22.28.8
Recall immediate actions and techniques for identifying the failed engine.

Immediate actions are as follows;

• Prevent any further yaw with rudder
• Prevent any unwanted roll with aileron

The correct engine must be identified. There have been accidents in the past where the incorrect engine has been identified.

The sudden failure of an engine in a multi engine aircraft requires the quick and correct identification of the failed engine. Appropriate actions must be carried out at this point.

The most immediate indication that an engine has failed is the yawing towards the failed engine. Most pilots will instinctively apply rudder pressure to prevent this yawing moment.

At this point it is easy to say to yourself “dead leg, dead engine” which should help identify the failed engine. At this point the failure must be confirmed with engine instrumentation to ensure the correct engine is identified.

22.28.6
Define critical engine.

The critical engine of a multi-engine, fixed-wing propeller-driven aircraft is the one whose failure would result in the most adverse effects on the aircraft’s handling and performance.

When one of the engines on a typical multi-engine aircraft becomes inoperative, a thrust imbalance exists between the operative and inoperative sides of the aircraft. This thrust imbalance causes several negative effects in addition to the loss of one engine’s thrust. For reasons listed below, the left engine of a conventional twin-engine propeller-driven aircraft is usually considered critical.

When one engine becomes inoperative, a torque develops which depends on the lateral distance from the center of gravity (C.G.) to the thrust vector of the operating engine, multiplied by the thrust of the operating engine. The torque effect attempts to yaw the aircraft’s nose towards the inoperative engine, a yaw tendency which must be counteracted by the pilot’s use of the flight controls. 

Due to the asymmetric blade effect (P-factor), the right-hand engine typically develops its resultant thrust vector at a greater lateral distance from the aircraft’s C.G. than the left-hand engine. The failure of the left-hand engine will result in a larger yaw effect via the operating right-hand engine, rather than vice-versa, and it is termed the Critical Engine. Since the operating right-hand engine produces a stronger yaw moment, the pilot will need to use larger control deflections in order to maintain aircraft control. Thus, the failure of the critical (left-hand) engine is less desirable than failure of the right-hand engine. 

It is important to note, however, that this example depends upon both propellers turning clockwise as viewed from the rear. On aircraft with counterclockwise-turning engines (such as the de Havilland Dove), the right engine would be critical.

Aircraft which have counter-rotating propellers rotating toward the cockpit on the top side (such as the Beechcraft Duchess) do not have a critical engine, while both engines are critical on aircraft with counter-rotating propellers turning away from the cockpit. The Lockheed P-38 is an example of the latter.

Lift can be roughly defined as an upwards force resulting from an airstream going over and under a wing. On aircraft with propellers mounted on the wing, the prop-wash from the engine will accelerate the airstream over the portion of the wing directly behind the propeller. This results in greater lift behind the propeller than at other spots on the wing. From the P-factor effect, the right wing’s center of lift will be further from the C.G. than the left-hand wing. While failure of either engine will cause a rolling motion towards the inoperative side, the rolling motion will be more severe with the right engine operating. Thus, the failure of the left-hand engine is critical. Again, this example depends on both engines turning clockwise when viewed from the rear.

On certain aircraft, hydraulic, pneumatic or electrical systems may be powered by one engine. This engine would therefore be critical in this respect

Aircraft powered by turbojet or turbofan engines are not normally considered to have a critical engine.

22.28.4
Explain the factors affecting yawing and rolling moments.

Yawing moment is due to the asymmetry of thrust and drag about the C of G and it’s strength is proportional to;

• Thrust from the live engine. The higher the thrust the greater the yawing moment.
• The distance of the thrust line to the C of G. An increased distance from the centreline of the aircraft increases the arm through which thrust from the live engine acts and this will cause an increased yawing moment.
• Directional stability. To have directional stability the aircraft must be built in such a way that there is a greater proportion of fin and rudder behind the C of G. This provides a weather-cocking effect which acts to keep the fuselage aligned with the direction of flight. This weather-cocking tendency tends to resist the thrust-created yawing moment and is improved with increasing airspeed. Directional stability is reduced with an aft C of G and the weather-cocking moment is reduced.
• Rate of thrust decay. If the engine failure is gradual then the yawing moment onset will also be gradual
• Drag of the failed engine. The drag of the failed engine will be higher than the one operating normally. Especially if the propeller is un-feathered. The more drag on the dead engine side, the greater the yawing moment.

                                                

22.28.2
Explain the consideration involved in coping with asymmetric thrust/drag and reduced power.

When dealing with a
failed engine in a twin engine aircraft there are several things we need to consider.

Because it’s engines do not share a similar thru line, failure of one of the engines will cause an “asymmetric thrust” problem in that:

• the line of total thrust will be offset from the normal axis, causing a yawing moment towards the failed engine..
• the line of total drag moves towards the failed engine, which adds to the asymmetric thru yawing moment.
• there is a reduction of total thrust available, which leads to a deterioration in performance. 

Following an engine failure, control of yaw and roll must be maintained to ensure a safe flight path. Then once the engine has been correctly identified and secured, the aircraft is flown in such a way as to achieve the best performance possible with
asymmetric thrust and reduced power.

22.26.22
Explain ground effect, and relate it to take-off and landing.

Ground effect is the cushioning effect aircraft experience when very low level above a smooth surface. It is noticeable in less than one wingspan and increases the closer to the ground.  It is the wing vortices rotating downwards and under the aircraft. 

During takeoff, as the aircraft leaves the ground effect, lift will decrease and drag will increase. A slight sagging in performance will be experienced briefly. 

On landing, ground effect generally makes the aircraft float briefly before touchdown. 

22.26.20
Describe cross-wind take-off and landing techniques.

To takeoff and land an aircraft in high crosswinds can be very tricky, that is why we use the crosswind landing technique. 

On takeoff, we point the ailerons into wind and point the aircraft into wind with rudder once off the ground. 

When we approach the runway to land, we position the aircraft down the centre-line holding the needed drift angle. Just prior to touchdown, we yaw the aircraft straight down the centre-line using rudder, and the wind-side wheel is touched down first using aileron, and then the rest of the wheels. 

22.26.18
For a single-engine propeller aircraft, explain the factors affecting swing on take-off.

Swing on takeoff in single engine propeller aircraft, particularly with tail-draggers, is due to a variety of reasons. 

The causes of swing are:

• Slipstream effect – A/C propeller that spins clockwise creates slipstream that meets the rudder which causes the A/C to yaw left.

Insert Figure 13-22 Page 13-15 Waypoints

• Torque effect – Engine torque creates opposite reaction that is forced onto the left wheel. The wheel then has a greater resistance to roll that causes the A/C to yaw left.

Insert Figure 13-23 Page 13-15

• Gyroscopic effect – In a tail wheel configuration the tail wheel lifts on take-off and applies a force to the top of the propeller disc. The force is precessed 90* causing a swing to the left. 

Insert Figure 13-24 Page 13-15

• Asymmetric blade effect – The down-going propeller produces more thrust due to it travelling further which causes a yaw to the left. More pronounced in a tail wheel configuration. 

• Crosswinds – Cause the A/C to weathercock away from the runway. Use aileron into wind technique and reduce throughout the take-off run and use small inputs of rudder to prevent any swing. 

22.26.16
With respect to stability and control on the ground, explain:
(a) the importance of CG position;
(b) the differences between nosewheel and tailwheel configurations;
(c) handling of controls in strong crosswinds.

(a) The C of G position plays an important part in how the aircraft controls behave. 

With a forward CG position, the aircraft is more stable than a rearward CG position. 

(b) An aircraft with a tail wheel configuration is inherently unstable. Once turning, CFF tends to tighten the turn. If the aircraft turns at too high a rate, the ability to control the rudder will be lost and the aircraft could ground-loop. 

An aircraft with a nose wheel configuration is the most stable configuration for control on the ground. This is due to two reasons; one is that the pilot can see more out of the windscreen due to a lower nose attitude, and the other due to no tendency to ground roll or ground loop. 

(c) The CG position must remain in the specified limits, which can be looked at as the area bounded by the three wheels. Widely spaced wheels reduce the tendency to tip the A/C in high winds. 

With a CG behind the main wheels, an A/C has the tendency to want to carry on in a straight line due to momentum when disturbed by turning or the rudder. 

When taxiing an aircraft on the ground, with a head wind, point the ailerons into wind, and the elevator neutral or back. With a wind from behind, you must push the control wheel forward and ailerons out of wind. 

22.26.14
Explain the conditions of spiral instability, dutch roll, and snaking.

Spiral Instability is a condition that exists when the static directional stability of the airplane is very strong compared to the effect of its dihedral in maintaining lateral equilibrium. e.g  An aircraft with a large vertical stabilizer and no dihedral.

Dutch Roll is a combination of rolling and yawing (coupled lateral/directional) oscillations that normally occurs when the dihedral effects of an aircraft are more powerful than the directional stability. For example, when an aircraft is disturbed in yaw, there is little force from the fin = slow/damped recovery. A/C then slips and rolls from its dihedral = yaw+roll motion.

Snaking is essentially a dutch roll but the yaw is more pronounced than the roll. (Snaking motion)

22.26.12
Explain the requirement to match lateral and directional stability.

Matching the lateral and directional stability is an essential part of aircraft design. 

It is important to have the side-slip which the roll disturbance causes. This side-slip provides sideways component of airflow which is necessary for the dihedral and other lateral stability features to work and provide a restoring moment in roll. 

However, when slip or skid is introduced, the aircraft’s directional stability is brought into play. When an aircraft side-slips, its directional stability will cause it to yaw in the direction of slip, and make it want to continue rolling in the direction of disturbance. 

Lateral stability wants to return the AC to wings level, but directional stability wants to make the AC roll further. 

Therefore, the designer must ensure lateral and directional stability are correctly matched, and neither predominates too much.