The Cobra maneuver is also known as
Pougachev's Cobra or
Pugachev's Cobra after
Victor Georgievich Pugachev, the
test pilot who pioneered it. It is an impressive bit of flying that showcases the
aerodynamics and performance of the
aircraft that performs it as well as the skill of the pilot.
The Cobra can only be performed by a few aircraft types. At present, these are limited to the Sukhoi-27 Flanker and its variants, and the MiG-29 Fulcrum. While the maneuver is more easily attained in those models of the Su-27 that have thrust vectoring controls, it can be done in the straight-pipe models as well (and was invented in one). The Su-27 is the only aircraft that can perform a Cobra from straight and level flight; the MiG-29 can only enter it from a climb of approximately 30 degrees in order to safely recover.
In order to perform the Cobra (in this example, in a Su-27 Flanker) the pilot reduces speed to approximately 275 knots in level flight. S/he then must disable the AOA limiter on the Flight Control System, as this serves to limit the airplane to angles of attack not exceeding 30 degrees in normal flight. Once this is accomplished, the pilot sharply pitches up the nose of the airplane. If the speeds are right and the pitchup is done properly, the aircraft will rotate around its horizontal axis until the nose is past vertical - the single-seat Flanker can achieve between 110 and 120 degree AOA! - while continuing to move in its prior flight path as the maneuver is too quick and there isn't enough energy to allow the airplane to climb as it pitches up.
Once the pilot has reached the desired attitude, s/he sharply increases throttle and releases the stick. The airplane has managed to rotate back past vertical on the initial rotational energy of the pitchup maneuver; once it approaches vertical, however, the rear half of the aircraft (now the 'lower' half) generates much more drag than the front (or 'top') half due to the larger cross-section of the wings and stabilizers. This will cause the rotation to stop and then reverse, the nose pitching sharply 'down' relative to the airframe, back into level flight. The throttle added during the maneuver will, if done properly, prevent the airplane from losing any altitude during the process. In sum, the maneuver should take no more than a few seconds. The aircraft wll exit the maneuver at around 135 knots, which means it is in a fairly precarious position until it gains airspeed.
The MiG-29 and Su-27 are both designed to have extremely large tolerances for airflow deviation into the engine inlets. This is what permits them to perform this maneuver without suffering an engine unstart (normally). In addition, their postive lateral stability and clean lines reduce the risk of a full stall during the procedure. They have high thrust-to-weight ratios as well. The MiG-29 must enter a climb of around 30 degrees before performing the Cobra as it will not recover quickly enough to avoid losing altitude.
Debates continue over the utility of this maneuver in air combat. While 'hitting the brakes' to avoid a tailing opponent is indeed sometimes useful (and was popularized in the recruiting propagan...er, film Top Gun) the vulnerability of the aircraft as it exits this maneuver mean that it would be useful, if at all, only if a few restricted circumstances - and would likely not be preferable to other choices which might leave the pilot with more energy (and hence options). It is, of course, possible that the Western scoffing at the maneuver might be due in part to sour grapes, as Western aircraft cannot perform it.
It is extremely dangerous, especially performed near the ground (as during air shows, which have been where it has been seen). A MiG-29 crashed at Le Bourget's Paris Air Show in 1989; it was performing a low, high-angle maneuver which might have been similar to a Cobra when it lost one of its two engines. The airplane spun to the side and down into the ground; the pilot ejected horizontally at less than 100 feet of altitude, but survived to eject from another airplane a few months later - Russians build the best ejection seats in the world.