Is there a difference if you put the engines to idle or if you shut them completely down, when you are on.....

Question

......... cruising level?

I mean normally, even idle engines do not make thrust (i.e. when you are on ground and they are idle, the plane will not move).

Answer 1

engine on idle still provides thrust, and the value is significant enought to make difference in the rate of descent between two configurations you mentioned.

the important thing why they do not shut down engines during descent is that the engine will be needed during the rejected landing /missed approach procedure and starting a jet engine takes quite a while, and increasing thrust is just a thing of seconds.

Answer 2

The brits fly a plane called the NIMROD which is actually a remodeled old Comet.  It's used for anti sub warfare amongst other things.   This plane has four internal jet engines inside the wing close to the fuselage.  Once the aircraft gets up to it's working altitude which is around 290 or 300 it turns off two of it's engines to save fuel.  But for takeoff and landing they are all on.

Answer 3

yes they can go on idle but it depends on a lot of things around

Answer 4

As mentioned previously, ground idle and flight idle are different. Flight idle is established based on things like anti - icing requirements at altitude and allowable descent rate. Thrust resulting from either condition is not insignificant. When I flew T38s, we used to save fuel (a little) by shutting one engine down to taxi in after our final landing (this was during the Carter years). I know of no self - respecting pilot who would intentionally shut an engine down in flight for reasons other than an emergency.

Answer 5

If you shut off an airliner's engines at cruising level, residual thrust will go away, and then you're going to have added drag from the engines (which aren't running, but now turning or windmilling).  

Air for pressurization and electricity is not available now from those engines (presuming aux power unit isn't being used for that), and the rate of descent from cruise altitude will be a little higher than with idling engines.

And, the majority of airliners will roll at idle, certainly at low weights.  There is some residual thrust at idle.

Answer 6

Modern aircraft as soon as the landing gear leg has been stowed (shock strut compressed) the aircraft is in flight configuration. what used to be idle is now flight idle a solenoid in the Fuel Control Unit or the Main Engine Control is energized to gives a 10% more fuel or above idle.

Answer 7

"idle engines do not make thrust"?  

Idle engines do make thrust.