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When an airplane is reducing altitude, say due to preparation for landing, the nose is tilted down. That I got from a video on Youtube which explains the way an airplane is going down until it reaches a certain altitude and until the nose is revert to tilt up. Then my question:

  • Is that explanation true that during reducing altitude the nose is tilted down?
  • Which one is more efficient compare to if the airplane is tilted up as the position of an airplane when it landing. "Efficient" here is about which one faster, more fuel efficiency.
  • What is the allowed maximum angle tilt down nose?

Airplane reduce altitude

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    $\begingroup$ You should only ask one question here. Could you please edit? $\endgroup$ – Bianfable Aug 7 at 11:52
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There are (mostly) two ways to reduce altitude:

  • Reduce speed until your wings don't generate enough lift in level flight. Typically the nose will drop by itself since you are no longer at your trimmed airspeed. You might be able to re-trim so that you are in a level descent.
  • Drop the nose manually without reducing (or even increasing) speed

Airliners at altitude operate very close to what is called the coffin corner where an increase in speed means you overspeed the aircraft, and a reduction in speed means you stall. So preferably the pilot will simultaneously reduce the throttles while lowering the nose to maintain a specific speed.

Tilting the aircraft up (nose up) will reduce your speed and eventually you will fall to the earth (as you stall). This is a very inefficient way to get down (not to mention it scares the hell out of the passengers). The aircraft buffets, a wing may drop if the plane is not kept coordinated, and is overall a very dangerous thing to do (see the coffin corner link above).

The reason the nose is raised while landing is so that the aircraft can bleed off extra speed and reduce the descent rate for touch down (as well as reducing the stress on the nose gear). This is also a high-drag situation and is, in that effect, inefficient.

What is the allowed maximum angle tilt down nose?

90° because after that you're tilting up...

In all seriousness you can nose-down until you hit the maximum airframe speed without causing damage. For airliners this is usually a lot more than passengers are comfortable with (especially if the stewards have the rolling carts out), so pilots make a concerted effort to keep the floor as level as possible. For smaller aircraft like the 172, you can configure it such that you won't exceed this speed and point the thing almost straight down, it's actually pretty fun.

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  • $\begingroup$ "The reason the nose is raised while landing is so that the aircraft can bleed off extra speed and reduce the descent rate for touch down (as well as reducing the stress on the nose gear). This is also a high-drag situation and is, in that effect, inefficient." This statement is incomplete and misleading. The primary reason that a plane noses up prior to touchdown is to increase the wing's angle of attack, increasing lift so that the plane can continue flying at slower airspeeds (which decrease lift) prior to landing. $\endgroup$ – Skip Miller Aug 7 at 13:43
  • $\begingroup$ @SkipMiller I assumed they would understand that "reducing the descent rate" means you have to add lift. As the speed reduces further, more "lift" needs to be added so that you don't increase your descent rate, so you pull back more. Eventually you stall (in a full-stall landing) or touch down. $\endgroup$ – Ron Beyer Aug 7 at 13:50
  • $\begingroup$ @RonBeyer, very nice explanation. But there is confusion for me since this statement: "90° because after that you're tilting up...", which I believe it is the answer for my third question: "What is the allowed maximum angle tilt down nose?". Is that mean 90 degree tilted down (which is mean, vertical)? $\endgroup$ – AirCraft Lover Aug 7 at 14:41
  • $\begingroup$ @AirCraftLover Yes, you can point it straight down, unless the aircraft has some kind of artificial limiting (would depend on a specific aircraft) then the only limit is structural damage speed, nothing else limits it. $\endgroup$ – Ron Beyer Aug 7 at 14:44
  • $\begingroup$ Thank you for the nice explanation. $\endgroup$ – AirCraft Lover Aug 7 at 14:45

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