0
$\begingroup$

"If a climb is started from cruise flight, the airspeed gradually decreases is the airplane enters a stabilized climb attitude. The thrust required to maintain straight-and-leve flight at a given airspeed is not sufficient to maintain the same airspeed in a climb. Increase drag in a climb stems from increased lift demands made upon the wing to increase altitude. Climbing requires an excess of lift over that necessary to maintain level flight Increased lift will generate more induced drag. That increase in induced drag is why more power is needed and why a sustained climb requires an excess of thrust.

For practical purposes gravity or weight is a constant. A vector diagram shows why more lift is necessary during a climb, as the vertical component of lift generated from the wings is no longer perpendicular to the wings and adds to drag. The total vertical force is increased by adding a vertical component of thrust from the powerplant and the power should be advanced to the recommended climb power"

The above is what the FAA Airplane Flying Handbook says. However, I don't understand the bold statement. Why is more lift needed in a climb? Does it mean that more lift is needed to initiate a climb? Isn't it true that less lift is needed during a climb? Also I can't figure out how a vector diagram shows more lift is needed. I understand that the vertical component of lift is no longer perpendicular to the wings but it doesn't add to drag, does it? It is the horizontal component of weight that adds to drag, right?

Improve this question
$\endgroup$
13
  • $\begingroup$ I'm no expert on this sort of stuff, but isnt it a duplicate of aviation.stackexchange.com/questions/100378/… and/or aviation.stackexchange.com/questions/40921/… (if so please VtC as duplicate rater than answer again) $\endgroup$
    – Jamiec ♦
    Commented Aug 11, 2023 at 13:11
  • 1
    $\begingroup$ Also, to @hitomhi you've now asked basically the same question 3 times. At least 2 (I suspect soon to be 3) are marked as a duplicate, If you do think you have a question not covered already please distinguish why and stop just repeating the same question. $\endgroup$
    – Jamiec ♦
    Commented Aug 11, 2023 at 13:15
  • $\begingroup$ Depends on how you define "Lift". If you only include aerodynamic Lift from the wing, then the fact that the lift vector points slightly aft of pure vertical is of course relevant. But remember, that in level flight, the total aerodynamic force is also tilted backwards slightly! If, otoh, you define lift to include the component of all forces (including thrust) that is normal to the earth, (purely vertical), then the answer to your question is, by definition, that the "Lift" in a steady state climb must be the same as the aircraft weight. It's all a matter of definition. $\endgroup$
    – Charles Bretana
    Commented Aug 11, 2023 at 13:45
  • $\begingroup$ I've read aviation.stackexchange.com/questions/40921/…. It says less lift (only the force generated by the wing and is perpendicular to the wing) is needed during a climb. I understand but it opposes what the FAA says, right? since the FAA says more lift is needed. Or what does the "lift" mean in the FAA book? Correct me if I've made anything wrong. Thank you. $\endgroup$
    – Hitomhi
    Commented Aug 11, 2023 at 13:51
  • $\begingroup$ @Hitomhi: I agree that the text you cited is very unclear... From level flight you need a short "spyke" in lift to change the attitude of the airplane and start the climb. Once you've reached the needed climb angle you reduce again the lift but to a value which is lower than the one at level flight. Drag also reduces consequently. Thrust must be anyway increased because now it has to compensate for the relevant weight component (think about an airplane flying straight up). Let me know if this answers your question, I'll be glad to elaborate an answer if needed. $\endgroup$
    – sophit
    Commented Aug 11, 2023 at 17:05

1 Answer 1

Reset to default
1
$\begingroup$

"Increased drag in a climb stems from increased lift demands made upon the wing to increase altitude."

False.

"Climbing requires an excess of lift over that necessary to maintain level flight."

False.

"A vector diagram shows why more lift is necessary during a climb, as the vertical component of lift generated from the wings is no longer perpendicular to the wings and adds to drag."

False.

"The above is what the FAA Airplane Flying Handbook says. However, I don't understand the bold statement. Why is more lift needed in a climb? Does it mean that more lift is needed to initiate a climb?"

It is certainly true that the initiation of a climb is generally accompanied by a slight,temporary increase in lift force-- any bend (curve) in the flight path is a form of acceleration, and some force is needed to accomplish that-- but it's pretty clear that the FAA source is not trying to convey that particular nuance. The committee that wrote this book is clearly incapable of understanding such details. Rather, they are repeating the falsehood that more lift is needed in steady-state climbing flight, than in steady-state horizontal flight at the same airspeed.

Isn't it true that less lift is needed during a climb?

Yes.

Also I can't figure out how a vector diagram shows more lift is needed. I understand that the vertical component of lift is no longer perpendicular to the wings but it doesn't add to drag, does it?

Correct, it does not.

It is the horizontal component of weight that adds to drag, right?

Not exactly. The component of weight that acts parallel to the flight path must be offset by thrust for steady-state flight. In other words, making the simplifying assumption that thrust acts exactly parallel to the flight path, in steady-state climbing flight thrust must equal drag plus the component of the weight vector that acts parallel to the flight path. So you could say that in climbing flight, the component of the weight vector that acts parallel to the flight path acts similar to drag, and must be offset by thrust, but doesn't actually increase the drag force.

For more, see various answers to the related ASE question Does lift equal weight in a climb?.

Take caution in treating FAA sources as authoritative in the matter of flight dynamics. Sources written for basic pilot training are written by committee and tend to be riddled with errors. See for example the confusing and incomplete diagrams addressed by this related ASE question: What is missing from these diagrams of the forces in slips and skids?.

Improve this answer
$\endgroup$
1
  • $\begingroup$ @Hitohmi -- this answer might be expanded to note that we usually choose to fly at a increased lift coefficient when we want to climb, as opposed to cruising flight. Which is another way of saying that we usually climb slower than cruise speed. For any given speed, increasing the lift coefficient increases lift, and drag. But we aren't free to hold airspeed constant and vary the lift coefficient. Otherwise we'd end up flying loops, sooner or later. Anyway you cut it, the FAA is wrong on this. $\endgroup$
    – quiet flyer
    Commented Aug 12, 2023 at 16:41

Not the answer you're looking for? Browse other questions tagged .