RCU Forums - EDF Bungee

Voodoo,

I had one heck of a time trying to squeeze info out of people when first wanting to build a launcher and sympathize with you! For this reason, I have a couple places to compliment the build that is shown at the “zagi” site. I use a modified version of the Bungee Launcher found at www.yourzagi.com/launcher and I would recommend this one as it is cheap and easy to build.

I built my launcher a bit different. Mine was shortened to 48” long and works just fine with the jets I launch, which means it can handle just about anything. It also makes it easier to transport in a car if needed. I also made three types of launch platforms, a Padded Rail, a Launch Ramp and a Low Friction Rail. The Ramp is a piece of 1x12x48” white shelving board I got from Lowes or Home Depot and it works great. The Padded Rail uses the stiff insulation; don’t use the soft rubber type insulation as the wings/fins tend to dig into it. The Low Friction Rail was made from 1” PVC bored to accept the ¾” PVC short tube and coupler. I glued a short piece of ¾” PVC to a coupler, then inserted and glued it into the hole I bored in the 1” Rail…that way there is no interference as the width of the coupler doesn’t exceed the width of the 1” PVC. You can drill a small hole into the ¾ PVC from inside the 1” and use a screw so it definitely won’t come apart when dismantling.

Here are some pics and tips:

My first launcher, a wood one from old plans-
http://www.rocketryforum.com/ctulank...=bungee%2Fwood

My PVC Bungee Parts and some assembly-
http://www.rocketryforum.com/ctulank...r=bungee%2Fpvc

The Bungee Assembled showing different setups and how it hooks up-
http://www.rocketryforum.com/ctulank...%2F&startpic=0

The Bungee in use showing new Low Friction Rail(see pics at end)-
http://www.rocketryforum.com/ctulank...f4dfirstlaunch

Here are some tips:

I used Surgical Tubing for my Bungee cord rather than Bungee

Use the ½” Surgical Tubing, ¼” diameter center with 1/8” walls

You can also use the 7/16” bungee sold by www.hobby-lobby.com

Length of the Bungee was 30-33 feet.

Use at least 12” long steel nails to secure your launcher

Get a fish scale at the store

Set tension using the fish scale to 5 times your aircrafts weight. My FA-18 weighed in at 43 oz and the bungee was stretched and tension was set to 19 lbs. My friend had a digital scale and it showed up 15 lbs, so the digital ones do make a difference.

Use Quick Links to hook up your system…it makes assembly and takedown easy

I lengthened my legs by 5 ½” all the way around on my bungee to get it up off the ground a bit.

Do not exceed a 10 degree angle

Make sure your launch rails/ramp are in a straight line with the bungee cord

FYI, since I wrote this, I have switched pretty much to a foot pedal launch across 25' of carpet runner that acts like a runway...it works great and takes less time to set up.

I hope this helps and gets you started on your way to launching. I use mine a ton and keep in the the car at all times these days. Let us know what you come up with and how it worked out.

Cya,

Carl