RB211-22B Actual Thrust Produced vs N1 Speed
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RB211-22B Actual Thrust Produced vs N1 Speed
Hi,
I have an interesting question. Being well aware that, like most Rollers the original RB211-22B used EPR as the primary power setting while in operations, what was the actual thrust curve like throughout the rotational envelope? I guess, in laymans terms what I am trying to say is how much thrust, in lbs (or kN, not fussy) is produced at idle, at 30% N1, 40% N1 etc up to the rated limit of 99.5% N1, in ISA SL conditions. Logic would say this is a straight line, but obviously it is not.
Anybody?
I have an interesting question. Being well aware that, like most Rollers the original RB211-22B used EPR as the primary power setting while in operations, what was the actual thrust curve like throughout the rotational envelope? I guess, in laymans terms what I am trying to say is how much thrust, in lbs (or kN, not fussy) is produced at idle, at 30% N1, 40% N1 etc up to the rated limit of 99.5% N1, in ISA SL conditions. Logic would say this is a straight line, but obviously it is not.
Anybody?
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Thrust is more or less proportional to fuel flow.
Also, for a single-spool engine, thrust is roughly proportionally to N1**4 (N1 to the 4th power). The different speeds of the multiple spools make the equation much more complex, but that is a starting point...
Also, for a single-spool engine, thrust is roughly proportionally to N1**4 (N1 to the 4th power). The different speeds of the multiple spools make the equation much more complex, but that is a starting point...
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Does this apply even to high bypass units? It makes perfect sense with a turbojet, that thrust would be proportional to fuel flow but as the LP speed increases surely that would be responsible for more of the thrust generated? I remember reading somewhere that approximately 20% thrust was generated at 40% N1 and 50% thrust was generated at 70% N1 but I was looking for some concrete figures really if available.
What makes a bypass even more complicated is the fact that the thrust ratio produced by the fan and the core varies with altitude. Someone told me that the fan of a bypass engine with a ratio of four produces roughly 75% of engine thrust at sea level but only 25% at cruise altitude.
Last edited by wondering; 26th May 2014 at 18:43. Reason: *
Mistrust in Management
Logic would say this is a straight line, but obviously it is not.
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Bingo! Well, if it was for the -22B 
Are these found in the performance manuals for the aircraft (L1011 in this case) or the maintenance manuals for the engine itself?
Are these found in the performance manuals for the aircraft (L1011 in this case) or the maintenance manuals for the engine itself?
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Sorry to be pedantic Tom355uk, but the old 211-22B used IEPR, not EPR as most modern engines do. IEPR (Integrated Engine Pressure Ratio) is a mix between P1 (fan inlet), P204P (or PF if you like), and P500 (LP turbine). 
