ngr
Posts: 172
Joined: Fri Apr 13, 2001 6:38 am

Differential Thrust During Taxi

Tue Feb 01, 2005 1:39 pm

Do pilots on airliners or multi-engine aircraft use differenential thrust to aid in making turns while taxiing? If so, is it only effective on wing-engined aircraft, or all types?
 
pilotpip
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Joined: Fri Sep 19, 2003 3:26 pm

RE: Differential Thrust During Taxi

Tue Feb 01, 2005 1:47 pm

Yes. When taxiing in a crosswind condition or needing to make a tight turn it does help. I can only say this for piston twins. I'm sure that even on aircraft with fuselage mounted engines it is used but with the engines closer to centerline the effect is not as great.
DMI
 
avt007
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

RE: Differential Thrust During Taxi

Tue Feb 01, 2005 2:05 pm

I found that differential thrust helps on the Dash 8, but is less useful on the F28 due to the thrust being closer to the centreline, although it does help.
 
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HAWK21M
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Joined: Fri Jan 05, 2001 10:05 pm

RE: Differential Thrust During Taxi

Tue Feb 01, 2005 5:35 pm

I know B737 pilots that use Differential Braking while making turns regularily just to keep in touch.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
LimaFoxTango
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Joined: Wed Jun 16, 2004 11:33 pm

RE: Differential Thrust During Taxi

Tue Feb 01, 2005 9:45 pm

I know pilots use differential thrust while making sharp turns. For example, if a Dash 8 needs to turn left into a gate, the trick used would to apply brakes to the left tire, and apply right thrust. You would be surprised to know how an aircraft like the a Dash 8 can turn on a dime. I've seen it done many times.
You are said to be a good pilot when your take-off's equal your landings.
 
air2gxs
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Joined: Mon Jun 18, 2001 1:29 pm

RE: Differential Thrust During Taxi

Tue Feb 01, 2005 11:30 pm

If I was taxiing a particularly heavy B747, I would use the outboard engines to assist in the turn. Never used differential braking though, didn't like the way it handled through the turn.
 
SlamClick
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Joined: Sun Nov 23, 2003 7:09 am

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 12:12 am

After pushback we are sometimes required to begin our taxi with a sharp turn in one direction or the other. It always requires "breakaway" thrust to start the thing moving. In a case like this many will use both to get rolling then pull back the lever on the engine inside the turn to help get it started.

Once rolling, we have a lot of steering authority with that hydraulic nosewheel steering.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
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BALandorLivery
Posts: 313
Joined: Mon Jan 17, 2005 7:54 pm

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 2:04 am

I flew a 777 sim once and needed to do a 180 on the runway to take off.

The instructor told me to use differential foot braking and also only the right throttle for power (it was a left turn).

VERY EFFECTIVE.

Regds.
 
jeb94
Posts: 587
Joined: Mon Oct 04, 2004 9:19 pm

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 2:10 am

It is very much a factor on an MD-80. Not as effective compared to a 737 I'm guessing but it really helps making tight turns on the MD-80.
 
411A
Posts: 1788
Joined: Mon Nov 12, 2001 10:34 am

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 8:36 am

I have just returned from GQNN, and the runway is rather narrow for a TriStar, and backtracking is required in the turning bay at the runway end.
Differential power, using the engine on the outside of the turn makes life a whole lot easier, and reduces nose wheel scuffing on tight turns, especially on the rough pavement surfaces found in Africa.
This differental power needs to be used carefully, as FOD damage can be a problem at some locations.
 
Yikes!
Posts: 284
Joined: Sat Oct 13, 2001 4:51 pm

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 10:58 am

Agreed with the above. A major concern though when doing a 180 at the threshold prior to takeoff is tire temperature. Additionally, the inside bogeys may actually turn backwards during a tight turn further increasing their pre-takeoff temps.

Tire heat is a potential problem with all heavy aircraft takeoffs. Turns prior to takeoff add to that heat.
 
777wt
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Joined: Wed Jan 19, 2005 7:45 am

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 11:39 am

How about a really tight left 180 turn, say in a 737 or a 777 (expertimental test).
Would it work if you used left brake, right ENG left thrust, left ENG in reverse thrust?
 
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Starlionblue
Posts: 17208
Joined: Fri Feb 27, 2004 9:54 pm

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 12:08 pm

Most airlines don't approve of reverse at low speeds (the exception being powerbacks when necessary). The risk ofr FODding and reingestion of air is too big.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
777wt
Posts: 828
Joined: Wed Jan 19, 2005 7:45 am

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 12:56 pm

Starlionblue,
I am aware of that due to FOD and other reasons.

I was saying it to see what it'd be like if you tried it that way, not for normal OPS.
 
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HAWK21M
Posts: 29917
Joined: Fri Jan 05, 2001 10:05 pm

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 8:21 pm

Considering Wing mounted Engines I dont think Reverse thrust on One Engine would be considered wise from an FOD point of View.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
PhilSquares
Posts: 3371
Joined: Sun Mar 28, 2004 6:06 pm

RE: Differential Thrust During Taxi

Wed Feb 02, 2005 8:30 pm

The FCOM for the 744 specifically prohibits reverse thrust for situations like you describe. Most airlines have a further restriction of no reverse thrust below a certain airspeed, for example 60 or 80 knots.

On the 744, for especially tight turns, a technique is to use a little outboard thrust to help you keep your momentum. If you're heavy and don't have enough speed, the aircraft won't make the turn at idle power and then you have to use quite a bit to get it going in the turn.
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