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sheepfu

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Posts posted by sheepfu


  1. I find that if you can hit the top of descent calculated by the FMC at 190 knotts, you can pull the engines to idel and set the autopilot to IAS hold. Usually if winds co-operate, she will stay within a few hundred feet of the calculated path without any issues and when you get to the bottom, you won't be struggling to slow down.


  2. Maybe what was insinuated but not stated was add fuel to bring you into a good CG. Add enough fuel that when you reach your destination you will still be in that green zone. You can use the load manager to help. In the load manager, empty the jet of passengers and cargo, add fuel until your the center of gravity enters the green zone. Then add enough fuel for your flight and a 1 hour reserve. Keep in mind however, this way of doing things limits your range, so no long distance ferry flights. If you want to do a long distance flight, you may have no choice but to add some cargo.


  3. That isn't how the JT8D fuel control unit is designed. You don't have to monitor EPR in the climb that closely. In the real aircraft you can set climb power after takeoff and not have to adjust the throttles much if at all as you climb. I have that on the very good authority of a Lufthansa 727 F/E. I agree the Coolsky EPR model is good, but it lags rather too much. It makes power setting for takeoff much more difficult than it should be.

     

     

    It really seems strange that you would be able to leave the throttles at what constitutes climb thrust all the way up. I would be curious to pick your friends brain on that one as it doesn't seem to make sense to me. But maybe my understanding of EPR is worng. My assumptions have always been that EPR has nothing to do with the throttle position and everything to do with differential pressure between inlet and outlet. Sure adding fuel through the throttle will cause the engine to turn faster which generates a a greater differential pressure.

     

    So.....here is the question for someone much smater than I am. As you go up, inlet pressure decreases. If the engine speed remains constant, then the ratio should stay the same. However, as you increase altitude, though the ratio would stay the same, the thrust would decrease. This is based on my understanding of Boyles law which summed up in this situation basically boils down to volume in = volume out. Now as the engines reach lower ambient temps, they are able to run a higher EPR and thus compensate for the loss of thrust that would exist if a constant EPR was kept. So whithout outside influence of throttle increase how is this possible? Does the 727 have better fuel control requiring less manual inputs?

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