Jet Tech: Compressor Stall
This is the long awaited video about what causes “compressor stall” and how those clever people that design jet engines have tried to stop their engines from suffering from it. The compressor is the front section of a jet-engine. It is formed of “stages” of spinning blades, which accelerate the air flowing through the engine, compressing it, before it is combined with fuel, burned and exhausted from the rear of the engine. Compressor stall is where the compressor stages lose the ability to force air backwards, through the engine. You don’t need to be a rocket surgeon to know this is a bad thing that should be avoided wherever possible. Like. Ever.
Compressor stall is definitely something you don’t want to be near when it happens – especially if you are a passenger in the aircraft that has the problem while in flight. Compressor stall usually happens when a pilot changes the power requested from a jet-engine too quickly for the engine to respond and can cause the engine to lose a significant amount of power/thrust – sometimes completely, often with catastrophic results.
“Stalling”, in the context of flight, usually relates to the wings of an aircraft losing lift – because their angle of attack, in relation to the airflow that surround them, has increased beyond the point where lift is created. This is almost always a bad situation and can, if insufficient altitude is available, result in the loss of the aircraft. The usual solution is to reduce the angle of attack and/or increase the speed of the aircraft – in an attempt to re-attach the airflow to the aerofoil and increase lift. This approach doesn’t work for the blades of the compressor, if they stall, for two reasons. Firstly – Compressor blades cannot be adjusted – to change their angle of attack to the airflow through the engine. And secondly – compressor stall is usually caused by increasing the thrust demanded from an engine too quickly. The very act of increasing thrust from the engine causes the compressor to stall – so increasing the requested power is only going to make the situation worse (as if that was possible).
AgentJayZ explains in this video how, even though the blades of the compressor cannot directly change their angle of attack, other changes in the engine can affect their “apparent angle of attack.”
It’s a great video, as always, and AgentJayZ explains the problem and solution in a clear way using the minimum of technical language and a few simple diagrams. As with most things that involve jet-engines, the problem (and, therefore, the solution) is counter intuitive – as most people appear to think the problem is caused by back-pressure from the combustion section of the engine – rather than a fundamental limitation of compressor blades and the demands that can be made of them.
It was a long time coming, but it’s a great addition to AgentJayz’s library of informative, educational and often funny content.
A description of anti-stall technology applied to axial compressors in gas turbine engines. This video is not for experts, and not for pilots. It’s for the many people who are interested in turbine engine function, but may not be involved in the industry. If you have a question, please check the index of my playlist called Your Questions Answered… first. Thanks in advance.