22.30.12
State the factors affecting endurance and explain practical endurance flying techniques.

Factors affecting flying for endurance

Effects of Altitude

The minimum power speed will coincide with a given IAS for a particular weight. As altitude increases, drag remains the same as IAS is constant, but TAS increases as altitude increases. Since Power = Drag X TAS power required will increase as altitude increases. Therefore flying for endurance is best done at the lowest safe altitude.

Effect of Weight

The minimum power speed increases with increased weight and because there is more drag, more power is required; therefore GFC will also increase. Thus endurance is reduced at higher weights.

Engine Considerations

To achieve maximum endurance, the engine must be operated with minimum gross fuel consumption (GFC). This is achieved at the lowest permitted rpm with the engine operating in the lean range with MAP set to maintain minimum power speed. The mixture must be leaned correctly to ensure maximum range is achieved 

Practical Application 

• Fly at the recommended gliding speed and with small adjustments to power, determine the lowest power setting that will comfortably hold the aircraft in level flight.
• Use the lowest permitted rpm for the lean range which will give smooth running and enable the generator/alternator to charge. Adjust the MAP to maintain the selected speed.
• In turbulent conditions or for manoeuvring, fly at a slightly higher speed (e.g. 10% higher) to avoid having to apply large increases in power to overcome the effects of gusts/increased drag
• Ensure the mixture is correctly leaned
• Fly at the lowest practical altitude but if you have the luxury of high altitude, descend slowly, power on at the endurance speed until the lower altitude is reached (the aircraft descends at a lower power setting than is needed for level flight, thus increasing endurance)

22.30.10
Define flying for endurance and differentiate between range flying and endurance flying (piston engine).

When considering flying for endurance we are talking about staying in the air for the longest possible time. We are not trying to go anywhere –  all we are attempting to do is stay airborne as long as possible.

This is different to flying for range where we are attempting to get to the furthest possible distance.

When we are flying for endurance we are interested in the lowest possible fuel flow. So we use the lowest possible power setting to maintain level flight. This will maximise the time in the air, thus maximising endurance.

22.30.8
Apply performance tables or graphs from an aircraft manual to determine best SAR under given conditions.

Below is an example of a cruise performance table. It is possible to use this table to work out the maximum range for a specific power setting. In the manual there are multiple graphs for different power settings. This one is for 55% power as can be seen

                                              

22.30.6
Explain the airframe and engine considerations of flying for range (piston engine).

22.30.4
State the general conditions for achieving maximum SAR.

For maximum range flying you must operate the aircraft and engine in such a way that maximum efficiency is obtained over the distance to be flown. Do that by keeping the following factors in mind:

22.30.2 specific fuel consumption (SFC).

Specific fuel consumption (SFC)

Specific fuel consumption is defined as the GFC (or fuel flow) per unit of power produced, or in simple terms the fuel efficiency of an engine. 

How to calculate SFC

Specific fuel consumption (SFC)= GFC/Power

                                        or GFC= SFC X power

substituting in the equation above:

                                            SAR= TAS/power X 1/SFC

Thus to achieve maximum specific air range (SAR) the aircraft must be flown at the maximum airframe efficiency (TAS/power) and engine efficiency (1/SFC)

Turboprop efficiency is only good at high power; SFC increases dramatically for approach at low power (30% P_max) and especially at idle (7% P_max) :

22.30.2 Define specific air range (SAR).

Specific fuel consumption (SFC)

Specific fuel consumption is defined as the GFC (or fuel flow) per unit of power produced, or in simple terms the fuel efficiency of an engine. 

How to calculate SFC

Specific fuel consumption (SFC)= GFC/Power

                                        or GFC= SFC X power

substituting in the equation above:

                                            SAR= TAS/power X 1/SFC

Thus to achieve maximum specific air range (SAR) the aircraft must be flown at the maximum airframe efficiency (TAS/power) and engine efficiency (1/SFC)

Turboprop efficiency is only good at high power; SFC increases dramatically for approach at low power (30% P_max) and especially at idle (7% P_max) :

22.28.12
Define Vmca and Vmcg.

In an aircraft being flown asymmetrically, as airspeed is decreased with the live engine at full power, a point will be reached where full rudder is required to prevent further yaw. This point is the minimum control speed beyond which yaw control cannot be maintained by normal means.

VMCA is the minimum control speed following a sudden failure of the critical engine after takeoff, at which an average pilot will be able to maintain directional control with full rudder and no more that 5° angle of bank applied. 

To obtain airworthiness certification, VMCA must be demonstrated under a very specific set of circumstances. These include: critical engine wind-milling, full power on the live engine, flaps set for takeoff, undercarriage retracted, C of G at the aft limit and under ISA sea level conditions. This speed must be not greater than 1.13 times the level flight stalling speed in the same configuration. This is shown as a red line on the airspeed indicator.

VMCG is defined as the minimum speed, whilst on the ground, that directional control can be maintained, using only aerodynamic controls, with one engine inoperative (critical engine on two engine airplanes) and takeoff power applied on the other engine(s).

22.28.10
Explain the three modes of constant-heading asymmetric flight.

The three modes of constant-heading asymmetric flight are

• All rudder
• All aileron
• Combined bank and rudder

All Rudder

When using this method, rudder is used to prevent yaw from asymmetric thrust and the wings are held level with the use of aileron. This will mean the aircraft is ‘crabbing’ along slightly sideways with the nose pointing a few degrees off the direction of flight.

When using rudder alone to prevent yaw, a lateral side force is generated which if left unbalanced, would tend to push the aircraft sideways toward the failed engine. To counter this a rudder side force is created because of the inherent stability of the aircraft. When just enough rudder is used to prevent any yaw and the wings are held level, the aircraft adopts a small sideslip angle and a weathercock sideslip force is generated, which opposes the rudder side force. When the forces are in balance the aircraft will maintain a constant heading wings-level with the rudder yawing moment equal and opposite to the thrust yawing moment plus the weather-cocking yawing moment.

The aircraft is constantly side-slipping at a small angle and thus the heading and direction of flight will be different. Because of this sideslip the dihedral of the wings generates a rolling moment which must constantly be countered with the application of aileron toward the failed engine. The forces are in balance and in spite of the sideslip angle with weight and lift vertically aligned, no side slip will be indicated on the coordination ball.

Instrument indications are

• Wings level
• Ball centred
• Apparent drift toward the failed engine

All Aileron

In this mode, the asymmetric thrust yawing moment is counteracted without the use of rudder. The aircraft is rolled and is constantly side-slipped toward the live engine. The resulting weather-cocking yawing moment is used to counteract the thrust yawing moment.

This involves a relatively large sideslip angle and a high angle of bank, (as much as 15°). It is difficult and uncomfortable to fly and very inefficient. The tilting of the lift vector requires the aircraft to be flown at a higher angle of attack to counteract the weight in level flight and this coupled with the sideslip angle results in higher drag than is necessary.

Combined Rudder and Aileron

The more normal method of controlling the aircraft on a constant heading in asymmetric flight is to use a combination of rudder and aileron. The amounts of rudder and aileron can be varied between the two extremes. Either all rudder, no aileron or all aileron, no rudder. The ideal arrangement is with the longitudinal axis of the aircraft aligned with the direction of flight to have sufficient rudder applied to counteract the thrust yawing moment, together with a small amount of roll towards the live engine to balance out the rudder side force.

This provides optimum performance since with zero sideslip angle the extra drag is kept to a minimum. In attempting to fly this mode however the bank angle should be contained to between 5 to 10° otherwise the gains made by having zero slip will be offset by having to fly at a higher angle of attack to maintain the vertical component of lift.

In this mode the aircraft will be flown with

• A small sideslip angle with the nose slightly offset toward the live engine ( and therefore a small amount of apparent drift)
• A small amount of bank ( around 5°) toward the live engine
• A small amount of slip indicated towards the live engine