I have read Bryan Litz's paper "Gyroscopic (spin) Drift and Coriolis Effect" and I am quite puzzled about a passage from that paper.
The passage at issue is this one:
Consider a bullet fired at some angle on a long range trajectory. The bullet starts
out with its spin axis aligned with its velocity vector. As the trajectory progresses, gravity
accelerates the bullet down, introducing a component of velocity toward the ground. The
bullet reacts like a spiraling football on a long pass, by 'weather-vaning' it's nose to
follow the velocity vector, which is a nose-down torque. The price you pay for torqueing
the axis of rotation is that the nose points slightly to the right as it 'traces' to follow the
velocity vector. This slight nose right flight results in a lateral drift known as ‘gyroscopic
drift’.
The problem is that a nose-down torque for a right hand spin will produce a nose left torque,
(basic gyroscopic precession) not a nose right torque. But since Bryan has forgotten more about
ballistics than I ever knew, I have to assume his assertion of weather-vaning is correct. Thus I need
to find an explanation for the apparent contradiction.
Here is what I conclude.
I believe that for the sake of brevity, Bryan cuts directly to the net of all effects, that being a nose right
torque. But what is left out (again I assume for brevity's sake) is that the nose down "weather-vaning"
creates lift that causes an overturning moment. It is the overturning moment that generates a nose right
force *AND* between the nose left force from weather-vaining and the nose right force from the overturning
moment the right hand moment prevails.
I have hopes (probably futile) that Bryan might see this post and comment, but I'm truly interested
in a concrete explanation as to how weather-vaning produces a right hand torque when
gyroscopic precession clearly indicates the opposite.
The passage at issue is this one:
Consider a bullet fired at some angle on a long range trajectory. The bullet starts
out with its spin axis aligned with its velocity vector. As the trajectory progresses, gravity
accelerates the bullet down, introducing a component of velocity toward the ground. The
bullet reacts like a spiraling football on a long pass, by 'weather-vaning' it's nose to
follow the velocity vector, which is a nose-down torque. The price you pay for torqueing
the axis of rotation is that the nose points slightly to the right as it 'traces' to follow the
velocity vector. This slight nose right flight results in a lateral drift known as ‘gyroscopic
drift’.
The problem is that a nose-down torque for a right hand spin will produce a nose left torque,
(basic gyroscopic precession) not a nose right torque. But since Bryan has forgotten more about
ballistics than I ever knew, I have to assume his assertion of weather-vaning is correct. Thus I need
to find an explanation for the apparent contradiction.
Here is what I conclude.
I believe that for the sake of brevity, Bryan cuts directly to the net of all effects, that being a nose right
torque. But what is left out (again I assume for brevity's sake) is that the nose down "weather-vaning"
creates lift that causes an overturning moment. It is the overturning moment that generates a nose right
force *AND* between the nose left force from weather-vaining and the nose right force from the overturning
moment the right hand moment prevails.
I have hopes (probably futile) that Bryan might see this post and comment, but I'm truly interested
in a concrete explanation as to how weather-vaning produces a right hand torque when
gyroscopic precession clearly indicates the opposite.
