aledmb Posted January 5, 2009 Posted January 5, 2009 during pre-flight tests, while checking the engine anti-ice system, the manual says to look for changes in the GG (high gas-generator) RPM. where's that gauge? also, that's a part the manual leaves me guessing so much! :(
AlphaOneSix Posted January 5, 2009 Posted January 5, 2009 On the right side of the forward panel next to the ABRIS.
aledmb Posted January 5, 2009 Author Posted January 5, 2009 thanks! the manual doesn't say "gg rpm gauge = engine rpm gauge"...
Acedy Posted January 5, 2009 Posted January 5, 2009 (edited) There are actually two engine RPM gauges: gas generator(GG)/compressor turbine RPM and free turbine(FT)/rotor RPM. For the difference see: http://en.wikipedia.org/wiki/Turboshaft Edited January 5, 2009 by Acedy [sIGPIC][/sIGPIC] *** SERVMAN SERVER MANAGEMENT MOD V2 FOR DCS:BS V1.0.1 *** *** VERSION FOR FC2 ***
miguez Posted January 5, 2009 Posted January 5, 2009 Hi Acedy, Technically speaking, the free power turbine RPM is not the same as the rotor RPM, since the gearbox converts the very high revolutions of the free power turbine to something that works for the rotor blades, right?
aledmb Posted January 5, 2009 Author Posted January 5, 2009 There are actually two engine RPM gauges: gas generator(GG)/compressor turbine RPM and free turbine(FT)/rotor RPM. For the difference see: http://en.wikipedia.org/wiki/Turboshaft sorry but now i'm lost again... can you please tell me what applies to the ka-50? it has only one gauge, right?
miguez Posted January 5, 2009 Posted January 5, 2009 aledmb, As I understand it, we have a compressor RPM gauge, which is on the Right Forward Panel, below the EGT gauge, and we have a rotor RPM gauge, which is on the Left Forward Panel. The compressor (or "engine" to be generic) RPM gauge measures the percentage of RPM of the compressor stages. The rotor RPM measures percentage of main rotor blade RPM. The two are not directly related, as the engine could be spinning at near max RPM, when you have a relatively low rotor RPM due to maneuvering/collective use. This is due to the fact that the gearbox, which drives the main rotors, is connected to the free power turbine. This turbine is called "free" because it is not coupled to the compressors. It is spun by the hot gases that came out of the combustion chamber. In some turboprop aircraft, you can start the engine while holding down the propeller. You will more than likely ruin the engine, but you'll be able to keep it stationary, as the turbine is not mechanically driven. Does that make sense? Best regards,
nightlynx Posted January 5, 2009 Posted January 5, 2009 I was about to ask something related but upon thinking about it I think I figured it out, let me know if I'm wrong. I was wondering why low rotor rpm kills the electric to the ka-50 even if engines are at or near max rpm. Is it because of the free power turbine being connected to both the generators and the main rotors, so if one slows it slows the other?
Acedy Posted January 5, 2009 Posted January 5, 2009 (edited) Hi Acedy, Technically speaking, the free power turbine RPM is not the same as the rotor RPM, since the gearbox converts the very high revolutions of the free power turbine to something that works for the rotor blades, right? That's correct of course, but since there is a mechanical link between both, their RPM are proportional. Because the FT/rotor RPM gauge is calibrated in percent of max. RPM, it measures both values. Edited January 5, 2009 by Acedy [sIGPIC][/sIGPIC] *** SERVMAN SERVER MANAGEMENT MOD V2 FOR DCS:BS V1.0.1 *** *** VERSION FOR FC2 ***
AlphaOneSix Posted January 5, 2009 Posted January 5, 2009 I was about to ask something related but upon thinking about it I think I figured it out, let me know if I'm wrong. I was wondering why low rotor rpm kills the electric to the ka-50 even if engines are at or near max rpm. Is it because of the free power turbine being connected to both the generators and the main rotors, so if one slows it slows the other? The generators are attached the the main gearbox, thus are directly tied to rotor RPM.
RvETito Posted January 5, 2009 Posted January 5, 2009 On western helicopters (Bell-407 for example) there is one pointer for PT RPM and one for rotor RPM on the same gauge. In powered flight (clutch engaged and PT transfering torque to the rotor) the two pointers match. In autorotation (free-wheel clutch disconencted) you can see the PT pointer falling behind. Russian helicopters use only rotor RPM gauge concept. There is no direct indication whether the free-wheel is engaged or not. "See, to me that's a stupid instrument. It tells what your angle of attack is. If you don't know you shouldn't be flying." - Chuck Yeager, from the back seat of F-15D at age 89. =RvE=
AlphaOneSix Posted January 5, 2009 Posted January 5, 2009 The compressor (or "engine" to be generic) RPM gauge measures the percentage of RPM of the compressor stages. Very good post overall, I just jave one correction. It's not compressor RPM, is "gas generator" RPM. It's a technicality, since they are both physically connected and therefore have no choice but to spin at the same speed. The gas generator (GG) turbines are immedaitely behind the combustion chamber. Many people will also refer to engine RPM as "N1" and rotor RPM as "N2". The only other thing I would mention is that there is a clutch between the free turbines on the engines and the main gearbox. This allows the engines to drive the main gearbox, but prevents the main gearbox from driving the free turbines. This is important if your free turbine can no longer spin because of damage.
miguez Posted January 5, 2009 Posted January 5, 2009 That's correct of course, but since there is a mechanical link between both, their RPM are proportional. Because the FT/rotor RPM gauge is calibrated in percent of max. RPM, it measures both values. Acedy, Great point, percentage works for both!
miguez Posted January 5, 2009 Posted January 5, 2009 Very good post overall, I just jave one correction. It's not compressor RPM, is "gas generator" RPM. It's a technicality, since they are both physically connected and therefore have no choice but to spin at the same speed. The gas generator (GG) turbines are immedaitely behind the combustion chamber. Many people will also refer to engine RPM as "N1" and rotor RPM as "N2". Hi AlphaOneSix, Thanks for the correction, very warranted!
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