I guess this has already been answered, but there is a Wiki on the Magnus effect (which I presume is what you were getting at) which actually addresses this, so figured I’d like to it and quote the relevant part:
So, basically it’s insignificant, though since bullets tend to wobble when they leave the gun (which is why you spin stabilize them in the first place), it’s not zero. Still, it’s not going to make much difference (you aren’t going to be able to fly the bullet further due to lift, basically) and over short distances (which we are talking about with any sort of bullet except maybe a sniper rifle…from memory the earth curves a few inches per mile, but most bullets don’t go nearly that far) other forces are going to have a much more substantial impact.
I’m surprised no one has mentioned ground effect forces yet. I would think ground effect could produce measurable lift over some part of a long-range bullet’s trajectory, especially if it’s still traveling relatively straight (and spinning) rather than tumbling by the time it gets close enough to the ground for ground effect to matter.
Actually, I don’t have to show anything. The argument, “X cannot have result Y because it is intended to produce Z” is self-evidently fallacious. And gyroscopic effects have nothing to do with fluid dynamics, anyway.
Ground effect is generally held to mean the reduction in induced drag experienced by an airfoil operating close to a horizontal surface (e.g. ground or water). It’s negligible when the aircraft is more than a wingspan from the surface, and becomes significant when the distance is less than half a wingspan.
I think this means that it would not be important in analyzing the flight of a bullet.
I think the point is that they are equivalent - though they appear different, they yield the same conclusions and in no way conflict with each other.
Bernoulli explanation (simplified) says: Airflow results in lower pressure above a wing than below - hence lift. [Left unsaid: This of course requires that air be deflected downward.]
Newtonian explanation says: Wing continuously deflects air downward, resulting in a upward force known as lift. [Left unsaid: This of course must result in lower pressure above the wing.]
These two statements are false. Lift is caused by asymmetry of the shape of the object with respect to the air flow. Symmetrical shapes, the forces from the airflow are symmetrical and cancel out, thus giving no lift.
You can make anything “fly” by launching it with sufficient force, if you count any parabolic motion as “flying”. But if you are talking about generating lift, then no, mere velocity alone will not generate lift.
I should point out (and I think it was mentioned) that air foils generate lift via asymmetry, but the asymmetry might be due to shape, or might be due to angle of attack, i.e. being pointed at an angle to the direction of motion.
For bullets, it was mentioned in another post from the previous thread that spinning bullets do have an asymmetry due to angle of attack. As the bullet leaves the barrel, it is aimed horizontally (for example), but as it starts to fall, the actual path of motion changes due to gravity. That curving arc means that the rotation of the bullet is not aligned with the direction of travel, direction of travel being the vector sum of the horizontal path and the effect of gravity. Ergo, that “nose angle” creates an asymmetry that can provide lift.
More precisely, we cannot measure time to the precision required to observe the effect, because the curvature is so small at short distances.
“Accuracy” and “precision” are, strictly speaking, two different concepts. To illustrate, a shotgun blast provides a bunch of projectiles into an area. A well-aimed shotgun blast may put a lot of shot across the target area, providing an accurate shot, but the precision is very low. It puts a few in the bullseye and a bunch of holes in various other places, including off the target. Whereas a rifle shot puts one hole in the target. That is a precise shot, but the shot might be a foot to the left of the bullseye – not very accurate.
Or take a rifle, I can shoot 12 shots. If I put all 12 shots through the same hole, that is very precise, but if that hole is 12 inches left of the bullseye, it isn’t accurate. Or I can fire 12 shots and have them hit 12 different locations centered on the bullseye - highly accurate, but low precision.
All airplanes gain lift from deflection of air. Asymmetrical air flow due either to wing shape, angle of attack, or both causes deflection of air. Asymmetrical air flow also causes pressure differences. The Bernoulli equation is a means to determine the pressure differences, and thus calculate the lift. The two concepts are different ways to look at the same thing, or different elements of one cohesive picture. They aren’t competing theories.
Aircraft with symmetrical wings get asymmetry due to the angle of attack, i.e. the wings may be mounted with the leading edge higher than the tail, and the airplane itself will fly with the leading edge higher than the trailing edge, possibly with the nose of the plane high.
Golf balls get lift by rotating perpendicular to the direction of travel with the axis horizontal. I.e., lift is generated by the golf ball spinning bottom edge toward the front. Bullets spin along the long axis of the bullet, i.e. into the direction of travel*. This will not generate lift from the rotation.
*Not really into the direction of travel, as the nose angle is slightly off the direction of travel once gravity comes into play.
Strictly speaking, there is asymmetry in the bullet shape due to angle of attack, i.e. the “nose-up trajectory” being described. The bullet is spinning along the long axis, but as the bullet travels further in the arc, the path of the bullet is aimed more and more downward due to gravity. The spin stabilization causes the nose to lag the direction of travel - giving asymmetrical shape and thus causing lift.
Unfortunately, that link keeps calling it “yaw”. Strictly speaking, yaw is rotation from side to side. Rotation up and down is “pitch”.
“Nose high” in this context means from the perspective of the flight path, not with respect to the horizon of Earth. And yes, that nose high trajectory can cause lift.
Technically, a Formula One race car has negative lift. But yes, that does keep them from flying.
Historical trivia note: I’ve read that World War I is the first time when weapons had a long enough range that curvature of the Earth had to be taken into consideration as a practical matter.
No, you used the phrase “That does not mean” which means that the opposite of what follows that phrase is true. That’s how that phrase works in English.
If I say “The fact that I do not play baseball does not mean I can’t throw a mean curveball,” I am making the claim that I throw a mean curveball.
By saying “That does not mean that gyroscopic effects do not produce apparent lift,” you are inherently making the claim that gyroscopic effects do produce apparent lift. You don’t get to backtrack by claiming some robotic interpretation of common English phrases.
If the Magnus effect is the answer, it seems to be the answer to an exterior ballistics question that isn’t required in order to determine bullet flight. There are existing formulas that can be used to determine the path of a bullet. Combining the ballistic coefficient, the muzzle velocity, and the speed and direction of the wind along the flight path, you can calculate a bullet’s impact point before the bullet is fired. There are variables, of course, but those can easily be accounted for. Not every bullet leaves the muzzle at exactly the same speed. Crosswinds change direction and intensity.
If the Magnus effect does effect bullet flight, why assume it would it only produce lift in an upward direction (12 o’clock)? From it’s description, the Magnus effect could cause a bullet to move in any direction. Or all directions. Lift in one direction would be counteracted by the same lift in other directions.
Just some additional addled thoughts -
A modern bullet spins at a very high rate.
Bullet RPM = Muzzle Velocity X 720 / Twist Rate
Assuming a barrel has a 1" in 10" rifled twist, and a bullet exits that barrel at 3,000 fps, the bullet’s rate of spin will be 216,000 rpm. That’s a whole lot of energy.
A fired bullet’s surface is no longer smooth. The barrel’s rifling has scored it’s surface. A scored surface is more likely to interact with the wind but gravitational force will be the same.
It’s the raised seams of a spinning baseball, and its interaction with the air, that results in a baseball curving more to the left, right, up, and down along its intended arc, than a smooth surfaced ball. A knuckleball still has raised seams but has little, or no, spin. The air/raised seam interaction will still cause the knuckleball to drift away from it’s intended path, but that path is unpredictable, which makes it as hard to hit as it is to catch.
Wind drift can also be calculated. Knowing the time of flight to target, balistic coefficient, distance to target, muzzle velocity, and the speed of a 90 deg crosswind in feet per second, it can be determined how far to the left, or right, of a target that a bullet will impact. Crosswinds of less than 90 deg will have a decreased effect.
A bullet with a BC of .300, exiting a muzzle at 3,000 fps, will reach 200 yds (600 ft) in .2244 sec. Assuming a steady, 30 mph (44 fps), 90 deg crosswind moving right-to-left along the entire length of the bullet’s flight, the bullet will be pushed 1.0736 feet to the left of it’s expected point of impact.
TOF - (range to target / muzzle velocity) x crosswind fps = drift
.2244 sec - (600 ft / 3000 mz) x 44 fps = 1.0736 ft
My rule of thumb is that the Magnus Effect moves the projectile in the same directiopn as the front of the projectile. In a fastball the front rotates up and the ball tends to rise. On a slider the front of the ball rotates to the 10 o’clock position so you have a fast ball breaking to the left (assuming a righty) so I’m not sure what effect the ME would have if the axis of rotation is not perpendicular to the direction of motion.
The flow of the conversation is somewhat convoluted.
waddlingeagle made the original claim
bump replied
bump was basically directly refuting waddlingeagle’s claim that bullets spin to provide lift, stating that the purpose for spin (i.e. rifling) was purely stabilization.
John W. Kennedy replied that, regardless of the intent behind rifling, it is possible that the gyroscopic effects could produce lift. He’s making the purely logical claim that just because the spin was added to produce one effect does not preclude a second, unintended effect from occurring. In medicine, we call those “side effects”.
**gnoitall **apparently took JWK’s statement to mean that he knows lift does occur, and called for a cite.
John W. Kennedy replied that he doesn’t need a cite to prove the logical condition of the statement he made. He wasn’t trying to assert lift occurs, only state that the added spin might have an effect beyond the intended effect of stabilization.
doorhinge, I don’t think the Magnus effect is in play on bullets, at least for creating significant lift. The external ballistics cite indicates that the bullet flies ever so slightly off alignment, which it refers to the yaw angle (rotation about the vertical axis). It also is slightly off alignment in the vertical direction (i.e. pitch). Pitch effect might contribute lift from aerodynamic asymmetry. The yaw effect I guess, in theory, could produce a slight magnus effect giving either a slight lift or a slight drop depending on if the nose is yawed left or right out of the barrel. And assuming precession doesn’t balance that and negate any effects.
You seem to have cited the equations for rifle targeting. That shows magnus doesn’t really come into consideration.
Almost. Bullet spin does not generate lift, in and of itself. It MAY generate lift, or increase drop, depending on the direction of spin and the direction of any crosswind. The Magnus effect is what produces the lift in a crosswind - analogous to spin on a baseball, where the backspin produces lift, and the topspin makes the ball sink. One thing spin does do is produce lateral motion, as the bullet drops - for the same reason, via the Magnus effect. In effect the vertical drop produces a “crosswind” moving upward relative to the bullet. For a bullet spinning clockwise, that will produce a deviation to the left of the path of travel.
Since we’re nitpicking, this isn’t true, either. There are lots – perhaps most – places on the earth where the curvature is negated by local geography, at least over distances equal to the flight path of a bullet. The earth is universally curved only if you look at it from far enough back.
But then, it’s not just the curvature of the surface itself which is relevant, but the curvature of the gravitational equipotential surfaces. In other words, as you travel significant distances, the direction of “down” changes.