Dynamic Fluid (airplane landing/decrease altitude)

[Arif Setiawan]

Hi guys.. I've some discussion with my friend. We are teacher. So we must carefully to answer question for student.. there the question is

From figure below, p2 and p1 applied on plane's wings. When airplane landing/decrease altitude, which condition must occupied
A. P1=P2 and v1=v2
B. P1<P2 and v1>v2
C. P1<P2 and v1<v2
D. P1>P2 and v1>v2
E. P1>P2 and v1<v2

On my opinion, at any rate we total force by bernoully equation must upright vertical oposite weight. Because, without Force of wings plane will fall. So, when take off/increase altitude F>w .. stay at certain height F=w.. and when landing F<w.. But F must remain positive. So P1>P2 and v1<v2 (E)

At opposite, my friend though that when take off P1>P2 and when landing P1<P2.

OK guys.. may you all give us your though.. thanks.. regrads

 

[russ_watters]

On my opinion, at any rate we total force by bernoully equation must upright vertical oposite weight. Because, without Force of wings plane will fall. So, when take off/increase altitude F>w .. stay at certain height F=w.. and when landing F<w.. But F must remain positive. So P1>P2 and v1<v2 (E)

At opposite, my friend though that when take off P1>P2 and when landing P1<P2.

OK guys.. may you all give us your though.. thanks.. regrads

You are correct: when decreasing in altitude, the wing is still producing positive lift...just less of it.

 

[rcgldr]

You are correct: when decreasing in altitude, the wing is still producing positive lift...just less of it.

In a steady descent, the total net force is zero (otherwise the aircraft would accelerate). A component of drag in addition to most of the lift opposes gravity. In a steady climb, lift is also less than the weight, and a component of thrust (in excess of drag) opposes gravity.

 

[russ_watters]

In a stead descent, the total net force is zero (otherwise the aircraft would accelerate). A component of drag in addition to most of the lift opposes gravity. In a steady climb, lift is also less than the weight, and a component of thrust (in excess of drag) opposes gravity.

Thanks for the clarification. I did fall into a little trap there, though it doesn't impact the problem answer.

 

[rcgldr]

So, when take off/increase altitude F>w .. stay at certain height F=w.. and when landing F<w ..

If the aircraft is not accelerating, then total net force = zero. In level flight, lift = weight (ignoring direction). In a steady climb or steady descent, lift < weight (ignoring direction). In a steady climb, a component of thrust (minus drag) opposes gravity. In a steady descent, a component of drag (minus thrust) opposes gravity.

 

[Arif Setiawan]

That's the aspect that I haven't see before..
Thanks for these clear information