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For a car, we know that we need to use the gear system in order to move the car forward. For the aircraft, I don't know if there exists any gear system within it? I have seen aircrafts staying at the same position when the engine is running on the ground, rather it be a turboprop, turbofan or just a simple jet engine. Why does this happen? What kind of controls are used on the aircraft that doesn't make it move forward. Its not because of drag, since the aircraft is still on the ground. Is it because of gear system, or we are using brakes to keep the aircraft still, or something else?

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  • $\begingroup$ The airplane is idling to warm the engine up prior to flying. No, or very minimal amount of thrust is produced. It is similar to a car in "neutral" or "parking" gear with the engine running. $\endgroup$
    – r13
    Aug 29, 2021 at 22:40
  • $\begingroup$ @r13 The question simply then becomes what is the "parking gear" for an airplane since the propeller or fan is obviously spinning and in a car in drive but with your foot off the pedal still does inch forward. $\endgroup$
    – DKNguyen
    Aug 31, 2021 at 17:45
  • $\begingroup$ @DKNguyen I don't know what type of car you have. On mine, when the gear is in "Park" or "Neutral" with the engine running, I can put my foot on the gas padel and pumping as hard as I can without moving the car an inch but wasting my gasoline. I guess what you are talking about is the nature of manually operated transmission, which requires engaging the parking break while idling for safety. $\endgroup$
    – r13
    Aug 31, 2021 at 18:08
  • $\begingroup$ @r13 Except that the on an airplane the engine clearly is engaged to the propeller/fan since it is turning so to an observer it would not like the equivalent would be park or neutral on a car. Instead, to an observer similar it would appear similar to if the drive gear was engaged so the wheels were slowly spinning under the small amount of torque being produced at idle, yet the car isn't moving forward despite the wheels spinning. Which then begs the question that what really is the "parking gear" on an airplane? $\endgroup$
    – DKNguyen
    Aug 31, 2021 at 18:26
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    $\begingroup$ @DKNguyen According to the linked article (1st), for airplanes, the wheels aren't connected to the engine, the wheels move is due to the thrust propel the plane forward. After reading another article, I guess there is a so-called "ground idle mode" that lets the engine running st its minimum sustainable speed, which could be the state of the airplane in parking, but I am not certain about it. thepointsguy.com/guide/…, quora.com/What-is-the-idling-of-a-jet-engine $\endgroup$
    – r13
    Aug 31, 2021 at 18:53

2 Answers 2

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Brakes are used. And tyre wedges are also used.

Turbo prop has the blades feathered to not produce any thrust.

A jet is producing enough mass flow to run and little thrust.

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  • $\begingroup$ Might as well mention variable pitch and fixed pitch propellers while you're at it. $\endgroup$
    – DKNguyen
    Aug 31, 2021 at 19:04
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Although, there is a perfectly acceptable answer, I wanted to give another perspective (/analogy) that sprung to mind (See at the end of the answer). in the mean time: TL;DR: the plane brakes are probably on.


Take the example the embraer 170 specs which has one of the shortest take off distances of a commercial plane:

  • the take off distance is between 1150 and 1580 meter depending on specs. (The take off speed is at 138 kts).
  • the landing distance is about 1230 meters. (some people refer to the landing speed at 170kts, while stall speed is 109 kts )

So in approximately the same distance, the engines and brakes can accelerate/decelerate the plane at approximately the same velocity.

My point is that brake system is equally (if not slightly more) potent to the engine power in terms of accel/deceleration (and therefore in terms of forces applied on the structure). So, even though engines are at full throttle, the brake system is able to stop the airplane at its tracks.


Initially, your question was very similar to the following:

why doesn't a car move when I am pushing it will all my might on a flat piece of road

enter image description here

There can be a number of reasons, either

  • the force is not enough to overcome the resistance,
  • or the handbrakes is on.
  • Or even both.

there can really be no way of telling, unless you know the specific. However, in both cases (airplane and car), its usually because the brakes are on.

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