Hi guys, haven't posted here for a while... but recently I did some work with Dr. John Reid of the Trimontium Trust. These guys did some excavations at the 2nd century (AD) battle ground at Burnswark/Scotland, where a Roman legion laid siege (and eventually stormed) a Caledonian fort.

The Romans bombarded the hilltop fort with thousands upon thousands of missiles. Arrows, ballista ball, and many many sling balls. Launching distance 120 to 180 meters, steeply uphill.

Curiously, about 20% of the balls they found at excavations were smallish (20 grams) and had a precisely drilled hole, 4mm wide and 6mm deep.

There are several theories why the Romans drilled those holes, one of them says that the balls whistle that way and it was psychological warfare...

John came out for some experimental archaeology - it was fun! Maybe this is interesting for you guys too.

https://www.youtube.com/watch?v=7vJBKfQFD8I

So the holes didn't go all the way through the balls ?

And next time you need a proper slinger - let me know, have slings - will travel  :-)

The sling pouch on your trebuchet, didn't look great for imparting spin. Nees to be a lot flatter so the ball more or less rolls out.

But great experiment and worked really well with the slingshot :thumb: 

The holes are drilled in 5 to 6 mm, no more.

The pouch for the rubbuchet has to be boat shaped because otherwise it may not catch the ball at the start of the throw.

Who knows, in case the video is a success we might all meet in Scotland for a follow up!

could be fun. Not been up north to the barbarian lands for decades.

I'll design and print a mould to make concrete, clay etc whistling balls.

Figure either clay or cement with lead shot mixed in for weight.

Wonder if you still get the noise if you scale everything up and keep the holes proportional.

Or will the same size hole in a larger sphere make the same sound.   


There is experimenting to be done :-)

Actually I saw a documentary on TV where people shot a bowling ball from a cannon, and it DID whistle. The bowling ball has finger holes of course.

Taofledermaus (Jeff) also wants to make a shotgun slug with holes, to see if it whistles...

Also, I have received many comments saying my penetration tests were useless because I shot at point blank. I did use the online trajectory calculators and the result was that the speed of a lead ball lobbed by a sling did not decrease much at all during its flight, maybe 5% or so. Can you confirm?

As far as the lead balls losing velocity, it doesn't matter how it is launched, once it achieves velocity, it will slow the same due to gravity and air resistance. 

Gravity does NOT slow down the horizontal speed of a bullet. It simply adds a downwards vector. Air resistance does slow things down, but the air resistance of a lead sling ball is low.

over that short a distance (150-180 metres with lead is short distance for slings), and given that gravity accelerates the downward velocity - it's going to hit pretty damn hard and still be spinning very fast at the point of impact.

So we're going for the size and depth of hole is the relevant part not the size of the ball  Which make sense.
Lead bullets were small for the obvious reasons. Density means they still have a serious impact and smaller bullets means you had more of them.

Okay i'll make a decent sized mould for clay balls, say 30mm diameter,  with a 4mm x 6mm hole.
And see what happens. 

Figure the easiest way is to make a cylindrical insert and cutout on the edge of the mould, so that the hole is made when you press the two halves together.

Script is totally parametric. So I can make any size mould with any size insert. same script will be used to generate the insert cylinder.

I'll do the inserts and then print a couple out for testing purposes :-)

These are all the things you can change:

bd=20; //ball diameter
hl=6; // hole length
hd=4; // hole diameter
mb=4; // mould border width
pl=4; // peg length
pd=4; // peg diameter
pde=4; // peg distance from edge

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Okay should have a20mm mould set in an hour or so.

Just doing 20mm to check all the calculations are correcrt. And the mould and insert mesh properly. 

Great! Can't wait for the results.

currently got a 20mm set and should be a 30mm on the machine. like an idiot I only measured the clay balls I like after startnig the 30mm mould.

So that's a 40mm I also need lol

Had a go with some playdoh on the 20mm - yeah that works. the hole is really small. Guess it works like blowing over the neck of a beer bottle or a set of pan pipes.

Don't be fooled by the large picture of the insert, in reality it's really quite tiny.

I'll take some pics later 

pics of the 20mm and 40mm in playdoh.
They look a a bit out of round as they stretch when you remove them.

The hole on the 20mm looks bigger because playdoh dries out and shrinks, as it shrinks the hole gets bigger and i made that one yesterday.

I'll dig out the clay and make some slingable  ones later.

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So, do they whistle?

JeorgS  Normally, gravity does not have any effect on a projectile if it is launched in a perfectly horizontal trajectory.  However, most of the time we launch, shoot, throw or whatever, we go above the horizontal and the projectile arcs up and then comes down.  Gravity has a part in that.  The faster the velocity and the closer the target, the less the arc over the horizontal line. 

So, gravity does affect the trajectory, as does air resistance.  And as you pointed out, usually air has a greater effect on a projectile, but it is lessened as the surface area of the projectile decreases, so air doesn't affect a lead projectile as much as it would a larger surface area, but equal weight,  projectile.

no idea - those are made of play doh :-)
You can't sling them.

Can't get any sound by blowing over the hole, tried that.

gravity is a conservative force

the amount of energy gravity takes out of the projectile when it goes up it will give it back when it goes down.
when the target is at the same height as the release point is then there is no loss of energy due to gravity.
the amount of energy lost if you aim something higher than you is

U=mass*g(9.81m/s^2)*height

and vice versa it is the amount of energy you get when aiming something lower than you.

lmao - can we just say that lead bullets come down damn fast and hurt a lot.

Nope, gravity robs some of the acceleration as the projectile goes up, when it comes down gravity does not accelerate the projectile as fast as the initial velocity.  It does give some back just not as much as it took.

Bill Skinner wrote on Aug 18^th, 2016 at 8:30pm:

Nope, gravity robs some of the acceleration as the projectile goes up, when it comes down gravity does not accelerate the projectile as fast as the initial velocity.  It does give some back just not as much as it took.

correction:
air resistance robs some of the kinetic energy as the projectile goes up(and then down), when it comes down gravity does not accelerate the projectile as fast as the initial velocity.  It does give back the amount that air resistance didn't took.

in vaccum where there is no air resistance it would come down in the same velocity
the real energy (or velocity)stealer is not gravity it is air resistance.

another explanation:
it's like going uphill then downhill , with no friction you will have the same velocities at the same heights, but when friction comes into play all changes that means energy leaks through friction not gravity

what no one has yet mentioned (if you're going to be pedantic - then do it right :-) is the effect the gravity of the missile has on the earth.

As the earth's gravity pulls the missile down, the missiles gravity pulls the earth up !

Enough slingers, in the right place, with big lead missiles could alter the earths orbit and change the world's weather !

Oh yeah  :nana2:

The terminal velocity of a lead ball is greater than the speed at which it can be launched from a sling.


Whenever I have launched lead glandes on high arc distance shots, they almost seemed to accelerate on the way down.

If you can keep track of it that long.


Those balls are pretty small. The whistling grapeshot theory makes the most sense to me, if indeed they were used as projectiles...

Then, you'd think there would be a lot of them in one area.

Sub cal training, maybe?  You have to launch something or all the force never leave the launcher, which results in some very violent recoil that can damage the launcher.

If you draw a bow to full draw and release the string without an arrow, the bow can and will literally explode from the recoil forces.  It can also do that with an arrow that is too light.

So maybe the projectiles are or were loaded in a cup or bag and only partially drawn.  After the shot, the crew retrieves the bag and shoots it again.  The scattered balls are from rips on the bag?

Try pouring a dipper of lead from about shoulder high into water and see what the results are.

why have balls in a bag ?  (um, yeah lol)

Just have a ballista with a cup.
Or launch from a trebuchet.

I slung some old lug nuts yesterday and they whistled pretty well.  Though only the ones without a hole going all the way through.  It is an interesting sound and en masse would be very disconcerting.

Guys, I did work some more on the issue. In fact two young physicists calculated the effect, but I was skeptical. So I put this to a test, by building a proper test device.

Turns out the boys had a big error in their calcs and in reality things are different. The air resistance on a 22mm lead ball weighing 60 grams is quite substantial. When shot at 45 m/s (ancient sources named this as the average speed of the slingers), then the ball will fly about 160 meters far. Its end speed will be around 36 m/s, so it has lost 20% of its initial speed.

The Burnswark scenario was such that the slingers had to hit a target 120 meters away, but 40 meters up. The only way they would have hit is to shoot at an angle of around 2 degrees.

The clever Romans set their launch position exactly far enough for their average slingers to hit the target. Even five more meters and the Caledonians on the hilltop would have been out of reach.

https://www.youtube.com/watch?v=0MB7M27WnG0

@JoergS
there are a lot of variables at the experiment.
the condition of the roman slingers, were they just soldiers or professional slingers?
what slings they used? (material bulky,heavy ,longish ?)
pros with good slings would reach 50-60m/s an average soldier levied just for the occasion would reach 45m/s


about aerodynamics : projectile shape plays a huge role, bbs have a lot of drag in comparison to oblong streamlined body.
as the guy mentioned in the video magnus effect also plays a huge role
slings can orient their spin and they produce a lot
whereas slingshots they produce a lot less spin but you cant predict the axis of rotation

,so we can take advantage of magnus effect when throwing a ball shaped projectile
and we can "rifle" spin an oblong shaped projectile (most of the time)


the funny thing with physics is that it cannot predict real world situations that easily so it ends up doing the explaining afterwards

actually the balls don't need to spin to whistle.
It's just fast air moving over the surface and going into the hole that produces the sound.
Like a set of panpipes.  That's one reason the size and depth of the holes is so consistent in the found ammunition.


Quote:

Even five more meters and the Caledonians on the hilltop would have been out of reach.

No they would not have been.  The slinger would just have slung harder.
Seriously, next time you;'re doing this let me know - you need a proper slinger up there.
That distance with a lead ball is pretty much point blank range for me. Even at that low a trajectory, it's not an issue.
I've slung those distances and angles with 60gram clayballs - all day long for two days. Lead goes further with less effort.
Credit your slingers with more ability.

What historians almost never seem to understand is that our ancestors were extremely competent with their everyday tools and weapons. Far more so that most people alive today.
A sling is a tool, even the roman soldiers would have used regularly them for hunting.
So even your bog standard sling conscripts would have been a lot better than most contemporary slingers. They would also have trained regularly to keep up a long bombardment. They also would have been usign slings from childhood.

A decent slinger with a lead bullet/glande could expect to exceed 250 metres fairly easily.
Initial sling engagement of the enemy, with lead bullets would most likely have been at the 300-350 metre range.

Even with spherical ammunition you are looking at an average of 200-250 metres range. 

The 120 metre mark is most likely to avoid the larger stones that the defenders would have been slinging back. Hillfort caches do show that the defenders favoured big rocks. 120metres would put the romans out of the range of the largest rocks and shields could have deflected most of the rest.

That's the most likely explanation of the range used - absolutely nothing to do with the sling range of the attackers using small dense missiles and everythign to do with the defenders using large not so dense missiles. 

I see this has been tried.. Im am also looking into what sounds i can make with a sling glandes.

All for the fun of 3d printing, Im not trying to recreate anything historic as im sure it was with just a hole drilled in.

Worth noting that solid 3d printed Glandes hold up well in most filaments. I throw them in a place where they often hit rocks too.

Some tests... more to come https://www.instagram.com/p/Cilok-Xpvwb/

What filaments are you making the solid glande from ?

Also to properly hear the sound you need to be at the impact end :-)

I've had a lead glande slung directly at me, and just one glande sounds like a swarm of bees !
But makes no real noise at the slingers end