Lecture 6: CRUISE

PERFORMANCEAIRCRAFT WEIGHT &

PERFORMANCE

Introduction To Cruise• The cruise phase of flight starts after aircraft has leveled

off from the climb and it ends when the descent for landing is initiated by the pilot.

• In short word, cruise is the phase of flight that falls between climb and descent.

ClimbCruise / En-route

DescendApproach & LandingTake-off

Cruise

• The cruise phase involves level flight most of the time and very few level changes.

• The largest percentages of trip time and trip fuel are consumed typically in cruise phase.

The factors that affect the total time and fuel burn are:• Speed selection and• Altitude selection.

Cruise

There are three options for cruise which are:• Best range cruise• Best speed cruise• Best endurance cruise

Range

• Range refer to distance aircraft can fly on a given amount of fuel.

• The maximum range means to fly the greatest possible distance with available fuel.

Specific range

Specific Range (SR) express the range performance of the aircraft at a moment in time.

Flow Fuel

Knots

Fuel/hour

NM/hour Range Specific

Endurance

• Endurance is the time that aircraft can remain airborne with the fuel available.

• In other words, how long an aircraft is able to remain airborne on a given amount of fuel.

• It will be greatest when the fuel is used at the lowest possible rate, that is, the fuel flow is minimum.

Specific range

Specific Endurance will have units of time/units of fuel.

Flow Fuel

1

Fuel/hour

hours/hourFlight Endurance Specific

Short Range Jetliner

Characteristics Boeing 737-300 Airbus 320

Passengers (pax) 149 150

Maximum Fuel 20,000L 22000L

Maximum Range 4,180 km 4,815 to 5,555 km

Cruise Speed 910km/hr 845 km/hr

Service Ceiling 40,000ft 39,000 ft

Medium Range Jetliner

Characteristics Boeing 767-300 Airbus 330

Passengers (pax) 218 in three classes

253 in three classes

Maximum Fuel 90,770 L 139,090 L

Maximum Range 11,320 km 11,850 km

Cruise Speed 850 km/h 880 km/h

Service Ceiling 39,000 ft 39,370 ft

Long-Range Jetliner

Characteristics Boeing 747-400 Airbus 380

Passengers (pax) 416/524 525 (max:800)

Maximum Fuel 216 800 L 310 000L

Maximum Range 13 450km 15 200km

Cruise Speed at FL35

910km/hr 900km/hr

Service Ceiling 41,000 ft 42,980 ft

Factors Affecting Range & Endurance

• There are several factors will have effect on the maximum possible range which are aircraft’s mass and speed, density altitude and wind.

Aircraft mass

• Increased aircraft mass, increases the drag.• This requires greater thrust to balance the drag, which

increases the fuel flow and reduces the specific range.• Approximately 10% increase in mass will require 10%

increase in thrust and fuel flow and 5% decrease in range.• Since fuel flow increases, endurance also decreases.

Air density (altitude)

Range increasing with altitude• Increasing altitude, decreasing air density• As the air became less dense, so drag is less.• Less drag means that aircraft can fly faster.• And engine also burn less fuel to create thrust • Thus fuel flow decrease and range increase.

If drag keeps decreasing as density decreases and the aircraft can fly faster and faster, then why don't planes fly at even higher and higher altitudes until

the density, and the drag, become zero?

Maximum Altitude (Service Ceiling)

• Engine performance that limits the maximum altitude that an aircraft can reach.

• Engine process becomes more difficult as the air density decreases .

• Compressor less efficient and the burning of fuel and air is also impossible.

• When this occurs, the engine will "flame out" and the plane falls into a dive until density increases enough for the engine to be restarted.

Altitude

• The optimum altitude for best range increases as weight decreases.

• The procedure to give maximum range would therefore be to allow the aircraft to climb as the weight decreases during the flight.

• This is achieved with few step climbs during the cruise phase of the flight.

Speed Selection

1. High-speed Cruise.2. Best range speed.3. Low-Speed cruise.

Speed

High-speed Cruise • Means Cruise at the maximum indicated airspeed

(IAS).• Provides the quickest en-route time, but sacrifices

fuel efficiency. • Because, when flying at higher speeds, drag

increases, thus the fuel flow also increases.• Not normally used by airlines.

.

Speed

Best range speed is the most efficient speed in terms of distance and fuel usage. Also known Long-range Cruise speed.

• It is the speed that will provide the,

a) Furthest distance traveled for a given amount of fuel burned.

b) Minimum fuel burned for a given cruise distance.

• Typical cruising speed for long-distance commercial passenger flights is 878-926 km/h

Speed

Low-Speed cruise. • This speed reduce the drag and the fuel flow, but

they also reduce the distance traveled per time, and therefore reduce the range

Performance Speed

• TAS (True Airspeed) – aircraft speed in relation to the air mass in which it is flying.

• IAS (Indicated Airspeed) – aircraft speed as indicated on the ASI (Airspeed Indicator).

• CAS (Calibrated Airspeed) – IAS corrected for installation and instrument errors

Wind

• The best range will be reduced in a headwind condition.

• The opposite occurs in a tailwind condition, the best range will be increased.