Lawrence W.
Member
Lift in this situation is a misnomer. Basically the bullet just falls a little less.
r44astro
New member
I agree, for lift, an angle of attack is needed greater than the relative wind, at least I think so, physics could have changed while asleep or too much hooch. Gyroscopic precession explains the behaviour of the bullet in left or right crosswinds.
Gravity is unaffected by velocity, let us not forget that one. That is why a bullet dropped at the exact time the bullet leaves the barrel they both hit ground same time, in a perfect world. Bore parallel to Earth, no wind and so on, and at short distance we can ignore curvature of Earth Coriolis effect, or is it scoliosis? A bullet is a gyroscope, it wants to stay where it is. Is it 5 0clock yet? Got to be somewhere.
Bill
M
mks
Guest
I see your point, but don't get too hung up on the terminology. An aerodynamicist calls the vertical force on a wing "lift" even if it's less than gravity and the plane crashes! If the wing is upside down, its "negative lift." Same with the bullet. It's just a name for the vertical force from the wind, regardless of whether it is larger or smaller than other forces.
Cheers,
Keith
Joe Woosman
Member
So if you're flying away from the earths surface it's positive lift. If upside down towards the earths surface it's negative lift. What is it called when you are turning left or right with no up or down change? Gyroscopic precession?
M
mks
Guest
Sounds like there's a good story there!
M
mks
Guest
So if you're flying away from the earths surface it's positive lift. If upside down towards the earths surface it's negative lift. What is it called when you are turning left or right with no up or down change? Gyroscopic precession?
Joe,
At the risk of getting even more obsessed with terminology… Yes, positive lift is usually defined as upward for a plane in normal flight. But more fundamentally, lift is perpendicular to the wind direction and to the span of the wing. The positive direction along this axis is usually chosen as the direction that you want the force to be. So if the plane is banking left or right, or upside down, the direction defined as positive for lift follows the orientation of the aircraft. If the whole plane is upside down, positive lift is downward. Other examples: For a sailboat, lift on the sails is sideways. For wind turbine blades, the direction of lift rotates with the blade.
http://www.mpoweruk.com/flight_theory.htm
In my previous post, I was referring to an upside down wing on an upright plane, so that the direction of positive lift is still upward. With the upside down wing, the lift is downward and, thus, negative according to this definition. Sorry if that was confusing.
Did I make this a clear as mud?
Cheers,
Keith
Joe Woosman
Member
Crystal clear with me Keith. Hopefully nobody reads the play on terminology as being argumentative. It's hard writing in a way to relay humorous sarcasm. For all practical discussion on bullet flight it just don't matter I suppose.
B
Brian Adams
Guest
His questions assumes the bore is horizontal, not angled upward for some downrange POI.
B
Brian Adams
Guest
At risk of possibly stating the obvious:
If Earth had no atmosphere, two bullets - one fired perfectly horizontally, and one dropped free fall from the same bore height at the same time - would theoretically both strike the ground at the same time (assuming the Earth is flat under the distance the fired bullet traveled.)
If, in our atmosphere, the fired bullet struck the ground slightly later than the dropped bullet, then a small net lift effect will have been created by the interaction of the spinning bullet with the air. My understanding is this is usually the case in the typical downrange POI trajectories we create, but it is essentially insignificant compared to other variables.
Any crosswind present would create a slight change, positive or negative, in any lift coefficient, depending on the rate and direction of bullet spin (as discussed elsewhere in this thread.)
If Earth had no atmosphere, two bullets - one fired perfectly horizontally, and one dropped free fall from the same bore height at the same time - would theoretically both strike the ground at the same time (assuming the Earth is flat under the distance the fired bullet traveled.)
If, in our atmosphere, the fired bullet struck the ground slightly later than the dropped bullet, then a small net lift effect will have been created by the interaction of the spinning bullet with the air. My understanding is this is usually the case in the typical downrange POI trajectories we create, but it is essentially insignificant compared to other variables.
Any crosswind present would create a slight change, positive or negative, in any lift coefficient, depending on the rate and direction of bullet spin (as discussed elsewhere in this thread.)
r44astro
New member
So if you're flying away from the earths surface it's positive lift. If upside down towards the earths surface it's negative lift. What is it called when you are turning left or right with no up or down change? Gyroscopic precession?
Do not know about the neg/pos lift never heard the terms before, If in turn constant altitude then my guess, lift equals gravity. If in 60 degree bank how many G's. What's standard rate turn? I think this thread going wrong direction. Original question bullet above the bores axis? I say no.
That's all I have to say, no it does not, not including one gentleman's explanation of recoil. As far recoil in this matter I have no opinion.
Bill
B
Brian Adams
Guest
I understand the confusion over "negative lift" but for this discussion the definition of "lift" I am using is:
"That component of the force of a fluid flowing past the surface of a body that is perpendicular to the oncoming flow direction"
Such a component may have a positive or negative value.
Earlier I was discussing a lift component on a bullet, but I did not attempt to answer whether the bullet ever rises "above the bore". If there is a positive lift component, it would rise above the trajectory it would follow in a vacuum, but for it to "fly" above the line of departure seems impossible given the miniscule value of lift we are discussing. It would have to start rising a lot, and too soon after departing the muzzle, it seems to me.
Joe Woosman
Member
I think the term "lift" is confusing to people in this thread depending on if you are interpreting the word in a scientific manner or in a general sense of relative to gravity and level.
For scientific clarification refer to the following links:
http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
http://www.nennstiel-ruprecht.de/bullfly/liftf.htm#header
For practical conversation - DO NOT click on the previous links. Bullets do not glide like airplanes.
For scientific clarification refer to the following links:
http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
http://www.nennstiel-ruprecht.de/bullfly/liftf.htm#header
For practical conversation - DO NOT click on the previous links. Bullets do not glide like airplanes.
B
Brian Adams
Guest
True. But if they arrive late and overshoot the landing (compared to in a vacuum) in a sense they do glide - if more like a manhole cover than a frisbee.
Last edited by a moderator:
A
Alaninga
Guest
Or,......
Take bullet, spin it at same rate when fired out of a 10" twist (common) bore at say 2,800 fps. Bullet used has rifling marks on it. Assume we have a way to 'project it' perfectly sideways horizontal through air which will be considered the 'wind' force. Is there a speed at which the bullet would curve up as with what happens with a 'Trac Ball'?
Same physics as if this bullet were ALSO fired point forward, but eliminating forward movement that theoretically should not otherwise affect it.
(No Scotch was consumed during the formation of this post ...LOL)
Take bullet, spin it at same rate when fired out of a 10" twist (common) bore at say 2,800 fps. Bullet used has rifling marks on it. Assume we have a way to 'project it' perfectly sideways horizontal through air which will be considered the 'wind' force. Is there a speed at which the bullet would curve up as with what happens with a 'Trac Ball'?
Same physics as if this bullet were ALSO fired point forward, but eliminating forward movement that theoretically should not otherwise affect it.
(No Scotch was consumed during the formation of this post ...LOL)
carolinachuck
New member
Gravity works on objects the same regardless of mass. Please recall the Falcon feather and hammer experiment done on the Moon by Astronaut David Scott on Apollo 15.
If you drop a bullet at the same height one is fired from a firearm both will hit the ground at the same time. Sorry folks, just simple physics. Bullets do not rise above the bore line, period, ever. Any "crawling the wall" effect by wind is from the same aerodynamic properties found in our atmosphere that make a baseball curve. The two have no relevance to each other.
There is no lift produced by a bullet; it is round... None, zero, zip, zilch.
It takes the same speed (velocity) to keep the space shuttle in low Earths orbit as it would a .22LR bullet; approximately 17,500 mph. It just takes a whole lot more energy to get the shuttle up there then it would a little .22 bullet. Ballistics has to do with a coefficient and velocity. In Earths atmosphere it is different than in space where it is an effect of gravity based on the mass of the object, and not aerodynamic drag found here on Earth.
The .22 would stay in orbit longer than something the mass of the shuttle given the two entered the same orbit at the same time and velocity. This may sound contradictory to my original statement, but in reality it is not. The weight of the two differ only by their mass, but have the same gravitational pull on them. Because there is more mass to the shuttle, there is more of it for the same gravity to pull on which slows the larger mass faster than our little .22 bullet. It is velocity loss that brings the shuttle home first.
I hope this helps to clear up some of the fun everyone is having here with this thread by the OP.
On to the next Caper,
CarolinaChuck
If you drop a bullet at the same height one is fired from a firearm both will hit the ground at the same time. Sorry folks, just simple physics. Bullets do not rise above the bore line, period, ever. Any "crawling the wall" effect by wind is from the same aerodynamic properties found in our atmosphere that make a baseball curve. The two have no relevance to each other.
There is no lift produced by a bullet; it is round... None, zero, zip, zilch.
It takes the same speed (velocity) to keep the space shuttle in low Earths orbit as it would a .22LR bullet; approximately 17,500 mph. It just takes a whole lot more energy to get the shuttle up there then it would a little .22 bullet. Ballistics has to do with a coefficient and velocity. In Earths atmosphere it is different than in space where it is an effect of gravity based on the mass of the object, and not aerodynamic drag found here on Earth.
The .22 would stay in orbit longer than something the mass of the shuttle given the two entered the same orbit at the same time and velocity. This may sound contradictory to my original statement, but in reality it is not. The weight of the two differ only by their mass, but have the same gravitational pull on them. Because there is more mass to the shuttle, there is more of it for the same gravity to pull on which slows the larger mass faster than our little .22 bullet. It is velocity loss that brings the shuttle home first.
I hope this helps to clear up some of the fun everyone is having here with this thread by the OP.
On to the next Caper,
CarolinaChuck
r44astro
New member
Is this why geosynchronous orbits must be much higher where the approx 1000 miles an hour of earth rotation (centrifugal force) would cancel the mass of object leaving it in free fall? Is not also true astronauts experience zero g forces because of free fall and gravity in earth orbit is over 90 percent as on the surface?
Bill in warm sunny Florida
M
mks
Guest
CarolinaChuck,
You could benefit from reading the nennstiel-ruprecht website.
Cheers,
Keith
You could benefit from reading the nennstiel-ruprecht website.
Cheers,
Keith
A
Alaninga
Guest
I, the OP'er...will.....
...will put this post to bed, unless any additional thoughts need posting : )
Let's sum it all up as....DMA,..( or, 'Don't Matter Anyway').
Unless someone does some testing in a strong crosswind with a 'well known behavior' bench gun that wants to show us all something when tested in a strong crosswind, either side!
Hope you didn't consume all your scotch for this, or if you did you are happy about it.
...will put this post to bed, unless any additional thoughts need posting : )
Let's sum it all up as....DMA,..( or, 'Don't Matter Anyway').
Unless someone does some testing in a strong crosswind with a 'well known behavior' bench gun that wants to show us all something when tested in a strong crosswind, either side!
Hope you didn't consume all your scotch for this, or if you did you are happy about it.