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Originally Posted by KevinPlante
You do not get more lift by flying in ground effect. You do, however, have less drag because the wingtip vortices are disrupted by the ground being there.
Don't believe me? Think of it this way - How many g's are you pulling in ground effect? I would hope about one. g = L/W and we can assume weight will not change a noticable amount while going into and out of ground effect. Since you are not pulling more g's, the only variable left is lift, which cannot change by itself.
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Not being an expert in aeronautics I may not have said it quite properly but let me check if my understanding (however worded) is basically proper. While you are correct about the less drag due to vortex disruption, I also believe there's less downdraft as a result of vortex disruption as well. This reduction gives the wing more ?lift? than it would have were the ground not there. Take away the ground (changing nothing else, airspeed, AOA, wingform, etc) and the "aircraft" (flying @ GE altitude) will fall. Imagine WIG'ing along on a mesa top and "flying" off the edge. Equivalently the "aircraft" would (for a given wing design) have to fly faster, or at a different/higher angle of attack, to maintain a steady altitude at a higher (say 1000 ft) altitude than it would at a ground effect altitude. Alternately the wing could be smaller, generating less total lift, if the "aircraft" were to be confined to GE altitudes, but thus loosing the ability to truely fly in the conventional sense. It was the stubby nature of the winglets on the "Howerwing" that reminded me of the Russian ekranoplans I've seen pictured and read about before. I recall reading an article on how the US military is looking into WIGs as a gap filling transport craft (btw C5's and naval ships). In this case the military was looking to get greater payload carrying capability via a WIG, vs a conventional airplane, by virtue of the added ? lift ? (for lack of a better word) afforded by ground effects. Anyway that's my understanding.
ps - Great link RG ! I've not thought about hovercraft in probably 20 years. I was amazed to see what relatively sophisticated craft even a semi-handyman could build for pretty small $$. Aaah if only I had the time. I'd build one with a daggerboard (and retractable rudder ?) so it would corner more like a boat. It'd be fun to pull up to Wolfeboro some Sat noon in July, past the waiting boats and up the launch ramp to "dock" in the auto parking lot.
pps - Now I'm wondering if you couldn't give up the amphibious nature of a hovercraft and use an outboard (or some kind of outdrive) to propel the hover, err boat, err hoverboat. I don't know about the relative efficiencies of air vs water props, might not be too different if I understand the lesson of MITs "Decavitator" correctly. Any person standing nearby would sure appreciate the screw design rather than the prop wash. Perhaps another hybrid design is the ticket ...
