Help: Need a physics teacher to calculate something
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Help: Need a physics teacher to calculate something
I'm going to fire the working electric torpedo from my Vosper MTB using compressed air. Need to know a few things to size tubing, air storage tank and working pressure to push a 1 pound torpedo to splash down 30 inches in front of the boat. Here's all the data:
Torpedo tube - 1.546" I.D. x 22" long
Torpedo - 1.500" O.D. x 17" long and 430 gram mass
The system must deliver enough force to propel the torpedo 30" to clear the boat's deck (measured from the front end of the torpedo tube to the back of the torpedo at impact with the water.) The torpedo tube center sits 7 inches above the surface of the water.
The torpedo must travel the first 12 inches as measured from the front end of launch tube to the back end of the departing torpedo without dropping more than 1 inch, or it will hit the deck.
Need to know:
Storage capacity of compressed air cylinder when released to shoot 2 fish clear of the deck, one at a time (thinking of the Robart Air Tank with volume of 43 cu-in at 150psi. I will fire two torpedoes from one air charge or mount two air tanks if I have to.
Working pressure of cylinder needed to shoot 2 fish clear of the deck
I.D. of tubing to deliver enough volume over time to do all of the above
Will be using a Clippard EV-2-6-H electrical pneumatic valve with a 0.060" orifice to blow down the compressed air tank. This valve opens very quickly so I'm told.
Any physics teachers or engineers out there who would like to tackle this engineering challenge? Otherwise I'll do it by trial and error and a good old fashion SWAG (Scientific Wild-Assed Guess) or two...
Thanks,
Mike J.
Torpedo tube - 1.546" I.D. x 22" long
Torpedo - 1.500" O.D. x 17" long and 430 gram mass
The system must deliver enough force to propel the torpedo 30" to clear the boat's deck (measured from the front end of the torpedo tube to the back of the torpedo at impact with the water.) The torpedo tube center sits 7 inches above the surface of the water.
The torpedo must travel the first 12 inches as measured from the front end of launch tube to the back end of the departing torpedo without dropping more than 1 inch, or it will hit the deck.
Need to know:
Storage capacity of compressed air cylinder when released to shoot 2 fish clear of the deck, one at a time (thinking of the Robart Air Tank with volume of 43 cu-in at 150psi. I will fire two torpedoes from one air charge or mount two air tanks if I have to.
Working pressure of cylinder needed to shoot 2 fish clear of the deck
I.D. of tubing to deliver enough volume over time to do all of the above
Will be using a Clippard EV-2-6-H electrical pneumatic valve with a 0.060" orifice to blow down the compressed air tank. This valve opens very quickly so I'm told.
Any physics teachers or engineers out there who would like to tackle this engineering challenge? Otherwise I'll do it by trial and error and a good old fashion SWAG (Scientific Wild-Assed Guess) or two...
Thanks,
Mike J.
#2
RE: Help: Need a physics teacher to calculate something
The maximum volume will be the length of the torpedo at it's full diameter.
Once the taper at the tail reaches the front edge of your launching tube, any
additional volume is wasted. Once you have your maximum volume calculated, then
it becomes a matter of pressure.
Now if you are shooting the "fish" consecutivley... one, then two...
Then what must be considered, is that the valves can ofter dump
fourteen cubic inches of air a second. If you have held the valve open
for two seconds to fire the first torpedo, you may not have the volume or
pressure to launch the second torpedo if you are using a fixed volume air resevoir.
Once the taper at the tail reaches the front edge of your launching tube, any
additional volume is wasted. Once you have your maximum volume calculated, then
it becomes a matter of pressure.
Now if you are shooting the "fish" consecutivley... one, then two...
Then what must be considered, is that the valves can ofter dump
fourteen cubic inches of air a second. If you have held the valve open
for two seconds to fire the first torpedo, you may not have the volume or
pressure to launch the second torpedo if you are using a fixed volume air resevoir.
#3
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RE: Help: Need a physics teacher to calculate something
ORIGINAL: Umi_Ryuzuki
The maximum volume will be the length of the torpedo at it's full diameter.
Once the taper at the tail reaches the front edge of your launching tube, any
additional volume is wasted. Once you have your maximum volume calculated, then
it becomes a matter of pressure.
Now if you are shooting the ''fish'' consecutivley... one, then two...
Then what must be considered, is that the valves can ofter dump
fourteen cubic inches of air a second. If you have held the valve open
for two seconds to fire the first torpedo, you may not have the volume or
pressure to launch the second torpedo if you are using a fixed volume air resevoir.
The maximum volume will be the length of the torpedo at it's full diameter.
Once the taper at the tail reaches the front edge of your launching tube, any
additional volume is wasted. Once you have your maximum volume calculated, then
it becomes a matter of pressure.
Now if you are shooting the ''fish'' consecutivley... one, then two...
Then what must be considered, is that the valves can ofter dump
fourteen cubic inches of air a second. If you have held the valve open
for two seconds to fire the first torpedo, you may not have the volume or
pressure to launch the second torpedo if you are using a fixed volume air resevoir.
Mike
#4
RE: Help: Need a physics teacher to calculate something
I don't think I can add any more hints to the concept than I have..
My college physics book is,... well I hope I haven't carried it around with me
all this time... I do have a trig book though.
My college physics book is,... well I hope I haven't carried it around with me
all this time... I do have a trig book though.
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RE: Help: Need a physics teacher to calculate something
The important clever bit is making sure the torp doesn't foul the deck, and that means getting it forward so far before it drops by one inch at 1G, or 32 ft/sec/sec.
My old school books have had nearly half a century to hide away, so I leave the actual calculation of muzzle velocity to someone younger and smarter, possibly the physics teacher.
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RE: Help: Need a physics teacher to calculate something
Here's a link to a balistics forum you could post your question:
http://www.absoluteastronomy.com/topics/Ballistics
http://www.absoluteastronomy.com/topics/Ballistics
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RE: Help: Need a physics teacher to calculate something
Since starting this part of the build, I've spent time digging around physics texts and can come up with simple formulas telling me how fast the torpedo must be traveling to clear the edge of the deck. But what is more difficult to determine is the actual rate of compressed air delivery, which I'm calculating to be at least 19 CFM per launch tube injected in less than a second. Then the final part of the puzzle is to find the correct air pressure at that flow rate to give me a launch velocity of around 3.6m/s. This will place the point of water impact .7 meters ahead of the launch tube. With the right valve, I'll be able to dial in the best pressure. It's been fun working this all out, and I thank all of you for your input. Once I dial in all the variables and get this thing working, I'll post videos of the testing and final result. It should be very impressive to see a 60-inch long Vosper MTB charging along with all three motors at max speed, fire a two fish spread and watch as the torpedo wakes race to their target, which will be me standing on the shore. I don't want to go swimming to retrieve these things. Our salt water pond is not the cleanest body of water around Honolulu.
Mike
Mike