What you Need
What to do
Attach the elastic to the middle of one of the long sides of your table so it stretches about 2/3 of the length of your table.
Point this side at a lot of space (7-8m at least)
roll the elastic stretched onto the centre of your tube until it is on the far side of the table to where the elastic is attached. This works best if you put 1-2 turns on the tube while the elastic is quite loose, then stretch the elastic and add another 2-3 turns.
What may happen
With any luck the tube will lift up as it flies through the air instead of just falling down. It will probably take some experimentation with how tight and how much to roll up the elastic, but it looks cool when it works!
Why does it happen?
If the tube is not moving too fast the air going past the tube will tend to stick to it (the Coanda effect). If it is not spinning the air will stick to it symmetrically so leave the back of the tube symmetrically.
If the tube is spinning however the air will stick to the part of the tube moving with the air (the top) as opposed to the part moving against it (the bottom) where it tends to separate from the tube earlier. This means that overall the air passing the tube ends up being pushed downward, so because for every action there is an equal and opposite reaction the tube gets pushed upwards, and flies.
If you fire the tube too fast the air will separate earlier on both sides and there will be less of an effect.
David Beckham's kicks swerve in the air, he gives the ball spin when he kicks it so it will generate lift, the direction of this lift depends on which way he spins the ball. They tend to swerve late because he judges the speed exactly right so the air streams start off seperating from the ball and then reattaches to it late on in the flight producing a swerve.
Tennis players also use top and back spin extensively, because they need to get the ball over the net and still stay in the court. If they hit the ball too fast they will overshoot, but if they use topspin the ball pushes the air upwards, so it gets pushed downwards, staying in the court.