coriolis effect?

[people]

I would think the coriolis effect would only be an issue if the earth stopped rotating part way thru the match...

Depends on the match. Square range with sighting shots does not matter as long as you hit paper.

The real question is would the oceans wash over all the land or just most of it. Now if the rotation around the sun was stopped would the water make it to space?

 

[Hondo]

Perhaps a retired or active military artillery range officer could tell us if they use the Coriolis effect in their long range calculations.

 

[M-61]

Perhaps a retired or active military artillery range officer could tell us if they use the Coriolis effect in their long range calculations.

That would be interesting. In 1968 the USS New Jersey was firing 16" shells approx. 23 miles in a westerly direction. Would like to know what was figured in by the fire control folks.

 

[NealC]

The effect you seem to be talking about is known as the Eötvös effect. This IS dependent on direction of fire with bullets fired East impacting high and vice versa. The Eötvös effect is similar in magnitude to the Coriolis effect. At 1000 yards it will change the POI about 3 inches, more or less.

OK, I have been designing guidance (flight directors), autopilots algorithms, and writing flight simulation for 30 years and I have never heard of Eötvös. Is this related to gravity or the non roundness of the earth or what?

 

[Keith Glasscock]

The effect you seem to be talking about is known as the Eötvös effect. This IS dependent on direction of fire with bullets fired East impacting high and vice versa. The Eötvös effect is similar in magnitude to the Coriolis effect. At 1000 yards it will change the POI about 3 inches, more or less.

OK, I have been designing guidance (flight directors), autopilots algorithms, and writing flight simulation for 30 years and I have never heard of Eötvös. Is this related to gravity or the non roundness of the earth or what?

From my limited knowledge of physics, I think it is mostly related to the rotation of the earth and its roundness. In airplanes, I suspect that the effect is lost in the noise of aircraft performance. If we could measure it, I'd suspect that the result would be a slight decrease in AOA and required thrust while going east. On the other hand, when was the last time that an airliner flew and anyone knew the actual weight of the airplane?

 

[Mozella]

The effect you seem to be talking about is known as the Eötvös effect. This IS dependent on direction of fire with bullets fired East impacting high and vice versa. The Eötvös effect is similar in magnitude to the Coriolis effect. At 1000 yards it will change the POI about 3 inches, more or less.

OK, I have been designing guidance (flight directors), autopilots algorithms, and writing flight simulation for 30 years and I have never heard of Eötvös. Is this related to gravity or the non roundness of the earth or what?

If you're a software guy, you may not have heard of him. However, he's rather well known by those who study physics. In short, he performed some famous experiments concerning inertial mass.

As far as we shooters are concerned, the Eötvös effect has to do with the apparent change in gravitational effect on a bullet. It is latitude and direction-of-fire dependent, but it is not aerodynamic neither does it have to do with the fact that the earth isn't round.

The effect is relatively small (like the coriolis effect). Nevertheless, it's real and the effect at 1000 yards is significant enough so that it's included in long range ballistics calculations.

 

[NealC]

The effect you seem to be talking about is known as the Eötvös effect. This IS dependent on direction of fire with bullets fired East impacting high and vice versa. The Eötvös effect is similar in magnitude to the Coriolis effect. At 1000 yards it will change the POI about 3 inches, more or less.

OK, I have been designing guidance (flight directors), autopilots algorithms, and writing flight simulation for 30 years and I have never heard of Eötvös. Is this related to gravity or the non roundness of the earth or what?

My degrees are in engineering so if you can add a link to a reference of this so I could understand what you are taking about I would appreciate it. We have models that vary the gravity of the earth at different lat/longs and models that vary the obliqueness of the earth as well as atmosphere models, aerodynamics, and well as the dynamics. I have never heard of this effect.

 

[JRS]

The Eotvos effect - Physics Articles

 

[fivering]

Simply Google it, there will pop up many references to read.
Another great example of spending time on minute details that would be far more productive if spent practicing shooting.

 

[Rope2horns]

Just shoot a Dasher,,,you don't have to worry about wind or Coriolis. ;D

 

[johnfred1965]

I'm sure there are a lot smarter people on here than me, but I googled and it seems these effects are related to the apparent gravitational change of the projectile due to increase(east) and decrease(west) of centrifugal forces. If I read right, the Coriolis effect is the horizontal component of this change and the Eotvos effect is the vertical component. I'm not a physicist, but I did stay at a holiday inn express once. hopefully, a real professor can give us the lowdown.

 

[M14AMU]

Never shoot east or west....just north or south!!

 

[Mozella]

I'm sure there are a lot smarter people on here than me, but I googled and it seems these effects are related to the apparent gravitational change of the projectile due to increase(east) and decrease(west) of centrifugal forces. If I read right, the Coriolis effect is the horizontal component of this change and the Eotvos effect is the vertical component. I'm not a physicist, but I did stay at a holiday inn express once. hopefully, a real professor can give us the lowdown.

Well, I'm not a real professor but I've certainly listened to plenty of them explain these two distinctly different effects. They are similar to each other in magnitude if you shoot in North America; i.e. 3 or 4 inches at 1000 yards for most target rifles used in that particular discipline.

And, the two are both caused (as far as we shooters are concerned) by the rotation of the earth. But it's not correct to say that they are both related to the apparent change in gravitation; one horizontal and one vertical.

These two forces are really two different things. The Coriolis effect has to do with a rotating reference frame. It's a pseudo force and works just the same in zero gravity. Here on earth it is at a maximum at the poles and zero at the equator. The Coriolis effect doesn't depend on the direction you're shooting.

Eotvos effect is the change in the centrifugal component of gravity. It's effect is maximum at the equator which is just the opposite of the Coriolis effect. And, unlike the Coriolis effect, the Eotvos effect DOES depend on the direction of the shot.

Bottom line: They ain't simply two different flavors of the same thing.

 

[NealC]

Ok, I read the "Eotvos" effect. This is just part of the equations of motion as is coriolis and spin drift. I just never heard it referenced this way before. I have to admit I am a little rusty on dynamic equations since I have not needed to change these equations in the past 30 years in my tools (and will never need to change them). It was a good reminder to myself to let the equations do the work.

This book has a full equations of motion in the first chapter. I don't have the book in front of me but I believe the coordinate frame are earth fixed.

Aircraft Control and Simulation 2nd Edition
by Brian L. Stevens (Author), Frank L. Lewis (Author)

This book is extremely thorough. This one is tougher to read and probably has both fixed to the earth and fixed with rotating earth reference frames.

Modeling and Simulation of Aerospace Vehicle Dynamics (Aiaa Education Series) 3rd Edition
by Peter H. Zipfel (Author)

I am sure there are books related just to ballistic projectiles but the equations of motion do not change. I would assume they would have more detailed aerodynamic effects like Magnus, etc.

I bought a ballistics calculator for my Andriod phone for $5.00. It even includes the ability to use the phone camera to get the azimuth and elevation to the target for the calculation as well as the lat/long position. So to answer the original question to the thread, for $5.00, you can see for yourself how much the trajectory is affected without the need to listen to old guys trying to remember how this works.

Neal

 

[mikecr]

It seems a mistake to correlate flying things from falling things.
Planes fly
Bullets fall

 

[NealC]

It seems a mistake to correlate flying things from falling things.
Planes fly
Bullets fall

I never suggested correlating their trajectories but their equations of motion are identical. The external forces and moments applied on the airframes are different. The trajectories will be different as the airplane will not be spinning. There are some projectiles that are fired and spin like a bullet and then pop out canards, stop spinning, and then fly controlled (https://en.wikipedia.org/wiki/M982_Excalibur). There is also the RAM airframe that spins under control during it's entire flight (https://en.wikipedia.org/wiki/RIM-116_Rolling_Airframe_Missile). All of these systems use the exact same math to describe their motion.

 

[mikecr]

The math is not the same.
Bullets are not propelled. So they're continually decelerating, and falling at ~32ft/sec/sec.
The only correlation is drag, not drift, and not drop.

 

[Mozella]

The math is not the same.
Bullets are not propelled. So they're continually decelerating, and falling at ~32ft/sec/sec.
The only correlation is drag, not drift, and not drop.

Well, it's pretty clear to most of us that bullets aren't airplanes, if that's what you're trying to say. But as someone who was educated in "airplanes" and who later in life became interested in bullets, I can say that the math is indeed the same.

It's pretty much all about physics, the laws of which are obeyed by both airplanes and bullets. And you don't have to delve too deep into physics to require some familiarity with math where you will find the math skills needed to study the aerodynamics and structures of aircraft are essentially the same as those needed for the study of ballistics.

Indeed, when you look into the physics associated with firing cannons from an aircraft, you combine the two. The calculations performed by a gunsight system, for example, are rather complex, especially when it comes to shooting at maneuvering targets. You have a bullet traveling down a barrel under high g force caused not only by the propellant but also by the aircraft itself. The round exits into what amounts to a terrific wind at a steep angle relative to the bore at which moment the g forces change completely as the now decelerating bullet travels toward a moving target which is changing in azimuth, elevation, and range. The lead solution for that situation is more difficult to find that that for shooting ducks in a barrel; however, the math skills learned by the aerodynamicist will be more than sufficient for him to understand the ballistics of aircraft cannons. Why? Because the math is the same.

 

[DocUSMCRetired]

Since this thread is specifically about Coriolis effect, I will leave out spin drift in this post, however to answer the original question. Everyone has experienced the Coriolis effect. Their are two parts to this. A Horizontal Component, and a Vertical component. For target shooters, shooting at known distances with sighters, the Coriolis effect can mostly be ignored. It has over all a very minimal effect, however it is present and does need to be accounted for. If you only get 1 shot at a long range target, with no sighters to fine tune with, it can become important. The horizontal and vertical effects are completely independent of each other. You guys should read Applied Ballistics for Long Range Shooting, it covers most of what is being asked here. Specifically in chapter 7 on page 97. However I can cover this a little bit.

The horizontal aspect (Page 98) is determined only by your latitude:

Horizontal Deflection = Ω * X * sin(Lat) * tof

Ω = rotation rate of the earth (=0.00007292 rad/s)
x = range to the target in feet
Lat is + for north and - for south of the equator.

Time of flight can be calculated using a ballistics program

For example, the target is at 1000 yards, the Latitude of the shooter is 45 degrees North, and the time of flight is 1.5 seconds
Horizontal Deflection = 0.00007292 * 3000 * sin(45) * 1.5
This equals .23 feet or 2.8 inches.

Travel east or west has no effect on the horizontal shift due to Coriolis effect, only north and south. So while 2.8 inches may not seem like much, and could easily get lost in the noise, or even ignored if you only ever shoot at the same range. A great example can be found in the book where if you come from Australia around 45 degrees South, then you can double that, since you are set up for 2.8 inches left, and now have 2.8 inches right. You now sit at almost 5.5 inches of Coriolis effect at 1000 yards.

The Vertical Component (page 99) aka Eötvös Effect is a bit more complicated and involves the Azimuth (direction of fire) and the Latitude:

Notes: Technically you want to use true north, not magnetic. But magnetic will get you close enough. Vertical deflection is at its maximum for azimuths that are parallel to and near the equator. The vertical Coriolis Effect is an acceleration like gravity, except that it depends on your latitude and azimuth of fire. This can be accounted for by scaling the effect of gravity. In short a "Gravity Correction Factor" that can be used to modify your predicted drop. The formula:

f = 1 - ((2 * Ω * MV)/ g)cos(Lat) * sin(Az)

f = Gravity Correction Factor
Ω = Spin of Earth (=0.00007292 rad/s)
MV = Muzzle Velocity
g = Acceleration of Gravity (32.2fts^2)
Lat = Latitude + for North - for South
Az = Azimuth of fire, clockwise from north.

In short the way to correct for Vertical Coriolis Effect at long range is to scale the effect of gravity.

Example, 155 grain .308 cal bullet fired at 3000 fps. Trajectory Zeroed at 100 yards, and their is -307" of drop predicted at 1000 yards before accounting for Coriolis effect. The shot is fired due east at 45 degrees North Lat.

f = 1((2 * 0.00007292 * 3000)/32.2)cos(45)*sin(90)
f=.9904
Gravity correction factor can now be multiplied by the drop to get the correct firing solution. -307"*0.9904=-304"

The bullet will drop 3 inches less when shooting East. If you reversed the firing direction to West, the result would be the opposite giving you a corrected firing solution of -310".

Summary The horizontal and vertical components of Coriolis Effect are independent of each other. The Vertical Component of Coriolis effect can be potentially troublesome due to the sensitivity of firing direction. In order to drastically change horizontal component you need to travel a great deal across the planet. The vertical component can be altered by simply changing firing direction, so to most shooters, this will be much more prevalent. You guys would really benefit from reading the Applied Ballistics for Long-Range Shooting book, chapter 7 to grasp a full understanding of this. The examples and formulas found here were pulled directly from the book. Some of the most important aspects of this were best said by Bryan Litz "For target shooters who are always shooting at known distances with sighters allowed, the Coriolis Effect is as inconsequential as spin drift because it's the same for every shot. If you're a long range hunter or tactical shooter who doesn't have the luxury of sighter shots, and may find your targets in random directions, you may want to consider the Coriolis Effect, especially when shooting at extended ranges." "Firing East will cause you to hit high. Firing West will cause you to hit low. When shooting North or South the Vertical Component is zero regardless of latitude."

 

[M14AMU]

I attached a picture of a ballistic calculator drift due to coriolis. It is around 14" drift at 1000 yards for my 308.

Same amount Aberdeen Proving Grounds came up with many years ago but I believe this referred to 'spin drift'!!