This has been a good thread.
Here is what I need to do: at our slope site we have to launch 14-26 ounce foamies
(many times Zagi wings) off the slope into 10-25 mph winds. Trees down below generate
turbulence to 8-10' above the launch zone, so what we need is an upstart/bungee system
to pop the planes up to an altitude of 20-25' into the zone of lift. From the lip of
the slope to the road is 60 feet, so that defines the maximum stretch of the
upstart/bungee. Initial tests with a shortened Dynaflite 2m Upstart (3/16" surgical
latex) showed that it didn't have enough oomph to launch into a stiff wind. I'll try
to double the tubing for the next test.
The idea I'm toying with is 15' of tubing (stretched 3x to 45') with 15' of line for a
maximum stretch of 60' and an altitude of some 30'. I'm guessing that 4-6 pounds of
pull would be adequate.
If I can't get the doubled upstart surgical tubing to give the required pull at the
required extension, I have some tubing from an NSP "standard" Pinnacle histart that I
can also try. I don;t know if there is a minimum length of tubing that can be used,
but I don't think that 15' of tubing will be too short.
Am I on the right track here?
--Bill
On Mon, 12 Feb 2001 10:50:30 -0400 Dick Williamson <[EMAIL PROTECTED]> wrote:
Dave,
You said:
>Using a 50 ft piece of rubber and some nylon line (50 ft ?) to create an
>upstart (or mini-hi-start), what is the normal max stretch allowed. I heard
>3 to 1. Is that 100 ft of stretch making the final length of the rubber
>150 ft or is the stretch itself 3 to 1 making the stretch 150 ft and the
>final length of the rubber 200'.
Perhaps the article:
http://www.charlesriverrc.org/articles/design/dickwilliamson_histartphysics.htm
might provide some insight concerning your question.
Also, Rich Hollyday's web site includes some data on force versus
distance for surgical tubing:
http://www.hollyday.com/rubberdata.htm
The tubing stretches rather benignly out to 3.5 times, i.e., a
100-foot piece of surgical tubing stretched by 350 feet out to a
total length of 450 feet. I regularly stretch my high starts to at
least 3 times.
Regards,
Dick
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