Basic Turns

LESSON OBJECTIVES

1.- Learn to perform a change in direction through 360º up to 30º bank angle
2.- Maintain the altitude and coordination during the turn
3.- Understand the physics behind the manoeuver

Air Battle

-Introduction-

A turn is in simple words a change in direction, depending on the angle of bank (AoB), there are three different types of turns:

- Medium < 30º
- 30º < Steep < 45º
- Aerobatic > 45º


The bank angle is the angle between the aircraft lateral axis and the horizontal. The aircraft in the image would be performing a medium turn with a 20º bank angle

Captura.JPG

-Principles of Flight-

As we saw in the Lesson Nº4 - Straight and Level, the lift mission is to counteract the weight of the aircraft, in a turn the lift is splited into two, a vertical and a horizontal component:

- Vertical Component -> Counteracts Weight
- Horizontal Component -> Provides the acceleration required towards the centre of the turn

Captura.PNG

With the lift vector inclined, the vertical component of lift is no longer strong enough to support the aircraft weight, so the aircraft pitch down and start sinking. In order to maintain altitude, the total lift vector must be increased so that the vertical component equals weight again

- This is achieved by applying more backpressure on the control column, this movement increases the angle of attack, which in turns increases the total lift.

If you remember from Theoretical Knowledge - Basic Aerodynamics, any increase in lift has a penalty in the form of drag, to be precise, induced drag that results in a decrease in airspeed:

- In the medium turns (up to 30º), the lift and drag increments are very slight and the decrease in airspeed is minor. But for steep and aerobatic turns (higher than 30º), the airspeed effect is very noticeable and a compensation in form of power must be applied

One of the side-effects of increasing lift is a corresponding increase in drag. We know that but the distribution of the drag produced by the wings is not the same. The up-going wing produces more drag than the down-going wing

- The extra drag slows down the up-going wing creating an imbalance between the two wings. The unbalance produce a yaw motion to the opposite direction of the turn

What can we do about it? 

- Well actually the solution is fairly simple the only thing that we have to do is apply rudder in the direction of the turn to bring the nose to the correct position

How much rudder do I need to apply? 

- The answer to this question will be given to you by one of the flight instruments on the cockpit, the turn and slip indicator (Refer to Lesson Nº1), just follow the "Step on the Ball" rule

- Once the required bank angle is achieved and the ailerons are in the correct position, the rudder pressure required to overcome adverse yaw is reduced, but not removed. So, you will still need to apply pressure on the pedals to maintain the aircraft coordinated

Factors affecting the rudder pressure required:

- Rate of Roll -> Faster rolls require higher rudder inputs than slower rolls

- Airspeed -> At low airspeed, you need more aileron deflection for a determined bank angle, which in turn increases the drag produced by the up-going wing requiring more rudder than at higher airspeeds

Captura.JPG

Another tendency of an aircraft during turns is the tendency to overbank, meaning that the aircraft tend to continue the roll into the turn increasing the bank angle if not corrected

Depending on the type of turn that we are performing, the effect can be higher or lower or even dissapear in some cases:

- Level Turn / Climbing Turn -> As the outside wing travels faster than the inner wing, it also produces more lift. This lift difference create a tendency to roll into the turn

- Descending Turns -> In a descent the relative airflow comes from below the wing increasing the AoA of the inner wing, thus creating more lift, that helps to reduce or in some cases even neutralize the overbanking trend

These tendencies must be counteracted by applying opposite aileron to maintain the required bank angle. So remember to apply opposite aileron to maintain the wings in the required attitude:

-Air Exercise-

In this part of the lesson, we will need to apply everything that we learn in previous lessons, in order to appropriately use the controls in a precise manner. We will see how to:

- Enter the Turn
- Maintain the Turn
- Exit the Turn

-Entry into the Turn-

Before we enter into the turn, we must select a reference altitude and a good visual reference point in order to know in which heading we will start and finish the maneuver. Also, we should perform a intensive lookout to check any nearby traffic that could be flying around: 

-1º.-> Take three reference points: One at the front, and the other 2 at 90º to your left and right

-2º.-> Start a 90º turn to the right and check your right side

-3º.-> Perform a 180º turn to the left and check the opposite side

-4º.-> Do a 90º turn to your right to finish in your initial heading and altitude

Captura.JPG

Once the lookout is completed, we can start the turn maneucer itself:

-1º.-> Take a reference point to know where did you start the maneuver and where you should end it
-2º.-> Apply aileron in the direction in which you wish to turn, at the same time apply rudder to the same side to maintain the aircraft coordinated
-3º.-> As the aircraft starts increasing its bank angle, it will tend to pitch down and lose altitude. To prevent that increase the back-pressure on the controls to control the altitude
-4º.-> Once the bank angle of 30º is established apply opposite aileron to correct for overbanking and reduce rudder pressure to maintain the aircraft coordinated

-Maintaining the Turn-

Now we are established at 30º bank angle and maintaing the initial altitude. Maintaining the turn will require to perform the same steps that we have seen in other maneuvers:

- Lookout -> While we are turning, we still have to look for traffic and our ability to detect it will vary depending if we are in a low-wing or a high-wing aircraft, In the last one, more body and head movement will be required to perform a correct scan.

- Attitude -> we must ensure that we are maintaing the required 30º angle of bank and the altitude is being maintained. To do that we must check the position between the horizon and the aircraft cockpit position. The bank angle will be the angle between the cowling and the horizon, To maintain altitude we must know where the horizon cuts the cowling at the correct altitude. If the point where the horizon cuts the cowling is higher than the original, we are descending, if it is lower we are climbing

- Instruments -> We have the correct picture required to maintain the bank angle and the altitude. Now we must crosscheck with our instruments to ensure that we are in the correct position. We do not check all the instrument, only the ones that tells us the information we want to check (height - bank - ball / altimeter - attitude indicator - turn coordinator)

-Exit the Turn-

As important to know how to perform the entry into the turn and how to maintain it, it also essential to know how to finish it in a correct way.

First of all, perform a quick scan into the turn to check for other traffic nearby and the upcoming reference point selected at the beginning of the manoeuver.

After this, you must start the rollout before the final heading is reached. Due to the inertia, you will still be rolling as you level the wings.  The anticipation formula is:

- Degrees of Anticipation (º) -> Bank Angle / 2 -> 30º/2 = 15º

So, if you was doing a left turn with a final heading of 360º, you must start the rollout at 345º. The full rollout consist of:

- Smoothly use opposite aileron to achieve a wings level position
- As you use the ailerons, you must apply rudder in the same direction to correct for adverse yaw and maintain coordination
- As the bank angle starts to diminish, all the extra lift generated to maintain the altitude in the turn will translate in the aircraft pitching up as you level the wings. To prevent this you must pitch down to counteract the effect and maintain the altitude