Ng

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N(?) generator.

What does the N stand for? I know the simple answer is "gas" but...the only sense I can make of this is that N is the symbol for the most abundant gas nitrogen. However, it is not flammable so that doesnt make much sense either to attach it to an engine. I just have to think about it too long to spit out what it stands for because I always want to say the "g" stands for gas instead of generator. Thanks.
 
It's a nitrogen generator which supplies nitrogen gas to the fuel tanks to prevent fumes from igniting due to faulty wiring. (This ain't the place for TWA800 conspiracies!)
 
waaahhh? seriously? How does it separate the gasses? the centrifugal force turbine pushes the heavier gasses to the outside? Please, you can't just stop there.

Don't know anything about TWA800.
 
splash said:
waaahhh? seriously? How does it separate the gasses? the centrifugal force turbine pushes the heavier gasses to the outside? Please, you can't just stop there.

Don't know anything about TWA800.
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Not in this case, but a gas centrifuge is a way of separating gases. It doesn't work very well, compared to exploiting different evaporation temperatures, but it is possible. It is a viable way of separating isotopes of the same gas, which is where most people know of the technique.
 
DE727UPS said:
So, why does the N1 go over 100%? Seems like it would make more sense to have 100% be the max and anything over that is too much. Always wondered about that. Or maybe it goes back to my high school PE teacher wanting me to give 110%...
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I was told one time after asking the same question that it was based on the original design of the engine where the target max RPM would be 100%. Then as the design progresses, or is later scaled, they retain this target speed as 100%, so if 6239 RPM is 100%, it remains 100%.

Example, the early PT6s were 100% Ng limits, now it's around 101-102 depending on the engine.
 
I'm sure an actual engineer could explain this far better but I believe the percentage limitations are based on standard environmental conditions to give pressure ratios and temperatures that balance component longevity with power output. In the real world those numbers would be variable based on ambient conditions.
 
The g on the Ng in the PT6 refers to the gas generating section of the engine. That would be the compressor, combustor, and compressor turbine. All those function to provide energy, in the form of gases moving at a very high velocity, to turn the power turbine. Hence, "gas generator."
 
milleR said:
N is used in fluid dynamics to denote RPM when calculating turbine specific speed or Ns.

On a turboprop Ng typically denotes the RPM (N) of the compressor/gas turbine (g).
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In addition what you stated, from an aircraft mechanics' point of view (I know I don't wear that hat any more, but I never could get ride of it.) I was taught in the armed service to view it as N = Nomenclature.

It was often applied in concept, for identifying the section (depending on engine & type).

PT6 example given, So
N1 = Ng = Gas Generator Section
N2 = Np = Power Section
Etc...

The RPM gauge in the cockpit will tell you how fast N1/Ng is spinning, given in percentage %. OP @splash , I hope this helps in answering your question. Good question btw.
 
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@splash for the PT6 example and question regarding why N (g),

It's Name or Nomenclature is "Gas Generator", because that's it's main purpose in actuality. This is the section where Gas is being "Generated." The majority of this gas energy being "generated" goes to turning/spining critical items such as the compressors (axiel & centrifugal flow), as well as engine accessories which require a lot of energy.

Think of the Np/Power Section as being called that because this is really where the Reduction Gear, Prop & Torque energy originate (Power). It's purpose is in it's name/nomenclature.
 
DE727UPS said:
So, why does the N1 go over 100%? Seems like it would make more sense to have 100% be the max and anything over that is too much. Always wondered about that. Or maybe it goes back to my high school PE teacher wanting me to give 110%...
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100% is an agreed upon design point that predates actual prototype testing and specification finalized data.

Basically when some engineer put pen to paper the transducer provided a specific electrical indication which was caged as 100%... From there during testing the actual operational range was established, but it's far easier to teach pilots that 106% is the operational limit for normal ops vs go back into miles of coding and change the engine to re-baseline whatever operational limit was established as 100%.

Same thing happens on all aircraft designs. The D model Apache has optimal rotor and engine RPM as 101%..... E model changed the baseline to 100%.... It's the exact same RPM.
 
Lawman said:
100% is an agreed upon design point that predates actual prototype testing and specification finalized data.

Basically when some engineer put pen to paper the transducer provided a specific electrical indication which was caged as 100%... From there during testing the actual operational range was established, but it's far easier to teach pilots that 106% is the operational limit for normal ops vs go back into miles of coding and change the engine to re-baseline whatever operational limit was established as 100%.

Same thing happens on all aircraft designs. The D model Apache has optimal rotor and engine RPM as 101%..... E model changed the baseline to 100%.... It's the exact same RPM.
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False, you can't teach pilots anything.
 
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