BASIC TURNS

LESSON OBJECTIVES

  1. Learn to perform a change in direction through 360º up to 30º bank angle

  2. Understand the physics behind the manoeuver

  3. Maintain the altitude, bank angle and coordination during the turn

Air Battle

-Bank Angle and Types of Turns -

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

Bank Angle in Aircraft

The lift mission is to counteract the weight of the aircraft, but in a turn, the lift is split into two, a vertical and a horizontal component:

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

With the lift vector inclined, the vertical component of the 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 turn increases the total lift.

Turn Aerodynamics

If you remember from Theoretical Knowledge - Basic Aerodynamics, any increase in the lift has a penalty in the form of drag, to be precise, induced drag that results in a decrease in airspeed. In 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, the airspeed effect is very noticeable and compensation in form of power must be applied

Induced Drag in Turns

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? 

We only need to apply the rudder in the direction of the turn to bring the nose to the correct position

How much rudder do I need to apply? 

It is necessary to check 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, pressure on the pedals is still necessary 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:

- Level Turn / Climbing Turn -> As the outside wing travels faster than the inner wing, it also produces more lift. This lift difference creates 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 over banking 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

-Aerodynamics in Turns-

-Turn Procedures-

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 manoeuvre. Also, we should perform an 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

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

  1. In S&L flight, take a reference point for the initial and final heading of the manoeuver

  2. Apply aileron in the direction of the turn, at the same time apply rudder to the same side to maintain the aircraft coordinated

  3. 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 maintain altitude

  4. Once the bank angle of 30º is established, neutralize the ailerons and note where the horizon cuts the instrument panel, that would be your reference to maintain altitude. Apply opposite aileron to correct for over banking and reduce rudder pressure to maintain the aircraft coordinated

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Captura.JPG

Now we are established at a 30º bank angle and still at the initial altitude. Maintaining the turn will require performing the same steps that we have seen in other manoeuvres:

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

-
Attitude -> We must ensure that we are maintaining 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 instrument panel and the horizon. To maintain altitude we must know where the horizon cuts the panel. If this point is higher than the original, we are descending, if it is lower we are climbing.

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               Climbing Medium Turn
- Rate of Climb is lower than in normal climbs due to the drag produced by the additional lift required to turn

- Limited to max 20º bank angle to reduce lift required and thus drag 

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Medium Level Turn
- 30º bank angle
- Horizon on proper position
- Zero Rate of Climb

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             Descending Medium Turn
- Rate of Descend is higher than in normal descends due to the drag produced by the additional lift required to turn
- Power controls the rate of descent. Higher power produces a lower Rate of Descend and viceversa

- Instruments -> Crosscheck with the flight instruments to verify that the turn is being flown correctly (height - bank - ball/altimeter - attitude indicator - turn coordinator)

To finish the turn, 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.

Next, start the rollout before the final heading is reached. Due to the inertia, the aircraft will continue rolling as you level the wings. Levelling off in your final heading will end in the aircraft overshooting.  The anticipation formula is:

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

So, if you were doing a left turn with a final heading of 360º, you must start the rollout at 345º. The full rollout consists 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 to the aircraft pitching up and gaining altitude as you level the wings. To prevent this gradually increase the forward pressure on the control column to counteract the effect