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Topic: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Tarantine
Posted 2005-12-15 18:13:39 and read 14596 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)?

Thanks, RT

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: SlamClick
Posted 2005-12-15 18:18:48 and read 14593 times.

Quoting Tarantine (Thread starter):
I guess that it is cheaper to use brakes only.

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.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Zvezda
Posted 2005-12-15 20:20:52 and read 14525 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.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Matt72033
Posted 2005-12-15 20:24:34 and read 14521 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!

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Starlionblue
Posted 2005-12-15 20:33:22 and read 14517 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.

As this celebrated topic http://www.airliners.net/discussions...h_ops/read.main/109779/6/#ID109779 indicates, brakes are better than reverse thrust. Note that I have linked directly to SlamClicks great reply #15. Read and learn.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Jspitfire
Posted 2005-12-16 00:10:36 and read 14426 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.

Jason

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Grbld
Posted 2005-12-16 00:24:50 and read 14416 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  Smile

Quoting Tarantine (Thread starter):
I guess that it is cheaper to use brakes only.

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  Smile

Grbld

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: SlamClick
Posted 2005-12-16 00:58:51 and read 14399 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.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Wingscrubber
Posted 2005-12-16 02:28:33 and read 14346 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

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: FLY2HMO
Posted 2005-12-16 04:17:56 and read 14304 times.

Quoting Tarantine (Thread starter):
Can An Airliner Stop By Only Using Reverse Thrust?

If the engines dont get f'ed up by FOD at low speed, yes Big grin

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Airgypsy
Posted 2005-12-16 04:39:54 and read 14291 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.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Mr.BA
Posted 2005-12-16 05:02:29 and read 14280 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.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Starlionblue
Posted 2005-12-16 20:10:23 and read 14173 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 doubt they would surge. If it's idle not much is happening. That is, there is a not a lot of stress put on the engine.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Grbld
Posted 2005-12-16 23:28:26 and read 14147 times.

They won't surge at all, there's no reason to. If required, you can keep the reverse thrust all the way down to a stop.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Jetstar
Posted 2005-12-17 17:25:27 and read 14068 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.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thr
Username: MD-90
Posted 2005-12-19 21:52:25 and read 13905 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?


[Edited 2005-12-19 21:52:47]

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: HAWK21M
Posted 2005-12-20 16:30:56 and read 13808 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?

http://www.airliners.net/discussions/tech_ops/read.main/136068

regds
MEL

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Grbld
Posted 2005-12-20 18:01:14 and read 13774 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.

Interested in your thoughts on this!

Grbld.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Matt72033
Posted 2005-12-20 19:17:52 and read 13756 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!

Topic: RE: Can An Airliner Stop By Only Using Reverse Thr
Username: MD-90
Posted 2005-12-21 01:07:35 and read 13703 times.

Quoting Grbld (Reply 17):
A turbofan engine has its maximum thrust while the airspeed is zero

Of course, if the airspeed is zero, then the engine is producing no power.

Unless you measure power as being a really big, really hot hairdryer, I guess.

[Edited 2005-12-21 01:08:14]

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: EMBQA
Posted 2005-12-21 01:39:23 and read 13693 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.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Starlionblue
Posted 2005-12-21 01:43:41 and read 13691 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 Big grin

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Grbld
Posted 2005-12-21 12:02:56 and read 13645 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.

Grbld

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: David L
Posted 2005-12-21 22:16:48 and read 13585 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?

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Starlionblue
Posted 2005-12-21 22:57:36 and read 13575 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.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: David L
Posted 2005-12-21 23:11:04 and read 13581 times.

Quoting Starlionblue (Reply 24):
I think this is true for carbon brakes but not other types.

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]

Topic: RE: Can An Airliner Stop By Only Using Reverse Thr
Username: Starlionblue
Posted 2005-12-21 23:56:46 and read 13573 times.

Quoting David L (Reply 25):
ing Starlionblue (Reply 24):
I think this is true for carbon brakes but not other types.

Ah, of course - I hadn't thought of the distinction. But haven't carbon brakes been The Latest Thing for a while now?

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 advantages of carbon brakes is that less time is required after a rejected take-off for cooling. Also there is less risk of overheating during a long taxi.

[Edited 2005-12-21 23:59:47]

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: David L
Posted 2005-12-22 00:43:13 and read 13567 times.

Quoting Starlionblue (Reply 26):
One of the big advantages of carbon brakes

I assume asbestos used to be present. If so, there's a health benefit for the maintenance guys, too!

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Zed
Posted 2005-12-22 05:38:26 and read 13534 times.

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, spoilers extended, Anti-Skid On, Maximum brake effort, the airplane decelerated from 125kt (GS) to 35Kt in 1,468 Ft.

The closest case I could find to compare deceleration distance with that using Reverse Thrust Only:

205,000 lb / spoilers extended / maximum reverse thrust, deceleration from 125kt (GS) to 35 kt used about 4,500 Ft.

This is an RB211-535 powered 752.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: HAWK21M
Posted 2005-12-22 11:30:27 and read 13486 times.

Quoting Zed (Reply 28):

Intersting Statistics.
Tells us the Importance of Brakes  Smile
regds
MEL

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Sovietjet
Posted 2005-12-23 02:06:51 and read 13441 times.

Quoting SlamClick (Reply 1):
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.

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 on most planes outside the airport perimeter. A Tu-134, MD-80 or -154 is definetly audible for miles and miles when using reverse but it really isn't that loud not nearly as loud as a plane taking off. A car passing on the street would drown it out in most cases. But I've never heard Boeing or Airbus reverse outside the airport and I used to live right by O'hare.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: David L
Posted 2005-12-23 11:39:16 and read 13400 times.

Quoting Sovietjet (Reply 30):
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 on most planes outside the airport perimeter.

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 silently towards the runway and then... well, I don't know how to spell the sound the reverse thrust makes.  Smile

Of course, that was in the latter days of the Tridents and 707s.

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: Grbld
Posted 2005-12-23 14:14:21 and read 13390 times.

Quoting Sovietjet (Reply 30):
How would reverse thrust break noise restrictions???

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, unless you're in trouble. In fact, some of them even have it during the day (Rome Fiumicino is a big one, for example).

And yes, when the wind is blowing my way, I can definitely hear the reverse thrust at AMS, which is 3 miles away from my house.

Grbld

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: HAWK21M
Posted 2005-12-23 16:06:41 and read 13385 times.

Quoting Sovietjet (Reply 30):
You can't even hear the reverse on most planes outside the airport perimeter.

Out here you sure can hear the B732s,IL76s & An124s reversing quite some distance away  Smile
regds
MEL

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: MikeyCpvd
Posted 2005-12-27 21:26:55 and read 13262 times.

Quoting Sovietjet (Reply 30):
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 on most planes outside the airport perimeter.

Oh Yeah you can!

Quoting David L (Reply 31):
You can, especially if the wind's in the right direction. I used to hear it occasionally a mile or so from Glasgow airport.



Quoting Grbld (Reply 32):
And yes, when the wind is blowing my way, I can definitely hear the reverse thrust at AMS, which is 3 miles away from my house.

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 due south direction, I can hear it well. And most of the a/c landing at PVD now are stage 3/4 737s, Airbuses and RJs. We also have one of the shortest commercial runways in the northeast for an airport our size, which is surrounded by sprawl and residences so the motivation to stop is definitely there!

Topic: RE: Can An Airliner Stop By Only Using Reverse Thrust?
Username: ATCme
Posted 2005-12-31 01:05:03 and read 13102 times.

WOW, this is a really funny thread, or at least some of the comments such as:

Quoting MD-90 (Reply 19):
Unless you measure power as being a really big, really hot hairdryer, I guess.

and

Quoting David L (Reply 31):
I'd see a plane sliding silently towards the runway and then... well, I don't know how to spell the sound the reverse thrust makes.

Even if unintentional...I'm really bored, so they're funny to me!

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?

Also MD-90, don't even try bringing that up, that thread started interesting but got kinda boring (  ) after the 400th post. But I think eventually the plane would magically exit the belt after hitting a few birds that couldn't escape the conveyor belt's power.

ATCme  spin 

Edit: Small errors

[Edited 2005-12-31 01:06:54]


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