See how afterburners work, when pilots use them, why they burn so much fuel, what can fail, and how simulators model the extra thrust.
In aviation, an afterburner increases a jet engine’s thrust by spraying extra fuel into the hot exhaust behind the turbine and igniting it. The added combustion accelerates the exhaust through a variable-area nozzle. It is used briefly when maximum thrust matters, chiefly for military take-off, climb, acceleration and supersonic flight.
How does an afterburner produce extra thrust?
An afterburner, also called an augmentor or reheat, is a combustion section between the turbine and exhaust nozzle. It supplements the engine’s main combustor rather than replacing it. Our explanation of the compressor-to-nozzle jet-engine cycle provides the underlying process.
- Hot exhaust reaches the afterburner: A gas turbine runs with more air than its main combustor needs, so the gases leaving the turbine still contain oxygen.
- Spray bars inject fuel: When reheat is selected, the engine meters additional fuel into the exhaust duct. Systems may introduce it in stages rather than going immediately from dry thrust to maximum augmentation.
- Flameholders stabilise combustion: Exhaust is moving too quickly to support an exposed flame. Flameholders create small recirculation zones where the mixture can ignite and remain alight.
- The gas becomes hotter and expands: Afterburner combustion raises the exhaust temperature substantially without sending that heat through the turbine.
- The nozzle converts that energy into velocity: The engine control schedules a larger nozzle throat to accommodate the expanded gas and avoid excessive back-pressure. The variable nozzle then accelerates the exhaust, producing additional thrust.
The increase comes mainly from higher exhaust velocity, not from drawing much more air through the compressor. On an afterburning turbofan, the precise arrangement depends on the engine, but reheat commonly acts on mixed core and bypass flow downstream of the turbine.
The bright plume is not a direct thrust gauge. Diamond-shaped shock cells can appear when supersonic exhaust pressure does not match the surrounding air pressure; their size and visibility vary with altitude, throttle, nozzle scheduling and atmospheric conditions.
When are afterburners used?
Pilots use afterburners when the immediate need for maximum thrust outweighs the heavy fuel consumption, noise and reduced range.
- Take-off: Military aircraft may use reheat for short runways, heavy loads or carrier operations when the approved procedure calls for it. It is not required for every take-off.
- Rapid climb and acceleration: Fighters use it to gain speed or altitude quickly, intercept another aircraft or recover energy during manoeuvring.
- Supersonic acceleration: Many aircraft need reheat to pass through the high-drag transonic region. Some also require it to remain supersonic.
- Short high-speed dashes: Combat aircraft may accept the range penalty when tactical speed is more valuable than endurance.
An aircraft capable of supercruise can maintain supersonic flight without afterburner under suitable conditions, although it may still use reheat to accelerate. Supersonic flight and afterburner use therefore are not the same thing.
Afterburners are overwhelmingly associated with military aircraft, but there have been civil exceptions. Concorde used reheat for take-off and transonic acceleration, then switched it off for efficient supersonic cruise.
Why do afterburners use so much fuel?
Afterburning is inefficient because the extra fuel burns downstream of the turbine at relatively low pressure. It creates a large increase in fuel flow, but the thrust gain is much smaller in proportion; claims that every afterburner simply doubles an engine’s thrust are incorrect.
Reheat also increases infrared signature, noise and thermal stress on the tailpipe and nozzle. Crews therefore distinguish between maximum non-afterburning or dry thrust and afterburning or wet thrust. Permitted duration and operating limits vary by engine and aircraft, so there is no universal time limit.
Do all jet aircraft have afterburners?
No. Afterburners are fitted mainly to turbojets and low-bypass turbofans designed for high-performance military or supersonic operation.
The system adds weight, length, fuel plumbing, controls and a complex variable nozzle. High-bypass airliner engines prioritise fuel economy and lower noise, so installing reheat would impose major penalties for thrust that normal airline operations do not need.
What happens if an afterburner fails to light?
A failure to light normally leaves the affected engine producing dry thrust, while an unstable flame may cause reheat to drop out. Depending on the engine, its control system may inhibit or cancel augmentation when it detects unsuitable conditions.
On a twin-engine aircraft, one afterburner lighting while the other does not can create strong asymmetric thrust and yaw. A nozzle-scheduling fault is more serious because incorrect back-pressure can affect engine stability. Indications and procedures differ substantially between aircraft, so pilots use the type-specific flight manual rather than a generic remedy.
Why will an afterburner not engage in a flight simulator?
In a flight simulator, failure to engage is usually caused by aircraft modelling, throttle calibration or control bindings. A flame graphic alone does not prove that the flight model is producing augmented thrust.
- Confirm that the aircraft models reheat: Some add-ons provide only a visual exhaust effect, while more detailed aircraft also change thrust, fuel flow, nozzle position and engine indications.
- Check the required control: One aircraft may engage reheat beyond a throttle detent; another may require a separate command. Follow the controls supplied with that model.
- Calibrate the throttle: An axis that stops just short of its full range may never cross the afterburner threshold.
- Remove conflicting bindings: Duplicate throttle or reheat assignments can cause intermittent engagement or immediate cancellation.
- Verify performance, not just appearance: Look for the expected acceleration, fuel-flow increase, nozzle movement and cockpit indication.
For older simulator aircraft, our tutorial on adding and aligning afterburner effects in FSX covers single- and twin-engine visual installations. Those effects may still require separate flight-model work before they alter actual thrust.