Ceiling (aeronautics)

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In aeronautics, a term ceiling has different meanings depending on the context. With respect to an aircraft, a ceiling is the maximum density altitude an aircraft can reach under a set of conditions. With respect to weather conditions, a ceiling refers to the height of the lowest obscuring cloud layer above the ground, below which visual meteorological conditions (VMC) exist, permitting flight by visual flight rules (VFR).

Contents 1 Aircraft ceiling 1.1 Service ceiling 1.2 Absolute ceiling 1.3 Combat ceiling 1.4 Dynamic ceiling 2 Cloud ceiling 3 References

Aircraft ceiling

Service ceiling

The service ceiling attempts to capture the maximum usable altitude of an aircraft. Specifically, it is the density altitude at which flying in a clean configuration, at the best rate of climb airspeed for that altitude and with all engines operating and producing maximum continuous power, will produce a given rate of climb (usually 100 feet per minute climb or 30 meters per minute).^[1] Margin to stall at service ceiling is 1.5g.^{[citation needed]}

The one engine inoperative (OEI) service ceiling of a twin-engine, fixed-wing aircraft is the density altitude at which flying in a clean configuration, at the best rate of climb airspeed for that altitude with one engine producing maximum continuous power and the other engine shut down and feathered, will produce a given rate of climb (usually 50 feet per minute).^{[citation needed]}

However some performance charts will define the service ceiling as the pressure altitude at which the aircraft will have the capability of climbing at 50 ft/min with one propeller feathered.

Absolute ceiling

A less often used term is the absolute ceiling – the highest altitude (calculated on the ground and which will never be reached in flight except during flight testing) at which an airplane can sustain level flight, which means the altitude at which the thrust of the engines at full power is equal to the total drag at minimum drag speed. In other words, the altitude where maximum thrust available equals minimum thrust required, so the altitude where the maximum sustained (with no decreasing airspeed) rate of climb and angle of climb reach 0. Most commercial jetliners have a service (or certificated) ceiling of about 42,000 feet (12,802 m)^{[citation needed]} and some business jets about 51,000 feet (15,545 m).^[2] While these airplanes' absolute ceiling is much higher than standard operational purposes, it is impossible to reach (because of the vertical speed asymptotically approaching to zero) without afterburners or other devices temporarily increasing thrust. Flight at the absolute ceiling is also not economically advantageous due to the low indicated airspeed which can be sustained: although the true airspeed (TAS) at an altitude is typically greater than indicated airspeed (IAS), the difference is not enough to compensate for the fact that IAS at which minimum drag is achieved is usually very low, so a flight at an absolute ceiling altitude results in a low TAS as well, and hence in a high fuel burn rate per distance traveled. Also, it must be noted that the absolute ceiling varies with the air temperature and, overall, the aircraft weight (usually calculated at MTOW).^[1]

Combat ceiling

Combat ceiling is the highest altitude at which an aircraft is expected to have a given (usually 500 feet per minute) climb.^{[citation needed]}

Alternatively, combat ceiling is defined as the highest altitude at which an airplane can sustain altitude and airspeed during a horizontal maneuver with a given bank angle (usually 15-20°).^{[citation needed]}

Dynamic ceiling

Dynamic ceiling is the highest altitude an airplane can reach by using its kinetic energy while still maintaining minimum controllable airspeed.^{[citation needed]}

Cloud ceiling

With respect to weather conditions as they relate to aeronautics, a ceiling refers to the height of the lowest obscuring cloud layer above the ground, below which visual meteorological conditions (VMC) exist, permitting flight by visual flight rules (VFR). For example, a layer of overcast or broken clouds having a base of 3,000 ft. above the ground would constitute a ceiling of 3,000 ft. The absence of any overcast or broken cloud layers is referred to as an "unlimited" ceiling.

In United States, the Federal Aviation Regulations define ceiling as the height above the Earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as broken, overcast, or obscuration, and not classified as thin or partial.^[3]

References