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Experimental Fuel-Cell Airplane's 2nd NASA Test
js7a writes "The Helios prototype, holding the sustained flight altitude record, having unsuccessfully completed its first test with a fuel cell, is almost ready for its first night flight this Thursday, Friday, or Saturday. Helios uses solar panels for flight with payloads over 600 lbs. planned for up to six months using regenerative electrolysis. What good is a plane that will fly for six months without refueling? Besides providing a UAV alternative to AWACS, they can improve internet connectivity."
I wonder about the engineering tradeoffs. The electrolyzer and the tanks add weight, compared to the other approach to nighttime operation of solar powered aircraft -- drift downward. There's quite a bit of stored energy in an airplane that's been lifted to 100,000 feet. At low speed with a good glide ratio, you can coast until dawn.
If you incur the weight penalty to stay at 100,000 feet, you get continuous radio coverage over a ~500 mile radius. If I were Indonesia and trying to deploy broadband over hundreds of islands I'd be really interested in this.
I feel compelled to add another comment here. Everyone is focusing on gravity here as the big factor as to this things glide time. Although this is obviously an issue in the big picture it's not the real issue. Didn't your teachers ever show you the experiments where people would drop a feather and a bowling ball in a vacuum and they would both hit the ground at the same time? Does this mean anything to anyone. I can hear the light bulbs go off now.
The real issue is DRAG a.k.a. FRICTION. If there were no or negligible drag this thing could fly forever. It's the drag that slows it down and causes it to drift back to earth. So what do you need to increase your speed? Propellers. And what drives the propellers? Fuel cells. What these scientists are doing is trying to make their fuel cells more efficient so they can over come their ultimate enemy, drag. Just a little insight for everyone. Cheers again!