Author Topic: Wrong N1  (Read 3254 times)

Offline will

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Wrong N1
« on: November 05, 2007, 06:50:53 PM »
Hey,

I've noticed that when I calculate the T/O perf, the assumed temperature generated by TOPCAT always gives a lower N1 than the FMC. For example, say the maximum power reduction is TO2 +35 and that gives an N1 of 99%. When I enter that information into the FMC, the target N1 is 105% (for example).

I've checked to make sure that all the weather conditions and weights are accurate. Is this how it should be, or is there something wrong?

Offline Christian Grill (TOPCAT)

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Re: Wrong N1
« Reply #1 on: November 05, 2007, 08:57:33 PM »
Hello,

could you please give a detailed example please (airport, runway, conditions, ...)?
So I can cross-check with book values.

Best Regards,
Christian Grill

Best Regards
Christian Grill
TOPCAT

Offline will

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Re: Wrong N1
« Reply #2 on: November 05, 2007, 09:28:48 PM »
Will do. I'm not at the sim right now, so it will be a few hours before I can reply.

Offline will

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Re: Wrong N1
« Reply #3 on: November 07, 2007, 05:14:00 PM »
Sorry for the delay. For some reason, the numbers differenced seemed higher when I wnt on my trip. Maybe I had selected the wrong takeoff rating. Below you will find the results of my experiment. S you can see, the difference between the TOPCAT N1 and FMC N1 is about 1%. The FMC rating is the higher one, so if anything, the error has been on the side of caution. I think Iíll be able to live with that.

Thanks for a wonderful program!

Keep reading if youír still interested in my findings.

All data was colleted for a TOGW of 601,700lb, with optimum flap setting and A/C on, wit anti-ice off. The weather was set to ISA. The N1 column shows the N1 generated by TOPCAT. The FMC N1 column shows the N1 computed by the FMC for the rating and assumed temperature. The Req. Assumed Temp. column is the Asumed Temperature I had to give the FMC to get the TOPCAT computed N1. This was done to the nearest tenth.

Again, a very good program. Thanks!


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