I had originally intended to write about predicting how far a model would fly. Some time ago I had developed a spread-sheet to predict the flight-path under a wide range of conditions, but only in two-dimensions (ie in a vertical plane).

When I started to write the introduction I found that I began my story with my surprise at the world record distance for a hand-thrown glider made by folding an A4 sheet of copy paper. I couldn’t see my gliders getting anywhere near 68m.

Is there something special about deltas?

Some time ago I made deltas in the format of ‘Suzanne’ – a holder of the distance record. I could do this because the designer has posted a video of how to make his creation.

But after I made one I made the rest by cutting out the wing plan and glueing it on to a fuselage. By shaping the top end in various ways I could see the effect of varying the angle of attack.

Now, that was some time ago and I have forgotten what I concluded, but the models were hanging on my wall so I took one and tried it.

It few well. To get repeatable results I used a launcher made from a strand of rubber from a length of shock cord (like the one I used with the aluminium glider).

If I launched it gently it flew steadily, and it was stable, despite having no dihedral angle. In fact it flew better with no dihedral at all.

When I increased the launch speed, it started to turn to the right or left, before it seemed to remember what it was meant to do and flipped back to stable level flight.

At a launch speed that was higher still it immediately went into a spiral dive straight into the ground.

What’s going on?

I’m not sure, but I am making more delta models to see if I can find out.