I am a little disappointed if this is true.
I still feel that using a single, large thrust engine would be a better solution to using two medium thrust ones.
Some back of the envelope calculations.
Firstly, the 8.5t and 9.5t figures are full afterburner thrust, which isn't all that useful.
Since the WS13 is pretty much the same as an RD93 in terms of thrust, I am just going to use RD93 figures for it as there are no reliable WS13 figures around that I know of.
Each RD93 weight 1.15t and produce 5t of thrust. So taking we have combined weight of 2.3t and 10t thrust.
I will use AL31FN figures with the WS10A, since again I am not 100% that the figures are reliable for it, so that is 1.54t weight and 7.8t dry thrust.
In terms of net thrust, a WS13 powered J19 will have 2.2t more net thrust compared to a WS10A powered J19.
But bare in mind that two WS13 is 0.75t heavier than a single WS10A. There will also be additional structural weight from having two medium engines compared to a single large one, but since I cannot find a reasonable estimate for how much this could be, and to make the calculations easier, I am going to assume that the two planes will have exactly the same weight excluding the engines (and I am going to say 8t excluding engines just for illustration purposes), which is very generous for the WS13 powered J19.
So, the WS13 powered J19 (which I shall be referring as the J19A for simplicity sake) will weight 10.3t and have 10t dry thrust to give a dry T/W ratio of 0.97.
The WS10A powered J19 (referred to as J19B from here on) will have a weight of 9.54t and 7.8t thrust to give a T/W ratio of 0.83.
However, WS13 and WS10A will only be an interim solution, and the full spec J19 will have either the next gen medium thrust engines (and I will call them WS16 for illustration sake) or the WS15.
Now, assuming a similar wet to dry thrust ratio between the WS13 and WS16 would yield a dry thrust of 5.9t for a 9.5t full afterburning engine. Assuming a similar (dry) T/W ratio as that for the WS15 (which I will use F119 figures to proxy since that is the closest estimate we have for the WS15, Bill Sweetman give an estimate of 26000lb/11.79t dry thrust for the F119, and the F119 weighs 1.77t) of 6.66, gives an engine that weighs 0.89t each.
So assuming everything else is constant, with the WS16 weighing 0.89t and producing 5.9t of thrust, the J19C will have a T/W ratio of 11.8t/9.78t=1.21.
A WS15 powered J19D will have a T/W ration of 11.79/9.77=1.21
Bare in mind that the empty weight net of engines of a single engined J19 is going to be considerably less than that of a twin engined version, and you can see that the J19D is almost certain to have a better T/W ratio than a J19C.
In addition, the J19D would enjoy all the additional advantages of having a single large engine compared to two medium ones like lower fuel consumption and operational costs; more internal room for fuel, weapons bays and avionics; which together translates into greater payload and range; additional logistical savings from sharing the same engine as the J20 and so on. All that with a better T/W ratio to boot, and with at the very least the same drag ratio, but probably better, it will translates into a more agile aircraft to boot.
