Alright, since leddit is full of retards, I'll post here:

>implying /k/ isn't full of retards

>>34735677
like owl wings

>>34735714
I mean, at least (some) of /k/'s retards know that they're retards, reddit is full of retards pretending to be particle physicists.

>>34735677
first I assumed it was a simple google question.
Zero mention anywhere about how fins stabilize super sonic

Second I assumed tenk bullets dropped subsonic.
they velocity like 5k FPS


So I guess bump...

>>34735714
the world is full of intelligent lazy poor people.

>>34735677
Reduced effectiveness? Yes. However they are fin stabilized not fin controlled. You don't need very much control surface or force to stabilize.

They're not, that's how.
If they're in the wake you need to fire the faggot that designed it.

>>34735782
I know that they're passively stabilized, but to me, those fins should do jack shit. Have you ever seen those homemade shotgun darts where people put insane CNC machined fins in? They totally don't work, even when the dart is put through a rifled choke, mostly because the fins look like they're not doing shit.

https://www.youtube.com/watch?v=coWJDfcdR60

it wiggles without the fins, but why?

>>34735807
Doesn't the wake extend out conically from the furthest forward point on the projectile?

>>34735811
See
>>34735807
When designed by a competent engineer who knows what the fuck they're doing the fins stabilize just fucking fine. A guy designed a fuel-air gun that worked at 200 atmospheres several years ago and made a nylon saboted tungsten carbide cored penetrator to shoot out of it. Because he actually designed the fucking thing properly, it flew laser fucking straight going fuckoff fast and punched through the equivalent of a Panzer IV's side armor.

>>34735830
Yes you dilweed, but APFSDS darts are long as fuck and mega thin for a fucking reason.

File: Obus_501556_fh000022.jpg (64KB, 1077x1077px) Image search: [Google]

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>>34735811
How well does a rod with no spin stabilization fly at 1800m/s? It doesn't.

You have to look at this objectively. The APFSDS darts don't tumble, therefore there must be some stabilizing force. Furthermore I guarantee the projectiles where designed by multiple aerospace engineers and test aerodynamically hundreds of times.

Also APFSDS darts have pretty considerable control surfaces for their size.

>>34735677
If you look at a bullet traveling in slow motion, it almost acts like a loose spiral football, with the back of it rotating around a small axis while the front is more stationary. Rear fins on tank and artillery shells increase friction on the back end, which in turn helps tighten the spiral for more accurate flight at longer ranges.

>>34735920
Aren't M1 Abrams barrels smoothbore now?

>>34735920
whaaaaat?
Is it a two part bullet?

>>34735677

how does a boat float when it's following it's own wake?

there's still air behind the shockwave, retard.

>>34735677
>How do APFSDS fins work if they're in the supersonic wake of the projectile tip?
Is the supersonic wake a vacuum?
If no, then you're looking at friction in fluid medium - just like with any other fin.

>Shouldn't the low pressure zone reduce the effectiveness of an aerodynamic surface?
Yes, it should.
Does 'lowered effectiveness' mean 'no effect at all'?

>>34735938
Yes, but that's only because they are designed to penetrate heavy armor russian tanks such as the T90. Rounds that do NOT rotate penetrate heavy armor better because the force of impact is localized more in the impact zone, instead of being pushed outwards by spiral motions.

The main rounds used for this, such as the M829A2, has no fins, because it does not spin and is not guided.

Another round used in the smoothbore, the M1028, is basically a big ass shotgun shell that's used to clear out areas of light armored interest, such as infantry, light vehicles, shrubbery, etc.

File: Anglo Saxon Wat.jpg (65KB, 305x450px) Image search: [Google]

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>>34736017
This is wrong on so many levels.

>>34736056
explain

File: Lazy Dog Bomb in Hand.jpg (133KB, 800x600px) Image search: [Google]

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>>34736056
War is full of many fun weapons. Canister shells, beehive flechet shells, and so on.

Pic related is super fun. They're called Lazy Dog bombs and you'd throw a few thousand out of an airplane and they would annihilate anything below.

>>34736056
Kinetic energy can be dispersed by centrifical force in a rotating object

>>34736017
>M829A2, has no fins
it has aluminum fins what are you smoking?

>>34735677
>Shouldn't the low pressure zone reduce the effectiveness of an aerodynamic surface?
guess you just have to do the fucking math how big fins you need for a given velocity am i right?

>>34736017
>instead of being pushed outwards by spiral motions.
hahahahahahhaha

no, it's because a smoothbore fires faster than a rifle because no energy is wasted trying ti spin it

>>34736733
The reason tank guns are smoothbore is the switch from HEAT (High Explosive Anti-Tank) to kinetic energy rounds sabot as the primary anti-tank round. Kinetic energy rounds are subcaliber rounds (smaller than the bore) and aren't effective if the spun by rifling. The use of a sabot around the penetrator provides a better gas seal and the smaller projectile achieves much higher muzzle velocity.

The reason for the shift was advances in protection against HEAT rounds via explosive reactive armor, spaced armor, composite armor and so on. Their effective penetration began to fall and with the development of kinetic energy penetrators, they found not only was the KE round easier to make, it was able to slice through the defenses arrayed against HEAT rounds. HEAT rounds were (and still are) popular in missile warheads, the dominant anti-tank weapon other than another tank. So HEAT defenses dramatically reduced the effective of HEAT warheads, especially those on man-portable anti-tank missiles.

Taken together, the smoothbore kinetic energy round can penetrate twice or more the amount of armor as compared to a HEAT round. HEAT rounds also required a smoothbore to eliminate the spin to allow them to be effective. Previous generation kinetic armor piercing round needed rifling to work and were more accurate at long range but lacked HEAT penetrating power. HEAT lacked accuracy at long range due to the smoothbore design and lack of stabilization for the round.

Smoothbores are easier to manufacture as they don't require rifling or a separate lining. There are rifled guns that fire sabot rounds now due to the development of driving bands that can spin around the penetrator without spinning it up and allow it to retain its effectiveness. But those came later and the smoothbore gun and sabot combination is simpler and cheaper to make and was an easier solution at the time of its mainstreaming in the 1970s.

>>34735677
If the fins extended past the shock boundary, they would create hellacious drag, but it's not like the air inside the shock cone is stationary relative to the projectile. The fins interact with the airflow inside the shock cone.

The dumbfucks who can't make a shotgun APFSDS round aren't aerodymamicists.

>>34735850
better penetration

>>34735677
Don't ask here. Nobody on /k/ knows anything about penetration.

>>34735677

I'd assume that at a basic level it would work like a badminton shuttlecock. It's stabilized by having greater density at the nose, and greater drag at the tail.

File: 600px-M829A2.jpg (17KB, 600x300px) Image search: [Google]

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>>34736017
>Rounds that do NOT rotate penetrate heavy armor better because the force of impact is localized more in the impact zone
Moron.

>the M829A2, has no fins
Pic related.

>>34736377
Hello mr "I'm too fucking stupid to remember there's a difference between APFSDS and HEAT"

>>34738675
OP's point is that you need air at the tail to have drag at the tail.

>>34736796
Smoothbores gun barrels are much smaller in thickness than rifled guns, making larger guns lighter. A 105mm rifled gun is noticeably thicker than 120mm smoothbore.

HEAT is fired from both rifled and smoothbore guns. In the rifled guns they have a slip ring or driving band that doesn't let the round take up as much of the spin as they would otherwise have because that spinning action disrupts the HEAT round's cutting cone of explosively propelled metal. They still spin just not as much.
Similar for sabot that was fired from rifled guns. They had driving bands to lower the amount of spin but fins for flight stability.
On smoothbore and rifled guns the fins are slightly canted to impart and keep spin on the rounds. IIRC it's about 1 spin per 100m, or 15 rotations a second.

Both HEAT and sabot were highly accurate from rifled guns if the fire control computer had a good range finder. You can expect to hit a stationary vehicle sized target at 4km with either round with the first shot. They are still both accurate on more modern smoothbores.

Rounds like HESH and WP used the rifling to make the rather slow rounds accurate at long range. I'm not sure if anyone uses HESH on smoothbores yet.

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>>34735677
>How do APFSDS fins work if they're in the supersonic wake of the projectile tip? Shouldn't the low pressure zone reduce the effectiveness of an aerodynamic surface?

Control surfaces in the wake of the cone still work. It's actually better for them to be behind the main shock cone, actually (not that these surfaces don't have their own shock structure though).

Schlieren of jet fighter geometries shows how the whole body of the aircraft is behind the shock cone, and yet, they can still be controlled (obviously).

However, since your control surfaces will be in high-transonic, you might see control reversal if your wing isn't stiff enough (i.e: aeroelastic effects). Not a problem in current aircraft.

>>34738915
>OP's point is that you need air at the tail to have drag at the tail.
There's plenty of air at the tail.

>>34735840
>A guy designed a fuel-air gun that worked at 200 atmospheres several years ago and made a nylon saboted tungsten carbide cored penetrator to shoot out of it. Because he actually designed the fucking thing properly, it flew laser fucking straight going fuckoff fast and punched through the equivalent of a Panzer IV's side armor.

Link?

>>34738635
Ooh, three snaps in a circle.