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A380 2 Engine Reverse Thrust  
User currently offlineColAvionLover From Panama, joined Dec 2008, 107 posts, RR: 0
Posted (2 years 11 months 4 days 2 hours ago) and read 9304 times:
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Hi! I had this question since a long time ago. Why the A380 only have two engines with reverse thrust instead of 4?


JDM's
21 replies: All unread, jump to last
 
User currently offlineYokoTsuno From Singapore, joined Feb 2011, 345 posts, RR: 0
Reply 1, posted (2 years 11 months 4 days 1 hour ago) and read 9300 times:

This might help Why The Airbus A380 Has Only Two Thrust Reverser? (by 747400sp Jul 2 2006 in Tech Ops)

User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 2, posted (2 years 11 months 4 days ago) and read 9262 times:

There have been several threads but to summarize:

- Reversers are not a major part of an aircraft's stopping power (in fact in most cases they are only a "bonus" in stopping calculations) but require a disproportionate amount of weight and maintenance to achieve what they do. AFAIK Airbus wanted no reversers at all but was not allowed by authorities.
- The wingspan of the aircraft is such that the outer engines often hang at the edge of the runway. So reversers there would have an increased FOD risk.
- Reversers are heavy. The 380 had weight issues anyway.
- The plane can pass certification with only two so why have four.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinelppr95 From Portugal, joined Mar 2010, 100 posts, RR: 0
Reply 3, posted (2 years 11 months 3 days 13 hours ago) and read 9101 times:

Quoting Starlionblue (Reply 2):

There have been several threads but to summarize:

- Reversers are not a major part of an aircraft's stopping power (in fact in most cases they are only a "bonus" in stopping calculations) but require a disproportionate amount of weight and maintenance to achieve what they do. AFAIK Airbus wanted no reversers at all but was not allowed by authorities.
- The wingspan of the aircraft is such that the outer engines often hang at the edge of the runway. So reversers there would have an increased FOD risk.
- Reversers are heavy. The 380 had weight issues anyway.
- The plane can pass certification with only two so why have four.

And because of its powerful breaks.



"Cathay 018, expect very late landing clearance, 747 departing ahead", tower said.
User currently offlinenomadd22 From United States of America, joined Feb 2008, 1764 posts, RR: 0
Reply 4, posted (2 years 11 months 3 days 11 hours ago) and read 9028 times:

Quoting lppr95 (Reply 3):
And because of its powerful breaks.

I hope that was a mis-spelling.



Andy Goetsch
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 5, posted (2 years 11 months 3 days 7 hours ago) and read 8921 times:

Quoting lppr95 (Reply 3):
And because of its powerful breaks.

I sort of implied that when I said "reversers are not a large part of an aircraft's stopping power" no?  



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinejoffie From Australia, joined Mar 2006, 802 posts, RR: 2
Reply 6, posted (2 years 11 months 3 days 5 hours ago) and read 8891 times:

I do remember reading here that Airbus were not going to put reversors on the A380 because the brakes were quite strong, but the FAA required it before it passed?

User currently offlineStitch From United States of America, joined Jul 2005, 29689 posts, RR: 84
Reply 7, posted (2 years 11 months 2 days 14 hours ago) and read 8705 times:
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Quoting joffie (Reply 6):
I do remember reading here that Airbus were not going to put reversors on the A380 because the brakes were quite strong, but the FAA required it before it passed?

As I recall it was indeed an FAA certification requirement that the A380 have at least two thrust-reversers.


User currently offlinechuchoteur From France, joined Sep 2006, 750 posts, RR: 0
Reply 8, posted (2 years 11 months 2 days 10 hours ago) and read 8634 times:

actually the thrust reversers may not brake the aircraft much, they do help in the braking action as they deflect the water in front of the tyres. Pretty handy when there is standing water.

User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 9, posted (2 years 11 months 2 days 7 hours ago) and read 8588 times:

Quoting chuchoteur (Reply 8):
actually the thrust reversers may not brake the aircraft much, they do help in the braking action as they deflect the water in front of the tyres. Pretty handy when there is standing water.

First I've heard of this. Do you have a source?



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMax Q From United States of America, joined May 2001, 4072 posts, RR: 19
Reply 10, posted (2 years 11 months 2 days ago) and read 8538 times:

Quoting chuchoteur (Reply 8):


actually the thrust reversers may not brake the aircraft much, they do help in the braking action as they deflect the water in front of the tyres. Pretty handy when there is standing water.

Er, are you serious ?



The best contribution to safety is a competent Pilot.
User currently offlinechuchoteur From France, joined Sep 2006, 750 posts, RR: 0
Reply 11, posted (2 years 11 months 1 day 22 hours ago) and read 8516 times:

Quoting Max Q (Reply 10):

Quoting chuchoteur (Reply 8):


actually the thrust reversers may not brake the aircraft much, they do help in the braking action as they deflect the water in front of the tyres. Pretty handy when there is standing water.

Er, are you serious ?

Yes.
My own experience on the A380 program as an engine, wheels, tyres and brakes support engineer.
The inner thrust reverser assys are set to contribute to water clearance in front of the MLG to reduce the risk of aquaplaning.


User currently offlineYokoTsuno From Singapore, joined Feb 2011, 345 posts, RR: 0
Reply 12, posted (2 years 11 months 1 day 16 hours ago) and read 8436 times:

Are there airplanes that have electric retarders, these things installed on trucks, or is this a weight issue agein?

Quoting lppr95 (Reply 3):
And because of its powerful breaks.
Quoting nomadd22 (Reply 4):
I hope that was a mis-spelling.
No, no misspelling. The QF31 A380 had a very powerful break when it made an emergency landing in SIN 
Quoting chuchoteur (Reply 8):
actually the thrust reversers may not brake the aircraft much, they do help in the braking action as they deflect the water in front of the tyres. Pretty handy when there is standing water.
LOL LOL.


User currently offlineMax777geek From Italy, joined Mar 2007, 538 posts, RR: 0
Reply 13, posted (2 years 10 months 2 weeks 2 days 11 hours ago) and read 7941 times:

Quoting chuchoteur (Reply 11):
The inner thrust reverser assys are set to contribute to water clearance in front of the MLG to reduce the risk of aquaplaning.

This is interesting. How much inches of water would be needed for a full weight a380 to acquaplan ? I assume (not an engineer) that speed, weight and surface area of contact with the water are key factors in the result of acquaplaning, since weight is obviously play far for the a380 to need more water than a cessna172 to acquaplan, I would wonder how much water would it take.


User currently offlineaklrno From United States of America, joined Dec 2010, 872 posts, RR: 0
Reply 14, posted (2 years 10 months 2 weeks 2 days 3 hours ago) and read 7843 times:

Quoting YokoTsuno (Reply 12):
Are there airplanes that have electric retarders, these things installed on trucks, or is this a weight issue agein?

It may be more a heat issue. The energy has to go somewhere. In my hybrid car it charges the battery so I can beat everyone else coming out of the next traffic light without feeling too guilty about wasting energy. If batteries weighed nothing than you could build a hybrid airplane that used the saved energy for the next take-off roll. Such batteries are currently unavailable.


User currently offlineMax777geek From Italy, joined Mar 2007, 538 posts, RR: 0
Reply 15, posted (2 years 10 months 2 weeks 1 day 17 hours ago) and read 7742 times:

Quoting aklrno (Reply 14):
Such batteries are currently unavailable.

not sure about the weight, but with the old equation that an airplane is convenient as its fuel uses is comparable to a car (per pax) Opel has built Ampera which works basically like a cruise ship : the fuel engine works only to recharge the batteries if needed, while the motion is only provided by the elecrical engine, all power immediately available as the switch is on. The batteries delivers a 16kwh which is kind enormous, and it gives an authonomy of 40/80 kilometers depending on the speed average. Sounds me we're not to wait that long before to see an electric assisted takeoff.

The most heavy modifications goes to the engine, anyhow. Batteries aren't the problem, as now.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 16, posted (2 years 10 months 2 weeks 1 day 17 hours ago) and read 7727 times:

Quoting Max777geek (Reply 15):
Batteries aren't the problem, as now.

Actually batteries are entirely the problem. Electric engines can be pretty efficient relative to weight, but storing electricity is not. Batteries weigh a lot more than hydrocarbons for equivalent energy storage. On a ship or a car that isn't a huge issue, but on a plane any extra weight is a problem.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineBaroque From Australia, joined Apr 2006, 15380 posts, RR: 59
Reply 17, posted (2 years 10 months 2 weeks 1 day 16 hours ago) and read 7720 times:

Quoting chuchoteur (Reply 11):
Yes.
My own experience on the A380 program as an engine, wheels, tyres and brakes support engineer.
The inner thrust reverser assys are set to contribute to water clearance in front of the MLG to reduce the risk of aquaplaning.

   Oh I just love the expertise that shows up on a.net just when some least expect it.   

First an expert in the sound-proofing, now a thrust reverser. I just love it.


User currently offlinebikerthai From United States of America, joined Apr 2010, 2011 posts, RR: 4
Reply 18, posted (2 years 10 months 2 weeks 1 day 11 hours ago) and read 7642 times:

Too bad Tom has not chimed in yet.

The answer is:

Airplanes are certified to operate without reversers. (Max weight rejected takeoff tests are done without reversers).

Reversers do work and significantly reduce the runway lengths needed to slow down the aircraft.
They are used to reduce wear and tear on the brake pads (when brake pads were really expensive).

With cheaper/better brake pads, it is now possible to talk about eliminating the reverser - but it is strictly a cost benefit analysis..

bikerthai



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlinebikerthai From United States of America, joined Apr 2010, 2011 posts, RR: 4
Reply 19, posted (2 years 10 months 2 weeks 1 day 11 hours ago) and read 7640 times:

Quoting chuchoteur (Reply 8):
actually the thrust reversers may not brake the aircraft much, they do help in the braking action as they deflect the water in front of the tyres.

Someone really screwed up in the design huh?   

bikerthai



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlinebikerthai From United States of America, joined Apr 2010, 2011 posts, RR: 4
Reply 20, posted (2 years 10 months 2 weeks 1 day 11 hours ago) and read 7637 times:

Quoting Baroque (Reply 17):
Quoting chuchoteur (Reply 11):
Yes.
My own experience on the A380 program as an engine, wheels, tyres and brakes support engineer.
The inner thrust reverser assys are set to contribute to water clearance in front of the MLG to reduce the risk of aquaplaning.

Oh I just love the expertise that shows up on a.net just when some least expect it.

First an expert in the sound-proofing, now a thrust reverser. I just love it.

A little information can go along way . . .

I can see what he means by "inner thrust reverser assy". I think the A380 have the "door" type thrust reversers.
There may be 4 or more "doors", and the "inner doors" is designed to point away from the fuselage or any location that may send debris back into the inlet. So why not push the water away from the MLG?

Even with the cascade type reversers (which are more efficient) there are sections along the engine that gets blocked to prevent debris ingestion.

I used to deal with reversers once . . . now I'm just a cabin-et boy.   

bikerthai



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 21, posted (2 years 10 months 2 weeks 1 day 2 hours ago) and read 7548 times:

Quoting bikerthai (Reply 18):
Too bad Tom has not chimed in yet.

I've been watching the thread, I just haven't seen anything that I thought I could meaningfully contribute to until now (lots of good information but me repeating what's already been said isn't productive).

Quoting bikerthai (Reply 20):
I can see what he means by "inner thrust reverser assy". I think the A380 have the "door" type thrust reversers.

Yes, although they're more usually called petal reversers.

Quoting bikerthai (Reply 20):
Even with the cascade type reversers (which are more efficient) there are sections along the engine that gets blocked to prevent debris ingestion.

Cascade reversers are more aerodynamically efficient, but that's not the whole story. Some parts (actuators, hinges, drag links, etc.) don't scale as well as the aerodynamic components (cascades, sleeves, doors). As a result, you take a weight/complexity/maintenance hit. There's a crossover point where you trade off from petal reversers to cascade reversers for overall system efficiency. However, manufacturers tend to specialize in one or the other (the devil you know) so you tend to see the same type perpetuate by OEM regardless of size.

I worked thrust reversers exclusively for about two years...I hate the things. They're heavy, complex, expensive, easily damaged, maintenance intensive, used for about 10 seconds per cycle, and you can't even take credit for them in almost all circumstances. Yes, they're nice to have in a crisis, but I can't help but think a really big one-time-use drag chute for when you really need it would be far more weight/cost/performance effective than normal thrust reversers.

Tom.


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