Reynolds number because low Re airfoils are quite different than high Re airfoils and it could be that the first ones wont work well in high Re conditions and viceversa.
Secondly, you should make sure that the stall is smooth and not abrupt. If you go for high lift airfoils, you could save some wing surface but you may have anticipated stall and ... see below
Third, talking about tail, have a look to the moment coeffcient of the airfoil you select. Large (negative) values of Cm will mean large camber and so high lift performance. You may then need larger tail surface or tail arm to balance the UAV. Larger tail area will increase the total drag because of the drag of the tail airfoil (trim drag).
concerning the NACA23015 airfoil, it has small Cm so in that respect it could be convenient. Howver, I don't know about L/D performance and low Re performance. Some of them (NACA23012) is famous for very sharp stall that caused airplane crash (ATR42)... so I would really check the actual Re number and then select the best airfoil.
I realized now you study in Delft. have you talk to Nando Timmer?
Thanks everybody for their replies and sorry for the late reaction. I appreciate your answers and will take a close look at them.
The glider will be let lose from a helium balloon around 30km altitude, and should be able to stabilize itself and glide back to a pre-defined point. Problem at the moment is chosing the proper airfoil and parameters or this.
This is a project for a university in Central America, and there is really not much knowledge in aircraft design. So, they are struggling and learning about this by themselves.
(Dear Francesco, unfortunately I am not longer at the TU Delft)
My students are working on a similar project. We intend to send the glider to stratosphere with balloon and rocket (to stabilize it off after the balloon). We are developing the airfoil, we'll do testing and then I can send you. This is nothing new and has been tried before in Europe
Dear Mr. Abdalla, I would be very grateful if you can share information with us. We currently have the machinery to fabricate but the groups lacks the know-how on aerodynamic design.
Dear all.
I am interesting of this idea. Anybody can give me some update on this project?
Thanks in advance.
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