Reverse thrusters?

Question

when the engines reverse thrust the back half of the engine cover slides back. Exactly what is going on here, how does the engine "reverse" the thrust?

Answer 1

http://youtube.com/watch?v=Q8hNd01ynYw

http://youtube.com/watch?v=DHYI7bKNhZg

For jets there are basically 2 types of thrust reverser's, the first video is the clam-shell type (B737-200) and the second is the cascade vane type. This is the type you ask about. When the shroud or cover slides back it opens the area around the engine allowing the exhaust to exit the engine through what look like slots that angle forward. After landing the pilot pulls the throttle to idle which unlocks the reverse lock allowing the pilot to pull up on the reverse levers(located on top of the throttles on the front side) This increases the engine thrust, usually limited to about 80% of thrust.

The clam-shell type blocks the thrust coming out of the engine and re directs it forward.

http://www.boeing.com/commercial/aeromag...

Look at the bottom of the page@fig.#4 on the above link. It is a poor picture of the reverse thrust levers for a B737.

Answer 2

When the engine cowling moves, it exposes vents to allow the engine thrust to go forward. At the same time blocker doors deploy to prevent the fan exhaust from exiting the back of the engine. So, with the back blocked and the sides open, the thrust is redirected forwards.

Answer 3

Years ago i was on a wing seat on a Piedmont i believe 737 from Florida to new york when those reverse thruster flipped into reverse and redirected the thrust to the front I thought the swivel pin was going to rip right out of it's socket. Like sticking a

a cup out the window of a car doing 150 mph

if you couldn't let

go you might rip your wrist off.

Answer 4

In the cascade type of thrust reverser what's happening is the the bi-pass air is directed forward to help stop the plane.  The engines are not idled in fact they go to full power for maximum stopping power.

Answer 5

Thrust 're-directors' is a better term.

The engine's thrust still exhausts the same way, it's just re-directed forward.

Answer 6

the engine thrusts forward causing the plane to move in the opposite direction. as it is already moving forward at a high speed, it slows down quickly.

Answer 7

The exhaust is diverted so that it has some forward component, but it isn't fully reversed.  

To pull the thrust reverse levers the main thrust levers have to be back at the idle setting.  Pulling the thrust reverse levers increases fuel flow and hence increases the resulting thrust to be "reversed."  During reverse, there are EPR and ITT limits to consider.

Answer 8

There are three main tyoes of thrust reversal systems:

1. Cold Stream Reveses - There is a series of cascade vanes set into the wall of the bypass duct which are covered by a blocker door in normal flight. An actuation system folds the blocker doors to blank off the cold stream final nozzle, thus diverting the airflow through the cascade vanes. The cascade vanes are all slanted so the airflow changes direction oppostie to its path through the bypass ducts. C-17's have this technology.

2. Bucket Door -  This system uses bucket type doors to reverse the hot gas stream. The thrust reverse doors are actuated by a conventional hydraulic powered pushrod system. In the forward thrust mode the bucket doors form the convergent-divergent final nozzle for the engine. When they are actuated they change position and form a barrier where the exhaust and bypass air is redirected.

3. Clamshell Door - This system is a pneumatically operated system. Normal engine operation is not affected by this system, because the ducts through which the exhaust gases are deflected remain shut until reverse thrust is activated by the pilot. When this happens, the clamshell doors rotate to uncover the ducts and close the normal exit. Then the thrust is directed in a forward direction by vanes to oppose the aircraft's motion.

Pictures would help!!

Answer 9

This was the answer given by a retired Air Force Pilot.

Reverse thrust is really a cool thing.  First off, no the engine does not go into reverse.  That is actually an engine stall if that happens and is not good.  By the way, that very rarely happens and is usually associated with ingesting a bird or something else in the engine.  There are two ways that I've seen, to produce reverse thrust.  Like you said, the cowling moves.  Some airplanes have a clamshell type method to do this.  The rear panels on the engine swing back and meet at 45 degree angle or so deflecting the thrust forward instead of letting it go back.  Some thrust still goes back must a good chunk is deflected.  The other system I've seen just has the mid-section panels slide back.  Think of it like you're taking a bottle out of a koozie.  The whole thing just slides back from a certain point.  The same thing happens again with the deflectors.

You might be surprised for in-flight braking.  If the pilot quickly reduces the thrust it is a pretty quick decceleration.  However, there are also speed brakes on the plane.  On commercial jets they are usually on the top side of the wing.  They are basically just big panels on each wing that raises up into the airstream.  This actually does two things.  It creats more drag, thus slowing down, but it also spoils some of the lift being created by the plane, also slowing the jet down.  Generally, the pilot can command how much the speed brakes go up so they can slow down a little or slow down a lot.  Next time you fly try to get a window seat.  On landing you'll notice the speed brakes on the wings are nearly straight up and the thrust reversers are open.  

Hope this helps.

Answer 10

hope i do a better explanation: As the T/R is deployed the translating sleeve moves aft, carrying with it blocker doors located circumferentially  to the closed position.When the T/R sleeve is fully deployed this blocker doors are fully now closed and block the thrust where the only way out  is to go back or out through the cascading vanes ( a series of holes that direct the reverse thrust  either upward or downward this is in case of foreign object will not be ingested by the other engine ( this esp true in 747 1 & 4 engine the cascading vanes are all going outboard.

As for the throttle lever must be at idle before the T/R handle can be deployed it is just a safety design, imagine a T/R deploying at high power in the air. Even though an Air/Ground switch logic must be satisfied first before a  T/R can be deployed nowadays.

Answer 11

Zach -

There are several ways that reversers can block the flow, but they don't really thrust it forward to any great degree. All they have to do is turn the flow from axially inward at the fan inlet to radially outward at the reverser. When this occurs - due to a combination of sliding panels or curved vents - then all the momentum from the inlet air (a huge number when the engine is running at full throttle) is converted to braking when it encounters the "brick wall" of the reverser instead of going out the aft end as in normal flight. Some reversers turn the flow slightly forward to provide additional braking, but this is icing on the cake. The majority of the braking occurs because the axial inlet flow is suddenly and forcefully prevented from going out the aft end of the engine. It's a momentum transfer.

ADDED: The throttles are normally set to idle at touchdown, and then returned to a high throttle setting during reverser deployment. Without high shaft speeds, the fan won't pull in the air and the momentum transfer cannot occur by any significant amount.

Answer 12

Thrust reversers change the direction of the fan air, directing it forward. The cover sliding back is the translating cowl which serves two purposes. As the translating cowl moves back, it exposes the cascade vanes which turn the fan air around by up to 130 degrees. So instead of going out the back of the engine, it is re-directed mostly forward and provides a backward thrust on the engine. Also, as the cowl slides back it pulls blocker doors into the fan air  stream so the fan air has nowhere to go except out the cascades.