Hi Vince,
A few years back, I became intrigued with high-start launching and
began to look at how to optimize a launch. My ruminations have been
included on the Charles River Radio Controllers web site:
http://www.charlesriverrc.org/articles/design/dickwilliamson_histartphysics.htm
To translate between the table in CRRC article and the tubing
supplied by Mark Mech and NSP, I have created the following table
which I hope survives transmission via email without screwing up the
formatting. Tubing sizes are listed in order of increasing cross
section.
Cross Inside Wall CRRC Mech NSP
section dia.
(sq. in.) (in.) (in.)
0.024 1/16 1/16 hand launch - -
0.025 1/8 3/64 - - upstart
0.037 1/8 1/16 2 meter 2 meter -
0.049 3/16 1/16 - - M
0.064 1/8 3/32 - comp 2 meter -
0.074 5/16 1/16 - - standard
0.098 1/8 1/8 standard 3 meter -
0.101 1/4 3/32 - - L
0.138 1/8 7/16 heavy duty - -
High starts work nicely, especially with some head wind. However,
you need a strong arm to launch a heavy plane.
Regards,
Dick
The end of the soaring season is close here in Ohio,
and the sun was out this morning. I had previously
test launched my newly acquired 150" Aquila XL off of
a histart made for a 2 meter (wimpy), but I thought
today would be a great chance to try the bigger
hi-start.
Loaded up the car and drove to the club field. Range
check OK. Walk WAY down the runway to stake down the
end of the histart. I have only done a dozen histart
launches in my life, and only 2 in front of anyone
other than my dad and brother, so I am a bit nervous.
I put about 60% of the stretch to try it out, point
the nose at the horizon and give it a heave. WOW! I
mostly let it do it's own thing, with very minor
rudder corrections and just a bit of down elevator, it
climbed in a nice arc. Don't know if that was right,
but it felt good. Since I had not given it a full
stretch, it ran out of pull before it had more that
about 200 feet of altitude (guess) I did a lot of
lazy circles (sun hid behind the clouds, and no
thermal activity to be found with my meager skills)
Landing was great, and the next launch was with full
extension of the histart. Very impressive launch. I
think that it was nearly over the stake before the
line pulled off the hook. I played around, going
upwind hunting, but there was no sign of lift, so I
was back down in short order. 4 times in my RC career
I have specked out my birds (Zagi wings and Dads 2
meter electric) so I can't wait to try it with this
majestic sailplane! (plus it is bigger, so specking it
will mean even more altitude!)
Sorry for the novel, but I am stoked. I know that
this is an ancient design, but I was in heaven. Now
for the questions.
Our fish scale said I had 25 pounds of pull at full
histart extension. Is this too much? Can I try for
more?
Without a zoom launch at the top, a 510 foot histart,
and a mild headwind, am I really about 500 feet in the
air? (I am trying to come up with real world
estimates of altitude)
Does it sound like I am doing anything wrong or could
do them better? Our club is mostly nitro, with a
growing electric presence, so there was not much
sailplane guidance available (but a lot of willing
help with the line)
Thanks in advance,
Vince
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