Hi all,
I've only recently become part of the diy drones community and already I've learned a lot about amateur UA operations.
As my first contribution here I thought I'd share a design that I put together this morning based on some old research on laminar flow shapes.
It's a bit different. The fuselage here is a low drag shape developed by Fabio Goldschmied in the 60's, originally for airships. The principle involves a cusp at 82% along the body which the air over the fuselage is drawn through. This suction allows laminar flow to be maintained over up to 77% of the fuselage, reducing drag by 37% or more. Later Goldschmied proposed the use of this shape as an aircraft fuselage, in much the same configuration as I have here. The exhaust is spat out the back as shown below:
I decided to draw up a design for a hand-launched UA using this principle, with an EDF (small, around the size of the Zephy v70's) for propulsion. I have no idea how well this will work but at the very least the internal fan protect genius from the moving parts.
The specs for this are shown in the drawing above. I went for a mid-wing configuration to further reduce drag, but gave it some dihedral (3 deg) to maintain stability. This design should have good wing loading. The tail has been sized using volume ratios somewhere between that of gliders and homebuilts.
As an afterthought the housing for the fan is quite small, thus the fuselage may need to be scaled to accommodate an EDF with an outer diameter greater than 50mm.
Let me know what you all think!
- MB
PS. I have 8-10 weeks free over the summer and am looking for work experience, let me know if you are in the Melbourne area and have some work!
Comments
Yes, sizes are in mm, Vlad.
Thanks for the links Dave! I have been looking for that one! Yes I think you wouldn't be able to mount an external camera gimbal on this if you want to minimise drag.
In answer to most other questions about this concept, according to the article at the link Dave posted, the power required for the fan to maintain a given speed can be reduced by as much as 50% by using this setup, although my inlet shown here needs to be modified to match that shown in the article.
The momentum drag caused by the inlet is minimised because the air at the inlet is taken from the boundary layer of the fuselage. Extensive wind tunnel tests were conducted that verify this concept (over 85 test runs).
Thanks for all of your feedback!
Your fan will be operating at a reduced pressure and probably burn out the motor. Fans need to accelerate a lot of air to create thrust. It won't be able to draw it in fast enough. It may greatly reduce fuselage drag, but at what cost? Extremely inefficient propulsion.
Actually this paper shows a cutaway of inlet lip and fan exhaust configuration that Goldschmied used in a windtunnel model to validate the drag reduction and resulting power reduction on the fan unit.
AIAA-84-2163
On the Aerodynamic Optimization of Mini-RPV and Small GA Aircraft
F.R. Goldschmied
found here
http://cafefoundation.org/v2/pdf_tech/Drag.Reduction/10.AIAA-1984-2...
Looks promising. I wonder what the best way to integrate electronics and camera's would on this concept so that you don't lose the laminar flow. Conformal antenna's and camera windows seem to be in order for this...
This is very interesting. I read the following papers on the theory listed below a few years back.
Integrated Hull Design, Boundary-Layer Control, and
Propulsion of Submerged Bodies
F. R. GOLDSCHMIED*
University of Utah, Salt Lake City, Utah
and
Shaping of Axisymmetric Bodies for Minimum Drag
in Incompressible Flow
Jerome S. Parsons* and Raymond E. Goodsont
Pur due University, Lafayette, Ind.
and
Fabio R. Goldschmiedt
Westinghouse Electric Corporation, Pittsburgh, Pa
Both of these papers were on NASAs CAFE Green Challenge website at one time so you may be able to still download them. I believe the trick will be the shaping around the boundary layer inlet lip. Also, it may be difficult to get this to work at these low Re. Good luck and let us know how it works if you build it.
Agreed with Zachary.Just stick on folding prop.Nice Design.
The lack of combustion prevents any thrust from being produced in your model. The intake pulling from the rear to be routed and pushed out the rear cancel out each other's forces. The EDF will move a decent amount of air, but there will be no thrust produced that allows the plane to fly.
With that being said, if you took your design and adjusted your intake, I see this being a fairly efficient design.
EDF's convert electricity to noise and little else. Cool in a scale jet for 5 minutes thrashing around the field but not for a UA.