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Differential Thrust During Taxi  
User currently offlineNgr From United States of America, joined Apr 2001, 176 posts, RR: 0
Posted (9 years 9 months 3 weeks 6 days 8 hours ago) and read 4942 times:

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?

15 replies: All unread, jump to last
 
User currently offlinePilotpip From United States of America, joined Sep 2003, 3151 posts, RR: 11
Reply 1, posted (9 years 9 months 3 weeks 6 days 7 hours ago) and read 4921 times:

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
User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 2, posted (9 years 9 months 3 weeks 6 days 7 hours ago) and read 4906 times:

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.

User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 3, posted (9 years 9 months 3 weeks 6 days 4 hours ago) and read 4734 times:

I know B737 pilots that use Differential Braking while making turns regularily just to keep in touch.
regds
MEL



Think of the brighter side!
User currently offlineLimaFoxTango From Antigua and Barbuda, joined Jun 2004, 800 posts, RR: 2
Reply 4, posted (9 years 9 months 3 weeks 5 days 23 hours ago) and read 4691 times:

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.
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 5, posted (9 years 9 months 3 weeks 5 days 22 hours ago) and read 4666 times:

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.

User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 6, posted (9 years 9 months 3 weeks 5 days 21 hours ago) and read 4659 times:

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.
User currently offlineBALandorLivery From UK - England, joined Jan 2005, 360 posts, RR: 1
Reply 7, posted (9 years 9 months 3 weeks 5 days 19 hours ago) and read 4619 times:

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.


User currently offlineJeb94 From United States of America, joined Oct 2004, 608 posts, RR: 5
Reply 8, posted (9 years 9 months 3 weeks 5 days 19 hours ago) and read 4618 times:

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.

User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 9, posted (9 years 9 months 3 weeks 5 days 13 hours ago) and read 4558 times:

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.


User currently offlineYikes! From Canada, joined Oct 2001, 284 posts, RR: 1
Reply 10, posted (9 years 9 months 3 weeks 5 days 10 hours ago) and read 4513 times:

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.


User currently offline777WT From United States of America, joined Jan 2005, 877 posts, RR: 1
Reply 11, posted (9 years 9 months 3 weeks 5 days 10 hours ago) and read 4508 times:

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?


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17109 posts, RR: 66
Reply 12, posted (9 years 9 months 3 weeks 5 days 9 hours ago) and read 4501 times:

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."
User currently offline777WT From United States of America, joined Jan 2005, 877 posts, RR: 1
Reply 13, posted (9 years 9 months 3 weeks 5 days 8 hours ago) and read 4486 times:

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.


User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 14, posted (9 years 9 months 3 weeks 5 days 1 hour ago) and read 4445 times:

Considering Wing mounted Engines I dont think Reverse thrust on One Engine would be considered wise from an FOD point of View.
regds
MEL



Think of the brighter side!
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 15, posted (9 years 9 months 3 weeks 5 days 1 hour ago) and read 4461 times:

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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