The inability to control roll and yaw channels when flying at low speeds because the engines are located close to each other.
Ummm... it contradicts itself... this problem with the PAK FA design is a stupid comment when in the paragraphs before this the article states:
The engines are also placed at an acute angle relative to the vertical plane, allowing thrust vectoring – an area in which Sukhoi excels – in the longitudinal, transverse and travel channels. The engine nozzles point outwards, which transfers a significant portion of the control of the aircraft to them even at low altitudes. This considerably improves flight safety.
So with the engines placed far enough apart for there to be a large weapon bay between them how can the engines be located too close together?
The Typhoon and Rafale have engines that are too close together for roll control at low speeds using thrust vector control, but they don't have thrust vector control so it doesn't matter for them.
Like the Flanker and the Fulcrum the PAK FA has spaced engines and is perfectly able to use thrust vectoring for roll and yaw control at low speeds or no speeds in stalls and super stalls (ie flying backwards).
The curved shape of the air intake duct requires an increase in their length, and therefore, the mass of the airplane.
The tiny increase in weight is totally unimportant compared with the reduction in RCS by not having the engine visible to enemy radar.
The inability to ensure the “vanishing” of the aircraft during supercritical angles of attack.
No stealth aircraft ever created is stealthy from all angles... the fact that the PAK FA might not be so stealthy when nose up at 120 degrees is irrelevant... it is not going to remain in that position long enough for an enemy to get a missile lock and fire a missile to hit the target... when the PAK FA drops its nose and continues normal flight the RCS will drop down to stealthy figures and the missile and enemy aircraft will lose radar lock... and the datalink between the launch aircraft and the missile will be an active radar signal the PAK FAs L band wing mounted radar can detect and track.
The use of fixed keels with rudders requires increasing the required area of the vertical stabiliser to provide directional stability at supersonic flight conditions, which leads to an increase in weight tail, and hence, the aircraft in general, and to an increase in drag.
the vertical tail surfaces on the PAK FA are tiny compared with the F-22 and F-35.
What else are they going to complain about... have they painted it the wrong colour?