Dave317 Posted December 26, 2014 Posted December 26, 2014 I've only just got this the other day so forgive me if this has already been asked, I've searched but can't find an answer. The question is why are there 2 rpm needles on a single engined jet?
Grizzly1606688174 Posted December 26, 2014 Posted December 26, 2014 Good question. :) Because there are two engine compressors. So you have LP and HP compressors (Low power / high power). EDIT: Something like this illustration: http://upload.wikimedia.org/wikipedia/commons/c/c0/Turbofan_operation.png
impact480 Posted December 26, 2014 Posted December 26, 2014 Correct, it indicates the low-pressure and the high-pressure compressor section rpm where the low-pressure compressor section rotating faster :) Mig-21 - Mig 15 - Mi-8 - F-86 - FC3 - Ka-50 - CA - L39 - Hawk - M2K - NTTR - A10C - FW190 - L39 - F-5E - AJS 37 - Normandy - F/A-18C - Persian Gulf -
PiedDroit Posted December 26, 2014 Posted December 26, 2014 I addition I'd say that #1 is low pressure and also the one your refer to when you give / are given throttle % values ;)
Art-J Posted December 27, 2014 Posted December 27, 2014 ...where the low-pressure compressor section rotating faster :) Hmmm... You might want to re-check that ;). i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.
Golo Posted December 27, 2014 Posted December 27, 2014 Hmmm... You might want to re-check that ;). You too, well because on some engine setings (high power) it realy happens:smilewink:
sobek Posted December 27, 2014 Posted December 27, 2014 You too, well because on some engine setings (high power) it realy happens:smilewink: Very unlikely. The blade tips must under all circumstances stay subsonic. Since the low pressure discs are usually bigger (or at least same size) than the high pressure discs, they must make less revolutions per minute (or at least the same, not more). The instruments are in percent, just because it shows higher percentage doesn't mean it is rotating faster. Good, fast, cheap. Choose any two. Come let's eat grandpa! Use punctuation, save lives!
Golo Posted December 27, 2014 Posted December 27, 2014 Very unlikely. The blade tips must under all circumstances stay subsonic. Since the low pressure discs are usually bigger (or at least same size) than the high pressure discs, they must make less revolutions per minute (or at least the same, not more). The instruments are in percent, just because it shows higher percentage doesn't mean it is rotating faster. The indicator shows RPM of the compressors, and LP shows at times more RPM than HP. Unless it shows specific RMP range of given compressor and not their relative measurements, I have to double check that.
sLYFa Posted December 27, 2014 Posted December 27, 2014 Unless it shows specific RMP range of given compressor and not their relative measurements, I have to double check that. FYI, all soviet/russian built jet aircraft, military or civil, show engine rpm in percent, i. e. relative to a theoretical maximum value FOR THAT compressor stage. Therefore, a higher rpm reading for n1 does not necessarily mean a higher total rpm for n1 compared to n2. In fact, n2 has always a higher total rpm value than n1 for most engines. i5-8600k @4.9Ghz, 2080ti , 32GB@2666Mhz, 512GB SSD
Golo Posted December 28, 2014 Posted December 28, 2014 FYI, all soviet/russian built jet aircraft, military or civil, show engine rpm in percent, i. e. relative to a theoretical maximum value FOR THAT compressor stage. Therefore, a higher rpm reading for n1 does not necessarily mean a higher total rpm for n1 compared to n2. In fact, n2 has always a higher total rpm value than n1 for most engines. I see, its settled than. My bad.
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