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Comment by danielvf | Hacker News Reader

Take a cube, half the size of each edge, and the cube weighs one eighth as much.

In this case, the 20% reduction in diameter, while keeping the same shape means the projectiles are less than half the size.

In a counter-insurgency role, the A-10 fires roughly 65 13.3 ounce high explosive shells in one second. Roughly 54 pounds of high explosive shells per second.

The F-35 is planned to fire 55 6.5 ounce projectiles per second. That's 22 pounds of shells per second.

54 lbs vs 22 lbs is a significant difference.

Though, as others have said, it's the ammo capacity that is the major problem with the F-35's proposed gun. Only being able to make one or two guns runs before being out of ammunition precludes any kind of sustained ground support.

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If you’re shooting tanks then sure it's a significant advantage, but when the target is a pickup truck with a machine gun mounted on the back you don't need that much penetrating power.

There are walls and other obstacles in the field that a gun designed to shoot through a tank can go through. You do need that much penetrating power to make sure their hidey hole is not safe.

The A-10 was designed for an anti-tank role. So, I suspect there rounds are generally overkill. A smaller round than you might think can penetrate a brick/cinderblock wall. For hardened targets an Air-to-Surface missile can have a lot more penetrating power. In the end some compromise between the two is probably ideal.

That said if you’re doing dedicated ground support I think you’re going to want a lot more round than an F-35 is designed for.

I am not sure, if you even need 25mmm in this particular case. I would say that with the right aiming even a machine gun will do it.

But when you do not look at the penetrating power alone, but the blowing effect, than a bigger round can hold more explosives (of course, I don't know, if the A-10 Gatling cannon can also take explosive rounds instead of the armor breaking rounds).

But of course the parallel poster is right: there are several things to penetrate -- particularly when partisans are heavily covered.

A-10 cannot penetrate modern armor with it's gun. It had difficulty with T-72 when it was designed and could only kill them from the rear.

The A-10 cannon is not comparable with that of a modern tank. Just compare the numbers:

A-10: 30mm Gatling

M1 Abrams (and other comparable tanks): 120mm (Russland's newest tank has a 140mm gun as much I remember)

That is a huge difference! The only advantage of the Gatling is the high firing rate -- but it is definitively no match for the armor of a modern main battle tank. I also never implied that. When the A-10 was designed, tank armor was less advanced and today the A-10 is mostly fighting against light to medium armored targets. Many countries even in their regular army have still very old tanks in service.

You also get to add the forward velocity of the aircraft so it's Mass * (v1 + v2) ^2. Arguably the largest advantage of the A-10 is it keeps tank designs 'honest' as it's free to engage from just about any angle which forces tanks to add quite a bit more armor.

That is right. Most tanks are designed, that the frontal armor is the thickest and many of the WW2 tanks where very weak at the top. They where basically designed for frontal tank vs. tank (or anti-tank) attacks.

Today's tanks have to take air attacks into account -- with much better top armor but also better armor at the other sides too.

Your calculation is right, I guess, but still 120mm has just overwhelmingly more hitting power than 30mm rounds.

er that is the type of engament that the a10 is designed for top attacks on the thin armour - just as the ww2 stuka with 37 mm wasn't firing at the thick armour but the weaker top armour

Exactly. It is the same with artillery or tank ammunition -- a small increase in diameter makes a huge impact.

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