Hi Guys,
I have put together a bungee launching system that should take aircraft up to around 4kg. The table takes none of the bungee load.
The aircraft used was purpose built for the tests.
The system supports standard bungee tow hooks.
When I bring it to the airfield I am happy to make it available for others to launch their aircraft.
Great way of thinking out of the box Mark, by using a table rather than the usual ramp.
I have read that the amount of tension needed on the bungee is about 5:1 for the aircraft being used, which means you are aiming at something around 20 to 25kg of tension, which requires a very long single line … can either multiple short lengths of the bungee or a pulley system be used to increase the tension over a shorter distance.
Love the look of the dog watching on – wondering if you can launch his stick again, far further than any of his humans can do.
This is an interesting thread with all the maths if anyone wants a read
https://www.rcgroups.com/forums/showthread.php?404254-Dynamics-of-Bungee-Launching
Looks great Mark. And I really like the multi-purpose design. Launch a plane, and then set up for high tea!
Thanks. My reading has the bungee tension between 4 and 6 times the aircraft weight. Interestingly, the aircraft I used in the test was under a 13:1 tension!
My aircraft are 1.5kg and 2.6kg AUW respectively. Using the 5 times rule this sets the bungee (it is shock cord) tension at 7.5kg and 13kg. I will be returning to the sports field to test the system under these tensions. I will let you know how it goes.
Dave was correct about the need for two cords. The single shock cord maxed out at 10kg. This will be sufficient to launch the Mini Drak. The second series of tests was more like a ‘blooper’ reel. I have added the second series to the end of the original video (from time index 3:35 onwards)