RedMercury
Junior Member
Dug up an old article about the research and development of the Chinese 120mm smoothbore in the Type-89 tank destroyer.
It mentions that at 1000m, 50 m/s of velocity was lost. Since velocity loss (friction) is proportional to velocity squared, more velocity is lost when the projectile is faster, so the velocity over time curve is lower than a straight line (concave), so the velocity versus distance curve is also concave. The muzzle velocity on the 125mm from the ZTZ-99 is something like 1780 m/s.
At 2km, the loss would probably be somewhat less than 100m/s. Assuming it is 100m/s, and the ZTZ-99's APFSDS round is similar in drag as the experimental 120mm roundn, then the velocity at 2km would be about 1680m/s. This is about 6% loss in velocity or 12% loss in energy.
Now let's make a whole lot of assumptions to compute a ballpark estimate. If the old 125mm APFSDS round which penetrates 600mm at 2km has similar drag and energy to penetration efficiency as the new round, then...
Let's assume this old 125mm APFSDS round also lost 12% energy. This is a optimistic assumption because we know it travels slower so it should lose less energy from drag.
ME_old x 0.88 x E = P_old = 600mm
where ME_old is muzzle energy of old 125 mm APFSDS, and E is efficiency factor (energy to penetration conversion), and P_old is penetration of old 125mm round.
ME_new x 0.88 x E = P_new
From our assumptions, E is the same. From Challenge's post, ME_new is ME_old x 1.45. It follows that P_new is 1.45 x P_old, or 870 mm.
Let's review our assumptions. First, we assumed similar drag. A new generation of round would probably be similar or better in drag. Second, we assumed the old round lost as much energy at 2km as the new round, this is a optimistic assumption, as it probably lost less energy because it was slower. The third assumption is similar efficiency, which is probably reasonable or pessimistic. Another assumption for convenience I made was the linearity of slow down versus distance, which is pessimistic. I would guess the true figure is somewhat lower than 870mm, which is pretty close to the chief designer's claim of 850mm. That's with tungsten APFSDS. With DU, add about 10% so, something like 935mm. So the chief designer's claims are quite reasonable.
Now for some fun. At 1km, assume 50m/s slow down, or 1730m/s terminal velocity for ZTZ-99's 125mm. This is like 6% energy loss. Penetration would be 600 mm x 1.45 x 0.94 / 0.88 = 930 mm for tungsten or 1020mm for DU. Most MBT combat distances in Europe are around 1.5km. China and periphery is known to be bad for tanks, except for the flats near Mongolia and perhaps open spaces in central asia. So 1.5km engagement distance is not too unreasonable. At 1.5km, energy loss is 9%, so 600 mm x 1.45 x 0.91 / 0.88 = 900 mm for tungsten, 990 mm for DU.
From these ballpark estimates, it is plausible that the designers of the ZTZ-99 are quite satisfied with its firepower. They went the route of high velocity (versus the route of high mass penetrator with relatively lower velocity, as in the M829A3). High velocity has higher dropoff in penetration versus distance, but at point blank, the penetration is quite high. High mass has better energy retention, but the max penetration at point blank is not as high. So Chinese tanks are suited to fight in closer quarters, where its high close range penetration makes its weapon more effective, while a heavier, lower muzzle velocity round should be paired with the doctrine of sniping from distance.
It mentions that at 1000m, 50 m/s of velocity was lost. Since velocity loss (friction) is proportional to velocity squared, more velocity is lost when the projectile is faster, so the velocity over time curve is lower than a straight line (concave), so the velocity versus distance curve is also concave. The muzzle velocity on the 125mm from the ZTZ-99 is something like 1780 m/s.
At 2km, the loss would probably be somewhat less than 100m/s. Assuming it is 100m/s, and the ZTZ-99's APFSDS round is similar in drag as the experimental 120mm roundn, then the velocity at 2km would be about 1680m/s. This is about 6% loss in velocity or 12% loss in energy.
Now let's make a whole lot of assumptions to compute a ballpark estimate. If the old 125mm APFSDS round which penetrates 600mm at 2km has similar drag and energy to penetration efficiency as the new round, then...
Let's assume this old 125mm APFSDS round also lost 12% energy. This is a optimistic assumption because we know it travels slower so it should lose less energy from drag.
ME_old x 0.88 x E = P_old = 600mm
where ME_old is muzzle energy of old 125 mm APFSDS, and E is efficiency factor (energy to penetration conversion), and P_old is penetration of old 125mm round.
ME_new x 0.88 x E = P_new
From our assumptions, E is the same. From Challenge's post, ME_new is ME_old x 1.45. It follows that P_new is 1.45 x P_old, or 870 mm.
Let's review our assumptions. First, we assumed similar drag. A new generation of round would probably be similar or better in drag. Second, we assumed the old round lost as much energy at 2km as the new round, this is a optimistic assumption, as it probably lost less energy because it was slower. The third assumption is similar efficiency, which is probably reasonable or pessimistic. Another assumption for convenience I made was the linearity of slow down versus distance, which is pessimistic. I would guess the true figure is somewhat lower than 870mm, which is pretty close to the chief designer's claim of 850mm. That's with tungsten APFSDS. With DU, add about 10% so, something like 935mm. So the chief designer's claims are quite reasonable.
Now for some fun. At 1km, assume 50m/s slow down, or 1730m/s terminal velocity for ZTZ-99's 125mm. This is like 6% energy loss. Penetration would be 600 mm x 1.45 x 0.94 / 0.88 = 930 mm for tungsten or 1020mm for DU. Most MBT combat distances in Europe are around 1.5km. China and periphery is known to be bad for tanks, except for the flats near Mongolia and perhaps open spaces in central asia. So 1.5km engagement distance is not too unreasonable. At 1.5km, energy loss is 9%, so 600 mm x 1.45 x 0.91 / 0.88 = 900 mm for tungsten, 990 mm for DU.
From these ballpark estimates, it is plausible that the designers of the ZTZ-99 are quite satisfied with its firepower. They went the route of high velocity (versus the route of high mass penetrator with relatively lower velocity, as in the M829A3). High velocity has higher dropoff in penetration versus distance, but at point blank, the penetration is quite high. High mass has better energy retention, but the max penetration at point blank is not as high. So Chinese tanks are suited to fight in closer quarters, where its high close range penetration makes its weapon more effective, while a heavier, lower muzzle velocity round should be paired with the doctrine of sniping from distance.
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