Can a smaller wing area smooth the ride during turbulence?

Question

Amid the recent incident of Singapore Airlines flight 321, leaving one dead after a severe turbulence, I ask myself if having an aircraft with smaller total area, there is less turbulent air that touches the aircraft hence the less it can 'push' the aircraft which would translate in smoother ride.

In other words, if you make an airliner essentially a 'flying fuselage'/rocket, can we say that the ride would be smoother than an normal airliner flying at the same speed, alt, weight, etc, ... correct?

I was thinking of a similar real life example and thought of the F-14 Tomcat and I ask if anybody knows if this aircraft experienced less bumps when the wings were swept while flying trough turbulence?

(source)

If that is the case then, would building an aircraft with more retractable areas on the wing(like the flaps are) and combining maybe with something like the F-14 swept wings design be a posible solution to lessen the effect of unexpected severe turbulence? Maybe something like this:

Answer 1

Gust analysis is a quite complex matter, so complex that big airplane companies have dedicated departments only for this topic.

Anyway an easy way to understand how a gust influences the flight behaviour of an airplane is by considering a so-called "step" (or "sharp-edge") vertical gust (figure (a) in the following picture - source):

Before encountering the gust, the wing was developing a lift that, as usual, is expressed by:

$$L=½ \rho V^2 S C_L$$

As a good approximation we can consider $C_L$ as being linearly dependent on the AoA $\alpha$ and therefore:

$$L=½ \rho V^2 S k \alpha$$

Upon encountering the gust, the lift $L$ changes both due to the increase in the AoA and in the total speed (plot source):

$$V \rightarrow \sqrt{V^2 + U^2}$$

$$\alpha \rightarrow \alpha + \frac{U}{V}$$

where $\frac{U}{V}$ is an approximation valid when $U$ is much smaller than $V$, as it is usually the case. Substituting we get:

$$L=½ \rho (V^2 + U^2) S k (\alpha+ U/V)$$

Since we are interested only in how much the lift has changed due to the gust, we subtract this latter equation for $L$ from the former getting, after some simplifications:

$$\Delta L = ½ \rho S k (VU + U^2 \alpha)$$

Now, in order to reduce this $\Delta L$, we can reduce:

• $S$ - wing surface - and/or
• $k$ - slope of the lift curve - and\or
• $V$ - flying speed.

Obviously the wing surface cannot be changed in flight (except when flaps are deployed but that's another story) so the only way to counteract a gust is by:

• reducing speed - this is normally done by the pilot - and/or
• decreasing the slope of the lift curve - this is normally done by some automated gust-alleviation system using the spoilers or other control surfaces to change the slope; yes, changing the wing geometry as on the F-14 can be a way to change the slope of the lift curve since wings with lower aspect ratio tend to have lower slope of the lift; anyway this is not going to work since gust is, by definition, something relatively sudden while changing the wing geometry on the F-14 takes some seconds; this is why gust-releaving system are automated system whose sensors are placed as forward as possible on the airplane in order to give the system enough time to elaborate the signals and move the control surfaces on the wing.

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P.S.: please note that the wing surface of the F-14 does not change, the geometry of the wing does.

Answer 2

Excellent question presentation, because this one was originally designed in a similar manner as the F-14.

Not only faster, but higher, in the Stratosphere, where turbulence is less common.

The effect of turbulence on an aircraft is a function of wind speed, density, and cross section area to the change in wind direction.

Higher, faster, with smaller wings all minimize turbulence effects.

Fuel costs ended the anticipated transition to supersonic passenger flight in the 1970s, leaving us with slower, more economical designs with lower wing loading, with the exception of the Concorde.

Because the slower aircraft are more economical, efforts may focus on improved detection and/or forecast of turbulence.

Answer 3

The F-14 with highly swept wings is less affected by air loads like turbulence than at low sweep, as shown by maximum allowed airspeed. Max speeds (TMN is true mach number) are higher when wing sweep is higher. From the flight manual:

So the answer to your second question is yes, variable wing sweep would reduce felt turbulence, but this is expensive and would cost more than it was worth.

Answer 4

A better example would be the B-1. It began as a supersonic, high-flying bomber (B-1A) but was soon converted to a subsonic, terrain-following intruder (B-1B) with limited stealthing to increase survivability in a high-intensity conflict. The variable sweep was a big help in this conversion, as the swept-back wing gave the best possible ride qualities at low level due to the reduction in the lift curve slope from the high sweep angle.

A smaller wing will help again to reduce buffet loads. If we consider a vertical gust and assume that its additional wind speed will increase angle of attack by a given amount, this amount will become relatively smaller for a smaller wing flying at a higher lift coefficient.