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FLEX Temp after engine start


Nicco54
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I think I figured it out. On Perf page 2/3 you have to enter ISA. By default its set to +32. I change that in Celsius only for some reason? ex. I enter +20 and it converts it to enter an ISA value of 68 Fahrenheit. Then I can enter a flex temp (also only in Fahrenheit, ex. 90 flex) and flex is now working. 

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Strange that it would have that effect, that input should only really affect cruise and holding performance calculations (in the real plane). 

 

It is not actually ISA you are telling the FMS, but ISA deviation. So the 0C/32F default is correct in that the plane will assume ISA conditions. Entering 20 in that field would tell it that you expect ISA temperature plus 20 degrees Celsius on top. As far as I know, this should really not impact flex input. But at least you got it working :) .

 

Could you try perhaps to change it, set the FLEX, and then change it back to the default to see if it has any effect on the FLEX you just set? Just curious.

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A user of the Microsoft Flight Simulator Forum has attached this screenshot.

From the engine model it is for the CRJ900, maybe also CRJ1000.

Is this helpfull in the Flex discussion?

 

1329694678_CRJ_FlexTemp_CRJ1000.thumb.jpg.b6ef3b2887d5822ac77edb271c92b7a2.jpg

 

I set mostly AT 30, ActiveSky gives me the Temperature at flightlevel and I calculate the ISA dev. 

AT30 covers a wide temperature range.

On my side the CRJ climbs as they should do.

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It is really a matter of personal preference in the sim, since there is no access to everything needed to calculate proper assumed temperature (flex) v-speeds. The proper calculation includes considerations for runway length available, obstacle clearance, climb requirements and even maximum tire speed. These might all impact your V-speeds. So whatever you set in the sim, you will probably have V-speeds that are not accurate. At that point you are choosing whether you want to simulate putting in FLX temp but incorrect speeds or correct speeds and no FLX temp, so it is up to what you prefer for your sim experience.

 

All a bit going into details of course. For example, the table you show is for sea level pressure altitude. It is one of about 9 tables ranging from -1000ft to 10.000ft pressure altitude. And another nine for packs on :P .

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4 hours ago, Hoffie3000 said:

A user of the Microsoft Flight Simulator Forum has attached this screenshot.

From the engine model it is for the CRJ900, maybe also CRJ1000.

Is this helpfull in the Flex discussion?


 I had posted this screenshot coming straight from my manuals and I'm guessing someone copied and pasted it in the MSFS forum. This is for the CRJ 1000 but it's not what we actually use to determine the FLEX needed for takeoff.

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FLX Temp only affects TO thrust. After you have entered a valid temperature, the N1 thrust indications on the EICAS are displayed in magenta and the target thrust changes from "TO" to "FLX". When you advance the thrust levers to the TO detent the FLX reduction is automatically applied.

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