The MiG-19 was the first Soviet supersonic fighter built in series, and it carries two of these engines. Start the RD-9B, open the throttle all the way, then light the afterburner and see how much thrust you gain — and how much extra fuel it burns.
Air is sucked in at the front. A nine-stage compressor squeezes it 7 times. In each stage the spinning blades speed the air up, and the fixed ones slow it down again, turning that speed into pressure.
The squeezed air enters the combustion chamber, where kerosene is sprayed in and lit. The hot gas rushes through the turbine and spins it, and the turbine drives the compressor through a shaft. The gas carries the rest of its energy out through the nozzle, where it speeds up and pushes the engine forward.
Every second the engine throws dozens of kilograms of gas backwards at hundreds of metres per second. By Newton’s third law, the gas pushes the engine forward with the same force.
Thrust grows if you throw more gas or throw it faster. The afterburner does the second: behind the turbine more kerosene is sprayed in, the gas gets hotter and leaves the nozzle faster.
Open the throttle fully and note the thrust and fuel flow. Then hit “Afterburner”. Thrust goes up by 28%, but fuel use more than doubles. For every kilonewton of thrust the afterburner burns 1.7 times more fuel.
That’s why pilots use it only briefly: on takeoff, to break the sound barrier and in combat. With the afterburner on, the nozzle flaps open wider: there is more gas, and it needs a bigger exit.
One stage squeezes the air only about 1.24 times. To reach 7.14 the stages are stacked one after another: 1.24 to the ninth power is just about 7.
The gas hitting the turbine is hotter than 860 °C, and the blades spin 186 times a second. Each one is pulled outward with a force of several tonnes. That’s why turbine blades are made of heat-resistant nickel alloys.
The engine can’t start by itself: while the compressor stands still, nothing squeezes the air. First a starter motor spins the rotor up, then kerosene is fed in and lit by an igniter plug. From then on the turbine drives the compressor on its own.
1. At max dry power the RD-9B makes 29 kN of thrust and burns 27 g of kerosene per second for every kilonewton. With the afterburner it makes 37 kN at 45 g/(kN·s). How many tonnes of fuel per hour does it burn in each mode?
2. A compressor of 9 identical stages squeezes the air 7.14 times. How much does one stage squeeze it?