[Lash]

I am attempting to build a launcher for Habu and smaller size airplanes. Need to know what length of rubber and cord I should be using.

[Narly1]

Not an expert on the subject but wondering if you could "calibrate" the bungee cord material.

Suggest doing this by attaching a fish scale to a known, unloaded length of bungee cord and then draw it back to a force value that is equal to (or some multiple of) the mass of your jet., again recording the cord's length. From the equation Force = mass x acceleration, solve for acceleration.

Then knowing acceleration and distance (amount bungee stretches between unloaded and loaded conditions), solve for velocity.

Compare the velocity developed by the launcher to the minimum airspeed required by the model for flight to see if you are there or not.

Either that or stretch the bungee as far as it will go and let'r rip, LOL!

I'm sure more experienced modelers will chime in now, LOL!

Earl "Narly1" Anderson

[Narly1]

Duplicate post

[Lash]

I'm of the " let'r rip" crowd but it would be good to get a starting point. Not sure how long to make each part .. rubber to cord lengths.. never done it or seen it in person.

[Angus]

just tie a 50 cord to Terry, shoot him in the arse with a pellet gun and you'll be up in no time

Hope your keeping well

Angus

[mikecoul]

From what I have read in other posts 24feet+15foot tether pulled to 5x the weight of your airplane.

[Lash]

Originally Posted by Angus

just tie a 50 cord to Terry, shoot him in the arse with a pellet gun and you'll be up in no time

Hope your keeping well

Angus

Great idea, but with his bum knee I don't think he'd ever get to Vr.
All is well here , I am still crashing with great regularity.
Are you sick of that turboprop yet ???

[Lash]

Originally Posted by mikecoul

From what I have read in other posts 24feet+15foot tether pulled to 5x the weight of your airplane.

Thats where I will start, thanks !!

[SARPLT]

I just went through this as well. After two recent crashes from club members hand launching my smaller EDFs, I decided it was time to build my own launcher. After reading multiple forums I put together the following launcher with 1/2 inch PVC and a simple hinge for the foot launcher. I am using 12 ft of line from the pin to the surgical tubing, 10 ft of surgical tubing (from HomeDepot) and then 10 ft of the double line from the tubing to the foot launcher and aircraft hook. I used the rectal pluck method (guess) when trying to figure out the distance to stretch the line. Basically once the line is laid out I am stretching the line four paces (4M) for 1lb models and then adding two additional paces for each additional pound of weight. So far this has worked perfectly in launching three different 50mm EDFs and my Great Planes F20. I am not sure what the weight of the Habu is so I can't help you there. I have included a few photos of the launcher and the method I used for connecting the surgical tube to the string. A simple eyelet screwed into the end of a small piece of dowel and on the other end I sanded a small dent in the dowel and then pulled the tubing over it and secured it with a zip tie over the indent. I have stretched this tubing 30 ft to check its security with no problem. Also don't forget to make sure you use a method of making the launcher safe once you stretch the line as it quickly becomes a weapon. I used a screw used for installing drop ceilings. This was large enough to be securely screwed into the PVC and it had a hole through the other end that I could put a pin through until I was ready to launch.

Hope this helps.

Cheers Marty

[Lash]

nice launcher! Hope to get this going before it snows. I'll try and remember to post the results with some pics.