Winch launch speed versus height gain

Ok, I could probably arrange with the winch driver to experiment, but is
there any definitive guidance on getting the greatest height off a winch
launch? (eg. Skylaunch).

i.e. if I'm "driven" at the higher end of the speed range acceptable to my
gliders placarding, will I get higher or lower than a lower speed launch?
I used to consider faster meant higher, but last weekend a most experienced
colleague said you'd end less high, as you spend less time gaining height.
I'm sure there's a set of graphs that would show a polar curve type
trade-off, but is there a simple way of looking at this?

Neil

Check out this Yahoo Group:

http://groups.yahoo.com/group/winchdesign/

There is a tremendous amount of information in this group about winch
launching.

Mike Schumann

"Neil" wrote in message
...
Ok, I could probably arrange with the winch driver to experiment, but is
there any definitive guidance on getting the greatest height off a winch
launch? (eg. Skylaunch).

i.e. if I'm "driven" at the higher end of the speed range acceptable to
my gliders placarding, will I get higher or lower than a lower speed
launch? I used to consider faster meant higher, but last weekend a most
experienced colleague said you'd end less high, as you spend less time
gaining height. I'm sure there's a set of graphs that would show a polar
curve type trade-off, but is there a simple way of looking at this?

Neil






--
Posted via a free Usenet account from http://www.teranews.com

Lowest safe speed gains most height -- twenty years experience with Bluenose
winch


"Neil" wrote in message
...
Ok, I could probably arrange with the winch driver to experiment, but is
there any definitive guidance on getting the greatest height off a winch
launch? (eg. Skylaunch).

i.e. if I'm "driven" at the higher end of the speed range acceptable to
my gliders placarding, will I get higher or lower than a lower speed
launch? I used to consider faster meant higher, but last weekend a most
experienced colleague said you'd end less high, as you spend less time
gaining height. I'm sure there's a set of graphs that would show a polar
curve type trade-off, but is there a simple way of looking at this?

Neil

On Thu, 1 Nov 2007 14:43:47 -0300, "Charles Yeates"
wrote:

Lowest safe speed gains most height -- twenty years experience with Bluenose
winch

Definitely not with our 280 hp Turbo Diesel winch and an ASK-21.

90 kp/h gets about 350 meters, 115 kp/h gets over 400 meters.



Bye
Andreas

Neil wrote:
Ok, I could probably arrange with the winch driver to experiment, but is
there any definitive guidance on getting the greatest height off a winch
launch? (eg. Skylaunch).

i.e. if I'm "driven" at the higher end of the speed range acceptable to my
gliders placarding, will I get higher or lower than a lower speed launch?
I used to consider faster meant higher, but last weekend a most experienced
colleague said you'd end less high, as you spend less time gaining height.
I'm sure there's a set of graphs that would show a polar curve type
trade-off, but is there a simple way of looking at this?

If you want all of the gory mathematics, I suggest you join the Winch
Design Group at:

http://groups.yahoo.com/group/winchdesign/

Oversimplifying, "best" launch height will be achieved by maximizing the
tension on the cable while minimizing the drag produced by glider. With
a sufficiently powerful winch, the weak link establishes the upper limit
on the cable tension. Minimum drag is produced by flying at the best
L/D speed given the polar curve adjusted to the effective wing loading
of the glider, which is the weight of the glider plus the cable tension
divided by the wing area...

Marc

Good answers all so far.

The correct answer is to fly the angle of attack corresponding to best L/D.
This can be determined with "pitch strings" attached to the sides of the
canopy. Once you know the corresponding airspeed, you can remove the
strings although many people find the strings useful enough to keep them.

Launching into a strong headwind, there is an advantage in slowing down a
bit but not so much that your AOA approaches that corresponding to Min Sink.
FWIW, the stall AOA is MUCH greater than even Min Sink.

We really need a practical AOA indicator.

Bill Daniels


"Neil" wrote in message
...
Ok, I could probably arrange with the winch driver to experiment, but is
there any definitive guidance on getting the greatest height off a winch
launch? (eg. Skylaunch).

i.e. if I'm "driven" at the higher end of the speed range acceptable to
my gliders placarding, will I get higher or lower than a lower speed
launch? I used to consider faster meant higher, but last weekend a most
experienced colleague said you'd end less high, as you spend less time
gaining height. I'm sure there's a set of graphs that would show a polar
curve type trade-off, but is there a simple way of looking at this?

Neil

I can't imagine a more practical AOA indicator than pitch strings.

Mike Schumann

"Bill Daniels" bildan@comcast-dot-net wrote in message
...
Good answers all so far.

The correct answer is to fly the angle of attack corresponding to best
L/D. This can be determined with "pitch strings" attached to the sides of
the canopy. Once you know the corresponding airspeed, you can remove the
strings although many people find the strings useful enough to keep them.

Launching into a strong headwind, there is an advantage in slowing down a
bit but not so much that your AOA approaches that corresponding to Min
Sink. FWIW, the stall AOA is MUCH greater than even Min Sink.

We really need a practical AOA indicator.

Bill Daniels


"Neil" wrote in message
...
Ok, I could probably arrange with the winch driver to experiment, but is
there any definitive guidance on getting the greatest height off a winch
launch? (eg. Skylaunch).

i.e. if I'm "driven" at the higher end of the speed range acceptable to
my gliders placarding, will I get higher or lower than a lower speed
launch? I used to consider faster meant higher, but last weekend a most
experienced colleague said you'd end less high, as you spend less time
gaining height. I'm sure there's a set of graphs that would show a polar
curve type trade-off, but is there a simple way of looking at this?

Neil








--
Posted via a free Usenet account from http://www.teranews.com

Well, yes, pitch strings 'work' but it's not really slick. They have to be
on the outside of the transparent canopy where you can see them. On most
gliders, that puts them too high on the side of the fuselage and further aft
than the ideal location making them sensitive to yaw. They really should be
at the maximum width or 'beltline' of the fuselage. Every time I've tried
them, the strings get caught under the canopy frame as you close up unless
someone stood by to ensure they didn't.

Pitch strings are fine for calibrating the best winch launch airspeeds or
illustrating AOA to a student but they're too crude for a permanent
installation IMHO.

Bill Daniels


"Mike Schumann" wrote in message
.. .
I can't imagine a more practical AOA indicator than pitch strings.

Mike Schumann

"Bill Daniels" bildan@comcast-dot-net wrote in message
...
Good answers all so far.

The correct answer is to fly the angle of attack corresponding to best
L/D. This can be determined with "pitch strings" attached to the sides of
the canopy. Once you know the corresponding airspeed, you can remove the
strings although many people find the strings useful enough to keep them.

Launching into a strong headwind, there is an advantage in slowing down a
bit but not so much that your AOA approaches that corresponding to Min
Sink. FWIW, the stall AOA is MUCH greater than even Min Sink.

We really need a practical AOA indicator.

Bill Daniels


"Neil" wrote in message
...
Ok, I could probably arrange with the winch driver to experiment, but is
there any definitive guidance on getting the greatest height off a winch
launch? (eg. Skylaunch).

i.e. if I'm "driven" at the higher end of the speed range acceptable to
my gliders placarding, will I get higher or lower than a lower speed
launch? I used to consider faster meant higher, but last weekend a most
experienced colleague said you'd end less high, as you spend less time
gaining height. I'm sure there's a set of graphs that would show a polar
curve type trade-off, but is there a simple way of looking at this?

Neil








--
Posted via a free Usenet account from http://www.teranews.com

Neil wrote:
Ok, I could probably arrange with the winch driver to experiment, but is
there any definitive guidance on getting the greatest height off a winch
launch? (eg. Skylaunch).

i.e. if I'm "driven" at the higher end of the speed range acceptable to my
gliders placarding, will I get higher or lower than a lower speed launch?
I used to consider faster meant higher, but last weekend a most experienced
colleague said you'd end less high, as you spend less time gaining height.
I'm sure there's a set of graphs that would show a polar curve type
trade-off, but is there a simple way of looking at this?

Read the glider's Flight Manual, which should tell you the optimum
speed. For example, mine (an H.201 Libelle) says:

Winch tow: Max. tow speed 65 kts, most agreeable 50-54 kts.

Of course this is relative to the other numbers: stall 36 kts, min sink
42 kts, best glide 52 kts at my usual flying weight. The most agreeable
speed should be 5 or 6 kts faster with water (not being a B series, mine
doesn't carry water).

We have a 240 hp Supacat and usually launches are pretty much on Vwinch.
Usually I'm grateful if the winchie stays below Vwinch at the top so I
don't have to pull off early. A few times I've managed to talk a driver
into slower launches and have been launched at around 55 kts, which
certainly feels a lot nicer. Its not happened enough times for me to
have compared launch heights, though I don't think theres much in it.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Pitch strings are fine for calibrating the best winch
launch airspeeds or illustrating AOA to a student but
they're too crude for a permanent
installation IMHO.

Bill Daniels


Thats just cause' you haven't tried bumper's new MK
II 'High Tech' Pitch String yet...

Paul