What are these on the engines?

[20Legend]

Are the bit sticking out on the engines auto reverse??
Why are the both not deployed at the same time?

http://www.airliners.net/open.file/1251427/M/

[MrHorgy]

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

[20Legend]

Thanks for the reply.

Yes I can see they are opening, maybe they are activated in a certain order? Can you put only 2 of the 4 engines in reverse or would that be plane stupid?

[bvcu]

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 !!!

[World of Tweed]

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.

[20Legend]

so does that mean there will they will have to make to "engines", one with and one with the thrust, should be a nice spares issue.

[Contacttower]

so does that mean there will they will have to make to "engines", one with and one with the thrust, should be a nice spares issue.


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

[hvogt]

Actually the A380 will only have reversers on 2 of its 4 powerplants. This is to save weight.

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.

[landing-gear]

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.

[landing-gear]

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

[spannersatcx]

so does that mean there will they will have to make to "engines", one with and one with the thrust, should be a nice spares issue.
No, as with a lot of engines the reverser stays on the wing when the engine is removed.
Airbus is different to Boeing in that they have 'doors' that pop open from the side of the engine
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.

[XPMorten]

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

[bri1980]

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

[mustafagander]

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.

[7p3i7lot]

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.

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.

[Richae]

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.

[gengis]

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?

[Intruder]

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??
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

[nalak_yc]

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?

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!

[spannersatKL]

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.

[spannersatcx]

yes I know, got my airbus and engines mixed up meant 346.

[spannersatKL]

Easily done these days!!

[XPMorten]

Thanks Intruder :)

M

[bjones4]

On the subject of the A380, an alternative to reducing the number of reversers being studied by Airbus was dropping them all together, that decision came about as part of a massive weight loss and cost cutting program circa 1998 with the aircraft on offer at that time being not being anywhere near close to the ~20% cost reductions that Airbus wanted (and needed to sell any) over the 747-400.

To quote from 'Airbus A380' by Norris/Wagner,

Another cost and weight saving change discussed at great length with the airlines involved reducing or eliminating the use of engine thrust reversers. As the name suggests, these devices redirect the engine power - or some of it - forward to help slow the aircraft after touchdown. Whereas some early low bypass engines redirected all thrust by blocking the entire flow out of the exhaust, the later generation and much larger high bypass ratio engines deflected only the bypass stream. This limited but valuable reverse thrust was generally seen as a supplement to the stopping forces and helped reduce break wear on landing.

In itself, cutting wear and tear on brakes was a major cost saver, and the decision to eliminate some of even all the reversers was not to be taken lightly.

Airbus canvassed airlines on the proposals about November 1998, emphasizing potential weight saving and performance improvement from the the move. In the end, a compromise was reached and the reversers were dropped on the outside engine pair only, particularly since most airlines agreed that the increased braking thrust, from the improved efficiency engines to be used on the A3XX would help achieve a predicted stopping distance similar to, or better than the A340.

[easyduzzit]

20legend:
to answer your query more accurately, looking at the image(A343 on TDown),
this particular crew still had the nose extremely high for thrust reverser activation!
was it not for the spoilers all being extended, one could mistake the image for a take off, with the nose so high.(thrust reversers deploying, excluded)
as for the different stages of deployment,(#3 full open & #4 just cracking) this is also dependant on how synchronously the pilot selects all 4 levers, plus some doors on some engines may deploy/stow at diffferent rates, due friction/winds etc.
NOTE: no reverser can/should be operable until the landing gear has contacted the ground, plus time delay, couple of seconds, however this can be activated before all 4 wheels on each main gear, touch the tar.

no eng power can be applied in reverse until all 4 doors on each respective engine is fully open, & furthermore, #1 and 4 engines cannot be powered up until both engines have all 4 of their doors fully open, this to prevent an asymetric yaw situation, should 1 of the outboard engs not open fully, and the opposite goes to max reverse power! bad situation.
outboard engines have a far greater yaw effect on an aircraft due to the distance from the centre turning point, & the lever-arm length.

As already mentioned, modern reversers only deflect the fan or low pressure air, which on this particular engine is approx. 65-70%. small fan.
trust this clarifies, an unusually captured shot!

[20Legend]

Well thanks for all the great replies, certainly learn't a lot there!


http://www.airliners.net/open.file/1254670/M/ (http://www.airliners.net/open.file/1254670/M/)