Welcome, Guest
Username: Password: Remember me
Photobucket image links are no longer allowed, as a matter of forum policy.
Your Mods have been doing a massive job in sorting out the photobucket issue, please assist them by posting directly to the thread and not through a 3rd party host.
Read More...
  • Page:
  • 1

TOPIC: 20mm Cannon 60 Yards Velocity and Pressure Range

20mm Cannon 60 Yards Velocity and Pressure Range 19 May 2015 20:05 #1

  • Paul Francis
  • Paul Francis's Avatar Topic Author
  • Offline
  • Moderator
  • Moderator
  • Posts: 5632
  • Thank you received: 391
I am carrying a out a bit of research into the above 2-point WWII range. The velocity side was measured by a chronometer, located inside a chrono house close by. The pressure measurement is unknown, hense this post. Any idea?

Edit: back to the chronometer, which I assume is a sophisticated clock or measuring device that I assume times a shell over the course of a known distance in this case 60 yards. The data must have been fed electrically to the chrono device which is (was) some distance from the range. The chrono being mounted onto a pillar fixed to a cork base. More info would be appreciated.

The target was mounted on rails fixed to a wall and pulled by overhead pulleys and cable into position from a target room so that it is aligned over a 14 inch diameter metal tube some 9 inches deep that was fixed flush to the brick target wall. Behind the tube is the butt.

Please Log in or Create an account to join the conversation.

You can tell a builder from an archaeologist by the size of his trowel. Mine is a small one!

20mm Cannon 60 Yards Velocity and Pressure Range 19 May 2015 20:31 #2

  • Alec
  • Alec's Avatar
  • Offline
  • Junior Member
  • Junior Member
  • Posts: 88
  • Thank you received: 7
A method of pressure measurement was by copper crusher as described here https://en.wikipedia.org/wiki/Copper_units_of_pressure
This was subsequently replaced by piezoelectric gauges the output of which, in addition to peak pressure, could also be used to produce a pressure time graph.

Please Log in or Create an account to join the conversation.

20mm Cannon 60 Yards Velocity and Pressure Range 19 May 2015 21:03 #3

  • Paul Francis
  • Paul Francis's Avatar Topic Author
  • Offline
  • Moderator
  • Moderator
  • Posts: 5632
  • Thank you received: 391
Thanks. I am not sure I quite understand that Wicki article.

Please Log in or Create an account to join the conversation.

You can tell a builder from an archaeologist by the size of his trowel. Mine is a small one!

20mm Cannon 60 Yards Velocity and Pressure Range 20 May 2015 00:07 #4

  • Alec
  • Alec's Avatar
  • Offline
  • Junior Member
  • Junior Member
  • Posts: 88
  • Thank you received: 7
I was being lazy, try this:

Chamber pressures were recorded using copper crushers, small cylinders of identical size and hardness made from copper. The cylinders deformed by a known amount when subjected to pressure. A cylinder was fitted in to an adaptor that screwed in to a pressure barrel and sat between a piston and a closure cap. The piston was exposed to chamber pressure on firing via a hole drilled through the barrel in to the chamber. Chamber pressure acting on the piston crushed the copper and this deformation was measured and converted to a pressure from a table. Cartridges used had a hole drilled through the side that was covered by tape and inserted in the chamber so the hole lined up with the hole drilled through the barrel.

Now it's late, I'm tired and off to me bed. I'll comment on velocities in the morning.

Please Log in or Create an account to join the conversation.

20mm Cannon 60 Yards Velocity and Pressure Range 20 May 2015 06:36 #5

  • Alec
  • Alec's Avatar
  • Offline
  • Junior Member
  • Junior Member
  • Posts: 88
  • Thank you received: 7
Have a look at http://www.eugeneleeslover.com/USNAVY/CHAPTER-XV-PAGE-1.html If you look some way down there is a section on velocity measurement involving the Boulengé chronograph which I remember seeing but never using. That required a solid mounting ISTR and may fit what you described.

While screens were still used to provide triggering, at some time Light Intensity Detectors or Sky Screens came in to use to trigger the chronometer. As the bullet passes over each detector the change in light intensity produces a pulse to start and stop the timer. Quite when there came in I don't know.

Velocities were expressed as Observed Velocities at x over y where y is the distance the detectors were apart and x was the distance the mid point of y was from the muzzle.

If you then carry on down there are a couple of illustrations of copper crushers assembled in adaptors which will make more sense than the nonsense wrote in a previous post.

Please Log in or Create an account to join the conversation.

20mm Cannon 60 Yards Velocity and Pressure Range 20 May 2015 07:53 #6

  • Paul Francis
  • Paul Francis's Avatar Topic Author
  • Offline
  • Moderator
  • Moderator
  • Posts: 5632
  • Thank you received: 391
Thanks Alec, that web site is very interesting even if some of the text is hidden behind photos. As far as I can tell, in the ROF chronometer house there were two columns fixed to cork insulation below floor level which rise about 3 ft above floor level and on top of these was a 2in thick slate base plate (16 in by 16 in square) for mounting the chronograph tripod on. There were also two large cupboards for housing the chrono when not in use.

Please Log in or Create an account to join the conversation.

You can tell a builder from an archaeologist by the size of his trowel. Mine is a small one!
  • Page:
  • 1
Time to create page: 0.557 seconds
Powered by Kunena Forum

We use cookies to improve our website and your experience when using it. Cookies used for the essential operation of this site have already been set. By continuing to use this site you are agreeing to this. To find out more about the cookies we use and how to delete them, see our privacy policy.

  
EU Cookie Directive Module Information