As an example, to use the formula for changing the velocity  of 100 pounds of mass airflow per second from 600 ft/sec to  800 ft/sec, the formula can be applied as follows: In any formula involving work, the time factor must be  considered. It is convenient to have all time factors in  equivalent units (i.e., seconds, minutes, or hours). In  calculating jet thrust, the term “pounds of air per second” is  convenient, since the second is the same unit of time used  for the force of gravity. As shown by the formula, if the mass airflow per second and  the difference in the velocity of the air from the intake to the  exhaust are known, it is easy to compute the force necessary  to produce the change in the velocity. Therefore, the thrust of  the engine must be equal to the force required to accelerate  the air mass through the engine. Then, by using the symbol  “Fn” for thrust pounds, the formula becomes: Using the formula below, compute the force necessary to  accelerate a mass of 50 pounds by 100 ft/sec$^{2}$.  Thrust of a gas turbine engine can be increased by two  methods: increasing the mass flow of air through the engine  or increasing the gas velocity. If the velocity of the turbojet  engine remains constant with respect to the aircraft, the thrust  decreases if the speed of the aircraft is increased. This is  because V$_{1}$ increases in value. This does not present a serious  problem, however, because as the aircraft speed increases,  more air enters the engine, and jet velocity increases. The  resultant net thrust is almost constant with increased airspeed. This illustrates that if the velocity mass per second is  increased by 100, the resulting thrust is 155 pounds. Since the turbojet engine accelerates air, the following  formula can be used to determine jet thrust: The Brayton cycle is the name given to the thermodynamic  cycle of a gas turbine engine to produce thrust. This is a  variable volume constant-pressure cycle of events and is  commonly called the constant-pressure cycle. A more recent  term is “continuous combustion cycle.” The four continuous  and constant events are intake, compression, expansion  (includes power), and exhaust. These cycles are discussed  as they apply to a gas-turbine engine. In the intake cycle, air  enters at ambient pressure and a constant volume. It leaves  the intake at an increased pressure and a decrease in volume.  At the compressor section, air is received from the intake at  an increased pressure, slightly above ambient, and a slight  decrease in volume. Air enters the compressor where it is  compressed. It leaves the compressor with a large increase in  where: F =  Ms (V$_{2}$ – V$_{1}$ ) G 1-59 F = force in pounds Ms = mass flow in lb/sec V$_{1}$  = inlet velocity F = MA G F = 50 lb × 100 ft/sec$^{2}$  32.2 ft/sec 2 F =  5,000 lb-ft/sec$^{2}$  32.2 ft/sec 2 F = 155 lb Fn =  Ms (V$_{2}$ – V$_{1}$) G F =  100 lb/sec (800 ft/sec – 600 ft/sec) 32.2 ft/sec 2 F =  20,000 lb/sec  32.2 ft/sec 2 F = 621 lb F = A or F = MA  M G G V$_{2}$ = jet velocity (exhaust) V$_{2}$ – V$_{1}$ = change in velocity; difference between inlet velocity and jet velocity where: F = force M = mass A = acceleration G = gravity Also, a force of 10 pound accelerates a mass of 10 pound at  the rate of 32.2 ft/sec$^{2}$. This is assuming there is no friction  or other resistance to overcome. It is now apparent that the  ratio of the force (in pounds) is to the mass (in pounds) as  the acceleration in ft/sec$^{2}$ is to 32.2. Using M to represent the  mass in pounds, the formula may be expressed thus: G  = Acceleration of gravity or 32.2 ft/sec 2 Thrust