The fighter after all mainly is an export commodity. Advertising is critical to its success.
The leaks also are fodder for analysts. Whether the plane Sukhoi is showing off at MAKS is a mock-up or a flyable demonstrator, its design elements are telling.
Sukhoi is developing a small, maneuverable and potentially highly stealthy fighter, one whose greatest liability—beside its potential cost—might be its obviously limited internal fuel capacity and resulting short combat radius.
Checkmate’s low-observable features are numerous. The chin air-intake with its distinctive underbite strongly hints that Sukhoi’s engineers incorporated a divertless inlet that could partially obscure the fighter’s most radar-reflective component—its engine turbine. The inlet alone could account for much of Checkmate’s stealth.
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Now consider Checkmate’s tail. Instead of separate horizontal and vertical stabilizers with moving rudders and elevators, the new fighter has what are called “ruddervators.” A pair of single-piece control surfaces that cant at roughly 45-degree angles relative to the horizontal plane of the fuselage.
Ruddervators can help to reduce the number of highly-detectable surfaces on a jet while still affording it good maneuverability.
Wings and horizontal control surfaces with their straight edges and huge surface areas are a major source of radar reflectivity. Vertical stabilizers also are radar-reflectors from certain angles relative to the enemy.
Eliminate the horizontal and vertical stabilizers and you’ve cut the number of edges and flat surfaces off which radar energy can reflect back to the emitter. The problem is that an airplane needs elevators and rudders.
Ruddervators essentially combine both elements while mitigating their observability. A whole angled ruddervator moves, pushingthe jet’s nose up or down and to one side or the other—and it does so without offering radars on the ground strictly horizontal or vertical surfaces off which to bounce their energy.
Checkmate’s ruddervators likely make it stealthier than, say, a MiG-29—but not without a cost. Ruddervators require sophisticated flight-control systems.
When Northrop engineers designed the YF-23—the big, weird fighter that lost out to the YF-22 in the U.S. Air Force’s Advanced Tactical Fighter competition—they had to invent a new kind of actuator to move the plane’s ruddervators.
Sukhoi obviously decided the downside of ruddervators is worth the upside. That is to say, their stealthiness is worth the difficulty in controlling them.