En Route PerformanceCPL Performance

Aim

To introduce the performance aspects associated with the climb, cruise and descent segments of flight

Objectives1. State the factors effecting climb performance2. Calculate the Climb Gradient3. Calculate the maximum Rate of Climb (or descent)

required to avoid controlled airspace 4. State the factors effecting cruise performance5. Define Range and state how to fly for maximum

range6. Define Endurance and state how to fly for maximum

endurance

1. Climb Performance

We can describe climb performance as either Rate of Climb or Angle of Climb

Rate of Climb (RoC): 

Altitude gained over time. Expressed in feet per minute (fpm).

Angle of Climb (AoC): 

Altitude gained over distance. Expressed as an angle.

1. Climb Performance

Types of Climbs

Whenever we fly we generally aim for a particular performance

For the climb we can choose from:• Best Rate of Climb (Vy)• Best Angle of Climb (Vx)• Cruise Climb

1. Climb Performance

Cruise Climb

Best Rate of Climb (Vy)Best Angle of Climb (Vx)Cruise Climb

1. Climb Performance

Factor Effect on RoC Effect on AoC

 Power

 

Altitude 

Weight 

Flap 

Wind

(Headwind)N/A

(Extended)

(Tailwind)

During your BAK studies we discussed factors effecting climb performance. A summary can be found below.

1. Climb Performance

Climb Planning

In the POH for each aircraft you will find details about climb performance.This will include the time fuel and distance required to climb to each altitude It may be in the form or a table or a graph

1. Climb Performance

A measure of climb performance is the climb gradient which can be achieved

Climb gradient is a measure of the height gained per distance travelled expressed as a percentage

ie, Climb Gradient = %

2. Climb Gradient

Height Gained500 ft

Distance Travelled 8000 ft

The climb gradient can be calculated as follows:

Climb Gradient = = 0.063

That is, for each 1 ft travelled we climb 0.063ft

To Convert to percentage multiply by 1000.063 x 100 = 6.3%

For example, you climb 500ft while covering a distance of 8,000ft. What is your climb gradient?

2. Climb Gradient

We can also work out our climb gradient based on our current Rate of Climb and Groundspeed

Climb Gradient =

2. Climb Gradient

Climb Gradient =

= = 6.5 %

650fpm

TAS +- Wind = Groundspeed110-10=100kts

For example, you are climbing at 650fpm with a TAS of 110kts and a 10kt tailwind. What is your climb gradient?

2. Climb Gradient

When climbing (or descending) you may have a requirement to remain in a certain class of airspaceDue to the structure of controlled airspace there are “steps” which you must be aware of

CLASS C

25nm

35nm

50nm

3000

4000

6000

CLASS G

3. Avoiding CTA

When calculating a climb to remain outside of CTA the first thing to do is check if there is a limiting step A limiting step has the shallowest profile; least height gain for a given distanceThis is important as you may have to lower your climb rate or delay the climb.

CTA

25nm

35nm

50nm

Critical

Non critical

3000

4000

6000

3. Avoiding CTA

CTA

25nm

35nm

50nm

Critical

Non critical

10nm/1000 step 15nm/2000 step3000

4000

6000

Limiting Steps: we can see that the 10/1000 step profile is has a shallower profile than 15/2000, therefore if you wish to climb at a constant RoC you will need to determine a RoC which will not infringe this limiting step

Required RoC = x

3. Avoiding CTA

CTA

25nm

35nm

50nm

Critical

Non critical

10nm/1000 step 15nm/2000 step3000

4000

6000

3. Avoiding CTA

Required RoC = x

= x = 200fpm

For example, the steps are as pictured below and you have a groundspeed of 120kts. What is the maximum rate of climb you can maintain without entering CTA?

The method is the same for calculating a descent profile to remain inside or outside of airspaceWhen planning our descent we must also calculate where we will be starting the descentThe formula we use for this is:

Distance on Descent = x

3. Avoiding CTA

CTA35nm

50nm

Critical Non critical

15nm/2000 step

3000

4000

6000

8000

25nm

10nm/1000 step

For example, the steps are as pictured above, you are cruising at 5500ft and you have a groundspeed of 130kts. You are planning to descent to 2000ft. What is the minimum rate of descent you require without entering CTA?

Required RoD = x

= x = 216fpm

3. Avoiding CTA

Cruise performance data is presented in either tabular or graphical format. Both show fuel flow and TAS for conditions of engine RPM and percentage power, against cruise level and temperatureCruise performance assumes correct leaning of the mixture

PRESSURE ALTITUDE(FT) RPM

20C - STANDARD TEMPERATURE STANDARD TEMPERATURE 20C + STANDARD TEMPERATURE

%BHP KTAS GPH %BHP KTAS GPH %BHP KTAS GPH6000 2600 --- --- --- 77 119 8.6 72 118 8.1

2500 73 114 8.2 69 113 7.8 66 112 7.4 2400 66 108 7.4 63 107 7 60 106 6.7 2300 60 103 6.7 57 101 6.4 55 99 6.2 2200 54 96 6.1 52 95 5.9 50 92 5.8 2100 49 90 5.7 47 88 5.5 46 86 5.5

8000 2650 --- --- --- 77 121 8.6 73 120 8.1 2600 77 119 8.7 73 118 8.2 69 117 7.8 2500 70 113 7.8 66 112 7.4 63 111 7.1 2400 63 108 7.1 60 106 6.7 58 104 6.5 2300 57 101 6.4 55 100 6.2 53 97 6 2200 52 95 6 50 93 5.8 49 91 5.7

4. Cruise Performance

PRESSURE ALTITUDE(FT) RPM

-20C STANDARD TEMPERATURE STANDARD TEMPERATURE 20C +STANDARD TEMPERATURE

%BHP KTAS GPH %BHP KTAS GPH %BHP KTAS GPH6000 2600 --- --- --- 77 119 8.6 72 118 8.1

2500 73 114 8.2 69 113 7.8 66 112 7.4 2400 66 108 7.4 63 107 7 60 106 6.7 2300 60 103 6.7 57 101 6.4 55 99 6.2 2200 54 96 6.1 52 95 5.9 50 92 5.8 2100 49 90 5.7 47 88 5.5 46 86 5.5

8000 2650 --- --- --- 77 121 8.6 73 120 8.1 2600 77 119 8.7 73 118 8.2 69 117 7.8 2500 70 113 7.8 66 112 7.4 63 111 7.1 2400 63 108 7.1 60 106 6.7 58 104 6.5 2300 57 101 6.4 55 100 6.2 53 97 6 2200 52 95 6 50 93 5.8 49 91 5.7

To use the tables find the desired % power for the intended cruise level then read off the TAS, fuel flow and RPM

For example, if the planned altitude is 6000ft on an ISA day. What RPM should we use and what TAS and fuel flow should we expect if we want 65% power?

4. Cruise Performance

When considering cruise performance we can elect to cruise in a number of different configurations based on our specific requirementsThese requirements may be:• Travel the furthest distance for the fuel on board• Stay in the air for the longest possible time• Operate the aircraft at the lowest cost• Get to the destination at in the minimum amount of time

4. Cruise Performance

Range

We may be given the requirement to “travel the furthest distance for a given amount of fuel”This is known as flying for Maximum Range

Flying for maximum range is often a requirement if we need to carry the maximum amount of payload

5. Range

Range

To fly for Maximum range we require the best ratio of TAS to fuel flowFor our aircraft the fuel flow relates directly to the PWR required

Pow

er

Velocity (TAS)

Pwr Reqd.

5. Range

Range

To find the best ratio of TAS to fuel flow (in nil wind) we plot a tangent to the PWR required graph which intersects at the origin

Pow

er

Velocity (TAS)

Pwr Reqd.

5. Range

Range

If we have any wind we must take this into accountTo do this we move the point where we draw the tangent from to a location on the graph where the groundspeed is 0Eg, if we have a 20kt headwind:

Pow

er

Velocity (TAS)

Pwr Reqd.

20kt

5. Range

Range

Eg, if we have a 20kt tailwind:P

ow

er

Velocity (TAS)

Pwr Reqd.

20kt

5. Range

Range

Comparison of wind conditions on rangeP

ow

er

Velocity (TAS)

Pwr Reqd.

20kt 20kt

5. Range

Nil Wind

HeadwindTailwind

Ground Nautical Miles per gallon =

RangeIn practice we do not have a PWR required graph for our aeroplane so we must derive this information from the cruise performance tablesWe need to determine the maximum distance we can travel for the minimum fuelIf we divide the groundspeed by fuel flow we can determine our Ground Nautical Miles per gallon of fuel

5. Range

PRESSURE ALTITUDE(FT) RPM

-20C STANDARD TEMPERATURE STANDARD TEMPERATURE

%BHP KTAS GPH %BHP KTAS GPH GNMPG6000 2600 --- --- --- 77 119 8.6 13.83721

2500 73 114 8.2 69 113 7.8 14.48718 2400 66 108 7.4 63 107 7 15.28571 2300 60 103 6.7 57 101 6.4 15.78125 2200 54 96 6.1 52 95 5.9 16.10169 2100 49 90 5.7 47 88 5.5 16

8000 2650 --- --- --- 77 121 8.6 14.06977 2600 77 119 8.7 73 118 8.2 14.39024 2500 70 113 7.8 66 112 7.4 15.13514 2400 63 108 7.1 60 106 6.7 15.8209 2300 57 101 6.4 55 100 6.2 16.12903 2200 52 95 6 50 93 5.8 16.03448

Green Line shows best range in nil wind in ISA conditionsOccurs at higher altitude and 2300 RPM for 8000ft

5. RangeRangeHere is a cruise performance chart for a typical C172For nil wind conditions the GNMPG has been calculated

Endurance

If we have a requirement to “stay in the air for the longest time”This is known as flying for Maximum Endurance

Flying for maximum endurance is often a requirement if we need to hold for weather

6. Endurance

Endurance

To fly for Maximum Endurance we require the minimum fuel flowFor our aircraft the fuel flow relates directly to the PWR required

Pow

er

Velocity (TAS)

Pwr Reqd.

6. Endurance

Endurance

When PWR required is at a minimum fuel flow is at a minimum therefore that is the PWR required for maximum range

Pow

er

Velocity (TAS)

Pwr Reqd.

6. Endurance

Endurance

Wind has no significant effect on endurance as the distanced covered is not important

When flying for maximum endurance you should fly at the minimum altitude (safely!) as PWR required increases with an increase in altitude

The speed for maximum range corresponds to Vy

6. Endurance