Rate of climb

When we consider rate of climb we are primarily concerned with increasing the potential energy of the aircraft as quickly as possible, and we will assume that we do not wish to change the forward speed at the same time so that the kinetic energy remains unaltered in the steady climb (Fig. 7.16).

Horizontal velocity

Rate of increase in potential energy
climb velocity x aircraft weight

Fig. 7.16 Rate of climb

Increased potential energy must be provided by excess engine power over that required for level flight

If we have a piston-engined aircraft, the required operating conditions are now quite clear. All we need to do is to make the difference between the power produced by the engine and the power required to overcome the drag as large as possible. This will provide the largest possible excess power to increase the aircraft potential energy at the highest possible rate (Fig. 7.17).

If we make the simplifying assumption that the engine power is constant, then we should operate at the forward speed corresponding to the minimum required power – the same speed that we found was required for maximum endurance in level flight.

For a turbo-jet engine, the power increases with speed and so we shall, once more need to compromise between the engine and airframe requirements. To get the maximum excess power we must operate at a speed in excess of the minimum required power speed (Fig. 7.18).

RATE OF CLIMB 211

Speed

Fig. 7.18 Maximum climb rate – jet engine

Because engine power increases with speed, maximum power for climb is obtained at a speed in excess of minimum power required speed and minimum drag speed