Hai-Lee
Old and Bold RC PILOT
The normally recommended tension/pull weight is 5 times the aircraft weight.I have read through a few articles on these and I like your design. One thing everyone seems to let out is speciifics on the bungee cord itself. The bungee straps i have for holding things on my trailer vary greatly in pull strength, so I would think that longer cords would vary too. Is there a specific spec I should be looking for?
The bungee itself can be short or as long as you require it BUT a longer bungee gives a more constant acceleration and a greater launch speed. So if the bungee is short you normally increase the maximum tension to upto 10 times the weight and get a more explosive launch with far greater acceleration. (Make sure your plane can handle the forces)..
To measure the tension you can do a relative distance measure from the anchor to the aircraft to be launched or you can use a fishing scale for a more accurate measure.
I use shock cord for my launcher and I use only 10 metres of the cord with a 2 metre length of cord to affix to the model. See:- https://forum.flitetest.com/index.php?threads/the-best-20-i-invested.53587/
It has been working for me for over a year now!
Have fun!