The SU-34 and its cousins typically carry around 150 rounds of ammo for their 30mm gun. That’s a fraction of what the A-10 carries.
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That's a part of my point. The SU-34 is somewhat of a "one size fits none" A/C -- but not nearly as much so as the F-35.
For example, the SU-34's 30mm round is probably on a par with some of our chaingun rounds -- and is nowhere near as large and devastatingly kinetic as the GAU-8 30mm round.
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IMO, it would take some serious design, engineering, and materials work to outdo the A-10's purpose-built design -- for CAS and armor-killing.
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But the SU-34 shows how certain parameters could be extended (i.e. range/loiter time) without totally ruining the A-10's CAS functionality...
One example of optimization that could be done might be in the cyclic rate of the gun. (Most folks haven't noticed that the GAU-8's ferocious max operating rate has been quietly "dialed back".)
Optimizing the rounds-on-target for a two-second burst -- to give a high kill probability on a MBT -- might allow for a less aggressive (smaller and lighter) drive and feed system design for the same devastating round... And, pairing that with improved target lock-on/tracking (a la Abrams fire control) could improve that efficiency even farther.
The A-10 is a phenomenally successful second generation CAS platform -- but, it's time to start thinking -- hard -- about an optimized third generation dedicated CAS platform. ~~~~~~~~~
Bottom line: somewhere between the A-10 and the SU-34 lies a design for an unbelievably effective "Thunderbolt III" CAS platform. (But, don't try to make a fighter or bomb truck or cargo plane out of it, too...)