I have created a modification of the Captain Sim EPR gauge so as to give accurate readouts.  The FSX EPR variable simply does not work properly and I don't even know if that is what Captain Sim uses.  Anyhow, my modified gauge expresses EPR as a function of corrected N1.

Does Captain Sim have any position on distributing its XML files in modified form? I am not going to do that without its permission.  However, I could simply post instructions on how to modify the necessary files.  Does Captain Sim have any problem with my doing that on this forum?

To properly set power you still need a TAT gauge and power setting tables.  I am using a TAT gauge from another product -- it's not particularly difficult to find a gauge and add it to the panel.  The power setting charts are available on the web as part of the manual for another product. I don't think this is the place to give the details for that.

I would be interested in getting this information (the xml code or at least the formulas) if permitted.

I would certainly be very interested in this too.  It was one thing I noticed and submitted to Captain Sim and I was told it was 'on the list for the next update'.  EPR behaviour in their 757 is the same.  I don't think it's an FSX limitation, as other developers (forum deleted the names) have modelled it ok.

I believe it is a well documented limitation of FSX and other developments have also used Corrected N1 as the basis for generating EPR values.  My modified guages work quite well based on the data I have. It may be a little off at very low values -- less than 1.3 as I could not fit a curve to that part of the data.  Also, the relationship between N1 and EPR is going to vary a bit with engine variants. I believe the data I have used is for one of the earlier engine types. So you need the performance charts for the same data, which is readily available to download from another developer that did an FS9 727.

I don't want to annoy Captain Sim, so I guess I'll just post the code and how to use it on the un-official CS forum on Avsim within the next day or so, when I have some time.

The other thing I really would like to fix is the inability to descend at engine idle at a realistic speed, although I think that might be quite difficult to do without messing up the rest of the flight model.

I posted how to edit the files on the Avsim forum. Please backup files as suggsted and proceed at your own risk.

Where have you got the engine data please? I mean how do you know your correctons are correct?

There are charts available on the web that show N1, N2 and EGT for varying TAT values for JT8D engines. I used the data points for a TAT of 15'C, since Corrected N1 is supposed to show what N1 would be at that temperature.  I used the charts published by another developer for its FS9 727 for my data.  You can see my Avsim post to determine which one.  But I also found another set of charts at a site called "my cockpit" for a later engine variant for the 727-200 -- I haven't made use of that yet.  Finally there is also a 727 website (www.boeing-727.com) with engine data for many variants ; it only gives a few data points for each engine type.

I used a regression program to fit a curve to the data points.

I don't have the source documents used to create the charts mentioned above, but I believe the original authors had something authoritative.

Good afternoon Michael -

Just FYI, there are two small glitches with your instructions. I figured it out though and they seem to work great...at least the gauges appeared and the needle moved.

I'll reply in the AVSIM forum to clarify where I ran into trouble.

Thanks for doing this!

Thanks Matt for pointing that out.

You bet.

I'm making a nice approach into Bermuda right now with it...

I'm probably not the guy to pull out complex performance charts, but I do find that expanding the gauge's range (now tops out well above 2.0 instead of 1.8) makes it easier to get feedback on my current power setting.  In other words I feel like I can fine-tune my power better.

So even for that, it's worth it!

Matt

Michael2 wrote on Nov 25^th, 2009 at 7:23pm:

I don't have the source documents used to create the charts mentioned above, but I believe the original authors had something authoritative.

Also do we. Anyways, if the community will confirm your mod is better than the original we can include the mod into the next update.

That would be great -- you are very welcome to do so.