I suspect the answer here is to do with the level of risk. When you compare the risks associated with a group of people travelling at 5 to 10 mph with backsides six inches from the ground, the risk of major injury is lower than if that same group were travelling 50 feet above ground at 50 mph (not sure if those figures apply to gliding). Cheers, John Browning Ickenham and District SME MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.