Flight envelope

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.

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".

However modern jet engines can provide considerable power with the equivalent of 50,000 horsepower (37 MW) not being atypical.

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 outer edges of the diagram, the envelope, show the possible conditions that the aircraft can reach in straight and level flight.

This maximum altitude is known as the service ceiling (top limit line in the diagram), and is often quoted for aircraft performance.

A chart of velocity versus load factor (or V-n diagram) is another way of showing limits of aircraft performance.

In unusual weather conditions this may make it unsafe or uneconomical to fly, occasionally resulting in the cancellation of commercial flights.

[4][5] Although it is easy to compare aircraft on simple numbers such as maximum speed or service ceiling, an examination of the flight envelope will reveal far more information.