FYI: How to get real N1% Flex settings

[Guest ciropv]

This post is for those of you that want a workaround to get real N1% settings using Flex temps.(before you continue, you need the document a340performance.pdf. You can find it: -http://perso.wanadoo.fr/hsors/FS_Soft/acftdata.html -or at avsim, searching "a340perf.zip" (searching by filename)As you should know, there is a bug in pss buses MCDU in the use of Flex temps. I have read a lot in this forum about flex temps, how it shoud be, how it is, the minus "-", the 999...Well, at least I have found where exactly is the BUG, and how to bypass it; what value you have to put in the mcdu, etc. (and it is not as simple as putting a minus "-" before).I am NOT going to explain WHAT IS the flex temp (you have some really nice posts in this forum that explain it much better than I would). I am going to explain WHAT YOU HAVE TO PUT in the MCDU and WHAT YOU GET (N1%).____________________________________________WHAT WE WANT TO GETWhat we are trying to get is a N1% power for takeoff, that has to be: - Lower than the Max TO power (TOGA Power), but not lower than 75% of that power, at that conditions (OAT and Alt) - Higher than the CLB power in the same conditions. - Enough for letting the craft take off with a given TOW and a given runway lenght and OAT.This N1% setting will be computed by the MCDU using a value that we put in the Flex field of the Perf TO Page of the MCDU.(we all already know this)____________________________________________HOW WE GET THAT VALUEYou can get the Flex temp: -Using the charts provided in the document mentioned above -Using free/pay tools like TPC (http://www.flightxpress.de/files/0604/Tools/TPC.exe) or Tomaflex (http://www.tomaflex.net/)(we all already know this, too)____________________________________________THE PROBLEMOk, the bug is a question of concepts:In real life, pilots put that value in the Flex field of the Perf TO Page of the MCDU. The MCDU using some calculations taking into account Altitude, OAT and the given Flex Temp, gives as a result a N1% setting for takeoff. (Chart on page 11).In PSS MCDU, when you assume a higher temp (e.g. OAT=35, FLEX=50), PSS gives you the N1% setting you should get at TOGA power when OAT=50. TOGA N1% when OAT=50 is something like 96.3%. If you use the real chart on page 11, you will see that at Sea level, OAT=35 and FLEX=50 your N1% setting is = 88% (92% if we are talking about PSS -I'll talk about this later-), wich by the way, is neither the "96%" you get if you type "50" at the Flex field nor the "85%" you get if you type "-50" (as someone has suggested). So for OAT=35 at SL:[blockquote]TOGA --> 98%We need --> 92%FLEX50 --> 96% (almost TOGA)FLEX-50 --> 88% (too low!)[/blockquote]____________________________________________THE WORKAROUNDSo I have prepared 2 tables (one for ALT=SL, another for ALT=2.000 ft) so you can know what is the N1% setting you should get for a given data (Flex, OAT, Alt). The PSS bus gives 4 points more power than the real thing at CLB (if the real thing will give you N1=88%, at the same conditions PSS gives you N1=92%), and 2.5 more points at TO. The tables are already corrected to take this into account.http://forums.avsim.net/user_files/124919.gif***** This is TABLE 1 *****And one more table that has the N1 settings you should get for a given OAT (wich is what the pss MCDU will use as flex).http://forums.avsim.net/user_files/124920.gif***** This is TABLE 2 *****____________________________________________THE PROCEDURE1. Get your Flex temp using any valid method (charts, TPC, tomaflex,...)2. Enter Table 1, cross OAT and FLEX and get your N1% setting. (take into account ALT; if you are between SL and 2.000, interpolate).3. Enter Table 2, and check that your N1 is higher than the CLB power for your OAT.4. Look into the TO column, search for your N1, and take the OAT for that value. THAT IS THE VALUE YOU SHOULD USE AS FLEX IN YOUR MCDU.____________________________________________THE EXAMPLEWe are at GCLP03L. 3100m. Sea Level. No wind. 26

[Guest vrandar]

This is really interesting stuff and well worth studying. I too have been working on a (personal) flex temp calculator spreadsheet for the A319/A320 to correct the programming error with the PSS MCDU but I've certainly not got as far as you with it. As to entering the minus figures for the flex temp, I don't think anyone has ever suggested just putting in the minus. Life is never that simple. I will go through your post in detail over the weekend, but it refers to only the PSS A340: is there any adjustment you would recommend for the A320 family or can your method be used pretty much for any one of the PSS Airbuses?

[Guest ciropv]

>with it. As to entering the minus figures for the flex temp, I>don't think anyone has ever suggested just putting in the>minus. Life is never that simple. Well, believe me, somebody has, and to be honest, it was not such a bad idea as it gives you much lower values (in fact the problem, is that it gives too low values, and too far from reality)>I will go through your post in detail over the weekend, but it>refers to only the PSS A340: is there any adjustment you would>recommend for the A320 family or can your method be used>pretty much for any one of the PSS Airbuses?Well, the method is based on a real chart of the A340 CFM engines (page 11 of the A340Performance.pdf document). If somebody would provide me the same chart for another plane, I can make the new tables. (Remember the chart gives the N1% setting for a given Flex temp with a given OAT and Altitude). I would also like to get the Flex temp charts for the rest of the buses (I only have the A340 charts)Using logic, the charts should be similar but not exactly the same.(All this, talking about the N1%-Flex-OAT-Alt chart, or what I called "Table 1")The second table (N1% TO and CLB for a given OAT) is easier to get. (Change FS weather OAT, engines stopped, move throttle to TO, then again to CLB, write down the two values. Do the same for OATs from "50" to "-60". Little boring, but easy). I can do it for the A320 family if you want. Knowing the TO and CLB N1% for an OAT, you can select a value in between as Flex. It will not be accurated, but should do the trick.If I can help you in this, just ask.Thanks, Ciro.PS. Very nice page, yours. I have downloaded lots of info from it, some months ago, and still go from time to time to see if you have uploaded something new :)

[Guest vrandar]

Re the minus figures I didn't make my point very well. I do use and recommend using appropriate minus figures, but what I meant was that if you were going to put in a flex temp of say 45 don't just use -45 instead.I also thought that the tables should be similar for the A320 family nut havne't done any tests as I rarely fly the A340.I can't update the airbus hangar at SOL at the oment as there is a block on this while the whole site is being re-designed. Once this is complete I have a whole batch of stuff to publish.

[Guest giln]

Dear Ciro,I have a quetion. What happens if your N! setting is higher that the CLB power?

[Guest ciropv]

It has to be higher!You have the problem if it is lower.Look at this example.Sea Level, OAT=35, Flex=55 TOGA =98.2%CLB =91,2%Flex =90.8% This is lower than CLB (90.8 < 91.2), use a lower FLEX. Next in the table, OAT=35, Flex=50TOGA =98.2%CLB =91,2%Flex =91.8%This could make it. If you want more margin, use a lower Flex. (OAT=35, Flex=45).SeeU,Ciro