"How far can we push the envelope?"

[G/A]

Hi,


i am a reader of pprune for a long time and today i registered, because i have got a question.

My mother is a translator, and is translating a book at the moment. Now she came to me and asked what the following expression means:
"in an expression borrowed from the world of aviation, "how far can we push the envelope"?"

I never heard this expression before, and i hope you cand help me. What does it mean, can someone please describe it?
What is meant with envelope?

I thought something like the limit, but what limits? The physical or technical limits?

Would be nice if someone could help me.

best regards
G/A

[nosefirsteverytime]

Allllrighty, I think I'll have a go at this one. G/A, I'm an aengineering student, so I'm sorry if there's a lot of technical language in my answer.

Well G/A, the "envelope" in this instance is not a white paper package to put letters into, but something known as the "flight envelope". If you draw a graph with an aircraft's speed on the x axis, and its altitude on the Y axis, then the "envelope" would be the area within the graph in front of you where the aircraft would be able to fly without stalling or crashing. If you're too slow, or too high, not enough air flows on the wings, and the aircraft either re-enters the flyable envelope or crashes. If an aircraft goes too fast, the air hitting it will start to weaken the airframe, and so something will break.

Back to the term "pushing the envelope". Each aircraft type has different size "envelopes" within which they operate. When fighter planes were/are being developed, and a prototype is built for flying tests, the test pilots deliberately fly an aircraft to the limits of the envelope, pushing the aircraft ever higher and faster.

To "push the envelope" is to push an aircraft, or anything else for that matter, to its very limits.

Does that answer your question?

[G/A]

Thank you very very much!
The answer helped me, thanks a lot.

best regards
G/A

[chrisN]

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. "

--------------------------------------------------------------------------------

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.

[Intruder]

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.

Actually, there is no single "envelope" when it comes to aircraft performance. The total performance "envelope" is represented by a series of graphs, charts, and tables that represented the designed, tested, certified, and/or operational limits of performance.

Common charts/diagrams include altitude vs airspeed, weight & balance, gross weight vs G forces, airspeed vs G forces, and a host of others.

We are in agreement that "Pushing the envelope" does seem to mean taking the aircraft to the extreme of what is permissible.

That part is true. Often the pushing is beyond what is permissible to the limit of what the aircraft will endure or what can be attained.

[visibility3miles]

Actually, it has become a part of the English language (at least in America), and means trying to go as far as you possibly can to see where the limit is. As slang, it can refer to atheletic activities or social behavior, for example. It often means, "How much can we get away with?"

(Other people besides test pilots used it before the book "The Right Stuff" was published.)

It's a concept that any German engineer should be familiar with, so your mother might try to contact a scientist or engineer to ask what phrase they would use.

http://www.worldwidewords.org/qa/qa-pus1.htm

PUSH THE ENVELOPE

[Q] From Claire Walsh (related questions came from Clive Pullinger, Linda Webb, Brian MacWhinney, Sue McCoy, and others): “I’ve always been puzzled by the phrase pushing the envelope; it’s an incongruous image that doesn’t seem to have any relationship to its meaning. Can you tell me where it comes from?”

[A] It comes from mathematics, specifically as it is used in aeroplane design. It was popularised by Tom Wolfe’s book of 1979, The Right Stuff, about test pilots and the early space programme. It’s an excellent example of the way that a bit of specialised jargon known only to a few practitioners can move into the general language.

In mathematics, an envelope is the enclosing boundary of a set or family of curves that is touched by every curve in the system. This usage is known from the latter part of the nineteenth century. It’s also used in electrical engineering for the curve that you get when you connect the successive peaks of a wave. This envelope curve encloses or envelops all the component curves.

In aeronautics, the envelope is the outer boundary of all the curves that describe the performance of the aircraft under various conditions of engine thrust, speed, altitude, atmospheric conditions, and the like. It is generally taken to be the known limits for the safe performance of the craft.

Test pilots have to test (or push) these limits to establish exactly what the plane is capable of doing, and where failure is likely to occur—to compare calculated performance limits with ones derived from experience. Test pilots called this pushing the edge of the envelope in the 1950s and 1960s, but this was soon shortened.

Following Tom Wolfe’s book and film, the phrase began to move out into the wider world; the first recorded use in the more general sense of going (or attempting to go) beyond the limits of what is known to be possible came in the late 1980s.

[G/A]

Ok, thank you guys, you helped me very much. Now it is clear to me, what "pushing the envelope" means.
At the moment i am searching for an German word for it, which is clearly understandable not only for Aviation Fans.
If i have any further question i will post them here.

Thanks for the moment
G/A

[square leg]

Die Grenzen zu erweitern...

Die Limiten zu erweitern/verschieben...

Neues Land zu betreten... in Bezug auf...

Basically pushing the envelope to new limits, discovering whether or not the old limits are really limits or whether something more can be squeezed out of the lemon. Stretching the boundries...

edited for spelling

[dada]

i can push an envelope right the way through a letterbox

[Frankfurt_Cowboy]

And I bet it's a letter bomb through a green tinged letterbox!

[Vee One...Rotate]

If the envelope's not taut, you're not pushing hard enough.

V1R :p