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)

Power (kW)	Year	Engine type	Application	SFC (lb/(hp⋅h))	SFC (g/(kW⋅h))	Energy efficiency
93	1942	Lycoming O-235 piston, gasoline	General aviation	0.43	262[1]	31.4%
63	1991	GM Saturn I4 engine, gasoline	Saturn S-Seriescars	0.411	250[2]	32.5%
150	2011	Ford EcoBoost gasoline, turbo	Ford cars	0.403	245[3]	33.5%
1,305	1973	General Electric CT7 turboprop	Let L-610G airliner	0.413	251[4]	33.6%
300	1961	Lycoming IO-720 piston, gasoline	General aviation	0.4	243[5]	34.2%
2,000	1945	Wright R-3350 Duplex-Cyclone gasoline, turbo-compound	Bombers, airliners	0.380	231[6]	35.5%
57	2003	Toyota 1NZ-FXE, gasoline	Toyota Prius car	0.370	225[7]	36.4%
550	1931	Junkers Jumo 204 two-stroke diesel, turbo	Bombers, airliners	0.347	211[8]	40%
36,000	2002	Rolls-Royce Marine Trent turboshaft	Combat ships	0.340	207[9]	40.7%
2,340	1949	Napier Nomad Diesel-compound	planned (aircraft intended)	0.340	207[10]	40.7%
165	2000	Volkswagen 3.3 V8 TDI	Audi A8 car	0.337	205[11]	41.1%
2,013	1940	Klöckner-Humboldt-Deutz DZ 710 Diesel two stroke	none (aircraft intended)	0.330	201[12]	41.9%
42,428	1993	General Electric LM6000 turboshaft	Ship, electricity	0.329	200.1[13]	42.1%
130	2007	BMW N47 2L turbodiesel	BMW cars	0.326	198[14]	42.6%
88	1990	Audi 2.5L TDI	Audi 100 car	0.326	198[15]	42.6%
3,600		MAN Diesel 6L32/44CR four-stroke	Ship, electricity	0.283	172[16]	49%
4,200	2015	Wärtsilä W31 four-stroke	Ship, electricity	0.271	165[17]	51.1%
34,320	1998	Wärtsilä-Sulzer RTA96-C two-stroke	Ship, electricity	0.263	160[18]	52.7%
27,060		MAN Diesel S80ME-C9.4-TII two-stroke	Ship, electricity	0.254	154.5[19]	54.6%
34,350		MAN Diesel 12G95ME-C9 two-stroke	Ship	0.254	154.5[20]	54.6%
605,000	2016	General Electric 9HA combined cycle gas turbine	electricity generation	0.223	135.5 (eq.)	62.2%[21]

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) :

2,050 kW Pratt & Whitney Canada PW127 turboprop (1996)^[22]

Mode	Power	fuel flow	SFC	Energy efficiency
Nominal idle (7%)	192 hp (143 kW)	3.06 kg/min (405 lb/h)	1,282 g/(kW⋅h) (2.108 lb/(hp⋅h))	6.6%
Approach (30%)	825 hp (615 kW)	5.15 kg/min (681 lb/h)	502 g/(kW⋅h) (0.825 lb/(hp⋅h))	16.8%
Max cruise (78%)	2,132 hp (1,590 kW)	8.28 kg/min (1,095 lb/h)	312 g/(kW⋅h) (0.513 lb/(hp⋅h))	27%
Max climb (80%)	2,192 hp (1,635 kW)	8.38 kg/min (1,108 lb/h)	308 g/(kW⋅h) (0.506 lb/(hp⋅h))	27.4%
Max contin. (90%)	2,475 hp (1,846 kW)	9.22 kg/min (1,220 lb/h)	300 g/(kW⋅h) (0.493 lb/(hp⋅h))	28.1%
Take-off (100%)	2,750 hp (2,050 kW)	9.9 kg/min (1,310 lb/h)	290 g/(kW⋅h) (0.477 lb/(hp⋅h))	29.1%

                                                  

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)

Power (kW)	Year	Engine type	Application	SFC (lb/(hp⋅h))	SFC (g/(kW⋅h))	Energy efficiency
93	1942	Lycoming O-235 piston, gasoline	General aviation	0.43	262[1]	31.4%
63	1991	GM Saturn I4 engine, gasoline	Saturn S-Seriescars	0.411	250[2]	32.5%
150	2011	Ford EcoBoost gasoline, turbo	Ford cars	0.403	245[3]	33.5%
1,305	1973	General Electric CT7 turboprop	Let L-610G airliner	0.413	251[4]	33.6%
300	1961	Lycoming IO-720 piston, gasoline	General aviation	0.4	243[5]	34.2%
2,000	1945	Wright R-3350 Duplex-Cyclone gasoline, turbo-compound	Bombers, airliners	0.380	231[6]	35.5%
57	2003	Toyota 1NZ-FXE, gasoline	Toyota Prius car	0.370	225[7]	36.4%
550	1931	Junkers Jumo 204 two-stroke diesel, turbo	Bombers, airliners	0.347	211[8]	40%
36,000	2002	Rolls-Royce Marine Trent turboshaft	Combat ships	0.340	207[9]	40.7%
2,340	1949	Napier Nomad Diesel-compound	planned (aircraft intended)	0.340	207[10]	40.7%
165	2000	Volkswagen 3.3 V8 TDI	Audi A8 car	0.337	205[11]	41.1%
2,013	1940	Klöckner-Humboldt-Deutz DZ 710 Diesel two stroke	none (aircraft intended)	0.330	201[12]	41.9%
42,428	1993	General Electric LM6000 turboshaft	Ship, electricity	0.329	200.1[13]	42.1%
130	2007	BMW N47 2L turbodiesel	BMW cars	0.326	198[14]	42.6%
88	1990	Audi 2.5L TDI	Audi 100 car	0.326	198[15]	42.6%
3,600		MAN Diesel 6L32/44CR four-stroke	Ship, electricity	0.283	172[16]	49%
4,200	2015	Wärtsilä W31 four-stroke	Ship, electricity	0.271	165[17]	51.1%
34,320	1998	Wärtsilä-Sulzer RTA96-C two-stroke	Ship, electricity	0.263	160[18]	52.7%
27,060		MAN Diesel S80ME-C9.4-TII two-stroke	Ship, electricity	0.254	154.5[19]	54.6%
34,350		MAN Diesel 12G95ME-C9 two-stroke	Ship	0.254	154.5[20]	54.6%
605,000	2016	General Electric 9HA combined cycle gas turbine	electricity generation	0.223	135.5 (eq.)	62.2%[21]

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) :

2,050 kW Pratt & Whitney Canada PW127 turboprop (1996)^[22]

Mode	Power	fuel flow	SFC	Energy efficiency
Nominal idle (7%)	192 hp (143 kW)	3.06 kg/min (405 lb/h)	1,282 g/(kW⋅h) (2.108 lb/(hp⋅h))	6.6%
Approach (30%)	825 hp (615 kW)	5.15 kg/min (681 lb/h)	502 g/(kW⋅h) (0.825 lb/(hp⋅h))	16.8%
Max cruise (78%)	2,132 hp (1,590 kW)	8.28 kg/min (1,095 lb/h)	312 g/(kW⋅h) (0.513 lb/(hp⋅h))	27%
Max climb (80%)	2,192 hp (1,635 kW)	8.38 kg/min (1,108 lb/h)	308 g/(kW⋅h) (0.506 lb/(hp⋅h))	27.4%
Max contin. (90%)	2,475 hp (1,846 kW)	9.22 kg/min (1,220 lb/h)	300 g/(kW⋅h) (0.493 lb/(hp⋅h))	28.1%
Take-off (100%)	2,750 hp (2,050 kW)	9.9 kg/min (1,310 lb/h)	290 g/(kW⋅h) (0.477 lb/(hp⋅h))	29.1%

                                                  

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 

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.