Bungee ramp and attachment hooks
GWS Formosa Test Mule
A few details of my bungee ramp and hooks fitted to the aircraft.
The ramp was built from 15mm PVC pipe and 15mm connectors. You'll need:
The whole ramp and bungee breaks down to a small bag (pinched from an outdoor chair) that I can sling over my shoulder for my short walk to the airfield. Also takes up next to no room in the boot (trunk) of the car for drives to other fields.
I have glued the 90 degree pieces to spreaders/bottom feet and the end of the rails as shown in the photos. This keeps the parts count down and speeds up assembly and disassembly.
The tee pieces have to tops cut off so there is no "step" in the rail to impeded the accelerating aircraft. These are also glued to the bottom of the rails.
The nylon cord is tied off on the ring attached to the end of the bungee cord such that there is one 2m length (for the aircraft attachment ring) and one 4m length (for the release ring).
You will note I use 4 metal tent pegs to secure everything. One peg has the end straightened out. This is my launch peg, it gets hammered into the ground leaning slightly towards the bungee anchor and with about 5cm out of the ground. The idea is that the end is turned away from the anchor peg when setting up. Then, when you are ready for a launch, using your foot, simply swivel the peg around towards the anchor peg and the forward lean will assist the launch ring release.
The other pegs anchor the end of the bungee and the ramp - one on each spreader/foot.
Use this safely and with common sense, there is a lot of potential energy in the armed bungee with 1kg or so of model at the end. Make sure no one or nothing is in front of the bungee when armed, and only arm the bungee as you are ready to launch. Use this system at your own risk - I take no responsibility for any injury or damage caused through its use.
I use this on models ranging from a 450g Alfa up to a 800g GWS FW190A. Use the 5:1 rule for working out your tensions as a starting point. If in doubt it is better to err on the side of too much tension (within reason) rather then too little. My first Alfa launch gained about 100ft straight off the ramp. I have since re-calibrated the tension down somewhat - thank goodness I strengthened the tailplane with a carbon rod
Pictures tell 1000 words, so here goes:
Edit:- Formosa and Alfa Corsair videos added.
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Last edited by CaseySP; Jan 07, 2012 at 04:15 AM.