On Tue, 7 Jan 2003, Randall Clague wrote:
> I'm a big fan of being able to stand on your own gear at will. OTOH,
> I've never done a mass estimate for landing gear.
The numbers are, unfortunately, unpleasant. Orthodox aircraft landing
gear weighs about 3% of maximum takeoff weight, which is really bad news
for an SSTO, especially a non-hydrogen SSTO. Lots of concentrated stress,
plus mechanical complexity; it's one of the few places where steel gets
significant use in aircraft structure.
Now, you may be able to do better than that; the B-58 gear was 1.5%,
Voyager's was 0.89%, and Skylon's is about 1.5%. On the other hand, there
were reasons why the B-58 routinely tanked up after takeoff to reduce
takeoff weight, I don't think Voyager ever made a landing at near max
weight, and Skylon is a paper design, so those numbers should be taken
with a large grain of salt (say about 10cm on a side). But speaking more
generally, the real limits, given cleverness and willingness to limit the
operating environment, are poorly characterized.
VTVL gear also ought to be better than HTHL. For one thing, there's no
need to absorb large amounts of energy in brakes. (One of the tricks
Skylon used to get full-takeoff-weight gear that light was water-cooled
brakes, the water supply being jettisoned after a successful takeoff.)
Henry Spencer
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