Every week I try to bring up some phrases and their origins for your reference:

Balls to the wall
Meaning:
To push to the limit, go all out, full speed.
Example:
If you study balls to the wall from now on, you just might pass your algebra class.
Origin:
A very colorful phrase, one needs to be careful when using "balls to the wall". Although its real origin is very benign, most people assume it is a reference to testicles.
In fact it is from fighter planes. The "balls" are knobs atop the plane's throttle control. Pushing the throttle all the way forward, to the wall of the cockpit, is to apply full throttle.
Alternatively,
Early railroad locomotives were powered by steam engines. Those engines typically had a mechanical governor. These governors consisted of two weighted steel balls mounted at the ends of two arms, jointed and attached to the end of a vertical shaft that was connected to the interior of the engine. The entire assembly is encased in a housing.
The shafts and the weighted balls rotate at a rate driven by the engine speed. As engine speed increases, the assembly rotates at a faster speed and centrifugal force causes the weighted balls to hinge upward on the arms.
At maximum engine speed - controlled by these governors - centrifugal force causes the two weighted balls to rotate with their connecting shafts parallel to the ground and thereby nearly touching the sides - the walls - of their metal housing.
So, an engineer driving his steam locomotive at full throttle was going "balls to the wall". The expression came to be used commonly to describe something going full speed.
Thanks to Virgil Jose
This may also be an example of rhyming slang.
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Flying by the seat of your pants
Meaning:
To do something without planning, to change course midstream, to figure things out as you go.
Example:
Most stock investors are not making educated decisions, they are just flying by the seat of their pants.
Origin:
Before airplanes had sophisticated instruments and flight control systems, and even today, planes are piloted by feel. Pilots can feel the reactions of the plane in response to their actions at the controls.
Being the largest point of contact between pilot and plane, most of the feel or feedback comes through the seat of the pants.
If you are "flying by the seat of your pants" your are responding to the feedback received.
See the related "on the fly".
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Pushing the envelope
Meaning:
To approach or exceed known performance boundaries.
Example:
Your performance at work is not exactly pushing the envelope.
Origin:
This expression comes out of the US Air Force test pilot program of the late 1940's.
The envelope refers to a plane's performance capabilities. The limits of the planes ability to fly at speeds and altitudes and under certain stresses define what is known as its performance envelope. It's an "envelope" in the sense that it contains the ranges of the plane's abilities.
"Pushing the envelope" originally meant flying an aircraft at, or even beyond, its known or recommended limits.
Thanks to Kensmark
A safe bet is that many who pushed the envelope crashed.
The expression was popularized by Tom Wolfe in his book "The right stuff" (1979) and later the movie of the same name.
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Wing and a prayer
Meaning:
Hopeful but unlikely to succeed.
Example:
She is driving on a wing and a prayer in that old jalopy.
Origin:
During World War One airplanes were still a novelty and untested in war. A "wing and a prayer" was first uttered when an American flyer came in with a badly damaged wing.
His fellow pilots and mechanics were amazed he didn't crash. He replied he was praying all the way in. Another pilot chimed in that "a wing and a prayer brought you back."
Thanks to Keith R. Dutton______________________________________________________________________