What are these on the engines?
 

Those are the reverse thrust buckets. Airbus is different to Boeing in that they have 'doors' that pop open from the side of the engine and divert the flow forward. Boeing's have a moving section of cowling that slides backwards.

As to why some aren't open, as the aircraft has just touched down, i'd hazard a guess they were in the process of opening - you can see this from the No 4 engine bottom scoop being only half open.

Horgy

All airliners that i am aware of [Boeing/Airbus] have a reverser control on each throttle and each has to be activated, so on a 4 engine jet/prop thats a big handful ! bear in mind you can have them deactivated so it wouldnt be uncommon to see not all of them deployed, especially on an old 747 !!!

Actually the A380 will only have reversers on 2 of its 4 powerplants. This is to save weight. I' believe on the the inboard engines are fitted with reversers.

Generally speaking reverse thrust only reduces the wear on the brakes by allowing the use of a lower braking force. The actual "legal" performance of the aircraft is calculated without the use of reverse thrust and purely based on what energy the wheel brakes can absorb. To summise without reverse thrust the aircraft is more than capable of stopping in the required distance.

After a while there will probably A380s with three reverse thrusters on them!

I have been told that engines 1 and 4 had no reverse thrust because, due to the large wing span, reverse thrust on these engines would blow up too much dust from the strips. However, this might be an additional reason besides the weight issue.

Correct me if i am wrong..is another eason for only two reversers on the inboard engines of the A380 is to counter any FOD in the hard shoulders and grassed areas around the runways..with such a large wingspan they can overhang these areas somewhat.

we must have typed these replies at the same time..lol

No, as with a lot of engines the reverser stays on the wing when the engine is removed.
The engine in the picture is a CFM56, Airbus A340-600's that have RR engines use a thrust reverse sleeve or translating cowl, so it's not strictly an Airbus/Boeing thing.

efficiency of the thrust reversers?
 

Slightly OT, but does anyone know the efficiency of the thrust
reversers?
I mean, lets say an engine outputs 20.000 lbf
of thrust at e.g N1 80% in "normal forward" setting.
At N1 80% REVERSE, will it have a 20.000 lbf opposite thrust??

I would hardly think so since part of the blast (energy) will be directed
to the side, and not forward?

Cheers,

M

In 'reverse' mode, the thrust doesn't necessarily come out along the axis of the engine so you wouldn't expect 100% translation of forward to reverse thrust.

The Jet Engine by Rools Royce (ISBN 0 902121 2 35) has good info. on this point.

B

AFAIK the major effect of reverse thrust is that the plumes exhausted to the sides of the engine cowls act as large spoilers. Apparently the airflow sees it as almost solid.

A fringe benefit for B747 is that the inbd engine reversers tend to clear excess water from the path of the WLG trucks, enhancing their braking in adverse conditions.

Actually the 737NG FAA certified landing data allows for use of partial reverse (1 eng credit worth I think) when landing on runways with less than normal (ie GOOD) braking. Of course if an MEL item exists on the reversers then the credit is not allowed.
Certification rules are not cast in stone so whatever the manufacturer can propose to the certifying authority and convince them that it is equally safe they can accept and put in the type cert documents.

20Legend - the 380 engines themselves are all the same. The nacelle contains the reverser so it is this that will vary depending on position.

The design of the reverser is usually carried out by the nacelle manufacturer - most of Airbus' are now manufactured by Aircelle - they have the 380 contract.

re 380 inboard reversers, that's wonderful! what happens when they get number 2 or 3 failure 3 kts below V1 on a balanced field with braking action medium in a 15 kt x-wind?

or landing at regulated landing weight on a snowed out airfield with MEL 1 rev inop?

On the order of 40% or less.

First, the fan on a high-bypass turbofan produces about 75% of the thrust.

Second, only the fan exhaust is diverted by the reversers.

Third, there will be some efficiency losses.

Fourth, max RPM or thrust will be less in reverse than in normal operation.

So, the basic equation is Reverse thrust = [Fan thrust (reversed) - HP thrust (residual)] x Efficiency factor

or

Trev = [75% Tfwd - 25% Tfwd] x Fe
Trev = 50% Tfwd x Fe

Given the RPM restrictions and efficiency losses, a 20% efficiency loss is reasonable, so

Trev ~~ 50% Tfwd x .8 ~~ 40% Tfwd

well how is that different to a 777 with a left engine failure 3kts below V1? :rolleyes:

3kts below V1 with an engine failure seriously i would much rather continue the takeoff with a early rotation if necessary to get the darn thing off the ground then dump the gas and come back for a easy landing!

Spanners at CX the A330 T700 dosen't have a sleeve, has the 4 buckets very similar to the as 340 illustrated.. Unlike all the other RR Big Fan engines in the 22B / 524 series that have a sleeve and blocker doors. The reverser is made by Herle Dubois on the 330/RR.

Reverser on the B777 is a Boeing design by Rhor I believe for ALL engines on that aircraft.