# Talk:Flight envelope

WikiProject Aviation / Aircraft (Rated Start-class)
Start  This article has been rated as Start-Class on the project's quality scale.

## Merge

Support This is a more developed page. - Emt147 Burninate! 23:47, 8 May 2006 (UTC)

I'm definately in favour of a merge, but I'm not sure at what page it should be done at. To get things started already I'll start the merger on Performance envelope/Merge and we can decide on where it should go later. - Dammit 20:40, 14 May 2006 (UTC)
I'm basically done with the new text (sorry it took so long, forgot all about it) so it can be moved when concensus is reached on the article title. - Dammit 19:16, 7 June 2006 (UTC)

## pushing the envelope

Where did this term come from????..... Pushing the envelope...

It refers to flying at the edge of the doghouse plot, attempting to "push" outside the known limits. Maury 23:51, 14 March 2007 (UTC)

every aircraft manual have charts where you define pushing the envelop. Could be weight and balance .speed limits. ex .max. structural speed on the clean configuration or dirty configuration. Exeding angle of attack were to experience stall of the wing ,exeding roll angle resulting in a spin or nonrecuperable flat spin. for aircraft exeding mach they can x=stall the inlet due to the shock wave.

## need axes with labels

The plots included in this article need axes with labels. The first plot has no axes at all, making it difficult to comprehend for the uninitiated. The second plot has axes but no labels, indicating both what parameter each axis represents and, in this case, since there are numbers on the axes, the labels should include units, or "dim" or "dimensionless" if they represent dimensionless quantities. JDHeinzmann (talk) 15:47, 17 June 2008 (UTC)

I would remove that plot: without labels, it causes only confusion. dima (talk) 08:32, 30 July 2008 (UTC)
If needed I can provide a vectorized graphics SVG. Mariostorti (talk) 19:09, 9 June 2009 (UTC)

## Definitions

The section definition is absent. I suggest:

The main parameters that describe the state of an airplane are the airspeed and the altitude. (Additional parameters could be its orientation and direction of its speed). The concept of the flight envelope deals with conditions when the aircraft flies horisontally with constant direction of speed. Then, the state can be caracterised as point in the two-dimensional space, speed ${\displaystyle v}$ and altitude ${\displaystyle h}$.

The set of values ${\displaystyle (v,h)}$, at which the aircraft can fly and the flight is considered as safe, is called Flight envelope.

It is limited at low velosity, when the aircraft is close to the stall and unstable.

It may be limited at high velosity; slow aircrafts (especially gliders) loss stability and/or shape, if forced to move with speed of a jet plane.

it is limited at high altitude, when the pressure of the air is not sufficient for the efficient work of the engine and/or to provide the sufficient lift at reasonable angle of attack.

it is limited by the closeness to the ground, at which the aircraft is still save to avoid collision and damage of the people at the ground by its sound or the Shock wave. In principle, the flight envelope could be also limited due to the high pressure at negative altitude above the sea level. That could correspond to the pressure of the air, say, twice the normal atmospheric pressure; but usually such conditions are not available at the Earth: the lowest air-filled area is Dead Sea, which is only a hundred meter below the sea level.

Usually, the flight envelope is 2-dimensional region of simple topology and shape; although some aircrafts, al low speed, must be either very close to the ground (that allows the landing, voluntary or emergency, if full stall) or at high enough altitude (that allows the safe recovery from stall).

dima (talk) 08:26, 30 July 2008 (UTC)

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