The pilot manages controls called the collective, cyclic, and foot pedals, as I once had the chance to try very briefly. Sikorsky’s work on coaxial helicopters dates back to a first flight in 2008. The initial version of this helicopter, called the SB>1 Defiant, flew for the first time in March of 2019, and Popular Science has also recognized it in its Best of What’s New awards. The aircraft is still in the planning phases, so Macklin cautions that the design could change. “You fly up with the prop going, you reverse pitch on the prop, you immediately slow down,” he says, comparing it to the feeling you get when an airliner lands, the jet engines reverse their thrust, and you feel a push forward towards your tray table. Because the Defiant can stay level, it can get into a landing zone quickly, Macklin argues. That allows the craft to accelerate or decelerate without tipping forward or backward as a Black Hawk would as one of those choppers lands, for example, its nose flares up, and its nose pitches down as it accelerates. The propeller in the back helps with that it can push the craft quickly through the air and even help it slow down, too. Since this aircraft would need to quickly deploy troops in an area that might be unfriendly, getting in and out quickly is key. “The faster you go, you create an area of instability on the blade.” But that doesn’t occur with two counter-rotating rotors up top, like the Defiant has. In that case, “you’re a victim of physics,” says Macklin, who is also a former Black Hawk pilot. This issue is called a retreating blade stall.
But the blade moving backwards can run into trouble in the form of reduced lift, since it’s moving in the same direction that the air is as the helicopter flies forward through it. As the top rotor spins, one side of the rotor is traveling forward in the same direction of flight, while the other side is moving backwards, as the blades complete their circle. Picture a regular helicopter cruising quickly through the air. That double-rotor setup also solves a problem that is a nerdy-yet fascinating-aerodynamic issue. That’s fine for a Black Hawk, but untenable when it comes to two rotors on top of one another. That’s different from the rotor blades at the top of a regular Black Hawk, which has a “fully articulated rotor system-it flaps up, flaps down, leads forward, lags back-so it’s constantly moving, adjusting in the air,” says Jay Macklin, the business development director for Future Vertical Lift at Sikorsky. This coaxial setup means that the whirlybird doesn’t need a traditional tail rotor, which exists to keep a regular helicopter from spinning around in dizzying circles in response to the motion of that top rotor.Ĭrucially, the Defiant’s top rotors are rigid enough to prevent them from colliding and causing a disastrous failure. The most eye-catching feature is at the top, where two stacked rotors spin in opposite directions for maximum lift. Right away, its appearance sets it apart from a regular helicopter. Here’s what to know about how the Defiant works, and how the design informs what it should be able to do. This machine, which is made by Sikorsky and Boeing, is competing with a rival aircraft from Bell as part of an Army initiative called the Future Long-Range Assault Aircraft program. While it doesn’t exist as a production aircraft, it’s one of two candidates that could be the new Black-Hawk-type helicopter for the U.S. One problem with an autorotation is that it will be difficult or impossible for the pilot to align the landing gear with ground track during touchdown.The Defiant X is a sleek, futuristic helicopter that’s designed to go fast and far.
Most manufacturers call for an immediate autorotation.Īn autorotation is a natural way to deal with an inflight tail rotor failure since it reduces torque to zero. If the tail rotor fails in flight, engine torque can no longer be countered by the tail rotor, and uncontrolled spinning of the aircraft is a possibility. One method of recovery is to immediately shut off the engine, and allow the helicopter to autorotate which, although disorienting to the pilot, will reduce the spinning of the helicopter body. If the tail rotor failed on the above helicopter, it would spin in the opposite direction as a consequence of the law of conservation of angular momentum.
How Helicopters Fly gives you more details.
There is plenty of footage on YouTube, if you have the stomach to watch it, of what happens when the tail rotor fails. Yes, without a means of counteracting the torque caused by the main rotor, the helicopter will rotate pretty much uncontrollably.
0 kommentar(er)
