It's been a while since my last 763 flight and so am somewhat out of the loop with up-to-date heavy jet ops. After watching a series of A380 landings, I noticed only engines 2 & 3 seemed to use reverse after landing - some with idle reverse; some with full on reverse.

https://fb.watch/aL9wmMdvX4/

Can any A380 operators on this forum elaborate?

Thanks!

I'm not an operator, but only the inboard engines of the A380 have thrust reversers due to the possible FOD ingestion with the outboard engines hanging over the edge of the runway.

Yikes! wrote:

It's been a while since my last 763 flight and so am somewhat out of the loop with up-to-date heavy jet ops. After watching a series of A380 landings, I noticed only engines 2 & 3 seemed to use reverse after landing - some with idle reverse; some with full on reverse.

https://fb.watch/aL9wmMdvX4/

Can any A380 operators on this forum elaborate?

Thanks!

Interesting fact, Airbus originally wanted to certify it with no reverse at all! I believe the American regulators would have none of it and the compromise was on the inboards only, due to FOD risk given how far out the outboards hang (well over the grass at most airports) as per the previous post. It has really good brakes on 16 of the 20 main gear wheels (the last pair on each 6-wheel truck having no brakes, although the F version, never built, would have.)

Great answers, makes sense. Thanks.

My recollection was Airbus was looking to save weight and therefore deleted the two outboard engines fairly late in the development program, providing numbers on how little impact it would have had on the stopping margin.
There should be an article on it out there somewhere, at least there was at the time.

Mainly due to FOD prevention on Engine 1 and 4…

77west wrote:

Yikes! wrote:

It's been a while since my last 763 flight and so am somewhat out of the loop with up-to-date heavy jet ops. After watching a series of A380 landings, I noticed only engines 2 & 3 seemed to use reverse after landing - some with idle reverse; some with full on reverse.

https://fb.watch/aL9wmMdvX4/

Can any A380 operators on this forum elaborate?

Thanks!

Interesting fact, Airbus originally wanted to certify it with no reverse at all! I believe the American regulators would have none of it and the compromise was on the inboards only, due to FOD risk given how far out the outboards hang (well over the grass at most airports) as per the previous post. It has really good brakes on 16 of the 20 main gear wheels (the last pair on each 6-wheel truck having no brakes, although the F version, never built, would have.)

Are you sure the FAA would not allow the A380 to operate without thrust reversers? Do you have a source? The KC-46 is an FAA certified airplane and doesn’t have thrust reversers.

BoeingGuy wrote:

77west wrote:

Yikes! wrote:

It's been a while since my last 763 flight and so am somewhat out of the loop with up-to-date heavy jet ops. After watching a series of A380 landings, I noticed only engines 2 & 3 seemed to use reverse after landing - some with idle reverse; some with full on reverse.

https://fb.watch/aL9wmMdvX4/

Can any A380 operators on this forum elaborate?

Thanks!

Interesting fact, Airbus originally wanted to certify it with no reverse at all! I believe the American regulators would have none of it and the compromise was on the inboards only, due to FOD risk given how far out the outboards hang (well over the grass at most airports) as per the previous post. It has really good brakes on 16 of the 20 main gear wheels (the last pair on each 6-wheel truck having no brakes, although the F version, never built, would have.)

Are you sure the FAA would not allow the A380 to operate without thrust reversers? Do you have a source? The KC-46 is an FAA certified airplane and doesn’t have thrust reversers.

I admit I do not have it in writing, but am reasonably sure they originally wanted no reversers and either ICAO or FAA said no, and having them on the inboards was the compromise. There may be a difference for scheduled passenger ops vs military, it would be good if someone could find out though as some basic googling has not given a conclusive enough answer.

The KC-46 might be FAA cert’d but I’m sure they’d make an exception as it’s a military only aircraft. Probably an agreement it never gets sold in the civilian market.

GalaxyFlyer wrote:

The KC-46 might be FAA cert’d but I’m sure they’d make an exception as it’s a military only aircraft. Probably an agreement it never gets sold in the civilian market.

Interesting, the military connection. I was amazed seeing Canada's RCAF C-17's, up close and personal, to see not only the fan thrust was "reversed" but the core thrust was blocked during landing ops. Given the ratio of 75/25 for fan/core thrust production on landing, that extra 25% blocked reduces the landing distance significantly. Does the A380 have strictly fan reverse thrust on 2 & 3 or does it also have "blocking" as do our C-17s?

FYI, I'm now retired from my Transport Canada surveillance job and nearly 15 years away from the heavy jets. Still, some interest remains!

Yikes! wrote:

GalaxyFlyer wrote:

The KC-46 might be FAA cert’d but I’m sure they’d make an exception as it’s a military only aircraft. Probably an agreement it never gets sold in the civilian market.

Interesting, the military connection. I was amazed seeing Canada's RCAF C-17's, up close and personal, to see not only the fan thrust was "reversed" but the core thrust was blocked during landing ops. Given the ratio of 75/25 for fan/core thrust production on landing, that extra 25% blocked reduces the landing distance significantly. Does the A380 have strictly fan reverse thrust on 2 & 3 or does it also have "blocking" as do our C-17s?

FYI, I'm now retired from my Transport Canada surveillance job and nearly 15 years away from the heavy jets. Still, some interest remains!

I can't think of any modern civilian turbofans that reverse core thrust. If nothing else, the A380 engines, like other large modern turbofans, have a fan/core thrust ratio is more like 90/10 than 75/25.

IIRC, the reason the C-17 has core thrust reverse is that they can use reverse in flight for very high rates of descent into dodgy places where someone might want to take a potshot at the aircraft.

Starlionblue wrote:

I can't think of any modern civilian turbofans that reverse core thrust. If nothing else, the A380 engines, like other large modern turbofans, have a fan/core thrust ratio is more like 90/10 than 75/25.

IIRC, the reason the C-17 has core thrust reverse is that they can use reverse in flight for very high rates of descent into dodgy places where someone might want to take a potshot at the aircraft.

I don't think that's the reason, per se. The Barney uses both core and fan reverse inflight - there's no differentiation: it's just reverse idle and not even a separate TR lever from the throttles.

If memory serves, the fan TR moves air forward and up and the core moves air up only. For why, think both FOD damage from jet blast when operating on dirt airfields, as well as the outstanding virtue of ease of operation for ground equipment and troops during an ERO: a C-130's reverse pitch will exfoliate an elephant, but you can light a cigarette behind a C-17 in reverse idle.

Airliners generally don't have to worry about that sort of FOD. Unless they're in Philadelphia

Yikes! wrote:

Interesting, the military connection. I was amazed seeing Canada's RCAF C-17's, up close and personal, to see not only the fan thrust was "reversed" but the core thrust was blocked during landing ops. Given the ratio of 75/25 for fan/core thrust production on landing, that extra 25% blocked reduces the landing distance significantly. Does the A380 have strictly fan reverse thrust on 2 & 3 or does it also have "blocking" as do our C-17s?

Hello,

The thrust reversers on any modern turbofan of current production is limited to the bypass flow.
The entire thrust was reversed on "clam shell" type reverser systems e.g. on the JT8-D and similar low-bypass systems. Early large turbofans were equipped with a double system - a sliding door reverser like on current engines and, additionally with a separate reverser for the core flow. See an illustration here:
https://aviation.stackexchange.com/questions/77539/what-mechanism-did-the-turbine-reversers-of-early-high-bypass-turbofans-use
This system was abandoned / deactivated pretty soon, as the added reverse thrust was small vs. a relatively maintenance-intensive apparatus.

It's comparable to the today abandoned idea of NLG brake - it existet (at least) on the 727 and was cancelled for the same reason.

Kind regards,
Hendric

hitower3 wrote:

Yikes! wrote:

Interesting, the military connection. I was amazed seeing Canada's RCAF C-17's, up close and personal, to see not only the fan thrust was "reversed" but the core thrust was blocked during landing ops. Given the ratio of 75/25 for fan/core thrust production on landing, that extra 25% blocked reduces the landing distance significantly. Does the A380 have strictly fan reverse thrust on 2 & 3 or does it also have "blocking" as do our C-17s?

Hello,

The thrust reversers on any modern turbofan of current production is limited to the bypass flow.
The entire thrust was reversed on "clam shell" type reverser systems e.g. on the JT8-D and similar low-bypass systems. Early large turbofans were equipped with a double system - a sliding door reverser like on current engines and, additionally with a separate reverser for the core flow. See an illustration here:
https://aviation.stackexchange.com/questions/77539/what-mechanism-did-the-turbine-reversers-of-early-high-bypass-turbofans-use
This system was abandoned / deactivated pretty soon, as the added reverse thrust was small vs. a relatively maintenance-intensive apparatus.

It's comparable to the today abandoned idea of NLG brake - it existet (at least) on the 727 and was cancelled for the same reason.

Kind regards,
Hendric

I did specify "blocked core" rather than any kind of reverse on the C17. During traditional reverse thrust ops on modern hi-bypass engines, the engine is spooled up to nearly maximum. Given the ratio of thrust by the fan (on landing and on takeoff at about 75/25 vice 60/40 in cruise), the fan reverse far outweighs the core thrust increase producing a net deceleration. When that core thrust increase (on landing) is blocked, it effectively removes the core thrust during reverse/deceleration ops. Hope that clarifies what I asked/wrote.

Yikes, the A380 is fan only reverse. It doesn’t block core exhaust.

If you’re wondering why, commercial airliners rely primarily on their brakes to stop, with reverse thrust as a bonus - especially important on a contaminated runway, such as covered with snow. They’re usually at reverse idle ~ 60 knots and then restowed. They don’t back up, nor do they do really steep descents. Those might spill the champagne in first class.

The C-17, on the other hand, uses its TRs more like another kind of brake; it’s an integral way to stop a 450-ish-585K aircraft in a few thousand feet of earth, whether dirt or asphalt, so it’s used differently. Not only does it slow the jet, it can back it up. At max T/O weight. Up a 2 degree slope. Arrive over the field at FL400 to avoid manpads and AAA? No problem! Reverse idle on all 4 engines (+ boards) are a fantastic drag device and spiral down! That’s a much different method of operation to a commercial airliner’s, with a correspondingly different design.

The C-17's capability to mimic a a falling manhole cover is impressive indeed. The 380's TR design is very simple. The only thing that stinks is getting the Safran spares to repair it.

BoeingGuy wrote:

77west wrote:

Yikes! wrote:

It's been a while since my last 763 flight and so am somewhat out of the loop with up-to-date heavy jet ops. After watching a series of A380 landings, I noticed only engines 2 & 3 seemed to use reverse after landing - some with idle reverse; some with full on reverse.

https://fb.watch/aL9wmMdvX4/

Can any A380 operators on this forum elaborate?

Thanks!

Interesting fact, Airbus originally wanted to certify it with no reverse at all! I believe the American regulators would have none of it and the compromise was on the inboards only, due to FOD risk given how far out the outboards hang (well over the grass at most airports) as per the previous post. It has really good brakes on 16 of the 20 main gear wheels (the last pair on each 6-wheel truck having no brakes, although the F version, never built, would have.)

Are you sure the FAA would not allow the A380 to operate without thrust reversers? Do you have a source? The KC-46 is an FAA certified airplane and doesn’t have thrust reversers.

Its amazing how one can still learn new things from time to time after so many years. Never knew the KC-46 has no reverse thrust, do you know why?

DLHAM wrote:

BoeingGuy wrote:

77west wrote:

Interesting fact, Airbus originally wanted to certify it with no reverse at all! I believe the American regulators would have none of it and the compromise was on the inboards only, due to FOD risk given how far out the outboards hang (well over the grass at most airports) as per the previous post. It has really good brakes on 16 of the 20 main gear wheels (the last pair on each 6-wheel truck having no brakes, although the F version, never built, would have.)

Are you sure the FAA would not allow the A380 to operate without thrust reversers? Do you have a source? The KC-46 is an FAA certified airplane and doesn’t have thrust reversers.

Its amazing how one can still learn new things from time to time after so many years. Never knew the KC-46 has no reverse thrust, do you know why?

My guess is that it only really operates from large runways at military bases and the added weight and complexity was deemed un-necessary.

DLHAM wrote:

BoeingGuy wrote:

77west wrote:

Interesting fact, Airbus originally wanted to certify it with no reverse at all! I believe the American regulators would have none of it and the compromise was on the inboards only, due to FOD risk given how far out the outboards hang (well over the grass at most airports) as per the previous post. It has really good brakes on 16 of the 20 main gear wheels (the last pair on each 6-wheel truck having no brakes, although the F version, never built, would have.)

Are you sure the FAA would not allow the A380 to operate without thrust reversers? Do you have a source? The KC-46 is an FAA certified airplane and doesn’t have thrust reversers.

Its amazing how one can still learn new things from time to time after so many years. Never knew the KC-46 has no reverse thrust, do you know why?

Yes, I was involved in the program for many years.

There was a corner case performance condition that the USAF required. It could be met by eliminating the extra weight of the thrust reversers. The Boeing pilots were not happy with that program decision.

Also, the USAF requested a low bid low cost airplane. Eliminating the thrust reversers saves money. There is no specific requirement for thrust reversers. Also the mission of the KC-46 doesn’t require short gate turns, so brake cooling isn’t a factor.

It’s all of the above.

I operated high bypass engines with turbine reversers at the 747 classics.
During end of the 70's, start of the 80's, they were removed due bad reliability, due heat built up during reverse operation, causing frequently jammed turbine reversers.
Especially at the PW JT9D engines the turbine reversers got stuck, because the reverser was operated by 4 push/pull cables, two long ones and two shorter ones, because the reverse motor was positioned at the top of the engine. The reverser got misaligned and then got stuck (always at a remote airfield with limited maintenance facilities !).
On the GE CF6-50 engines the failure rate was far less.
As a F/E we got a special training to deactivate the (turbine) reverser at outstations.
After several years it was finally decided to deactivate the turbine reversers, and later the entire system was removed (weight saving),
However, especially during landings at MLW the deletion of the turbine reversers caused more hot (steel) brakes, also the actual stopping distance increased a lot after the removal of the turbine reverses.

Note : the calculated stopping distance remained the same, because (fan and/or turbine) reversers are not included in the landing runway length calculations.

Question, and a bit off topic, but would an airliner benefit from a split-rudder airbrake like the space shuttle had? Or would the complexity outweigh any benefits. The same could be said for the H-Stab.

See Fokker 28 speed brake. Spoilers are multi-function, so the rudder brake would just be an unnecessary complication.

77west wrote:

Question, and a bit off topic, but would an airliner benefit from a split-rudder airbrake like the space shuttle had? Or would the complexity outweigh any benefits. The same could be said for the H-Stab.

Spoilers are important to dump lift after touchdown and ensure that the wheels have good grip on the runway. That they create drag is just a nice secondary benefit.

The BAe-146 uses a split tailcone to act as an additional airbrake. I suspect that a split-rudder or split-elevator would reduce the respective control surfaces' control authority. Not a big deal for the space shuttle landing in calm weather but you need an effective rudder when landing in crosswinds.

LyleLanley wrote:

Yikes, the A380 is fan only reverse. It doesn’t block core exhaust.

If you’re wondering why, commercial airliners rely primarily on their brakes to stop, with reverse thrust as a bonus - especially important on a contaminated runway, such as covered with snow. They’re usually at reverse idle ~ 60 knots and then restowed. They don’t back up, nor do they do really steep descents. Those might spill the champagne in first class.

The C-17, on the other hand, uses its TRs more like another kind of brake; it’s an integral way to stop a 450-ish-585K aircraft in a few thousand feet of earth, whether dirt or asphalt, so it’s used differently. Not only does it slow the jet, it can back it up. At max T/O weight. Up a 2 degree slope. Arrive over the field at FL400 to avoid manpads and AAA? No problem! Reverse idle on all 4 engines (+ boards) are a fantastic drag device and spiral down! That’s a much different method of operation to a commercial airliner’s, with a correspondingly different design.

Thanks Lyle - additionally, I believe it's a FAR25 (izzat the right one?) requirement that brakes alone are used for takeoff/landing stopping distances for certification. Not necessarily applicable to military aircraft. Reverse taxiing in both the 757 and 767 was prohibited in part, I would think, due to the high core thrust produced in presumably a ramp environment.

extender wrote:

The C-17's capability to mimic a a falling manhole cover is impressive indeed. The 380's TR design is very simple. The only thing that stinks is getting the Safran spares to repair it.

LOL!

A good friend's Dad use to fly the DC-10 for KLM in the 1970's until he was forced to retire after Tenerife due to his hearing degeneration. It was an SOP to use idle reverse during an emergency descent from altitude. Can't remember if it was #2 only or all 3. It too came down like a rock!

77west wrote:

DLHAM wrote:

BoeingGuy wrote:

Are you sure the FAA would not allow the A380 to operate without thrust reversers? Do you have a source? The KC-46 is an FAA certified airplane and doesn’t have thrust reversers.

Its amazing how one can still learn new things from time to time after so many years. Never knew the KC-46 has no reverse thrust, do you know why?

My guess is that it only really operates from large runways at military bases and the added weight and complexity was deemed un-necessary.

Canada actually operates it off gravel at Resolute Bay and CFS Alert. Pretty impressive to watch!

DLHAM wrote:

Never knew the KC-46 has no reverse thrust, do you know why?

My guess would be about mission profile: The KC-46 being a tanker aircraft, it will usually come back very light after the mission, since it did not only consume most of its trip fuel, but also its payload. Less landing weight means less energy to dissipate.


Kind regards,
Hendric

77west wrote:

Question, and a bit off topic, but would an airliner benefit from a split-rudder airbrake like the space shuttle had? Or would the complexity outweigh any benefits. The same could be said for the H-Stab.

I doubt it as typical touchdown speeds for heavy jets is usually well below 200 KIAS. Touchdown speed for the Space Shuttle was a nominal 214 - 226 K IAS (here's a great site for that info: https://www.nasa.gov/mission_pages/shut ... ng101.html ) The Shuttle also had large drogue chutes for its deceleration. Seems the brakes were not as reliable as they wished: https://www.upi.com/Archives/1985/05/25 ... 485841600/

Nice discussion!

Yikes! wrote:

Canada actually operates it off gravel at Resolute Bay and CFS Alert. Pretty impressive to watch!

KC-46 or C-46? . The prefix makes all the difference!

hitower3 wrote:

DLHAM wrote:

Never knew the KC-46 has no reverse thrust, do you know why?

My guess would be about mission profile: The KC-46 being a tanker aircraft, it will usually come back very light after the mission, since it did not only consume most of its trip fuel, but also its payload. Less landing weight means less energy to dissipate.


Kind regards,
Hendric

That was the SAC mentality vis-a-vis the KC-135R, but the 46 is another matter…

Boeing underestimated the KC-46’s basic aircraft weight during the competition, which really means they overestimated the amount of gas they could offload (the KC-46 is limited to a MTOW of 415K) and this meant it couldn’t meet certain required missions (‘must be able to offload 100K at 1000 miles’ sorta requirement). As such, Boeing slashed weight wherever they could: removed forward door slide rafts, etc. The TRs also saved a decent amount of weight, and when they proposed removing them, the prior-135 AF rep’s were easily persuaded, since the 135R also didn’t have TRs.