ELI5: why does a plane have to bank while turning?
Posted by Wrong-Camp2463@reddit | aviation | View on Reddit | 37 comments
I know nothing about aviation. I get that the rudder controls the left and right direction of the plane. But why does the plane have to tilt in the direction of the turn?
Knarlus@reddit
The wings pull the plane "up", but "up" here means the direction where the roof of the plane is, it tilts with the plane. To fly a curve, you need something pulling you to that side. By tilting this "up", you get a part of it pulling you into the curve.
frigginjensen@reddit
Nice ELI5 answer
Scriefers@reddit
Aka Lift Vector
Go_Loud762@reddit
Roger, Roger.
2020pandemicisreal@reddit
Over oeuvre
Regular-Employer-431@reddit
Lookup "horizontal component of lift"
Regular-Employer-431@reddit
https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/airplane_handbook
Fowti@reddit
look how much horizontal surface area there is (wings + horizontal stabilizers) compared to vertical (just the vertical stabilizer).
When you turn in the pitch axis you have all that area to hold your position. If you try to turn using the rudder, the moment you let go the plane snaps back to the direction it was flying before.
You'd have to have the vertical stabilizers with an area comparable to the wings (like in missiles, that's why they don't have to bank to turn)
Dangerous_Mud4749@reddit
If a vessel is buoyant (that is, fully supported by what is underneath it), it turns by pushing against that thing. Banking is not required.
Examples include cars (front wheels push against the road), ships (rudder pushes against the water), blimps (rudder & propeller pushes against the air).
If a vessel is more dense than what is underneath it, it needs a constant lifting force to stop from sinking. The most efficient way to manoeuvre is to tilt the lifting force in the direction you want to go. Obviously the most common example is an aircraft, which tilts the lifting force left or right by banking, in order to change direction. Helicopters tilt the lifting force by tilting the rotor only, but it’s the same principle.
fellipec@reddit
Same reason Nascar cars turn in banked curves
BandicootNecessary26@reddit
A turn is one wing having more lift than the other meaning one is higher.
stickysharticus@reddit
JPAV8R@reddit
Wings are what keep the plane in the air. When you bank you have part of the lift vector pointed in the direction of the turn helping to turn the plane.
If you tried to turn wings level the outside wing will be traveling faster than the inside wing. The outside wing will therefore generate more lift making that wing lift up and putting it into a bank.
Either way you’re getting a bank. Dipping the wing and using the rudder to keep the plane coordinated is more comfortable than pushing a rudder and then the plane gets into the bank.
gansett@reddit
Your second paragraph about the different speeds of the wings was key to getting me to understand this.
E2TheCustodian@reddit
To build on what others are saying here: Imagine a racecar as it comes to a turn. The turn can be either flat or banked. If you turn the wheel on the flat track, you can only turn as far as your tires can laterally grip. nIf you go more than that, you start to skid, slide, then maybe even roll over.
But if the turn is banked, the earth that is holding up the car changes angle to not only hold it up but also push it into the turn, right? The banked turn becomes partly like it has hit a hill and is adjusting direction to follow the hill. And so you can tuen more sharply and more safely before you turn the wheel far enough to cause the car to skid or slide.
Well, the wings of the plane here are the road. Just like the road holds the car and prevents it from falling, so do the wings. And thus, when turning the plane it is most efficient and safe to use the ‘banked turn’ where SOME of the force holding the plane up is directed to the side to help it along. When you lessen the force holding you up to move some it towards pushing you into a turn, that is what moving the total vector of lift over to an anglenos doing.
meathooks@reddit
BS in aerospace and a airline pilot here. The rudder/vertical stabilizer is primarily for stability, not for directional control.
Turning with the rudder, aka yawing, will give a limited amount of turn. Also, by using the rudder you’re also sliding through the air sideways so it feels uncomfortable and jarring.
The wings are so much bigger than the rudder, and provofe a grater ability to turn.
On multi-engine planes, the biggest use for the rudder is during engine out scenarios when you need to counter the extremely large asymmetric thrust. In fact the size of the rudder is designed around that specific scenario. Try to notice how big an airline rudder is vs a small single engine GA plane.
EngineerFly@reddit
Turning requires a centripetal force, that is, a force towards the center of the turn. The wing is the only significant force generator on most airplanes. Tilting the lift vector provides a horizontal component of lift in the direction of the turn.
Educational_Clothes2@reddit
The rudder keeps you “coordinated” which basically means that you are turning the aircraft at the proper ratio and not slipping (creeping towards the inside of the turn) or skidding (sliding outside of the turn). A boat turns with a rudder because it acts in a two dimensional plane. An airplane rolls to turn since it is acting in a three dimensional plane.
TheOriginalJBones@reddit
Same reason as a bicycle.
Late-Mathematician55@reddit
Or the banked turns at the Daytona 500
TheEvilMonkey7@reddit
Well, that one is more to prevent slip/skid due to lack of traction at high speed; allowing for turns to be made at faster speeds.
TheEvilMonkey7@reddit
https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/04_afh_ch3.pdf
Disastrous-Trash1025@reddit
Best description I’ve seen is in the book, stuck and rudder:
A plane turns by banking which then causes the centre of gravity to shift and stabilizer pulls the plane around, the steeper you bank, the steeper you will turn.
The rudder is used to counter adverse yaw from the ailerons.
Ficsit-Incorporated@reddit
It’s not that a plane HAS to bank to turn, but it helps a lot to do so. For both comfort and aerodynamics reasons.
If lift is applied to both wings evenly, the plane will more or less stay level. If one wing produces slightly more or less lift than the other, such as in a bank, then the plane will more easily change direction.
DexicJ@reddit
Idk if I quite follow your second paragraph. In a steady level coordinated turn the sideslip is 0 and neither wing sees a difference in lift. The behavior you are talking about would only be true if there was sideslip (beta) present. It's truly just that the lift vector gets tilted.
You are describing more the aileron behavior that causes a change in roll not really the steady level turning condition.
Reasonable-Start2961@reddit
This, and what everyone else is saying.
It isn’t the only way, but it is by far the best and most efficient way. You -could- optimize a plane to be better at turning left or right with the rudder, but it would be very much like trying to force a square peg into a round hole by trying to make the hole bigger. A round peg is just a better solution. You’re kind of trying to make a plane turn a bit like a car, for no other reason than maybe it’s what you’re used to seeing on the ground.
Banking the plane leans in to what the plane is already optimized for: Flight.
BigZombieKing@reddit
Pilot with many years experience here.
Lift vector is the reason here. Imagine a toy airplane hanging from a string. This is level flight. If you want to turn, you need to move thst string in the direction you want to turn. The string is at somewhat of an angle relative to the ground but still straight up relative to the aircraft.
At full scale you are also using the elevator (vertical pitch control) and rudder (horizontal yaw control) to maneuver around the turn. If everything is done right, "down" in the cabin remains "down" towards the floor.
If you turn with just rudder and hold the plane level, this is a skidding or flat turn. It will feel a lot like going arround a corner too fast in a car. It means the aircraft is plowing through the air sideways. Much like skidding your car, this is not an energy efficiant way to make a turn. At slow speed this can lead to one wing stalling while the other is still flying. This is the opening sequence for a spin. If unintentional, that would be considered loss of control in flight. In many circumstances that is extremely hazardous and may lead to a total loss type event.
DexicJ@reddit
An aircraft has two options to turn. Bank to turn or skid to turn.
Skid to turn uses sideslip to generate side loads. For most winged aircraft this would be highly inefficient because it will generate very little side force and a strong tendency to roll the aircraft which will use a lot of your aileron and rudder capabilities to balance. Missiles on the other hand... this may be a viable strategy.
For bank to turn the idea it pretty simple. Your wings get you a lot of lift. If you angle the plane sideways and pitch up the nose a bit you can generate enough vertical force to balance gravity and a lot of horizontal force to start a turn. So it's actually pretty simple... you want to use the wings for lift, pull the nose up to increase the lift and bank the vehicle to tilt the lift. You will get significantly more turning capability than a skid to turn approach.
martianfrog@reddit
work out the inertial direction, resultant vector of gravity down and centrifugal horizontally, roll the aircraft to where the wing lift is in the opposite direction, then you have balanced flight physics in a turn, this is simplified... something like that anyway.
Colt653@reddit
same as a motorcycle or bike
you can turn an airplane with rudder only, but it doesn't work as well
Complete_Cod_8222@reddit
Good question and you should ask over at r/physics too.
Tthink about the principal of lift, a difference in pressure causes lift, Bernoulli principal. The rudder applies a small difference in that pressure, straightening out the whole aircraft frame.
It's a coordinated event in which the turn comes from the ailerons on the wings that bank the aircraft. The bank induces centripetal force that allows the plane to turn in the direction of bank. And the rudder keeps the fuselage pointed in the direction of motion with the nose leading the tail.
Winter_Ad_7583@reddit
If you used the rudder to turn it would be like doing a very sharp turn in a car but more extreme - you would be shoved to the side. Banking helps not have this happen, you get pushed down in your seat a bit instead of being pushed sideways. It is mainly about comfort.
SlippinYimmyMcGill@reddit
You are using the lift force vector at an angle to turn. It doesn't require heavy rudder input and nominally increases drag. It is the best way to turn in terms of efficiency, equipment rigidity (i.e. making a ridiculously strong/heavy vertical stabilizer), and turn radius by far.
BarleyWineIsTheBest@reddit
You rotate on the long axis of the plane to turn (most of the time), because it using the main lifting wing’s force to change direction. This bank then removes some lift fighting your weight, which then rudder is used to force the nose up.
The rudder is small and large control inputs to it are not generally a good idea for several reasons. One is that it’s not pleasant to experience kind of a sideways skid. Whereas a. Slight bank can be almost unnoticeable. Also, because you have to smash the rudder to turn very much, it’s a larger disruption of the airflow over the plane. So it’s less efficient. For the most part with a fixed wing aircraft you want to use the least rudder possible to get the job done.
Independent-Mix-5796@reddit
Think about how you ride a bike. When you’re making a turn, you need to both turn your handle bars and lean into the turn.
An airplane is similar; turning in a plane is a coordinated effort between the rudder and the bank angle. Too much rudder or too much aileron results in an uncoordinated turn where the plane ends up “slipping” through the air, resulting in uncomfortable sideways flying.
Complex-Value-4722@reddit
Lift is one of the largest forces on an aircraft. When you bank, the lift vector changes from pointing straight up to pointing up AND sideways. That sideways component of lift turns the aircraft.
The rudder changes the direction of the nose. Think about rudder inputs as someone pushing on the tail and the aircraft rotating about center of mass. It's like if someone pushed on the rear tire of a bicycle - you wouldn't really turn, just slide/skid.
d4m1ty@reddit
It doesn't have to bank, it is just makes turning a lot easier.
Since a plane has upward lift, if you bank, you have upwards lift into the bank, and the plane will turn itself without using rudders.