FS2004 Throttle to n2 question

[vololiberista]

Currently my table 1503 is



0 56 82.5
42 78.8 91.4
51 89.8 97.7
61 97.1 102.3
70 101.3 106
79 104.9 108.5
93 106.6 108.8
100 107 108.8
Which is not really correct because as you can see 80%n2 occurs between 42 and 51% of throttle position.
Also the graph is non linear.
Should the graph be linear?
And, if not what would be the ratio between then n2 numbers in order to have 80%n2 more or less at 80% throttle posiiton?
The start and finish numbers are correct!

 

[Heretic]

The shape depends on where you might want to have slightly greater throttle input precision. But other than that, I can see no reason why 1503 shouldn't be linear.

 

[vololiberista]

The shape depends on where you might want to have slightly greater throttle input precision. But other than that, I can see no reason why 1503 shouldn't be linear.

Thanks H. That will make it much easier to work out! I presume I'll have to adjust 1504 as well. Any others? could you remind me how to calculate the second line?

 

[Roy Holmes]

How to do 1503 and 1504 is covered in:
http://www.fsdeveloper.com/forum/th...titude-calculation-method.327725/#post-519944.

I use 100% CN2 at full throttle in this paper, but you can just scale up to cater for your 107%.

I would suggest you have more than two columns for the CN2 values because that will only give you answers for two altitudes. In between the sim will do a linear interpolation of a non-linear function. Having say 5 columns still has errors, but they are much less
Roy

 

[vololiberista]

How to do 1503 and 1504 is covered in:
http://www.fsdeveloper.com/forum/th...titude-calculation-method.327725/#post-519944.

I use 100% CN2 at full throttle in this paper, but you can just scale up to cater for your 107%.

I would suggest you have more than two columns for the CN2 values because that will only give you answers for two altitudes. In between the sim will do a linear interpolation of a non-linear function. Having say 5 columns still has errors, but they are much less
Roy

Hi Roy,
Yes, I downloaded the pdf. I tried mirroring your callculations and results but still can't get any agreement. So clearly I'm not doing something correctly.
Step 1 on the ground zero altitude is ok. But I couldn't repeat your figures.
Would you be kind enough to step through each calculation with an example so that I can follow the thread.
So that I can stick it in a spreadsheet.
Many thanks and Buon Natale

 

[Roy Holmes]

Page 6.
In 1503, for each IAP column the value should be calculated as 1/Sqrt(theta) for that IAP times the SL column value.
Altitude SL 10,000 20,000 30,000 36,089 50,000
IAP 1.0 1.4538 2.1743 3.3608 4.4593 8.6869
1/Sqrt(theta) 1.0 1.0362 1.0767 1.1222 1.1533 1.1533

 0       1        1.4538    2.1743    3.3608    4.4593    8.6869
0.0         56.00    58.03      60.30      62.84      64.58      64.58
.42         77.42    80.22       83.36     86.88      89.29      89.29
.51         82.01    84.98       88.30     92.03      94.58      94.58
.61         87.11    90.26       93.79     97.75    100.46    100.46
.70         91.70    95.02       98.73    102.91    105.76    105.76
.79        96.29     99.78      103.68    108.06    111.05    111.05
.93        103.43    107.17    111.36    116.07    119.29    119.29
1.00      107.00    110.87    115.21    120.08    123.40    123.40

Note:
1. The column 1 sea level percents are a straight line from zero throttle and 56% to full throttle and 107%.
2. If you use this and a corresponding 1504, see below, your N1 (not CN1) values will be correct and should be used for display.

1504.
In 1504 the values for each IAP column are the corresponding 1503 values times 1/Sqrt (1+.2*(M)^2). If High mach is 0.9 the scalar would be 0.9277.

1504            
   0.9   1        1.4538    2.1743   3.3608   4.4593   8.6869
0.0     51.95   53.83     55.94     58.30     59.92    59.92
.42    71.82    74.42      77.33    80.60    82.83      82.83
.51    76.08    78.83      81.92    85.38    87.74      87.74
.61    80.81    83.74      87.01    90.69    93.20      93.20
.70    85.07    88.15      91.59    95.47    98.11      98.11
.79    89.33    92.56      96.18    100.24    103.02    103.02
.93    95.95    99.43    103.31    107.68    110.66    110.66
1.00    99.26   102.86    106.88    111.39    114.48    114.48

Roy
PS I struggled with the table format!

 

[vololiberista]

Many thanks Roy,
It's a little clearer now! Hope you're enjoying your Christmas.

 

[vololiberista]

Another question relating to Aired. In tables 1503-4 it only seems to allow two lines of data to be displayed. Do you know how to create more lines of data?

 

[Roy Holmes]

Get a copy of AirUpdate, It is the easiest way to modify airfiles with tables. You can download it from the Mudpond site.
The update file would be called Update 1503.txt, or whatever the record number is.
The format in the update file is:
Record: 1503 Turbine LoMach CN2 vs Throttle and Pressure Ratio
columns: 7 rows: 9
0 1 1.4538 2.1743 3.3608 4.4593 8.6869
0.0 56.00 58.03 60.30 62.84 64.58 64.58
.42 77.42 80.22 83.36 86.88 89.29 89.29
.51 82.01 84.98 88.30 92.03 94.58 94.58
.61 87.11 90.26 93.79 97.75 100.46 100.46
.70 91.70 95.02 98.73 102.91 105.76 105.76
.79 96.29 99.78 103.68 108.06 111.05 111.05
.93 103.43 107.17 111.36 116.07 119.29 119.29
1.00 107.00 110.87 115.21 120.08 123.40 123.40

Same for 1504. The columns and rows data is included as part of the record. If you get it wrong all sorts of unspeakable things may happen to your airplane in the sim.

Roy

 

[vololiberista]

Many thanks Roy.

 

[vololiberista]

Did everything correctly (thanks for that), but could you confirm or deny if FS2004 willl accept more than two lines in those tables. The sim wouldn't start posting a sim1.dll error. The aircraft is set up as the default on start-up. I re-created the files 1503/4 with 2 lines i.e. the first and last lines and the sim loaded ok. I did a low altitude test which went ok. Will do a high alt test tomorrow.

 

[Roy Holmes]

That is a good question. It was not until the ESP SDK was made public that the structure of air files was officially described by Microsoft.
Currently the table is described as:

"Commanded N2 (corrected) vs. Throttle table at 0 Mach (max 9 rows, 11 columns)"

I assume you have changed the file to be 3 columns and 9 rows. That is one column for throttle position, one for sea level and one for high altitude.

I would recommend that if you only have one high altitude column to use the one headed by IAP=4.4593 . This is for 36089 ft (tropopause). If you fly higher FS2004 will try to extrapolate, so it may become inaccurate, but you are better off with the tropopause value because it will give a better result at lower altitudes than the 50,000 ft column=8.6869The reason is that the sim interpolates linearly. So with the 50K high altitude, if you are at 25K the sim will take values mid way between the 50K and 0K columns. This would give you a full throttle 115.2 value, which should occur at 20K.

I have not used FS2004 for a long time, but I note that none of the old ex 2004 airplanes I still have in FSXA have more than 3 columns in 1503.
I will try to find out from some of my fellow greybeards
Roy

 

[vololiberista]

Thanks for your reply Roy.
In Aired the columns are rows and rows are columns. I have already done as you have suggested and have one row for sea level and the other set to
tropopause.
Now I have to also reset the throttle setting for reverse. It's currently giving max reverse 85%n2 instead of 93%. There was a film called Never Ending Story, but I don't recall any scenes about aircraft modelling!!

 

[vololiberista]

I've put everything into a spreadsheet so if I need to change a throttle setting everything else changes too. And, displaying all the numbers as a graph in excel makes everything a lot easier to see.
I might still change the throttle reference percent points as there is still a little more movement in the throttle at the top end than there should be. But, otherwise it's on the nail.
Many thanks.

 

[Roy Holmes]

Glad you were able to do this.
BTW, I checked with my FDE Guru, Jerry Beckwith and he sent me an example air file that works with FS2004. The 1503 and 1504 entries have 9 throttle position rows and 7 columns (one for throttle, six for different altitudes.
So it appears the 1503 and 1504 I sent you should work. They will if you use AirUpdate to insert them into the air file. Key is getting the columns and rows numbers correct and in the right place. Since the air file is binary, these numbers tell the software that reads the data how long the Record is. Without that correct, the air file is,essentially, corrupt.

Up to you, If you want I can send the data in an update file that AirUpdate can read. If your are happy with what you have, so be it.


Roy

 

[vololiberista]

Many thanks Roy. I would very much appreciate having a look at your update file as well. I have another question relating to a reply to me on another forum."VC10.net"

Slamming the throttle to max, the engine could go over 100% at isa conditions but the engine would normally be limited by the max P3 pressure (HP comp outlet pressure).
The engine limiters and controls are valid thoughout the aircrafts entire flight envelope inc on the ground.

In my numbers i.e 56% to 107% n2 in table 1503 I made the assumption that full throttle would take the engine into "limitations" territory therefore I supposed 50% throttle to be around the 80% plus mark. So from the reply I got it looks as though I'll have to revise down some numbers. So.....
Q1. I don't think that there is a method in the sim to "limit" n2 other than in the airfile tables?
Q2. Assuming then that 100% throttle equals 100% n2 in ISA conditions at sea level that would change would it not at a hot and or high airfield?
I'll have another bash at re-creating 1503/4 but aired did present the correct format for the table so I was surprised fs2004 didn't like it.

PS revising down the key n2 numbers in 1503 means does it not that I'll have to play with 1505 too "I think!" (though thinking for me is a dangerous pastime!)

 

[Roy Holmes]

Here are the update files for 1503 and 1504 using the values I sent earlier, ie not adjusted to give 100% max. I can easily do that if you decide to go that way. These files are for use with AirUpdate, to ensure you get the row/column issues sorted out.

Without using SimConnect, which does not work for FS2004, I think you are stuck with the CN2 values in 1503 and 1504. You can fudge them for CN1 being something else in 1502. However, as soon as you have different values for CN1 and CN2 in 1502, all bets are off as regards thrust and altitude in 1506 unless you do an awful lot of empirical screwing around.

A slam to full throttle could in theory cause a temporary overshoot in RPM, but it is so slow to get to 100% or whatever max you have that I doubt it would happen.

Q2. Assuming then that 100% throttle equals 100% n2 in ISA conditions at sea level that would change would it not at a hot and or high airfield?

If you have 1503 and 1504 set up properly, N1 will stay at 100% (or whatever max you have) as altitude is increased, though thrust will decrease. AFAIK the atmosphere is FS is always standard.

I no longer use aired because AAM is better at presenting tables. I use AirUpdate for any table issues in the airfile because of the ease in copying and pasting data from Excel into Notepad++.

PS revising down the key n2 numbers in 1503 means does it not that I'll have to play with 1505 too "I think!" (though thinking for me is a dangerous pastime!)

Probably not. In general, you need to make sure that 1505 has CN2 values at least as high as any of the other turbine tables, or it will limit those.

One final point. The turbine tables use "corrected" values like CN2. Do not confuse them with real values like N2. They are only the same at SSL.

Roy

 

[vololiberista]

Many thanks Roy. Another late night for me then!! Yes I am aware N2 =CN2 at sea level only. As far as 1505 goes I might chip a couple of percent off the top but from what you say it might not be necessary. The engine limitations schedule for RR Conway 550B(installed into the Super VC10) allows 102%n2 for 5 minutes whereas for the RR Conway540 (installed into the Standard VC10) only 100% for 5 minutes. So yes one can indeed firewall the throttle for take-off. What a sight they would have been if they had ever flown into St. Maarten. They would have blown the entire tourist population into the sea!

 

[vololiberista]

Hi Roy,
Here is the table 1503 as created by air update and displayed in aired. As you can see it's perfect. Apart from one entry which I corrected later.

But, fs2004 v.9.1 will have none of it and crashes with the same sim1.dll error as before. Why is a mystery. I'll fiddle around a bit more to see if I can get it to work. But if not I'll have to revert to plan Z with just 2 lines :-(

 

[vololiberista]

Hi Roy,
There were some discrepancies in the text files you sent which I thought might be the problem viz. in 1504 the throttle %s were all whole numbers instead of decimals. Also in 1503 there was an 8 instead of 108. Plus lots of spaces here and there. I tried every permutation and both AAM and aired always display correctly. But, fs2004 refuses to work with anything over 2 lines.
The only thing left to do is to find an air file with 1503 and 1504 tables similar to yours that apparently does work in fs2004 and substitute it and see if that is accepted. However, none of my aircraft have more than 2 lines. So it looks as though I'll have to remain with 2 lines :-(