5. climb

5. CLIMB5. CLIMB

Performance JAR 25Performance JAR 25

CLIMBCLIMB

Engine ratings

Climb analysis

Climb speeds

• Maximum angle

• Maximum rate of climb

• Constant IAS

• Constant IAS/MACH

• Optimum climb speed

Factors affecting climb

Operative ceilings

Step climb

ENGINE RATINGSENGINE RATINGS

Engines are certified to deliver standard thrusts depending upon atmospheric conditions:

Maximum Takeoff Thrust: This is the maximum thrust that the engine can deliver for 5 minutes at standard sea level atmosphere.

MCT - Maximum Continuous Thrust: This is the maximum thrust that the engine can deliver with no time limit.

MCL - Maximum Climb Thrust: This is the maximum thrust certified for en-route climb; sometimes it is the same as MCT. (not certified)

MCR - Maximum Cruise Thrust: This is the thrust allowable for unlimited flight duration at the design altitude. (not certified)

CLIMB ANALYSISCLIMB ANALYSIS

φ

φ

T

D

L

W

Forces involved in climb


From the previous graph it can be deduced that:

sin φ = (T – D) / W

In addition, the rate of climb (R/C) is the vertical component of the True Airspeed of the aircraft, so it is affected by the climb angle:

R/C = TAS · sin φ

φR/C

TAS


Combining the two previous formulas we obtain:

Therefore, the rate of climb will increase then with: a higher TAS, a higher excess of thrust and with a lower weight.

W

D - T · TAS R/C


TAS

R/C Vx : Best angle speed

Vy : Best R/C speed

VyVx


TAS

DRAG

DMIN

THRUST (JET)

POWER (PISTON)


TAS

POWER

VxP

JET

PISTON

VyP VxJ VyJ


In general terms, it can be concluded that:

Vy is always greater than Vx.

As the altitude increases, Vx increases and Vy decreases (IAS).

A higher flap setting will decrease both speeds.

Vx (piston) is close to Vs, while Vx (jet) is close to the L/DMAX speed. Therefore, Vx is greater in jet aircraft than in piston-powered aircraft.

Vy (jet) is also greater than Vy (piston).


Climb position

A320 Thrust levers

CLIMB SPEEDSCLIMB SPEEDS

CLIMB AT MAXIMUM ANGLE SPEED

Climbing at maximum angle speed (Vx) enables a given altitude to be reached over the SHORTEST DISTANCE.

CLIMB AT MAXIMUM R/C SPEED

Climbing at maximum R/C speed (Vy) enables a given altitude to be reached within the SHORTEST TIME.


CLIMB AT CONSTANT IAS

Climbing at a constant IAS would simplify the operation, but it have some disadvantages. As the aircraft climbs TAS increases, drag increases (due to compressibility effects) and therefore R/C decreases. This results in a long and inefficient climb.

% Climb capability FL330

IAS

FL290

FL250

FL200

100

90

80

70

60

50


CLIMB AT CONSTANT IAS/MACH

Since it is impractical to climb at decreasing IAS speeds, the constant IAS/M climb is usually performed, simplifying the operation:

The climb is performed at a constant IAS until a certain MACH is reached. Then the climb is continued keeping this MACH number.

For instance, a climb profile for an A320 is:

250kt / 300kt / M.78

Below FL100(due to ATC) Above FL100

until reaching M.78

(crossover altitude)

Until the end of climb


In the first part of the climb (constant IAS), TAS is increased as the aircraft climbs.

In the second part of the climb (constant MACH), TAS is decreased as the aircraft climbs.

TAS

Theoretical R/C

TROPOPAUSE

25%

9%

30%

R/C

PA PA

Real R/C


OPTIMUM CLIMB SPEED

The optimum climb speed is the result of taking into account all the factors that affect climb in terms of efficiency and operative costs.

It is usually higher than the best R/C speed (Vy).

Factors that affect this speed:

Weight: Optimum climb speed increases with more weight.

Wind: It barely affects optimum climb speed (+5 kt / 100 kt HW).

Fuel price: If it increases the optimum climb speed will decrease.

Maintenance and crew costs: If they increase the optimum climb speed will also increase.

OAT and final cruise level do not affect the optimum climb speed.

SOME FACTORS AFFECTING CLIMBSOME FACTORS AFFECTING CLIMB

Climb gradient ↓

PRESSURE ALTITUDE ↑

Rate of climb ↓

Climb gradient ↓

TEMPERATURE ↑

Rate of climb ↓

Climb gradient ↓

WEIGHT ↑

Rate of climb ↓

OPERATIVE CEILINGSOPERATIVE CEILINGS

ABSOLUTE OR AERODYNAMIC CEILING

The aircraft cannot climb beyond the aerodynamic ceiling, which is determined by the aerodynamic properties of the aircraft. This situation of R/C = 0 fpm (impractical) could only be established at one speed (Vx equals Vy at this point).

In this case, the aircraft reaches a situation in which a higher speed would produce a high-speed stall, and a lower speed would produce a low-speed stall. This situation is known as “coffin corner”.

PROPULSION CEILING

Is that altitude that the available thrust provided by the engines permits to reach. It is usually lower than the aerodynamic ceiling.


SERVICE CEILING

Since reaching the absolute ceiling is impossible in practice, the service ceiling is considered. At this altitude the aircraft has a maximum rate of climb of 100 fpm.

DESIGN CEILING

It is the maximum altitude that the aircraft can reach taking into account the structural limits (maximum differential pressure, etc).


OTHER CEILINGS

Other ceilings have been established as a reference. To sum up, we have four ceilings based upon the maximum rate of climb:

Absolute ceiling: R/CMAX = 0 fpm

Service ceiling: R/CMAX = 100 fpm

Cruise ceiling: R/CMAX = 300 fpm

Combat ceiling: R/CMAX = 500 fpm

STEP CLIMBSTEP CLIMB

The optimum cruise altitude is increased as the aircraft loses weight (due to fuel consumption). Since it is impractical to perform a continuous and slow climb during the cruise phase, a solution known as step climb has been established.

Step climb is only used in long haul flights, and consists of climbing from time to time at a higher level in order to keep the aircraft close to the optimum altitude.

Optimum altitude

5. climb

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