Standoff placement -how does it influence performance?
Subject: Standoff placement -how does it influence performance?
From: email@example.com (Ronald S. Reich)
Date: Thu, 27 Jan 1994 20:41:06 GMT
~Date: Wed, 26 Jan 1994 21:50:44 GMT
~From: firstname.lastname@example.org (Andre The Great)
~Subject: Standoff placement -how does it influence performance?
Andre The Great, writes:
>A friend of mine is considering building a kite- the original
>plan is for a kite without standoffs- however, he wishes to
>modify the design so as to incorporate a pair. The question is :
>where along the trailing edge should one attach the standoffs?
The rest deleted:
Here is a Theoretical Analysis for the placement of the Standoffs
for a Delta shaped Dual Line Kite.
1. Nose angle is about 90 degrees.
2. Wing Span is about 8 feet.
3. Depth of Billow is about 10 inches.
4. There is a ridged center spine.
Purpose of the Standoffs:
The primary purpose of the standoff is to reduce the amount
of time required for the Sail to acquire the Billow position.
This is a definate advantage in light and gusty winds when flying
the kite near the edge of the wind window.
Primary Balanced Placement of Standoff:
Hang the kite from the ceiling with the bridle side up.
Adjust the angle such that the back side of the sail is parallel
to the floor. (frame will be tilted nose down) Lay a dowel or
kite stick on each side of the center spine. The dowel should
create the natural billow. (valley from nose to trailing edge)
The point at which the valley meets the trailing edge is the
Natural Balanced Position for a Standoff. The center of pressure
of the sail should be very near the line created at the bottom of
the valley. The flight characteristics will be different for a
center of pressure on the outboard side of the valley then for a
center of pressure on the spine side of the valley. But that is
a whole other design consideration.
Theory of Turning: Top View
___ /\ /\
/.|.\ / \ / \
/ . | . \ / A B \ / C D \
/ . | . \ /------------\/------------\
/ . | . \
/ A . B | C . D \ __
/ . | . \ Line of | \ Wind
/------*------|------*------\ Sight \
Considering the active surfaces for a Right Turn. The Line
of Sight represents the effective wind direction when you pull on
the right line and tilt the right side of the kite into the wind.
The surfaces B and D are positioned "Edge to the Wind" and there-
fore have limited effect on the turn. However, surfaces A and C
have been positioned to become the active surfaces with more wind
pushing on them. Notice that surface A is further away from the
center spine than surface C and that the Plane of surface A has
increased its angle of attack due to its slope from the trailing
edge toward the nose of the kite. Conversely, the plane of
surface C has become almost vertical.(flat to the wind) This is a
stalled position. Therefore surface A advances and surface C
slows down. Consequently the kite turns to the right.
Effect of Standoff Position:
When you move the standoff out toward the leading edge, the
effect is to reduce the area of surface A and increase the area
of Surface C. At some point, Surface C will dominate and the
kite will have difficulty turning. However, The position of the
bridle pick point (Tow Point) will also play a part in the kites
ability to turn. The placement of the Pick Point is a whole
other design consideration.
When you move the standoff in toward the center spine, the
effect is to increase the area of Surface A and decrease the area
of Surface C. Turns should become faster and tighter. An ex-
treme case would be to Standoff the center spine from the cross
bar. (No central Dihedral.) The Speed Wing is an example of
this concept. (Though it has no center spine)
I hope that this has shed some light on the effects of the place-
ment of the standoffs for a delta dual line kite.
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