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One thing I noticed with the A380 is that it only seems to use the inboard thrust reversers while landing. I suspect it relates to FOD ingestion or perhaps damaging the runway. This is strange though, because the 747-8 (which also has a large wingspan and very large engines), does use all of its thrust reversers during landing. Does anyone have an official answer on why this is?

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Federico
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Bryson S.
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    I know :) but I got really embarrassed when my six yo noticed that while I have been playing FSX with him. – matcheek Mar 17 '19 at 20:46

1 Answers1

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Why doesn't the A380 use its outboard thrust reversers?

Because it doesn't have (or need) any.

The A380 has reverse thrust on the inboard engines only. This saves weight and since the outboards are often way out over the edge of runways, decreases the risk of FOD.

From Airliners.net

Like all certified transport aircraft of this type, the A380 can stop from V1 on brakes alone with disks worn to minimum.

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I've read that most airliners are allowed to take off even when all reverse-thrusters are inoperative. Most of the deceleration is handled by the brakes normally.

With the Airbus A380 weighing in fully loaded at 1,265,000 pounds, you might think stopping it within a reasonable distance after landing would require a Phalanx of Heavy-duty thrust reversers.

Truth be told, in the megaliner’s braking system, thrust reversers are the least critical components. Airliners are not required to have thrust reversers, and only the two inboard engines on the A380 are equipped with them. The decision not to install reversers on the A380’s two outboard engines saved weight and lowered the chances that those engines, which sometimes hang over runway edges, would be damaged by ingesting foreign objects.

The two reversers do help slow the A380—but not by much. In fact, unlike the thrust reversers on most airliners, including the Boeing 747 jumbo, they do not stop the aircraft in a shorter distance than brakes and spoilers alone. They do, however, take some of the strain off the brakes and are useful if water or snow makes the runway slippery.

From Airspace Magazine

More details of braking system

1. General
The aircraft has:

  • Two Wing Landing Gears (WLG) with four wheel bogie assembly and related doors
  • Two Body Landing Gears (BLG) with six wheel bogie assembly and related doors
  • A Nose Landing Gear (NLG) with twin wheel assembly and related doors.

...

  1. Braking
    A. General
    Carbon brakes are installed on each wheel of the WLG and on the wheels of the front and center axles of the BLG.
    The braking system is electrically controlled and hydraulically operated.
    The braking system has four braking modes plus autobrake and anti-skid systems:

    • Normal braking with anti-skid capability
    • Alternative braking with anti-skid capability
    • Emergency Braking (with Ultimate Braking)
    • Emergency braking without anti-skid protection is also available as an alternative function of the alternate braking system.
    • A park brake system that is manually set is available for the BLG only. This system can also be used to supply emergency braking.

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FOD risk

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A380 Landing at Farnborough Airport

A380 vs 747

The design of the A380’s wings, with their large area, comparatively gentle sweep (33.5 degrees), and massive flaps, give the Airbus a landing speed that is 20 knots slower than that of a 747. An A380 crosses the landing threshold at a docile 140 knots and touches down, depending on its landing weight, at a speed as slow as 130 knots, about the same touchdown speed of some corporate jets that weigh 1/50th as much as the world’s biggest airliner.

AirspaceMag

RedGrittyBrick
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  • If most deceleration is handled by the brakes, then why even have thrust reversers in the first place? I find it hard to believe that millions of man-hours (and dollars) went into designing, optimizing, and engineering entirely unnecessary equipment. – Bryson S. Jun 18 '14 at 13:53
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    Millions of man-hours and dollars are spent on duplicate, triplicate (or more) redundant heterogeneous systems on aircraft. See Perdue University, College of Engineering – RedGrittyBrick Jun 18 '14 at 14:06
  • So does the difference ultimately boil down solely to the number of braked axles? – Bryson S. Jun 18 '14 at 14:31
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    If there is fear that the outboard engines would ingest crap (FOD) because they overhang the edge of the runway, why wouldn't that also apply to takeoff, when the outboard engines are presumably at high thrust? Does an engine at reverse thrust kick air (and debris) far enough forward that there is a real risk of ingestion and FOD? Could that be negated by designing the reverse thrusters to go mostly sideways? – Phil Perry Jun 18 '14 at 17:11
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    @Phil: That looks like a question (or three). You could click the "Ask Question" link at top right of page. – RedGrittyBrick Jun 18 '14 at 17:25
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    @BrysonS.: Not really. All main gear axles are usually braked. The difference is in cooling of the brakes. Every aircraft has to be able to stop without reversers, because the probability of their failure is too high to rely on them, but it might be at the cost of overheating the brakes. A380 brakes have sufficiently good cooling that they deemed two reversers sufficient. – Jan Hudec Jun 18 '14 at 18:08
  • @Jan Hudec I think my main question was why the A380 can get away with such minimal thrust reversal, while the 747-8 (and many other aircraft like it) rely on it to a far greater extent. – Bryson S. Jun 18 '14 at 18:57
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    @Phil I second RedGrittyBrick's suggestion on making your comment a question. If you do, I'll provide an answer far longer than what I can get into a comment here. – Terry Jun 18 '14 at 20:14
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    " It can stop from V1 on brakes alone with disks worn to minimum." - All aircraft can do this, it's a certification requirement and (partly) used to determine the runway requirements. But it's really bad for the hardware. White-hot brakes can (and do) set tires on fire, and replacing half of your undercarriage every time the pilot tries to exit on Charlie instead of Delta gets rather expensive. – paul Jun 18 '14 at 21:23
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    @PhilPerry doesn't apply on takeoff because the jet blast is behind the engine, and it's accelerating away from the debris. Point your exhaust forward while slowing down, and you will at some point inhale any debris you kick up. Some small bizjets do use sideways "reversers" but they are more "thrust cancellers" as they do not slow the aircraft in any way. – paul Jun 18 '14 at 21:27
  • OK, @Terry new question at [A380 v B-747 Thrust Reversers on outboard engines] – Phil Perry Jun 18 '14 at 23:35
  • @PhilPerry Link to new question: A380 v B-747 Thrust Reversers on outboard engines – Volker Siegel Jun 02 '15 at 00:52
  • So why does the last picture in the question show both engines on that side with deployed reversers? – Lnafziger Apr 19 '16 at 01:39
  • @Lnafziger: Whether the pictured 747 pilots deployed all 4 thrust reversers or not on the 747 doesn't tell us much about whether or why Airbus installed 4 or 2 on the A380 - or did your question mean something else? – RedGrittyBrick Apr 19 '16 at 08:57
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    @RedGrittyBrick Well, I suppose that it meant that I didn't notice that it was a different airplane than what he was asking about! :) – Lnafziger Apr 19 '16 at 13:27
  • You wrote that A380 has 10 braked axles. Note that it has 16 main wheels with brakes and 4 main wheels without brakes. – bogl Dec 07 '16 at 15:51
  • @bogl: thanks, answer updated. – RedGrittyBrick Dec 07 '16 at 16:18
  • @RedGrittyBrick What does FOD means? – Gabriel Brito Dec 07 '16 at 18:16
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    @Gabriel: Foreign Object Damage. The outboard engines can be at the edge of the runway or over a grassed area, Reverse thrust on the outboard engines can throw debris (any loose material or objects) up in front of the engines where they will be sucked in (ingested) and may cause damage to the engine. – RedGrittyBrick Dec 07 '16 at 23:03
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    @RedGrittyBrick during the A380s design phase, Airbus originally wanted to do away with thrust reversers altogether - they add weight and maintenance cost to the airframe, and as all landings in commercial aircraft are required to be calculated without the use of thrust reversers, they are more of an unneeded item these days. The FAA said no, Airbus had to include a pair. So Airbus included a pair. There was lots of discussion on this online a decade ago, but much of it has been lost in the annals of time. – Moo Dec 10 '16 at 16:50