Originally Posted by
Ascend Charlie
Geez, Bront, why then is a bleed valve or a bleed band fitted to turbine engines? To remove the excess air that can build pressure at the back of the compressor, and cause the flow to break down and stall the compressor blades.
A C20 on start-up has the bleed valve open to allow acceleration of the compressor without getting too much air into the combustor. It stays open, closing gradually, until around 92% N1 when the engine can take all the air OK. It opens again on sudden accelerations. To let out the back pressure and allow the wheels to spin up faster.
Try leaving the wedge in the bleed valve when you go to start next time, hear the stalls start very early on. Too much back pressure.
Anti-ice is still turned on in hot countries too! Because it removes some of the excess air and pressure, not because there is ice in the intakes.
We are not talking about operating at low N1 speeds, we are talking about operating at high N1 speeds where the bleed valve will be closed so what the engine does during starting is irrelevant.