> With my GL, I started "highstarting" with a Dynaflite 2M
> Upstart and then graduated to an NSP Standard Hi-start
> Upstart has 30' of latex and 200' of line with a tension
> of 7 pounds. The Hi-start has 100' of latex and 400'
> of line at a tension of 15 pounds. The first launch of
>the GL with the Hi-start was done conservatively: I pulled
>the Hi-start back to only 7 pounds tension and launched.
>And a winpy launch it was-- no velocity, no height.
>I attributed that to the greater weight of the Hi-start
>_cf_ the Upstart and the greater drag of the Hi-start
>line _cf_ the Upstart line.
The weight and drag probably wasn't the issue, it was the
"wimpy" launch. With the "up-start", the seven pounds
of tension reduces gradually as the tubing "unstretches",
but with the "hi-start" seven pounds of tension is only
a tiny pull and reduces very rapidly (see chart below).
With 100 feet of hi-start, a 7 pound pull is 50 feet,
and it does about 175 ft lbs of work, because the
tension reduces so rapidly.
With 30 feet of up-start, a 7 pound pull is 69 feet,
and it does about 330 ft lbs of work, because
the tension initally is reducing gradually while
the tubing "unstretches".
This is because tubing doesn't stretch linearly.
After the initial force to get the tubing stretched
an additional 50%, it doesn't take a lot more force
to stretch the tubing further still.
strain versus force in pounds
up-start hi-start
000% 0.0 0.0
050% 3.5 7.0
100% 4.5 9.0
150% 5.5 11.0
200% 6.5 13.0
250% 7.7 15.4
300% 8.5 17.0
350% 9.5 19.0
You can also see a plot of data for black tubing
which has about the same tension numbers a latex tubing
at http://www.hollyday.com/www/rubberdata.htm
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