The pictured configuration will require very delicate throttle adjustments to maintain attitude. Better control than I thought of as attainable with rockets. The calculations would be easier with three engines rather than four... John Ferrell 6241 Phillippi Rd Julian NC 27283 Phone: (336)685-9606 Dixie Competition Products NSRCA 479 AMA 4190 W8CCW "My Competition is Not My Enemy" ----- Original Message ----- From: "Roman Black" To: Sent: Saturday, December 08, 2001 9:04 AM Subject: Re: [OT]: Amateur manned "rocketship" > Russell McMahon wrote: > > > I have very great respect for Roman's electronics abilities but in the case > > of rocketry I have to (gently) suggest that John's understanding of the > > subject is somewhat greater. > > Hee hee! Don't be gentle with me buddy, i'm > not delicate. ;o) > > > While intuitively it is obvious to many people that having your motors high > > and your c of g low makes for stability, it happens that intuition is wrong. > > This subject has been debated in many forums on many many many occasions and > > it takes the non-believers quite a long time to come to believe that it is > > the case. We could have just such a discussion here if people wanted but it > > would be easier to trust me on this one :-). > > For good descriptions search for "pendulum fallacy", which is the name given > > to the incorrect intuitive belief. Robert Goddard's first rocket was built > > with the motor at the top for this reason. He rapidly realised that his > > original assumptions were eroneous and all his later rockets were of what is > > now thought of as "conventional" layout. > > > > But I know people wont believe me. > > > > Re rocket motor count. There is indeed one large central motor which provide > > most of the thrust and there are 4 smaller outboard motors which provide > > orientation and directional control. > > I'm aware of the pendulum argument. Not that I > totally agree either. Show me helicopters > (or the Osprey?) with the props at the bottom? > ;o) > > But I do confess to ignorance of the large > central lift engine, I thought there were just > 4 radially mounted lift engines. That does > change things. > > But I do stand by my argument re the ground > effect issue. When you originally posted about > John's work (thanks!) I downloaded some of the > landing videos and saw the landing instability > due to their mounting positions of the vector > engines and closeness to the ground with the > ground effect. > > Just changing the chassis shape and lifting > these engines a foot or two would make the > world of difference with the problems they > are having on landing by slowing the loop. > As would directing the vector thrusters outwards > slightly like the Harrier etc. > > I REALLY respect their commitment in time and > money to the project, and good luck to them. > But none of their mechanical platforms impress > me in the least, in terms of strength to weight > or overall design concept, etc. It still looks > like they just bolted some engines on a couple of > bits of steel pipe and rely on the software to > make it not-crash. But I would LOVE to see them > succeed, don't get me wrong there. :o) > -Roman > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads