NP WM asked in Cars & TransportationAircraft · 1 decade ago

What is the "reverse" after touchdown in an airplane?

What is the "reverse" after touchdown in an airplane?

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  • 1 decade ago
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    There are several things an airliner uses to slow down when landing:

    1) Flaps. These increase lift, but also increase drag. You'll see these extend from the rear of the wing (and sometimes the front too) while the pilot prepares for landing.

    2) Spoilers: These pop up from the top of the wing to 'spoil' the airflow over the wing & increase drag. They're usually only used on or near the ground, but some models (called "speed brakes") can be used at altitude to slow more rapidly & increase decent rate.

    3) Brakes - just like on your car. In fact, anti-lock brakes were first developed for airplanes.

    4) Jet engines (and some turboprops) can reverse the thrust direction of their engines - this feels like 'reverse' to some, and is what you're probably referencing. It's really easy to see looking at the airplane from the outside, but hard to see from inside the plane (on jets anyway). Propeller planes that have thrust reversing can rotate their propeller to push the air backwards. Check the Wikipedia link in my resources for a great description with photos. Some jets have a "squat switch" that prevent thrust reversers from engaging until the plan is solidly on its landing gear (757 is one).

    Interesting side-note: You can also see an interesting experiment on reverse thrust on YouTube. Have you seen the C130 (propeller driven) cargo plane that uses little rockets on the side to assist in take-off? (Called Jet Assisted Take Off or JATO - even if it uses rocket engines) Well, the military experimented with reverse-mounted JATO thrusters to help the C130 *land* on a short field, since the JATO engines only help them *take off* on short fields. Well, you'll see on the YouTube video, the pilots hit the "reverse thrust JATO" switch *before* the plane was on the ground - and the plane fell out of the sky!

    Hope that helps!

    Source(s): http://en.wikipedia.org/wiki/Thrust_reverser Letter from Airline Pilot in Feb 2009 AOPA Pilot Magazine http://www.youtube.com/watch?v=93DAMQQ8SNI http://en.wikipedia.org/wiki/JATO Pilot's License Training
  • 1 decade ago

    Most airliners use reverse thrust after touchdown in order to slow the airplane more quickly and reduce wear and tear on the wheel brakes.

    They may also use airbrakes or spoilers, which are panels on the wings that are extended into the airstream in order to create drag (which slows the airplane) and destroy lift (which helps keep it on the ground) after touchdown. These don't actually provide any reverse thrust, though.

    Of course, ordinary wheel brakes are used to slow down as well, but they don't provide reverse thrust either.

    So the reverse thrust comes from the engines. Jet engines always turn in the same direction—they cannot simply be run in reverse—but the thrust from the engines can be redirected by special vanes so that it is sent forward instead of backward. It's not very efficient, but it works well enough to add substantially to the slowing of the aircraft. Reverse thrust is used from touchdown down to about 40 knots or so. At low speeds reverse thrust can blow debris into the engine intakes, so it is not used at very low speeds.

    This is why you often hear the engines roar after touching down in an airliner. The pilots have set reverse thrust and increased the throttles to provide more braking action. If you have the rear of the engines in sight, you can often see the reverse vanes or cowls extending to direct thrust forward.

    Some propeller aircraft can also reverse the pitch on the prop to provide reverse thrust.

  • Anonymous
    1 decade ago

    Reverse thrust is used to rapidly slow the aircraft after touchdown. The thrust from the fan on a jet engine is redirected forwards to create a wall of drag to slow the aircraft down. The standard thrust reverser's found on modern aircraft are either blocker or transition doors. Older generations such as bucket reverser's can still be found.

  • 1 decade ago

    Contrary to the first guys answer, "speed brakes" are some panels that extend to slow the aircraft in flight and at landing if need be. The slower you go, the less effective they are. They have nothing to do with "reverse thrust" on an aircraft.

    "reverse" means you "reverse thrust". Most airliners and the cargo variants have reverse thrust. Some turbo props do also. On jets they have a system that directs the thrust foreword. On the turbo prop aircraft they change the pitch of the prop to push the air foreword.

    I am sorry but some people have no business answering questions when they have no idea what they are talking about. Don't listen to the first answer, he is one of them.

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  • 1 decade ago

    Great point specwar.....

    As mentioned, thrust reversers are used to slow the airplane usually to 60kts, then brakes after that. The engines deflect the thrust forward.

    Spoilers are used to slow an airplane while flying and also to destroy any residual lift during landing roll. In other words, they make sure the airplane cannot become airborne again.

    Source(s): And to the first answer: When you show us your Private Pilot Certification, I will post a video of me burning my SEL rating. I wouldnt share the sky with you for all the tea in China.
  • 1 decade ago

    Reverse thrust slows down the Aircraft.

    Nice answer Tam !! Betcha you drive a car right ?

  • T
    Lv 6
    1 decade ago

    Do you mean "take off"?

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