I'd imagine not much, but maybe none? I wouldn't be surprised if the plane moves forward without brakes alone.
$\begingroup$
$\endgroup$
2
asked Jan 1, 2020 at 19:47
George Clooney In a MooneyGeorge Clooney In a Mooney
4,4217 gold badges29 silver badges57 bronze badges
-
$\begingroup$ It's definitely not none. You'll hear the engines spin up significantly past idle when a commercial airliner taxis. The answer is going to be "it depends" - if Kennedy Steve is asking you to get a move on, you'll probably use more to get up to speed faster, or if you're going up a slight grade. $\endgroup$– ceejayozCommented Jan 1, 2020 at 19:55
-
2$\begingroup$ The CRJ200 had too much idle thrust and would slowly accelerate on level ground to probably 20kt at idle. You're not supposed to ride brakes so you have to apply them on and off to keep from going too fast,although if you do single engine taxi that takes care of it for you. The bigger RJs needed more than idle to get going, and most larger airliners also do. $\endgroup$– John KCommented Jan 1, 2020 at 20:14
Add a comment
|
2 Answers
$\begingroup$
$\endgroup$
From the 737 (Classic and NG) normal procedures section of the flight manual:
Aircraft response to thrust change is slow, particularly at high gross weights. Idle thrust is adequate for taxiing under most conditions. A slightly higher thrust setting is required to start taxiing. Allow time for aircraft response to each thrust change.
To initiate taxi, release brakes, smoothly increase thrust to minimum required for the aircraft to roll forward and reduce thrust to idle. Under normal conditions, 45% N1 should be considered the maximum N1 for breakaway thrust. Do not start a turn until sufficient forward speed has been attained to carry the aircraft through the turn at idle thrust.
In short, advance the levers a little, achieve breakaway, then back to idle.
Smaller jets with higher thrust-to-weight ratios, such as business jets, often taxi with one of the engines in idle reverse, instead of having to ride the brakes.
$\begingroup$
$\endgroup$
Aircraft weight, slope of the tarmac, and headwind or tailwind play a huge role in this. With a heavy aircraft, it can take significant power to start moving. However, a light aircraft, particularly with a little tailwind or favorable slope, may be ready to roll with idle thrust as soon as the brakes are released. The Max aircraft, particularly, generate more thrust at idle than the NG's so, and on those especially, advancing power is often unnecessary to start rolling.
Typically, though, advancing to 30 to 35% N1 is generally what a Next Gen takes to get rolling.
Interestingly, asphalt, which some of the taxiways at LGA and DCA are made of, can be harder to get moving on, especially in warm weather. The tires sink in just slightly, and it can take significantly more power than usual to get going - maybe even more than the 45% "maximum" value in sufficiently adverse conditions. Ideally, you'd like to keep the aircraft rolling forward slowly so you don't have to start from a full stop, but sometimes that isn't possible. (Delays at DCA & LGA??? Nah...) It's times like those that you're glad that they don't have light aircraft lined up behind you at these places... a two-seat Cessna won't do well with lots of jet blast!
