Fri Mar 26, 2010 11:34 am
Kudos for an inventive idea and perhaps a fun toy. But like Amelia Earhart's last flight, IMHO it suffers from some apparently poor decisions that will have only one end result.
First, he has only rudder and elevator control. Like any old broken down model airplane builder, I can vouch for the idea that this works OK... ASSUMING that you have a lot of dihedral angle (which he doesn't), and assuming that you are not designing the aircraft for low altitude maneuvering (which he is). Using yaw/roll coupling works great but it is less precise and takes more time and more room when you are maneuvering around real low. So the previous comment about dragging a wingtip and a cartwheel is absolutely right on.
If you are doing low altitude maneuvering, you need 3 axis control not 2 axis. There's part of that video clip showing him doing turns with the tip just inches above the water and one where it looks pretty close to a tree.
Second, his wing attachment looks like it is not very well thought out. Sliding one tube over another and putting a pin through it is common in ultralight design but it is part of a system where there are flying wires, a kingpost, or struts, etc.Any trained engineers out there can feel free to set me straight, but to my amateur eyes this looks awful.
I think it is a function of the ratio of the tube diameter to the wing thickness. On the Grumman Yankee and AA-5 series, the tubular spar worked fine. This is because it was a much larger tube. The tube on Heeman's ground effect toy looked like a 1 inch or 1.5 inch tube, where the wing thickness was 5 or 6 inches. You can see in the videos that the spar "carry through" tube in the boat hull is bending visibly in 1G flight.
Again, this toy looks like a lot of fun - and I for one salute his back-woods ingenuity !. But it just seems that just a little bit of aero engineering knowledge would add a lot of safety. He should be using carbon fiber windsurfer masts as spars, because they're strong, not too expensive, pre-made, very flexible, and the tube will not buckle in high deflections. He needs a better spar attach system. He needs good old fashioned "polyhedral" like a 70 year old free flight rubber powered model airplane, which will give him a lot more roll coupling with yaw-only... and it will increase the height of his wingtips above the water in a turn.
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