stancrist said: I think your "area of fragments" comparison is badly flawed, because it assumes that (a) the entire ammo load will be fired, and (b) there would be an even distribution of projectiles and their fragments

Which is better for hitting such a target as fast and as hard as possible

Its not so much firing the whole load, but rather showing area per loadout. I'd think the #'s would hold up the same for comparing say 25rd bursts between weapons; basically the point is that for any given burst size, the 30mm will be able to have a much higher area of fragments / greater fragment density per area. 

Now in terms of destroying vehicles, 30mm is rated to defeat 25mm RHA at 50 degrees using its HEDP design. I've not been able to find an exact penetration level for the 20mm (Nammo says over 10mm at 1000yd) but I'd be surprised if the HEI/SAPHEI was equal/better then the 25mm at 50 degrees of the 30mm HEDP. 

ROF and time of flight is better for 20mm though, which could be important for hitting a target while flying. 

One transonic round every few seconds, far away from flak's effective range.

Seriously now, if they're thinking about dealing with air defenses better than AKs (or the occasional MANPADS / RPG wielder), then neither 20mm nor 30mm won't do it.

If they do want to use it for spray and pray against scattered soldiers, either will do, but I'm also of the '30mm is better' team.

gatnerd said:

Its not so much firing the whole load, but rather showing area per loadout.

Yeah, I understood that.  And I still think it's a meaningless comparison, for the reasons previously stated.

gatnerd said:

I'd think the #'s would hold up the same for comparing say 25rd bursts between weapons; basically the point is that for any given burst size, the 30mm will be able to have a much higher area of fragments / greater fragment density per area. 

1.  Your focus is still on fragmentation, which doesn't seem very relevant to neutralizing what the Army perceives as the primary threat to FARA.

2.  If you want to make such a comparison, it seems like it would be more realistic to compare 1-second bursts (25 rds 20mm vs 10 rds 30mm).

gatnerd said:

Now in terms of destroying vehicles, 30mm is rated to defeat 25mm RHA at 50 degrees using its HEDP design. I've not been able to find an exact penetration level for the 20mm (Nammo says over 10mm at 1000yd) but I'd be surprised if the HEI/SAPHEI was equal/better then the 25mm at 50 degrees of the 30mm HEDP. 

As would I.  All I can say is that apparently the Army thinks 20mm has sufficient penetration capability.

stancrist said:

If you want to make such a comparison, it seems like it would be more realistic to compare 1-second bursts (25 rds 20mm vs 10 rds 30mm).

Thats fair.

20mm x 1 Second @ 1m radius = 25x 3.14m2 = 78.5 m2 frag coverage

20mm x 1 second @ 2m radius = 25x 12.57m2 = 314.25 m2 frag coverage

30mm x 1 second @ 4m radius = 10x 50.27m2  = 502.7 m2 frag coverage 

So for say, quickly strafing an ATGM team or eliminating a guy with a MANPAD, 30mm still seams the way to go even with the lower ROF. 

Ultimately, theres a reason that the US went to 30mm from 20mm when it went from Cobra to Apache, and why nearly every modern attack helicopter has also gone 30mm. 

gatnerd said:

Ultimately, theres a reason that the US went to 30mm from 20mm when it went from Cobra to Apache

Yup.  And there are reasons why FARA, like its predecessor, the RAH-66 Comanche, has a 20mm gun.

From gatnerd

"Ultimately, theres a reason that the US went to 30mm from 20mm when it went from Cobra to Apache, and why nearly every modern attack helicopter has also gone 30mm. "

The FARA is supposed to be a light scout with limited attack capability. Not an attack chopper. 

A big gun with high rate of fire and large amount of ammunition is ideal. But weight of  gun and ammunition and recoil forces have to be taken into consideration. These are even more important consideration on a light helicopter. 

The OH-58 that the  U.S. Army previously used in the scout role only had a .50 machine gun. So a 20 mm is an upgrade. 

17thfabn said:

The FARA is supposed to be a light scout with limited attack capability. Not an attack chopper.

Well, like the Comanche program before it, and several others (this is the 4th program to replace the Kiowa) there appears to be pretty serious mission creep, and the design is looking increasingly geared as a next generation mini attack helicopter.

Specifically, its become envisioned as a 'day 1' attack asset operating in A2AD contested zones against peer enemies. 

https://www.forbes.com/sites/erictegler/2020/07/22/army-eyes-replacing-apache-with-fara-as-its-kick-in-the-door-attack-helicopter/

Another article showing that FARA is really more 'attack' then scout, and would indeed likely be better off with a 30mm if recoil forces will allow.

https://www.thedrive.com/the-war-zone/27170/army-to-replace-nearly-half-of-its-apache-gunships-with-future-high-speed-scout-helo

“The FARA will only replace Apaches in our heavy attack reconnaissance squadrons and this represents about half of the Apache fleet,” the spokesperson said. “The FARA will not replace Apaches in the Attack Reconnaissance battalions.”

“We’re looking for an aircraft that, without going into specific requirements or classifications, essentially goes further, can see further, can acquire specific targets further and can engage at greater ranges than current exist, and has greater legs – can fly further with a greater payload of weapon systems,” Milley explained on Capitol Hill. “We’re already moving in that direction with research and development and the development of prototypes.”

If the Army existing AH-64-equipped units  – Attack Reconnaissance Squadronsand Attack Reconnaissance Battalions – seem confusingly similar, that’s because they are. 

The assumption is that any successor to the OH-58 would not have the capability to provide the same volume of fire as the AH-64, but this might not necessarily be the case.

The Army's abortive RAH-66A Comanche stealth helicopter was also supposed to be an OH-58D replacement and work in concert with AH-64s. But its "Reconnaissance Attack" designation was also reflective of the fact that it had provisions to carry a loadout very similar to that of the Apache, and certainly much heavier than that of the Kiowa Warrior, in a non-stealthy configuration, as necessary.  

“We’re looking for an aircraft that...can engage at greater ranges than current exist..."

Perhaps 20mm provides longer effective range with shorter time of flight than 30mm?

Thats possible, it would be cool if we had a BC calculator for those.

Offhand though I don’t think it would have much more effective range if any.

30mm has ~2.5x the mass of 20mm, so even with an inferior shape, it probably has a higher BC and velocity retention then 20mm.

Beyond that, 20mm relies on kinetic energy for metal penetration, whereas 30mm uses a shaped charge HEDP, which should function pretty much the same across a wide velocity envelope (guess on my part based on 40x46/53 and various LAW/RPG HEAT/HEDP warheads penetrating steel well at 230-800fps)

Happy Thanksgiving Stan.