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  • CRJ start-up question

    I've been wanting to ask this one for a while now, but didn't quite know how to phrase it correctly. Btw, ths applies only to the 40 and 50 seat CRJ's.

    Back in '02 on my very first CRJ ride, I noticed the engine start-up was very slow (like the startup on the classic and NG 73's). Later on beginning in '03 when I flew in CRJ's, the startup began slowly in the usual manner, but there was some kind of sound like a knock from the engine and the startup was completed fairly quickly, but it revved the engine up rapidly and also produced another sound which made it really loud in the last few seats in the back. I'm wondering, is that some kind of a quick-start option? It's really interesting to note that in CRJ's with the slow gradual startup, you hear a sound similar to compressed air the first few seconds when the engines are spooled up for takeoff; in the ones with the quick-starting engines, you don't, any insight into all this? Sorry if this is more confusing than not, but the CRJ is the only aircraft so far that has so many little quirks that I've noticed lol.

  • #2
    I'm not sure if one of these is any faster than the other, but there are 3 ways you can start the engines in the CRJ. APU, crossbleed, and external power source. I start "flying" the CRJ sim in a couple weeks, if I learn anything I'll let you know.

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    • #3
      Re:

      Awesome! Thanks man. I bet you're pretty excited to start training for a jetliner!

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      • #4
        Originally posted by Foxtrot
        Awesome! Thanks man. I bet you're pretty excited to start training for a jetliner!
        yeah, a little. Its kinda a waste of money as I dont get a type out of it, and I'll just have to go through the same training when I finally hire on with an airline, but if they say I need it to graduate, I should probably do it.

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        • #5
          The compressed air noise you hear is the APU bleed air being routed through ducts to the starter. The thump you hear is the ignition in the engine.

          The engines will spool slowly at first, then you'll hear the thump as fuel is introduced. After that the engine accelerates rather quickly to its idle speed.
          Bite me Airways.....

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          • #6
            Re:

            Originally posted by LRJet Guy
            The compressed air noise you hear is the APU bleed air being routed through ducts to the starter. The thump you hear is the ignition in the engine.

            The engines will spool slowly at first, then you'll hear the thump as fuel is introduced. After that the engine accelerates rather quickly to its idle speed.
            Ahh, that makes more sense now. So were the earlier CRJ engines not equipped with the quick-starting ignition system? Also, why was the compressed air sound also audible when the engines were throttled up for taxiing or takeoff? These days you don't hear that.

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            • #7
              Originally posted by Foxtrot
              Ahh, that makes more sense now. So were the earlier CRJ engines not equipped with the quick-starting ignition system? Also, why was the compressed air sound also audible when the engines were throttled up for taxiing or takeoff? These days you don't hear that.
              The ignition has not changed.

              The CRJ is equipped with 2 ignition systems, A and B. The only difference between them is that the B system is powered off a static inverter off the battery.

              Generally the differences in the time it takes for an engine to start can be attributed to air temperature, amount of presure in the bleed lines, fuel control unit settings, etc.

              Some airplanes will "thump" when the engine is lit off because the fuel controller might be pumping too much fuel (fractionally larger amount) into the burner can of the engine.

              Some engines will spool slower if the fuel controller is set too low.

              Another limitation on the CRJ is that fuel cannot be introduced until the ITT is lower than 120 degrees. This comes into play during quick turns at outstations where your engines may have not had long to cool. So you motor the engine longer to blow ambient air through the engine and bring the ITT down below 120 before bringing the Thrust Lever to Idle.

              Just a few factors that can make every start different.
              Anybody can fly a round airplane....

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              • #8
                Re:

                ^Cool info, that explains a whole lot. Thanks!

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                • #9
                  I realized I didn't answer the air conditioning noise question...

                  On the CRJ you can either run the A/C Packs off the APU or the Engines. When the packs are being run off the APU, you won't hear any change in pressure/air flow when engine power is changed. Because the APU is providing all the air and does so at a constant rate.

                  When the packs are being run off the engines, the higher the power setting, the more airflow and the sound will get louder.

                  Generally takeoffs are performed with the APU off and the bleeds on the engines. But in conditions where you want max engine performance or when you might be using cowl and wing anti-ice you will takeoff with the APU running and the bleeds on the APU. The APU would then be shut off and the bleeds transferred as a part of the climb checklist.
                  Anybody can fly a round airplane....

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                  • #10
                    Re:

                    ^Umm, I didn't really ask an air conditioning noise question, but I'm thinking you mean that's the sound that you sometimes hear when the engines are spooled up is just that-the A/C noise, right?

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                    • #11
                      Yes, thats the one I was answering, that's the only "compressed air" sound I could think of.
                      Anybody can fly a round airplane....

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