Solving Launcher Induced Torpedo Instability Problem
A Report to the Cabal:
For an in-depth discussion of the Caswell-Merriman 1/72 weapon system, examine this pdf at: http://support.caswellplating.com/in...l-instructions
About 80% of the torpedoes launched from our system run, 'hot-straight-and-normal'. But, 20% will run other than straight/ those gas propelled weapons will swerve up, down, left, or right from course -- the desired course being parallel to the launchers centerline.
Why?
The Problem: The four stabilizing fins at the stern of each torpedo are canted to induce a left-hand roll as the weapon races through the water. Roll stabilization is an important element of total weapon stability as it races through the water. however, that same fin displacement works to rotate the weapon to the right -- the wrong direction -- at the moment of launch, as a significant fraction of the impulse gas (a mixture of water and the rapidly expanding propellant gas ejected behind the weapon) rushes forward, through the annular space between weapon and launcher bore.
During those critical moments of launch, as the weapon travels through the launcher, even out of the muzzle, the torpedo is still in a gas rich environment. In fact, it is not until the weapon has traveled several inches past the launcher that it finally punches through the water-gas plume surrounding it, and into the water. It's that critical transition point, the interface between the two forms of fluid, where things go crazy 20% of the time.
The Solution: Modify the torpedo stop-disc (an internal structure near the breech end of the launcher, against which the tail fins of the weapon rest) so that it also functions as a flow stator -- to induce a left-hand swirl to the impulse water-gas impulse jet as it pushes and rushes past the body of the weapon as it starts its advance forward through and eventually out of the tube.
Illustrating perfectly the gas-water interface point of the weapon -- launched from a submerged 1/72 ALFA class model submarine -- a torpedo is seen completing the transition of flight through a compressible gas fluid and into an essentially non-compressible liquid fluid. Do to the wide clearance between torpedo body and inside bore of the launcher (that tolerance to account for pressure and temperature induced changes in the physical dimensions of launcher and weapon), a significant amount of impulse gas surrounds and rushes ahead of the weapon as it races out the tube and into the water. The result is a 'bubble' of gas that encases the weapon even a few inches past the launchers muzzle opening, the expanding gas plume displacing the water around it.
A Polaris missile rising up from launch-depth never gets wet -- it too encased in the gases that envelope it, those gases expanding as the missile ascends to the surface; those gases introduced during tube equalization and launch.
(yeah ... I was a Torpedoman/Launcher Tech in the Navy. Duh!).
You can see in the above picture, the ass-end of the torpedo has just broken through the gas-water interface point. If the weapon is not spinning in the correct left-hand direction at this point, the water flowing aft along the torpedo body, acting on the canted stabilizing fins, will arrest its right-hand roll and will start to spin it in the left-hand direction. It's that transition, from right to left-hand roll, that invites outside de-stabilizing forces -- asymmetric pressure waves shaped by the form of the submarine bow and well from which the launchers muzzle projects -- to change the course of the torpedo.
The objective is to get the weapon into a left-hand spin while it's still in the launcher.
And that's the nut of this discussion today, boys and girls: How to induce a left-hand directed fluid helical swirl within the launcher in order to start the weapon spinning in the correct direction as it makes the transition between gas and liquid.
This cut-away launcher shows off the torpedo stop-disc -- its that item near the movable breech-block, against which the trailing edge of the torpedo stabilizing fins rest, preventing any further after travel of the weapon within the tube. During the launchers transition from battery to launch -- as the breech-block moves aft, stripping the weapon charging O-ring away from the nozzle end of the weapons nozzle tube -- its the torpedo stop-disc that retains the weapon in position as the O-ring, with some resistance, is pulled clear of the weapons nozzle.
The upper launcher is in the battery condition. The stop-bolt ball preventing forward motion of the weapon and the breech-block O-ring made up tight around the weapon nozzle.
The lower, cut-away launcher is in the launched condition. The stop-bolt ball clear of the weapon and the breech-block O-ring pulled aft and clear of the weapons nozzle.
Early versions of the launcher featured a stop-disc with only the central hole through which the weapons nozzle tube projected aft and into the seating O-ring of the Breech-block. The problem is that this hole, once the weapon clears it at the moment of launch, directs the impulse gas to travel down the tube, axially. Some of that expanding gas races through the annular space between torpedo and torpedo tube where the canted stabilizing fins are acted upon, rotating the weapon to the right, the wrong direction!. By providing the stop-disc with four canted holes, the impulse gas is fed into the tube bore with a significant right-hand helical twist, starting the desired direction of rotation of the weapon as it advances toward the muzzle end of the launcher.
This is an extreem close-up of the breech end of the launcher. The 45-degree canted holes within the outer diameter of the torpedo stop-disc are evident here.
Illustrating how my gas propelled torpedoes are arranged. Note that the stabilizing fins are canted to twist the body into a left-hand roll as the weapont travels through the water. But, given a little thought, you can see that a forward advancing plume of axially oriented impulse gas would also work on the fins at the moment of launch, rolling the weapon to the right. The wrong spin!
As an aside to this discussion: Note how simple of design the gas propelled weapon is. Just a hollow cast resin body, a pick-up tube (to gather gas, not liquid propellant) terminating at its end into a divergent-convergent nozzle. The one type of body is painted to either reflect a modern, acoustic weapon or a WW-2 era weapon.
A major source of the forces that tug and push the torpedo body around as it leaves the launcher, is the shape of the bow and well from which the weapon is projected. Here you see the worst possible situation -- a model GATO class submarine: a deep trench with three very close faces across which the weapon passes at considerable velocity. The Venturi and Coanda (look them up) forces at work, coupled with the asymmetric wave front presented by the bow, and you can see that there is much going on at the muzzle end of the launcher to push off-course an unstable weapon as it punches through the gas-water interface. Either that weapon hits the wall (the gas-water interface) spinning in the right direction, or there is a one-in-five chance it will be knocked off-course.
Before getting into a production mode with the new, improved torpedo stop-discs, I wanted to see if indeed the flow of impulse gas was re-directed by the stator element of the disc into a helix that would twist the weapon to the left as it traveled down the launchers bore. Employing an old NACA-NASA trick, I stick short lengths of cotton string to some masking tap and wrapped these 'tufts' around the muzzle end of a test article. Blowing air through the breech end of the torpedo tube stood in for the ejection gas liberated during launch. The air-stream emerging from the muzzle end would carry the tufts along with it, giving the observer a visible representation of the streamlines.
First, to establish a base-line to the study, I pumped air into a tube with the earlier version of the torpedo stop-disc, just a straight hole in its center, insuring an axially directed flow through the tubes bore. The assumption confirmed through experiment: Yes, the streamline was indeed axially oriented with the bore of the tube. So far, so good ...
... Then, blowing air through a launcher with a torpedo stop-disc outfitted with the four canted holes, the disc also serving as a helix inducing stator. Note the helical streamlines coming out the nozzle -- it's a fair assumption that this helical orientation of the air flow originates downstream of the disc and is nearly constant throughout the length of the bore. The cant of the disc holes is 45-degrees. At the nozzle the tufts indicated a helical twist of about 30-degrees. Not bad! That more than the cant (angular displacement) of the weapons stabilizing fins. Perfect!
Mass production of the 'improved' torpedo stop-disc and stator parts starts with taking a length of machine brass round stock, the blank -- of a size that sleeves within the torpedo tube bore -- drilling out a center hole on the lathe, then transferring the work to a rotary head, and then punching out the four holes around the face of the blank with the drill press. All holes drilled to the shank of the drill bit, making each hole about a half-inch deep.
The blank transferred back to the lathe. The discrete torpedo stop-discs blanks where then parted off and caught onto the tip of the center hole boring drill bit -- this trick keeps the parts from flying across the shop (never to be seen again!) as they part away from the spinning work. That half-inch of bore length produces five pieces.
The work goes very quickly ... it took more time for me to write this up for you than to do the work itself!
Torpedo stop-disc blanks to the right, canted stator holes completed on the torpedo stop-disc stators to the left. Canting the holes for a left-hand helix flow is an easy matter: Secure the blank in the jaws of a Jeweler's hand-vice so that just one hole is accessible above the jaws, insert the drill bit through it, bring the bit up to speed, and cant the bit slowly to a 45-degree angle to form the stator holes. Repeat the operation three more times and you have a completed torpedo stop-disc stator part, ready to be soldered within the breech end of a launcher.
The sleeved tool above is used to push the interference-fit discs (a little hammer-and-anvil action required to slightly increase the diameter of the disc) into the bore of the launcher. The tool insures a disc is positioned the right distance from the breech opening and that the face of the disc is perpendicular to the axis of the bore. Once installed, the union between bore and disc is saturated with liquid rosin, a small shard of solder placed within the bore, against the disc, heat applied from the outside of the tube, and the molten solder permitted to spread around the perimeter of the disc, bonding disc and launcher tube permanently.
Production work. I make as many as forty launchers per sitting. There's economy in numbers. Thank you, Mr. Ford.
Yeah ... I can solder.
But I take my hat off to Ron Perrott! This guy is a master of the Craft. Check out his brass submarine deck and AA guns! That maniac can solder wax-paper to a greasy crayon! You gotta check out his work.
David D Merriman III
A Report to the Cabal:
For an in-depth discussion of the Caswell-Merriman 1/72 weapon system, examine this pdf at: http://support.caswellplating.com/in...l-instructions
About 80% of the torpedoes launched from our system run, 'hot-straight-and-normal'. But, 20% will run other than straight/ those gas propelled weapons will swerve up, down, left, or right from course -- the desired course being parallel to the launchers centerline.
Why?
The Problem: The four stabilizing fins at the stern of each torpedo are canted to induce a left-hand roll as the weapon races through the water. Roll stabilization is an important element of total weapon stability as it races through the water. however, that same fin displacement works to rotate the weapon to the right -- the wrong direction -- at the moment of launch, as a significant fraction of the impulse gas (a mixture of water and the rapidly expanding propellant gas ejected behind the weapon) rushes forward, through the annular space between weapon and launcher bore.
During those critical moments of launch, as the weapon travels through the launcher, even out of the muzzle, the torpedo is still in a gas rich environment. In fact, it is not until the weapon has traveled several inches past the launcher that it finally punches through the water-gas plume surrounding it, and into the water. It's that critical transition point, the interface between the two forms of fluid, where things go crazy 20% of the time.
The Solution: Modify the torpedo stop-disc (an internal structure near the breech end of the launcher, against which the tail fins of the weapon rest) so that it also functions as a flow stator -- to induce a left-hand swirl to the impulse water-gas impulse jet as it pushes and rushes past the body of the weapon as it starts its advance forward through and eventually out of the tube.
Illustrating perfectly the gas-water interface point of the weapon -- launched from a submerged 1/72 ALFA class model submarine -- a torpedo is seen completing the transition of flight through a compressible gas fluid and into an essentially non-compressible liquid fluid. Do to the wide clearance between torpedo body and inside bore of the launcher (that tolerance to account for pressure and temperature induced changes in the physical dimensions of launcher and weapon), a significant amount of impulse gas surrounds and rushes ahead of the weapon as it races out the tube and into the water. The result is a 'bubble' of gas that encases the weapon even a few inches past the launchers muzzle opening, the expanding gas plume displacing the water around it.
A Polaris missile rising up from launch-depth never gets wet -- it too encased in the gases that envelope it, those gases expanding as the missile ascends to the surface; those gases introduced during tube equalization and launch.
(yeah ... I was a Torpedoman/Launcher Tech in the Navy. Duh!).
You can see in the above picture, the ass-end of the torpedo has just broken through the gas-water interface point. If the weapon is not spinning in the correct left-hand direction at this point, the water flowing aft along the torpedo body, acting on the canted stabilizing fins, will arrest its right-hand roll and will start to spin it in the left-hand direction. It's that transition, from right to left-hand roll, that invites outside de-stabilizing forces -- asymmetric pressure waves shaped by the form of the submarine bow and well from which the launchers muzzle projects -- to change the course of the torpedo.
The objective is to get the weapon into a left-hand spin while it's still in the launcher.
And that's the nut of this discussion today, boys and girls: How to induce a left-hand directed fluid helical swirl within the launcher in order to start the weapon spinning in the correct direction as it makes the transition between gas and liquid.
This cut-away launcher shows off the torpedo stop-disc -- its that item near the movable breech-block, against which the trailing edge of the torpedo stabilizing fins rest, preventing any further after travel of the weapon within the tube. During the launchers transition from battery to launch -- as the breech-block moves aft, stripping the weapon charging O-ring away from the nozzle end of the weapons nozzle tube -- its the torpedo stop-disc that retains the weapon in position as the O-ring, with some resistance, is pulled clear of the weapons nozzle.
The upper launcher is in the battery condition. The stop-bolt ball preventing forward motion of the weapon and the breech-block O-ring made up tight around the weapon nozzle.
The lower, cut-away launcher is in the launched condition. The stop-bolt ball clear of the weapon and the breech-block O-ring pulled aft and clear of the weapons nozzle.
Early versions of the launcher featured a stop-disc with only the central hole through which the weapons nozzle tube projected aft and into the seating O-ring of the Breech-block. The problem is that this hole, once the weapon clears it at the moment of launch, directs the impulse gas to travel down the tube, axially. Some of that expanding gas races through the annular space between torpedo and torpedo tube where the canted stabilizing fins are acted upon, rotating the weapon to the right, the wrong direction!. By providing the stop-disc with four canted holes, the impulse gas is fed into the tube bore with a significant right-hand helical twist, starting the desired direction of rotation of the weapon as it advances toward the muzzle end of the launcher.
This is an extreem close-up of the breech end of the launcher. The 45-degree canted holes within the outer diameter of the torpedo stop-disc are evident here.
Illustrating how my gas propelled torpedoes are arranged. Note that the stabilizing fins are canted to twist the body into a left-hand roll as the weapont travels through the water. But, given a little thought, you can see that a forward advancing plume of axially oriented impulse gas would also work on the fins at the moment of launch, rolling the weapon to the right. The wrong spin!
As an aside to this discussion: Note how simple of design the gas propelled weapon is. Just a hollow cast resin body, a pick-up tube (to gather gas, not liquid propellant) terminating at its end into a divergent-convergent nozzle. The one type of body is painted to either reflect a modern, acoustic weapon or a WW-2 era weapon.
A major source of the forces that tug and push the torpedo body around as it leaves the launcher, is the shape of the bow and well from which the weapon is projected. Here you see the worst possible situation -- a model GATO class submarine: a deep trench with three very close faces across which the weapon passes at considerable velocity. The Venturi and Coanda (look them up) forces at work, coupled with the asymmetric wave front presented by the bow, and you can see that there is much going on at the muzzle end of the launcher to push off-course an unstable weapon as it punches through the gas-water interface. Either that weapon hits the wall (the gas-water interface) spinning in the right direction, or there is a one-in-five chance it will be knocked off-course.
Before getting into a production mode with the new, improved torpedo stop-discs, I wanted to see if indeed the flow of impulse gas was re-directed by the stator element of the disc into a helix that would twist the weapon to the left as it traveled down the launchers bore. Employing an old NACA-NASA trick, I stick short lengths of cotton string to some masking tap and wrapped these 'tufts' around the muzzle end of a test article. Blowing air through the breech end of the torpedo tube stood in for the ejection gas liberated during launch. The air-stream emerging from the muzzle end would carry the tufts along with it, giving the observer a visible representation of the streamlines.
First, to establish a base-line to the study, I pumped air into a tube with the earlier version of the torpedo stop-disc, just a straight hole in its center, insuring an axially directed flow through the tubes bore. The assumption confirmed through experiment: Yes, the streamline was indeed axially oriented with the bore of the tube. So far, so good ...
... Then, blowing air through a launcher with a torpedo stop-disc outfitted with the four canted holes, the disc also serving as a helix inducing stator. Note the helical streamlines coming out the nozzle -- it's a fair assumption that this helical orientation of the air flow originates downstream of the disc and is nearly constant throughout the length of the bore. The cant of the disc holes is 45-degrees. At the nozzle the tufts indicated a helical twist of about 30-degrees. Not bad! That more than the cant (angular displacement) of the weapons stabilizing fins. Perfect!
Mass production of the 'improved' torpedo stop-disc and stator parts starts with taking a length of machine brass round stock, the blank -- of a size that sleeves within the torpedo tube bore -- drilling out a center hole on the lathe, then transferring the work to a rotary head, and then punching out the four holes around the face of the blank with the drill press. All holes drilled to the shank of the drill bit, making each hole about a half-inch deep.
The blank transferred back to the lathe. The discrete torpedo stop-discs blanks where then parted off and caught onto the tip of the center hole boring drill bit -- this trick keeps the parts from flying across the shop (never to be seen again!) as they part away from the spinning work. That half-inch of bore length produces five pieces.
The work goes very quickly ... it took more time for me to write this up for you than to do the work itself!
Torpedo stop-disc blanks to the right, canted stator holes completed on the torpedo stop-disc stators to the left. Canting the holes for a left-hand helix flow is an easy matter: Secure the blank in the jaws of a Jeweler's hand-vice so that just one hole is accessible above the jaws, insert the drill bit through it, bring the bit up to speed, and cant the bit slowly to a 45-degree angle to form the stator holes. Repeat the operation three more times and you have a completed torpedo stop-disc stator part, ready to be soldered within the breech end of a launcher.
The sleeved tool above is used to push the interference-fit discs (a little hammer-and-anvil action required to slightly increase the diameter of the disc) into the bore of the launcher. The tool insures a disc is positioned the right distance from the breech opening and that the face of the disc is perpendicular to the axis of the bore. Once installed, the union between bore and disc is saturated with liquid rosin, a small shard of solder placed within the bore, against the disc, heat applied from the outside of the tube, and the molten solder permitted to spread around the perimeter of the disc, bonding disc and launcher tube permanently.
Production work. I make as many as forty launchers per sitting. There's economy in numbers. Thank you, Mr. Ford.
Yeah ... I can solder.
But I take my hat off to Ron Perrott! This guy is a master of the Craft. Check out his brass submarine deck and AA guns! That maniac can solder wax-paper to a greasy crayon! You gotta check out his work.
David D Merriman III
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