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|QUESTION (in english... my german language is too poor, sorry)|
Ron Graziano (US champion, RonG) has writen about basic STX bridle adjustments (updated version) :
Original version (extract) :
"MOVING KNOT D outwards (towards wing) :
Bad : wider turn radius, wider spin.
Good : improve precision (more stable, less twitchy).
MOVING KNOT D INWARDS (towards spine) :
Bad : makes the kite more twitchy.
Good : tighter spins."
And RonG explains the interaction of the displacements of the knots due to the bridle design (1).
Thus, wider space between tow points => wider turn radius.
Is that true for all bridles (static & active) ?
PRO (active bridle)
- Mark Reed, rec.kites 11.05.1997 & Bridle adjustments at the center T fitting.
- Marty Sasaki, rec.kites 10.08.1995 & forum GWTW 17.05.2004.
- Paul May.
CONTRA (static or active bridle)
- Andy Wardley, rec.kites 9.06.1997 (end of point 3)) & Tuning a Dihedral Active Brilde (alinea 8).
- Bert Tanaka, rec.kites 14.07.1994 & 1.02.1995.
- Marty Sasaki, rec.kites 8.08.1995.
- Peter de Jong (Dual line kites, 5th problem).
- Peter Peter's (Adjusting, alineas 3 & 4).
TRYING OF ANSWER
With wider space between the 2 tow points and same bridle depth, you can tilt more the kite => you can tilt more the aerodynamic force => you can tighten more the turn (2).
If you move the knots D outwards => tow points moves upwards (interaction (1)) => angle of attack reduces => aerodynamic force reduces.
If you reduce the aerodynamic force while turning => wider turn radius (2).
Perhaps the variation of the angle of attack has more effects than the variation of the bank angle ?
But, with a turbo bridle, when you increase the angle of bank of the kite, you increase the angle of attack => aerodynamic force increases.
And, if you pay attention to interaction (1), you move the tow points only outwards.
Thus, I think that, with static or active bridle, wider space between tow points
=> tighter turn radius.
=> more precision.
I think that RonG confuses precision with wide turn and radicalness with tight turn ?
(1) Bert Tanaka, rec.kites 27.06.1993.
Attention to the type of bridle : European kites vs USA kites (Peter de Jong).
(2) R = V^2/a (Object Motion with Side Force, Nasa GRC).
R = radius of curvature
V = velocity
a = acceleration generated by the side force
- Editiert von Gerard P. am 26.06.2004, 17:45 -
in my opionion this question is very interesting. I'd read several clarfication attempts but none of them was 100% satisfying.
If I get the time, I'll translate your question in the next days, hoping for some more answers.
Bye for now
|Short report of the GWTW forum :|
Gerard P. : "I'm only speaking about an other point of view, the turn radius.
- Wider towing points allows greater banking.
- Narrow towing points the opposite.
Do you have observed that wide towing points can't give tighter turns and narrow towing points can give tighter turns ?
Do you have observed that in a turn when you pull more and more one line, the kite reaches a point where there is no more traction in the line outside the turn ?
I think that the kite reaches the maximum value of angle of bank.
While the kite tilts, the axis of the line inside the turn moves outwards & the center of pressure of the whole sail moves also outwards (1), till a point where they line up together.
In straight flight, the center of pressure of the whole sail is just between the two axis of the two lines.
In a turn, the axis of the line inside the turn & the center of pressure move from their initial position to a point where they are line up together.
Do you have observed that when you reach that point the turn radius is different with wide or narrow towing points ?"
Marty Sasaki : "I never really consider the amount of input you need to get a turn. After a few minutes of flying a kite I've already adjusted to what needs to be done. I'm not quite sure what Ron means when he says the turning radius is larger. If he means that given the same amount of input moving the tow points outward will result in a larger turning radius, then we agree.
What I meant in my rec.kite postings is that the tightest turning radius is smaller when you move the points outward. This is certainly true of a static/3 point bridle. I believe it is also true of a turbo bridle. As Walter says a turn also has the result of moving the tow point down.
The tighter turning does require more input, ie, a greater difference in the line lenghts.
There is a point where the turn won't go any tighter. It will either result in the outer line being slack, or the kite actually turning with a wider turning radius, or sometimes just falling out of the turn completely."
RonG : "I have posted the edited document."
(1) The relative wind speed is higher on the portion of sail outside the turn => the lift is higher on this portion of sail (The lift Equation, Nasa GRC).
- Editiert von Gerard P. am 26.06.2004, 17:42 -
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