Russell McMahon wrote: > You mentioned "ground affect" below. I suspect this applies much more to a > craft which uses air displacement as its main motive force and which has a > large area over which it distributes its air into (ie under the rotor > "shadow" ). In the case of helicopters they tend to turn into hovercraft > when the ground deflects and traps the downwards air from the rotor. Many > accidents have been caused by this effect. In the case of a rocket there > will indeed be some potential effect from exhaust products being deflected > by the ground but the pressure build up will be minimal compared to a > helicopter and the rocket is NOT "ingesting" external air to act as its > reaction mass - any ground effect would be that which acted on thge > superstructure plus, perhaps, a minimal rsult from increased local pressure > on the rocket nozzle exhaust conditions. Maybe i'm mistaken but one of the videos you posted links to seemed to be suffering from real obvious ground effect instability when it was trying to land, when the rockets got maybe 6 inches from the ground. I just looked at it and thought "rocket position redesign". Obviously the crew there thought "faster more expensive control computer". $8000 US for the control computer?? Wow. I'm sure you could use one PIC, any takers guys? -Roman -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.