How do I calculate the X coordinate in .air file Record 1505

How do I calculate the X coordinate in Record 1505 of the .air file from the information provided in the attachment? For the purpose of the exercise please assume the figures provided are correct.

The progression of the columns in the attachment is from right to left. The blue figures are, or are the equivalent of, published figures.

I am aware of the formula in the help section of R1505:

FF (pph) = Thrust_Reference * R1505 (N2) * Delta_t / sqrt (Theta_t)

but don't know what Delta_t or Theta_t are and am not sure about Thrust_Reference.

Some assistance would be appreciated.

Hi,

It appears that the chart is showing fuel consumption under varying conditions of speed and thrust. Referring to "X" as a coordinate doesn't seem to apply here. Perhaps a dependent variable but of what I have no idea.

Are you trying to correct a problem you perceive or simply trying to learn how things work? It's all okay with me but you'd likely get a better informed response at FSDeveloper.

Jim F.

Sections 1502 up through 1507 are all mutually interdependant. To try and look at just one, and just one small statement within it is meaningless. Personally, I'm not sure which .air file editor you are using. I use AIrEd, and it represents 1505 as a graph, which makes adjusting the Y values (it uses) very easy.

For a fantastic, if a bit simplified explanation of how those section all interleave, do a Google search for jet_flow_chart.pdf. It's a little one-page PDF but it explains those sections, and how the inter-relate very well, to include a "flow chart" for how FSX performs jet engine calculations utilizing those 6 sections.

EDIT:

Also, you may want to take a glance at THIS SITE, and THIS SITE. The first is an actual Jet_Aircraft.ASM file, with explanations of each section, and the second (yeah I got them bass-ackwards), is an explanation of how the ASM files are made and then converted into .air files. This is all from the ESP SDK, and the whole thing over-all is an amazing wealth of information on every aspect of making flight sim aircraft.

end edit

Just some thoughts on all this to try to help.

Pat☺

Attached is a full set of the JT8D-17 engine parameters I am currently using, and a copy of the chart/graph from which the figures in R1502, 1506 and 1505 were obtained. I've set up parameters for JT8D-7, -9, -11 and 15 engines using the same method.

I decided to ignore the word "corrected" as being beyond my capabilities to work out and to see what would happen if I constructed the engines using only basic published N1, N2 and Thrust lb data, and ignoring the difference between high speed and static and high altitude and MSL.

There must be some merit to the way I've set these parameters up as Tom Ruth's B727 N2-N1 gauge couplings agree exactly with the N2-N1 couplings listed under R1502 (much to my surprise).

The aircraft achieves max cruise (514 knots, M0.845 at 22,000 feet) at N2 89.7 N1 87.7 (below published max cruise N2 90.0 N1 88.4) at a weight of 203,000 lb, and max level speed (548 knots, M0.900 at 21,600 feet) at N2 91.1 N1 91.2 (below published max continuous N2 91.4 N1 91.8) at the same weight 203,000 lb. While the published figures don't include the aircraft weight at which these two speeds should be achieved or tested, the results of these two tests appear to indicate that the thrust in R1506 is being delivered. I may even have to increase drag a little.

My problem appears to be a slight lack of something (?) in the takeoff roll (see Post: "Saved from a watery crash by the aircraft's shadow") and, as I don't know how to calculate the X coordinate in R1505 or Mass Flow in R1507, I think the problem might lie there.

I checked out the suggested sites (thank you). Some of the content was already known, the rest beyond my abilities to understand or apply.

Some constructive advice would be appreciated.

I just dug up a PDF that may prove of assistance in your situation. FS Thrust vs Altitude calculations.zip I have no idea where I found it, but i am sure a quick Googe search will turn it up. It explains extremely well how to find all values needed and where to place what value in the records in the .air file.

Essentially, you need a freeware program from NASA and Airwrench, a payware program, and they will either generate the values you need, or verify what values you have input already.

I'm sorry I'm not much more help in this, but take a look at the PDF I named above. It IS a lot of help. Truuuust me! I used to work for the government!

Pat☺

Thanks for those links Pat. I just started out with Air files. Lots to learn. This comes in handy! (bit of an information overload, but I'll manage eventually.)

I'm so dizzy... my head is spinning...:)

FS Thrust vs Altitude calculations.zip comes from

http://www.fsdeveloper.com/forum/resources/fs-thrust-vs-altitude-calculations.43/

There are several other threads ion that forum dealing with engine performance for those who are interested.