NL Fluctuations Question, any A&P's here?

RightSeatGirl

RightSeatGirl

KA'PLAH BITCHES!
We have an aircraft that has a wildly fluctuating indication on the #1 NL. It's a Dash8 100 with a P&W 120 btw. It's been written up numerous times, gauge replaced, wiring harness replaced, probe replaced, canon plug replaced and still the problem persists. The #1 ITT is also running unusually high on this engine. My question is could the indication actually be accurate? Can there by a high fluctuation on the low pressure side of the engine with the engine running normally otherwise?
 
LOL...I agree, but I really want to understand this problem because we have more than one aircraft doing it. I know on our engine we have a two stage compressor and two stage turbine and each stage turns relative to each other but the the stages turn at different speeds. What I don't know is if one starts to seize or slip would it effect the other. My feeling is that this engine may be ready to fail but I'd love to hear from someone who knows way the hell more about engines then me.
 
Cessnaflyer said:
Is there any fluctuation of torque?
Click to expand...

Nope. Not beyond the normal touchy nature of the antique ECU's. Only two out of whack indications are the NL itself and a higher than normal ITT which is still well within limits. All other temps and pressures indicate normal.
 
It depends on how much it is fluctuating. I would think that you would hear/feel significant speed fluctuations in the low speed compressor... Not an A&P, but my guess would be that there's a loose connection/bare wire between the sending unit and the gauge. Unfortunately, this is day 3/4 sitting reserve with no call for me, but next time they let me in an airplane I'll watch the Nl gauge (on a Q200)
 
It drops up to 50% down then shoots right back up again, goes back and forth continuously. I would think a problem wire might cause it drop to zero then come back up as in a total loss of signal. But that never happens. It never drops below %50.
 
If the NL is "shooting" up and down with no other indications, you have an electrical/wiring problem. Cruising around at 93% NL your compressor is spinning at about 25,800 RPM. There is no way that mass of metal can shoot down to 13,900 RPM without suffering catastrophic failure.

Since the low speed compressor is driven by the same combustion chamber exhaust as the NH compressor. It will follow what the high speed compressor is doing, just at a bit slower speed. That is, unless you suffered a catastrophic failure, such as turbine blade failure, bearing failure, etc...
 
It shouldn't be doing anything if it's working right except registering normal levels. When it starts going bunkers you tend to notice it.
 
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