Note also that erosive burning is also a function of the Core Complexity
Factor, see Pages 34-35 and Equation 13 from the technical article.
From the motor thrust curve backed out from the flight acceleration data for
the 2004 CSXT GoFast rocket, the erosive burning for the early part of the
motor burn was higher than I predicted. This was due to the erosive burning
characterization tests being done with cylindrical cores, with a Core
Complexity Factor (X in Equation 13) of 1.0. We had planned a short series of
subscale tests with Finocyl grains, but ran out of time. But using the Erosive
Burning Design Criteria from the technical article, we were able to achieve the
design objective of putting the maximum amount of propellant in the motor so
the rocket could exceed 100 km, but not having the motor fail from erosive
burning, which was a real concern.
The Erosive Burning Design Criteria from the technical article will work fine
for cylindrical cores, and is a good place to start for Finocyl grains. Just
be aware that you should calculate your Core Complexity Factor for your grain,
and note that the higher the Core Complexity Factor, the higher your erosive
burning will be, compared to a cylindrical core with the same core Mach number
and core mass flux.
Chuck Rogers
CRogers168@xxxxxxx
-----Original Message-----
From: dmarc-noreply <dmarc-noreply@xxxxxxxxxxxxx>
To: arocket <arocket@xxxxxxxxxxxxx>
Sent: Wed, Apr 12, 2017 3:47 pm
Subject: [AR] Re: Erosive burning rule of thumb?
There's a technical article I authored on Erosive Burning Design Criteria for
Solid Rocket Motors which was published in High Power Rocketry Magazine which
can be downloaded from the RASAero web site from the Solid Rocket Motor
Technical Report Downloads page at:
http://www.rasaero.com/dl_solid_motor.htm
Scroll down to the bottom for the Erosive Burning Design Criteria for High
Power and Experimental/Amateur Solid Rocket Motors technical article. There's
a short technical summary available of the article, and the full article for
download.
The combined Core Mach Number/Core Mass Flux design criteria is what was used
to design the core of the 2004 CSXT GoFast rocket. The technical article
includes data for burn rate as a function of chamber pressure and core mass
flux for the Derek Deville D8 propellant which was used for the 2004 CSXT
GoFast S motor. The core mass flux for the onset of erosive burning can be
seen in the D8 propellant burn rate experimental data.
Chuck Rogers
CRogers168@xxxxxxx
-----Original Message-----
From: William Claybaugh <wclaybaugh2@xxxxxxxxx>
To: arocket <arocket@xxxxxxxxxxxxx>
Sent: Wed, Apr 12, 2017 1:54 pm
Subject: [AR] Erosive burning rule of thumb?
Is there any experience-based rule for erosive burning in cylinderical-type
grains (Bates, Finocyl, etc.)? I am particularly looking for experience as to
how small the core diameter can be as a percentage of grain diameter: 50%
appears to assure no erosion at L/D of 10:1 or less, what about 33%?
When does overall length begin to play? I know that around 15:1 will lead to
erosion with a 50% core diameter, for example. What is the "critical" length at
33%? What about other core diameters?
Bill
