Tarantine From United States of America, joined Sep 2000, 210 posts, RR: 0 Posted (7 years 5 months 1 week 1 day 15 hours ago) and read 5167 times:
I have noticed more and more that is seems like reverse thrust is not being used when landing. I guess that it is cheaper to use brakes only. Now I have a couple of questions.
1. Can thrust reversing stop an airplane without applying the brakes?
2. How does an aircraft stop on a snowy or icy runway w/o using thrust reversing or if it does not have the ability (ie. military KC-135R)?
SlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 71 Reply 1, posted (7 years 5 months 1 week 1 day 15 hours ago) and read 5162 times:
Noise abatement policies at certain airports are a bigger factor. "Easy on the Jake Brake" to borrow a phrase from our 18-wheel brothers, is the rule at many places.
Yes, a plane would stop eventually on reverse thrust alone. It would be a lot greater distance than using wheel brakes alone, but within the length of many of the world's longer runways. Frankly, when landing on twelve thousand feet at lighter weights, I often would use only reverse idle (call it thrust attenuation, rather than reversing) and would not touch the brakes until down around forty knots or so, just to make a specific runway turnoff. Without jet thrust we just won't roll forever.
Happiness is not seeing another trite Ste. Maarten photo all week long.
Zvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 65 Reply 2, posted (7 years 5 months 1 week 1 day 13 hours ago) and read 5096 times:
Quoting Tarantine (Thread starter): Can thrust reversing stop an airplane without applying the brakes?
Yes, elementary physics says "of course."
Quoting Tarantine (Thread starter): How does an aircraft stop on a snowy or icy runway w/o using thrust reversing or if it does not have the ability (ie. military KC-135R)?
More slowly than on a dry runway i.e. by using more runway.
Matt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4 Reply 3, posted (7 years 5 months 1 week 1 day 13 hours ago) and read 5092 times:
Quoting Tarantine (Thread starter): 2. How does an aircraft stop on a snowy or icy runway w/o using thrust reversing or if it does not have the ability (ie. military KC-135R)?
well the anti skid system will ensure that the brakes are applied as hard as possible without locking the wheels!
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 4, posted (7 years 5 months 1 week 1 day 13 hours ago) and read 5088 times:
Quoting Matt72033 (Reply 3): Quoting Tarantine (Thread starter):
2. How does an aircraft stop on a snowy or icy runway w/o using thrust reversing or if it does not have the ability (ie. military KC-135R)?
well the anti skid system will ensure that the brakes are applied as hard as possible without locking the wheels!
Indeed. The antilock brakes in your car were developed from aircraft brakes.
Jspitfire From Canada, joined Feb 2005, 308 posts, RR: 2 Reply 5, posted (7 years 5 months 1 week 1 day 9 hours ago) and read 4995 times:
Not too long ago Westjet had some troubles departing in Abbotsford. They were backtracking down the runway, but were not told that the last 1000' was still ice covered. When they tried to hit the brakes and turn around, there was nothing, so they engaged reverse thrust, and managed to stop it and turn it around. The pilot wasn't too happy with ATC for not telling them, and I'm sure the passengers were wondering what was going on.
Grbld From Netherlands, joined Dec 2005, 353 posts, RR: 3 Reply 6, posted (7 years 5 months 1 week 1 day 9 hours ago) and read 4985 times:
I tell ya, you know that feeling when you're in your car and you're just sliding over a big patch of ice, no response to braking and steering? Well it's a lot scarier in a Boeing
Actually, it's the other way around. It's better to use reverse thrust and not really use the brakes, than to use the brakes without reverse thrust, saves a lot on wear of the brakes. The engines are designed to do reverse mode without virtually any wear. The thing is usually noise abatement.
Plus, to the passengers it seems like a smoother (less violent) landing if you don't have the thundering noise of the reversers
SlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 71 Reply 7, posted (7 years 5 months 1 week 1 day 8 hours ago) and read 4969 times:
Quoting Grbld (Reply 6): Well it's a lot scarier in a Boeing
A friend of mine once parked a DC-10 at a high-altitude airport where the apron was covered with ice. After he shut down, the plane started sliding sideways across the ramp. He said: "What was I going to do? Put on the brakes?"
I got a a jet stuck in a snowbank twice in one morning just trying to get from remote to a gate. Powered back once or twice trying to stay on the very narrow plowed path and blew snow all over up into the gearwells, flap tracks etc. Had to get seriously deiced.
Sat through all of last winter rejoicing that I didn't have to deal with any of it. I might miss flying but I don't miss my shoes smelling of glycol.
Happiness is not seeing another trite Ste. Maarten photo all week long.
Wingscrubber From UK - England, joined Sep 2001, 834 posts, RR: 0 Reply 8, posted (7 years 5 months 1 week 1 day 7 hours ago) and read 4917 times:
Quoting Slamclick-
Quote: I often would use only reverse idle (call it thrust attenuation, rather than reversing) and would not touch the brakes until down around forty knots or so,
Is it not good practise/standard precedure to cancel reverse thrust at 60 knots to avoid FOD ingestion? I was taught this at College during my aircraft maintenance diploma. I note that you did say you would do this at idle though.
-Pete
Airgypsy From United States of America, joined Nov 1999, 129 posts, RR: 2 Reply 10, posted (7 years 5 months 1 week 1 day 4 hours ago) and read 4862 times:
Aircraft are certified with stopping distance by brakes alone. Thrust reversers are "auxilary deceleration devices".
I have witness a DC-9 stop in less than 2k feet only reversers on an iced runway. FOD is the reason that most aircraft cancel T/R at around 60-80kts and brake from there. Brake and tire wear are a factor in keeping braking to a minimum.
Mr.BA From Singapore, joined Sep 2000, 3423 posts, RR: 23 Reply 11, posted (7 years 5 months 1 week 1 day 4 hours ago) and read 4851 times:
Just wondering as well, at what airspeed would cause the engines in idle reverse to surge, if it would at all? I've come across many landings that have engines deployed at idle reverse even at the turn-offs.
Jetstar From United States of America, joined May 2003, 1523 posts, RR: 10 Reply 14, posted (7 years 5 months 6 days 16 hours ago) and read 4639 times:
Thrust reversers are most efficient at the higher speeds on landing. as the airplane decelerates, the efficiency is reduced to the point that the wheel brakes have more braking power than the reversers. An airplane can be stopped just on reverse thrust alone and also can back up, which is done regularly with the DC-9/MD-80 series airplanes.
On some airplanes at the lower speeds using thrust reversers the engines can ingest some of the exhaust gases which can cause problems such as compressor stalls.
MD-90 From United States of America, joined Jan 2000, 8418 posts, RR: 13 Reply 15, posted (7 years 5 months 4 days 11 hours ago) and read 4476 times:
Now, if the runway was a giant conveyor belt, and it instantly accelerated to the velocity of the aircraft upon touchdown (in the opposite direction), would the airplane ever be able to exit the runway?
HAWK21M From India, joined Jan 2001, 31201 posts, RR: 58 Reply 16, posted (7 years 5 months 3 days 17 hours ago) and read 4379 times:
Quoting MD-90 (Reply 15): Now, if the runway was a giant conveyor belt, and it instantly accelerated to the velocity of the aircraft upon touchdown (in the opposite direction), would the airplane ever be able to exit the runway?
Grbld From Netherlands, joined Dec 2005, 353 posts, RR: 3 Reply 17, posted (7 years 5 months 3 days 15 hours ago) and read 4345 times:
Quoting Jetstar (Reply 14): Thrust reversers are most efficient at the higher speeds on landing. as the airplane decelerates, the efficiency is reduced to the point that the wheel brakes have more braking power than the reversers.
Howdy Jetstar,
Can you elaborate on these two statements? A turbofan engine has its maximum thrust while the airspeed is zero, as I remember from my aerodynamics classes. That is why you see all turbofan engines rated at a certain amount of "static thrust". The second you start accelerating, its thrust starts to deteriorate. You can find some formulas and graphs here. Even though the article is about turboprops and propellers, the fan is nothing but a big propeller, albeit a ducted one.
Second, from experience, the brakes clearly have much more stopping power than the reversers, at any speed. It's easy to distinguish because sometimes I do a full reverse landing without (auto or manual) brakes and sometimes just braking and using no or idle reverse.
Matt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4 Reply 18, posted (7 years 5 months 3 days 14 hours ago) and read 4327 times:
Quoting Mr.BA (Reply 11): Just wondering as well, at what airspeed would cause the engines in idle reverse to surge, if it would at all? I've come across many landings that have engines deployed at idle reverse even at the turn-offs.
i cant think of any reason why they would surge or stall in reverse at low airspeeds and operate normally in "forward" at low airspeeds!
the only diference is the direction the thrust is being directed!
EMBQA From United States of America, joined Oct 2003, 9286 posts, RR: 13 Reply 20, posted (7 years 5 months 3 days 8 hours ago) and read 4264 times:
Quoting Tarantine (Thread starter): Can thrust reversing stop an airplane without applying the brakes?
An airliner can stop using NO brakes and NO reverse thrust....and actually more quickly then you would think. The slowing friction from the tires, wheels and axles and air resistance is actually pretty high.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 21, posted (7 years 5 months 3 days 7 hours ago) and read 4262 times:
Quoting EMBQA (Reply 20): Quoting Tarantine (Thread starter):
Can thrust reversing stop an airplane without applying the brakes?
An airliner can stop using NO brakes and NO reverse thrust....and actually more quickly then you would think. The slowing friction from the tires, wheels and axles and air resistance is actually pretty high.
Especially if you overrun
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
Grbld From Netherlands, joined Dec 2005, 353 posts, RR: 3 Reply 22, posted (7 years 5 months 2 days 21 hours ago) and read 4216 times:
Quoting MD-90 (Reply 19): Of course, if the airspeed is zero, then the engine is producing no power.
Not true! If you put the parking brake on in your car, put it in gear and floor the gaspedal, it's still producing lots of power (resulting in either wheelspin, a damaged axle or engine but oh well).
On a turbofan/jet they use the term "static thrust" as I said. Because it's dependent on the air acceleration, you have the highest thrust when you accelerate air at standstill (ie. the air in front of the engine, relative to the aircraft speed is zero, and full blast behind it). If you accelerate, the air in front of the engine, relative to aircraft speed also increases and as such decreases your thrust because the engine doesn't provide a certain air acceleration factor, it more or less puts out the same thrust.
This is why it's so different from piston engines (in your car or plane) or even turboprops, because they measure thrust or power in terms of force exerted on the shaft. This is a fixed value for a given RPM.
Quoting EMBQA (Reply 20): An airliner can stop using NO brakes and NO reverse thrust....and actually more quickly then you would think. The slowing friction from the tires, wheels and axles and air resistance is actually pretty high.
True, but if you try this in a 737 or bigger with a full payload and a normal approach speed, it will go off the end of almost any runway.
David L From United Kingdom, joined May 1999, 9213 posts, RR: 42 Reply 23, posted (7 years 5 months 2 days 11 hours ago) and read 4156 times:
Quoting Grbld (Reply 6): It's better to use reverse thrust and not really use the brakes, than to use the brakes without reverse thrust, saves a lot on wear of the brakes.
Not wishing to upset the apple cart (but probably failing, as usual) I seem to recall discussions here some time ago where the conclusion was that braking without reverse thrust allowed the brakes to reach optimum temperature thus actually reducing brake wear. Answers on a postcard?
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 24, posted (7 years 5 months 2 days 10 hours ago) and read 4146 times:
Quoting David L (Reply 23): Quoting Grbld (Reply 6):
It's better to use reverse thrust and not really use the brakes, than to use the brakes without reverse thrust, saves a lot on wear of the brakes.
Not wishing to upset the apple cart (but probably failing, as usual) I seem to recall discussions here some time ago where the conclusion was that braking without reverse thrust allowed the brakes to reach optimum temperature thus actually reducing brake wear. Answers on a postcard?
I think this is true for carbon brakes but not other types.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
25 David L: Ah, of course - I hadn't thought of the distinction. But haven't carbon brakes been The Latest Thing for a while now?[Edited 2005-12-21 23:14:20]
26 Starlionblue: Indeed they have. I think they could probably be called "standard" nowadays. The first airliner to have carbon brakes was Concorde. One of the big ad
27 David L: I assume asbestos used to be present. If so, there's a health benefit for the maintenance guys, too!
28 Zed: I checked some flight test data I use to certify a B-757 flight simulator and found: A Stopping Time & Distance test run at 207,000 lb gross weight, s
29 HAWK21M: Intersting Statistics. Tells us the Importance of Brakes regds MEL
30 Sovietjet: How would reverse thrust break noise restrictions??? It's not like the plane flies over a neighborhood using reverse. You can't even hear the reverse
31 David L: You can, especially if the wind's in the right direction. I used to hear it occasionally a mile or so from Glasgow airport. I'd see a plane sliding s
32 Grbld: Oh, very easily. Many airports that have housing in the vicinity have rules that prohibit using more than idle reverse thrust during landing at night
33 HAWK21M: Out here you sure can hear the B732s,IL76s & An124s reversing quite some distance away regds MEL
34 MikeyCpvd: Oh Yeah you can! I concur. I'm about 3 miles from PVD as the crow flies and arrivals on runway 23 with a slight crosswind with winds blowing from a d
35 ATCme: WOW, this is a really funny thread, or at least some of the comments such as: and Even if unintentional...I'm really bored, so they're funny to me! Al
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