It was asked that if the Su-47 Berkut with its forward swept wings is more agile and maneuverable than the F-16.
The answer is: Not necessarily. The reality is that little is known about the -47's flight characteristics and its enabler: flight controls avionics.
Here is why...
People uses the word 'aerodynamics' pretty casually. Even aerodynamicists are guilty of it. The word 'aerodynamics' is about the study of air flow over structures, whether that structure is a brick or an arrow, it does not matter. As long as the structure is experiencing airflow over its body, whether it is moving or simply standing still and the wind blowing across it, we want to understand the behaviors of that flow. When we commented 'more aerodynamic' or 'improved aerodynamics', we really mean that air flow over an arrow is
MORE EFFICIENT than air flow over the brick. The word 'efficient' implies a sort of balance between many competing and even conflicting factors with conflicts the worst and most problematic to meet a goal of a certain measure of 'efficiency' in doing some things. Lift conflicts with weight, for example, so then in aviation, weight is a penalty. Profiles (drag) conflicts with speed so sailboats wants hulls to present as small the profiles as possible, even down to the millimeters when a lot of money and national pride are at stake in international competitions.
Can the brick be as agile and maneuverable as the arrow? Absolutely. Provided that is has an overwhelming potential power in propulsion and flight control capabilities to compensate for its far far less efficient aerodynamics. So to be 'efficient' in aerodynamics and in flight is to have the least of anything to achieve a certain flight condition and maneuvers are conditions. We want the smallest frontal profile against the air flow, be it in the fuselage or wing leading edge (LE). We want the best combination of wing surface area to provide lift and at the same time, minimize drag. We want maximum control of the aircraft when we transition from one flight condition/state to another, aka 'maneuvers', but we want the least quantity of flight control surfaces/elements to make those transitions. So if we have to skew so terribly propulsion and flight controls for the brick so that it can perform as well as the arrow, we can make the brick airborne but it would not be a very efficient aircraft compared to the arrow.
Look at the P-47 (Thunderbolt) , P-51 (Mustang) , F-86 (Sabre), and the F-16 (Falcon). Yes, I know about the MIG-15/17 who were technical peers to the Sabre.
The T-bolt and the 'Stang represents the 'old school' of aerodynamics and flight controls with the 'Stang pretty much the end of the evolution of that 'old school'. Both aircrafts were designed to be stable in flight, hence the straight wings and quite conventional flight controls elements layout. With the Sabre and its swept wings, we began to move into the 'unstable' flight regimes but there is a catch: flight controls.
We had nothing revolutionary in terms of flight controls for the Sabre. Yes, we added hydraulic power but essentially it was just mechanical muscles for the pilot. The entire flight control system came from the 'old school' of the WW II era fighters and the truth is that this system severely limited what the Sabre could have done. Yes, there were structural and human limitations. The Sabre could not have reach the Falcon's 9gs capability or have the same turn rates. But within those limitations, the Sabre could have done better as a fighter, as in more efficient, than what we know of it today. Back in WW II, when pilots put the T-bolt and the 'Stang into dives, aerodynamic forces put so much of a 'clamping' force on the aircraft that it took all of a pilot's physical strength to pull aft on the stick to get out of that dive. And sometimes some pilots did not have the necessary physical strength. The Sabre's hydraulics remedied that one danger and provided additional power to actuate the flight controls surfaces at high speed, but conceptually no more.
The F-16 radically altered the aviation arena and still to this day, aviation enthusiasts, military and civilian, still have no idea or at best underestimate that radical change. The Falcon's 'inherent instability' phrasing is casually thrown about but the reality is much more profound than that: Inherent instability opened up the
RANGE of maneuvers an aircraft can do.
To appreciate what the Falcon did, we must accept a basic understand of aerodynamics and flight controls relationship: Aerodynamics is about the study of air flow over a structure and is not the same as flight controls stability, which is about maintaining controlled flight through transitions of conditions/states.
The more aerodynamic, or more efficient air flow, an aircraft, the better it will transition from state to state. Flight controls is about the
EXPLOITATION of that efficiency to maintain controllability through those transitions. That is why for the arrow, it requires three or four flight control elements to maintain stable flight while with the brick, we would have to install dozens of little fins on all sides.
But the problem is still the same for the Falcon as the Sabre: Flight controls limitations.
Inherent instability often induces oscillations. Oscillations occurs when a body under aerodynamic forces tries to return to a controlled/stable state, failed, tried again, and failed again, and so on. We already know, since the WW II era German aerodynamicists with their aft swept wings design, that swept wings tends to produce oscillations. But we are not designing a stable aircraft. We want a maneuverable aircraft and a tendency to change conditions/states is favorable to maneuvers. The oscillation problem arises when we force the aircraft to return to its previous stable condition, we failed by overcompensation, and repeat the failure one cycle after another. Improved FLCS fixed this problem and therein lies the clue to maneuverability, or rather clue to the limiting factor to greater maneuverability and controllability through state transitions: Flight controls.
Coupled flight controls system (FLCS) means all flight controls surfaces works in concert to execute a stable and controlled transition. The 'coordinated turn' interconnect is an excellent example of a C-FLCS in state transition. In the early days of aviation, that interconnect is the pilot, and those early days went from WW I to the Korean War era. Every pilot is trained on how to use the stick and rudder pedals appropiately to make a nice smooth maneuver. Take-offs and landings are necessary but if a candidate cannot make a coordinated turn, his IP would dismiss him from flight training immediately. Then from the Korean War era to the Vietnam War era, we introduced mechanical interconnects, then computer assisted mechanical interconnects, like in the F-111 and F-15, to the point where coordinated turns remains in training while the aircraft does the work in real life.
Inherent instability threw all of what we know of flight control systems engineering out the window. Now we have an aircraft -- the basic layout of fuselage, wings, and stabilators -- that has such a high tendency to change conditions/states that we simply cannot fly it. It is aerodynamics, as in efficient more to the arrow than the brick, to be sure, so aerodynamics is not an issue. So when the aerodynamicist turned the aircraft over to the FLCS engineers, the problem for those engineers is how to make this aircraft go from A to B destinations without crashing in between. When we installed rate gyros, accelerometers, computers, large stabilators, static fins, and so on, this is a clue -- that the limits on what an inherently unstable aircraft can do is: Flight Controls.
In manned flight, the flat turn is a bad thing. No pilot wants to be in those rapid transitions of conditions/states. But the pilot of the F-16/CCV (Controlled Configured Vehicle) did. The F-16/CCV aircraft had two vertical canards that is
NOT coupled to the rest of the FLCS. The pilot would actuate these canards, entered the aircraft into that dreaded flat turn, thereby radically altering air flow over the aircraft, increasing the tendency to uncontrolled flight, but then the other flight control surfaces which remained coupled together, would work in concert to prevent oscillations, and the result is the aircraft able to make a
CONTROLLED flat turn. Another clue that the limits on what an inherently unstable can do is: Flight Controls.
Another clue is the F-18's air/speed brake system. Most aircraft have dedicated speed brake structures. The F-16 has split rear strakes. The F-15 has a canted structure topside.
But not the F-18...
Flying the F/A-18F Super Hornet
2.2 The Virtual Speedbrake
The next handling demonstration involved involved the speedbrake and some high alpha low speed handling, an area in which many fighters experience problems in maintaining direction and avoiding a departure into uncontrolled flight.
The first demonstration involved the virtual speedbrake effectiveness and handling in this configuration. The F/A-18A-D, like the F-15 series, employs an upper fuselage hydraulically deployed speedbrake. The Super Hornet has no such device, yet achieves the same effect through what can only be described as digital magic. The speedbrake function is produced by a balanced deployment of opposing flight control surfaces, generating drag without loss of flight control authority or change in aircraft pitch attitude.
...the rudders are splayed out, and the ailerons, spoilers and flaps are generating balanced opposing pitching moments.
For the -18, obviously it has a C-FLCS, but it also has programming to work in concert in a unique situation to play the role of a structure that is necessary on other C-FLCS aircrafts. If the FLCS can work together to play the role of a speedbrake, it can also limit, for whatever reasons/justifications, the performance of an aircraft as well.
So the answer to the question on how maneuver is the Su-47 Berkut must be the unpopular: We do not know.
Absent hard data, or even reasonably educated data, on its FLCS, there is simply no way to make any declaration. From WW I to the Korean War, FLCS engineering have been able to keep up with whatever the aerodynamicists can create. From the F-16 on, we have not since. The Berkut is not as revolutionary as the F-16, but it has all the potentials that an inherently unstable aircraft can do.
The limits that FLCS engineering put on an inherently unstable aircraft is technological. Fly-by-wire FLCS extended those limits. We need more sensitive and responsive gyros and accelerometers. We need faster computers. We need more powerful hydraulics. We need more reactive actuators so may be hydraulics may not last much longer. We need better conductor, purer wires or change to light, to transmit commands and receives feedbacks. We need better materials. Believe it or not, it is materials that limits the F-16 to 9gs, discounting the pilot. Materials affects structures and with better materials, the F-16 as it is designed can fly 9gs fully loaded, instead of having limiters, which also is a clue that FLCS is the limiting factor.
It is a long post but I really cannot 'dumb' it down any further, no offense intended for any interested layman, about FLCS engineering and its relationship to aerodynamics and its priests.
