[jscott817]

Similar to balls to the walls (or similar). Coming from the analog aviation controls I believe.

[buildsjets]

Example, throttle controls on a Dogulas DC3. All engine controls forward is the typical convention for full power. (At sea level, neglecting the altitude effect on required engine fuel/air mixture.)

https://www.douglasdc3.com/dc3throt/dc3throt.htm

[conartist6]

That said, i'm sure the pilots were aware of the double entendre

[CalRobert]

Balls to the van der Waals

[taneq]

Engaging in a little hydrogen bonding, eh?