Can all airliners be turned without rudder input?

Question

Is it possible for pilots to make a right or left turn, using just the ailerons and without rudder input in all airliners? If not why so, for what reason?

Answer 1

It depends on the aspect ratio of the wing and the lift coefficient. Short, stubby wings at low angle of attack will not create much adverse yaw with aileron input, especially when the ailerons have differential linkage (more deflection on the trailing-edge-up side and less on the opposite side). Differential gearing is also beneficial in reducing stick forces, so many small aircraft with manual controls employ it. Therefore, turning with ailerons alone is possible with low aspect ratio wings.

Airliner wings have aspect ratios between 7 and 11, so here it is helpful to reduce the lift coefficient by flying fast and lower than at maximum cruise altitude if you want to turn with the ailerons alone. If you allow rudder movements but just want the pilot to rest his/her feet on the floor: Almost all jets have yaw dampers, that is a device which will deflect the rudder automatically such that yaw is minimized. Therefore, airliners can be flown with the feet off the pedals and still ailerons and rudder will keep the plane in a coordinated turn.

With gliders and their high aspect ratio wings, however, using only ailerons will mostly yaw the aircraft, especially at low speed when the lift coefficient is high. The wing also has high roll damping from its high aspect ratio and low flight altitude, so the roll angle achievable before yaw becomes dominant is small. The yawing condition will now create its own rolling moment due to the dihedral effect of the wing. Unfortunately, this effect counters the intended rolling motion and prevents the aircraft from turning with ailerons alone. If adverse yaw is large enough, the aircraft will not even begin to roll but will only yaw with aileron input. Some glider pilots even apply cross controls when entering a thermal in order to maximize their rolling speed (rudder into the turn and aileron against to provoke more yaw and let the dihedral effect roll the glider).

If you find yourself in a high-performance glider with a jammed rudder, speed up in order to fly turns with the ailerons (and elevator) only. The lower lift coefficient will reduce adverse yaw so direction can be controlled with ailerons and elevator only.

Answer 2

For most aircraft, it is. Deflecting ailerons only results in adverse yaw: the aileron deflecting downwards has higher drag than the one deflecting upwards, and the nose turns away from the direction the pilot wishes to bank into.

Image source

The relative magnitude of this effect depends on wing span and airspeed: hardly noticeable in jet fighters, highly disturbing in gliders.

Answer 3

In fighter simulators I almost never used the rudder: I just rolled to almost 90° then applied the elevators...

IRL I tried this with gliders (we even had to learn how to fly if one of the 3 controls were lost - elevators are the worst, one of the other two you can get by without much easier). You can turn with gliders really well by just using the ailerons, and compensating with the elevators to not drop your nose too much (and if you are rolling, then your elevators are partially working as rudders anyway). Not good enough to do thermals with great efficiency, but good enough to get back home and land.

Answer 4

Very short answer: Yes, you can turn an airplane without using rudder input. Simply rolling the airplane to an appropriate bank angle, combined with applying aft stick pressure to maintain altitude, will cause an airplane to turn. The horizontal component of the lift vector the wings banked in the direction of the turn will cause the airplane to turn in the direction of the bank.

_{(source: flightliteracy.com)}

As to maintaining a coordinated turn, that’s another story altogether. Rolling an aircraft using ailerons will generate an imbalance in induced drag between the two wings, causing adverse yaw. Other solutions can mitigate this, such as differential spoilers, as in the case of the MU2 aircraft. Airliners also use this method for lateral control during high subsonic flight encountered in cruise. As Peter Kämpf pointed out airliners also use yaw dampers to mitigate other undesirable flight characteristics in high speed cruise so they can and are maneuvered using no rudder pedal input from the pilot. In propeller driven airplanes, the left or right turning tendencies caused by the propeller will almost always result in an uncoordinated turn if no rudder input is used. But the airplane will still turn in the direction it’s banked regardless.

Answer 5

I just came across your question by accident regarding turning an aircraft with the use of rudder.

The simple answer is YES.

You NEVER lead a turn using Rudder. Its a combination of of Aileron to lead into a bank (left or Right). Back pressure is then applied on the yoke/ stick to maintain altitude. Reason, additional drag encountered resulting in a loss of lift. Back pressure provides this additional lift required to maintain altitude.

The rudder's part is all this is to balance the turn. This means that aircraft "slip" or "skid" during a turn. Basically slip into towards the centre of the turn or skid outwards not maintaining a fixed radius turn in otherwords.

The "Ball" on the Turn Coordinator should be centered during the turn. So if the ball go to the left "then stand on the Ball" = left rudder to balance and coordinate your turn.

All this is a very smooth coordinated movement in practice.

If I may, just go one stage further regarding Adverse Yaw.

I also see some comments on the subject. Adverse yaw is one of these "Strange but True" issues.

Firstly, if you were to gently deflect the rudder (the Action) either side of center in normal controlled flight, two things will happen:

1. It will produce a movement about the vertical axis.This is the Yaw. The Primary effect of rudder.

2. Lots of groaning and moaning from the aircraft as if to say, Hey what are you doing to me ?.. reason the aircraft is being knocked out of balance.

The Secondary effect of rudder is to Roll. If you prolong the defection of the rudder the aircraft initially yaws followed swiftly by a rolling movement about the longitudinal axis.. dangerous if maintained..spiral dive follows..

Now, the main part. The adverse bit.

When a turn is initiated using aileron to lead into the turn the up-going aileron enters a reduced pressure area. Remember relatively low pressure on top surface of wing. While the down-going aileron enters relatively higher pressure area.

For example: Left turn.

The left aileron is deflected upward and the right aileron moves downward. As the chord line on the left wing is altered in an upward direction (The Chord line runs from the leading edge directly to the trailing edge of the wing or a control surface.), this effectively reduces lift on that wing. The opposite happens on right wing.. Lift increases. Result a left-hand bank should occur.

But, oops. a Surprise awaits us, We started a Left turn using Aileron but we initially get a RIGHT YAW effect..just as if we applied Right Rudder. So now after scratching our heads for a while, lets see what happened there....

In brief, as the lift changes on the outer parts of the wing, so also does the associated drag. Known as Induced Drag. A By-product of lift.

So the down going left wing, has reduced lift and reduced drag by association Right wing has increased lift and increased Induced drag.

Net result drag on left side - Reduced. Right side increased, so its acts like a "brake effect" on the right side, and relieved on the left side. Produces a Yaw to the RIGHT initially.

Solution: In aircraft nowadays the angular movement of the ailerons is arranged so that the up-going aileron travels further up than the down-going one. For example full up deflection say 50 degrees, Full Down movement 25 degrees and proportional in between.

This limits the effect of Adverse yaw due to up-going aileron traveling further into lower pressure area and likewise, down going moves down less in higher pressure area as the Chord line is altered differentially. This system is known as Differential Ailerons.

One further development on this was the Frise Differential Aileron, which allows the top side leading edge, of the aileron, to protrude into the airflow on the down-going aileron, creating a Parasite Drag on that side to counter the Induced Induced drag on the other wing. Combined its known as the Frise Differential Aileron.

You might need to read the last paragraph again, but the penny will soon drop for you.

Answer 6

Lots and lots of radio-controlled model airplanes lack rudders and fly just fine. Some are even shaped like airliners. No reason this shouldn't scale up to full scale. (The point being that this strongly suggests that airliners can turn without deflecting the rudder, not that there's "no reason" not to design a full-scale airliner entirely lacking a rudder.)

Answer 7

Of course! Neither the rudder, not the ailerons, actually turn the aircraft. It is LIFT that turns the aircraft. It "turns" the aircraft in the direction that the Lift vector (perpendicular to the wings) is pointed in. So to turn, you need to point the Lift vector in the direction you wish to turn, (roll into a bank) and apply some Lift (Pull back on the stick/yoke).

To turn up (increase pitch attitude) leave the aircraft in zero bank angle, and pull on the yoke. To turn left , place the aircraft in a left bank, and pull on the yoke, etc.

To roll into a bank in a coordinated manner, you generally need both ailerons and rudder, but if you're not picky about being uncoordinated, you can roll into a bank with either one.

Answer 8

I've some small experience on the MU-2 series aircraft, which has no ailerons. It uses full span flaps and spoilers. The autopilot can reflex flaps to control roll and function as a wing leveler, but is not available in landing configuration.

Moreover, there are large amounts of mass at the outer wing, considering that there are wing tip tanks. This short-coupled twin will give you an appreciation for controlling the direction of the total lift vector and using all available runway on takeoff.

Using rudder to control small rolling moments when close to Vs is the second thing I learned training in simulator; the first is to stay away from Vs. Being close to Vs, stalling the rising wing by using spoiler roll control results in a snap roll into the rising wing creating a stall condition on one side and once there you become another stall/spin statistic. It is difficult but not impossible to reestablish the lift vector to the centerline of the aircraft – the first order of business – given time, space, and engine power in order to recover. This is usually not available in landing configuration.

During a turn, the yaw damper and down wing spoiler will coordinate the turn with feet on the floor. You must use nose up elevator to compensate changes in lift vector caused by a sustained maneuver. I have noticed in flight the almost zero displacement of the rudder during a two-minute turn at cruise airspeed. That was some time ago, but my experience, for what it's worth.