Citation N2 Question

[JediNein]

Greetings,
I'm digging through the CE-500's systems and stumbled across the various things that happen at specified %N2 turbine. For example, at 85% N2, the speedbrakes retract & the cabin outflow valves close.

The books also state at 35-42% N2, cabin pre-pressurization occurs. How does this pre-pressurization occur? Outflows start moving closed? Bleed air re-routing? Little hamsters start running in the ACM?

Thanks,
Jedi Nein

 

[KeroseneSnorter]

I guess you are dealing with an older model 500 of which I have no manuals for.

On the late model 550's prepressurization does not occur until 85% N2, at which time the outflow valve begins driving closed (20 second cycle rate for full clousure) The 550's also use a squat switch to tell it when it is on the ground.(Left Main)

My Manuals make no mention of a 43% value but if I had to guess it may be due to bleed air (or the lack of) when N2 is low. I do get a slight pressure spike after decending at flight idle when power is brought back up. This is indicitive of the engines not putting out quite enough bleed air to counter the leak down rate of the cabin. Anything over idle even by a couple of percent prevents the spike, and seeing as how the Citation is the only jet on earth that you have to carry power to decend it is normally not an issue! (Straight wings and all)

As to the 85% speed brake retract, that is actually a throttle position microswitch and not actually an engine rpm item. When the trottles are placed in a position that will result in about 85% the speed brakes retract. The ground test simply calls for a quick cycle of the lever to verify microswitch operation, and the engine never has time to spool up to 85%.

Again this is for a late model 550 and not the 500 so there are probably some system differences between them.

Bottom line, 500, 550, and 560 (not XL) are all so close that you probably won't notice the difference except for performance. All of them are slow, some are just slower than others. Citation 500's......the light beer of jets!!!

If you need near jet speed and still get into less than 4000 foot strips then that is where the 500's really shine. They will do runways that would scare the crap out of you in anything with a swept wing. Basically they will do 130 knots better than a king air 200 and still get into the same airports that a King Air can.