747-400 range question
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747 400 N1/ epr question
MD and Random Person thanks for the clarification. if i may ask you further, over the life of an RB-211-524, PW 4056 and GE CF6, does the thrust produced by the engines decrease over time? would a constant N1 or EPR setting over time equate to a reduction in total thrust of that engine??
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Yes....most of the airplanes at my company came with CF6-80C2B5F engines installed, rated for 62,100 lbs of Boeing equivalent thrust. Over time, they become de-rated to CF6-80C2B1F engines which are rated for 56,500 lbs. The decisions regarding when and why to accomplish these de-rates are usually made by the engine owner/lessor, to the best of my knowledge.
Maximum N1 & N2, 117.5% and 112.5% respecitvely, remain the same for both B1F and B5F variants. Therefore, one might conclude that for a given N1 value, less thrust is being produced by the derated engine.
So...does the thrust produced by engines at a given N1/EPR degrade over time? Yes, I would say so. Does this happen appreciably even prior to the de-rates being established for a given engine? I do not know for certain, but logically one would say yes, a new engine probably performs closer to rated specifications than an old and worn out one. Wear and tear on the engine's blades likely leads to less efficient compression and therefore less thrust being produced at a given RPM. An engine mechanic would be a much better person to ask this question to, since they are undoubtedly the ones responsible for monitoring engine performance and making sure the engine is overhauled or replaced once it degrades beyond limits.
Maximum N1 & N2, 117.5% and 112.5% respecitvely, remain the same for both B1F and B5F variants. Therefore, one might conclude that for a given N1 value, less thrust is being produced by the derated engine.
So...does the thrust produced by engines at a given N1/EPR degrade over time? Yes, I would say so. Does this happen appreciably even prior to the de-rates being established for a given engine? I do not know for certain, but logically one would say yes, a new engine probably performs closer to rated specifications than an old and worn out one. Wear and tear on the engine's blades likely leads to less efficient compression and therefore less thrust being produced at a given RPM. An engine mechanic would be a much better person to ask this question to, since they are undoubtedly the ones responsible for monitoring engine performance and making sure the engine is overhauled or replaced once it degrades beyond limits.
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does the thrust produced by the engines decrease over time? would a constant N1 or EPR setting over time equate to a reduction in total thrust of that engine??
EPR is a fairly direct measure of thrust, thus assuming the pressure/temperature probes/gauges are working correctly, 1.72 EPR on a new engine should be equal thrust to 1.72 on an old one. What will change is how hard the engine has to work to produce that thrust: the older engine will probably show a higher EGT, fuel flow and indeed N1 to produce the same thrust.
N1 is a measure of engine rotation, so I would imagine an older engine turning at 111.4% N1 will not be producing as much thrust as a new one showing 111.4%... stand to be corrected though.
MD
PS When's a techie when you need one?
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747 400epr
Thank you for your insights into my inquiries... your explanations make sense to me. And your're right, a mechanic would be more appropriate to ask however i think that some commercial companies ask this type of question in a pilot interview. just trying to prepare myself.
Regards,
Regards,
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Over time, they become de-rated to CF6-80C2B1F engines which are rated for 56,500 lbs.
How does the engine designation change after leaving the factory. I appreciate that an older engine may not pack as much of a punch as a new engine, but how does one change the model number of an engine?
How does the engine designation change after leaving the factory. I appreciate that an older engine may not pack as much of a punch as a new engine, but how does one change the model number of an engine?
Last edited by Check Airman; 20th Mar 2011 at 05:09.
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The B5F/B1F switch is apparently just an EEC "software change". That's why it can be done after the engines leave the factory. I've seen similar model designation and thrust changes take place on other FADEC equipped engines.
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Random person, before you start scaring pilots out there.
Engines do not become derated over time. They always produce rated thrust if requested.
As the engines get older the EGT margin decreases. ie The older the engines get the closer they get to max EGT on a max rated thrust takeoff. When this happens you can remove them from a CF6-80C2B5F rated aircraft and install them on a CF6-80C2B1F rated aircraft (Rating change via plug change/pin programming). You then get longer out of them before you have to overhaul because at a lower rating it is like doing a derated takeoff and the EGT margin returns.For a while at least anyway.
So in summary. If the book says the engine is good for 63500 lbs. Then a new engine and a 30000hr engine will produce said thrust. The older one will be hotter.
744's do have EEC's. EEC is a generic term, possibly even a Boeing term. Each manufacturer has their own term.
Rolls Royce call them FAFC. Full authority fuel control.
Pratt & Whitney call them FADEC. Full authority digital engine control.
GE call them ECU. Electronic control unit.
You are correct that on a 744 RR that the FAFC doesn't control the VIGV's or bleed valves, but thats only because RR choose to do it that way. (They are pneumatically controlled)
GE do however control both of those items by the ECU via the HMU (Hydromechanical unit or carby)
Engines do not become derated over time. They always produce rated thrust if requested.
As the engines get older the EGT margin decreases. ie The older the engines get the closer they get to max EGT on a max rated thrust takeoff. When this happens you can remove them from a CF6-80C2B5F rated aircraft and install them on a CF6-80C2B1F rated aircraft (Rating change via plug change/pin programming). You then get longer out of them before you have to overhaul because at a lower rating it is like doing a derated takeoff and the EGT margin returns.For a while at least anyway.
So in summary. If the book says the engine is good for 63500 lbs. Then a new engine and a 30000hr engine will produce said thrust. The older one will be hotter.
I believe the 744's EECs don't qualify as FADECs because they don't control variable bleed valves or variable stator vanes (VIGVs for the RR), but I defer to any engineer on these finer points of engine control
Rolls Royce call them FAFC. Full authority fuel control.
Pratt & Whitney call them FADEC. Full authority digital engine control.
GE call them ECU. Electronic control unit.
You are correct that on a 744 RR that the FAFC doesn't control the VIGV's or bleed valves, but thats only because RR choose to do it that way. (They are pneumatically controlled)
GE do however control both of those items by the ECU via the HMU (Hydromechanical unit or carby)
