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

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