Posted: 12/30/2008 4:26:03 PM EDT
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I've been flying a lot lately and the other day I thought to myself "I wonder how effective reverse thrust is on a commercial airliner?"
So on a normal landing, dry runway, lots of room left to stop, what % of the "braking force" do the reverse thrusters provide? How about if you were trying to stop ASAP? RF |
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Damn effective. But also noisy and uses a bit of fuel. But they cannot be used at full throttle settings. Now the C17 can do some good effort but its reversers are more suited to reducing the need for tug/push ground handling equipment.
As far as percentage, it all depends on the aircraft. |
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Im licensed aircraft tech... Info from an old text book that I got up out of my chair to look it up for you... T/R provide approx 20% of breaking force under NORMAL conditions. However they are capable of producing up to 50% under icy/rainy conditions.
Landing weight on a DC-9 type(used in diagram) is 60,000lbs, landing speed is approx 105knots. With T/R deployed under normal conditions (ie 20%) landing distance is 2000-2100ft. With BRAKES ONLY, distance is approx 2700ft |
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Thrust reversers can shorten the landing roll by a third or more. (Typical airliner usage) Some military aircraft get even more out of them.
Having flown on various commercial airliners several times recently, I can tell you that you'll ALWAYS know when they kick in the thrust reversers. It's very obvious and they WORK, every bit as good as the wheel brakes. There's really no doubt in my mind that a 747-400 can come to a complete stop after landing faster than it can go from a full stop to takeoff. CJ |
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The landing distance calculaations do not include the braking provided by the thrust reversers. However, this being said they are very effective. Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief.
And the plane will take off on the treadmill. |
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It is true that T/Rs can and are used to back-up. For non-prop engines that can be an expensive price to pay. There is a good chance of injesting something in the engine, especially low engine AC. Like Boeing 737,747,757,767,777 and prob the 787. Some airlines use it to back out of gates but the one I worked for wouldnt alow it.
I was layed of in '04 |
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Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief. I had the pleasure of being on one of those "aborted takeoff" flights many years ago. Got on the plane in Philly, stopped in St Louis, and TRIED to get back in the air to Phoenix... with no luck. Scared the fuck out of me (and everyone else on the plane for that matter). I had NO IDEA an airplane had THAT kind of mechanical braking ability. I don't recall what model plane it was... but both engines were mounted on the back end of the plane... As we approached take-off speed... maybe halfway down the runway... the G-force went from a cool accelleration feeling to an "Oh-shit" we are stopping like RIGHT FUCKING NOW and turning left to go back to the hangar. We turned so hard and fast I thought the fucking plane was 'gonna tip over. Turns out... one of the engines wasn't getting up to speed and the plane was grounded. We got pushed off the plane and on to another flight. The scary part was... I just flew into the airport on that plane. |
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Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief. I had the pleasure of being on one of those "aborted takeoff" flights many years ago. Got on the plane in Philly, stopped in St Louis, and TRIED to get back in the air to Phoenix... with no luck. Scared the fuck out of me (and everyone else on the plane for that matter). I had NO IDEA an airplane had THAT kind of mechanical braking ability. I don't recall what model plane it was... but both engines were mounted on the back end of the plane... As we approached take-off speed... maybe halfway down the runway... the G-force went from a cool accelleration feeling to an "Oh-shit" we are stopping like RIGHT FUCKING NOW and turning left to go back to the hangar. We turned so hard and fast I thought the fucking plane was 'gonna tip over. Turns out... one of the engines wasn't getting up to speed and the plane was grounded. We got pushed off the plane and on to another flight. The scary part was... I just flew into the airport on that plane. I'm sure you'd have been fine on one engine while landing(scary nontheless). Taking off is when you need all the juice. |
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Check this out: Rejected takeoff test for the Boeing 777. The plane is at the maximum weight it will ever carry, and at 210 MPH (takeoff speed), brakes are applied with maximum force....and the brakes are worn down to the minimum service thickness.
The spec is "No fire for five minutes". http://www.youtube.com/watch?v=f4LFErD-yls CJ |
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Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief. I had the pleasure of being on one of those "aborted takeoff" flights many years ago. Got on the plane in Philly, stopped in St Louis, and TRIED to get back in the air to Phoenix... with no luck. Scared the fuck out of me (and everyone else on the plane for that matter). I had NO IDEA an airplane had THAT kind of mechanical braking ability. I don't recall what model plane it was... but both engines were mounted on the back end of the plane... As we approached take-off speed... maybe halfway down the runway... the G-force went from a cool accelleration feeling to an "Oh-shit" we are stopping like RIGHT FUCKING NOW and turning left to go back to the hangar. We turned so hard and fast I thought the fucking plane was 'gonna tip over. Turns out... one of the engines wasn't getting up to speed and the plane was grounded. We got pushed off the plane and on to another flight. The scary part was... I just flew into the airport on that plane. Not as scary as an aborted landing. We had just cleared the fence in a MD-80 when the pilot aborted at about 100 feet off the ground. Engines went to full and it was MUCH LOUDER than normal TO. We rotated to what felt like 45 degrees...probably a bit less due to the extreme acceleration. Why? Another airplane on the runway. Ground had messed up in a pass-off or the GA screwed the pooch. |
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Check this out: Rejected takeoff test for the Boeing 777. The plane is at the maximum weight it will ever carry, and at 210 MPH (takeoff speed), brakes are applied with maximum force....and the brakes are worn down to the minimum service thickness. The spec is "No fire for five minutes". http://www.youtube.com/watch?v=f4LFErD-yls CJ I've always liked this one: http://www.youtube.com/watch?v=m1dv_y_3EK0&feature=related |
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There are a lot of factors at play here. As one person pointed out, TR's will be much more effective as a part of the stopping distance, when the runway is contaminated...as the tires will not have good grip on the runway. We have anti-skid, but friction is still a limit as to how much brake is applied.
When we do land on a very slippery runway, and use the TR's...often times we will get into and out of the TR's multiple times as they tend to slew the airplane around pretty good. Reverse on turbo-props is extremely effective at all speeds and conditions. As for the Airbus and most newer equipment, we have carbon fiber brakes. Very effective even when hot. SOP for my airline and several others, is the slip the TR's into reverse idle, and apply brakes at a certain speed. Moving the reverser's up into full reverse, simply puts additional wear and tear on the engines...which is significantly more expensive to repair than brake pads. Not to mention, as the plane slows down below 80 knots, you run a higher risk of sucking FOD up into the engines. For those that referred to thrust reversers being used in flight, not many airplanes are designed for that. DC-8 and the C-17 are the only two certified that I know off the top of my head. The DC-8's wings would move around pretty good. Buddies that fly the C-17's, have told me stories about doing aversion maneuvers, doing 22,000 fpm down with their TR's in flight. Completely unnatural. |
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Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief. I had the pleasure of being on one of those "aborted takeoff" flights many years ago. Got on the plane in Philly, stopped in St Louis, and TRIED to get back in the air to Phoenix... with no luck. Scared the fuck out of me (and everyone else on the plane for that matter). I had NO IDEA an airplane had THAT kind of mechanical braking ability. I don't recall what model plane it was... but both engines were mounted on the back end of the plane... As we approached take-off speed... maybe halfway down the runway... the G-force went from a cool accelleration feeling to an "Oh-shit" we are stopping like RIGHT FUCKING NOW and turning left to go back to the hangar. We turned so hard and fast I thought the fucking plane was 'gonna tip over. Turns out... one of the engines wasn't getting up to speed and the plane was grounded. We got pushed off the plane and on to another flight. The scary part was... I just flew into the airport on that plane. Not as scary as an aborted landing. We had just cleared the fence in a MD-80 when the pilot aborted at about 100 feet off the ground. Engines went to full and it was MUCH LOUDER than normal TO. We rotated to what felt like 45 degrees...probably a bit less due to the extreme acceleration. Why? Another airplane on the runway. Ground had messed up in a pass-off or the GA screwed the pooch. Exactly, most accidents happen in approach and landing. Most FATALITIES though happen on takeoff. With an aborted takeoff youve left a lot of runway behind you already. Its usually a better idea to take off unless its a loss of directional control thing or it happens early in the run. Thrust reversers work great. On a 6 or 7 thousand ft runway in a Lear 31 will wont even touch the brakes until making the turn onto the taxiway. Manual says to discontinue anything above idle reverse once you slow to 60kts or else you can blow debris up in front of the engines. The thing with thrust reversers is it works better when youre going fast. The slower you are going the less effect it has. In the Lear during a max effort braking attempt, youll be slowed down to below 60 knots before the engines even get spooled up in reverse. To deploy them the engines have to be at idle first, then they are deployed and then you gotta wait for the engines to spin back up. |
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Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief. I had the pleasure of being on one of those "aborted takeoff" flights many years ago. Got on the plane in Philly, stopped in St Louis, and TRIED to get back in the air to Phoenix... with no luck. Scared the fuck out of me (and everyone else on the plane for that matter). I had NO IDEA an airplane had THAT kind of mechanical braking ability. I don't recall what model plane it was... but both engines were mounted on the back end of the plane... As we approached take-off speed... maybe halfway down the runway... the G-force went from a cool accelleration feeling to an "Oh-shit" we are stopping like RIGHT FUCKING NOW and turning left to go back to the hangar. We turned so hard and fast I thought the fucking plane was 'gonna tip over. Turns out... one of the engines wasn't getting up to speed and the plane was grounded. We got pushed off the plane and on to another flight. The scary part was... I just flew into the airport on that plane. Not as scary as an aborted landing. We had just cleared the fence in a MD-80 when the pilot aborted at about 100 feet off the ground. Engines went to full and it was MUCH LOUDER than normal TO. We rotated to what felt like 45 degrees...probably a bit less due to the extreme acceleration. Why? Another airplane on the runway. Ground had messed up in a pass-off or the GA screwed the pooch. done that here too, last year in charlotte, bout crapped my pants |
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There are a lot of factors at play here. As one person pointed out, TR's will be much more effective as a part of the stopping distance, when the runway is contaminated...as the tires will not have good grip on the runway. We have anti-skid, but friction is still a limit as to how much brake is applied. When we do land on a very slippery runway, and use the TR's...often times we will get into and out of the TR's multiple times as they tend to slew the airplane around pretty good. Reverse on turbo-props is extremely effective at all speeds and conditions. As for the Airbus and most newer equipment, we have carbon fiber brakes. Very effective even when hot. SOP for my airline and several others, is the slip the TR's into reverse idle, and apply brakes at a certain speed. Moving the reverser's up into full reverse, simply puts additional wear and tear on the engines...which is significantly more expensive to repair than brake pads. Not to mention, as the plane slows down below 80 knots, you run a higher risk of sucking FOD up into the engines. For those that referred to thrust reversers being used in flight, not many airplanes are designed for that. DC-8 and the C-17 are the only two certified that I know off the top of my head. The DC-8's wings would move around pretty good. Buddies that fly the C-17's, have told me stories about doing aversion maneuvers, doing 22,000 fpm down with their TR's in flight. Completely unnatural. Yeah,rode around in DC-8s alot,pax today would be scared shitless,seeing the reverser buckets slide back,especially an old -30 model.(yes,Delta had a few,in the late '60s-early '70s). |
C-17 thrust reverse compressor stall (fireball) 
http://www.youtube.com/watch?v=BPm2z4V43Bw&eurl |
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Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief. I had the pleasure of being on one of those "aborted takeoff" flights many years ago. Got on the plane in Philly, stopped in St Louis, and TRIED to get back in the air to Phoenix... with no luck. Scared the fuck out of me (and everyone else on the plane for that matter). I had NO IDEA an airplane had THAT kind of mechanical braking ability. I don't recall what model plane it was... but both engines were mounted on the back end of the plane... As we approached take-off speed... maybe halfway down the runway... the G-force went from a cool accelleration feeling to an "Oh-shit" we are stopping like RIGHT FUCKING NOW and turning left to go back to the hangar. We turned so hard and fast I thought the fucking plane was 'gonna tip over. Turns out... one of the engines wasn't getting up to speed and the plane was grounded. We got pushed off the plane and on to another flight. The scary part was... I just flew into the airport on that plane. Ever been on a 747 that the pilots accidentally over-rotated on takeoff? Try that for fun someday. "BANG!!!!!" EDIT: After I had that experience once, I later read that the 747 was designed to withstand that, but it will sure scare the hell out of you. |
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As has been posted, thrust reverse is most effective at high speeds when the wheel brakes are least effective.
There are other factors that go into using thrust reversers effectively, in the case of the E-6B, thrust reversers work best above 60-80 knots (depending on the airfield conditions) with the flaps/slats up and the spoilers (speedbrakes) deployed (get the weight on the wheels asap). The combined safe braking force the wheel brakes are capable of generating is 28 million (edit) foot pounds. |
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Kinda like this?
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I had the pleasure of being on one of those "aborted takeoff" flights many years ago.
Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief. Got on the plane in Philly, stopped in St Louis, and TRIED to get back in the air to Phoenix... with no luck. Scared the fuck out of me (and everyone else on the plane for that matter). I had NO IDEA an airplane had THAT kind of mechanical braking ability. I don't recall what model plane it was... but both engines were mounted on the back end of the plane... As we approached take-off speed... maybe halfway down the runway... the G-force went from a cool accelleration feeling to an "Oh-shit" we are stopping like RIGHT FUCKING NOW and turning left to go back to the hangar. We turned so hard and fast I thought the fucking plane was 'gonna tip over. Turns out... one of the engines wasn't getting up to speed and the plane was grounded. We got pushed off the plane and on to another flight. The scary part was... I just flew into the airport on that plane. http://www.youtube.com/watch?v=AzfEx_zBmek |
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Very effective. I use it sometimes when I taxi. Some airlines used to back out of the gates with their T/Rs. DC-9s I beleive. Yup....back when I flew CRJ's, you generally left one hanging out on a two engine taxi to keep the speed down....especially going downhill in the congo line, for 25R at Vegas. AA still backs their Maddogs (MD-88s) out of DFW gates sometimes. |
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Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief. I had the pleasure of being on one of those "aborted takeoff" flights many years ago. Got on the plane in Philly, stopped in St Louis, and TRIED to get back in the air to Phoenix... with no luck. Scared the fuck out of me (and everyone else on the plane for that matter). I had NO IDEA an airplane had THAT kind of mechanical braking ability. I don't recall what model plane it was... but both engines were mounted on the back end of the plane... As we approached take-off speed... maybe halfway down the runway... the G-force went from a cool accelleration feeling to an "Oh-shit" we are stopping like RIGHT FUCKING NOW and turning left to go back to the hangar. We turned so hard and fast I thought the fucking plane was 'gonna tip over. Turns out... one of the engines wasn't getting up to speed and the plane was grounded. We got pushed off the plane and on to another flight. The scary part was... I just flew into the airport on that plane. Not as scary as an aborted landing. We had just cleared the fence in a MD-80 when the pilot aborted at about 100 feet off the ground. Engines went to full and it was MUCH LOUDER than normal TO. We rotated to what felt like 45 degrees...probably a bit less due to the extreme acceleration. Why? Another airplane on the runway. Ground had messed up in a pass-off or the GA screwed the pooch. Anyone? |
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saw this video of a c-17
http://www.youtube.com/watch?v=GNRXAHasFvk&feature=related |
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Sheesh that stopped fast. |
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Im licensed aircraft tech... Info from an old text book that I got up out of my chair to look it up for you... T/R provide approx 20% of breaking force under NORMAL conditions. However they are capable of producing up to 50% under icy/rainy conditions. Landing weight on a DC-9 type(used in diagram) is 60,000lbs, landing speed is approx 105knots. With T/R deployed under normal conditions (ie 20%) landing distance is 2000-2100ft. With BRAKES ONLY, distance is approx 2700ft Sweet! Thanks for looking that up! RF |
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TRs can also delay the onset of when brakes are applied. Brake energery is not calculated on how hard you engage the brakes, but rather at what speed (and weight, field conditions, etc) you apply them at. So tapping the pedals 115 knots will use more brake energy than slamming them on at 105 knots.
Per the flight manual (at least for what I fly), landing distance is not calculated based on lightly applying brake pressure, its slamming them on. Let the Anti-Skid do the work. Granted, its not very comfortable for those in back when you do this, but that is the way you're "supposed" to do it. You invalidate your landing data when you try and grease the landing, gradually apply brakes, etc. |
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http://www.youtube.com/watch?v=hRzWp67PIMw
http://www.youtube.com/watch?v=UocxPoUUnIQ&feature=related Airbus SUCKS! Any way I look at these videos, I see FAIL. They didn't get to the 5 minute mark before tires were exploding and things were on fire. The 777-300ER test, at maximum weight and minimal brake shoe lining thickness, went a lot better than that! And frankly I think Airbus has some very fucked up engineers. To design the A340 with a central main gear truck may make sense to SOME people, but nobody else has seen the need for that and adding another landing gear system adds complexity and cost while doing nothing to improve reliability. Why use four gear systems when three properly designed systems are clearly more than adequate for the task? I really don't see how European engineering is better in any way, on average, than good American engineering. There's not much evidence to support that idea. CJ |
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Very effective. I use it sometimes when I taxi. Some airlines used to back out of the gates with their T/Rs. DC-9s I beleive. AA still backs their Maddogs (MD-88s) out of DFW gates sometimes. Watched them do that from the Terminal E ramp at DFW. Taxing a 550B or 560 XL we just use the TRs. |
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Hey, I was there.. and holy shit did that stop fast! Also, that runway is much longer than where he touched down. He was at about the last 3/8ths of the runway. |
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Both the DC-10-30/40 and MD-11s had a center truck,keeps the weight footprint to acceptable levels.
http://www.youtube.com/watch?v=hRzWp67PIMw http://www.youtube.com/watch?v=UocxPoUUnIQ&feature=related Airbus SUCKS! Any way I look at these videos, I see FAIL. They didn't get to the 5 minute mark before tires were exploding and things were on fire. The 777-300ER test, at maximum weight and minimal brake shoe lining thickness, went a lot better than that! And frankly I think Airbus has some very fucked up engineers. To design the A340 with a central main gear truck may make sense to SOME people, but nobody else has seen the need for that and adding another landing gear system adds complexity and cost while doing nothing to improve reliability. Why use four gear systems when three properly designed systems are clearly more than adequate for the task? I really don't see how European engineering is better in any way, on average, than good American engineering. There's not much evidence to support that idea. CJ |
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Maximum braking with maximum reverse when used in something like an aborted takeoff is beyond belief. I had the pleasure of being on one of those "aborted takeoff" flights many years ago. Got on the plane in Philly, stopped in St Louis, and TRIED to get back in the air to Phoenix... with no luck. Scared the fuck out of me (and everyone else on the plane for that matter). I had NO IDEA an airplane had THAT kind of mechanical braking ability. I don't recall what model plane it was... but both engines were mounted on the back end of the plane... As we approached take-off speed... maybe halfway down the runway... the G-force went from a cool accelleration feeling to an "Oh-shit" we are stopping like RIGHT FUCKING NOW and turning left to go back to the hangar. We turned so hard and fast I thought the fucking plane was 'gonna tip over. Turns out... one of the engines wasn't getting up to speed and the plane was grounded. We got pushed off the plane and on to another flight. The scary part was... I just flew into the airport on that plane. Not as scary as an aborted landing. We had just cleared the fence in a MD-80 when the pilot aborted at about 100 feet off the ground. Engines went to full and it was MUCH LOUDER than normal TO. We rotated to what felt like 45 degrees...probably a bit less due to the extreme acceleration. Why? Another airplane on the runway. Ground had messed up in a pass-off or the GA screwed the pooch. Aborted landings are... interesting. Coming back from Australia, chartered civilian flight and landing in the American Samoas in 60 plus mph winds. Going down, down.... landing gear lowered, I'd guess a hundred feet off the ground, plane was shaking like crazy, banking left and right and then "oh shit." Pilot went full throttle and banked, felt like we weren't gonna make it back in the air. First time I've seen a flight attendant with a terrified look on her face, and another one ran to the bathroom after we had made it back into the air. It was a bit amusing, most of the guys who had deployed were laughing, those who hadn't were damn near pissing themselves. Worst flight, military or civilian that I've ever been on. |
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Both the DC-10-30/40 and MD-11s had a center truck,keeps the weight footprint to acceptable levels.
http://www.youtube.com/watch?v=hRzWp67PIMw http://www.youtube.com/watch?v=UocxPoUUnIQ&feature=related Airbus SUCKS! Any way I look at these videos, I see FAIL. They didn't get to the 5 minute mark before tires were exploding and things were on fire. The 777-300ER test, at maximum weight and minimal brake shoe lining thickness, went a lot better than that! And frankly I think Airbus has some very fucked up engineers. To design the A340 with a central main gear truck may make sense to SOME people, but nobody else has seen the need for that and adding another landing gear system adds complexity and cost while doing nothing to improve reliability. Why use four gear systems when three properly designed systems are clearly more than adequate for the task? I really don't see how European engineering is better in any way, on average, than good American engineering. There's not much evidence to support that idea. CJ And to be fair about it, the 747 has five gear trucks. But those are all late 60s/early 70s vintage designs. These days the trend seems to get the weight distribution right by adding wheels to the main trucks instead of adding more trucks. That seems to be a lot more sensible to my way of thinking. Of course, there's a limit to how big a gear truck you want to have to haul out and then bring back in. Beyond that point, additional gear trucks are probably the better way to go, if you have to have the additional load bearing capacity. CJ |
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you'll ALWAYS know when they kick in the thrust reversers. It's very obvious and they WORK, every bit as good as the wheel brakes. Yes and no. Many airlines / aircraft are using autobrake systems. They will deliver and a selected decelleration RATE, not force. Therefore a given landing on a dry runway using autobrakes Medium will result in achieving taxi speed at a given point down the runway. Using max reverse, none, or anything in between simply adjusts how much kinetic energy is dumped into the brake system. No reverse, and the brakes will literally be smoking in the gate, while max reverse demands much less of the brakes to achieve the same felt rate of decel. On the Airbus series, "low" offers a 4 second delay after touchdown, and a very gentle decel, "medium" is subtle as a heart attack after a 2 second delay, and "max" can only be used for an aborted takeoff. Eat the seatback. Of course how all this is goes is on a case by case basis determined by runway length, following traffic, exit and taxi plannning, current brake temperature, outside air temperature, how long the brakes will have to cool, carbon vs steel brakes (carbon likes to be hot, steel doesn't), etc. |