RPM VS Velocity

[coloradoclyde]

This has to do with pump laws. The Archimedes screw is a positive displacement conveyor with no slip. A motor boat propeller has lots of slip. I can't go into specifics because I have forgotten most of my engineering classes.

No argument....My comparison was meant to be analogous.

 

[necchi]

Well there is that, but think of it as a fan or propeller actually being the stationary unit (opposite a barrel or screw) the propeller moves a mass by it's motion (get it?)
A boat moves forward because of Newtons third law,, if an outboard motor is attached to a pier, the water moves not the pier. The air in the house moves,, not the fan.

 

[azmntman]

ff

unless then fans off

ff

:shake: :surrender:

 

[coloradoclyde]

But the math is skewed just a bit.
A projectile is stationary until the charge is ignited, it doesn't immediately move to it's highest rate of speed. It accelerates as it moves down the barrel and doesn't reach maximum speed until it leave the barrel and no longer has acceleration behind it.
Ya can't really "simplify" the formula assuming top speed as it traverses the barrel, it's always under acceleration until it leave the barrel.
The charge determines how fast it moves in the barrel and reaches it's terminal maximum velocity at exit.

Hey John! did you hear that Space X just landed a rocket back on earth after it took off......Imagine the calculations involved in that... :shocked2:
Kind of like shooting your gun and having the ball reload itself back into the gun.... :grin:

 

[coloradoclyde]

Well there is that, but think of it as a fan or propeller actually being the stationary unit (opposite a barrel or screw) the propeller moves a mass by it's motion (get it?)
A boat moves forward because of Newtons third law,, if an outboard motor is attached to a pier, the water moves not the pier. The air in the house moves,, not the fan.

The movement of the fluid is the same in either case (Bernoulli not Newton)
If you Blow on a fan the fan blades will move.....
If you move the blades the air will move......

Remember these are analogies......

 

[fishmusic]

Necchi, I think you are correct. I also think you must consider the twist rate, barrel length and the time that the projectile is in the barrel. That makes for a considerable physics problem. But in short, the spin could be proportional to the muzzle velocity. I want to think about this some more because I think the time in the barrel is key.

 

[coloradoclyde]

I also think you must consider the twist rate, barrel length and the time that the projectile is in the barrel.

No!....not if we are talking about bullet stability......the bullet is stable while it in the barrel.....we are using the twist, velocity, Rpm data to determine stability in flight

 

[fishmusic]

I was thinking in terms of spin rate. The less time that bullet is in the barrel means a higher spin rate at the muzzle. Hence the idea that muzzle velocity and spin rate are proportional.

But I will let more experienced shooters guide me.

:surrender:

 

[coloradoclyde]

The less time that bullet is in the barrel means a higher spin rate at the muzzle.

Time spent in the barrel is a function of velocity and acceleration.....you can't change the time without changing the velocity....

 

[Gene L]

I don't think time in the barrel can be measured, it's way too short and we lack the measuring tools at this point. It has to be inferred from math...if at all. Same with RPM...has to be determined by math.

Exterior ballistics are quantifiable.

 

[coloradoclyde]

Now! velocity is a constant when making these calculations....acceleration and deceleration are variable....
We use a constant to make the calculations....
If you want to make calculations using variables, you can.......but you are going to need a lot more information.

 

[coloradoclyde]

I don't think time in the barrel can be measured, it's way too short and we lack the measuring tools at this point. It has to be inferred from math...if at all. Same with RPM...has to be determined by math.

Exterior ballistics are quantifiable.

So close Gene......but still making assumptions....
We can and have visually measured RPMs of a bullet using high speed film.

 

[leslie]

All this and a dollar will get you a cup of coffee most places but Starbucks.Having said that just what can I derive from this discussion that might have some practical application to shooting a muzzleloader?

 

[Gene L]

Ah, Clyde. You're overloading my computer's condescension filter.

I'm sure that's so on high speed film.

 

[coloradoclyde]

Here Gene....This might help you visualize it....
https://youtu.be/QfDoQwIAaXg

https://youtu.be/otpFNL3yem4

https://youtu.be/Z7FMki6dlKg



This one shows the supersonic shock wave and what a conical does without gyroscopic stability....it begins to tumble.
https://youtu.be/Num9TR7wlrw

 

[Stumpkiller]

This is much like knowing the atomic number of lead is 82, the symbol is "Pb" and the electron configuration is Xe] 4f^14 5d^10 6s^2 6p^2.

Someone cares . . . somewhere. But not at sunrise on opening day.

 

[necchi]

just what can I derive from this discussion that might have some practical application to shooting a muzzleloader?

Your right, I think we're all agreeing but just looking at it from a different view point.
The bullet is going to spin the same because of the twist rate, what changes is how many times it spins as it travels in the air at a given velocity,, what the discussions is about is time and distance and both are variables within each individuals load choices.
Muzzle loaders are vastly more forgiving then modern CF,, they're really not even comparable in practical terms.
I guess I've seen this kind of stuff happen before when a CF loader applies that skill set to ML's.
FWIW, myself any many other members here are CF loaders too, I'm not pointing fingers at anyone.

 

[coloradoclyde]

The problem isn't with not knowing how the things we use work.......but rather the consequences of postulating the answers to such ......

 

[necchi]

Yeah, there's an olde proverb;
You can lead a horse to water,,,

 

[Col. Batguano]

Ok math guys;

What twist rate will it take to stabilize the (now skinned) cat from page 1 of this thread?