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Hi everyone,
After some long months of design, tweaking and a lot of input from this community, I am facing an issue I’m bot sure how to solve.
All engine tables have been set accordingly, specially tables 1503-1504, 1502 and 1506 (for net thrust). Everything works fine and is on spot more or less during Cruise, but during takeoff the engine seems to have issues.
Starting at static, with full power (parking brakes on), engine primary parameters (N1 and N2) are right on spot and maintain their values (N1 at 84% and N2 at 104%). Now, when I turn off parking brakes and initiate the roll, N1 and N2 start coming down to around mid-70s N1 at VR. This is not what should happen.
I understand once we get rolling, thrust should come down slightly with speed due to ram drag, but N1 should be maintained (even increase slightly) to compensate. 1503 and 1504 should not be a problem; they are set such that at full throttle, with increase Mach N2 (uncorrected) is maintained. 1502 is set the same for low and high Mach, so that for that given CN2, N1 (uncorrected) is maintained constant. But then we come to 1506 ... since drag is degrading thrust, I understand CN1 degrades as well ... but shouldn’t it be compensated some how? I always thought the flow was 1503-04->1502->1506 ... not the other way around.
any help is much appreciated!
After some long months of design, tweaking and a lot of input from this community, I am facing an issue I’m bot sure how to solve.
All engine tables have been set accordingly, specially tables 1503-1504, 1502 and 1506 (for net thrust). Everything works fine and is on spot more or less during Cruise, but during takeoff the engine seems to have issues.
Starting at static, with full power (parking brakes on), engine primary parameters (N1 and N2) are right on spot and maintain their values (N1 at 84% and N2 at 104%). Now, when I turn off parking brakes and initiate the roll, N1 and N2 start coming down to around mid-70s N1 at VR. This is not what should happen.
I understand once we get rolling, thrust should come down slightly with speed due to ram drag, but N1 should be maintained (even increase slightly) to compensate. 1503 and 1504 should not be a problem; they are set such that at full throttle, with increase Mach N2 (uncorrected) is maintained. 1502 is set the same for low and high Mach, so that for that given CN2, N1 (uncorrected) is maintained constant. But then we come to 1506 ... since drag is degrading thrust, I understand CN1 degrades as well ... but shouldn’t it be compensated some how? I always thought the flow was 1503-04->1502->1506 ... not the other way around.
any help is much appreciated!