Like Chuck, I use a taut rope or webbing strap to secure an aircraft. Tying down an object is the same whether it's a load on the back of a truck, a structure to the ground or an aircraft on the apron. The goal is to 'weld' the object to the supporting surface and not to give it leeway to buck around in gusts or whatever. Ideally, an aircraft should also point into the expected wind. If it doesn't then there will be aerodynamic loads that will try to weathercock it.
The type of knot used makes a difference. I've lost track of the number of times I've seen people use what are effectively slip knots that aren't cinched tight against the bight. It's common in the SE USA for two widely separated single half hitches to be tied half way down the rope. Damned if I know why they bother. It's about as secure as wrapping a horse's reins a couple of times around a hitching post. If the two half hitches were tied against each other to make them lock and at the bight so the standing end can't be pulled through it would be reasonable, but the knot in use barely qualifies as a 'knot'.
Additionally, you should chock the wheels and use gust locks (at the surface if possible, as suggested by another contributor to this thread. If strong wings are expected, consider using spoilers on the upper surface of the wings. Mind you, if it's expected to get that bad, I'd be looking for hangar space or ferrying away if possible.
Last edited by Tinstaafl; 28th Jan 2009 at 03:55.