Rizzes From United States of America, joined Dec 2000, 5 posts, RR: 0 Posted (11 years 1 month 2 weeks 6 days 13 hours ago) and read 1520 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?
NZ767 From New Zealand, joined Nov 2001, 1620 posts, RR: 1 Reply 1, posted (11 years 1 month 2 weeks 6 days 13 hours ago) and read 1429 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.
Wing From Turkey, joined Oct 2000, 1552 posts, RR: 25 Reply 3, posted (11 years 1 month 2 weeks 6 days 9 hours ago) and read 1342 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 .
Panman From Trinidad and Tobago, joined Aug 1999, 789 posts, RR: 0 Reply 4, posted (11 years 1 month 2 weeks 6 days 8 hours ago) and read 1324 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.
Azjubilee From United States of America, joined Apr 2000, 3556 posts, RR: 30 Reply 6, posted (11 years 1 month 2 weeks 6 days ago) and read 1207 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...
TWAMD-80 From United States of America, joined Oct 2001, 1006 posts, RR: 4 Reply 10, posted (11 years 1 month 2 weeks 5 days 13 hours ago) and read 1091 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 .
Two A-4's, left ten o'clock level continue left turn!
NZ767 From New Zealand, joined Nov 2001, 1620 posts, RR: 1 Reply 13, posted (11 years 1 month 1 week 4 days 5 hours ago) and read 1006 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.
A320-Addict From Belgium, joined Apr 2001, 250 posts, RR: 7 Reply 14, posted (11 years 1 month 1 week 4 days 5 hours ago) and read 990 times:
I just can't believe what I am reading here.... all those so called 'experts'.....
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.
VC-10 From United Kingdom, joined Oct 1999, 3677 posts, RR: 37 Reply 15, posted (11 years 1 month 1 week 4 days 4 hours ago) and read 977 times:
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.
RayChuang From United States of America, joined Jun 2000, 7696 posts, RR: 5 Reply 18, posted (11 years 1 month 1 week 4 days 3 hours ago) and read 951 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.
IAHERJ From United States of America, joined Jun 2001, 677 posts, RR: 8 Reply 19, posted (11 years 1 month 1 week 4 days 2 hours ago) and read 941 times:
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.
CV640 From United States of America, joined Aug 2000, 948 posts, RR: 6 Reply 20, posted (11 years 1 month 1 week 4 days 1 hour ago) and read 922 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.
SAA-SAL From Belgium, joined Nov 2000, 356 posts, RR: 3 Reply 21, posted (11 years 1 month 1 week 3 days 23 hours ago) and read 908 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.
RayChuang From United States of America, joined Jun 2000, 7696 posts, RR: 5 Reply 22, posted (11 years 1 month 1 week 3 days 22 hours ago) and read 892 times:
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.
777236ER From , joined Dec 1969, posts, RR: Reply 23, posted (11 years 1 month 1 week 3 days 22 hours ago) and read 888 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.