On Tue, 8 Jun 2004 [EMAIL PROTECTED] wrote:
> But the requirement that the engines be matched is much reduced; control is
> now coming from the jet vanes and not differential throttling. As a result,
> any imbalance in the engines can be handled by the guidance system using the
> jet vanes.
Unfortunately, the torques induced by mismatched engine start sequences
(e.g., three engines are running and the fourth *isn't* yet) are much
larger than you can get out of any reasonable thrust-vectoring system, at
least until the number of engines gets considerably larger. No, the
guidance system can't just handle that kind of thing. Systems with small
numbers of engines require either close matching of engine startup
characteristics, or a pad hold-down system to absorb transient startup
torques.
Engine differences *after* startup are a lesser problem, and probably
could be dealt with by vectoring. (Sometimes they have to be, e.g. in the
shuttle SRBs... but elaborate precautions are taken to match the SRBs as
closely as possible.)
Henry Spencer
[EMAIL PROTECTED]
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