Hi-Start Bungees

A Hi-Start or (High-Start, or Towline Bungee) is a device used for launching F3L / F3RES gliders high into the air without the use of motors. It consists of a long piece of elastic rubber attached to an even longer piece of fishing line. The fishing line is attached to the airplane and stretched way back. When released, the rubber pulls on the line which pulls on the airplane and launches it rapidly into the sky. A good launch can release the airplane 300 or more feet into the air.

TPG has several identical regulation Hi-Starts that are used for our regular F3L / F3RES contests at the Encinitas Field. If you would like to build your own bungee for practice, they are fairly easy to make. By following this guide, you’ll be able to construction your own bungee that matches the one that we use at the field.

Rubber

You’ll need 15m (50 feet) of rubber. The highest quality silicone rubber can be purchased from Hyperflight already cut to the proper length with rings conveniently attached to both ends. If you prefer you can purchase 8mm (5/16") outer diameter latex rubber and attach the rings yourself.

Staked End of the Rubber

A good method for attaching a ring to the ends of the rubber is to take a small #8 eye-bolt with two nuts screwed on. Stick this inside the tubing and put a zip-tie around the middle. You can then clip this ring onto a swivel-eye bolt snap that can be staked into the ground as in the picture below.

Fishing Line

The official rules call for 100m (328ft) of fishing line with a minimum diameter of 0.7mm, however provisions are made in the rules to shorten the line for smaller fields. To accommodate the size of the Encinitas Field the TPG contest Hi-Starts have the line shortened to 90m which is conveniently the size of a 100 yard spool. Braided nylon fishing line in the 30-60lb test range is ideal. On both ends of the line, tie on a fishing swivel. The swivel is important because it will allow the line to easily untwist and avoid tangles. Clip one swivel to the ring in the loose end of the rubber tubing.

Leader Line and Airplane Hook

Lastly, get a 2 meter piece of paracord. A bright color will make it easier to spot on the field. Tie a small metal ring to both ends. A 1/2” to 3/4” diameter ring is a good size for the end that attaches to your airplane. A smaller ring can be used for the end that clips to the fishing line. Attach a flag or streamer to the cord, near the fishing line end. Hemmed rip-stop nylon or parachute silk works well. The streamer should be about 12 to 18 inches long.

Pull Strength

According to the rules, the bungee should have a pulling force of 2.75-4 kg (6-9 lbs) when stretched to a length of 45m (150ft). You can use a cheap fish weight scale to measure this.

Spool / Reel / Storage

To complete the package, you need to get yourself some sort of spool to wrap it all up on. Many people use extension cord reels. You can purchase a spool from Hyperflight, or if you have a 3D printer you can make your own using a compact design developed by a TPG member. To prolong the life of the rubber, store it in a cool dark place.

Mini Hi-Start

The Torrey Pines Gulls are promoting a class of F3L soaring for smaller gliders that weigh less than 250g. For these types of airplane, a less powerful Hi-Start is needed. You can build a mini bungee in the same way as above, except that the rubber should be a smaller 6mm (1/4”) outer diameter latex rubber. This mini bungee should have a pulling force of around 1.8 kg (4lb) when stretched by 45m (150ft).