Cheap Bungee

[portfoxdesign]

Just wanted some suggestions on a cheap bungee in Auz. Some people use the 8mm g-shock for launching aircraft.
I have two meter glider that is almost complete and dont want to spend too much as i'd reather save the $'s for a winch.

Any Idea's?

[Bsmooth]

you could find a bag of 500 rubberbands, link them together, and not leave it in the sun :D

[Ollie]

Some people have cut a long spiral strip of rubber from a truck tire (tyre for you blokes that speak the other English language) inner tube to make a high start. You can vary the width of the strip to adjust the power of the rubber to the size of the model.

[beefa]

I just went to Aussie hardware store, Bunnings warehouse (Hardware house) and bought 15 metres of bungee rubber cord @$3.40 p/m and 15 metres of the braided nylon cord @ 42cents p/m.
Cost aint toooooo bad.....My question is .. is this long enough ? I have never launched any other way except hand (and then only for sloping)

How long should the lengths be to reach a sufficient height?
I know my local site pumps big thermals so dont believe I need to get too high off the ground.... but what is the norm ?


TIA
Beefa.

[Ollie]

The norm is to be able to stretch the rubber to at least three times its relaxed length. If your rubber will stretch that well, then you can make the nylon chord about three times the length of the relaxed rubber. If the tension on the rubber , stretched to three times its relaxed length, is at least four times the weight of the model you are launching, then you will get a full height launch with a typical thermal soaring model. So, with 15 meters of good rubber and 45 meters of chord, you should get at least 50 meters of altitude in no wind and a bit more than 60 meters of altitude with some breeze.

[beefa]

Thanks Olllie,
much appreciated.

Just one last question.... whats the purpose of the chute i see in some of the bungee launch systems ?

[onlyfingers]

The chute brings the end of the line close to the starting point, given that you launch more or less into the wind. And the drifting line straightens itself out, rather than falling in a bunch.

[fledge]

its worth the effert to get a hold of someone in medical supply,most of the highstarts that you see use sergical tubing but as we all know,,our local hobby shops like to double the price of things!:D fledge

[Ollie]

Mandrel formed, UV protected rubber tubing will last about four times as long as extruded latex tubing normally used in medical applications. The mandrel formed tubing will stretch farther for ther same tension and therefore store more energy, giving a higher launch for the same size as extruded tubing.

" The bitterness of low quality remains long after the sweetness of low price is forgotten"

[ajroahkni]

Fishing/diving stores usually have surgical tubing (for spears/spearguns) and relatively cheap as sold by the foot.

One tent peg
20-50 ft of surgical tubing
Couple of D rings
100 ft of 60 lb test monofilament
1 parachute man toy - or a bright swatch of cloth.

Cheap, effective. Easily replaceable.

[SoaringDragon]

Always keep them out of the sun whenever you're not using them, UV will degrade them eventually.

Also, check out this dirt-cheap bungee launcher: http://www.rcgroups.com/forums/showthread.php?s=&threadid=33763