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Guest Dean Cross 4C

Boeing engine instrument question.

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Do the digital engine displays read beyond 99.9% in Boeings or do they stop at 99.9% if the engine RPMs (N1 and N2) go higher?I'm modeling the primary EIS display for a 737-300 but I've never seen three digits displayed before the decimal in video clips. Doesn't seem to be much space for another digit but I may be wrong.The one in the FS9 737-400 isn't correct - it's missing the decimal point and 10ths digit.ThanksPaul

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Hey, On the 737-300/-400/-500 older style EFIS, the N1 readout will read upto 99.9 and past i.e 101.1. On the newer EFIS I have never run the engines that high to see but I would have thought that it would just change to whole numbers i.e from 99.9 to 100, 101, 102.Kind Regards, Matt

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G'day Paul,On the B747-400 (with RR RB211 eng.) Up to the max value the digital readout displays (white) showing decimal place. On attaining the max value, the actual excedence is displayed and the colour changes from white to red. There is a tape display (for N1 and N3) as well as the digital. If the overspeed lasts for 20 secs. then the colour remains red.Maximum N1 values for RB211take off 104.4maximum continuous 103.7maximum climb 100.5maximum cruise 100.5MAXIMUM OVERSPEED 106.0maximum reverse 90.0The above information is very much type specific and I don't know about the latter B737's but it is illogical to drop the decimal point as you approach the RPM limitations (just when you need accurate readings). Assuming of course that the maximum limitation is greater than 100%.(which may or may not be the case)Roger

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Thanks guys. I'll make it a 4 digit display then. :)Paul

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The digital displays in the Citation series of aircraft simply do not display the hundreds position at all:99.900.001.903.9etc.Transient (TO) N1 limit on the Citation's is typically 104.3, and will display red if above the limit.

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Hey Roger. I had a look at the CMM for the Smiths EIS;DisplaysThe actual N1 %RPM parameter values are displayed on an LED matrix counter and a LED pointer. The matrix counter display range is from 0.0 to 120.0 %RPM and the pointer from 0 to 120 %RPM. The resolution of the matrix counter is 0.01 %RPM and the pointer 1.67 %RPM.The LED matrix counter simulates the action, appearance and sequential counting of a mechanical counter. The counter display has 3 1/2 digits which are green in colour. The least significant digit rolls in a downward direction for an increasing input value. The counter will not show leading 'zeros' to the left of the decimal point.Hope that clarifies this for you. This is specific to the B737 Classic!

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