Re: Re: Skydiver Design insights

I think any appearance similarity with the SNEB is purely superficial due
to the perforated cone shape of its nacelle, the Sky launcher would have to
be completely different on the inside. It certainly could be something
like a SNEB pod without being one, after all we're talking about just the
appearance of the carrier. That's just a bunch of tubes incased in an
aerodynamic shell. What SHADO puts in them is up to them entirely. There
are several guided and unguided missiles that are tube launched, (with
pop-out fins) the Tow and the Stinger are just two I can remember names to
right now. Like SNEB these are most all launched from light, empty tubes.

If the tubes were sealed, which they appear to be for Sky, there are
problems; the missile is popped out of the tube by the gas pressure of
it's engine firing and then its turned sideways (off course) by the gas
escaping from the uneven opening. Even if the missile can handle the
sideways kick at launch, the pod still is very heavy to withstand the
tremendous pressures of such a large diameter pressurized cylinder (or it
explodes). This won't work in the SNEB-like tube carrier which is light
weight, open backed and recoilless.

The Rail Gun: The problem with the rail gun is that it is way too heavy.
Imagine how much more a bunch of electro magnets would weigh above and
beyond what the heavy cylinders would have weighed. A rail-gun also
develops all of its force in its tube, that's really a lot of recoil to
shoot a missile sized projectile to speed... and the shorter the rail gun
the bigger and faster the magnets have to be, exponentially bigger and
using exponentially more power. Enough force to affect the flight of Sky
during launch with the jolt. A rail-gun launched missile (with engine) is
more practical but the magnets are still prohibitively heavy. Even if you
could use a rail gun you would only want to have one per pod with an
autoloader. The whole beauty of a rail-gun is that it is a repeater, 10 or
20 one-shot rail-guns would be a big waste.

What would work is a gas operated ejector. A long shaft that fits right
up inside the missiles engine nozzle about 80-90% of the length of the
engine. It would be retained in the pod after firing and could be removed
or ejected at time of reload. It is essentially a stationary piston, and
the walls of it's cylinder are the missile's rock-hard solid fuel given a
smooth finish on the inner surface. The missile's igniter is at the top of
this stationary piston, when lit, the missile's fuel burns and the gas
presses against the head of that piston, launching the cylinder (the
missile) without pressurizing the pod tube. Only the engine is pressurized
and it of course is designed for that. The ejector design also is not
recoilless and as such imparts significant force on its launcher, for a
SNEB this is impossible due to it's lightweight structure and open back but
the pod on Sky is backed up by a mooring that holds back a rocket motor
during launch, the missile launcher force is a non-issue for that mount.

--

ALSO, as for the Sky launching rocket motors, you get a far better thrust
to weight ratio for solid rocket motors rather than liquid propelled ones.
I firmly vote for solid fuel boosters. Solids are also very much more
reliable than liquid fueled motors, they can be waterproofed easily and
would be easy to auto-reload by diver with cartridges, (just like overgrown
Estes model rocket engine cartridges). Liquid fuel rockets often require
overhaul between firings, all large ones that I know of do, only the small
ones seem to tolerate multiple firings. Multiple firings of a liquid fuel
booster would also be complicated by being submerged between flights. I
see nothing in Sky1's launch characteristics (as shown to us) that indicate
other than SRBs and SRBs just make a lot more sense. A pilot could easily
nose down and fly level without throttling up the main engine if he wished
to stop climbing after launch, throttling up the main engine only after the
SRBs burn out. If he wished to go straight to max ceiling then he would
throttle up the mains as soon as he left the water and maintain his climb
using both until the SRBs burnt out.

BTW, the reason aircraft cannot fire guns at supersonic speeds is that they
may run down their own bullets. Many fighters can travel faster than the
nominal velocities of bullets. At supersonic speeds the bullets slow down
fairly rapidly while the plane holds its speed... it would really wreck
your whole day to catch up to, then hit or ingest your own bullets. :-(
Bullets also have difficulty (as do missiles) penetrating the supersonic
shock-cone from the nose of the aircraft that is firing them. The air
within the cone is subsonic and somewhat carried along with the aircraft,
penetrating that cone at an angle affects accuracy of unguided munitions
and the effect increases as speed increases and the cone gets narrower.
Eventually when the glancing angle got shallow enough, bullets would
ricochet off of the boundary layer loosing a large amount of speed and
immediately be run down by the aircraft firing them. Bad. :-(

LASTLY, Those doors on the bottom of Sky1... I would venture that they
are actually exit doors for water. First off, a large portion of sky will
have to be filled with water and pressurized to prevent sky from simply
being crushed by the water. Not so much by the static pressure of just
being submerged but more by the hydrodynamic forces of plowing through the
water at 40 knots. That water has to be expelled at launch. Also, there
is a huge scoop at the front of the plane, that scooped water has to go
somewhere during launch, probably not through the air-breathing engines. A
diverter in the engine duct could re-direct the water out these doors. So,
Sky would be expelling water from these doors during ascent as well as when
SkyDiver was under way.

Sorry this is so long, I have been very busy and although I have been
monitoring the conversations over the past few weeks I haven't had much
time to contribute. I just saved it all up 'till now. :-)

Shawn "GOT*SKY?" Kelly
www.sdaa.org


Date: Mon, 09 Jun 2003 20:53:30 -0400
From: "Michael Wolff" <[hidden email]>
Subject: Re: Re: Skydiver Design

Greetings, Kaoru

Something occurs to me. We presume that, because the missile pod resembles
a SNEB, it must therefore *be* one. But what if this is an advanced
design,
and the missiles are launched by, say, magnetic rail guns. Or the missiles
might actually be a variation on the SWARMJET or "Smart Pebble" concepts.