On Wednesday, January 16, 2013 6:06:59 PM UTC-6, Bill D wrote:
On Wednesday, January 16, 2013 2:52:14 PM UTC-7, Steve Leonard wrote:

On Wednesday, January 16, 2013 12:14:36 PM UTC-6, Bill D wrote:







"Plausible as a last resort. Lets look at the acceleration and rotation phase. 1G acceleration is 19 knots per seconds per second so let's set Vr at 100 kts and Vy at 120 kts. The glider would lift its nose wheel in 5.25 seconds and lift off in about 6 seconds. Vy would be achieved in 6.3 seconds. Vr would be reached in about 130 meters or 430 feet, Vy in about 200m or 656 feet. Assuming you start with a 10,000' runway, that leaves about 9300' left to land and stop straight ahead from 120 knots. You might be able to do this up to a height of 1200 feet AGL given good glide path control devices. Of course, the runway would have an over run braking surface at the departure end plus maybe, arresting wires. Above that, if the glider L/D is high enough, a circle-to-land maneuver should be possible. Do I think this is actually possible? With the right glider design, absolutely. I hope the Dillingham guys will put a winch on a boat and try for an altitude record as a proof of concept."







Minor and forgivable glitch, Bill. Knots is already velocity. Knots per second is acceleration. You said knots per second per second. That is rate of change of acceleration, or "onset". I won't use the other term, as some might think I am snarking at you.







Your boat will have to be anchored, or there will be many HP expended keeping it in place during the climb. So, no initial launch acceleration by having the boat moving. Dang it.







Ture airspeed as altitude increases? 200 feet per second true going through FL200 won't be much indicated airspeed. So, your rope speed will keep going up as the climb progresses. Try to take advantage of the wind aloft. Maybe you can reduce this effect?







You probably will start seeing significant horsepower lost due to the rope being dragged through the air by the glider, and it probably will have a lot more of a catenary. Yeah, tension will be high, but so will drag. And also, the weight will not be insignificant as far as power to lift the rope goes. How much will 15 miles of that 3.625 inch Amsteel blue weigh?







Things change a lot when looking at the horsepower required to lift and drag 20 lbs versus thousands of pounds. Percentages may be nearly the same, but absolute values are not. I think your fuel consumption estimate is low, Bill. :-)







And while we are talking of far out concepts, I still like the idea of being above the jet stream and dropping a chute on a long rope down into it.. It starts out falling behind you, but once the chute is in the high velocity "core" of the jetstream, you turn around, allow the chute to inflate and if the gradient is high enough and your plane can fly slow enough, the chute can drag you "downwind."



Thanks for the comments, Steve. Of course, you're right 1G is 19 knots/sec.



However, rope speed must sharply be reduced as the glider enters the climb - and even more if there are headwinds otherwise the glider over speeds. I suspect the true airspeed effect would be more than offset by upper winds.



15 miles = 269,280 lbs However, since the rope is getting shorter as you climb, you wouldn't have to lift that much. Drag is more important than weight. You'll gain a bit of Cd on Reynolds number compared to the thin ..188" diameter rope commonly used in glider winches.



Actually, I assumed full HP for the whole launch but it will have to be backed way off in the upper half. Tension stays constant but HP doesn't since rope speed has to drop to avoid over speeding the glider. (Water skier effect) I think I probably over estimated the fuel.



A big ocean going tug like the "Far Sampson" could be the ideal platform. It could maintain position with its monster engines. If that turns out to be a problem, a big sea anchor would be the next option. The big Sultzer diesel might not be the best choice for 10 minutes of power. A gas turbine might be a better choice.

Can't help myself but I have to add a 'political' comment: If we were on the metric system errors as made above would be unlikely. When oh when will this country ditch the silly medieval units of measure we use (and nobody else) and join the world and scientific community?
Herb