Turbine N1 values

[Luke Kolin]

I have been reading turbine N1 from 0x898 for jets, but I'm getting bad values on turboprop aircraft since this apparently returns back the prop RPM instead. I notice that there's an N1 value at 0x2000 that returns this data for jets and turboprops. I assume it's safe to use this offset instead?

Out of curiosity, why are there different offsets that seem to return the same data?

Cheers!

Luke

[Pete Dowson]

I have been reading turbine N1 from 0x898 for jets, but I'm getting bad values on turboprop aircraft since this apparently returns back the prop RPM instead. I notice that there's an N1 value at 0x2000 that returns this data for jets and turboprops. I assume it's safe to use this offset instead?

I'm not sure what you mean by "safe". You certainly can't blow anything up reading any of it! :-) But I don't really know one value from another when it comes to turboprops -- best to use FSInterrogate and check for yourself what the values are. That is why it is provided in the SDK.

Out of curiosity, why are there different offsets that seem to return the same data?

History? Most of the lower numbered engines data sets date back to FS98 (before, but at slightly different offsets). They are maintained for compatibility for the many programs developed then and since. As other values come to light, I map them in case they are of any use. It is up to aircraft experts (such as yourself perhaps?) to determine whether they are truly the same or not, useful or not. Many have been found by others and I've been asked to add them. I really can't remember the history of some.

The values listed in the second table in the programmer's guide may or may not be available in future versions of FS. If folks find stuff important there and can explain exactly what it is and how useful it is, I usually "promote" it to the first table so that I make an effort to find it in the next version, if possible.

Regards,

Pete

[Luke Kolin]

best to use FSInterrogate and check for yourself what the values are. That is why it is provided in the SDK.

Fair enough. I did a quick smoke test changing the offsets to read and it appears to work well. I do have one question - offset 0x2000 in the SDK refers to N1, whereas 0x2010 describes "corrected" N1.

What does "corrected" mean?

Cheers!

Luke

[Pete Dowson]

Fair enough. I did a quick smoke test changing the offsets to read and it appears to work well. I do have one question - offset 0x2000 in the SDK refers to N1, whereas 0x2010 describes "corrected" N1.

What does "corrected" mean?

Good question -- I assume it is meaningful to those who understand what N1 and N2 and so on really are. The descriptions are as provided to me by such an expert. Perhaps I should have asked for a definition, but I assumed anyone who was likely to want to use them would also understand what they meant. And it all happened at a time when I was extremely busy.

Can you tell anything by looking at the values?

Regards,

Pete

[lefteris]

Fair enough. I did a quick smoke test changing the offsets to read and it appears to work well. I do have one question - offset 0x2000 in the SDK refers to N1, whereas 0x2010 describes "corrected" N1.

What does "corrected" mean?

Good question -- I assume it is meaningful to those who understand what N1 and N2 and so on really are. The descriptions are as provided to me by such an expert. Perhaps I should have asked for a definition, but I assumed anyone who was likely to want to use them would also understand what they meant. And it all happened at a time when I was extremely busy.

Can you tell anything by looking at the values?

Regards,

Pete

Gents-

Ron Freimouth has this to say in one of his tutorials:

"* CN1/CN2 are 'Corrected N1/N2' The panel gauges indicate N1/N2.

N1=CN1*Sqrt(TAT/288).

Where TAT is Stagnation Air Temperature in degress Kelvin.

C deg = K-273. Note 288 K is 15 C, the standard reference

temperature. Since temperature is low at cruise altitudes,

N1/N2 are about 10% below CN1/CN2 at cruise conditions."

[Pete Dowson]

[

Ron Freimouth has this to say in one of his tutorials:

"* CN1/CN2 are 'Corrected N1/N2' The panel gauges indicate N1/N2.

N1=CN1*Sqrt(TAT/288).

Where TAT is Stagnation Air Temperature in degress Kelvin.

C deg = K-273. Note 288 K is 15 C, the standard reference

temperature. Since temperature is low at cruise altitudes,

N1/N2 are about 10% below CN1/CN2 at cruise conditions."

Thanks, Lefteris. Do you think he'd object to me putting something like that in the SDK?

Regards,

Pete

[lefteris]

I doubt it, Pete, but I can't vouch for Ron - I don't really know him personally...

If I were the author, I clearly wouldn't mind, provided you quoted me.

Also- you could look this stuff up on Google - there are plenty of similar explanations on there as well about it.

[Pete Dowson]

Also- you could look this stuff up on Google - there are plenty of similar explanations on there as well about it.

Done. Thanks!

Pete