Hi-Start or Bungee for RC gliders

Also know as Hi-Start, is a simple system to launch your RC glider.

Using a very long rubber band and an even longer fishing line you can tow a glider and make it take off like a kite, it is raised to an acceptable altitude where the glider can continue flight by catching thermals and other updrafts.

This system is really simple but it works very well, currently, most modelers use a motor with retractable propellers in their gliders instead of using this towing system, the advantages of using the integrated motor is that you can use it anytime you need to gain altitude and turn it off when not in use, with this you do not have to place the towing system and walk tens of meters at each launch, that last one is the great disadvantage of the Hi-Start, using the towing system requires some work for both when preparing it on the airfield and for each launch.

 

I would only recommend it for gliders that need to preserve their lightweight and therefore the motor is not an option.

hi-start sailplane glider
Four Possible Arrangements
Ground Length Required
Typical Situation
Rubber Length (relaxed)
Fishing Line Length
(based on stretching the rubber 3 times MORE than its original "relaxed length", plus an allowance for landing etc.)
30 metres
120 metres
250 metres -
"Very Large Field"
A large expanse of flat cleared land (uncommon in metropolitan area)
20 metres
90 metres
180 metres -
"A Large Field"
Large athletics /general sports area
15 metres
75 metres
150 metres -
"A Medium Field"
Typical Park without trees
10 metres
60 metres
120 metres -
"A Short Field"
School yard or limited area

Launch in action.

Materials

I’m not the most experienced person in bungee o hi-start launches and techniques but it is really as simple as it seems, the materials to use are rubber, fishing line or resistant nylon thread, a stake and some metal rings, the one used for common keys can be used but strong enough to stand the forces. The rubber can be from many sources but the one I recommend is the surgical tube, if it can be stretched about 5 times its size it works better, the length of each one depends on what is established in the table above where a ratio of length is set around of 1: 4, but some people prefer to use a 1:5 or even 1:8 ratio.

 

It is important that the fishing line is visible to recover it later in the field, do not use the transparent and thin lines because it will be an odyssey to find it after each launch, try to have a strength of between 10 and 20Kg (20 to 40lb).

The rubber is what will give the momentum, I recommend using a thin surgical rubber for a smoother and more controlled launch, also depending on the weight of your model aircraft. If you use the common 5mm tube that is strong and your glider is light, the thrust will be very strong and the climb very violent, if it is not what you want, consider a thinner rubber.

It is very important to tie the knots well, it is dangerous if you tie a knot wrong or the stake is not well ditched into the ground, resulting in lessons in case of an accident, it has happened to me personally.

The hook and the releasing

In the glider the hook is located almost below the CG, this can be a little ahead of the CG for more stability, a movable hook can be adapted to change the anchor point as needed, in terms of the ring that is placed on the line can be simply tied to it and a small flag is placed on it, the best option is to place a fabric parachute in between, this parachute will facilitate the release of the bungee and when it falls it’s more visible and controlled.

Watch the video here
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