Some clarification is perhaps needed. See attached pic that illustrates
difference in the two motors that were tested. The initial Kn is actually
slightly *higher *for the motor with the cone.
Kn is defined as burning area divided by nozzle throat area. The initial
burning area is the propellant area along the length of the core including
the conical area. The throat area is the based on the core diameter, which
is the same for both motors.
Now the *final *Kn (which occurs at burnout) will be slightly *less *for
the motor with the cone, as the region with the cone has a thinner web
which will burn out sooner than the region with the constant diameter core.
Richard
On Thu, Jun 20, 2019 at 6:45 PM Alex Kuehn <awkpilot@xxxxxxxxx> wrote:
Richard,
Looking at your drawing, unless I'm misunderstanding what you did, I think
the decrease in performance you saw is because the exit cone decreased the
initial Kn of the motor. I believe the same thing happened in the paper
that Serge shared when they did their experiments. I'd be curious if there
would be a significant improvement in performance if you were to simply
lengthen the motor the length of the exit cone when adding the exit cone
(thus having the same Kn and chamber pressure between the motor with the
exit cone and the one without) since I think that would be more telling.
-Alex
On Thu, Jun 20, 2019, 3:25 PM Richard Nakka <richard.rocketry@xxxxxxxxx>
wrote:
Yes, both motors were identical except the flight motor had an expansion
cone.
On Thu, Jun 20, 2019 at 1:47 PM <spas@xxxxxxxxx> wrote:
Regarding the addition of an expansion cone, I have tried that on oneof
the nozzleless motors that I flew a while ago
Did these motors have equal length of strait core?
(see attached pics). After
test firing a nozzleless motor with a straight core, I decided to addan
expansion cone, and fly the motor in a rocket. Well, the result waswill
disappointing. The rocket flew a fair amount lower altitude than
predicted.
So it seems that the expansion cone resulted in a loss in thrust. It
be interesting to see if Serge's upcoming test firing of such a motoris
inthe
agreement with this finding, or not.
Richard
On Thu, Jun 20, 2019 at 6:07 AM <spas@xxxxxxxxx> wrote:
attached picture
Ray, thank you for your kind words)
It is always a pleasure to read of your experiments, Serge.
Do you measure chamber pressure during these tests?
No, but I believe in nozzleless motors pressure may be calculated by
multiplying thrust on exit port area.
From the thrust curves, it does not seem that erosive burning at
andexit
is significantly affecting the grain geometry.
There is interesting paper on this matter: "Internal Ballistics
Considerations of Nozzleless Rocket Motors", Journal of Propulsion
thePower, 1999.speed
http://serge77-rocketry.net/nozzleless0/nozzleless.pdf
The main idea, confirmed by experiment and calculations: the burning
of propellant is approximately the same along the entire length of
nowcore, because the acceleration of combustion due to erosion near thepart
nozzle is compensated by the acceleration of combustion in the head
due to a much higher pressure than near the nozzle.is
Also, it is interesting
that the M16 test had a shorter duration than the M19 test.
I have used new coffee grinder for M19, so the most plausible reason
somewhat coarser KNO3. It is unfortunate, because it is impossible
canto
correctly compare these two motors.
Have you considered forming an expansion cone in the propellant?
Yes, but not now. Conical insert has long been waiting for its time
(attached).
At first, I want to determine what maximum pressure such an engine
https://www.facebook.com/groups/1396488870646273/permalink/1993969987564822/withstand. So I will try more and more long core. Yesterday I havepoured
motor with core length 700 mm, L/D = 14.wrote:
On Wednesday, June 19, 2019, 2:32:24 PM GMT, <spas@xxxxxxxxx>
(d/D)
now L/D = 12
and I prepare next motors with L/D = 14
I want to know what maximum L/D may be used for maximum Isp
core to diameter ratio (d/D)is about 1/3 in all tests
Very interesting, Serge. Previously you recommended a guideline of
length
to grain diameter ration (L/D) = 10 and a core to diameter ratio
=1/3
based on your earlier testing. What ratios are you using now?
Richard
On Wed, Jun 19, 2019 at 6:46 AM <spas@xxxxxxxxx> wrote:
More tests of nozzleless motors, previous tests are here
increase500,
Today's two tests differ by a longer channel, 600 mm instead of
Lengtheningand
a
greater mass of propellant KNSB, 1750 g instead of 1500.
the
core leads to an increase in pressure in the motor and an
https://www.facebook.com/groups/1396488870646273/permalink/2020337984928022/in
arethe
Isp, so I will increase core length further)
M18 - granulated nitrate
M19 - pure milled nitrate
Thrust curves of the motors with previous results for comparison
attached.
Video is here
aluminum.find
Serge Pipko
Kyiv, Ukraine
serge77-rocketry.net
I began a series of tests of nozzleless motors of differentconfigurations
and with different propellants. The purpose of the tests is to
differthe
optimal configuration that will give the maximum Isp.motors
I recently tested 4 nozzleless motors with KNSB propellant. All
have the same size and weight, grain outer diameter 50 mm, corediameter
19.3 mm, core length 500 mm, propellant mass 1500 g. Motors
sodiumin
used
potassium nitrate.
M14 - granulated KNO3 (contains 0.8% SiO2 anticaking agent)
M15 - granulated KNO3 + 0,5% red iron oxide
M16 - pure milled KNO3
M17 - granulated milled KNO3
The following tests will be with a greater core length, with
nitrate as an oxidizing agent and with the addition of
https://www.facebook.com/groups/1396488870646273/permalink/1993969987564822/
Thrust curves of the motors are attached.
Videos of the tests can be seen here
https://www.facebook.com/serge.pipko.5/posts/450824292327788
Attachment:
nozzleless motors comparison.jpg
Description: JPEG image
