velocity test of guns/cannon rounds

[niklas]

i run a test how the muzzle velocity changes with distance

The X-Axis is a linear distance unit (NOT yard or meter, but 7.5 is approximate the range where the mk108 30mm round disappears, 0.5 is ~50-100yards in front of the spinner)
The Y-Axis is a kind of time unit, the higher the slower is the muzzle flying (bad of course)

Because i got the impression that deceleration is a linear function of distance, i used only to points, at the beginning and at the end for the curve.


For Guns:
       

For Cannons:
       

mg151 and Shvak (seem to be almost equal)  are modelled to be at the beginning almost as fast as Hispanos and NIK cannons, but to slow down much faster. That makes long ranges shots almost impossible, while Hispanos and 99 M2 cannons.... you know it.
Zero cannons hold their velocity well too, but are slow from the beginning.

Strange is imo that small mg-guns have no high velocity, and they slow down very fast compared to heavy guns.
.50 cal are modelled to be fastest and to slow down least ...

niklas
 

[This message has been edited by niklas (edited 10-29-2000).]

[This message has been edited by niklas (edited 10-29-2000).]

[This message has been edited by niklas (edited 10-29-2000).]

[This message has been edited by niklas (edited 10-29-2000).]

[Hooligan]

 http://home.earthlink.net/~jayboyer/ballistics.htm

The customary measure of the ability of a round to retain speed is  by its Ballistic Coefficient (BC).  A higher BC indicates that a round retains its velocity better.

I have very good information on a number of rounds.  .50 BMG rounds typically have a G1-BC in the range of .65-.72 (this is quite good).  .30 cal rounds typically have a G1-BC around .50 (average) and the G1-BCs for Mg151/20mm rounds are typically between .30 and .50.

In general a heavy long round will have a higher BC.  i.e. if you have 2 rounds of identical caliber that are pushing aside the same amount of air the heavier round will hold its speed better because the force of the drag has to operate on a bigger mass.  A 130g 20mm round should hold its speed significantly better than a 90g 20mm round.  Similarly if you have identically shaped .30 and .50 rounds the larger round should have better ballistics because it has higher sectional density.  In this particular example the .50 round should generate about 2.8 times the drag of the .30 round but weigh 4.6 times as much.

Hooligan

[niklas]

Intersting site Hooligan, but i donīt think the AH code is handling those equations there

I had a look at the calculator site. The big question is what input did they use (geometry input). This is what the calculator needs.
Variables
a  total vector acceleration  aD  vector acceleration due to drag  
C  ballistic coefficient  CD  drag coefficient  
d  bullet diameter  F  vector drag force  
g  vector gravitational acceleration  G  "G" function  
i  form factor  KD  drag coefficient  
m  mach number  M  bullet mass  
p  atmospheric density  p0  sea level atmospheric density  
pi  3.14159...  SD  sectional density  
s  cross sectional area (pi d2/4)  v  vector velocity, | v | = (v·v)1/2 and v = u - w  
w  vector wind velocity  u  velocity of bullet relative to ground

The results of your site depend very much from the input values, especially CD, KD.

[Hooligan]

Niklas:

Sorry I forget to mention in my earlier post:  Thanks for going to all the work and producing this information  .

It is easy to determine the ballistic coefficient (upon which so much depends) if you have some actual trajectory data for the round in question.  This is what I did in my example.  

Also, ballistic calculations by numerical integration are well understood and accepted so I would be very surprised if AH does not use something very similar.  So IMO the AH code is "handling those equations".  As far as I can tell the outputs of the AH model certainly seem to indicate that the AH ballistics model is right on.  Frankly, compared to many other components of AH, ballistics of this sort are trivial and very easy to get right.  

Hooligan

[SageFIN]

There is always the chance that an error might slip in. No human is so perfect as to not make any errors.

In the case of AH there was an error in ballistics, trivial as you say it is. Gravity was applied twice in the equations. IIRC Hitech noticed this when he was working on the tank sight (I've been lurking on this BBS unregistered for a long time   ). As always, this error was swiftly corrected.

So what's my point? No matter how trivial something is, an error might still slip in(mark me, I am not implying that there are any errors in AH's ballistics) and it will only get noticed by chance if anyone does not investigate.

------------------
---
SageFIN

"The wolves are gathering, the stars are shifting...
come, join us in the hunt!"
---

[niklas]

Hooligan:
quote:" It is easy to determine the ballistic coefficient (upon which so much depends) if you have some actual trajectory data for the round in question".

Hmm when you have the data why do you need to recalculate them ??  

You see at the moment iīm interested in the difference of the weapons in AH, not in RL. And i find it quite interesting to see that a AH-hispano round has after ~1000yards  still the same velocity like a mg151 round after ~75yards (though your calculation says a cannon round loses ~half of itīs speed after 600-800yards...)

niklas

[Hooligan]

Niklas:

I don't think you understand what I said.
 
 

Hmm when you have the data why do you need to recalculate them?

I have trajectory data.  From that I calculate Ballistic Coefficients and these BCs can be used in ballistic programs to calculate trajectories under various conditions.

 

And i find it quite interesting to see that a AH-hispano round has after ~1000yards still the same velocity like a mg151 round after ~75yards (though your calculation says a cannon round loses ~half of itīs speed after 600-800yards...)

My calculations say that at sea level an Mg151 CANNON ROUND loses a very large part of its velocity in 600 to 800 yards.  Mg151 rounds have very poor ballistics (among the worst) Hispano rounds have excellent ballistics (among the best) both in the real world and AH.  Hispano rounds are pretty close to .50 M2 rounds in performance in AH so I will use .50 data from my example.

In my sea-level example, the .50 round loses about 25% of its velocity in 600 yards.  The 151 Mine shell loses about 60% of its velocity in the same distance.  Results for the Hispano should be similar to results for the .50 M2 so you charts and my example produce similar results.

Also according to your charts, an AH-Hispano round at 1000 yards does not have the same velocity of an Mg151 round at 75 yards.  On your chart the HS velocity at 750 yards is definitely less than the 151 velocity at 75.  It appears that the true range where this occurs is about 550 yards.

I am not certain how accurate your velocity measurements are, but at the relationships between the velocities of the Mg151, HS and .50 M2 seem fairly consistent with real world data.

Hooligan

[niklas]

Hooligan, again: 7.5 does NOT mean 750yards!!

i donīt know anything about supersonic aerodynamics.
All i know about simulation programs that it depends very much on your input.
Have you an origional trajctory picture for the hispanos?

[janjan]

Hooligan said: ...at sea level...

So, is it so that AH take air density in the ballistics calculations and, hence at high altitute, you are getting flatter trajectory and faster bullets at long range?

Or is the difference negligible?

[-ammo-]

 

Originally posted by janjan:
Hooligan said: ...at sea level...

So, is it so that AH take air density in the ballistics calculations and, hence at high altitute, you are getting flatter trajectory and faster bullets at long range?

Or is the difference negligible?

no its not negligible. the very thin air allows for an excellent extirior ballistics enviroment. However it is still relevant in that the the performance between the different rounds will still have the same gap.

Hooligan is also correct in his findings. One thing to add is that finding BC's is not always constant. The "static" ballistic Coeffecient of a projectile is easy to find. It is a basic formula using the sectional density and some other factors. But when the projectile is launched it changes constantly during its flight.

A basic way of looking at it is this.

the faster, most aero dynanmic, heaviest projectile will perform the the best in extirior ballistics. This is not to sya it will be the best performer in a terminal aspect however..ie..upon impact. However it has been said that the effects from supiorior energy outweighs  the effect of a small amount of HE.  the diameter of the round of course has a great effect on a projectiles destructive force, especially if it is combined with a alot of velocity.

ammo

[Vermillion]

Hooligan, did you ever get your copy of "Rapid Fire"? If you have, I would appreciate knowing what your opinon is.

Interesting test Niklas. How did you do it, and what are the scales/units of the test.

The results are pretty much what I would expect to see.

------------------
Vermillion
**MOL**, Men of Leisure

[Hooligan]

Vermillion:

I pre-ordered it months ago and my copy still has not arrived  .

Hooligan

[Fishu]

Looks like Hispano and .50 caliber has tiny rocket projectiles when those don't lose much with distance...
or other guns has flat tipped projectiles so that drag definetly would affect..

[Hooligan]

Fishu:

On my web site I pointed to some trajectory data which gives the Mg151 Mine shell a G1-BC of .263 (very bad) and ball Ammo for the .50 M2 a G1-BC of .72 (very good).

You seem to think that somehow the ballistics of these 2 rounds should be closer.  Do you actually have any data at all?  If not, why do you keep sharing your ignorance with us?

Hooligan

[This message has been edited by Hooligan (edited 10-30-2000).]

[lazs]

fishu.... all U.S. fifties and Hispano 20mm rounds did indeed have "tiny rockets" in their base.   The balistic coeficients of said rounds was of course twice as good as other rounds but that was tivial compared to the little rockets.   As you may have guessed.. the rockets were a very well guarded secret!   The information has only recently been declassified for everyone with the exception of Finland... No people from Finland are allowed to know about the little rockets to this day.   There is no reason to keep this info from them other than to frustrate them... Reason enough I suppose.
lazs