The light weight, low cost, sure fire, place anywhere,
Tow Release for Hang Gliders and Paragliders
PITCH & LOCKOUT
This diagram shows in scale
a Hewett Center-of-Mass bridle with the apex ARS (weaklink attachment
point) in a pendulum swing that covers positions from launch to top of
tow. The arcs show 2 different bridle lengths. Notice how as altitude
increases (pitch-up to the towline), the distance from the nose to the
release will also increase. The 40% mark represents a release position
just prior to the upper bridle line touching the base tube, a point where
(in my opinion) a newer tow pilot could easily release on his/her own
and have enough altitude to make it back to the LZ. But if an inadvertent,
uncorrected turn occurs, the release would activate before the bridle
begins pulling the nose of the glider down.
April 22, 2000
- Static line towing at Cullom IL, using 3000' of 3/16" hollow braided
poly towline. I set the nose line at the 40% length as described in the
copy below. My bridle is 20 feet long, divide by 10 and multiply times
4 gives a noseline length of 8 feet. As I climbed on tow I could see the
noseline tightening. At about 800 feet I could have easily pushed out
to release but chose to see how high I'd get. At 850 feet I had to pull
in slightly to keep it from releasing, but was still climbing at minimum
tension of 110 pounds. At 960 the line was sufficiently tight and I just
let the control bar out. It cut cleanly and I was off tow.
April 30, 2000
- Aerotowing at Leland IL. Arranged with the tug pilot to let him know
what I would be attempting. I set the glider on the dolly where the nose
angle is fairly high, pulled the apex of the bridle to just above ground
level, measured the distance at that angle and reduced it slightly to
6 feet long... I really had no idea how long it should be. During the
tow in very turbulent conditions I never climbed very high behind the
tug until about 1200 feet when I hit a boomer thermal. As I eased the
bar out and began climbing above the tug the noseline got noticeably tighter
(as expected) but it was too long and triggered the tug's release when
I was almost vertical to the tug. Next aerotow test will be with 5 feet
After these two
tests it's plain to me that the Pitch Limiter will work well if the length
is correct. So as I continue testing, I'll post the results for you to
2002 - Pat Denevan is using a "nose line" as an automatic release with great success... also see Dave Broyles' note below.
More on the concept
In all of towing
there is a potential for the dreaded LOCKOUT. This occurs when the pilot
or conditions allow the glider to get so far off the towing direction
that weight shift alone will not work to bring the glider back. The excellent
book, Towing Aloft, by Dennis Pagen and Bill Bryden, goes into
great depth on the causes and cures. Please read it as there's a wealth
of information within the covers.
Bottom line: YOUR WEAKLINK
WILL NOT SAVE YOU! Remember that fact and these simple corrective
actions: 1) stay on tow by correcting as necessary; 2) recognize an out-of-line
situation early; 3) release as quickly as possible; 4) throw your chute.
The lockout starts with a bit
of roll away from the tow direction. This rolling ultimately makes the
glider want to behave like a tail-less kite and turn 'round the line.
A short way into the turn there is a high degree of pitch-up attitude
relative to the towline, so having a release at the point of too much
pitch could automatically release the pilot and hopefully provide the
pilot with sufficient recovery time.
How it works:
With the release at the ARS
(Apex Release Site, as described above) a second release line will be
attached to the glider's nose. As the glider pitches up relative to the
towline, the release gets farther from the nose and tightens the line.
This arrangement will work
with most any release that activates reliably with side pulls,
not just the Linknife. It should work similarly with Aerotow launches
that use a main V-bridle and ARS release position. With a little modification,
it should also work with keel-mounted aerotow releases and with payout
Who would use it?
Every pilot new to towing could
benefit from the Pitch Limiter setup, not just brand new Hang 1's but
highly seasoned Hang 5's as well if they have never towed.
The needs of a new tow pilot,
in my opinion, to learn the launch style and towing requirements outweigh
the lure of a high altitude flight. The newest pilot, fresh from his/her
tandem lessons and soloing for the first time, should be "protected"
from his lack of muscle memory and short term brain/sensory translation
and so could make use of a Pitch Limiter until 10-25 successful tows are
completed, showing good control, staying on track, and no tendency for
oscillation. It might take a Hang 4/5 only 2-5 tows (or more) to develop
the necessary skills and understanding.
from Dave Broyles
I use a Linknife as an auto
release with my scooter tow system. I am very pleased with it's effectiveness.
I have also used the Linknife as a top release for aerotow. It worked
well there too.
I hang the Linknife from the
front wire ring or connector at the nose plate, and for low tows, I let
it dangle down to just touch the control bar. I have a primary release
attached to the pilot's waist and operated by a bicycle lever attached
to the downtube. The tow rope is attached to it via a weaklink through
the Linknife. If the pilot turns too much or lets the nose get too high,
voila, free flight.
For tows, I lengthen the line
so that the Linknife dangles about 4" below the control bar. It will reliably
release a lockout before it gets severe. It should release the tow line
if the pilot starts dragging it. (Adjustment length is critical here.)
It also provides a backup release if the main release fails.
Thanks for reading this far. Do you have an opinion? Comment? Story of your own lockout?
Drop a note to Peter
Birren if you have any comments on this proposal, want to discuss
it or want to learn of the results.
DISCLAIMER: As with
all aviation endeavors, your choice and use of equipment is totally up
to you. It is assumed you are an experienced HG or PG tow pilot who is
intimately familiar with the style of towing you will be doing. As such,
YOU ASSUME ALL RISK AND LIABILITY in the use of the Linknife, as well
as all other parts, functions and personnel involved in the towing and
flight operations. If you do not have experience in towing, please contact
an instructor for expert training. Trying to learn on your own can, and
probably will, result in your injury and even death. Many pilots have
paid the ultimate price so we may now tow as safely as never before possible.
Please learn from their lessons.
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Page last update:
August 9, 2009
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