Forum: Civil and General Aviation

I understand how the clamshell type of thrust reversers work, of course, but I don't quite understand how the ones on large aircraft like 737s and C-5s work. All I see is a door on the side of the engine open up. My guess is that the thrust reverser is tapping into the bypass air around the core of the engine, but I'm not sure. Can anyone help me here? Thanks in advance Very Happy

!

F-16.net Sponsor

The FADEC-controlled CF6-80C2 engine has a sliding cascade door as the reverser (where part of the nacelles slides aft exposing the reverser's deflecting vanes) and uses fan thrust only to slow the jet. Once the the reverser lever is activated in the cockpit, the FADEC waits for the reverser to verify that's it's at least 90% deployed before spooling up to almost takeoff RPM. That fan air is then ducted forward by the reverser and your head then bounces off the seatback in front of you. Wink

Once the jet has slowed to sufficient taxi speed the lever is stowed and the reverser resets to the closed and locked position.

Link, I kind of figured you might answer this one - Thanks

That's how I figured it worked, but I wasn't sure.

Hey Jeff, one photograph is worth 1000 words Wink

DeepSpace, you rock Very Happy

! That's the perfect picture!!!

Great topic everyone!
From the diagram above, the core turbine still functions normally, so the deflected bypass thrust is greater than the core thrust or is there something else going on?

Pat1 wrote:

Great topic everyone!
From the diagram above, the core turbine still functions normally, so the deflected bypass thrust is greater than the core thrust or is there something else going on?

Nope....you got it. The reason they're called "hi bypass" engines is just that. A large part of the intake air bypasses the turbine, not just for reversal but for normal flight, too. In fact most newer generation hi-bypass engines get over 80% of their flying thrust from just the fan alone, which explains why the fan discs are sooooo much bigger than the turbine inlet.

Quote:

In fact most newer generation hi-bypass engines get over 80% of their flying thrust from just the fan alone

Amazing!! Thanks LinkF-16SimDude!

Hey everyone, DEEP SPACE's illustration tells all, (translating sleeves, blocker doors, and cascades), procured thrust reverser maintenance procedures on the MD-11 to all 3 customer engine options, P&W, GE, and RR. - allenperos, questions? Drop me a private message.

Jeff, current turbofan bypass air provide about 70-80% of the overall thrust from the engine. The actual tubrojet portion only provides that last 20-30%. This when thrust reverse is deployed, the bypass air will provide that 80% or so forward, while the turbojet is still pumping out the rest, which of course cancels out some of that reverse thrust. But that still leaves about 60% of total engine thrust being used to slow the airplane down. The tradeoff works, and helps slow the aircraft on landing, along with airbrakes and finally, manual wheelbraking.

Thanks Habu Very Happy

! It's basically like the turbojet core is just there to provide energy to turn that big fan up front. You definitely hear it when a 747 comes into McCarren if you're nearby Wink

!

Basically, high-bypass turbofans are really just big ducted fans, yes.

Thrust Reversers on a Fan Jet engine use devices called Blocker Doors to redirect the thrust. The blocker doors are deployed in the fan duct and fan air hitting the doors is ducted overboard through openings called cascades. Once the doors are fully open more thrust can be applied to the engine thus increasing the mass of fan air hitting the blocker doors. The best way to explain what is happening is to visualize a billboard on a highway in Florida during a Catagory I hurricane. The wind is trying to blow the sign down. Now the sign is the blocker doors and the wind is the fan air. In both cases a force is being applied to both objects. Next lets increase the storm to a Category V Hurricane. The sign is blown down by the greater force of the wind. If we accelerate our engine the fan is applying a greater force on the blocker doors but unlike the sign the doors are secured to the structure. The greater force on the doors is reverse thrust therefore the airplane slows down.

Well, the middle of the engine and the aft goes back and makes the air curve towards the front, which i guess slows the aircraft in landing and helps it taxi backwards or twists. Cool

lawwende wrote:

Thrust Reversers on a Fan Jet engine use devices called Blocker Doors to redirect the thrust. The blocker doors are deployed in the fan duct and fan air hitting the doors is ducted overboard through openings called cascades. Once the doors are fully open more thrust can be applied to the engine thus increasing the mass of fan air hitting the blocker doors. The best way to explain what is happening is to visualize a billboard on a highway in Florida during a Catagory I hurricane. The wind is trying to blow the sign down. Now the sign is the blocker doors and the wind is the fan air. In both cases a force is being applied to both objects. Next lets increase the storm to a Category V Hurricane. The sign is blown down by the greater force of the wind. If we accelerate our engine the fan is applying a greater force on the blocker doors but unlike the sign the doors are secured to the structure. The greater force on the doors is reverse thrust therefore the airplane slows down.

The problem with the concept that the air directed forward provides reverse thrust is that the largest majority of the air is directed out the sides of the engine not directly forward.
This air would provide side thrust not reverse thrust so the statement that the Fan provides 100% reverse thrust would not be [Link pending approval]
In addition directing air forward could product a back flow in the engine creating a stall condition.

Forum: Civil and General Aviation

How do thrust reversers work on large aircraft?