Expert: Mark Janus - 12/17/2007

Question
Hello,
I have been researching and building my own Coanda aircraft (http://jlnlabs.online.fr/gfsuav/index.htm), which utilizes the Coanda Effect for lift.
I have built one but replaced the gyroscope by counter rotating the whole airfoil. Thus, the faster it rotates, the more stable it will be (at least more stable than shown on the website.
Yet mine does not fly even though it has the same weight. When I turned on the engine, the scale turned from 530 to 500 only, instead of turning to 0. Why is this? Is it because my battery/etc is blocking the propeller intake dramatically? Or is it because of my airfoil shape does not have a high chamber?
Here are my diagrams and results
diagram: http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01279.jpg
pictures:
http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01266.jpg
http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01269.jpg
http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01270.jpg
http://i145.photobucket.com/albums/r201/wildblueyonder/DSC01278.jpg
Thank you for the help!
Sincerely,
Eric

Answer
Sorry for the delay in getting back....  haven't been monitoring my e-mail adequately over the holidays....

I would say that yes your battery pack (and motor) may be adversely effecting the inflow....  also, what is the size of your motor....it need sto be adequately sized to do the job...  I wouldn't think the curvature is the problem, I would on the other hand try to contour the flow out of the fan a bit more such that it does not directly impact the upper surface quite as bluntly...the upper surface would be better served as a kind of an elongated (or stretched) S shape with the top curve on the S being much much smaller than the lower curve of the S ....  the lower curve is really the "airfoil" shape, the upper curve is the immediate outlet of the "ducted" fan. also the outlet of your shroud should have a radiused end such that the flow is smoothly guided over the surface of your vehicle

You could use a bit of smoke to see if the flow is following the contour of your vehicle....

Hope my suggestions help a bit...
mj