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Magnus effect And You...

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Magnus effect And You...

Unread postAuthor: jeepkahn » Tue Oct 13, 2009 2:26 pm

We all know what it is and how it works, But here's an illustration of how powerful it can be...

Yesterday, before it started raining cats and dogs, I was sighting in some ghetto sights on the decimater for some testing I've got to do with some rounds that a friend of mine made... Well, I was shooting 1" chrome steel bearings at a 8'widex7'tall backstop/target holder from 100yds and was hitting a 12" grouping with little problem(750psiand 900ish fps), then my little 5lb co2 starting dropping pressure (partly due to chiling and partly cause it was getting low) and once it dropped below 680psi(700ish fps) I literally couldn't hit the broad side of a barn... At first I thought that I was shooting low, so I started aiming lower... But looking through the sights, I couldn't see where the bearings were hitting, Sooo, I took aim and then opened my other eye to see if I could track the trajectory and guess what I saw???

Even though the gun was aimed near the bottom of the backstop, These frikkin heavy @ss bearings were CLIMBING faster than a Golf ball being hit off a tee with a sandwedge!!! Muzzle height was about 50", at the 50yd mark the balls were about 24" from the ground but by the time they got to the target they were about 96" high and 150yds later they were clipping treetops at about 80ft high and slightly to the right...

I would've never thought that almost perfectly smooth, shiny, and heavy steel ball bearings would hook that much just from magnus effect...

The other interesting note was that it wasn't effecting them at 900fps but was causing HUGE issues at below 800fps...

Anyway, the point is, with round ammo MAGNUS is NOT you're friend...

Time to start concentrating on Darts/Bolts for this thing...
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Unread postAuthor: CpTn_lAw » Tue Oct 13, 2009 2:46 pm

That is impressive jeepkahn!! I noticed this effect when i was shooting 1/2" steel balls from the galvanised steel barrel...they would have a visible "curve" in flight...Nt as pronounced as your chrome balls
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Unread postAuthor: Hubb » Tue Oct 13, 2009 2:53 pm

Anyway, the point is, with round ammo MAGNUS is NOT you're friend...
Only if you don't know how to control it. Adjustable hopups do just that and ends up making magnus a good thing. In the case of the Decimator, you would probably need to cut down on initial muzzle velocity (done by turning down the pressure) to see the magnus effect to an advantage. This, of course, would cut down the power, so that may not be an option for you. If you don't want to cut down on the power, just stick with darts, etc.
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Unread postAuthor: jeepkahn » Tue Oct 13, 2009 3:01 pm

Hubb wrote:
Anyway, the point is, with round ammo MAGNUS is NOT you're friend...
Only if you don't know how to control it. Adjustable hopups do just that and ends up making magnus a good thing. In the case of the Decimator, you would probably need to cut down on initial muzzle velocity (done by turning down the pressure) to see the magnus effect to an advantage. This, of course, would cut down the power, so that may not be an option for you. If you don't want to cut down on the power, just stick with darts, etc.


Or I could UP the pressure so that I hit the target before it takes effect!!!

DD1 shows the same thing with GBs, but exagerated, I can shoot paralel to the ground and the trajectory is flat until about the 150-200 yd range and then they'll climb several hundred feet on their way out of sight...
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Unread postAuthor: Hubb » Tue Oct 13, 2009 3:27 pm

That, too. Even in paintball (I use a hopup system), I can notice that the round will usually dip or remain straight before it begins to lift. But, again, I have adjusted my marker to use magnus to the maximum effect (the slightest dip with a decent rise to give it the straightest trajectory possible) so I don't really see the real effects of magnus too often.
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Unread postAuthor: POLAND_SPUD » Tue Oct 13, 2009 4:25 pm

this effect is quite easy to notice with marbles on a sunny day because they reflect light good
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Unread postAuthor: jrrdw » Tue Oct 13, 2009 4:31 pm

jeepkahn wrote:Or I could UP the pressure so that I hit the target before it takes effect!!!


Thats what I was thinking. You range at 900psi is short enough to escape the curve. Funny what a extra 100psi will do! :P
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Unread postAuthor: Ragnarok » Tue Oct 13, 2009 5:47 pm

jeepkahn wrote:Or I could UP the pressure so that I hit the target before it takes effect!!!

That is dependent on a few things.
If the lift coefficient is constant, then lift is proportional to the square of velocity. Fire it twice as fast - it'll make it there in half the time, but because there's four times the lift, it'll have risen just as much.

However, this is not the case with the Magnus effect, where C<sub>L</sub> is related to the spin ratio of the ball: (Angular velocity * Radius)/Linear velocity

In other words, for a crude model Magnus lift can be taken to be roughly linear with velocity (although a better model appears to be lift proportional to velocity<sup>1.5</sup>) - but only for a given angular velocity. But if you're firing it faster, then the angular velocity will probably increase as well, and angular velocity is lost much more slowly.

So, if angular velocity is proportional to muzzle velocity, a ball fired at 800 fps has less lift than one fired at 900 fps which has since slowed to 800 fps. So, in this case, increased muzzle velocity can be expected to increase the Magnus lift at a given distance from the muzzle.

However, from the way you're talking, I suspect that the angular velocity of your projectiles isn't relating all that closely to muzzle velocity. But I wouldn't be all that surprised if you found that increasing the velocity didn't help.

You'd be better off finding a way to stop the balls spinning. Perhaps using some kind of lubricant spray on the barrel would be a solution.
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Unread postAuthor: Technician1002 » Tue Oct 13, 2009 8:15 pm

At higher speeds, the round except the leading edge is in a low pressure zone. This low pressure zone has little force to drive the projectile off course. At lower speeds the pressure on the round is higher so a drop in pressure on any side can now re-direct the round. Near Mach1 or above it, most of the round is in pressure that is close to a vacuum.
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Unread postAuthor: jeepkahn » Thu Nov 19, 2009 12:51 pm

On my copper cane I found a perfect way to keep the ball from spinning...

I heatshrink yellow wirenuts to them as a tail... since 1/2" type L copper is actually.54" I use .5" balls and the heatshrink takes up about .03" they fit with very little slop, and the yellow fastenal wirenuts are right at .54" +/- .01" at the base...

I've actually noticed that these actually chrony slightly faster than 17/32"/.53125" balls I'd been using, and are way more accurate at 100yds+ than balls alone, and they have no problem poking holes in 3/4" ply at that range... the 2 rounds onthe left are my infamous .40cal casing/wirenut rounds that are great for plinking, but will penetrate a new 55gal drum at 100yds...
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