18 votes

Why do we monitor N2 speed rather than N1, when starting jet engine?

If it's a turbofan, N2 represents the core engine compressor/turbine spool that is creating the compress/burn/expand energy that drives the fan, and is exposed to the most energy, that is, velocity ...
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  • 105k
12 votes

How come a turboprop can't reach speeds as high as a turbofan?

The attributes of the incoming air for combustion matter less than how the thrust is generated. Many turbofans operate past Mach 1, but a turboprop's thrust comes practically entirely from the ...
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5 votes
Accepted

How does the F-16 engine startup work?

The START switch routes pressurized hydraulic fluid inside two canisters to the HSM (hydraulic start motor). This motor begins to spin up the JFS (Jet Fuel Starter, a small turboshaft engine) through ...
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  • 1,025
4 votes

Why does the X-3 have two oil pressure gauges per engine?

After some research, Ralph's comment is almost certainly the answer here: during the restoration they installed incorrect (though period-accurate) oil pressure gauges, rather than fuel pressure gauges....
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  • 23.1k
2 votes
Accepted

Why does the torque curve of free shaft gas turbines keep gradually dropping as RPMs increase?

Let's start with this example: Start up the turbine with no load connected to the shaft, then advance the fuel flow rate to the maximum allowable value. The output shaft will achieve some (very high) ...
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2 votes

A very loud, short- lived howl

Some airplanes make strange sounds when the landing gear is deployed/stowed, or flaps are lowered/raised. The BA-146 is famous for making a loud descending boooo noise when the flaps are lowered, for ...
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  • 49.6k
2 votes

Why do we monitor N2 speed rather than N1, when starting jet engine?

All correct answers here, N1 is the large fan at the front and suffers the same effects as turbo lag in a car. N2 does the main compression of the air before it enters the multistage combustion ...
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2 votes

Why do we monitor N2 speed rather than N1, when starting jet engine?

The N2 shaft is the actual jet engine proper, which has one job: turn fuel into thrust directly. It is akin to the crankshaft on a gas/diesel engine. The N1 shaft is an extra turbine put in the ...
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2 votes

How did the MiG-25M prevent a flameout?

The engine flamed out on the way up. Inertia alone carried the Ye-155M to its record altitude. Its high speed and its high supersonic load factor of 5 allowed to fly a zoom climb where the pilot pulls ...
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