Sponsor Message:
Civil Aviation Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Thrust Reverse Vs. Brakes  
User currently offlineRizzes From United States of America, joined Dec 2000, 5 posts, RR: 0
Posted (12 years 3 months 3 weeks 6 days 11 hours ago) and read 1985 times:

What role do thrust reversers play on braking a civil aircraft? Are they used to reduce wear on the wheel brakes? Are they used only for short runways? Are wheel brakes preferable to using the thrust reversers? Are they used on every landing?

Thanks.


23 replies: All unread, jump to last
 
User currently offlineNZ767 From New Zealand, joined Nov 2001, 1620 posts, RR: 1
Reply 1, posted (12 years 3 months 3 weeks 6 days 11 hours ago) and read 1894 times:

They are used immediately on landing to slow down the aircraft to around 60 knots.
Using the wheel brakes at such high speeds, eg, 140-150 knots would overheat the brakes not only wearing them out quite quickly, but risking a fire as well.

Thrust reversers are not used on every landing.
It depends on runway conditions, landing weight, where along the runway the aircraft wants to exit (might be the last taxiway, so they don't want to slow down too quickly) and a number of other factors.
There are also different levels (min,med and max) of reverse thrust as well which are preset by the crew during approach.


User currently offlineMr.BA From Singapore, joined Sep 2000, 3423 posts, RR: 22
Reply 2, posted (12 years 3 months 3 weeks 6 days 8 hours ago) and read 1828 times:

Full Reverse = Autobrakes 1


Boeing747 万岁!
User currently offlineWing From Turkey, joined Oct 2000, 1559 posts, RR: 24
Reply 3, posted (12 years 3 months 3 weeks 6 days 7 hours ago) and read 1807 times:

The system regulates itself the amount of the reverse you use and the amount of breaking.Which means the more reverse you use the less amount of auto breaking occurs.(As MrBA said above)But in a landing the most effective breaking is the speed brakes deployed over the wings.And the reversers to help them.In some longer runways,if you are not required to vacate the runway due to traffic we don't even use the wheel brakes .


Widen your world
User currently offlinePanman From Trinidad and Tobago, joined Aug 1999, 790 posts, RR: 0
Reply 4, posted (12 years 3 months 3 weeks 6 days 6 hours ago) and read 1789 times:

I can't believe what I'm reading here. Thrust reversers aid in landing but their effect is MUCH less than brakes alone.

Most of the retarding action comes from the brakes. The spoilers ensure that once on the ground the aircraft's weight is transferred to the brakes (instead of to the wings). Contrary to what NZ767 said the brakes are used at high speeds, and they do get very hot, but modern carbon brakes are made for this kind of abuse.

If an aircraft needs 4000 ft of runway to stop with brakes only then with thrust reversers this drops down to about 3000-3500 ft of runway with reversers.

You want to know how hot the brakes get? I foolishly (though accidentally - was trying to line the rotor with the key in the wheel) touched one of the discs last year September on a Virgin A340 when we were doing a wheel change. Needless to say the latex gloves that I had on, melted and fused onto my hand and gave me a lovely water bladder.

Panman


User currently offlineVapourTrails From Australia, joined Aug 2001, 1102 posts, RR: 1
Reply 5, posted (12 years 3 months 3 weeks 6 days 4 hours ago) and read 1766 times:
Support Airliners.net - become a First Class Member!

Similar topics..

http://www.airliners.net/discussions/tech_ops/read.main/33020/4/


Click for large version
Click here for full size photo!

Photo © Thomas Millard



Dangerous to land without flaps?
http://www.airliners.net/discussions/tech_ops/read.main/16502/4/

Thrust reversers after touchdown: yes or no?
http://www.airliners.net/discussions/tech_ops/read.main/9204/4/


Click for large version
Click here for full size photo!

Photo © Florian Kondziela



http://www.airliners.net/discussions/tech_ops/read.main/15215/4/

http://www.airliners.net/discussions/tech_ops/read.main/6463/4/


Click for large version
Click here for full size photo!

Photo © Philippe Gindrat



Am I the only one who thinks business class is boring because it's not near the wing? Laugh out loud



"Oh, I have slipped the surly bonds of earth, and danced the skies on laughter-silvered wings.." John Gillespie Magee Jr
User currently offlineAzjubilee From United States of America, joined Apr 2000, 3895 posts, RR: 28
Reply 6, posted (12 years 3 months 3 weeks 5 days 22 hours ago) and read 1672 times:

Interesting discussion... let's throw this into the ring for banter as well. The Avro RJ series has no reverse thrust on those 4 engines. Granted, the jumbolino is a rather slow jet, but that makes her unique. The airbrake, 6 lift spoilers that deploy on landing, the enormous 33 degree barn door flaps and very heavy duty brakes all allow us to slow very quickly upon landing. The only time that we could REALLY use reverse is on a contaminated runway. The brakes do get very hot, so BAE designed a brake fan that is located within the wheel on each of the 4 main landing gear tires.

It's a pretty unique jet. I think the Dornier Jet is also without reverse thrust, but I believe is even slower than the chubby jet. The ERJ and CRJ have them, but I've read where Coexpress has disabled their reverse...

AZJ


User currently offlineRamper@iah From United States of America, joined Dec 2001, 240 posts, RR: 1
Reply 7, posted (12 years 3 months 3 weeks 5 days 21 hours ago) and read 1649 times:

originally posted by AZJ
I've read where Coexpress has disabled their reverse...

Continental Express' EMB-145s thrust reversers have not been disabled. They work fine and are used on almost every landing and RTO.


User currently offlineAzjubilee From United States of America, joined Apr 2000, 3895 posts, RR: 28
Reply 8, posted (12 years 3 months 3 weeks 5 days 18 hours ago) and read 1628 times:

Cool, I was hoping a Coex person would read this and confirm either way if I was correct. I did think it was kinda dumb to disable them and not use them if they're available.


AZJ


User currently offlineRizzes From United States of America, joined Dec 2000, 5 posts, RR: 0
Reply 9, posted (12 years 3 months 3 weeks 5 days 12 hours ago) and read 1563 times:

Thanks for the info.

User currently offlineTWAMD-80 From United States of America, joined Oct 2001, 1006 posts, RR: 4
Reply 10, posted (12 years 3 months 3 weeks 5 days 11 hours ago) and read 1556 times:

To answer your question, no, I also think that sitting in business is boring because you don't get to sit by the wing. Sitting by the wing is one of the best seats on the airplane, well aside from the cockpit Big grin.

TW



Two A-4's, left ten o'clock level continue left turn!
User currently offlineVapourTrails From Australia, joined Aug 2001, 1102 posts, RR: 1
Reply 11, posted (12 years 3 months 3 weeks 5 days 11 hours ago) and read 1547 times:
Support Airliners.net - become a First Class Member!

 Big thumbs up When I sat in business class I wanted to go back into economy for the landing! Smile Yes the cockpit would be even better but I'm not qualified for that! Laugh out loud


"Oh, I have slipped the surly bonds of earth, and danced the skies on laughter-silvered wings.." John Gillespie Magee Jr
User currently offlineNZ767 From New Zealand, joined Nov 2001, 1620 posts, RR: 1
Reply 12, posted (12 years 3 months 3 weeks 4 days 11 hours ago) and read 1512 times:

I agree TWA........I always sit just aft of the wing so I can watch the flaps working.  Smile


User currently offlineNZ767 From New Zealand, joined Nov 2001, 1620 posts, RR: 1
Reply 13, posted (12 years 3 months 2 weeks 4 days 3 hours ago) and read 1471 times:

"I can't believe what I'm reading here. Thrust reversers aid in landing but their effect is MUCH less than brakes alone."

Panman, you've got me confused here.
If the effect of thrust reversers is MUCH LESS than BRAKES ALONE, then what's the point in having reversers at all then?
Are you suggesting that an aircraft will slow down more effectively without the thrust reversers?

"Most of the retarding action comes from the brakes. The spoilers ensure that once on the ground the aircraft's weight is transferred to the brakes (instead of to the wings). Contrary to what NZ767 said the brakes are used at high speeds, and they do get very hot, but modern carbon brakes are made for this kind of abuse."

I remember seeing an Airbus A340 land just with brakes alone (for certification purposes) with firecrews standing by in case fire broke out due to the brakes overheating.
I wouldn't want to see that too often.
I'm well aware of carbon brakes, but, why would they want to "abuse" them when they have thrust reversers available?
The cost would be horrendous!
Not disputing the word of an aircraft tech, I just can't understand it that's all.
Every 737 I see land here uses reverse thrust although admittedly we (NZWN) have a rather short runway.

"There are also different levels (min,med and max) of reverse thrust as well which are preset by the crew during approach."

My mistake here!
I think I got myself confused with the autobrakes; ie: autobrakes 1,2,etc.

Regards,
Mike  Smile


User currently offlineA320-Addict From Belgium, joined Apr 2001, 250 posts, RR: 6
Reply 14, posted (12 years 3 months 2 weeks 4 days 3 hours ago) and read 1455 times:

I just can't believe what I am reading here.... all those so called 'experts'.....


Some facts:

1. Thrust reverse is the most effective at high speeds, just after touchdown.
2. The deceleration effect of thrust reverse is far less than the brakes.
3. Modern Carbon Brakes will never "overheat" or burn.
They might get hot during a landing..... . The only case where they could overheat is during a high speed abort, but they are all certified so that no fire starts 5 min after the rejected take-off.
4. Ground spoilers cause a small amount of deceleration but their main purspose is to brake the lift, and put the aircrafts weight on the wheels so that the wheel-braking is very effective.

Some operational facts:

1. Thrust reverse is seldom used on bussy European airports which are almost all noise sensitive. We use 'IDLE' reverse in those cases. Idle reverse makes almost not more noise than an engine turing at idle.
Sometimes when safety requires it, more than idle is used, it is NEVER forbidden to use reverse for safety reasons. ( An aircraft that exits the runway makes far more noise than using reverse)
2. Charter operators use in generaly more reverse than others.... they operate to holiday destinations which are in generally not noise sensitive at all. It is more economic to use the reverse than to use the brakes for deceleration, the price of the brakes is far superior to the price of the extra kgs of fuel you use with the use of reverse.
3. In practise long runways: 'During the initial touchdown mostly idle reverse is used, or a bit more,.... once the aircraft is slowing down below 100kts, we use the wheelbrakes, and stow the reverse to idle....'

Very short runways: Full reverse, and autobrakes on medium, or full manual brakes.

I hope we cleared some things out here!!

 Smile/happy/getting dizzy  Smile/happy/getting dizzy


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3700 posts, RR: 34
Reply 15, posted (12 years 3 months 2 weeks 4 days 3 hours ago) and read 1442 times:
Support Airliners.net - become a First Class Member!

Some airlines who operate a/c with carbon brakes request the crews not to use T.Rev unless they have to for safety reasons. It has been found the Carbon Brake life is extended when they heat up to operating temp quickly and are used that range.

Use of T.Rev can prevent the brakes getting to their ideal operating range, or at the very least delay it. This procedure also has benefits in less wear & tear on the engine & reversers.


User currently offlineNZ767 From New Zealand, joined Nov 2001, 1620 posts, RR: 1
Reply 16, posted (12 years 3 months 2 weeks 4 days 3 hours ago) and read 1440 times:

Thanks for that A320.
I'm not an "expert".
That's why I tend to seek clarification and question things.

Cheers.  Smile


User currently offlineNZ767 From New Zealand, joined Nov 2001, 1620 posts, RR: 1
Reply 17, posted (12 years 3 months 2 weeks 4 days 3 hours ago) and read 1437 times:

Got ya VC.

User currently offlineRayChuang From United States of America, joined Jun 2000, 7993 posts, RR: 5
Reply 18, posted (12 years 3 months 2 weeks 4 days 2 hours ago) and read 1416 times:

Isn't that both US FAA and European JAA require that modern airliner stop in a reasonable distance without the need for thrust reversers?

With modern wing front and rear flap designs (which allow the plane to land slower) and wing spoilers (which help slow the plane down), I think even a 747-400 could land and come to a stop without using reverse thrust using just over half a 10,000 feet runway.


User currently offlineIAHERJ From United States of America, joined Jun 2001, 677 posts, RR: 7
Reply 19, posted (12 years 3 months 2 weeks 4 days ago) and read 1406 times:

Ray,

All aircraft with thrust reversers are certified for use without them. In fact the performance manuals for runway distance etc. usually are written based on no reverse being used and maximum braking.

On the ERJ-135/145, on the ground, you can deploy the buckets and once the nosewheel is on the ground, it will allow you to spool up into reverse. The new aircraft comming off the line will allow you to go right into reverse with only the main wheels on the ground. It is nice if you are flying a nose heavy 145 however I learned of this in a newer 135 up in Cleveland several months ago and it was a bit of a surprise. I set in full reverse after touchdown thinking I'd get the spool up after the nose hit. Well the engines spooled up right away and I had to push the nose down which is rarely ever seen on en embraer as they are all nose heavy. It was a nice surprise.

On the ERJ, if the winds are strong and or there is a gain or loss on final approach, you can elect to land at flapps 22. This configuration can lead to approach speeds pushing 150 knots and having reverse on a wet runway after touching down at speeds like that is comforting to us up front.



Actually flown: EMB-120 EMB-145 B717 B737 B757 B767
User currently offlineCV640 From United States of America, joined Aug 2000, 952 posts, RR: 5
Reply 20, posted (12 years 3 months 2 weeks 4 days ago) and read 1387 times:

I always use the revrsers on teh CRJ, sometimes only a little above idle, simply do to resdue thrust. At idle the CRJ engines poduce a lot of forwad thrust, so the use of reversers helps tremendously with it. It does take them a while to deploy and spool up though, if you go on the brakes hard upon touchdown you could actually be below 60 knots before they had a chance to spool up.

User currently offlineSAA-SAL From Belgium, joined Nov 2000, 356 posts, RR: 3
Reply 21, posted (12 years 3 months 2 weeks 3 days 21 hours ago) and read 1373 times:

Interesting fact concerning the A380 : in 1997-1998 Airbus examined the possibility of installing thrust reversers on two engines only to bring costs down. Never heard of that story since but I imagine they 've gone back to four. Big grin


SAA B747 SP, Luxavia B747 SP
User currently offlineRayChuang From United States of America, joined Jun 2000, 7993 posts, RR: 5
Reply 22, posted (12 years 3 months 2 weeks 3 days 20 hours ago) and read 1357 times:

SAA-SAL,

I think if BAE Systems designs the A380 wings correctly (e.g., enough front and rear flaps to keep the landing speed reasonable and big enough wing spoilers to slow the plane down quickly before application of wheel brakes), Airbus could get away from having only the inboard engines fitted with thrust reversers.

Which if feasible is a great idea for two good reasons: 1) it saves on weight (all that thrust reversing hardware adds lots of weight to the engine nacelle) and 2) the outboard engines on the A380 are far enough from airplane centerline that on many runways the application of reverse thrust on the outer engines could pose a major foreign object damage (FOD) hazard.


User currently offline777236ER From , joined Dec 1969, posts, RR:
Reply 23, posted (12 years 3 months 2 weeks 3 days 20 hours ago) and read 1353 times:

SAA-SAL, there are also problems with this. If an inboard TR is u/s, then you've still got the two outboard TRs avaliable. Commonality is an issue to. Designing and producing and maintaining one type of reverser is cheaper than two.

The semi-span of the A380 isn't actually that great, and A340s and 747s use outboard TRs without any FOD.

Weight savings? Not THAT significant.


Top Of Page
Forum Index

This topic is archived and can not be replied to any more.

Printer friendly format

Similar topics:More similar topics...
Jetblue And Thrust Reverse posted Sat Jul 24 2004 22:30:07 by JFK4EVA
How Does Thrust-reverse Work, Need Details...! posted Wed Jan 23 2002 08:47:46 by SJCguy
Thrust Reversers VS. Tow Tugs For Pushback posted Thu Dec 27 2001 06:48:11 by Rj777
Is Thrust Reverse Always Used? posted Wed Oct 31 2001 01:33:36 by Concorde1518
Which Plane HAS Loudest Thrust Reverse posted Sun Jun 10 2001 19:58:09 by Balkan,154m
BAe146, No Thrust-reverse? posted Mon Apr 10 2000 18:25:13 by Ab.400
DC-8 And Reverse Thrust Use In Flight posted Mon Jul 3 2006 05:50:58 by Ttailsteve
Reverse Thrust Explained! posted Tue Dec 20 2005 19:10:44 by Deaphen
Reverse Thrust Pushback From Gate posted Thu Dec 15 2005 20:00:15 by EFCar98
Northwest Using Reverse Thrust For Pushback posted Sun Nov 27 2005 18:53:54 by DLCnxgptjax