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Balance and Trim ATC Chapter 3. Aim To review principals of aerodynamics in balance and trim.

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Presentation on theme: "Balance and Trim ATC Chapter 3. Aim To review principals of aerodynamics in balance and trim."— Presentation transcript:

1 Balance and Trim ATC Chapter 3

2 Aim To review principals of aerodynamics in balance and trim

3 Objectives 1.Define balance 2.State the factors effecting balance 3.State the different pitching moments and their effects on flight 4.Discuss the principals of trim

4 1. Define Balance Balance Definition: Balance is achieved when no residual force is attempting to alter the position, direction or speed of an aeroplane

5 Balance Balance consists of two elements: Total forces acting on the aeroplane The alignment of the total forces When the forces are balanced the aeroplane is in equilibrium 1. Define Balance

6 If we consider a see-saw, when the beam is loaded equally the centre of gravity is located in the centre of the wooden beam aligned with the pivot point If one side of the wooden beam is loaded heavier than the other side, the CoG moves towards the heavier side, thus the pivot point and CoG are no longer aligned, the see-saw becomes unbalanced 2. Factors Effecting Balance Balance

7 When the weight is not equal on either side of the see-saw, we can move the CoG in 3 different ways: Move the fulcrum (pivot point) to where the CoG is located Move the heavier weight closer to the fulcrum Add weight to the lighter side to equalise the weight 2. Factors Effecting Balance

8 Balance Move the fulcrum (pivot point) to where the CoG is located: 2. Factors Effecting Balance

9 Balance Move the heavier weight closer to the fulcrum: 2. Factors Effecting Balance

10 Balance Add weight to the lighter side to equalise the weight: 2. Factors Effecting Balance

11 Balance An aeroplane needs to be balanced in the same way as the see- saw, however balancing an aeroplane is slightly more complicated In straight and level, unaccelerated flight the CoG must be aligned with the pivot point to be balanced During flight it is impractical to move the balance point or weight Therefore to achieve balance we must rely on aerodynamic forces to align the total lift forces with the total weight forces – similar to adding weight to the lighter side of the see-saw 2. Factors Effecting Balance

12 Balance On an aeroplane there are two types of forces: Static forces Dynamic Forces Static forces are acting all the time eg, weight Dynamic forces are created when moving through the air – aerodynamic forces eg, Lift 2. Factors Effecting Balance

13 Balance For an aircraft to be in a state of equilibrium: Lift must equal Weight Thrust must equal Drag 2. Factors Effecting Balance LIFT DRAGTHRUST WEIGHT

14 Pitching Moments 3. Pitching Moments However, these forces do not act from the same point WEIGHT CoP CoG LIFT DRAG THRUST Lift - Is produced by the wings and acts upwards through the centre of pressure Weight - Acts straight down through the centre of gravity to the centre of the earth Thrust - Is provided by the engine through the propeller Drag - Is the resistance to motion felt by all bodies within the atmosphere

15 Pitching Moments Because the forces are not acting from the same point they create a couple L / W Couple = Nose DOWN moment WEIGHT LIFT DRAG THRUST A couple is defined as two equal and opposite forces acting about a pivot point creating a torque or turning moment The two couple’s generate opposing pitching moments T / D Couple = Nose UP moment 3. Pitching Moments

16 Pitching Moments We said that the forces must be in equilibrium, therefore: LIFT = WEIGHT DRAG THRUST = (L / W Couple) (T / D Couple) For the aircraft to be in balance, the nose down moment must equal the nose up moment 3. Pitching Moments

17 Pitching Moments If the moments are not equal, the tailplane makes up the difference In a correctly loaded aircraft the tail plane will create a small force downwards WEIGHT LIFT DRAG THRUST Force The forces are now in equilibrium and the aircraft is now in balance 3. Pitching Moments

18 Pitching Moments When loading the aircraft it is essential that we keep the CoG within a certain range of locations This will ensure that at all times during the flight the CoG will be in front of the CoP causing the L/W couple to have a pitch down couple This is important to avoid an undesired high nose attitude in the event of an engine failure If thrust is lost, the nose down pitching moment will be greater than the nose up moment, allowing the aircraft to adopt a glide attitude 3. Pitching Moments

19 Pitching Moments WEIGHT LIFT DRAG THRUST Force If thrust is lost, the nose down pitching moment will be greater than the nose up moment, allowing the aircraft to adopt a nose low 3. Pitching Moments

20 4. Trim Trim An aircraft is said to be in trim if the aircraft will maintain a constant attitude without the pilot needing to apply any control input If the aircraft is trimmed correctly the only control inputs required will be to manoeuvre the aircraft into a different attitude Trim can be achieved by either: Adjustable springs to hold control position Trim tabs controlled via cockpit control

21 Trim Tabs Trim tabs work by creating a small amount of lift opposite to the control surfaces direction of travel Due to the long moment arm created this small force acts to offset the force created by the control surface 4. Trim

22 Trim Tabs Trim tabs can be either fixed or adjustable and fitted to any control surface In light single engine aircraft fixed tabs are usually fitted to the rudder and possibly ailerons These fixed tabs are adjustable on the ground Adjustable tabs are most commonly installed on the elevator 4. Trim

23 Questions?


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