GE90 Engine Start
Joined: Oct 2003
Posts: 577
Likes: 0
From: Gweriniaeth Cymru
Dear Lemon Drop,
kit available:
Advanced Ultra-High Blocking Ear Plugs-World-Wide Shipping
Best Regards,
N1 Vibes
kit available:
Advanced Ultra-High Blocking Ear Plugs-World-Wide Shipping
Best Regards,
N1 Vibes
Joined: Oct 2003
Posts: 577
Likes: 0
From: Gweriniaeth Cymru
Lemon Drop,
there was a modification to the Trent 800 inlet cowls to reduce the 'buzz-saw' noise on take-off, which was deafening biz class pax in row 15+16, as it exceeded basic H&S noise levels. I think the cost of replacing the inner barrel panels was around US$140k per a/c. Plus the panels were heavier, so we are still paying for them in fuel costs....
But of course, we do it because we love our customers and want to make them as comfortable as possible - fawn, fawn, fawn.
So still believe the earplugs are cheaper for the GE90 moo-cow.
Best Regards,
N1 Vibes
there was a modification to the Trent 800 inlet cowls to reduce the 'buzz-saw' noise on take-off, which was deafening biz class pax in row 15+16, as it exceeded basic H&S noise levels. I think the cost of replacing the inner barrel panels was around US$140k per a/c. Plus the panels were heavier, so we are still paying for them in fuel costs....
But of course, we do it because we love our customers and want to make them as comfortable as possible - fawn, fawn, fawn.
So still believe the earplugs are cheaper for the GE90 moo-cow.
Best Regards,
N1 Vibes
Joined: Aug 2009
Posts: 32
Likes: 0
From: 香港
from my experience the moo cow noise seems to always be at low N1 rpm when the initial light off occurs on any turbine engine. On the 777 fuel is automatically sequenced by the EEC, but even on previous jets and turbo props, it seemed to make little or no difference to the low growling noise during initial light off if you let the starter spin faster before introducing fuel. It was usually evident in the cases when you had to let the starter spin to get the ITT/EGT down before whacking the fuel in on a quick turnaround. Though I do remember it used to stop the 'boom' compared to introducing fuel at close to minimum light off N1.
Joined: Aug 2007
Posts: 16
Likes: 0
From: Honkers
8888
To eradicate that specific whine, you must understand what is happening first. Obviously turbines are meant to run at high revolutions - not at starter revs. At light off, you have a mass expulsion of exhaust gas being fed over an 'effectively stationary' high speed turbine. As the turbine is not aerodynamically suited to this slow state, it cavitates/stalls (not the typical compressor stall you know) in sections (that's the whine) until it accelerates and stabilises within its operating envelope.
If you can drive the high speed rotor faster before light-off, no whine is produced. A big engine with only 2 spools needs a massive amount of bleed air demand (high pressure) and hence more robust bleed plumbing and starter. In the interest of commonality and dollars... Question is, do you want to?
To eradicate that specific whine, you must understand what is happening first. Obviously turbines are meant to run at high revolutions - not at starter revs. At light off, you have a mass expulsion of exhaust gas being fed over an 'effectively stationary' high speed turbine. As the turbine is not aerodynamically suited to this slow state, it cavitates/stalls (not the typical compressor stall you know) in sections (that's the whine) until it accelerates and stabilises within its operating envelope.
If you can drive the high speed rotor faster before light-off, no whine is produced. A big engine with only 2 spools needs a massive amount of bleed air demand (high pressure) and hence more robust bleed plumbing and starter. In the interest of commonality and dollars... Question is, do you want to?
