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bensoncpwong

777~200er fuel pages

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Here's one of mine, taken over the Atlantic on the way back from Rio I seem to remember!

;-)

 

 

 

For those of you with sharp eyes, it's a Roller. :-D

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Here's one of mine, taken over the Atlantic on the way back from Rio I seem to remember!;-)attachicon.gifIMAG0053.jpgFor those of you with sharp eyes, it's a Roller. :-D

Speedbird 248! Definitely a 200/ER with those trents. Got any tips about going from N1 > EPR as primary engine gauge? Still trying to get my head around it. Also, why were you guys in True heading mode coming back from Rio?

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Got any tips about going from N1 > EPR as primary engine gauge? Still trying to get my head around it.

No offense Luke, but what is there to get your head around?  It's the same thing expressed in terms of a different engine parameter.

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No offense Luke, but what is there to get your head around?  It's the same thing expressed in terms of a different engine parameter.

Ha yeah I know - just mainly for Derates etc I'm so used to using the percentage for N1, not sure what to use for EPR and what will be too much or too little.

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I understand Luke and I question myself the same thing. What's the difference between using N1 and EPR as the primary parameter? Is it just manufacturer's choice or is there any advantage on using one or the other?

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What's the difference between using N1 and EPR as the primary parameter? Is it just manufacturer's choice or is there any advantage on using one or the other?

 

One aspect of it is that the N1 shaft speed does not linearly correlate with the actual thrust being developed by the engine; e.g. the difference between thrust deliverd from 95% N1 and 100% N1 is not the same as the difference between 55% and 60%.  The Engine Pressure Ratio, on the other hand, is nearly a direct measurement of thrust and thus changes in EPR are closer to linear with respect to the change in developed thrust.

 

I'm sure there are other aspects that would cause N1 to be so commonly used despite this one difference, and I'd enjoy hearing more.

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The prime difference is that Roll Royce patented the use of Engine Pressure Ratio as a way of showing high bypass thrust. Hence GE can't use it. As you can see in the picture N1 is also displayed below the EPR figures.

 

As far as 'derate' goes it is purely a function of the critical data setting procedure. We apply, through ACARS, for performance figures based upon the aircrafts TOW and the ambient conditions. The performance calculation comes back with three possible weights to allow for last minute changes, the associated de-rate and the V1, Vr and V2 figures.

 

We then enter the de-rate into the FMC which calculates whether it will be a full CLB power, CLB1 or CLB2. Once on the runway you advance the throttles until the EPR needle is pointing at the 'E' of EPR and that will stabalise the engine at approximately 55% N1.

 

Then press the TOGA switches to advance the power to the limit set by CLB, CLB1 or CLB2 and that's it.

 

As for True, we were out over the Atlantic tracking up the west coast of Africa on an oceanic route, hence True and Tracks.

 

Enjoy.

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I'm so used to using the percentage for N1, not sure what to use for EPR and what will be too much or too little.

 

What's the difference in getting used to pointing the RPM needle of your Piper at 2500 RPM and the N1 needle of your NG at 95%?

 

Part of the reason people started using N1 to begin with is to make the processing easier on your brain.  The brain picks up on issues on bounded numbers a little more readily with a bounded number (percentages are bounded between 0-100%), as compared to an unbound scalar (RPM).

 

While EPR is not bounded like %-based N speeds, it's giving a scaled pressure ratio between static (1.00) and how much is being developed by the engine.  Higher values = more thrust.  The difference is that N speeds are really rotational speeds for the engine, and EPR values are directly derived from thrust output.  If I removed the fan blades from an engine and spun it at whatever 95% N1 was, the N1 gauge would read 95% even though I wasn't developing thrust at all.  Looking at the EPR gauge, you'd only see 1.00, however, and would realize that you were developing no thrust even at 95% N1.

 

It's just a different way to show overall engine output.

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Hi, GregL

 

Thanks to you and the others for explaining the difference between N1 and EPR.

 

Also, I would like something clarified for my own understanding.  I am not a RW pilot so my experience is based entirely on flying FS T7s and other Boeings, such as the PSS T7 and Level-D 767.  So I am happy to have the chance to learn from a RW T7 pilot.

 

You said,

 

 

Then press the TOGA switches to advance the power to the limit set by CLB, CLB1 or CLB2 and that's it. 

 

 

My understanding is that when TOGA is pressed at takeoff the aircraft goes into TO, TO -1 or TO-2, or TO-D(derate) mode, depending on the FMC setting, until reaching acceleration altitude.  Then it goes into CLB, CLB1 or CLB2 depending on the FMC setting.  Is this wrong? 

 

Also, could you explain further why you were using true heading and track mode?  I thought true heading was only needed near the N & S Poles. 

 

Thank you very much,

 

Mike

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Mike,

 

You are quite correct I put the wrong abbreviations in my post, they should read TO, TO-1, TO-2. BA does not use TO-D.

 

Until 80kts the TOGA switches will select TO, TO-1 or TO-2. After 80kts the FMA annunciates HOLD mode.

 

After take-off with VNAV engaged the FMA will default to CLB mode. I will check on this, I'm flying this evening and I'll have a look and report back. Normally I'm a little busy at that point! :-)

 

The reason for using TRUE and TRK for the Atlantic crossing is purely to avoid GNE's, gross navigational errors. We can cross refer our flight plan to a book of tracks and distances that we carry to ensure that the track and distance between two way points is correct. Often the waypoint will be abbreviated in the FMS, N5030 for example should be 50 North 30 West but it can be 50 North 30.30 West so we must check the waypoints. As the flight plan gives us the tracks and distances based upon True and ground Track that is what we fly.

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GregL, thanks for your clarification.  Have a safe and pleasant flight!

 

 

 


After take-off with VNAV engaged the FMA will default to CLB mode.

 

I never paid much attention to this switchover until I started flying a certain Brand-X T7.  It does NOT automatically switch to climb thrust in VNAV, with the result that the aircraft climbs at a very high rate, puts too much virtual wear on the virtual engines, and often busts the first altitude constraint.

 

Mike

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GregL, thanks for your clarification.  Have a safe and pleasant flight!

 

 

 

 

I never paid much attention to this switchover until I started flying a certain Brand-X T7.  It does NOT automatically switch to climb thrust in VNAV, with the result that the aircraft climbs at a very high rate, puts too much virtual wear on the virtual engines, and often busts the first altitude constraint.

 

Mike

You have no acceleration altitude selected. Normally it will be 1000' above the field. It must be put in next to the Flap setting. If not the engines will stay in take off power and never return to CLB.

 

The standard profile is take off thrust to 1000ft with V2 selected as the climb speed. At the Acceleration Altitude the aircraft will nose over and accelerate as long as a speed profile say of 250kts below 10000' is selected.

 

If flying manually then select Vref30 + 80 at AA to accelerate the aircraft manually. If the engines remain at TO power then press the CLB/CON button or FLCH to the cleared altitude. Both will engage autothrust.

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Aha, got it! Thanks guys

 

Welcome.

 

Also, I don't see a reason to use True on the NATs, though I'd defer to Greg for a more accurate answer.

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Had a good look at it last night. Rather useful I must say. Often we do these things so many times it becomes 'habit' and therefore was quite a useful exercise to have a good look and re-familiarise myself with exactly what the FMS & Auto thrust is actually doing.

 

On the Thrust settings page you enter the de-reate temperature as given on the performance sheet taken from ACARS. This will give you D-TO and a temperature on Line 1 of the FMS. The computer will then select CLB, CLB-1 or CLB-2 for the thrust setting at take off depending upon weight, altitude of the airfield and ambient temperature.

 

Select the flap and the accel altitudes, enter the v1 and enter/confirm the Vr & V2 and put the MACTOW into the box for the stab trim.

 

Once on the runway the TOGA switches will give you the FMA 'THR REF' and the EICAS engine thrust limit will be set to CLB, CLB-1 or CLB-2. At 80kt's the FMA goes to HOLD and then after rotation and gear selection it reverts back to THR REF with the EICAS engine mode at CLB, CLB-1 or CLB-2. Once at level off (VNAV engaged throughout) it reverts to SPD.

 

That's the standard departure profile I flew last night.

 

NATS tracks are given with ITT between each point and must be flown in TRUE with TRK.

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NATS tracks are given with ITT between each point and must be flown in TRUE with TRK.

Interesting! Will be doing so in the future (-:

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The prime difference is that Roll Royce patented the use of Engine Pressure Ratio as a way of showing high bypass thrust. Hence GE can't use it. As you can see in the picture N1 is also displayed below the EPR figures.

Pratt and Whitney use EPR too and I'm sure they used it before Rolls Royce did, so I don't see how RR can have a patent on it.   RR (Bristol) used to use engine pressure difference as the basis of a percentage thrust indication.  Other RR engines used P7 (exhaust pressure) and RPM.  I believe the first engine RR used EPR on was the RB211 but I could be wrong.

 

On a high bypass turbofan N1 correlates quite well with thrust.  It really doesn't matter that much which parameter you use. The rated thrust limit (lb or kN) can be expressed as the equivalent in either EPR or %N1.

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Ha yeah I know - just mainly for Derates etc I'm so used to using the percentage for N1, not sure what to use for EPR and what will be too much or too little.

Probably better not to think in terms of the %N1 reduction at all, but the assumed temperature and/or the fixed derate level that comes out of the takeoff charts.  So it's essentially the same process for PW, RR or GE engines. 

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Had a good look at it last night. Rather useful I must say. Often we do these things so many times it becomes 'habit' and therefore was quite a useful exercise to have a good look and re-familiarise myself with exactly what the FMS & Auto thrust is actually doing.

 

On the Thrust settings page you enter the de-reate temperature as given on the performance sheet taken from ACARS. This will give you D-TO and a temperature on Line 1 of the FMS. The computer will then select CLB, CLB-1 or CLB-2 for the thrust setting at take off depending upon weight, altitude of the airfield and ambient temperature.

 

Select the flap and the accel altitudes, enter the v1 and enter/confirm the Vr & V2 and put the MACTOW into the box for the stab trim.

 

Once on the runway the TOGA switches will give you the FMA 'THR REF' and the EICAS engine thrust limit will be set to CLB, CLB-1 or CLB-2. At 80kt's the FMA goes to HOLD and then after rotation and gear selection it reverts back to THR REF with the EICAS engine mode at CLB, CLB-1 or CLB-2. Once at level off (VNAV engaged throughout) it reverts to SPD.

 

That's the standard departure profile I flew last night.

 

NATS tracks are given with ITT between each point and must be flown in TRUE with TRK.

 

Do you guys arm lnav and vnav before takeoff?

 

Alex

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GE engines move a lot of air from the N1 fan around the engine so that may be the reason they prefer to use N1 as an indicator. Sort of like a turboprop , the engine thrust is converted to mechanical energy to spin the fan and the GE's in particular give a high percentage of thrust from it. 

 

Eric W

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Do you guys arm lnav and vnav before takeoff?

 

Alex

Yes, after the thrust setting procedure the MCP is set up. If I expect to fly the departure as published laterally in the book then Lnav will be engaged. If I am expecting radar vectors after TO, especially in the USA, then runway heading will be selected in the MCP and Lnav left off. We always engage Vnav in order to get the correct noise reduction profile displayed on the flight directors during take off, even if manually flown. Vnav will also give you correct FD guidance in the even of a single engine failure.

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