Coriolis effect

[Brown Dog]

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR> I guess another way to think of it is, those velocities would only be unaffected if you fired the shot dead verticle at which time the projectile would act like a geo-synchronous sattelite and fall right back on the shooter. It would continue to rotate at exactly the same speed as the earth, then gravity would set in and bring it straight back down to the same spot. (regardless of the latitude) <HR></BLOCKQUOTE>

Oh no it wouldn't!

As with coriolis, you have to think in terms of vector velocities. A projectile fired vertically would actually land to the west of the firer!

Prior to firing it only has the vector velocity imparted to it by all the things holding it in place in the rifle's chamber at that spot on the Earth. Let's say that spot on the Earth is a radius of X from the Earth's centre. If it is fired vertically, I hope it is obvious that the horizontal component of its vector velocity remains as it was prior to firing. Vertical firing has only given it a vertical component. At any altitude (or radius in this example) greater than X it will have an insufficient horizontal component to maintain a 'geo-synchronous' position and -in effect- the Earth's surface will leave it behind.

This phenomenon is known as 'Projectile Lag'.

The more astute among you will note that Projectile Lag can negate, contradict or add to the effects of Coriolis depending on circumstance.

If anyone on this site is shoulder- firing a weapon that is affected, in measurable amount, by either coriolis or projectile lag I suggest they stay away from Kryptonite!

 

[Dave King]

I'll agree that Coriolis is probably not a contributor for our shooting but these discussion(s) give me an out... it's either sit here and chat about this "useless" stuff or mow the yard and rake leaves.... let me think on that for a while... nope, it's Coriolis and now projectile lag for me.

Hell... this could come in handy for all concerned. I've won several drinks in bars throughout the country with this type of useless information ( It's pretty easy to dupe a drunk!).

 

[Ian M]

Dave,
I have no idea what you guys are talking about. BUT, I believe that you've just given us poor numb-nuts who don't use words with more than five letters in them a great excuse for misses.

"Must have been that **** CORIOLIS EFFECT" again, Jim-Bob, gi'me a couple of clicks left and hurl another round..."

I think Darryl has it right, work from your sighters. Hey Darryl, sometimes we use a lot of sighters and call the ones that hit our called shots.

 

[4mesh063]

( It's pretty easy to dupe a drunk!).

Hell Dave, I was relatively sober!. (Had 1 beer). Doesn't say much for my handling alchohol.

I see now the effect. The OSU reference was the very first thing I chose to look at and after seeing him say that the effect is to the east regardless of the direction, I took my initial guess to be correct, however, the amount of effect north or south is less or greater than the surface speed at the destination. Gotcha, I stand corrected.

Sorry Blaine. Dave also.

Dog, I agree, a shoulder fired weapon would have little affect. However, after doing a search on Daves reference to the Falklands, in WW1, I do now vaguely remember a story about that from years ago. The corrected error for the ships was roughly 50 Yards. But since it was corrected for the wrong hemisphere, it amounted to 100 Yards. If that is the case for a projectile which flew say, 10 miles, then at 1000yds, your error from a north shot to a south shot could be 5.68 Yards. If back then they fired projectiles 15 Miles, and I don't remember what ranges they could fire in WW1, in WW2 it was about 16Mi, the error would be 2/3 that or 3.7Meters.

That should be easy enough for you to check out Darry. Wait for a super calm day, shoot 1 direction, then switch with the target and shoot the other. I'm leaving for the range in a half an hour and I'd check it myself, but, I shoot to the west at home and tward the east at the range. I'm afraid my example is not going to show much!

 

[baldeagle713]

What? who? All I know is loadem and shootem!
Kiss it. That is
Keep
IT
Simple
Stupid

In
Theory

 

[MAX]

Blaine, long time Sport! Don't think you'll find anything that counters McCoy's teachings on the subject since he is right. But then, who would believe me? I also recall from his book that he frequently disregarded those things that had no significant effect when doing his calculation. Ex. Coriolis Effect is signicant for long range(indirect)fire, but NOT for flat fire trajectories, which are the subject we discuss. He did say that fire parallel to lines of latitude are NOT affected which is logical.

Levity Break:
"East is east, west is west, and never the twain shall meet" - Kipling, NOT talking about coriolis effect.
"east is least, west is best" - student pilots learning about magnetic variation.
"when I shoot bullets vertically and try to catch them in my teeth, I always run to the west." - Max

See Ya

 

[Blaine Fields]

The university article was a big help in explaining why the bullet would appear to move right while shooting north. That was the part I was having trouble conceptualizing. So, thanks a lot.

As to the usefulness of this calculation, I agree that it is one of the more minor issues to deal with. At 1000 yds, Coriolis effect equals about 1/4 MOA, or around 2.5 inches. Not enough to get worked up about, but given the fact that most of us live north of the equator and most of use right twisting barrels, the two taken together, i.e., Coriolis plus spin drift do add up to a significan number.

In another post I was asking for help in coming up with a decent spin drift formula. Using the approximation I have (which I got on this site from S1), at 1000 yds. shooting a 300 WSM, 190 gr. bullet, spin drift plus Coriolis equals around 1 MOA. That is a significant deflection and even if a long range shooter will handle it with a spotting shot (as Darryl suggests) it is still good to know that at range when the POI moves to the right, there is not something wrong with the zero.

And, like Dave King says, this is a great beer topic.

 

[Brown Dog]

Following on from Dave's premise that there could be less interesting things to do...and besides, it's now dark in my part of the world.....

I just grabbed a few figures from an artillery firing table to try to quantify the sort of effects we're talking about. The proj in question has an mv of 820m/s and a BC of around 0.3 [which surprised me until I considered how much less dense HE is than lead].

Firing at latitude of 50 degrees North, with a target at a range of 2000m (chosen so that there might be some read across to rifle shooters):

Standard stuff:
Time of flight is 2.7 sec
Drift requires a 0.5mil left correction (ie 1 metre at this range).

Rotation of the Earth stuff:
On all bearings of fire a 0.1mil left correction is required (ie 20cm at this range).
Easterly fire requires an elevation reduction equivalent to the target being 13 metres closer.
Westerly fire requires an elevation increase equivalent to the target being 13 metres further away.
(in both cases this value gradually reduces to zero as the bearing moves to due N or S.)

Bet that's surprised a few people!

There are a bunch of factors resulting from the effects caused by the Earth's rotation -Coriolis is just one of them. They interact to sometimes cancel each other, sometimes add to each other -depends on lots of things [eg consider the difference between a shot fired from zero degrees to a target at 10 degrees North (not too big a difference between Earth surface speed at both locations) versus from 80 to 90 degrees North. Factor this against Projectile Lag (time of flight and max vertex height related) and don't forget that for Westerly fire the Earth 'rises' to meet the round whereas for Easterly it 'drops away' to let the round go long]

The artillery values given are therefore the overall result of the interaction of all the effects that can be grouped as being caused by the Earth's rotation. There's little point in considering Coriolis in isolation!

I hope that's thoroughly confused everyone!

 

[DANTEC]

Dear Brown dog

have a link with Brown Dog bullet maker in CA ????????

good shooting

DAN TEC

 

[4mesh063]

This is BS! I just got back from the range and BOTH of my guns shot to the right! Look what you guys did to my guns now!

 

[Brown Dog]

Dantec,

Apologies, no link to them. I'm more-or-less due North of your location; the other side of "La Manche" -hope that won't be a problem

 

[Dave King]

4mesh063

We should have listened to Darryl... All our guns are probably screwed up now. For years we shot in blissful ignorance , now were "edumacated" and can't hit anything.


Here's what I believe I'll remember best from this thread... "when I shoot bullets vertically and try to catch them in my teeth, I always run to the west." - Max

 

[Gustavo]

We must differentiate two distinct effects of the Coriolis acceleration ( not the force itself ) one a VERTICAL deflection which will make a shot to fall short or long in terms of range and a HORIZONTAL deflection, which will make a projectile to deviate left or right acording to the hemisphere the gun is, not the target.

 

[screech]

I didn't even get through the first page of this post. Mostly dont understand. just to help you guys, you need to get out and have a life or something because you are way to smart for you'r own good.