Lecture 5: Climb

PERFORMANCEAIRCRAFT WEIGHT &

PERFORMANCE

Introduction

• One of the most important aspects of aircraft performance is the ability to climb.

• CLIMB starts after take off and it ends when aircraft levels off at the cruising level.

ClimbCruise / En-route

DescendApproach &

LandingTake-off

Phases of flight

Introduction

• An aircraft can climb only if it can produce excess thrust (thrust minus drag).

• This excess thrust is needed to overcome drag.• For example, if an aircraft is producing 1,000

pounds of thrust and has 700 pounds of drag, it would have 300 pounds of excess thrust available.

Climb Gradient/Angle of climb

• For the first portion of the climb it is more important to consider the climb gradient or angle of climb.

• Why ??

Climb gradient or angle of climb is important to ensure aircraft overfly the obstacles in the departure area at a safe altitude.It is defined as minimum obstacle clearance

Climb Gradient

• The climb gradient by definition is the ratio of height gained to the horizontal distance traveled by aircraft.

• Basically, climb gradient depends on the difference between the thrust and drag (the excess thrust) and the mass of the aircraft.

• Factors that affect these forces will have affect on the climb gradient.

Climb gradient = (THRUST - DRAG) / WEIGHT

EXCESS THRUST

Angle of climb

• The angle of climb is the angle between height gained to the horizontal distance traveled by aircraft during climb.

WEIGHT / DRAG) - (THRUSTsin 1, climb of Angle

Climb gradient = tan() = sin() = (THRUST - DRAG) / WEIGHT

Climb Gradient/Angle of Climb

WEIGHT / DRAG) - (THRUSTsin 1, climb of Angle

Rate of Climb (ROC).

• When the obstacles are over flown it is the important to consider the rate of climb.

• Rate of climb is the vertical component of the speed, , expressed in feet per minute. It depends on the airspeed (V) and the angle of climb or climb gradient.

• Rate of climb = V x sin () = V x Climb gradient = V x (Thrust – Drag) / Weight

• Best rate of climb is important to ensure aircraft reach required altitude in the minimum time.

Three types of climb

NORMAL CLIMB

• Normal climb is performed at an airspeed recommended by the airplane manufacturer.

• Normal climb speed is generally somewhat higher than the airplane’s best rate of climb.

• The additional airspeed provides better engine cooling, easier control, and better visibility over the nose. Normal climb is sometimes referred to as “cruise climb.”

• Complex or high performance airplanes may have a specified cruise climb in addition to normal climb.

Two Airspeed during climb

• There are two airspeeds relating to climb performance which are, Vx and Vy.a) Vx is the indicated airspeed for best angle of climb.

b) Vy is the indicated airspeed for best rate of climb.

• Best Angle of Climb Speed (Vx)

• Gain maximum altitude in shortest distance

• Best Rate of Climb Speed (VY )

• Gain maximum altitude in shortest time• Best angle-of climb airspeed (Vx) is considerably lower

than best rate of climb (VY ).

Best Angle of Climb Speed (Vx)

• Best angle of climb airspeed for an airplane is the speed at which the maximum excess thrust is available over that required for level flight.

• The best angle of climb will result in a steeper climb path, although the airplane will take longer to reach the same altitude than it would at best rate of climb.

• The best angle of climb, therefore, is used in clearing obstacles after takeoff.

Best Rate of Climb Speed (VY )

• Best rate of climb (VY) is performed at an airspeed where the most excess power is available over that required for level flight.

• This condition of climb will produce the most gain in altitude in the least amount of time (maximum rate of climb in feet per minute).

• To calculate an aircraft's climb rate in feet per minute, multiply the constant 33,000 by the excess thrust horsepower divided by weight.

• The rate of climb (ROC) can be found by the simple formula:

000'33Power Excess

ROC Weight

Rate of climb = V x (THRUST - DRAG) / WEIGHT

Best V x or Best VY

• For each climb the pilot must determine whether it is more important to climb at the steepest angle (best Vx) to clear obstacles, or at the fastest rate (best Vy).

Example

• F-16 fighter aircraft, for example, according to the Lockheed Martin Corporation, climbs at 50,000 feet per minute at sea level.

An F-15 Eagle climbing and releasing flares.

Example

• The greater the excess thrust, the steeper(almost perpendicular) the possible climb.

• To perform this vertical climb, the amount of thrust created must equal the drag the aircraft is experiencing plus the entire weight of the aircraft.

• If a jet aircraft has more thrust available than the sum of weight and drag, not only could it climb straight up, it could also accelerate its airspeed while climbing

Factors Affecting the Climb performance (Climb Angle and

Rate of Climb)

Aircraft Mass

Retraction of flap and landing gear

Temperature& Air Density

Wind

Speed and Acceleration

Cabin Pressurization

SPEED AND ACCELERATION

• When the aircraft is accelerating during climb some portion of the excess thrust is required for the acceleration, so there will be less excess thrust and therefore reduce the angle of climb.

AIRCRAFT MASS

• Increased mass gives higher drag which reduces the excess thrust (the difference between the thrust and drag), and therefore reduces the climb angle for a given thrust & reduces the rate of climb.

TEMPERATURE

• The higher the air temperature, less thrust can be produced by the engines.

• Because of that the difference between the thrust and the drag during climb is smaller. Therefore the climb gradient & the rate of climb will be reduced.

AIR DENSITY

• Density Altitude (increasing altitude thus decreasing density) will reduce thrust and therefore reduce the climb angle & the rate of climb.

WIND

• In wind conditions, headwind or tailwind will have affect on the aircraft’s ground speed.

• So, a headwind will reduce the ground speed and therefore reduce the horizontal distance that an aircraft travels in comparison to the no wind conditions.

• Therefore a headwind gives increased climb angle, while a tailwind affects in opposite direction and gives reduced climb angle. Crosswind component has no effect on the climb gradient.

WIND HAS NO AFFECT ON THE RATE OF CLIMB

Retraction of flap and landing gear

• When the flap and landing gears are retracted, the drag is reduced, resulting in an increase in excess thrust, therefore the rate of climb is increased.

Cabin pressurization

• The rate of change of the cabin pressure has to be proportional to the rate of change of the atmospheric pressure (rate of climb).

• Modern aircraft operate at high altitudes and can achieve high rates of climb.

• In order to take advantage of these properties the interior of an aircraft flying at high altitude is pressurized to allow passengers and crew to function normally without any need for additional oxygen.

• Cabin pressurization systems are designed to produce conditions equivalent to those at approximately 8000 feet.

Cabin pressurization

• When the aircraft is climbing, the change of cabin pressure is proportional to the change of the ambient pressure, in order to control the structural stress on the fuselage from the inside.

• This is performed automatically by sophisticated control system.

• However, if the cabin pressure is manually controlled or in case of system degradation, care should be taken to ensure that the climb rates are safe and ensure that the structural stress is not exceeding the maximum limit.

Cabin pressurization

• The maximum rate of climb is therefore limited. • When exceeded the aircraft structure is overstressed from

inside and structural failure (explosion) is possible. • Passengers comfort is also a factor. • Usually the best comfort is achieved at rates of climb of

1500 feet per minute.

Summary

There are three climbing flight conditions:

1. Steepest climb (best angle of climb)-to clear obstacle after take-off

2. Fastest climb (best rate of climb)-to reach cruise altitude with minimum time.

3. Economical climb (less fuel consumption)

The airspeed for economical climb is lower than that for fastest climb but is much closer to the fastest climb airspeed than to the steepest climb airspeed.

Summary

Factors affecting climb performance• Greater mass reduced climb angle and rate of

climb.• Higher temperature, lower air density also

reduced climb angle and rate of climb.• Headwind condition, greater climb angle. Tailwind

reduce climb angle. Wind no effect on rate of climb.

• Quick retraction of flaps and landing gear, greater climb angle and greater speed.

Question Bank

1. An aircraft will be taking-off from a sea-level airfield, and climbing to a cruising level of FL75 (i.e. 7500ft pressure altitude). Using Fuel Time Distance Climb table & assume condition during no wind, calculate:

a) How long will the climb take (time)?

b) How much fuel used?

c) How far the climb distance?

2. Based on question 1, calculate the climb distance traveled if there is 15knot tailwind.