just show you what you want

 

 

*dont copy my photo

 

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

My reply to the OP is: Yes, I think so.

ha ha nice!!

Here's one of mine, taken over the Atlantic on the way back from Rio I seem to remember!;-)IMAG0053.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?

 

 

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.

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.

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?

Great Pics !

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.

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.

 

 

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.

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

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.

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