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Has anyone noticed that LRC has increased from the .85 area to over .86? 

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Hi,

If I'm not wrong the calculated Mach number with LRC depends on the cruise level and weight.

FCOM page PI.11.2 shows the long range cruise control. the Mach number ranges from .706 to .861.

Do you compare the LRC Mach number calculated by the FMC with a same weight and cruise level?

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Yes, very true. Good information. After looking over the chart, current GW of 811,000lbs at FL300, Mach .861 is within limits. I guess I just never saw it that high before. My EPR of 1.55 seems a bit high though? I notice that the chart is Performance Inflight - All Engines but also says 747-400/PW4056. I'm on RR engines. Could that be the reason for the difference in EPR values? My fuel flow is pretty close to the chart. 

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I read somewhere that EPR is not calculated the same way on RR and PW engines but I'm not an expert! :blush:

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1 hour ago, Budbud said:

I read somewhere that EPR is not calculated the same way on RR and PW engines but I'm not an expert! :blush:

I just checked, the Rolls-Royce engines can have a take-off power setting of up to 1.71 on the EPR, with the Pratt & Whitney engines being around 1.60 on the EPR.

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2 hours ago, Budbud said:

I read somewhere that EPR is not calculated the same way on RR and PW engines but I'm not an expert! :blush:

It's not so much that it's calculated differently but the engines have different characteristics. EPR is exhaust pressure divided by intake pressure. Force = pressure * area, so thrust will also depend on intake and exhaust areas. These of course differ between the RR and PW engines. There are other differences which affect things. So the same thrust will have a different EPR. This applies equally to different engines from the same manufacturer. An RB211 will have different a EPR to thrust relationship compared to a Trent.

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2 hours ago, Budbud said:

I read somewhere that EPR is not calculated the same way on RR and PW engines but I'm not an expert! :blush:

The RB211 uses IEPR (Integrated Engine Pressure Ratio) which takes in to account the fan bypass air as well as the core jet exhaust.

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Kevin and Simon, thanks for the info. I had an idea of what EPR is but not deep knowledge of the engines, not enough to be able to answer why the EPR values are different on both engines.

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