View Full Version : Eng n2 - apu - airbus320
Captain_BH
6th Aug 2011, 13:20
Hi guys just wondering why
sometimes during engine start .. i notice while monitoring parameters N2 rotates very slowly, and sometimes very fast why is that!!
and the same for APU sometimes when I press the start PB the APU N rotates and starts quickly and sometimes very slow.. why is that ??
barit1
7th Aug 2011, 15:27
Also depends on pneumatic pressure.
Green Guard
7th Aug 2011, 19:23
Well ..it also depends how "fast" you are observing those instruments...
AIR320
12th Aug 2014, 18:47
Most of the time it is related to bleed pressure
Mecaniquito84
13th Aug 2014, 01:39
Also depends on EGT. If you take a/c after a short time turnaround with eng EGT above lets said 100º C or more, Engine EEC will slow the start process by reducing fuel flow to avoid a high egt start.
The same is true for APU
On the RR 777 and the RR A330 the FADEC won't put the fuel in until the EGT drops below 100c during Auto start. It motors the Engine at Max Motoring until the temp drops.
As to the Engine N2 either accelerating fast or slow, that would depend on bleed pressure in the duct at the time wouldn't it? Have a look at the Duct pressure when it happens. :ok:
As to the APU N2 varying with speed, that would be down to the APU Battery condition?