(e)Gradient, Gross and Net Flight Paths.
Gradient of climb means the ratio of height gained over a horizontal distance travelled, expressed as a percentage
e.g. If the height gained is 500ft over a horizontal distance of 8000ft:
climb gradient = height gained/distance travelled = 500/8000 = 0.063
This means that for each foot travelled horizontally you climb 0.063ft
This can be converted to a percentage my multiplying by 100/1 so that:
Climb gradient = 500/8000 X 100/1 = 6.3%
Gross and Net Flight Paths
Gross flight path means the flight path it is assumed the aeroplane will follow then flown in a particular configuration in accordance with specified procedure.
Net flight path means the gross flight path reduced by specified margins. These margins, which will be specified in the rules make allowances for the reduced performance that could be expected in a real emergency situation in unfavourable conditions (i.e. severe turbulence)
(b) Takeoff Distance Available
Takeoff Distance Available (TODA) is defined as the length of the takeoff run available plus the length of any clearway
Clearway is defined as an area in which an aeroplane may make a portion of its initial climb to a specified height
(c)Takeoff Run Available
Takeoff Run Available (TORA) means the length of the runway declared by the aerodrome operator as available and suitable for the ground run of an aeroplane taking off
(d)Accelerate-Stop Distance Available
The Accelerate-Stop Distance Available (ASDA) means the distance specified by the appropriate authority as being the effective length available for use by an aeroplane executing an abandoned (or rejected) takeoff. The effective length includes any stop-way.
A stop-way is a defined as an area on the ground in which an aircraft can be stopped in the case of an abandoned takeoff. A stop-way must be included within the strip.
The longer the declared accelerate stop distance ..
- The higher the speed beyond which an aircraft can be bought to a halt in the case of an abandoned takeoff; and
- The greater the allowable takeoff weight
A stop-way does not necessarily have to be a prepared sealed or level grass surface, but a reasonably flat area suitable for braking and bringing an aircraft to a stop in an emergency.
The Accelerate-Stop Distance Available (ASDA) is promulgated as part of the runway information for appropriate aerodromes. The accelerate-stop distance required (ASDR) under varying conditions can be calculated from tables or graphs in the aircraft flight manual.
(a) Takeoff distance required (TODR), takeoff safety speed and screen height (or barrier)
Takeoff distance required (TODR) is the distance required to takeoff from a standing start at maximum takeoff power and reach a screen height (usually 50 feet) above the runway at the takeoff safety speed.
Takeoff safety speed (TOSS) is a speed that gives an adequate safety margin about the stalling speed. It must not be more than 1.2Vs in the takeoff configuration. TOSS will normally be incorporated in the takeoff climb speed given in the flight manual for the type.
Screen height The screen height for light aircraft is 50 feet, but for large aircraft and for commuter operations it may be 35 feet (or lower in some circumstances)
22.32.2
Define:
(a) Take-off distance required (TODR), take-off safety speed, and screen height (or barrier);
(b) Take-off distance available (TODA) and clearway;
(c) Take-off run available (TORA);
(d) Accelerate-stop distance available (ASDA) and stopway;
(e) Gradient and gross and net flight paths;
(f) Landing distance available (LDA), landing distance required (LDR) and landing threshold;
(g) Dry, wet, and contaminated (in relation to runway surface);
(h) Drift down.
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
It can be easily inferred from this graph that at 14,000 feet a range of 1018 nautical miles is possible. This gives us the maximum range possible in that configuration. It assumes maximum weight so a lighter aircraft will go further.
Note: Graph does not take into account effect of wind
22.30.6
Explain the airframe and engine considerations of flying for range (piston engine).
Airframe Considerations (piston engine aircraft)
Maximum airframe efficiency and the best range speed occurs at the speed for minimum drag maximum L/D ratio.
Effect of Altitude
At a given aircraft weight the IAS for minimum drag/Maximum L/D ratio and therefore best range speed remains constant with altitude. As altitude increases both TAS and power required at best range speed increase in the same proportion. The TAS/power ratio remains unchanged and therefore from the airframe point of view, altitude has no effect on the best range IAS but the best range TAS increases with altitude.
Effect of Weight
An increase in weight means that the angle of attack for best L/D ratio is reached at a higher IAS; the best speed for range is therefore increased. While this increase in IAS means TAS will be higher, drag has also increased and the power required has increased in proportion to the gain in TAS (power=drag X TAS) Range is therefore reduced as weight increases
Effect of Wind Velocity
A headwind component will decrease the range, while a tailwind will increase it. To obtain the maximum ground range we must fly at the speed which provides the highest ratio of groundspeed/power (i.e. the highest groundspeed for the least amount of power being used).
The optimum speed in headwind/tailwind conditions can be found by locating groundspeed on the PR/TAS graph and finding the speed (TAS) to fly below the redrawn tangent to the PR curve.
Engine Considerations
To fly for best range the aircraft should be flown for the maximum product of airframe efficiency (TAS/power) and engine efficiency (1/SFC). Airframe considerations mean that the aircraft should be flown at a recommended range speed (RRS) that is about 10% higher than minimum drag speed. To maintain that speed a certain amount of power must be used. If maximum range is to be achieved the engine must operate in such a way that this power is produced most efficiently. Therefore minimum specific fuel consumption is required.
Factors Affecting SFC
RPM and Manifold Pressure (MAP)
To obtain the power required a number of combinations of rpm/manifold pressure (MAP) may be used. The lower SFC is obtained by using the lowest rpm with the highest MAP (within allowable limits)
- Low RPM Use of low rpm reduces friction losses and improves volumetric efficiency. There will normally be a limit to the minimum useable fuel flow because a richer mixture is required at very low rpm to prevent rough running and some engine driven services (generator/alternator) may not operate properly
- High MAP Maximum MAP for the rpm being used is limited by the cylinder pressures above which a rich mixture must be used for cooling and the prevention of detonation.
Mixture Strength
Lean mixtures and the power setting that permits them are essential to achieving a low SFC
Altitude
The power required is produced more efficiently if the aircraft is at full throttle height (FTH) for the setting being used. The reason for this is that the engine breathes better and the power loss through friction in the induction and exhaust systems are reduced. Altitude also give the advantage of colder intake air which increases the temperature rise within the engine and improves thermal efficiency
Temperature
Cold air at a given altitude improves SFC since the power available can be achieved at a lower rpm and the power required by the airframe reduced (TAS reduced)
Carburettor Air Intake
Where the application of carburettor heat is necessary to prevent ice formation, the SFC will deteriorate. High carburettor intake temperatures reduce the density of the air intake, giving a richer mixture and reduced thermal efficiency. Ram air is also not generally available with carburettor heat selected and this lowers FTH.
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:
- Actual takeoff weight, lesser weight means less power required
- Wind direction and speed (velocity), a tailwind favors range
- Air temperature, the warmer the air (lower density) the more power required
- Altitude, higher is better for range as it increases TAS
- Aircraft configuration, keeping drag as low as possible
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