On Jan 16, 6:06*pm, Bill D wrote:

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.


Rope speed must be reduced on a NORMAL winch launch, where there is
not much density change between start and ending altitude. Remember.
This is NOT a normal launch we are talking about. And the wind
doesn't always blow, so you won't always get that effective horsepower
and the winch speed may have to increase at some point in the launch.
Agree that speed will hit a high right at rotate, and slow some from
there. But when you are talking of climbing to where air density is
just a fraction of what it is at launch, you may well be reeling in
the rope considerably faster for the last half of the launch than you
are at lift-off.

There is also the matter of accelerating a quarter of a million pounds
of rope in addition to the half million pounds of plane. And by the
way, the article references a paylod of 490,000. That is not the
total weight of the glider and payload package! Ugh! In your normal
winch launch of a 1000 lb glider, you aren't having to accelerate 500
lbs of rope, so you have an easier time accelerating the system.
There are scaling effects that have been missed in the first brush.
But, that is OK. It is fun to think about.

And you may get a Cd advantage, but you are still dragging something
through the air that is almost 20 times the diameter at over twice the
glider flight speed. So, your Cd may be down a hair, but your total
drag is going to go up a bunch. Even in terms of percentage of total
system. Again with that scaling. And again, drag is likely more
important than weight when the weight of the rope is less than 1 or 2%
of the weight of the glider. When the weight of the rope is 50% of
the weight of the glider, it is a whole other story.

Still think you have under-estimated the fuel consumed.

Now, how can you possibly claim that if the boat is using its engines
to hold position, that it is not fuel consumed for the launch? Just
drop the anchor and be done with that part of it! :-)

Enough of this semi-technical talk. This is, after all,
Recreation.Aviation.Soaring. The place where people bash the SSA
Rules committe for not adopting the IGC Rules, talk about how ugly the
PW-5 is, and in general, just waste time.

Steve
(Kill-Joy)