Bungee Launcher

Here I will show how you can get better launches for your EDFs and onther small high-wing-loading airplanes.

This how a hand launch can go:

This is my setup:

This is an example of how it works for me: Notice how I apply a little throttle prior to launch so that the plane does not torque roll when the throttle is advanced. 

So basically there are two main ways to construct a tow hook. The external and the concealed.

The simple way is to make a loop of heavy piano wire or coat hangar. Make a 90 degree bend and cut for the hook portion. The loop portion is then sandwiched between two pieces of hard balsa or ply and epoxied together. You can insert soft balsa between the two plates and carve out the imprint of the hook ring to ensure the hook does not twist. I use gorilla glue and it works great. Just make sure it is clamped when the glue is drying.

The complicated way is to embed a brass tube into your fuselage at an angle. The top of the tube should lean toward the nose. The cotter pin is attached to your bungee line. As the plane passes over your launch apex the cotter pin should fall out. This creates a cleaner finished look. Again, you should embed the brass tube in something harder than foam itself. 

After your hook is assembled it can be epoxied or glued with gorilla glue... but where?

I use the general rule of 60-66% distance from the nose to the CG point. I chose the center CG mark and went to about 60% of that distance. This is important because on launch if the tow hook is too far forward the angle of attack will be too shallow. The opposite is true if the hook is too far aft. This location is recommended by Nick Ziroli. I think he knows what he is taking about!

As a general rule use 5lbs of bungee tension per lbs of aircraft. For larger aircraft you can add a second bungee cord in a paralell configuration. If you want a more gentle take-off add one in series (ie. tied together end to end). 

This can ease your launches for many great models. It will give you better control over launches for maiden flights and those planes that require a high launch velocity. My model has a high wing loading but to put landing gear would be impossible on my grass field for how small the model is. 

Happy Building!