If a turbofan produces forwrad thrust and Newton's second low action and reaction are equal and opposite, how

Question

According to newton's second low action and reaction are equal,opposite so why does reverse thrust work if the engines still suck in air?

Answer 1

I think I know what you're asking, I thought the same thing.

The engines don't move the plane by sucking. The air getting sucked in the inlet comes from all directions, even from behind the leading edge of the inlet. All the thrust is made by blowing air and exhaust out the back. The thrust reverser's just redirect most or all of the thrust (air or air and exhaust) in a forward direction.

In order for your theory to be true a normal running engine will suck air from 100 feet in front of it and blow it back 100 feet behind it.

Think of a vacuum cleaner (shop vac), you can hold your hand 2 inches from the suction end and not feel anything but you'll be able to feel the air coming out of the exhaust more than 10 feet away. If you point the exhaust the same direction as the suction all you'll feel is the exhaust.

Answer 2

When airplanes apply reverse thrust, they revector the thrust in the opposite direction. Air still enters the engine through the the front compressor section and goes through the same compression and combustion process. The engine itself does not shift gears or anything. The only difference is that instead of the thrust energy exiting straight out and reward, it is either deflected by two steel plates that come over the exhaust end of the engine and divert it foward, or on other engines (most commercial airliners) the thrust is redirected foward through the sidewall of the engine at an angle.

Answer 3

Turbanfans work because the engine pods in which they sit are fixed to the wing .

The reverse thrust works not by "suction" by actually by thrust "deflection" some early jet engine reverse thrust systems work by buckets which open at the back of the engine on touch down, the buckets divert the air upwards and radially around the engine, causing the reverse of "wing lift" and slowing the aircraft right down, new jet engines work pretty much on the same principle, the air is pushed out of slots in the engine pods creating turbulence around the engine and a slowing action of the engine and wing to which it is fixed.

Contrary to popular opinion the reverse thrust is an integral part of aircraft braking and is nearly always the first part of braking on touchdown, followed closely behind or simultaneously by the "air/speed brakes" huge flaps which spring vertically upwards at about 90 degrees on top of the wings and then by the pilots using the footbrakes. I dont really understand how any aircraft can stop safely from 160mph on a dodgy runway with only one side of the reverse thrust system operable.

Answer 4

Engines when in reverse thrust do NOT:

A. Push the air out of the intake

or

B. Spin the opposite direction

What happens when "reverse" thrust is applied is this:

Blocker doors on the path of the thrust open up into that path to redirect the airflow

Translating sleeves slide aft to reveal the cascade vanes (which are like little vents) that are all slanted internally to direct the air forward.

The engines increase in thrust.

Fo older turbo-jet engines, clamshell doors deploy at the exhaust nozzle and have the same effect.

Answer 5

Watch reversers in action sometime. (They are external to the engine and visible.) The do not affect turbofan operation. They physically deflect at the exhaust point.
The turboban actually "produces" a rearward flow
of exhaust and bypass air. It is Newton's law which provides the forward motion of the aircraft in response. As mentioned, the reversers are "deflecters". And they are not necessarily "integral" to aircraft operation. Useful, helpful, but not necessarily "integral". For a particular aircraft, look at its performance data to see how reversers affect takeoff and/or landing distance, if at all. (Takeoff can be affected for abort purposes.) The deflection is generally forward and there is a small range of fan speed operation that is available using the "piggyback" reverser levers. You might find that other inop components incur a higher penalty (anti-skid brake function, for example). I have seen performance charts that provided landing data only for "no reversers" even though the aircraft was equipped with reversers. In other words, your required distance in those aircraft was based on no reversers all the time.

Answer 6

When reverse thrust is used the "force" (thrust) is re-directed forward. The equal and opposite force, therefore, acts in the reverse direction.

Answer 7

Duh, because engines operate on Bernouli's venturi principle.

Funny so do rockets!

The only part of an engine directly applying newtonian principles is the Turbine section. So if you deflect that out put forward...Thrust reversers!

Except new gen High By pass which deflect fan air(first three stages), but still Newronian Action/Reaction.

can't you just wikipedia these simple things?

Ret. USAF SNCO, Aircraft Maint.

Answer 8

A jet engine's exhaust pressure is usually greater than its intake pressure.