-Climbs and Descents-

LESSON OBJECTIVES

1.- See the relationships and changes of the four forces of the flight in climbs/descends

2.- Learn how to enter/maintain/finish a climb/descent

3.- Maintain the aircraft coordinated with constant airspeed and direction during the manoeuver

-Introduction-

This lesson helps to improve the coordination skills learnt in Lesson Number 4, with the addition of learning how to handle large changes of power (Refer to Lesson Nº3 - Power) and perform the adequate pitch and yaw corrections

Depending on the airspeed maintained, there are 3 types of climbs:

- Best angle of climb (Vx) -> At this airspeed, the aircraft gains height using less horizontal distance. For example, for the C172, this speed is 62 kts

- Best rate of climb (Vy) -> At this airspeed, the aircraft gains height using less time. For example, for the C172, this speed is 75 kts

- Cruise climb -> A climb at a higher airspeed to improve visibility and engine cooling (we will discuss this later on)

Depending on the power setting used, there are 2 types of descends:

- Power-Off Descend -> A descend in which the power is at idle, also known as a glide

- Power-On Descend -> A descend in which the power is higher than idle

Captura.JPG

As everybody knows a climb is a maneuver in which an aircraft gains altitude. The definition is simple but the explanation behind it is more complicated than that

Thats why we will start with the basic topics of the climbs such as the forces involved, then the factors that affect the climb performance and finally the manoeuver itself

-Climbs-

-Physics Principles-

As we said in the objectives, we need to maintain a constant airspeed and direction. In order to do that the forces of the aircraft must be in equilibrium (Refer to Lesson Nº4 - Straight & Level)

The forces involved in the climb are the same as always but they suffer some changes that affect the aircraft behaviour

- Lift -> It is still perpendicular to the RAF (Relative Airflow), but in a climb the relative airflow changes direction, so does the lift force

- Weight -> Its direction is the same (pointing towards the Earth centre), but due to the aircraft nose-up position, now it is divided into two (a vertical component / a horizontal component acting in the direction of drag)

- Drag -> It is still parallel to the RAF, but in a climb the relative airflow changes direction, so does the drag force

- Thrust -> It is the most essential force in a climb because it has the job to counteract and overcome the drag and the rearward component of weight (RCW) making the climb possible

So, we can say that the excess power (Thrust - (Drag + RCW)) is the variable that determines the climb performance:

- Higher Excess Power -> Higher Climb Performance

Captura.JPG

- Factors Affecting Climb Performance-

This section is very easy to understand as long as you remember the formula given to you in the last section:

- Excess Power = Thrust - (Drag + RCW)

- Higher Excess Power -> Higher Climb Performance

So every factor that affects thrust, drag or weight will affect the excess power and climb performance

These factors are:

- Altitude -> HIGHER Altitude -> LESS Air Density -> LOWER Thrust -> LOWER Excess Power -> LOWER Rate of Climb/Climb Angle

- Temperature -> HIGHER Temperature -> LESS Air Density -> LOWER Thrust -> LOWER Excess Power -> LOWER Rate of Climb/Climb Angle

- Humidity -> HIGHER Humidity -> LESS Air Density -> LOWER Thrust -> LOWER Excess Power -> LOWER Rate of Climb/Climb Angle

- Flap -> HIGHER Drag -> LOWER Excess Power -> LOWER Rate of Climb/Climb Angle

- Weight -> HIGHER Weight -> HIGHER RCW-> LOWER Excess Power -> LOWER Rate of Climb/Climb Angle

- Wind -> It doesn't affect ROC but it affects climb angle, You will see it better with an example:

-- Aircraft 1 (No wind) -> Airspeed (75 kts), Groundspeed (75 kts -> 1.25 NM/min), ROC -> 500ft/min

-- Aircraft 2 (15 kts Headwind) -> Airspeed (75 kts), Groundspeed (60kts -> 1NM/min), ROC -> 500ft/min

-- Aircraft 3 (15 kts Tailwind) -> Airspeed (75 kts), Groundspeed (90kts -> 1.5 NM/min), ROC -> 500ft/min

Captura.JPG

-Air Exercise-

In this section, you will find an explanation of how to:

- Enter the climb from S&L

- Maintain the climb

- Exit the climb and recover S&L

If you remember from Lesson Nº4 - Straight and Level, we discussed the steps followed to perform a specific manoeuvre. The same will apply now:

- Entry in the climb:

-- Power -> Smoothly increase power to maximum                     

-- Attitude -> Apply back-pressure to the stick/yoke, select and hold the nose-up attitude required, maintain wings level with ailerons and coordination with rudder

-- Trim -> Trim for nose-up attitude to remove excessive loads

- Maintain the Climb:

-- Lookout -> Keep scanning the sky to avoid other traffics that could be manoeuvring around you

-- Attitude -> As the power has been selected to full, the only control that is left to control the climb is the yoke/stick. So, in a climb, the elevator is the key to controlling the airspeed during the climb (For example, if our objective airspeed is 60 kts -> 70 kts (Nose-up to decrease airspeed) / 50 kts (Nose-down to increase airspeed)). Maintain wings level with ailerons and coordination with rudder

-- Instruments -> Take a look at the instruments to check that you have achieved the parameters required

- Regain S&L flight from a climb:

-- Attitude -> Use the stick/yoke to lower the nose to regain a level attitude while maintaining full power, now the power that allowed us to climb is used to accelerate the aircraft. Due to inertia, the airspeed will not increase immediately but rather gradually. As the airspeed increases, the lift will increase (Lift formula -> 1/2dV² x CL x S), and the aircraft will try to climb, to counteract this effect more nose-down input is required to maintain the desired altitude

-- Power -> Once you reach the cruising airspeed desired, you must reduce power from full to cruise power setting (Remember to correct for pitch/yaw movements with power changes)

-- Trim -> Remember to use nose-down trim to reduce control loads after you have the final attitude and power required for cruise

-Descends-

We have seen in detail what is a climb and how is performed. But remember everything that goes up sooner or later must come down, it is the pilot's task to descend in a proper and safe way

-Principles of Flight-

If you understood the physics behind the climb, you will find pretty easy to understand descend

Descends have many things in common with climbs, both of them are manoeuvres that imply an altitude change, obviously. But, also in both of them, the 4 forces of the flight must reach an equilibrium state between them to get a steady descend. 

- Lift -> It is still perpendicular to the RAF (Relative Airflow), but in a descend the relative airflow changes direction, so does the lift force

- Weight -> Its direction is the same (pointing towards the Earth centre), but due to the aircraft nose-down position, now it is divided into two (a vertical component / a horizontal component acting in the direction of thrust)

- Drag -> It is still parallel to the RAF, but in a descend the relative airflow changes direction, so does the drag force

- Thrust -> The amount of thrust used will determine the type of descend (Power-On/Power-Off), when thrust is used it has the job to counteract the drag. In both cases with or without thrust, there is a forward component of weight (FCW) that substitutes (without power) or helps (with power) the thrust force

Take a look at the next diagram to have a visual reference for the explanation:

Captura.JPG

In the diagram, there is a comparison between power-on and power-off descent, as you can see in the last one the aircraft has a steeper angle than the powered descend. This is because:


- If the forces must be in equilibrium then in both descends we need some type of force acting forwards to counteract the drag
- In a powered descend, thrust and weight act together to overcome drag
- In a power-off descend, there is no thrust so we need more weight acting forward to get the same result, to do that we must lower the nose descending with a steeper angle and at a higher rate of descent

-Factors Affecting Descend Performance-

We have discussed the forces in the descent and their relationship, so now we have to talk about the various factors affecting descent performance

These factors are:

- Power -> HIGHER Power -> LESS FCW Required -> LOWER Rate of Descend (RoD) / LOWER Descent Angle / Higher Range (Distance travelled over the ground in a descend)

- Lift / Drag Ratio -> A value to describe the wing efficiency (Higher Value -> MORE Lift / LESS Drag, Lower Value -> LESS Lift / MORE Drag) -> HIGHER L/D Ratio -> LESS Drag -> LESS FCW Required -> LOWER RoD / LOWER Descent Angle / Higher Range 

- Flaps -> MORE Drag -> MORE FCW Required -> HIGHER RoD / HIGHER Descent Angle / LOWER Range 

- Wind -> It doesn't affect RoD but it affects descent angle. You will see it better with an example

---- Aircraft 1 (No wind) -> Airspeed (75 kts), Groundspeed (75 kts -> 1.25 NM/min), RoD -> 500ft/min

---- Aircraft 2 (15 kts Headwind) -> Airspeed (75 kts), Groundspeed (60kts -> 1NM/min), RoD -> 500ft/min

---- Aircraft 3 (15 kts Tailwind) -> Airspeed (75 kts), Groundspeed (90kts -> 1.5 NM/min), RoD -> 500ft/min

Captura.JPG

-Air Exercise-

As we did in climbs, now we will take a look at how to execute the descend in 3 steps:

- Entry in the Descent

- Maintain the Descent

- Regain S&L from the Descent

- Entry in the descend:

-- Power -> Smoothly reduce power to the appropriate power setting depending on if you want to perform a power-off or power-on descent. (In this explanation, we will suppose a power-off descent)

-- Attitude -> With the elevator, hold the altitude by pitching up until you reach your desired descent airspeed, and once you reach that airspeed lower the nose to maintain it. For example, if you were cruising at 90 kts at 5000 ft, and you will perform a power-off descent at 60 kts. After selecting idle, pitch up to maintain 5000ft while the airspeed decreases, and once you reach 60 kts, lower the nose to maintain that speed. Maintain wings level with ailerons and coordination with rudder

-- Trim -> Use trim to remove excessive loads

- Maintain the descent:

-- Lookout -> Scan the sky for traffic and as you are descending to a lower altitude, keep an eye for any obstacles that you could encounter

-- Attitude -> As we did in a climb, the pitch will control the airspeed, remember to lower the nose to increase the airspeed and raise the nose to decrease the airspeed. In case of a power-on descent, the pitch controls the airspeed and the power control the rate of descent

-- Instruments --> Scan the instruments to fly an accurate descent

- Regain S&L from a descend:

-- Power -> Increase power to cruise power

-- Attitude -> Raise the nose to the required attitude to hold the altitude. Remember that as airspeed increases gradually, lift increase in consequence and higher forward pressure will be required

-- Trim -> Trim to maintain the altitude selected