6. Catapult (optional)

by Richard Frawley

After reading several of the emails about using slings, catapults and 'slope on rope' for launching of Pibri, I decided to have a go at making one for myself.

I had used a catapult on the Pibris before, but it was one that was designed for heavier models and it was rather long and actually was too fast on the Pibros, causing elevon flutter at terminal velocities, which in fact reduced launch height due to the excessive drag.

My aim was to make a more gentle, but highly effective unit, that was also small enough to stuffed into a coat pocket.

I also wanted to have a low weight tow hook, that could be easliy removed and was transferable between models. I find that Pibri are some what of a disposable item and I tend to replace them quite regularly.

The Catapult

The picture above shows the finished unit. It is made from 3 metres of standard bungee rubber. The 3 metres I have, is cut from one of Sals (NSP) standard orange bungee units, which I use for my 2M floater.

One end of the bungee rubber is looped over, to create a hole about the size of your small finger and simply tied with bungee line or similar. This is the end that attaches to ground stake, pole, fence or whatever is handy.

A 0.5M peice of bungee line or strong sting is tied to the other end. I use an inserted dowel, but as long as you tie it on in some manner that is not going to come loose, then all is OK.

Simply attached a ring of some kind onto the end of the bungee line, again, tie securely.

The Pibros hook

"U" sied of hook plate

The Pictures show a very simple tow hook arrangement. Mine is fashioned from a small section of of light ply, about 2.5cm wide and 5.0cm long. For the hook , I use standard push rod wire. Push rod wire is quite easy to work with and is plenty strong enough for the task at hand.

Drill two holes in the ply. Bend the wire into a large sqaure 'U' and insert into the holes. Slap thick Cyano over the wire, on the top side of the plate, give it a spray with Zap Kicker, if you have some. Cut off one leg of the U flush with the underside of the plate (see picture).

Bend the other leg back to make the hook. Mine is about 1cm deep and 2.5cm long. Nothing is critical here.

I just tape the plate to the bottom of the Pibros. The tape I use has excellent adhesive qualaties and is strong. Again, see the picture for details.

In the Field

Firstly make sure that your Pibros is in good trim, you dont want it diving off with a severe slice or hook, like some wayward golf ball. The catapault will amplify any minor trim problems.

For the first flight, just stretch the rubber to about 50% of its length, this will give you a feel for things.

On a full stetch, the Pibros should go staight ahead, fast and climbing slightly, a bit of up evevator at 60% of the way thru the zoom, will give you good height. Remember to apply down evelator near the top, so not to stall.

You can get 150 feet (50m) on a nice launch. As you get familiar, you can loop, roll and generally do crazy things while you have plenty of speed.

Enjoy !

Last updated January 13, 2000