Are there any aircraft geometries which tend to prevent excessive bank angles?

Question

For thousands of years humans have worked out that putting sufficient weight sufficiently far down in the hold of a ship makes it less likely to capsize. Obviously a ship tends to bounce back to an upright position if it has a good ballast arrangement, and it's only if you go beyond a critical tipping angle that the gravity situation works in the opposite way and you capsize catastrophically.

Are there or could there be any aircraft geometries which would do that somehow with respect to roll? I.e. tend to tip the plane back to level flight, with a higher force the greater the roll (until you get to a critical bank angle, when it doesn't work any more)? I realise that an aircraft's situation is nothing like a ship's, not least because a ship straddles two media.

I'm wondering about geometries where the wings are above the fuselage, for example... and maybe above the engines...? And/or possibly flexible geometries which somehow transform without being commanded, simply due to the effect of aerodynamic forces on them, but do so in such a way that they intrinsically promote stability.

I also realise the answer to this may be "no, absolutely impossible". But if so, how could that impossibility be proven?

Later edit
These are very interesting answers and give me much to think about.

I just thought of something rather extreme conceptually but quite ship-like: supposing after a plane took off, the luggage hold and maybe a fuel tank swung down on a pole a few metres long attached to the underneath of the fuselage, which then locked into position making it rigid? Wouldn't such a plane find banking very difficult, and wouldn't it be that the more you wanted to bank the harder it would be? In other words if the centre of gravity is located under the plane can't you achieve something like this?

NB I'm not advocating this as a desirable design, and shudder to think of the multiple technical reasons why this would be BAD, just wondering whether it would make rolling away from level flight difficult, and make righting occur without any intervention by human or computer, and making control surfaces less effective the greater the bank.

Answer 1

Dihedral angle

Virtually all airplanes have a certain amount of dihedral angle to the wings -- which is to say, the wings are angled slightly up when you look at the aircraft nose-on. This slightly decreases lift, as the direction of lift is no longer straight up, so there's a slight efficiency loss, but the benefit is that it makes the airplane inherently roll-stable.

The aerodynamics of how this work have been discussed in a previous post on this stack.

High wings

High wings do help with roll stability as well, but it's not as simple as it is in water, so I'm just going to link to a different discussion from this stack about how a low CG contributes to roll stability, and the previously linked post goes into this some as well.

But not to extremes

Now, that said, those are both relatively minor forces. They make a plane more stable in level flight, and if you put in a bank and then release the controls, they'll act to bring you slowly back to level, but they don't really act to stop the pilot from causing an extreme bank. Obviously we don't want innate roll stability to stop us from intentionally rolling the plane, and extreme roll is almost always the result of a pilot's inputs (unless it's physical damage to the wing, but that almost never happens).

A ship has no direct control over its roll and thus needs a strong self-righting impulse, while in an aircraft, roll is one of the main control inputs. We can trust the pilot to do most of the work of bringing the plane back to level after a maneuver, and the small self-righting effects are just making it easier to keep the wings level.

Answer 2

The shapes themselves do not affect roll stability, it is the effect of motion (and aerodynamic resistance, aka drag) that creates or inhibits rolling motion.

Going back to the ship. If one had sufficient force (wind, sails) to push it sideways with all the weight at its lowest point, it would roll (heel) sideways away from the wind.

does the weight right the ship like a "pendulum"?

When one considers torque around the Center of Mass, one can see that the bouyant force on the heeled over side counteracts the rolling force of the wind. Putting the weight lower in the ship increases the righting torque of bouyancy.

how else to increase the righting torque?

A wider beam. This is what humans may have done thousands of years earlier ... the catamaran.

How else? A lower sailtop, such as this. Lower draft enabled these ships to navigate much shallower waters ...

Back to aircraft. Dihedral creates a righting roll torque imbalance, but is counteracted by the turning tendency a roll creates. The correction for this is to have more side area above the center gravity$^2$ (such as a tall tail) to roll the plane away from the nascent turning motion. This is part of the reason "highwings" are considered more stable.

Lastly, we consider aerodynamic forces from the sideslip of an "uncoordinated" roll$^1$. Higher pressure under a highwing/fuselage area tends to roll back the aircraft upright, whereas lower pressure over a low wing/fuselage will not.

$^1$ where yaw is insufficient compared with bank angle

$^2$ or to lower the center of gravity!

Answer 3

Are there any aircraft geometries which tend to prevent excessive bank angles? Well, no, I'm not aware of any aeroplanes that cannot do a full 360° roll. Ailerons are deflected, and the result is an aerodynamic rolling moment dampened by the back pressure of the air. Sustain an aileron deflection high enough, and the aeroplane rolls through all 360° of bank angles.

What is desirable in this procedure is that there is a linear function between pilot wheel deflection and aeroplane sustained bank angle, which is provided by the side slip occurring in a turn, as depicted in this answer. And yes, high wing configurations have a built-in roll reduction factor, which sometimes needs to be reduced by anhedral (wings pointing downwards).

Answer 4

When searching for features which make airplanes inherently stable, I propose to look at free-flight model airplanes. What is it they do differently?

Long tail lever arm

The most striking difference to manned airplanes is a small tail on a very long rear fuselage. Since aerodynamic damping grows with the square of the distance between wing and tail, this gives model airplanes very high damping (not stability - this is in the ordinary range). As a consequence, all rotations happen very slowly. This includes roll, here because free-flight models also use high-aspect ratio wings. This also conveys high roll damping, so all three axes are highly damped.

Other features are more conventional.

Dihedral

What is striking is low dihedral of the center wing coupled with high-dihedral wing tips. The overall dihedral is, however, not so much different from regular airplanes because you want roll resulting from sideslip to be in a specific range. Too much and you will end up with an unstable dutch roll!

The high or low wing mounting will only affect how much dihedral is needed to achieve the right amount of sideslip-induced roll, so it does not affect stability directly. Please forget all the nonsense on the web about "keel effects" and "pendulum effects", which are a fallacy. Dihedral all by itself cannot prevent the buildup of roll angles. All it does is to add a correcting roll moment in sideslip conditions.

Answer 5

No. Aircraft geometry interacts with applied forces and gravity to produce a state space - position, velocity, acceleration, and attitude. The problem is the geometry can't tell the difference between applied forces and gravity, so it doesn't have any way of getting an Earth Horizon reference for roll angle.