It would seem considering the the size of the propellers to the wing, they would dominate the flowfield, regardless of rotation. I think I would be more concerned with their effect on alpha, more so than induced drag.AeroFranz said:Robunos,
thanks for taking the time to post parts of the article. I have been trying to figure out if there is actually truth to the widely reported statements of reduced induced drag thanks to counter-rotation of the props. In the book "Radical wind tunnels" the assertion is made that wind tunnel tests showed little or no difference with models having either sense of rotation. I need to find the relevant NACA paper on NTRS...
I am looking for more information on the Boeing 390, 391, 396 projects. Does anyone have any more, not posted here?cluttonfred said:I am sure everyone is familiar with the 1940s V-173 and XF5U-1 projects. If not, the Vought Heritage Museum has some nice pages and pics here: http://www.voughtaircraft.com/heritage/products/html/v-173.html
I know of the similar Boeing design from the same era, the Model 390/391. Aerofiles.com has a little info and a pic on that one here (scroll down to the 390): http://aerofiles.com/_boe.html
I know of some pre-war and WWII-era design like those, but does anyone know of any similar low aspect ratio designs in the post-WWII era?
And no, I don't mean something like the Lockheed F-104, which certainly has low aspect ratio wings. I mean low-aspect ratio flying wings or something otherwise similar to the Vought and Boeing designs above.
Thanks and regards,
Looks like this concept;hesham said:here is a flying flapjack concept,created by Mr. Charles Zimmerman,maybe it
was a real design.
The key invention of Zimmermann's 'Flying Pancake' design is that the propwash reduces drag. At low velocities it does enable the wing to generate lift and it provides control authority but the location and rotation of the propellers is all about drag. Low aspect ratio wings with high chords towards the tip (ie square or round wings but not deltas) have large wing tip vortices. These vortices generate induced drag and getting rid of them is what winglets do on your typical airliner. On the Flyjng Pancake the propellers are located along an axis very close to the wing tip and counter rotate against the wingtip vortices. So the propwash of the air screws cancels out the vortices and therefore improves the lift drag ratio if the wing. So you get the high lift at low velocity benefit of the very low aspect ratio wing without the high induced drag of the same wing especially at higher velocities._Del_ said:But you do lose the theoretical benefits of having the propwash pushing over the lift/control surfaces, I should think.
Hi;robunos said:Doing a bit more digging, it seems that Milt Hatfield built 3 Little Birds in total, each one differing from the others. #2 and #3 incorporated fibreglass in their construction, to varying degrees. All three still survive, but not in flyable condition.
See here :-
and here :-