Aircraft Performance

Aircraft performance is the branch of aerospace engineering that allows us to utilise relationships between thrust, drag, lift, and weight, such that we can determine allowable aircraft masses, fuel requirements, range limitations, and steady manoeuvre calculations.

By the end of this Chapter, you should be able to:

• Describe qualitatively the difference between indicated, calibrated, equivalent, and true airspeeds.

• Perform numerical conversion between those same airspeeds.

• Determine an aircraft’s stall speed and its variation with altitude.

• Plot the variation of thrust and power required, and their variation with altitude and aircraft weight.

• Understand the concept of speed stability in cruise, and demonstrate why flight below \(V_{md}\) is unstable.

• Determine maximum and minimum flight speeds, and the variation with altitude - for both turbojet, and propeller-driven aircraft.

• Define an aircraft’s absolute ceiling.

• Derive, from first principles, the Breguet range equation - and, using either the thrust-restricted, or the thrust-unrestricted cruise-climb technique, determine the Equivalent Safe Range for a given aircraft.

• Determine the conditions for smallest glide angle, and minimum sink rate in unpowered descent.

• Determine the conditions for maximum climb angle, and maximum climb rate, for both turbojet and propeller-driven aircraft.

• Perform calculations for minimum turn radius, and maximum turn rate, determining whether turn performance is limited by stall, load factor, or thrust/power.

• Define an aircraft’s load factor, an understand a manoeuvre flight envelope (\(V-n\) diagram).

• Draw a \(V-n\) diagram given load factors, and some means to define aircraft stall and dive speed.

These calculations are obviously dependent on the aircraft upon which we are working, and since 1903, aircraft have changed a tremendous amount:

	Wright Flyer	Boeing 747-400
Empty Weight	274kg	180,985kg
Wingspan	12.3m	64.4m
Max. Range	0.26km	13,445km
Max. Speed	16km/h	912km/h
Powerplant	Piston x1	Turbofan x 4
Available Thrust	~120lbf	63,000 lbf
Passengers	1	524

But the basic relationships are valid for all aircraft, and they will be developed in this course.