Bungee catapult ... where do I put this build thread???

[Hai-Lee]

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 normally recommended tension/pull weight is 5 times the aircraft weight.

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!

 

[CarolineTyler]

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?

I used the red silicon bungee from Hobbyking which is supplied in a 10 metre length.

 

[jross]

I used the red silicon bungee from Hobbyking which is supplied in a 10 metre length.

That's what I have. Seems adequate and I see lots of launchers made with it.

It's a plastic wall hook attached to a small ply plate glued to the plane. It should be around a quarter to a third of the way forward of the CofG and the nose.

Thank you! Was looking at those picture hangers in Walmart the other day. Funny how items take on a different significance after you start flying RC. I like the idea of beefing it up with a chunk of ply.

 

[CarolineTyler]

That's what I have. Seems adequate and I see lots of launchers made with it.


Thank you! Was looking at those picture hangers in Walmart the other day. Funny how items take on a different significance after you start flying RC. I like the idea of beefing it up with a chunk of ply.

As I was attaching it to a foam wing I needed a bigger area to glue to so it would take the pull without breaking.

 

[jross]

And the final touch, a small bungee added to ensure the foot release doesn't accidentally flip.

When I saw this, I thought to myself, "That looks like a pain in the butt." What about drilling a hole in the vertical pipe and putting a nail or such through it to stop the ring from slipping off should the foot pedal become accidentally activated? You could get really carried away and put it on a tether. Wanted to say thanks for this thread. Kick me in the butt to get mine finished. Even getting it started would feel like a victory.

 

[CarolineTyler]

When I saw this, I thought to myself, "That looks like a pain in the butt." What about drilling a hole in the vertical pipe and putting a nail or such through it to stop the ring from slipping off should the foot pedal become accidentally activated? You could get really carried away and put it on a tether. Wanted to say thanks for this thread. Kick me in the butt to get mine finished. Even getting it started would feel like a victory.

Well of course it needs a safety!!!
The completed foot pedal...

 

[Wildthing]

Well of course it needs a safety!!!
The completed foot pedal...
View attachment 133099

Simply awesome

 

[jross]

The completed foot pedal...

Even better.