Newsgroups: sci.space.history
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Flap Valve Altitude Compensating Nozzle
Date: Sun, 28 Dec 1997 02:13:33 GMT

In article <34A3ECDE.679@pacbell.net>,
Michael P. Walsh <mp_walsh@pacbell.net> wrote:
>I have never read any credible and reliable details on why
>either the interior multiple expansion ratio nozzles or the
>expandable external nozzles were not used on first stage
>launch vehicles...

It's really not hard to figure out.  How many first-stage launch vehicles
have been built in the West in the last thirty years?  And how many of
those were vital megaprojects which could not be allowed to fail, e.g.
because of unwise reliance on unproven technology?

>I believe expandable nozzles are in use
>on some upper stage vehicles and I believe I heard the
>RL-10 is one, but I also don't have any data on any
>launches on which it may have been used.

Telescoping nozzles are in routine use on submarine-launched missiles, the
IUS upper stage, and some variants of the RL10.  But these systems all do
their geometry changes *before* ignition -- their motivation is to stow a
long, efficient nozzle very compactly, not to adapt to changing external
pressure.

The SSME *almost* had a telescoping nozzle operating during the burn.
It was part of the original design, but eventually they decided that the
extra complexity and technical risk didn't quite pay for itself.

I'm told that P&W has tried operating a telescoping nozzle on a running
RL10, and it did work, although with some truly weird flow patterns while
the nozzle was in motion.  But there haven't been any customers for an
altitude-compensating RL10.  (The DC-X RL10 variant needed to run *only*
at sea level, so it just had a shortened nozzle.)
--
If NT is the answer, you didn't                 |     Henry Spencer
understand the question.  -- Peter Blake        | henry@zoo.toronto.edu

Newsgroups: sci.space.history
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Flap Valve Altitude Compensating Nozzle
Date: Sun, 28 Dec 1997 02:03:54 GMT

In article <19971226230101.SAA12452@ladder01.news.aol.com>,
JHare10079 <jhare10079@aol.com> wrote:
>A row of flaps around the nozzle would hang down on the launch pad. At sea
>level thrust, the partial vacuum in a large ratio nozzle would pull air through
>the flaps. At medium altitude, the top row of flaps would close when exhaust
>pressure matched ambient. In vacuum, all flaps would be closed for maximum
>expansion...

I've heard that P&W has fired an RL10 with such a nozzle, and it sort of
worked, but not well enough -- they concluded that active control was
called for.

In general, there are quite a few concepts for altitude-adapting nozzles
which have never been tried in flight, simply because rocket-propulsion
research in the US basically stopped in the late 1960s.  People making
plans for big operational rockets couldn't afford to gamble on unproven
engine technology, and nobody was flying experimental vehicles to turn
design studies into proven technologies.
--
If NT is the answer, you didn't                 |     Henry Spencer
understand the question.  -- Peter Blake        | henry@zoo.toronto.edu

Newsgroups: sci.space.history
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Flap Valve Altitude Compensating Nozzle
Date: Mon, 29 Dec 1997 02:05:34 GMT

In article <19971228161401.LAA21845@ladder02.news.aol.com>,
JHare10079 <jhare10079@aol.com> wrote:
>>quite a few concepts for altitude-adapting nozzles which have never been
>>tried in flight, simply because rocket-propulsion research in the US
>>basically stopped in the late 1960s...
>
>...Somehow though, I can't comprehend such
>an important part of the space program stopping. As far as I can tell, any
>operational rocket engine in service today would have been at home in
>Peenemunde.

No, I wouldn't go that far.  There was a lot of progress made between 1945
and 1965, and a little bit more between 1965 and 1975.  Just not much
since.  The fundamental problem is that rocketry was good enough, circa
1965, to meet the obvious immediate needs reasonably well... so the next
time money got tight, starting in about 1967, all the rocketry R&D not
immediately tied to the needs of near-future operational programs got
axed.  And of course, the operational programs couldn't take very many
chances, and by and large they weren't very ambitious, so everything
radical simply fell off the to-be-tried list altogether.  And it hasn't
come back, although some attempts are now being made to fix that.

>>...couldn't afford to gamble on unproven engine technology, and nobody
>>was flying experimental vehicles to turn design studies into proven
>>technologies.
>
>See, I told you I couldn't comprehend the reasoning. An X-vehicle (reusable)
>should have been able to test any number of engine concepts. Say a 3 engine
>propulsion with the test article as #3. Sort of like the JU52 or the current
>SR71 aerospike.

Yep, would have made a lot of sense.  But note that the X-planes stopped
around the same time.  Tight budgets, adequate technology for immediate
needs, and abandonment of long-term planning because saving over-ambitious
near-term programs had become so difficult.
--
If NT is the answer, you didn't                 |     Henry Spencer
understand the question.  -- Peter Blake        | henry@zoo.toronto.edu