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Guest jacob001

Do airliners use differential thrust to take tight turns?

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Hello all :)Just curious so I wanted to put this question to you heavy-airplane gurus http://www.planet-smilies.de/a_smilies/grinsende_3.gifI know that in light piston twins sometimes the pilot can use assymetrical thrust to take a tight turn while taxiing, (for example to take a hard left turn you can apply more power to the starboard motor).I was just wondering...do the big boys like A340-600, 777-300, 747-400, A330 etc - also do this? Or is it not necessary because of their power? I was wondering for example in the Airbus heavies if this was an automatic feature (you turn hard left and the computer cranks the power on the right engine to assist with the turn...)?

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>Hello all :)>>Just curious so I wanted to put this question to you>heavy-airplane gurus>http://www.planet-smilies.de/a_smilies/grinsende_3.gif>>I know that in light piston twins sometimes the pilot can use>assymetrical thrust to take a tight turn while taxiing, (for>example to take a hard left turn you can apply more power to>the starboard motor).>>I was just wondering...do the big boys like A340-600, 777-300,>747-400, A330 etc - also do this? Or is it not necessary>because of their power? I was wondering for example in the>Airbus heavies if this was an automatic feature (you turn hard>left and the computer cranks the power on the right engine to>assist with the turn...)?no. assymetrical thrust in a jet is bad as it puts undue stress on the airframe and main landing gear. the nosewheel is hydraulically powered and will turn the a/c on a dime with no help from power. a jet is pretty easy to taxi as you need the initial small application of thrust to get moving and then usually idle from there. some jets produce enough idle thrust that they have to taxi with their reversers on (some bizjets taxiing down a slight hill, etc).some carriers, like mine, use single engine taxis to conserve fuel. but on some of the bigger airplanes this is not allowed due to the assymetrical thrust hurting the airframe and gear (ie 777, 767, 757).

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At the Airline I was with before retirement we would shut down a wing mount engine during taxi in (also delay an engine start for long taxi out for takeoff)on DC-10's all the time. I also single engine taxied 757's many times. These were approved company and FAA procedures and on these airplanes did not cause any landing gear or brake problems. You had to be sure to not stop and keep it rolling until reaching the gate because if you stopped it required too much power to get it moving again which could blow things around. But as I said we used these procedures routinely and saved a lot of fuel.Ed Weber a.k.a tallpilot

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>At the Airline I was with before retirement we would shut>down a wing mount engine during taxi in (also delay an engine>start for long taxi out for takeoff)on DC-10's all the time. I>also single engine taxied 757's many times. These were>approved company and FAA procedures and on these airplanes did>not cause any landing gear or brake problems. You had to be>sure to not stop and keep it rolling until reaching the gate>because if you stopped it required too much power to get it>moving again which could blow things around. But as I said we>used these procedures routinely and saved a lot of fuel.at AA they are not allowed single engine taxi in the 7-5/6/7-7 due to the structural loads placed on the aircraft. the centerline thrust a/c do single engine taxi all the time. our goal also, if single engine taxiing, is to start the second engine 2 minutes prior to wheels up for fuel conservation. some carriers have stopped using APU starts and gone exclusively to cross bleed starts also to save money on fuel.i heard the DC-10 was a fun airplane to fly. the guy i'm flying with this month, his dad was a dc-10 ca for united and said it was the easiest airplane he ever flew to land. idle thrust on the center engine simply thrust vectored the nose up in the flare and greaser city he said.bottom line: differential thrust is never used on a large jet for turning, the nose wheel in conjunction with the tiller is used.

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Thanks all for your very interesting replies :) Fascinating about the single-engine taxiing, didnt know it was done on the jets. I like seeing the propjets land (like Dash 8 for example), they leave the runway, get on the taxiway and then u see one prop spin down and stop and it trundles along on one engine, that looks cool lol.Speaking of reverse thrust - the C-141 Starlifter could use them in flight right? Or am I mistaken...I could swear I read about some jet that could deploy them in flight (it was a quad-jet and only the inboard reversers could come on)

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>Thanks all for your very interesting replies :) Fascinating>about the single-engine taxiing, didnt know it was done on the>jets. >>I like seeing the propjets land (like Dash 8 for example),>they leave the runway, get on the taxiway and then u see one>prop spin down and stop and it trundles along on one engine,>that looks cool lol.>>Speaking of reverse thrust - the C-141 Starlifter could use>them in flight right? Or am I mistaken...I could swear I read>about some jet that could deploy them in flight (it was a>quad-jet and only the inboard reversers could come on)i do not know about the 707 (c141), but i think the dc-8 can use reverse in flight.

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>i do not know about the 707 (c141), but i think the dc-8 can>use reverse in flight.Why would you do that? To slow down obviously, but under what circumstances do you need to slow down like that?

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some DC-8 models can use idle reverse in flight on engines 2 and 3 only. The 707 and C-141 are not certified for reverser use in flight. Concorde can use idle reverse thrust on the inboard engines in flight.Idle reverse increases the descent rate so you can cruise longer at altitude before commencing your descent.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpgwww.SSTSIM.com

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Concorde used limited in-flight reverse to help descend faster. It was available only on the two inboard engines.

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Not to forget the Tactical Descent fully reversible thrust in flight procedure from the C17 a staggering 14000 fpm, i know it aint commerical but worth a mention ;) i mean wow, i would love to experience that :9

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No, not to slow down but to allow a higher throttle setting on approach for engine bleed air for the windshield rain removal system without increasing airspeed. The DC-8 doesn't use windshield wipers but has a curtain of high energy bleed air blasting over it to keep the rain off.My guess.Roger

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Yes, to slow down. Remember that the DC-8 did not have flight spoilers(speedbrakes). That's the only reason for using in-flight reverse on #2 and #3 engines. Extending the gear also helped it slow down.BTW, there is enough bleed air available with the gear and flaps down in approach config for the rain removal system. It was prohibited to use in-flight reverse during approach.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.sstsim.com/images/team/JR.jpg

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Whoops! Shows how I scan read things instead of slowing down and reading it all!

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