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View Full Version : do bullets on game take into account earth is rounded or they work on a flat system?



raaaid
06-23-2007, 08:23 AM
does il2 use flat earth physics for the tumbling of bullets or round earth physics?

on 1 of the 3 classes of physics which i went to i learnt parabolic shooting, it takes acceleration on the y axe and linear velocity on the x axe, you solve the equations and get where the bullet is

i suppose this is the system il2 uses it adding it slowing down of bullet due to drag

but this is not valid for supersonic bullets becaause gravity goes not downward but towards a point on the center of the earth because earth is rounded

so in a system where theres a fast bullet and a fixed massive spot bullets dont make parabolas but ellipses as kepler stated

using flat physics or rounded physics makes a dramatic change on tumbling of bullets and a very difficult problem

imagine you shoot a bullet at match 1 from 10km alt horizontally earth stands as a fixed massive point on the equations 15000km downwards

the bullet has 90º direction with respect to the massive point and being relatively low its speed it enters a very eccentric orbit, something like a cigar

kepler stated that the massive point will be the focus of the ellipse and being the initial trajectory of 90º with respect to the massive point when the bullets is shot it can only be on the ellipse on the farthest point from the focus or on the closest point to the focus and the focus in this kind of ellipse is very close to either one of the extremes

this means that when the bullet is in your antipodes it will have lost a lot of altitude or will have gain a lot

thats why i suppose il2 uses flat earth physics theres no way to solve rounded earth physics

DooDaH2007
06-23-2007, 09:14 AM
Not only that raaaid, but people tend to synchonise their guns to a point maybe 400 meters in front of them...

We are not talking about bullits entering earths orbit here...
And I believe, in this game, bullits disapear after about 1000 meters or so...

Platypus_1.JaVA
06-23-2007, 09:22 AM
Well, an average map in this sim is very small compared to the surface area of the whole earth. So I guess they did not take into account the roundness of the earth.

raaaid
06-23-2007, 09:25 AM
yes but tumbling differs a lot, if it makes a parabloa that starts horizontal tumbling is huge if its an ellipse thers much less tumble

XyZspineZyX
06-23-2007, 09:51 AM
What is the in-game effect that is "wrong" here? All this talk about parabolas and the earth's center is great, but what effect is in error and how has it been determined that there is a problem?

tigertalon
06-23-2007, 09:51 AM
Originally posted by raaaid:
yes but tumbling differs a lot, if it makes a parabloa that starts horizontal tumbling is huge if its an ellipse thers much less tumble

Parabola is one side of an ellipse that has been stretched into infinity. Compared to the general distances at shooting and speed of projectiles it's safe to assume center of Earth in infinitely far away. Difference between ellipse and parabola is neglible.

Your thinking would however become valid once the velocity of projectiles become comparable to first cosmic velocity, around 8 km/s.

Stew278
06-23-2007, 12:44 PM
Like people have said here, with the distances involved here the Earth's curvature is irrelevant.

If the radius of the Earth is 6378km and we take an 80kmx80km map then the height difference between the center of the map and the corners would only be ~250meters if you were to use a curved vs flat map. That would mean only ~4m of altitude per 1km horizontal traveled.

(6378km^2-56.7km^2)^0.5=6377.75km
6378km-6377.75=0.25km

or something like that.

If you move 2km on the surface of a 40000km circle, doesn't that only amount to 0.0001pi radians change? It's probably not worth the CPU power to calculate the change in the gravity vector over that small of a distance.

Curvature would become significant if we were talking about rockets or over the horizon shelling, but for MG and cannons with ranges of a few km it shouldn't matter.

raaaid
06-23-2007, 12:52 PM
i see i though there would be a difference in tumling but i see it doesnt

tagTaken2
06-23-2007, 08:06 PM
Originally posted by DooDaH2007:
.
And I believe, in this game, bullits disapear after about 1000 meters or so...

I'm not sure about this... I believe somebody posted about hitting a plane from 1.3 km away with 3.7cm and destroying it.
How long does it typically take a round to travel 1km?

Freelancer-1
06-24-2007, 02:00 AM
You need to find a battle ship sim forum for this one, Raaaid.

They shoot really big bullets 50 kilometers

not little tiny bullets 50 meters.

stansdds
06-24-2007, 05:44 AM
Before we consider flat Earth vs. round Earth physics, we need to determine if IL2 calculates the existence of a fired round to the point it would tumble. I'm thinking that after a relatively short distance, Il2 simple makes bullets disappear, otherwise the calculations for many thousands of bullets tumbling through the air until they impact terra firma would bring the average desktop computer to a crawl.

neural_dream
06-24-2007, 06:38 AM
Originally posted by Freelancer-1:
You need to find a battle ship sim forum for this one, Raaaid.

They shoot really big bullets 50 kilometers

not little tiny bullets 50 meters.
wwiionline ship bombardments and long tank battles take into account round earth physics. In IL2 it wouldn't be useful, as the loss of accuracy is insignificant for so short distances.

M_Gunz
06-24-2007, 06:52 AM
Originally posted by raaaid:
does il2 use flat earth physics for the tumbling of bullets or round earth physics?

on 1 of the 3 classes of physics which i went to i learnt parabolic shooting, it takes acceleration on the y axe and linear velocity on the x axe, you solve the equations and get where the bullet is

That would be introductory physics... in Jr. High to High School or never depending on the
person. Nothing is for everyone.

Flat earth physics model is good on a scale bigger than some countries, good enough for bullets!

M_Gunz
06-24-2007, 07:18 AM
Originally posted by raaaid:
i see i though there would be a difference in tumling but i see it doesnt

Bullets in the game do not last long in seconds, enough to go an certain extreme for shooting
range and then no longer supported by the game engine, which really helps with framerate and
memory space.

The bullets do not stay long enough for spin to slow down and tumble to happen.

The thing that looks almost like tumbling is the tracer smoke that leaves spiral trails.
That is from the spin of the shell, very high rpm (bullets go to 100,000-300,000 rpm), and
smoke moving out from spin speed into still air.

Im perfection of bullets/shell does cause some very small tumble that makes enough deviation
to notice, low single digit and fraction mm's at 100m-200m unless of course you have very
poorly made bullets!

SeaFireLIV
06-24-2007, 07:19 AM
I get an image of Raaaid sat in his room desperately thinking what weird, outlandish, but slightly steeped in reality stuff he can come out with, then rushing to his pC to type. In fact, I think he sits in his room everyday just doing that. Thinking too much can be bad for you. Sometimes it`s worth just to say for a little while `I don`t care` and forget about all those weird questions. You`ll feel better.

There`s a world out there- take a walk in the park - or have a Beer. Just don`t ask people strange questions while you`re at it.

raaaid
06-24-2007, 07:23 AM
i started this topic more than nothing because i dont believe that a bullet shot horizontally reaches ground at the same time that if you drop it by your hand but i see the difference would be minimal

M_Gunz
06-24-2007, 07:34 AM
I get an image of Raaid sitting back with a bong and the better part of a pound of pot,
thinking "this'll really screw with them" as he pulls the wireless keyboard onto his lap
and begins typing while he giggles quietly.

raaaid
06-24-2007, 07:47 AM
i only post things to upset people when im attacked, for example when i said darwin was a nazi thats actually something i told once to my father, no intention to upset he even told me of a guy who thought like me but didnt know the spelling

back on topic id say bullets desintegrate after a while, proof of it is people shooting a lot up to the air in the crowds but never a news of somebody dying from a falling bullet

neural_dream
06-24-2007, 08:00 AM
Originally posted by raaaid:
i only post things to upset people when im attacked
So you are something like a defensive troll.

raaaid
06-24-2007, 08:22 AM
nono i dont think im a troll, normally

i was a troll when to my post of thinking i had invented a shooting method on a past life everybody laughed at me so i became a troll and said the thing completely out of place on abrahan unethical attitude towards isaac, that i did it in order to upset but they had upset me first

but you should see the discussions i have with my father, he is a doctor on maths and we both agree telepathy is posible sending the brain EM waves, or how though eisntein was a genius he was also a b@stard, hell i even told my father once an ellipse couldnt be a conic section, obviously he proved me wrong

he knows im weird and rebel so he knows i have no bad intention when i say newton is wrong or he plagiarized the principles

i just say what i think and much more here where it doesnt really matter what people thinks of me

thats something i learnt from dysney if you want to like be yourself,well if im goofy should i behave like mickey?

WhtBoy
06-24-2007, 08:56 AM
Originally posted by raaaid:
back on topic id say bullets desintegrate after a while, proof of it is people shooting a lot up to the air in the crowds but never a news of somebody dying from a falling bullet

Are you seriously suggesting that if I take my AR-15 rifle and fire it straight up the bullet will magically disintegrate before it hits the ground???

--Outlaw.

LStarosta
06-24-2007, 09:07 AM
People die from falling bullets. The thing is that even assuming that someone shot the bullet perfectly straight up, the bullet is subjected to horizontal force in the form of wind both on the way up and down which will make x1 =/= x2 at y = 0.

I thought you and your superior understanding of physics could comprehend that. http://forums.ubi.com/images/smilies/mockface.gif

T_O_A_D
06-24-2007, 09:21 AM
Best thing raaid is to go out and test the threory yourself. http://forums.ubi.com/images/smilies/59.gif

Actually I had a friend do this with a Bow once, Freaken ******.

I dove under the porch and he followed, it fell within 10 feet of the launch point and stuck through the hood of his chevy truck.

It was a fairly calm day.

Oh you might talk Mythbusters in to this. http://forums.ubi.com/images/smilies/88.gif

raaaid
06-24-2007, 09:31 AM
well bullets are made of plumb and it has a low melting point 300º

a shot bullet has a temperature of 267º when it comes out

so air just has to increase its temperature 33º

so a bullet shot up that runs the maximum distance can easily reach the 300º after a distance

berg417448
06-24-2007, 09:35 AM
Originally posted by raaaid:


back on topic id say bullets desintegrate after a while, proof of it is people shooting a lot up to the air in the crowds but never a news of somebody dying from a falling bullet

What's all this then?

http://edition.cnn.com/2003/US/South/11/24/klan.initiation.ap/

http://www.local6.com/news/4084756/detail.html

http://starbulletin.com/98/01/02/news/story3.html

http://www.signonsandiego.com/uniontrib/20060102/news_1m2hail.html

http://www.freerepublic.com/focus/f-news/965672/posts

WhtBoy
06-24-2007, 09:44 AM
Originally posted by raaaid:
well bullets are made of plumb and it has a low melting point 300º

a shot bullet has a temperature of 267º when it comes out

so air just has to increase its temperature 33º

so a bullet shot up that runs the maximum distance can easily reach the 300º after a distance

What a comback!!!! After a crushing defeat raaaid has battered his way back to the top, delivering a stunning one-punch knockout to Josf!!!!


--Outlaw.

WhtBoy
06-24-2007, 09:47 AM
raaaid,
When did "go to" these 3 physics courses. The last statement you made about physics was that the last one you took was when you were 14 and it was self-taught?

--Outlaw.

raaaid
06-24-2007, 09:49 AM
JOHNSON CITY, Tennessee (AP) -- A bullet fired in the air during a Ku Klux Klan initiation ceremony came down and struck a participant in the head, critically injuring him, authorities said

thats funny

well i was wrong so what

if you pay close attention to what i said it was "last physic course i PAST i was 16..

Zeus-cat
06-24-2007, 09:49 AM
I think MythBusters did look into this. They decided that most bullets don't fall fast enough to kill people. I don't remember what guns they tested, but they probably tested "standard" gun and didn't test guns like a .50 caliber.

WhtBoy
06-24-2007, 10:15 AM
Originally posted by Zeus-cat:
I think MythBusters did look into this. They decided that most bullets don't fall fast enough to kill people. I don't remember what guns they tested, but they probably tested "standard" gun and didn't test guns like a .50 caliber.

If a bullet is fired vertically (or very, very, very close to it) it won't gain enough energy to do serious harm when it hits. However, since most of the idiots that fire guns in celebration type events don't fire them close enough to vertical, there are many people killed each year when hit by these stray rounds.

--Outlaw.

x6BL_Brando
06-24-2007, 10:15 AM
quote:
Originally posted by raaaid:
well bullets are made of plumb and it has a low melting point 300º

a shot bullet has a temperature of 267º when it comes out

so air just has to increase its temperature 33º

so a bullet shot up that runs the maximum distance can easily reach the 300º after a distance



What a comback!!!! After a crushing defeat raaaid has battered his way back to the top, delivering a stunning one-punch knockout to Josf!!!!


http://forums.ubi.com/images/smilies/88.gif
After a gruelling hour on the phone diagnosing a friend's networking problem, there's nothing like coming back to the comedy pages to lift the spirits.

thanks

B

WhtBoy
06-24-2007, 10:19 AM
Originally posted by raaaid:
if you pay close attention to what i said it was "last physic course i PAST i was 16..

Thank you for pointing out my error!!! Indeed I did not pay close enough attention. This sheds a lot of light on things.


Pleae check the following statements of mine for errors also...

The last physics class you passed was at least 16 years ago. Since that time you have taken at least 3 more course and did not pass them.

Are the above 2 statements correct?

--Outlaw.

raaaid
06-24-2007, 10:24 AM
anyway my reason for this topic is bullet tumbling:

lets suppose you fire horizontally a bullet at 300 m/s at a target 900m away

in 3 sec the bullet will have fall 45m

but you can see in the game bullet doesnt tumble so much

at firts i had though it was due to bullets making ellipses instead of parabolas but i was proved wrong now i think i found out why bullet doesnt tumble as much as physics say

its the same reason why sharks always move, theyd sink otherwise, velocity keeps them horizontal though they have vertical stabilizers

the same a bullet velocity keep them horizontal in the air because they get dynamic sustentatation, abullet drop from your hand will touch the ground first than a bullet shot horizontally, thats why this link is wrong:

http://www.worsleyschool.net/science/files/bullet/trajectory.html

right im 32 and still studyin, flunk a lot, i hardly spend an hour daily working the rest i think on stuff i like

Stew278
06-24-2007, 10:30 AM
I remember a few years back the police were asking people in my city not to fire their guns in the air when they were celebrating Cinco de Mayo because the year before there were a few cases of car windows getting shot out.

Maybe I misunderstood raaid's original post but I thought he was questioning whether or not this sim models the maps as a flat world and is that accurate? The distortion that results from approximating a curved surface as flat is less and less as you move to smaller length scales. At the range of a few km we'd be talking about for bullets, the vertical deviation from a flat plane or the Earth's curve would be <1m.

Having bullets disappear once they reach a certain range makes sense since it saves CPU resources and the bullets wouldn't have enough kinetic energy to do damage after a few km anyways. Didn't someone here calculate that after a few km a .30 cal would just bounce off a plane if it hit because there isn't enough energy to penetrate aluminum anymore?

WhtBoy
06-24-2007, 10:57 AM
Originally posted by raaaid:
...thats why this link is wrong:

http://www.worsleyschool.net/science/files/bullet/trajectory.html



Look at the assumptions they use raaaid, namely this one...

- air resistance (and the shape of the bullet) will be ignored

The link is NOT wrong. Physics is NOT wrong.

If you THINK that the reason the bullet doesn't hit the ground where the above link predicts is due to lift generated by the bullet, why don't you do the calcs? For someone who understands physics and aerodynamics at the elite level like you do, it ought to be simple.


--Outlaw.

Daiichidoku
06-24-2007, 11:04 AM
raaaid, fret not

u can use X4s instead, no traj worries there http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

raaaid
06-24-2007, 11:13 AM
bullet doesn generate lift as it has the same shape on the top than in the bottom its dynamic sustentation whats at work as the bullet if rounded has an horizontal surface of pi*r*r

well the link i provided was correct but is far from exaplining bullet tumbling if it doesnt take into account dynamic sustentation

WhtBoy
06-24-2007, 01:35 PM
Originally posted by raaaid:
well the link i provided was correct but is far from exaplining bullet tumbling if it doesnt take into account dynamic sustentation

What is your definition of "dynamic sustentation?"

Also, what is your definition of "tumbling" b/c in ballistics that is a very specific term.

--Outlaw

DuxCorvan
06-24-2007, 01:51 PM
Originally posted by raaaid:
i only post things to upset people when im attacked, for example when i said darwin was a nazi thats actually something i told once to my father, no intention to upset he even told me of a guy who thought like me but didnt know the spelling

In that thread you started by mistaking Darwinism for Lamarckism, which is a very weak way to start a debate, darling.

raaaid
06-24-2007, 02:15 PM
dynamic sustentation is aquired by speed in a fluid with an horizontal surface

tumbling in spanish is translated as falling thoug im not sure is 100%correct

well i suppose i can believe better lamarck theories than darwins im on my right though i understand this is not the place to tell

WhtBoy
06-24-2007, 03:04 PM
Originally posted by raaaid:
dynamic sustentation is aquired by speed in a fluid with an horizontal surface

Do you have a reference for the above phenomenon?



Originally posted by raaaid:
tumbling in spanish is translated as falling thoug im not sure is 100%correct


Simply "falling", or bullet "drop" is the English term you're looking for, not tumbling. "Tumbling" in ballistics terms is when a bullet loses stability and goes end over end.


Originally posted by raaaid:
bullet doesn generate lift as it has the same shape on the top than in the bottom its dynamic sustentation whats at work as the bullet if rounded has an horizontal surface of pi*r*r

Bullets experience a variety of aerodynamic lift forces during flight. Check out
this (http://www.exteriorballistics.com/ebexplained/5th/40.cfm) for a quick rundown.

--Outlaw.

DuxCorvan
06-24-2007, 05:05 PM
Originally posted by raaaid:
well i suppose i can believe better lamarck theories than darwins im on my right

Well, you can believe that the sun is the center of the universe, or that TVs work by magic, but that's not a right, it is just utter ignorance. Darwin's theories are empirically demonstrated, Lamarck's theories are proved... totally wrong. I thought it was not belief but science what interested you, maybe I was wrong.


though i understand this is not the place to tell

It wasn't either the first time.

raaaid
06-24-2007, 05:19 PM
dynamic sustentation is what makes fast boats go on small skates

same reason why sharks dont sink when they move

this is an obviety

then im not talking of tumbling of bullet but of dropping of the bullet

dynamic sustentation makes a bullet horizontally shot fall at a much slower rate than if you drop it from your hands contray to what is generally believed

this droping of the bullet much slower is not due to lift forces but to dynamic sustentation

i dont believe lamarck ideas nor darwins, both fail to explain wings creation

i think we are far from exaplining evolution

what i do believe is darwin can lead to ideas as handicapped spoil human evolution since now everybody reproduces which can lead to nazi ideas and be treated as if we were plants

WhtBoy
06-24-2007, 08:26 PM
Originally posted by raaaid:
dynamic sustentation is what makes fast boats go on small skates

same reason why sharks dont sink when they move


The above makes no sense. The last I heard skates were either roller or ice, and since you're talkin' fluid dynamics you must not be talking about ice boats. If you're talkin' about hydrofoils, then that is a lift force.

Sharks do sink when they move, otherwise they wouldn't be able to dive. They use those pointy things (not the ones in their mouths) to control their direction.


Originally posted by raaaid:
this is an obviety


If it's so obvious then just show us the calculation.


Originally posted by raaaid:
dynamic sustentation makes a bullet horizontally shot fall at a much slower rate than if you drop it from your hands contray to what is generally believed

this droping of the bullet much slower is not due to lift forces but to dynamic sustentation

Once again, just show us the calcs that prove that the aerodynamic life forces generated by a bullet are insignificant compared to the force caused by your dynamic sustentation.

--Outlaw.

stansdds
06-25-2007, 04:12 AM
Originally posted by raaaid:
well bullets are made of plumb and it has a low melting point 300º

a shot bullet has a temperature of 267º when it comes out

so air just has to increase its temperature 33º

so a bullet shot up that runs the maximum distance can easily reach the 300º after a distance

What? Bullets are made of lead alloy, melting point varies depending upon the alloy used. Rounds from machine guns, cannons, rifles, (and even handguns) are usually covered with a copper, copper-nickle alloy, bronze, or steel jacket and none of those are going to melt at 300F. Do some research before posting tripe.

Blutarski2004
06-25-2007, 05:24 AM
Originally posted by Zeus-cat:
I think MythBusters did look into this. They decided that most bullets don't fall fast enough to kill people. I don't remember what guns they tested, but they probably tested "standard" gun and didn't test guns like a .50 caliber.


..... Mythbusters did not use a 50cal because, if fired vertically, a 50cal bullet will reach a low orbit position and fail to immediately return to earth. After an extended period, the orbit will decay and the bullets will burn up on re-entering the atmosphere. They are in fact often mistaken for out-of-season Pleiades shower.

If you fire your IL2 P47 vertically into the air, you will never see the bullets falling back to earth. On that basis, it may be safely assumed that IL2 does model a spherical earth.

raaaid
06-25-2007, 05:39 AM
maybe dynamic sustentation is not the correct term in english

basically it is what makes paper planes fly or are you gonna tell me that a paper plane produces lift

the same for a bullet the faster it goes the more horizontal will remain without dropping

i was told several times that a bullet shot horizontally reaches ground at the same time that if you drop it from your hand, well this is false, only true in vacuum

WhtBoy
06-25-2007, 06:08 AM
Originally posted by raaaid:
i was told several times that a bullet shot horizontally reaches ground at the same time that if you drop it from your hand, well this is false, only true in vacuum

So, this "dynamic sustentation" force you speak of is exerted by the air on the bullet??


If it happens in a vacuum, then the statement is not false. It's only false if you don't pay attention to the assumptions.



--Outlaw.

raaaid
06-25-2007, 06:22 AM
i was wrong sayin the link i provided was wrong didnt pay attention to vacuum condition but the thing is that air changes conditions totally

anyway this has not been a waste of time ive just learnt why bullet spin avoid changes of direction by the wind:

the wind blows from the right so wind in combination with spin produces lift that moves the bullet to the right

a bullet spinning at an adequate velocity will always hit target however strong the wind, interesting

Akronnick
06-25-2007, 07:13 AM
Originally posted by raaaid:
basically it is what makes paper planes fly or are you gonna tell me that a paper plane produces lift

Are you saying that a paper airplane doesn't produce lift?

a paper airplane is subject to the same four forces as any other airplane, except that (most) paper airplanes do not produce thrust...

even a flat sheet of paper produces lift, otherwise it would simply drop like a stone.

re the mythbusters: in the falling bullet myth, they tested 9mm handgun and .30-06 rifle. In their tests, they were unable to demonstrate a round falling to earth with lethal velocity.(which is not to say they didn't fall, the bullets were found, they just did not penetrate the hard clay of the testing ground) however, they did find documented cases of people who were killed or injured by bullets falling to earth from a high angle trajectory.

WhtBoy
06-25-2007, 07:22 AM
Originally posted by raaaid:
a bullet spinning at an adequate velocity will always hit target however strong the wind, interesting

This is TOTALLY incorrect. You MUST compensate for the wind when shooting. This is obvious.

--Outlaw.

raaaid
06-25-2007, 07:30 AM
then whats the point of having a bullet spinning? i thought it was compensate for crosswinds

lift is generated by an aerodinamic wing with the shape of half drop which is different to sustentation heres an example of lift at work:

http://upload.wikimedia.org/wikipedia/commons/f/fe/Airplane_vortex_edit.jpg

notice that is a force that pushes the plane upwards while doesnt pull the air downwards

it means is a force with no reaction, spinned air have a vertical component of 0

so bernuolli explanation for lift is wrong http://forums.ubi.com/images/smilies/winky.gif

ive been searching the net on why bullets are made to spin and symply says they have more stability

i think you are right you have to make for cross winds, not only that you have to know sense of spin of the bullet a clockwise bullet will lift up with a wind from the right and lift down with a wind from the left

the question remains on why spin it makes it more stable when it even creates lifts which make it worse aiming

i have a theory spining bullets have more friction with air and therefore more sustentation so they drop less

i tested this theory with a top made out of a match and a circled carton if you drop it spinning it will take longer that if you drop it without spinning because air produces more friction so it gets more sustentated

besides i disagree a faliing bullet shot at 45º causing more damage if its shot vertically

if you bail out from a plane a match 2 youll end up with the same terminal velocity when you hit the ground that if you bail out at 0 speed independently of horizontal component 300 km/h

WhtBoy
06-25-2007, 08:23 AM
Originally posted by raaaid:
then whats the point of having a bullet spinning? i thought it was compensate for crosswinds

lift is generated by an aerodinamic wing with the shape of half drop which is different to sustentation heres an example of lift at work:

http://upload.wikimedia.org/wikipedia/commons/f/fe/Airplane_vortex_edit.jpg

notice that is a force that pushes the plane upwards while doesnt pull the air downwards

it means is a force with no reaction, spinned air have a vertical component of 0

so bernuolli explanation for lift is wrong http://forums.ubi.com/images/smilies/winky.gif

ive been searching the net on why bullets are made to spin and symply says they have more stability

i think you are right you have to make for cross winds, not only that you have to know sense of spin of the bullet a clockwise bullet will lift up with a wind from the right and lift down with a wind from the left

the question remains on why spin it makes it more stable when it even creates lifts which make it worse aiming

i have a theory spining bullets have more friction with air and therefore more sustentation so they drop less

i tested this theory with a top made out of a match and a circled carton if you drop it spinning it will take longer that if you drop it without spinning because air produces more friction so it gets more sustentated


raaaid,
How is it possible that someone as smart as you and who has taken as many physics classes as you have does not know the mechanism behind spin stabilization? It is well known and fully explained mathematically.

Similarly, how is it possible that, with your extensive aerodynamics background you still don't understand how a wing generates lift? All of the principles of lift are explained in a book I posted a link to in one of your previous topics. I asked you to show your calculations that prove the book is wrong. Why haven't you shown us your calculations?

You have not tested your theory of increased friction at all. All you have tested is whether or not it falls faster using a very poor (match stick and cardboard) testing apparatus.

--Outlaw.

WhtBoy
06-25-2007, 08:27 AM
Originally posted by raaaid:
besides i disagree a faliing bullet shot at 45º causing more damage if its shot vertically


Once again your lack of analytical ability shines. The reason is that a bullet fired vertically loses ALL of the energy imparted to it by the powder charge. Therefore, when it hits the ONLY energy it has is that gained by falling.

A bullet fired at a 45 degree angle, however, does NOT lose all the energy imparted to it by the powder charge and will be going much faster than it's terminal velocity when it impacts.

--Outlaw.

Capt.LoneRanger
06-25-2007, 08:34 AM
So much wasted energy... and I don't mean the bullet.

WhtBoy
06-25-2007, 08:38 AM
Originally posted by Capt.LoneRanger:
So much wasted energy... and I don't mean the bullet.

Not a waste at all for me considering the alternative is watching a progress bar for the next 2 hours. Besides, after taxes, benefits, etc, I'm clearing $36/hour for this.

--Outlaw.

BBB_Hyperion
06-25-2007, 09:13 AM
Always curious if they have indeed modeled the change of gravitation in upper atmosphere and the effects on the bullets flight path.

WhtBoy
06-25-2007, 09:20 AM
Originally posted by BBB_Hyperion:
Always curious if they have indeed modeled the change of gravitation in upper atmosphere and the effects on the bullets flight path.

Now that would be the definition of "negligeble effect" if I ever saw one (a definition that is)!!

--Outlaw.

M_Gunz
06-25-2007, 10:53 AM
Originally posted by raaaid:
maybe dynamic sustentation is not the correct term in english

basically it is what makes paper planes fly or are you gonna tell me that a paper plane produces lift

All the good ones do. Find a copy of Ralph Barnaby's "How to Make and Fly paper Airplanes"
to see his versions. Half the paper (and so weight) is folded into a front spar, the wing
paper gets warped by rubbing across an edge to make real camber and the rest keeps it in
balance. He even shows to make flying wings with rectangle shape.

But even on a dart paper plane the paper folded into layers is not flat against each other,
look at bottom as opposed to top. The difference is minor as is the weight of the glider.
Paper Darts are very inefficient though....


the same for a bullet the faster it goes the more horizontal will remain without dropping

Boat skimming water has surfaces against water, orientation is up. Shark has fins and body
with lifting shape. Your other examples are all with lift surfaces according to situation.

So where are the non-symmetric force-directional surfaces of the bullet?


i was told several times that a bullet shot horizontally reaches ground at the same time that if you drop it from your hand, well this is false, only true in vacuum

You can prove this within accuracy of measure of total test setup? Or is that another thought
experiment to add to perpetual motion and the like?

M_Gunz
06-25-2007, 10:57 AM
Originally posted by Akronnick:
re the mythbusters: in the falling bullet myth, they tested 9mm handgun and .30-06 rifle. In their tests, they were unable to demonstrate a round falling to earth with lethal velocity.(which is not to say they didn't fall, the bullets were found, they just did not penetrate the hard clay of the testing ground) however, they did find documented cases of people who were killed or injured by bullets falling to earth from a high angle trajectory.

State Troopers (highway police, Raaid) on duty New Years Eve here have been for generations
pulling over and parking under bridges right around midnight just because of falling bullets.

Chance is small but it only has to happen once to ruin your whole day.

M_Gunz
06-25-2007, 11:07 AM
Originally posted by raaaid:
then whats the point of having a bullet spinning? i thought it was compensate for crosswinds

Gyroscopic force of the spin keep the bullet pointed as straight as possible to path of flight.

In the US we have US football that uses a rugby ball (pretty sure, a pointed prolate spheroid).
We learn to throw those correct, to give them spin and they stay with points forward and aft
during the flight which reduces drag compared to wobble-tumble bad throws.

You fire a cannon shell, the fuse is on the tip, spin keeps the tip up front to strike.

Lastly muskets have smooth barrels and the balls fired do not stay on straight path nor do
they go far. Shotgun balls do the exact same thing, they slow very quickly.

M_Gunz
06-25-2007, 11:12 AM
Originally posted by raaaid:
then whats the point of having a bullet spinning? i thought it was compensate for crosswinds

lift is generated by an aerodinamic wing with the shape of half drop which is different to sustentation heres an example of lift at work:

http://upload.wikimedia.org/wikipedia/commons/f/fe/Airplane_vortex_edit.jpg

notice that is a force that pushes the plane upwards while doesnt pull the air downwards

it means is a force with no reaction, spinned air have a vertical component of 0

so bernuolli explanation for lift is wrong http://forums.ubi.com/images/smilies/winky.gif

Only someones simplistic explanation is wrong. Difference in pressure as Bernoulli showed
does work on wings but one result is also air mass moving downward, enough air fast enough
to equal weight of plane.

M_Gunz
06-25-2007, 11:29 AM
Originally posted by BBB_Hyperion:
Always curious if they have indeed modeled the change of gravitation in upper atmosphere and the effects on the bullets flight path.

You get more difference if you measure acceleration at the poles vs on the equator I think.
Earth is not perfect sphere and all objects below the pole have centripetal force of Earth
turn working against gravity. That is why equatorial space launch sites require less fuel
to get to orbit... where is the place in South America that many launches were/are made?

Earth Mean radius is about 6,373 km.
Add 15 km of alt, 6,388 km.
So the high alt is about 6388 / 6373 = 1.00235.... times sea level.
I square and invert to get difference in gravity, .9953.... G's.

Hey, it is larger than the difference between pole and equator but not much at all!

DuxCorvan
06-25-2007, 03:25 PM
Originally posted by raaaid:
Sir, I have a cunning plan...

http://www.icicom.up.pt/blog/take2/Blackadder.jpg

raaaid
06-25-2007, 03:42 PM
i think at higher altitudes bullet should fly worse and drop more due to thinner air

http://forums.ubi.com/images/smilies/88.gif

LStarosta
06-25-2007, 03:48 PM
And in space they wouldn't move at all due to vacuum because the air in front of the bullet actually goes around to the back of it and pushes it on.

Lurch1962
06-25-2007, 04:54 PM
I skipped right by all preceding stuff...

Why worry about this, Raaaid? The Earth's curvature at these scales is tremendously large. One nautical mile on the earth's surface is an arc of only 1 arcminute (1/60th of a degree). There's no way one could observe any discrepancy in bullet trajectories modeled for flat and curved Earths.

--Lurch--

BBB_Hyperion
06-25-2007, 11:28 PM
Actually that is only correct when you assume earth is a circle that is not the case. Systems like GPS work with a regional model of a rotations ellipsoid. As max pointed already out there are different zones of gravity. So the question itself that the earth is rounded can be misleading cause there are even small local differences in gravity fields. That has of course influence on flight path and on air pressure. http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

Launch Site must be somewhere around here max 05? 09' 35" N 52? 39' 1" W