In article ,
"Morgans" wrote:

"Ramapriya" wrote in message
roups.com...
I know that a car's engine needs to be mated to the transmission for
propulsion. This I know isn't the case with an aircraft with a jet
engine; if the engine is turned on without the brakes applied, the jet
of air leaving the engine will hurl the craft forward.

My doubt is, why does this forward motion effect not occur during
push-back, when the engines are normally turned on? Is it because at
low revs the engine would lack the punch to initiate the forward motion
of a heavy aircraft? If not, I'd imagine the push-back becomes a bit of
a tiresome affair by the time it's over...

Sorry if this is infuriatingly elementary, but I need to ask somewhere


Ramapriya


At idle, turbo fan engines, or turbo jet engines do not make a tremendous
amount of thrust. The push-back tugs are very powerful, with very low
gearing. They simply push harder than the engines are pushing.

Sometimes, the engines are not started until after push-back, or while the
push-back is taking place.

Some of the heavy metal pilots can tell you better than me, but it is my
understanding that it takes well over 50% RPM to get 50% thrust, so it
goes to follow that 10% RPM is way less than 10% thrust.

Where have you been? Kinda' lonely around here, without your constant
questions! g

Thrust and RPM do not have a linear relationship. Idle can be as high as
60%.

--
Ron Parsons