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3 Answers

Why does bank angle alone change load factor ? What about airspeed ?

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Aerodynamics, Commercial Pilot, Flight Instructor, General Aviation, Private Pilot, Student Pilot

Why is it that Load Factor is solely effected by bank angle ?

I've been told this, and read this before. But can't wrap my head around it.

I want to think -- that airspeed can change load factor. But my readings tell me otherwise.

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3 Answers

  1. Dale939ac on Oct 11, 2017

    The reason itself is a bit technical and you will only fully understand it once you get the aerodynamics and physics behind it. Basically, you start by looking at the definition of the load factor (n = L/W) in a banking turn. In this case, lets say the aircraft is banked to the left with some degree (theta=30 degrees e.g) which means that the lift vector is also tilted to the left by the same amount (theta). If we now draw the two forces lift and weight as vectors on the aircraft, the lift vector will be pointed 30 degrees to the left and the weight straight down (by definition of gravity). Now comes the part that is conceptually a bit hard to grasp: We can now fill in the expressions for Lift and Weight with lift being L=0.5* CL * rho * V^2. This is the Total lift vector, however, because the aircraft is still flying we assume that the vertical component of lift is counteracting the weight, therefore, W = vertical component of lift. Using some trigonometry we can find out that the vertical component of lift = 0.5* CL * rho * V^2 * cos(theta). if we now substitute both these equations into the definition of load factor we get n = (0.5* CL * rho * V^2) / (0.5* CL * rho * V^2 * cos(theta). Which if we look here that the airspeed and density and even CL of the aircraft are divided out and therefore if we simplify this equation leaves us with n = 1 / cos (theta). In this equation we see that the only factor affecting the load factor is theta (the angle of bank) and no other factors.

    I realize this is a bit technical and a drawing would make this a bit more clear, but if you have any more questions feel free to ask.

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  2. KDS on Oct 11, 2017

    Perhaps the best point to begin thinking about it is to imagine yourself in level flight (or driving on a flat road). The load factor is 1.0. Then imagine changing your speed. The load factor didn’t change. That is because load factor is just a function of the cosine of the angle of bank and the angle of bank didn’t change.

    Now, let’s take that imaginary car we were driving before and put it on a banked race track. Think of Daytona with its 31 degree bank. If we drive very slowly around the curve, we will be pulled to the downhill side of the track. If we drive extremely fast, we will be pulled to the uphill side of the track. There is only one speed we can drive that will allow us to go around that banked turn with our cup full of coffee sitting on the dashboard and not spill a drop. Any other speed will be slipping or skidding (the ball won’t be in the center).

    What changes in an airplane when the speed changes is that the radius of the turn. The higher the speed, the wider the circle. To see that conceptually, think of that 31 degree bank racetrack with a tight turn versus a very wide turn. To keep the coffee in your cup going around the tight turn, you would have to drive the slower speed. To protect your dashboard from spills on the wide turn, you would have to drive a faster speed.

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  3. fdzaviation on Nov 07, 2017

    Simple phisics. Load factor is all about force.

    In a straight and level path, all the wing’s lift is vertical and opposes weight, while the thrust is countered by drag. First law of Newton states that an object at a constant speed will have a force of 0 and remain in equilibrium.

    Force = Mass * acceleration
    Force = mass * (speed 1 – speed 2) / time
    Since both speeds are the same
    Force = mass * (100-100) / 30 secs
    Force = mass * 0
    Overall force will be 0.

    For an airplane to feel a load you need to change it’s direction. For a speed change to have a load impact it would have to be a VERY rapid acceleration or deceleration. Any sudden change of direction will create a speed change in a very short amount of time, which will increase the load force for a brief moment. This is not an issue as long as you’re under Vno. If you remain above Vno in turbulent conditions, the accumulation of Load forces can eventually damage the airplane.

    However, when you bank the airplane, lift is tilted and creates a horizontal component of lift and that reduces the vertical lift (which opposes gravity). If you pull back the yoke you’re generating more lift to compensate for this loss, and the amount of force needed to both turn the airplane AND oppose gravity will be felt as G’s. THIS FORCE IS SUSTAINED AND WILL HAPPEN REGARLESS OF SPEED.

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