ColAvionLover
Topic Author
Posts: 70
Joined: Wed Dec 17, 2008 7:07 pm

A380 2 Engine Reverse Thrust

Sun May 22, 2011 4:13 am

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
 
YokoTsuno
Posts: 319
Joined: Tue Feb 01, 2011 1:21 pm

RE: A380 2 Engine Reverse Thrust

Sun May 22, 2011 4:36 am

This might help Why The Airbus A380 Has Only Two Thrust Reverser? (by 747400sp Jul 2 2006 in Tech Ops)
 
User avatar
Starlionblue
Posts: 17208
Joined: Fri Feb 27, 2004 9:54 pm

RE: A380 2 Engine Reverse Thrust

Sun May 22, 2011 6:06 am

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." - John Ringo
 
lppr95
Posts: 72
Joined: Sun Mar 14, 2010 6:24 pm

RE: A380 2 Engine Reverse Thrust

Sun May 22, 2011 4:49 pm

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.
 
nomadd22
Posts: 1566
Joined: Fri Feb 22, 2008 7:42 pm

RE: A380 2 Engine Reverse Thrust

Sun May 22, 2011 7:05 pm

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

I hope that was a mis-spelling.
Anon
 
User avatar
Starlionblue
Posts: 17208
Joined: Fri Feb 27, 2004 9:54 pm

RE: A380 2 Engine Reverse Thrust

Sun May 22, 2011 11:21 pm

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." - John Ringo
 
joffie
Posts: 815
Joined: Sun Mar 26, 2006 5:45 pm

RE: A380 2 Engine Reverse Thrust

Mon May 23, 2011 1:19 am

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 avatar
Stitch
Posts: 23460
Joined: Wed Jul 06, 2005 4:26 am

RE: A380 2 Engine Reverse Thrust

Mon May 23, 2011 4:21 pm

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.
 
chuchoteur
Posts: 609
Joined: Tue Sep 12, 2006 9:17 pm

RE: A380 2 Engine Reverse Thrust

Mon May 23, 2011 7:45 pm

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 avatar
Starlionblue
Posts: 17208
Joined: Fri Feb 27, 2004 9:54 pm

RE: A380 2 Engine Reverse Thrust

Mon May 23, 2011 11:23 pm

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." - John Ringo
 
Max Q
Posts: 5693
Joined: Wed May 09, 2001 12:40 pm

RE: A380 2 Engine Reverse Thrust

Tue May 24, 2011 5:51 am

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.
 
chuchoteur
Posts: 609
Joined: Tue Sep 12, 2006 9:17 pm

RE: A380 2 Engine Reverse Thrust

Tue May 24, 2011 7:32 am

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.
 
YokoTsuno
Posts: 319
Joined: Tue Feb 01, 2011 1:21 pm

RE: A380 2 Engine Reverse Thrust

Tue May 24, 2011 2:13 pm

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.
 
Max777geek
Posts: 159
Joined: Wed Mar 07, 2007 6:20 pm

RE: A380 2 Engine Reverse Thrust

Wed Jun 08, 2011 6:36 pm

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.
 
aklrno
Posts: 1206
Joined: Sat Dec 04, 2010 11:18 pm

RE: A380 2 Engine Reverse Thrust

Thu Jun 09, 2011 2:27 am

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.
 
Max777geek
Posts: 159
Joined: Wed Mar 07, 2007 6:20 pm

RE: A380 2 Engine Reverse Thrust

Thu Jun 09, 2011 12:36 pm

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 avatar
Starlionblue
Posts: 17208
Joined: Fri Feb 27, 2004 9:54 pm

RE: A380 2 Engine Reverse Thrust

Thu Jun 09, 2011 1:02 pm

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." - John Ringo
 
baroque
Posts: 12302
Joined: Thu Apr 27, 2006 2:15 pm

RE: A380 2 Engine Reverse Thrust

Thu Jun 09, 2011 2:07 pm

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 avatar
bikerthai
Posts: 2211
Joined: Wed Apr 28, 2010 1:45 pm

RE: A380 2 Engine Reverse Thrust

Thu Jun 09, 2011 6:35 pm

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 avatar
bikerthai
Posts: 2211
Joined: Wed Apr 28, 2010 1:45 pm

RE: A380 2 Engine Reverse Thrust

Thu Jun 09, 2011 6:38 pm

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 avatar
bikerthai
Posts: 2211
Joined: Wed Apr 28, 2010 1:45 pm

RE: A380 2 Engine Reverse Thrust

Thu Jun 09, 2011 6:46 pm

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.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: A380 2 Engine Reverse Thrust

Fri Jun 10, 2011 4:26 am

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.

Who is online

Users browsing this forum: MrBretz, StereoTechque and 8 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos