laura@utzoo.UUCP (Laura Creighton) (06/02/84)
I have been reading about the Trident Missiles. I don't understand very much of it very well. The bottom line, as far as I can tell, is that if you want to build a missile you build one that has a metal spike on the end and a disk on the top of the spike. Then they fly faster and a lot more efficiently. Also, if you can get something to burn out by the nose then you are doing a good thing as well. Maybe I am misunderstanding, though, (I said I didn't understand this very well!) I have no idea why this works, but I would like to. What books do you read first so that you can understand such things? Laura Creighton decvax!utzoo!laura@BERKELEY -- Laura Creighton utzoo!laura
henry@utzoo.UUCP (Henry Spencer) (06/03/84)
The spike is a devious aerodynamic trick to make up for having a
relatively blunt nose. It's a specialized adaptation to the limits
imposed by launching from submarines.
The reason for the blunt nose is that the missile must meet certain
performance specs while being constrained to fit into rather cramped
missile tubes aboard submarines. Other things being equal, the blunter
the nose's taper is, the shorter it is. For a fixed-length missile
tube, this means more of the tube's length is available for the full-
diameter part of the body. And this in turn means more propellant,
giving longer range and heavier payload.
The trouble with a blunt nose is that it creates a lot of drag, most
especially so at supersonic speed. Hence the previous generations of
sub-launched missiles all had relatively long noses, despite the space
penalty involved. (Mid-life refits to some of the Polaris subs included
missile-tube caps with concave undersides, to give just a little bit
more room for the noses of newer missiles.)
For the Trident, some devious person at Lockheed came up with the idea
of sticking a little cone on a pole up ahead of the blunt nose, with
the whole assembly being retracted into the nose until the missile
leaves the tube. It turns out that having, essentially, the point plus
the base of a longer nose is almost as good as having the whole longer
nose, when supersonic drag is the issue.
Laura also notes:
................................................ Also, if you can
get something to burn out by the nose then you are doing a good thing
as well.
First I'd heard of this, but I think I know what it's about. You still
have a good bit of empty space between the point of the "invisible nose"
and the base formed by the real nose. There will be less of a tendency
for the slipstream to flow into this space if there is a modest stream
of gas emerging from it constantly. The gas helps "fill in" the nose;
you need a constant supply of it (e.g., burning propellant) because the
slipstream keeps carrying it away. (This basic method is known to help
in other situations, and the extrapolation to the Trident's nose seems
plausible.)
I don't know exactly what books I'd recommend for this. What I know
about the Trident's nose comes from places like Aviation Week and
Flight International; the fill-in-the-gap-with-combustion-gas is a
phenomenon known from model rocketry.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henry