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Does more lift cause a wing to stall later? (By more lift I mean a bigger wing) I was looking and saw this question, but the answers didn’t really address why more lift will help a plane not stall.

For flaps I understand, as they reduce the AoA needed to make the same amount of lift. Now that I think of it, is this also true for a bigger wing?

(All of this at the same speed)

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I was looking and saw this question, but the answers didn’t really address why more lift will help a plane not stall.

I agree that there's a bit of confusion in the answers to that question that you linked.

When you compare the lifting ability of one wing in different configurations (for example in clean configuration versus with flaps deflected) you have to define in respect to what you make the comparisons. For a wing, the basis for comparison is simply the wing surface in clean configuration: this is the $S$ that normally appears in the equation of any coefficient. If the wing geometry changes (for example due to flaps deflection) $S$ remains exactly the same and any change in the aerodynamic characteristics is condensed in the relevant coefficient. Yes, when the flaps are deployed the wing surface actually increases and therefore the lift as well but the $S$ used in the equation does not change; instead, the $C_L$ increases accordingly: this explains why you normally see a "jump" in the plot of $C_L$ when flaps are deployed:

enter image description here

This approach might sound a bit strange but it is actually the only way to make a fair comparison.


That being cleared up, it's now easy to understand what modifies the stall speed:

$V=\sqrt{\frac{W}{½\rho S C_L}}$

Where $W$ is the weight of the aircraft. If you want to minimise $V$ you can:

  • decrease the weight $\rightarrow$ toward the end of the flight the stall speed is lower (i.e. safer) than at take off;
  • increase $\rho \rightarrow$ lower altitudes are safer;
  • increase $S$ (in clean configuration!) $\rightarrow$ a 15m X 1.5m wing is safer than a 10m X 1m wing (again, both measured in clean configuration);
  • increase $C_{L_{max}}$ making it make a jump by deploying flaps and slats.
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  • $\begingroup$ RE:"increase CL increasing AoA", did you mean increase CL-alpha (the slope of CL curve) or simply increase CLmax? $\endgroup$
    – LJQCN101
    Commented Apr 28 at 4:12
  • $\begingroup$ I simply mean increase AoA: $C_l$ is proportional to $\alpha$ $\endgroup$
    – sophit
    Commented Apr 28 at 7:03
  • $\begingroup$ I ask because people would assume the AOA is already at α-crit when talking about stall, where CLmax is obtained. So the point is to make CLmax even higher, by deploying high lift devices, regardless of AOA as long as you're at α-crit, as α-crit would possibly change. $\endgroup$
    – LJQCN101
    Commented Apr 29 at 2:44
  • $\begingroup$ There's another aspect I would like to know, if pitching moment coefficient (Cm) should be also considered when calculating stall speed. Is that possible that some statically stable aircraft would not get a positive Cm above certain α that is lower than α-crit, so that it cannot keep nose up even with full elevator deflection, before reaching α-crit? $\endgroup$
    – LJQCN101
    Commented Apr 29 at 2:47
  • $\begingroup$ @LJQCN101: you're right thanks, I'll update my answer. $C_m$ is normally quite constant with $\alpha$ and changes only at stall. $\endgroup$
    – sophit
    Commented Apr 29 at 6:20
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A given level of wing technology (think airfoil choice and all high lift devices) applied to a planform family (same general shape wing, i.e. similar sweep angles and taper ratios and twist approach) will stall at the same $C_{L,max}$.

Since

$C_L=\frac{W}{q\,S_{ref}}$

Then when holding $C_{L,max}$ constant, decreasing wing loading $W/S_{ref}$ will allow you to push stall to lower dynamic pressure (lower airspeed and higher altitudes).

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Stall speed

If we decrease airspeed and want to stay level, we need to increase the AoA (actually the lift coefficient $\small C_L$ in the equation below).

As we continue to decrease airspeed, and to increase AoA, we ultimately reach the stall angle. At this point we cannot go slower, and remain level, because to remain level we'd need to have an AoA exceeding the stall angle and we'd stall.

Decreasing the speed while increasing the AoA to remain level is how all pilots are trained to stall and recover from stall. See this video.

Effect of area on lift: Lift is proportional to area

This is what the lift equation says:

$$L = \frac {\rho} {2} V^2 C_L A$$

$\small \rho /2$, which represents air density, can be seen as a constant for this purpose, $\small C_L$ depends on AoA, $\small V$ is the airspeed, $\small A$ is the wing area (and $\small \frac {\rho} {2} V^2$ is what is called the dynamic pressure).

A larger wing deliver more lift. It is also heavier, thus you need proportionally more lift to fly level, but the lift increase is, in some conditions, larger than the weight increase, so it's correct to say a larger wing produces more lift in excess of weight.

Why in some conditions? Because doubling the area doubles the lift produced, but it may more than double the weight, as weight is close to a function of volume. If it were possible to increase lift by increasing the area without limit, then aircraft would be gigantic. It's not the case.

How does area affect the "stall speed"

In our previous situation of decreasing airspeed while increasing AoA, we reached the stall angle at some speed. This speed was the one needed to create the lift required to stay level (so the amount of lift was equal to the weight).

With a larger wing, at the same stall angle and the same airspeed, we create more lift in excess of weight and we climb. We need to slow down to reach the airspeed required to stay level.

Does more lift cause a plane to stall at a lower airspeed?

With our previous definition of the "stall speed", we see with a larger wing, this speed is lower.

Stall occurs at a lower speed, however remember the speed is not the cause of the stall, it's our attempt to stay level by increasing the AoA past the stall angle which stalls the wing, because our airspeed is definitely too slow to stay level.

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  • $\begingroup$ I see. So I’m a little confused about the last paragraph of your answer. What would make it so a bigger wing would stall at a lower speed? Having more wing surface just increases lift for a given AoA, right? $\endgroup$
    – Wyatt
    Commented Apr 25 at 17:49
  • $\begingroup$ Ah that edit made it more clear, thanks. So I think another good way to think of it is because for flying level you trim the plane to make a certain amount of lift, large wing or not. This puts less loading per square foot on the wing (for a bigger wing) so it doesn't need to work as hard for the same level of lift, so to speak. Is that accurate? $\endgroup$
    – Wyatt
    Commented Apr 25 at 19:49
  • $\begingroup$ (tell me if that doesn't make sense haha) $\endgroup$
    – Wyatt
    Commented Apr 26 at 0:20
  • $\begingroup$ My understanding was that both AoA AND airspeed were relevant - ie at any specific A0A a stall will occur above, and not below a specific speed? $\endgroup$
    – MikeB
    Commented Apr 26 at 8:24
  • $\begingroup$ @MikeB: The critical angle (the stall angle) is the AoA where the slope stops being positive with a load factor of 1g in the $\small C_L$ curve (about 15°). This is where the boundary layer starts detaching from the airfoil. However the "stall speed", as defined in the answer, is influenced by the load factor: The apparent weight depends on total acceleration (gravity + centripetal), thus in a turn the lift required to maintain a level flight is increased, and the "stall speed" is consequently increased. $\endgroup$
    – mins
    Commented Apr 26 at 9:01
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Does more lift cause a wing to stall later? (By more lift I mean a bigger wing) (All of this at the same speed)

No, stall is related to flow breakdown at specific AOA in a specific configuration (i.e. a flapped configuration has higher amount of lift but slightly lower stalling AOA). At a given speed, more lift than is required to balance the weight will cause a gain in altitude. Think of it as excess power https://www.engineersvault.com/aerospace/a-beginners-guide-to-understand-flight/ since , as you mentioned, "at the same speed," a flapped configuration has both higher lift and drag. Therefore, maintaining the same speed requires pilot action on the throttle.

I was looking and saw this question, but the answers didn’t really address why more lift will help a plane not stall.

No, more lift will not help with stall, it will only lower the speed required to sustain the flight.

A fowler flap increases both camber and wing area, the effect of the lift is the same as explained above. Yes, an increase in area and camber will have the same effect, increasing the lift.

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Well, the mathematics is fairly straightforward. Because the speed is constant, and assuming the atmosphere is also, the factor $q$ is constant, and we can make the following statement where we will just consider lift (or weight), $W$, and the wing area, $S$, as follows -

$$q\cdot S = \frac{W}{C_L} $$

and rearranging -

$${C_L}\cdot q\cdot S = W .$$

Clearly, now, if we can see that $C_L$ and $S$ are inversely related to one another, with fixed $q$, to give constant lift, $W$. Consequently, if we increase the wing area, the coefficient of lift will decrease proportionately, to maintain the same lift, $W$. Of course, in this case, we have not considered the modest increase in weight that would occur by increasing the wing area.

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