The Su-27’s basic design is aerodynamically similar to the MiG-29,
but it is substantially larger. It is a very large aircraft, and to
minimize its weight its structure has a high percentage of titanium
(about 30%, more than any of its contemporaries). No composite materials
were used. The swept wing blends
into the fuselage at
the leading edge extensions and
is essentially a delta,
although the tips are cropped for wingtip missile rails or ECM pods.
The Su-27 is not a true delta, however, because it retains conventional tailplanes,
with two vertical tailfins outboard
of the engines, supplemented by two fold-down ventral fins for
additional lateral stability.
The Su-27’s Lyulka AL-31F turbofan engines
are widely spaced, both for safety reasons and to ensure uninterrupted
airflow through the intakes. The space between the engines also provides
additional lift, reducing wing loading. Movable guide vanes in the
intakes allow Mach 2+ speeds,
and help to maintain engine airflow at high alpha.
A mesh screen over each intake prevents debris from being drawn into the
engines during take-off.
The Su-27 had the Soviet Union’s first operational fly-by-wire
control system, developed based on Sukhoi OKB’s experience in the Sukhoi
T-4 bomber project. Combined
with relatively low wing
loading and powerful basic
flight controls, it makes for an exceptionally agile aircraft,
controllable even at very low speeds and high angles of attack. In airshows the
aircraft has demonstrated its maneuverability with a Cobra (Pugachev’s
Cobra) or dynamic deceleration - briefly sustained level flight at a
120° angle of attack. Thrust vectoring has also been tested (and is
incorporated on later Su-30MK and Su-37 models), allowing the fighter to
perform hard turns with almost no radius, incorporate vertical
somersaults into level motion and limited nose-up hovering.