Experimental Airframe - Goldschmied Pusher

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!

Views: 2646


Moderator
Comment by Vladimir "Lazy" Khudyakov on December 1, 2012 at 8:01am
Sizes in mm?
Comment by frederic reblewski on December 1, 2012 at 10:19am
I don't understand how this works. first if you take air from the back and send it to the back the force applied to the plane will be minimum at best. the intake section should be at least the same area as the exhaust I think. is it the case here? it seems that the papers from Fabio Goldschmied are based on a jet engine. in that case it works as the gas that is creating the propulsion comes mainly from the combustion and not from the intake. but I may miss something...

Moderator
Comment by Gary Mortimer on December 1, 2012 at 11:04am

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.

Comment by Zachary Toon on December 1, 2012 at 12:49pm

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.

Comment by Dez Socks on December 1, 2012 at 2:11pm

Agreed with Zachary.Just stick on folding prop.Nice Design.

Comment by Dave Faulkner on December 1, 2012 at 2:37pm

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. 

Comment by Dave Faulkner on December 1, 2012 at 2:58pm

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...

Comment by Greg Fletcher on December 1, 2012 at 4:02pm

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.

Comment by Martin Burston on December 3, 2012 at 9:05pm

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!

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