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Quote from: rcforall on October 12, 2009, 06:52:32 AM

I would be interested in knowing the AUW of you glider  and the average  altitude you achieve  with a high start  as I tried this with  an Easy Cub which is a standard airframe with a wing span of 54 " and AUW of around 800 gms ,with  my limited experience I got a feeling yesterday that a heavier and larger plane should do better than the easy cub as it was far smaller and lighter than the kind of plane this bungee was designed for.
Hence knowing your  glider details will help a great deal.

sai

Ok, i will weigh my 2M glider and post the AUW here later. However how did you assume that a heavier plane would do better than a lighter one ? In my opinion the lighter the plane the better ( in any scenario, including Hi-Starts) . With a heavy plane, you would not gain altitude as much as you would gain with the same, lighter airplane. Of course having a large wingspan would  help in gaining altitude. I use my 2M glider and been very happy with this way of launching.

Quote from: flyingboxcar on October 12, 2009, 08:37:22 AM
Sai sir,
Just a few word of caution for you and anyone else who is planning to use the high start technique.
1. Be very carefull of the stake driven in the ground when the bungee is stretched out. If the strake is not driven in proper or the earth is soft the stake can hurtle towards the person stretching the bungee with potentially fatal results.
2. High starts have the capability to rip off the wings of light models under full velocity
3. The ring should be tempered steel and not spoke material as this may deform and open up during stretch
4. The hook apart from being right angled also needsto be curved down a bit down at the rear (open end) this helps in the hook sliding off when the stretch is gone and glider is moving forward. All those who have been in tow line gliders would already know this.

Very very well said. #1 could be disastrous  ! I will add to this to ensure that the hook is placed at the CG, and the plane released carefully with a bit of forward velocity (run a few steps and release ) to ensure it does not stall at the time of release.

Gaurav,
The reason for heavy plane gaining more speed and hence more lift is due to mass. Take a catapult and now try a projectile of same size but one made of foam and one of say clay whic one gains more speed? You have your answer.
Also it is not necessary to fix the tow hook at CG, in fact you can play around depending on wind and ballast conditions. If you would have come across the GP Spirit series glider you can actually change the hook position in few seconds at the field. Also why do you need to run  while launching  from histart? The plane is going to shoot like an arrow the moment you release it under tension only thing you need to ensure is that the angle is not too steep,best is to launch parallel to ground and then blip the elevator to gain height     

Tow hook should be ahead of CG.  Closer to CG means less stable but greater height. forward away from CG means less height and more stability.  tow hook right on CG will make the model more or less unstable.