@kitefreak I appreciate your comments here, but to be frank you are not getting your message across to me. I don’t understand anything you are saying here. Perhaps if you could the essence of that repeat with a few more words and a “tighter” story?
Looking at the paper, and using your kite size of 1000m^2, we have:
- Area 1000 m^2
- Maximum force at 4 m/s
- Maximum reel out speed 5.5 m/s at 11 m/s wind
- Altitudes of 1000-2000 m
- Glide ratio E = 20 (the flying speed is stated to be 80 m/s in 4 m/s wind)
Lets also add a lift coefficient and rho, and looping radius
- Lift coefficient of wing 1.0
- air density rho 1.225
- looping radius R = 300 m
- drag coefficient of tether 1.0
I’ll leave out the cosine effect for now, to make things a bit simpler. I also assume using a single tether. Double tethers would increase the drag by \sqrt{2}. Also, I will assume that the tether drag cant slow down the kite.
The tether to support this would have to be approx 45 mm diameter. I guess UHWMPE is to be assumed as material (I believe this is quite optimistic though). Putting these numbers through my calculator gives me:
- Tension 7800 kN / 784 ton
- Tether 110 mm
- Power at 11 m/s wind 43 MW
The rig seems to fly well with 2 km tether / 1 km altitude.
So far these numbers look really good, if you believe tether drag does not affect the kite. Then we will look at the exact same scenario, but including tether drag into the total.
The effective glide number E is now E = 3
- Tension 176 kN / 18 ton
- Tether 17 mm
- Power at 11 m/s wind 1.0 MW
It is difficult to say whether the 1 MW rig is still worthwhile. Anyways it seems that if you are planning to fly at these altitudes, even with a 1000 square meter kite, you are not getting much benefit in having a high efficiency kite. Perhaps scale EVEN LARGER? (hint, my calculations show a 2000 sqm kite also has efficiency approx 3 at this altitude).
Now a simple question to “prove” that tether drag exists and slows down the kite: Where does the energy come from, to drag the 6 km x 17 mm tether through the air (total 2D area 100 square meters)? The drag forces are being converted into heating in the air, and energy cannot come from nothing… (it is simple to conclude that only the kite may provide this power)
Anyways, you guys are hijacking my thread. If you believe drag is zero, the whole thread is pointless…