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Flight envelope
In aerodynamics, the flight envelope, service envelope, or performance envelope of an aircraft or spacecraft refers to the capabilities of a design in terms of airspeed and load factor or atmospheric density, often simplified to altitude.
The term is somewhat loosely applied, and can also refer to other measurements such as maneuverability. For example, when a plane is pushed, for instance by diving it at high speeds, it is said to be flown "outside the envelope", something considered rather dangerous. During vehicle test programs, flight envelope simply means that part of the aircraft or spacecraft's design capabilities that have already been successfully tested, and have therefore moved from theoretical or designed capability into a demonstrated/certified capability.
Flight envelope is one of a number of related terms that are used in a similar fashion. It is perhaps the most common term because it is the oldest, first being used in the early days of test flight. It is closely related to more modern terms known as extra power and a doghouse plot which are different ways of describing the flight envelope of an aircraft. In addition, the term has been widened in scope outside the field of engineering, to refer to the strict limits in which an event will take place or more generally to the predictable behavior of a given phenomenon or situation, and hence, its "flight envelope".
Extra power, or specific excess power, is a very basic method of determining an aircraft's flight envelope. It is easily calculated but as a downside does not tell very much about the actual performance of the aircraft at different altitudes.
Choosing any particular set of parameters will generate the needed power for a particular aircraft for those conditions. For instance a Cessna 150 at 2,500-foot (760 m) altitude and 90-mile-per-hour (140 km/h) speed needs about 60 horsepower (45 kW) to fly straight and level. The C150 is normally equipped with a 100-horsepower (75 kW) engine, so in this particular case the plane has 40 horsepower (30 kW) of extra power. In overall terms this is very little extra power, 60% of the engine's output is already used up just keeping the plane in the air. The leftover 40 hp is all that the aircraft has to maneuver with, meaning it can climb, turn, or speed up only a small amount. To put this in perspective, the C150 could not maintain a 2g (20 m/s²) turn, which would require a minimum of 120 horsepower (89 kW) under the same conditions.
For the same conditions a fighter aircraft might require considerably more power due to their wings being designed for high speed, high agility, or both. It could require 10,000 horsepower (7.5 MW) to achieve similar performance. However modern jet engines can provide considerable power with the equivalent of 50,000 horsepower (37 MW) not being atypical. With this amount of extra power the aircraft can achieve very high maximum rate of climb, even climb straight up, make powerful continual maneuvers, or fly at very high speeds.
A doghouse plot generally shows the relation between speed at level flight and altitude, although other variables are also possible. It takes more effort to make than an extra power calculation, but in turn provides much more information such as ideal flight altitude. The plot typically looks something like an upside-down U and is commonly referred to as a doghouse plot due to its resemblance to a kennel (sometimes known as a 'doghouse' in American English). The diagram on the right shows a very simplified plot which shall be used to explain the general shape of the plot.
The outer edges of the diagram, the envelope, show the possible conditions that the aircraft can reach in straight and level flight. For instance, the aircraft described by the black altitude envelope on the right can fly at altitudes up to about 52,000 feet (16,000 m), at which point the thinner air means it can no longer climb. The aircraft can also fly at up to Mach 1.1 at sea level, but no faster. This outer surface of the curve represents the zero-extra-power condition. All of the area under the curve represents conditions that the plane can fly at with power to spare, for instance, this aircraft can fly at Mach 0.5 at 30,000 feet (9,100 m) while using less than full power.
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Flight envelope AI simulator
(@Flight envelope_simulator)
Flight envelope
In aerodynamics, the flight envelope, service envelope, or performance envelope of an aircraft or spacecraft refers to the capabilities of a design in terms of airspeed and load factor or atmospheric density, often simplified to altitude.
The term is somewhat loosely applied, and can also refer to other measurements such as maneuverability. For example, when a plane is pushed, for instance by diving it at high speeds, it is said to be flown "outside the envelope", something considered rather dangerous. During vehicle test programs, flight envelope simply means that part of the aircraft or spacecraft's design capabilities that have already been successfully tested, and have therefore moved from theoretical or designed capability into a demonstrated/certified capability.
Flight envelope is one of a number of related terms that are used in a similar fashion. It is perhaps the most common term because it is the oldest, first being used in the early days of test flight. It is closely related to more modern terms known as extra power and a doghouse plot which are different ways of describing the flight envelope of an aircraft. In addition, the term has been widened in scope outside the field of engineering, to refer to the strict limits in which an event will take place or more generally to the predictable behavior of a given phenomenon or situation, and hence, its "flight envelope".
Extra power, or specific excess power, is a very basic method of determining an aircraft's flight envelope. It is easily calculated but as a downside does not tell very much about the actual performance of the aircraft at different altitudes.
Choosing any particular set of parameters will generate the needed power for a particular aircraft for those conditions. For instance a Cessna 150 at 2,500-foot (760 m) altitude and 90-mile-per-hour (140 km/h) speed needs about 60 horsepower (45 kW) to fly straight and level. The C150 is normally equipped with a 100-horsepower (75 kW) engine, so in this particular case the plane has 40 horsepower (30 kW) of extra power. In overall terms this is very little extra power, 60% of the engine's output is already used up just keeping the plane in the air. The leftover 40 hp is all that the aircraft has to maneuver with, meaning it can climb, turn, or speed up only a small amount. To put this in perspective, the C150 could not maintain a 2g (20 m/s²) turn, which would require a minimum of 120 horsepower (89 kW) under the same conditions.
For the same conditions a fighter aircraft might require considerably more power due to their wings being designed for high speed, high agility, or both. It could require 10,000 horsepower (7.5 MW) to achieve similar performance. However modern jet engines can provide considerable power with the equivalent of 50,000 horsepower (37 MW) not being atypical. With this amount of extra power the aircraft can achieve very high maximum rate of climb, even climb straight up, make powerful continual maneuvers, or fly at very high speeds.
A doghouse plot generally shows the relation between speed at level flight and altitude, although other variables are also possible. It takes more effort to make than an extra power calculation, but in turn provides much more information such as ideal flight altitude. The plot typically looks something like an upside-down U and is commonly referred to as a doghouse plot due to its resemblance to a kennel (sometimes known as a 'doghouse' in American English). The diagram on the right shows a very simplified plot which shall be used to explain the general shape of the plot.
The outer edges of the diagram, the envelope, show the possible conditions that the aircraft can reach in straight and level flight. For instance, the aircraft described by the black altitude envelope on the right can fly at altitudes up to about 52,000 feet (16,000 m), at which point the thinner air means it can no longer climb. The aircraft can also fly at up to Mach 1.1 at sea level, but no faster. This outer surface of the curve represents the zero-extra-power condition. All of the area under the curve represents conditions that the plane can fly at with power to spare, for instance, this aircraft can fly at Mach 0.5 at 30,000 feet (9,100 m) while using less than full power.