Photos have appeared online depicting Russia’s new stealth fighter.
The single-engine warplane, which manufacturer Sukhoi calls “Checkmate,” reportedly will make its debut at the MAKS air show at Ramenskoye airfield in Moscow Oblast next week.
In the earliest images, Checkmate is covered in a tarp. In photos that appeared on Sunday, the tarp is gone. What’s underneath could be a nonflying mock-up. Or it might be a flyable prototype.
In any event, we now can try to assess Checkmate’s design.
At first glance, Checkmate has obvious low-observable qualities, including a chiseled nose and fuselage, V-shape tail control surfaces and internal weapons bays—all of which help to scatter, rather than directly reflect, radar energy.
Perhaps most notably, the chin inlet features a noticeable underbite.
That underbite is telling. A chin inlet—like the American F-16, European Typhoon and Chinese J-10 all have—moves air directly to the turbine and can improve performance at high angles-of-attack compared to planes with complex side inlets.
But there’s a downside. A chin inlet could require various gates and gaps in order to slow supersonic air to subsonic speed. Jet engines can’t handle incoming supersonic air.
At the same time, a chin inlet typically doesn’t give designers many options for curving the inlet passage in order to obscure the turbine face. That means that enemy radars, gazing at the fighter from head-on, could have a direct view of the fighter’s most reflective feature.
Chin inlets often require various weight-adding tweaks in order to solve the supersonic airflow problem. They also imply a large frontal radar signature—an obvious problem if a plane’s designers are aiming for stealth.
That said, the Eurofighter consortium reportedly found a way to snake the Typhoon’s inlet in order to obscure the turbine. And Lockheed Martin in the 1990s refined a new inlet design—a so-called “divertless supersonic inlet,” or DSI—that includes carefully-placed bumps and bulges as well as that distinctive underbite.
The shaping and underbite on a DSI achieves two things. They slow the incoming air and obscure the turbine. As a bonus, a DSI is mechanically simple, so it can drive down cost compared to more intricate inlet designs such as those on the American F-15 and Russian Su-27.
The main liability of a DSI is that it probably limits a jet’s top speed to slower than Mach two, whereas complex side inlets can produce top speeds exceeding Mach two.
So if you’re going for an affordable, maneuverable fighter that also has low-observable qualities and you don’t mind sacrificing some speed, a DSI chin inlet is a smart approach. It should come as no surprise, then, that Checkmate seems to include this kind of inlet.
After all, Sukhoi’s goal apparently is to develop a stealth fighter that foreign customers can afford. The Russian air force might also want to acquire Checkmates in order to complement its bigger, stealthier and likely very expensive Su-57s.
All that said, Checkmate might not be ready to fly—especially if the thing appearing at MAKS is a mock-up rather than a functional demonstrator. Most new fighter designs never enter production, owing either to developmental problems or a dearth of paying customers.
Only time will tell if Checkmate beats the odds … and actually enters production.