You’d probably need to measure the flow rates of both the main exhaust flow and
the back/side flow to demonstrate whether it’s actually useful ie. doesn’t
require too much mass flow to achieve the effect. You’d also need to provide
convincing evidence the *symmetry* of the flow separation can be controlled
tightly ie. there are other static concepts that have been developed that use
plain’ol geometry to promote (or supress) flow separation and for small rigid
expansion cones, minor asymmetries in flow separation might not be critically
detrimental to a typical mission.
If the additional gas flow can be utilised to both tightly control flow
separation and also *efficiently* contribute to thrust *on top of the
contribution of flow separation*, then I suppose much of what I’ve said above
could be moot.
Troy
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf Of
John Hare
Sent: Thursday, March 23, 2023 9:17 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Single throat compensating nozzle
General questions. It is within my capabilities to get another large tank and
set the experiment up again this summer after we complete some time eating
projects.
If I set up a large 200 psi air tank blowing down through a 1/2" throat to a
2" exit plane and can demonstrate the effect with video, would that be useful
or convincing? ER of 16 is overexpanded enough to prove or disprove the
concept? Threads glued on as in aero yarn for flow visualization and hooked to
a simple scale to see the variance at different pressures?
It is not within my capabilities to build a full up rocket to hot fire and
properly test with instrumentation.
On Wed, Mar 22, 2023 at 5:13 PM John Hare <ltolmasonry@xxxxxxxxx
<mailto:ltolmasonry@xxxxxxxxx> > wrote:
If I am right about the effects that I observed on the nozzle, your over
expanded could operate efficiently from sea level up without modification.
Capitalize and bold the IF.
Sent from my iPhone
On Mar 22, 2023, at 2:50 PM, eric.pillai01@xxxxxxxxx
<mailto:eric.pillai01@xxxxxxxxx> wrote:
Somewhat related to this topic - if I had an engine with a very large
expansion ratio and low exit pressure, are there any scrappy ways to test it
on the ground? Could always truncate the nozzle but since the entire nozzle
is regen cooled, there would be a pretty meaningful part of data missing
since the test nozzle would be way shorter.
I imagine that wrangling a professional scale vacuum chamber for engine
testing would be expensive and slow to arrange. Lack of ground test
capability is a huge bummer so I’m very interested in ways to mitigate the
problem.
Thanks,
Eric
On Mar 22, 2023, at 10:21 AM, Norman Yarvin <yarvin@xxxxxxxxxxxx
<mailto:yarvin@xxxxxxxxxxxx> > wrote:
On Sun, Mar 19, 2023 at 11:48:19AM -0700, roxanna Mason wrote:
John, when I was privileged to work with Bob Truax he taught me many
rocket and other related things including his Sea Dragon which had a
compensating nozzle on stage 2. It was merely a tubular shaped section of
corrugated sheet metal which would expand as altitude increases.
So a single sheet of metal that would bend into shape, starting out
corrugated and ending un-corrugated? Was there to be some sort of
actuator doing the bending, or just internal pressure? (Or was it a
more complicated thing with multiple pieces of metal?)
At any rate, the first stage is where an altitude-compensating nozzle
is most useful, but in this case it was on the second stage, which is
puzzling. Too flimsy to handle the rigors of water launch, perhaps,
to be put on the first stage?
