Kind of OT: Larger AK wanted

another thing, munk...


the karda and chakma that comes with these are usually large and outstanding work!
 
Daniel Koster said:
OK....got it (maybe...)


Whenever I think of chopping...I like to approach it from a Physicist's viewpoint. That is, looking at it in terms of Force = Mass * Acceleration, as well as Torque = Force * Length.

Chopping, after all, is Torque. You are holding a lever by one end and applying a rotating motion to it.

Now, let's take two objects of the same weight(mass) but different lengths. One is 20" the other is 25".

Now let's figure out what force is needed to apply the same torque (chop)....using this equation:

T1 = F1 * L1 = F1 * 20
T2 = F2 * L2 = F2 * 25

If T1 = T2

Then F1 * 20 = F2 * 25

Or F1 = F2 *(25/20) = 1.25 * F2

In layman's terms....The Force required to produce the chop with the 20" is 1.25 times greater than with the 25".

This seems rudimentary...almost too common sensical....but when you think about it's real world application, what it means is that you will have increased torque with a thinner, longer blade (weight remaining constant). More bang for buck, so to speak.

Now, whether or not the knife itself can withstand the torque you apply to it is a whole nuther game.
Click to expand...

This doesn't seem to be quite correct to me. It would take more torque to produce a chop on a longer blade of the same weight. You are calculating as if you are applying the torque to the end of the blade while pivoting off the handle. This isn't really correct, what happens is a twisting motion of the wrist and arms, so the forces applied are not at the end of the blade. The forces applied are basically at the same spots, close to the handle, regardless of the length of the blade.

The longer blade has a greater moment of inertia, and so it will take more torque (more force applied by the wrists and arms) to get it accelerate at the same rotational acceleration as a shorter blade.

However, the longer blade also will have more angular momentum, and the tangential velocity at a point farther out along the blade will be higher. So, each chop will do more.

The question is, what is the optimum amount of chopping power per amount of force required to make a swing? Chopping power may be related to angular momentum, but there are probably other factors to take into consideration. It may also not even be a linear relation.
 
thanks for the reminder about angular momentum....gotta rework my equation....back in a min or two...
 
OK

Uncle Bill has no AKs >20" in stock.

Thanks for the replies everyone.

Clearblue, thanks, but Im not looking for a sirupati.
 
just for the record:

Torque is rotational kinetic energy....use it or lose it.

Angular momentum is result of applied torque over a period of time.

We're going to solve for angular momentum, mostly because it's easier to understand. Think of a baseball player swinging a baseball bat. There is angular momentum along the entire bat. The farther out the ball is when it's hit by the bat, the more force, the farther it flies. Easy to observe and understand.



(We're going to treat the wrist thing in the following experiments as irrelevant, since you would be moving your arm as well. To simplify, we'll say that, like a newbie would, you swing your khukuri with a stiff wrist (no snap) and you start straight above your head and swing down to waist level. )


Experiment #1


So, assume the following:

2 objects

#1 is 20 inches long
#2 is 25 inches long

Equal Mass (same weight on earth)
Equal angular velocity (swung at the same speed)

The test person's "reach" is 25 inches. (reach = distance from point of rotation - shoulder - to the center of palm - where you'd grip a khukuri)

Radius #1 = 45 inches (1.14m for science folks)
Radius #2 = 50 inches (1.27m)


The equation for determining Angular Momentum is:

L = M V R = Mass * Angular Velocity * Radius



If M#1 = M#2 and if V#1 = V#2
(see assumptions above)

Then the ratio L2 : L1 can also be written R2 : R1

They are directly proportional.



Additionally, the torque is being applied at the point of rotation - again, oversimplified...but it's like saying we're comparing apples to apples....in other words, I'm assuming your swing/form will be similar between the two khukuris.


Experiment #2


Now, we look at it a different way.

Mass not Equal (we'll use a 1:1.25 ratio)
Angular Momentum held constant
Velocity held constant


L1 = L2

That would mean:

M1*V1*R1 = M2*V2*R2

(1)*V1*(1.14) = (1.25)*V2*(1.27)

Solve for the ratio of V1:V2

V1/V2 = [(1.25)*(1.27)]/(1.14) = 1.39

V1 = 1.39*V2

So a 20" would require 1.39 times the speed in order to equal the angular momentum created by a 25" of 1.25 times mass.

Kinda makes sense, don't it?





Experiment 3
(similar to 2)


As observed by me while testing the 22" GRS (#1) against a 20" AK (#2) of nearly equal mass.


Equal Mass


L=MVR

L1 = L2

M1*V1*R1 = M2*V2*R2

cancel out Mass numbers since M1 = M2

V1*R1 = V2*R2

V1*(1.19) = V2*(1.14)

V1 = 0.96*V2

V2 > V1

In other words, I would need to swing with less speed with the 22" GRS to achieve the same angular momentum.


Additionally, since Torque = Radius * Force

If I apply the same torque.....

T1 = T2

R1*F1 = R2*F2

1.19*F1 = 1.14*F2

F1 = 0.96 F2


...less force is needed to move the 22" khukuri.




This, at first seems counterintuitive....and please feel free to check the numbers.

But it's based on a few "givens"....

First, we're comparing khukuris of equal weight.

Second, we're applying the same torque, in order to generate the same angular momentum.



If you take a heavier/longer khukuri and swing it at the same speed as a short one, then yes, it will take more energy. But then that would fail our two assumptions.

A test that would get you equal results would be two khukuris that were each proportionately equivalent...that is, fit the ratio we like to use here in the forum of being 1.5 ounces per inch.

My test above was apples and apples. This test would be oranges and oranges.....just can't cross the two without serious complications....
 
Jebadiah_Smith said:
Uncle Bill has no AKs >20" in stock.
Click to expand...
:p :p :p :p :p



Did he say if he would be willing to order one?

(probably not due to problems in Nepal....:()
 
Dan I have no idea of what in the hell you said. Us ndns just have one helluva time trying to think in terms like that.:grumpy:
Being a lazy man with a consience I would just pick the one which would do the most work with the least effort.
The proof is in the swing and the amount of work done at the end of the shift.:rolleyes: :p
 
Sure....just unleash your easy-to-understand 100-words-or-less approach on me....I'm easy....:D :p



Observation is key.....and that's part of being an ole Ndn, I bet. ;)
 
Jebadiah_Smith said:
Right now i'd settle for a 20" AK.

Anyone have one that needs a new home?
Click to expand...
Never settle for less than you want, that is unless you're absolutely positive there's no way to aquire what you're wanting.
It hasn't been long enough to give up hope yet.
 
Yvsa said:
Never settle for less than you want, that is unless you're absolutely positive there's no way to aquire what you're wanting.
It hasn't been long enough to give up hope yet.
Click to expand...

Ha! Its never too soon to give up on the things you want! Just as long as a new thing comes around to want.

Thats the cosmic law of humanity, right?
 
Dan?

You do one more post that involves equations like that and I'm turning you in to the Principal, Cliff Stamp, physicist. :p



sheez.




muttermuttermutter.
 
Don't get me wrong - the 20" AK is a beast.

Still, it's just not a 30". What a bummer. But, I'll try to see the good in the bad here...I had to learn to be patient sometime anyway. If there's a 30" out there that needs me, it will find me eventually.

You've still got first dibs, Jeb.
 
IIRC, Bill doesn't usually keep that kind of stuff in stock....kinda big-n-bulky too....easier to just get it out of the way...

Shoulda got in on that 30" Sirupati sale....for what, $125 or something? crazy....:eek:






Kis - no more math for me..! I've gone nuts....completely and uttlerly nuts...!!!! :eek:
 
Well, I like large manual weapons, mostly. I have a 74" bo staff that weighs about 3x a purple heart bo of the same
width, and a purple heart 7' bo, and a canvas micarta training spear that's also very heavy.

The GRS, on the other hand, was too large for me. My 21" Chitlangi is not. :)

John
 
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