joriws wrote:Not wow, that was downhill assisted run, not kite powered only run
Sure, but my response was to the OP's concern about whether a kite could move through the air at 80knts without canopy deformation etc.
I still think two small lei kites with two operators in one craft would work more efficiently than a single operator using a larger kite. 80knts will require very high wind and therefore a large foil kite is certainly out, in fact, any foil kite is out of the question, imo.
Re: 80 knots on a foilkite
Posted: Thu Nov 21, 2019 1:22 am
by plummet
142kph even if dh assisted stand on some slabs of wood being pulled by and angry kite is a storm is still nucking futs. I say full credit to that man. He can still claim to be the fastest human pulled by a kite.
Max I've done in the kite buggy is 90kph. That's still silly as f***. But no where near as silly as on ski's at 142kph.
142kph even if dh assisted stand on some slabs of wood being pulled by and angry kite is a storm is still nucking futs. I say full credit to that man. He can still claim to be the fastest human pulled by a kite.
Sorry but I have to disagree. For example, the current world speed ski record is over 150 MPH. If they were to slow down to half their speed and happened to be flying a kite at the time, does that equate to some flavor of fastest human on a kite?
IMO a more accurate description would be "the fastest human pulled by a kite with gravity assist.' Slight inclines offer substantial influences in this respect. I'm not diminishing Felix's effort because it's a kick-ass run. But trying to keep it in perspective.
In regards to what this post is about. If I'm understanding the question, I think by and large most kites are capable of reaching and maintaining the speeds sought here without too much difficulty. I've seen a number of kites operating well into the 60 kn+ range with no noticeable effect on the wing. This includes Dual skin open cell and closed cell foils and LEIs. Some being race variant and some being much lower aspect freeride kites. Even single skins seem to be reasonably good in that range.
In my experience, the kites with the grunt get the job done better than highly efficient race rigs. My fastest speed were on 12m Peter Lynn Arcs. They hit the sweet spot for me between grunt, speed and the ability to dump power in between runs and getting back upwind.
It can be fascinating to see these computeranimated dreams indeed
But would much reather see even the slow attempts on video, to get there.
We never see this though, as usually secret maybe?
Only WHEN some has succeded
Peter
Re: 80 knots on a foilkite
Posted: Fri Oct 16, 2020 11:28 pm
by Schietwedder
The concept to align lift forces without any resulting moments heeling and roll moments at least, is not new.
They did 65+ knots on the sailrocket (don't remember the exact number in the end think it was 68 or something)
The problem as they say in the video is cavitation underwater which suggest the foil profile to be a supersonic profile, it doesn't look like a normal wing/hydrofoil profile, more like a sharp triangle.
The wing on the other side has to have a really high glide ratio (L/D) as when the drag increases more than the lift at high velocities it still produces a reasonable vector forwards (drive force). The clean wing as they had it on Sailrocket is already a ideal shaped kite so to say in my opinion.
Yes there is a bit of drag of the superstructure supporting it, but in a kite you also have ballooning, line drag, which is a considerable amount of overall drag. The problem with high AR kites is also a considerable amount of more lines. (Vmg 13^3 or what it was, Armin wrote something about the line drag on his FB and also in his Sonic 3 presentation you can see excels of their L/D tool which incooperates the lines at a decent amount.) Then there is an optimum somewhere between AR 7 and 13 but not higher for sure for foilkites.
Tube kites on the other hand have less line drag but the profile has a lot worse L/D.
If you look at paragliders and sailplanes, the glide ratio of the highest performing paraglider is at best somewhere at 15 without pilot, maybe even 18 but sailplanes with solid wings easily above 30.
Maybe the best solution is then a high AR solid carbon fiber kite wing with a starting/landing support structure which folds in and minimal lines to control power and twist.
The Sailrocket team took years and lots of breakages till they proceeded from the high 50s into the 60 knots range.
A lot of their issues I recall was in the steering/control systems/stability and of course on the hydrofoil cavitation.
To minimize aero drag they even built the hull with the cockpit not 90degrees to the cross beams but into the direction of the apparent wind at 65 knots of boatspeed.
Lots of interesting engineering challenges for sure.
Hehe and yes a bit more work and money needed than just a few cool graphics.
...
Tube kites on the other hand have less line drag but the profile has a lot worse L/D.
If you look at paragliders and sailplanes, the glide ratio of the highest performing paraglider is at best somewhere at 15 without pilot, maybe even 18 but sailplanes with solid wings easily above 30.
Maybe the best solution is then a high AR solid carbon fiber kite wing with a starting/landing support structure which folds in and minimal lines to control power and twist.
...
Lots of interesting engineering challenges for sure.
Hehe and yes a bit more work and money needed than just a few cool graphics.
Competition Paragliders get their best L/D near (11 to 13:1)
and the best sailplanes money can buy, will get you near 58 to 60:1 , but
competition sailplanes need to turn in thermals, so their best L/D
in around 50:1,(like the ASG 29 :https://en.wikipedia.org/wiki/Schleicher_ASG_29
and my Atos hang-glider clams a 19:1 L/d.
The Real difference between the gliders is the SPEED they get their best L/D
with PG near 20 Kt, Atos at 33 kt , and comp sailplanes at 52kt.
Fastest i ever bin on land, was at Ivanpah dry-lake, with a 2-liner Airush 3m
got me rolling at near 48kt, on GPS , (in only 31-kt wind). It showed me
how much drag those 4-line kites make ; the Airush 3m is Not a very
efficient kite , but had 1/2 the line drag of a 4-liner.
I think Schietwedder is correct with his assessment ; real speed is
gonna need to be done with some seriously efficient wings , (Not Kites)
as we know them now, and the bridle's, are gonna have to go ByBy !
By real speed, i mean 85kt + ; when a kite can get into the Greenburg
numbers of 126mph, (109-kt) , that's when we know were FAST !!
Bille
Re: 80 knots on a foilkite
Posted: Sat Oct 17, 2020 7:18 pm
by Schietwedder
Hi Bille,
Nice to know the more accurate numbers, they are even more extreme than I had in my head.
Hi Bille,
... they are even more extreme than I had in my head.
Germany is really Big on gliders ; this is what 47:1 in an Old
comp glider will get ya: he could really care Less ; if he fly's
through the Lift side of a mountain ; or the back-side, where
the rotor is , (the glider is SOooo efficient, it just takes it All) .
Most of this video ; the pilot keeps the glider , right next to
the mountain !!
Peter