If one wanted a nozzleless motor that maintained a constant kn, possibly a
rod & tube configuration is worth considering:
http://www.nakka-rocketry.net/th_pix/grains1.gif
Richard
On Thu, Nov 2, 2017 at 12:26 PM, <spas@xxxxxxxxx> wrote:
Trevor Mushung wrote:
Also I've been toying with the idea of a x core to increase burn area and
to even out the Kn over the course of the burn.
The X core will increase initial Kn and decrease final Kn, so it will
increase the scope of Kn change.
Trevor Mushung
On Nov 2, 2017 12:29 PM, "Dave Barr" <dhbarr@xxxxxxxxx> wrote:
I've been kicking around ideas for upping the initial burning surface
area
for a cored nozzleless motor, and it occurred to me that a tetrahedral
shaped expansion molded into the propellant, while less efficient than a
cone, should increase the surface area a bit without substantially
reducing
the propellant volume.
Further in that vein, intentionally disinhibiting the exterior of this
expansion tetrahedron should increase the initial thrust spike, as well.
Can anyone point to research / reading in this area?
On Thursday, October 19, 2017, <spas@xxxxxxxxx> wrote:
Richard wrote:outside
Cool. Serge, you 'forced' me to do some quick calcs :-)
With core diameter 1/3 outside diameter and a grain length of 10x
(regardlessdiameter, you have a kn range starting at 121 decreasing to 40
withof OD).
For nozzleless motor Kn can be calculated by simple formula:
Kn = 4 * L / D
where L and D are core dimentions.
Using my KNSB design chart:
http://www.nakka-rocketry.net/design1.html#Charts
your initial chamber pressure is around 215 psi or 15 atmospheres,
consistent with what you reported. Clearly you have 'choked flow'
youryour
core acting as a nozzle with sonic exhaust velocity.
That got me thinking. Perhaps a silly idea but what if you tapered
initiallycore at the exit? To act as a divergent section, that should
perhapsgive
you a boost in exhaust velocity (supersonic) and therefore thrust,
Butas much as 30% or so. What do you think? See attached graphic.
Yes, most industrial nozzleless motors have such divergent section.
at
15 atm its effectiveness will be low and as pressure quikly drops,with
effectiveness will quikly decrease even more. I plan to test motors
much longer core and I hope KNSB can withstand much bigger pressure.If
these tests will be sucsessfull, than I will try to make divergent.core
Serge Pipko
Kiev, Ukraine
http://serge77-rocketry.net
Richard
On Wed, Oct 18, 2017 at 11:29 AM, <spas@xxxxxxxxx> wrote:
Hi Trevor, the short ansver is - for a given propellant OD you need
otherdiameter about 1/3 OD and core length 10 OD. This is for KNSB or
informativecandy propellant with similar burn rate.
But give me a day or two, I'll collect all my data for more
theyansver.
I'd love to read up about your nozzleless motors. They sound like
I'mwould be very cool. What size/shape core? How long of a casing?
propellant.thinking of trying nozzleless in 1.5" pvc pipe with 6" of
Just
have to figure out the core to actually produce thrust.
Trevor Mushung