Climbing and Descending Lesson
Climbing Notes
Climbing
Climbing and Descending
This lesson builds on the coordination skills you learnt in the previous lesson, Straight and Level. Have you remembered the attitudes you looked at last time, and that all the controls need to be moved in a coordinated way?
There are a large number of power changes made during this air exercise and it is important your instructor reviews and shows the coordination of elevator and rudder adjustments with changes in power.
There are generally four types of climb: best angle, best rate, cruise and recommended (for visibility and engine cooling). There are also generally three types of descent: glide, powered and cruise.
It is recommended you learn the best rate climb and the glide, with a demonstration of the others as time permits.
The last lesson was Straight and Level, now we must learn how to climb and descend to and from straight and level flight, so that we can move towards the circuit lessons.
Objectives
Objectives
To enter the climb and the descent from straight and level flight.
To maintain a climb and a descent at a constant speed, constant rate, in a constant direction and in balance.
To level off at specific altitudes.
Principles of Flight Climbing
Principles of Flight Climbing
To maintain a constant speed and direction the aeroplane must be in equilibrium, as discussed in the Straight and Level lesson. We demonstrate the relationships between the four forces in the climb to show that the aeroplane is still in a state of equilibrium when climbing.
There is a common misconception that in the climb the lift is increased, since lift must equal weight in level flight, it might appear logical that lift should be increased to climb, but it is not so.
Drawing the forces to show that lift is not increased in the climb – but is slightly reduced – should illustrate that the aeroplane is in equilibrium during the climb.
The most important concept you should grasp, in simple terms, is that in order for an aeroplane to climb thrust must be equal to drag plus the rearward component of weight (T = D + RCW). The rate at which the aeroplane will climb, depends on how much more power is available, lots of additional power available will mean a high rate of climb.
The Forces Acting on the Aeroplane in a Climb
The Forces Acting on the Aeroplane in a Climb
From the previous lesson you will know that there are four forces acting on the aeroplane, lift, drag, thrust and weight, and that in straight and level the aeroplane was in equilibrium.
The same is true of the climb – the forces are in equilibrium. You will also know about relative airflow.
Understand that for simplicity your diagram will show the forces acting through just one point, and that the climb angle has been exaggerated for clarity.
| Explainations | Diagrams |
|---|---|
WeightActs straight down toward the centre of the earth. Unlike level flight, it can be seen that during the climb a component of weight will be acting backward along the flight path. Often called the “rearward component of weight” (RWC), would cause a car to roll backward down the hill. Thus, before we can even move forward, we need to compensate for this. | Weightw2 |
DragThe “Rearward Component of Weight” acts in the same direction as drag. | WeightDragw2 |
ThrustThe application of additional thrust over and above that required to maintain level flight at the same airspeed, is required to climb. The greater the additional thrust available, the better the climb angle. | WeightThrustDragw2 |
LiftInteresting point to note is that during a climb, lift is a little less than weight. Equilibrium is achieved by lift < weight and thrust = drag plus the “Rearward Component for weight”. | WeightLiftThrustDragw2w1 |
Climb Performance
Climb Performance
Having discussed the forces in the climb, the various factors affecting the climb performance are taken into account.
Power
You have just established that the more power available, the better the climb performance.
Altitude
Engine performance (power) decreases with altitude, so there will be a limit to how high the aeroplane can climb.
In addition, anything that opposes thrust is detrimental to climb performance.
Weight
The greater the weight, the greater will be the RCW (rearward component of weight). Therefore, weight reduces the rate of climb and the angle.
Flap
Increases lift and drag and alters the Lift/Drag ratio. Since drag opposes thrust, any increase in drag will reduce the rate and angle of climb.
Wind
Affects only the climb angle and the distance travelled over the ground (the range) to reach a specific altitude.
The various configurations for the four types of climb in your training aeroplane are:
| Performance = | Power | + | Attitude |
| Best rate climb | full power | no flap | knots |
| Best angle climb | full power | no flap | knots |
| Cruise climb | rpm | no flap | knots |
| Recommended climb | rpm | no flap | knots |
Understand that you will be using the best rate climb for this lesson and you will look at the others. You may experience these climbs at this stage but their application will become clearer in later lessons.
Descending Four Forces
Descending
| Explanations | Diagrams |
|---|---|
WeightActs straight down toward the centre of the earth. Unlike level flight, it can be seen that during the descent path. Often called the “forward component of weight” (FWC) | Weightw2 |
DragThe “Rearward Component of Weight” acts in the same direction as drag. | WeightDragw2 |
ThrustThe application of additional thrust over and above that required to maintain level flight at the same airspeed, is required to climb. The greater the additional thrust available, the better the climb angle. | WeightThrustDragw2 |
LiftInteresting point to note is that during a climb lift is a little less than weight. Equilibrium is achieved by lift < weight and thrust = drag plus the “Rearward Component for weight”. | WeightLiftDragw2w1 |
Equilibrium is required for a steady descent. If, while in level flight, the power is removed there will be no force balancing the drag. In order to maintain flying speed the nose must be lowered.
With the nose lowered and weight still acting down towards the centre of the earth, there is now a forward component of weight (FCW) that balances drag. For equilibrium there must be a force equal and opposite to weight. This force R is made up of lift and drag.
Therefore, the aeroplane is in equilibrium.
The relative airflow is now coming up the slope to meet the aeroplane and therefore the angle of attack is still approximately 4 degrees.
Descent Forces
Descent Forces
Power
Power controls the rate of descent (RoD), the more power used, the less the RoD. Power also reduces the descent angle and increases the distance travelled over the ground, increasing the range from a given altitude.
Lift/Drag ratio
The ratio of lift to drag is a measure of the efficiency of the wing, for example, the higher the lift to drag ratio the further the aeroplane will glide (its range). Another way to think of it is the L/D ratio determines the steepness of the glide, or descent angle.
If you then change this ratio by increasing the drag (by extending flap or flying at an incorrect airspeed) a greater forward component of weight is required to balance the drag – steepening the flight path.
Weight
A change in weight does not affect the descent angle. With an aeroplane flying at its best L/D ratio, an increase in weight will increase the FCW, increasing the speed down the slope, and therefore the rate of descent, but not the descent angle.
This is shown by increasing the length of the weight vector in your diagram. The FCW increases the airspeed down the slope, and the increased airspeed leads to an increase in lift and drag (with the L/D ratio remaining unchanged), and all the forces remain in equilibrium.
Flap
The increased drag produced by the flap requires an increased FCW to maintain equilibrium and thereby steepens the descent, increases the RoD, and reduces the range.
Wind
Affects only the descent angle and the range from a given altitude.
Learn the glide first, then the others can be taught as a variation of the glide.
Descent Performance
Descent Performance
The various configurations for the three types of descent in your training aeroplane should be stated, for example:
| Performance = | Power | + | Attitude |
| Glide | propeller windmilling | no flap | knots or ft/min RoD |
| Powered | 1500 rpm (guide only) | flap as required | knots or ft/min RoD |
| Cruise | rpm (within green range) | no flap | knots or ft/min RoD |
