On 01/11/14 18:55, Rick Newlands wrote:
From your descriptions, and the fact that the tank is more or less
intact, definitely sounds like an engine failure. If the tank had gone
up there's no way one of the pilots would have been alive to parachute
out.
I'd reckon that part of the fuel grain broke off and blocked the nozzle.
The chamber pressure then rose and one of the engine bulkheads blew off,
sending a huge shock through the airframe that broke it apart.
They've recently switched to a nylon fuel grain, which is a good thing
in general (nice, clean, almost transparent exhaust) but it might be
that they hadn't ground-tested the new grain sufficiently. It's cold
50,000 feet above the desert, a fuel fin might have become brittle and
snapped-off.
That's what I thought too. Or maybe just some energetic chugging. And
maybe the acceleration helped (aiui the new grain/engine had been tested
quite a bit on the ground, but hadn't been tested in flight before).
Isn't it long past the time VG scrapped the nitrous hybrid engine, and
went to a solid, or better a LOX/kero biprop?
Scaled won the Ansari X Prize contest because Bert Rutan is very good at
making lightweight aircraft, and the reusability rules meant that a
hybrid would be the cheapest and fastest engine to be developed. Plus
the angel helped.
Scaled did not choose a nitrous hybrid because they thought it would be
the safest or most reliable engine; and after the previous nitrous
fatalities I had hoped they would learn their lesson and stop using
nitrous hybrids.
AIUI, they didn't choose a solid because the rules wouldn't allow it for
the contest; and they didn't choose a liquid biprop because it would
take longer to develop for the contest.
But the contest is now over. Those reasons for choosing a nitrous hybrid
are now extinct. There is *no way* a nitrous hybrid is the best engine
choice for spaceship two.
Nitrous hybrids - well, I have never thought they were suitable for
human propulsion.
First, they chug. Does anyone know exactly how that works? Thought not.
Second, hybrids don't scale well. That is well-known, and has been known
for a long time.
And third, nitrous is a bipolar bitch - one minute she is pliant, the
next she cuts off your balls. Assuming we are correct, nitrous hybrids
have now bitten Scaled/successors twice.
Q particularly for Anthony Cesaroni, if he would like to answer, but
also generally - how much would it have cost to develop a human-suitable
solid for SS2, and how much per shot?
Q for the list - how hard/expensive/ would it be to develop a
human-suitable LOX/fuel biprop engine?
There is a saying in rocketry, don't develop a new engine for your
project - what does that say about the advisability of developing a
whole new class of engine? Especially for human passengers?
Kudos to the brave pilots, and my sympathy to their families.
But bad cess to the overall project design engineers, if such exist.
-- Peter Fairbrother
