[QUOTE=suninmyeyes;10738675]
Originally Posted by
RatherBeFlying
Horizontal velocity allows friction with the ground to dissipate kinetic energy at a gentler rate than happens with a completely vertical impact.QUOTE]
Ok I agree that if a Cirrus is coming down under a parachute with a 20 knot wind it would reduce the impact force on the occupants if it could go along the ground in the same direction as the wind for a bit after impact rather than coming to an immediate stop.
However if it is coming down with no wind at the same vertical rate surely the force experienced on touchdown by the occupants in a vertical descent would be less because you have no additional sideways kinetic energy to dissipate?
Your first statement is wrong, the second correct.
If there's a wind, we can take the view that there are two impact forces - a vertical one (same as if there was no wind) and a horizontal one where the plane needs to decelerate from the wind speed to rest relative to the ground.
So you don't reduce the impact force - you increase it. As you say in your second statement.
Paul