Coffin corner (aviation)

In aviation is as coffin corner (English, literally translated coffin corner) or Q- Corner as the area in high altitudes, converge strongly in the minimum flight speed and maximum speed. In this section, the aircraft may not fly faster or slower. In still greater height, it can not fly, because then the theoretical minimum speed on the theoretical top speed, so it is no longer flyable speed.

The term "corner " ( German: angle, corner) refers to the triangular shape of the envelope of the flight envelope. Here cross the curves for the stall speed and the maximum Mach number.

Stall - minimum flight speed

The dynamic lift of an aircraft is dependent upon the air density of the air speed and the angle of attack. If the speed is reduced, the aircraft must increase the angle of attack to produce the same lift and to maintain altitude. However, too high angles of attack leads to a stall ( stall ). Thus, the aircraft must maintain a certain minimum flight speed Vs, so that the flow is not interrupted. This minimum speed is called stall limit or stall speed.

The air density, and thus the altitude, also has an effect on the minimum airspeed. The thinner the air is, the greater must be the minimum speed (true airspeed - TAS) are recognized to avoid a stall.

A heavily loaded aircraft needs more lift than an empty aircraft. So it has to fly faster at a given angle of attack than a lighter aircraft to obtain the necessary higher lift. Therefore, the minimum airspeed is higher than with a lighter (Fig. 2) with a heavier aircraft.

Over speed - Mach limit

Because of the decreasing of the amount of air temperature decreases the speed of sound. Even at Mach numbers from about 0.8 to flow into a region above the support surface, the air faster than the sound ( Mach number ). The compression shock at the exit of the flow in this area is more pronounced in a developed for subsonic airfoil and is more forward. Behind the flow becomes detached, control flaps are losing influence. With increasing speed of the shock wave and with it the center of lift walking backwards. The plane lowers the nose and continues to accelerate. This technique, known as Mach tuck phenomenon was the cause of several crashes. As part of the approval, the aviation authorities certify a maximum operational Mach number ( MMO). In modern commercial aircraft, this is beyond the critical Mach number, but below 1.0.

In most smaller airplanes exceeding the maximum speed in horizontal flight, due to the power limits of the power plant is not possible.

Hazards

Threatening the coffin corner can be in high performance aircraft, from which the last reserves be retrieved (eg, Lockheed U -2). Here then is the difference between "too fast" and " slow " sometimes only five knots. Any increase in the angle of attack, by turning flight or air turbulence (Clear Air Turbulence ), leads to stall. The pilot must, if the plane starts to shake (buffet), and immediately know exactly whether he is too fast or too slow, since an erroneous correction would be fatal.

Service ceiling

The service ceiling is always below the Coffin Corner, as it is defined by the fact that there is still a climb rate of 100 ft per minute must be possible. However, this is no longer the case in the vicinity of the corner Coffin.

  • Flight Performance
  • Aerodynamics
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