G/A, the flight envelope as I understand it is not quite as nosefirsteverytime described it - it is rather G-forces on the vertical axis (plus and minus) plotted against airspeed on the horizontal axis. We are in agreement that "Pushing the envelope" does seem to mean taking the aircraft to the extreme of what is permissible.
I cannot quickly find a website with this shown in a diagram. A Google search quickly found this, however:
Search Result 21
From: highflyer (
[email protected])
Subject: Re: How to draw a Flight Envelope
Newsgroups: rec.aviation.student
Date: 2003-03-25 08:17:42 PST
"The "flight envelope" is a graph where the vertical axis is G loading.
1 G is the center of the vertical scale. The horizontal scale is airspeed.
Draw a vertical line at Vne [the speed which must never be exceeded - a key design limitation of an aircraft - CN]. That is the high speed end of the envelope.
Draw two horizontal lines, one at the positive design G limit ( usually 3.8 ) and one at the negative design G limit, usually 2 or so.
That establishes much of the envelope. Mark Va [I think this is the maximum speed at which you are allowed by the strength of the aircraft to operate the controls to their full deflection - CN] on the upper stall speed line. That is one corner of the upper left boundary. Mark Vso [the stalling speed] on the 1 G line. That is the lowest airspeed point of the envelope. The line between Vso and Va increases along an exponential curve from Vso to Va. The stall speed increases with the square root of the G loading. Plot that curve.
Do the same from Vso on the negative side until you cross the negative G limit line.
The resulting closed figure on the graph is the aircraft "envelope."
You can operate anywhere within that "envelope" without breaking the aircraft, but you cannot operate outside of that envelope without either breaking something, or being unable to sustain enough lift to fly. "
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For gliders at least, there is another limitation - the maximum G that can be pulled at Vne (the highest design speed) is less than, not the same as, the maximum permitted at Va. So the envelope is not a sort of rectangle at the right hand end, but is tapered to narrower limits.
Hope that helps.
Chris N.