IDLE TAXI with B744

[Michelmvd]

Hello,
In order to fine tune as real as possible the B744 airfile in my flightsimulator, I would like to ask following questions.
- I know that with a rather light taxiweight the B744 can taxi on idle engine power. Till which TOW is this the case and how much N1 is requested once engine more than idle thrust is necessary.

-when idle thrust is anove, must the brakes be used regularry to maintain the taxispeed?
Thanks a lot for the most appreciated information.
Ciao
Michel

[Notso Fantastic]

It's difficult to say as factors like slope of taxiway make so much difference and you really cannot assess how much upslope or downslope you are on unless it is significant. All I can say is on an RB211 powered 747, at heavy weights (340 tonnes +), anything up to 1.09 EPR to be sure of getting moving. Above about 280 tonnes, anything above 1.06 should get you going depending upon slope. There is no usable formula because you are affected so much by wind, slope, sticky brakes.

[Dan Winterland]

Lots of variations depending on the engine type. The GE (no EPR guage) has a max of 40% N1 to prevent blowing things away. The GE doesn't have a huge amount of residual thrust on the ground so you need a squirt of power occaisionally. The PW has lots of residual and controlling the speed at even quite high TOWs means using and warming up the brakes.

[northwing]

Can't speak about the 747 but it sounds to me as if these guys are lucky. With lower by-pass military engines optimised for high thrust and response it is quite common to find that idle thrust is too high and the brakes have to be used to maintain a reasonable taxi speed. A Hawk will stabilise at about 50 knots on a level runway at idle if you just let it go. Harrier pilots will often rotate the nozzles to 40 or 50 degrees to kill the effect of idle thrust while taxiing.

[decimal86]

we fly a PW 747-400 and anything more than 320 tons will require a squeeze of the throttles upwards to avoid the square wheels effect.

and that 40% guideline as post earlier? that's our limit too to prevent baggage trolleys from flying around i guess.

[Michelmvd]

Thank you all very much for the most interesting comments.
They helped a lot to tune the airfile.
Thks
Michel Vandaele