Aircraft terminology

[webley445]

heard a transmission on USCG and was wondering if someone could translate for me?

Base id'd themself as "maintenance' and was talking to an aircrew.
kept asking about readings re: "NP" and "NR" (or something similar), then some talk about a "lock out".

I got the impression it was about an engine going down. Anyone know what it all means?

 

[davidmc36]

heard a transmission on USCG and was wondering if someone could translate for me?

Base id'd themself as "maintenance' and was talking to an aircrew.
kept asking about readings re: "NP" and "NR" (or something similar), then some talk about a "lock out".

I got the impression it was about an engine going down. Anyone know what it all means?

NP usually refers to Propeller RPM on a free turbine engine. The power turbine, reduction gearbox, and propellor have no physical connection to the compressor section of the engine so they are able to turn at their own speed based on the amount of fuel being supplied to the burners which expand the gases and push the power turbine.

N1 will refer to the speed of the "first" section of the engine, ie the compressor. Some times you will have to independant sections to the compressor and will have NL, low pressure sectinon rpm and NH, high pressure seciton rpm.

NR does not ring any bells though.

Lock out could be a term they use to indicate they are shutting down the engine and or feathering the propellor.

Just occured to me being Coast Gaurd it is a good possibility that it was a helicopter and NR could refer to rotor rpm. Same deal as with a prop, they generally have no physical connection to the "N1" portion of the engine and turn at their own RPM. Maybe also it could be a twin engine model and they were reffering to "locking out" the bad engine from the transmission so the good engine could keep it flying, although that is usually done automatically with a one way dirve unit called a Sprag Clutch.

 

[AngelFire91]

NP usually refers to Propeller RPM on a free turbine engine. The power turbine, reduction gearbox, and propellor have no physical connection to the compressor section of the engine so they are able to turn at their own speed based on the amount of fuel being supplied to the burners which expand the gases and push the power turbine.

N1 will refer to the speed of the "first" section of the engine, ie the compressor. Some times you will have to independant sections to the compressor and will have NL, low pressure sectinon rpm and NH, high pressure seciton rpm.

NR does not ring any bells though.

Lock out could be a term they use to indicate they are shutting down the engine and or feathering the propellor.

Just occured to me being Coast Gaurd it is a good possibility that it was a helicopter and NR could refer to rotor rpm. Same deal as with a prop, they generally have no physical connection to the "N1" portion of the engine and turn at their own RPM. Maybe also it could be a twin engine model and they were reffering to "locking out" the bad engine from the transmission so the good engine could keep it flying, although that is usually done automatically with a one way dirve unit called a Sprag Clutch.

Your explination of Np is correct, it is the RPM speed of the power tubine section of the engine, also often refered to as the N2 rpm.

NR would be the Main rotor RPM in a helicopter.

 

[immelmen]

You guys have it backwards. N2 does not drive a prop, fan or rotor. In a two spool engine, N2 is the percent of arbitrary RPM of the compressor/high speed spool. N1 is the percent of RPM of the fan.

 

[davidmc36]

You guys have it backwards. N2 does not drive a prop, fan or rotor. In a two spool engine, N2 is the percent of arbitrary RPM of the compressor/high speed spool. N1 is the percent of RPM of the fan.

Actually it really depends on what engine you are talking about. For a PT6 N1 is the speed of the first stage turbine and compressor (one shaft), and N2 is the speed of the Power Turbine which drives the RGB and propellor (the other shaft).

If you take the example of the PW120 it has three shafts. NL (not monitored in the cockpit, only on FDAU) which is low pressure compressor RPM and it's turbine, NH which is high pressure compressor RPM and it's turbine, and NP which is output shaft (which drives the RGB/prop) RPM and it's turbine.

 

[immelmen]

for the monitoring laymen

Actually it really depends on what engine you are talking about. For a PT6 N1 is the speed of the first stage turbine and compressor (one shaft), and N2 is the speed of the Power Turbine which drives the RGB and propellor (the other shaft).

If you take the example of the PW120 it has three shafts. NL (not monitored in the cockpit, only on FDAU) which is low pressure compressor RPM and it's turbine, NH which is high pressure compressor RPM and it's turbine, and NP which is output shaft (which drives the RGB/prop) RPM and it's turbine.

The point of the OP referred to terminology heard over the radio, and the poster does not appear to have a background on turbine engines . My point In that respect; someone monitoring coms or listening to a pilot in any manner that hears him referring to % N1, it will virtually always be in reference to the fan speed of a jet.

Looking at the panel for a PT6 powered aircraft I see Torque, ITT, NG and NP, and similar on the PW120 powered ATR-42 panel .... Turboprops, which both the engines you referenced are, typically don't utilize the N1 and 2 terminology *in the cockpit*. It is not as useful a descriptor in props due to the different possible spool designs and configurations.

N1 and N2, when spoken by aircrew are generally associated with turbofan and turbojet engines, with most being axial flow having an inner (N1 low speed fan) spool and outer (N2 high speed compressor/gearbox) spool.

 

[davidmc36]

The point of the OP referred to terminology heard over the radio, and the poster does not appear to have a background on turbine engines . My point In that respect; someone monitoring coms or listening to a pilot in any manner that hears him referring to % N1, it will virtually always be in reference to the fan speed of a jet.

Looking at the panel for a PT6 powered aircraft I see Torque, ITT, NG and NP, and similar on the PW120 powered ATR-42 panel .... Turboprops, which both the engines you referenced are, typically don't utilize the N1 and 2 terminology *in the cockpit*. It is not as useful a descriptor in props due to the different possible spool designs and configurations.

N1 and N2, when spoken by aircrew are generally associated with turbofan and turbojet engines, with most being axial flow having an inner (N1 low speed fan) spool and outer (N2 high speed compressor/gearbox) spool.

So it would appear obvious that what he was hearing was in relation to a turboshaft engine since he heard NP/NR. Most likely a helicopter if it was NR which would fit with it being a coast gaurd A/C. Or NP of it was fixed wing. Does the coast gaurd have things like DHC-6, 7, or 8? It would seem to appear that it was not an ATR since there was no reference to NH, the other RPM indicator in a ATR-42 at least.

All of which does not change the fact that in some settings the RPM's on a PT6 are reffered to as N1 and N2. Generally in industrial applications or for us maintenance guys, not in the cockpit.

United Turbine - Troubleshooting