On Wednesday, January 16, 2013 10:38:02 AM UTC-7, Tony wrote:
On Wednesday, January 16, 2013 11:28:47 AM UTC-6, Bill D wrote:

Just for fun, lets work out the numbers. With that much tension, probably not too much catenary arc (droop). Taking advantage of the low specific gravity of Spectra (it floats) conducting the launch over water should be considered with the ground roll on a near-shore runway and the winch on a ship 15 miles or so offshore. Think Dillingham Field in Hawaii. Presumably the rope tension will need to be equal to the glider weight as is the case with glider winches so 1/4" Spectra isn't going to do it. The German DAeC winch guidelines require a minimum of 150% the strength of the heaviest glider to be launched so the rope will need a breaking strength of no less than 1,275,000 Lbs-F. Consulting the Samson Rope "Amsteel Blue" catalog you will need 3 5/8" diameter rope. ________________________________ And engineers, how many h.p. winch to pull 245 tons? (Electric/Diesel locomotive engine?) ________________________________ We know the force in Lbs but we need the giant glider best climb speed (Vy) so assume 120 knots or 202 feet per second. A simple formula with give HP but overestimate since the rope speed will reach 202 FPS only at the beginning of the rotation phase but it helps estimate the peak HP required. One HP = speed in FPS times force in Lbs divided by 550 so 245 tons is 490,000 pounds times 202 FPS gives 98,980,000 divided by 550 = 179,964 HP. For most of the launch 'merely'100,000 or so HP would be enough if the ship based scheme scheme was used. If the ship were sailing away from the glider at the start of the launch, its kinetic energy would supply any "excess" HP needed at the start of the launch. So what engine could do that? The Wärtsilä-Sulzer RTA96-C could. http://en.wikipedia.org/wiki/W%C3%A4...Sulzer_RTA96-C I'll estimate the launch will take about 10 minutes so with a specific fuel consumption of .28 Lbs of per HP/Hr the launch would consume about 520 gallons of heavy bunker oil or about what a 747 uses taxiing to the runway. _________________________________ Still sounds more appealing than 747 wake turbulence. ________________________________ Indeed! So what could go wrong? You'd need a well thought out "launch abort" plan so the glider could always be landed back on the departure runway if the launch fails very similar to the Space Shuttle abort procedure. Most likely, it would not be necessary to jettison the payload in an emergency. Bill D



i think the coolest way to deal with a failed winch launch in this scenario would be to fire the rocket, with the glider attached. this would quickly get you the altitude needed to be able to easily make it back to a runway..

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.