Solid fuel engines and "Resonance Rods"

I was over at "Ed's Nike Site" and found this cutaway of a Nike booster
motor: http://ed-thelen.org/booster.gif
which shows that it has 9 "resonance rods" mounted in the openings in
the fuel grain- are these to stop the "organ pipe effect" (a harmonic
that develops inside the firing engine that can lead to its destruction)
when the motor is fired? Also, this photo:
http://ed-thelen.org/korean_booster.gif shows a South Korean
Nike-Hercules with a large single booster motor, as opposed to the usual
four- is that a Nike-Zeus or Spartan booster hanging on the back? If so,
where exactly did they get it from?

Pat

In article ,
Pat Flannery wrote:
I was over at "Ed's Nike Site" and found this cutaway of a Nike booster
motor: http://ed-thelen.org/booster.gif
which shows that it has 9 "resonance rods" mounted in the openings in
the fuel grain...

That's one of the kludges people developed to control combustion instability
in solids -- a more difficult problem than in liquids because you have less
control over what's happening.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

Henry Spencer wrote:


That's one of the kludges people developed to control combustion instability
in solids -- a more difficult problem than in liquids because you have less
control over what's happening.


What was the principle they operated on? Were they intended to vibrate
during the fuel burn, or prevent harmonic vibrations from beginning
somehow?

Pat

In article ,
Pat Flannery wrote:
That's one of the kludges people developed to control combustion instability
in solids...

What was the principle they operated on? Were they intended to vibrate
during the fuel burn, or prevent harmonic vibrations from beginning
somehow?

A better name would have been "resonance prevention rods" -- they were
intended to prevent resonant pressure oscillations from building up, at
least partly just by getting in the way of gas flow.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

Found this at the following site:
http://www.tpub.com/content/combat/1.../14110_450.htm

"Resonance rods, mentioned earlier, may be used to offset the resonant
burning or "chugging" of a propellant. These metal or plastic rods are
sometimes included in the combustion chamber. They serve to breakup
regular fluctuations in the burning rate and accompanying
pressure variations. They do so by maintaining a constant burning
area while the surface of the grain is being consumed."

In the 70s & 80s, my Dad made "resonance rods" at a factory here in
Sheboygan, WI. As I recall, they extruded a plastic star shaped rod with a
central hole in it. A steel hanging rod was dipped in a solvent and the
extruded rod was slid onto it then set aside to dry.I knew they were used in
rockets but until now, I didn't know what they did.





"Pat Flannery" wrote in message
...
I was over at "Ed's Nike Site" and found this cutaway of a Nike booster
motor: http://ed-thelen.org/booster.gif
which shows that it has 9 "resonance rods" mounted in the openings in
the fuel grain- are these to stop the "organ pipe effect" (a harmonic
that develops inside the firing engine that can lead to its destruction)
when the motor is fired? Also, this photo:
http://ed-thelen.org/korean_booster.gif shows a South Korean
Nike-Hercules with a large single booster motor, as opposed to the usual
four- is that a Nike-Zeus or Spartan booster hanging on the back? If so,
where exactly did they get it from?

Pat

Randy Lutz wrote:

In the 70s & 80s, my Dad made "resonance rods" at a factory here in
Sheboygan, WI. As I recall, they extruded a plastic star shaped rod with a
central hole in it. A steel hanging rod was dipped in a solvent and the
extruded rod was slid onto it then set aside to dry.I knew they were used in
rockets but until now, I didn't know what they did.


I'd never even heard of the things before; and that Nike booster had a
very complex propellant grain design compared to what I was expecting;
in contrast, the motor for the Nike-Hercules second stage shown on the
same webpage has a very simple "star" type bore in it.

Pat

In article ,
Pat Flannery wrote:
I'd never even heard of the things before; and that Nike booster had a
very complex propellant grain design compared to what I was expecting...

Probably means they had serious stability problems, and had to fumble
around frantically trying to cure them, and what you're looking at is the
first configuration that worked!
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

Henry Spencer wrote:

In article ,
Pat Flannery wrote:


I'd never even heard of the things before; and that Nike booster had a
very complex propellant grain design compared to what I was expecting...



Probably means they had serious stability problems, and had to fumble
around frantically trying to cure them, and what you're looking at is the
first configuration that worked!

The grain design has so many circumferential channels running through it
that any unstable burning looks like it would lead to the interior grain
disintegrating and plugging the exhaust nozzle, followed by a big
explosion... the design reeks of "you can use any fuel composition to
achieve that required thrust curve you wish...as long as it's this
particular one" type designing.

Pat

Pat Flannery wrote:

Henry Spencer wrote:

In article ,
Pat Flannery wrote:


I'd never even heard of the things before; and that Nike booster had a
very complex propellant grain design compared to what I was expecting...



Probably means they had serious stability problems, and had to fumble
around frantically trying to cure them, and what you're looking at is the
first configuration that worked!

The grain design has so many circumferential channels running through it
that any unstable burning looks like it would lead to the interior grain
disintegrating and plugging the exhaust nozzle, followed by a big
explosion... the design reeks of "you can use any fuel composition to
achieve that required thrust curve you wish...as long as it's this
particular one" type designing.

Pat

The other thing to worry about is that when the chunks break off, all of the
sudden you have a bunch more surface area burning at one time. Chamber
pressure goes up... boom.

James

I'd never even heard of the things before; and that Nike booster had a
very complex propellant grain design compared to what I was expecting;
in contrast, the motor for the Nike-Hercules second stage shown on the
same webpage has a very simple "star" type bore in it.

Pat


The thing that surprised me the most was how much volume was empty
space. With that and several other missiles from that era it seems
they didn't pack things in as tightly as they do today. I wonder what
the performance of the Hercules would have been had the upper stage
been jammed with propellant like one of today's missiles.