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Flex temperatures again


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My previous thread got closed a bit prematurely.

We are talking about two things. What this diagram shows is obviously a clear indication for a flat rating at 30c. Fadec increases the n1 until it reaches oat 30c after that n1 decreases again to prevent overheating.

 

The whole point of flexing is to reduce n1 and not the opposite! The logic in this crj is somehow injecting (flex 40) a full rated toga n1 value for an oat of 40c instead of calculating oat 5c +flex 40 (which leads to a reduction of n1)

 

Basle Airport LFSB    5 C OAT

TOGA  86.7

F35 89 ?

F40 87.8 ?

F45 86.2

 

 

Flex.JPG.a746abed64f7c414279c987eeeeb8aee.JPG

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Hi Canonal,

I just read your original post and I have to agree with you that it's wrong. If you set a flex temperature, your N1 percentages will be reduced as you are indicating. The higher the flex temp, the higher the thrust reduction.
I've posted a CRJ 1000 table to compare.
 

Flex.jpg

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27 minutes ago, Alexander Pressley said:

Flex is voodoo magic. But I've changed my original stance on this. I went into a deep dive into my systems manual. We don't get those fancy assumed temp charts. And i believe you are right. 

 I just pulled the table out of my QRH 1. Even though I only fly the 1000, I doubt that the 700 is much different in terms of how the flex works. I'm no Bombardier engineer so I can't explain how the computer works out the flex, I just fly the thing, but one thing is for sure when you flex you simply can't have a N1 percentage that's higher than TOGA. The only way to have a higher percentage than TOGA is to push the throttles to MAX power and that's reserved for wind shear warnings.
Just my 2 cents ;)

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Hi guys! It is an interesting subject indeed.

Is flex 50 the max flex temp on the crj1000?

Lets see if or how it will be improved. No idea if it is a limitation of MSFS2020.

Have a nice weekend

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17 minutes ago, canonal said:

Hi guys! It is an interesting subject indeed.

Is flex 50 the max flex temp on the crj1000?

Lets see if or how it will be improved. No idea if it is a limitation of MSFS2020.

Have a nice weekend

Yes, kind of. CRJ's (at least here) are limited to operating in conditions no hotter then ISA +35 so you'll never see a flex temp in the real world greater then ISA+35. 50 just happens to be ISA+35 at sea level. I heard talk of increasing that to ISA+40 where I work but nothing yet has officially come of that.

 

Keep in mind what ISA +35 is changes with altitude. At 1000 feet pressure altitude it would be 48C at 5000ft pressure altitude it would be 40C. etc etc.

 

This is why you see stories like this involving the CRJ.

https://aeronauticsonline.com/too-hot-to-fly-extreme-heat-grounds-flights-in-phoenix/

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7 minutes ago, canonal said:

Hi guys! It is an interesting subject indeed.

Is flex 50 the max flex temp on the crj1000?

Lets see if or how it will be improved. No idea if it is a limitation of MSFS2020.

Have a nice weekend

 

Yes Flex 50 is the maximum for the CRJ 1000, but sometimes the aircraft won't let you insert 50 and will limit you to Flex 48. Happened quite a lot in Tenerife North (TFN).

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4 minutes ago, Nicco54 said:

 

Yes Flex 50 is the maximum for the CRJ 1000, but sometimes the aircraft won't let you insert 50 and will limit you to Flex 48. Happened quite a lot in Tenerife North (TFN).

This happens because what is ISA +35 and therefore the maximum flex temp changes with pressure Altitude.

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5 minutes ago, Alexander Pressley said:

This happens because what is ISA +35 and therefore the maximum flex temp changes with pressure Altitude.

 

Yes, I remember a Captain of mine back when I was doing my line training had said something similar when we were in TFN.

I still remember trying to insert flex 50 like 5 times before he told me the reason why the aircraft wouldn't let me 🤣🤣 

TFN being at 2000 feet, it makes sense 😄

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I can't enter a flex temp in the CRJ-550 or CRJ-700. When I try it just says 'not allowed' in yellow at the bottom of the FMS screen. Any idea how to get the FMS to allow me to enter a number value? Ive tried 46, 40, 32, 26 and none will go into the entry section for flex temp.

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57 minutes ago, FSHomeCockpit said:

I can't enter a flex temp in the CRJ-550 or CRJ-700. When I try it just says 'not allowed' in yellow at the bottom of the FMS screen. Any idea how to get the FMS to allow me to enter a number value? Ive tried 46, 40, 32, 26 and none will go into the entry section for flex temp.

From what I’ve seen an engine needs to be off to enter a flex temp in the sim. Not how the aircraft actually works as our procedure is to only enter our flex temp after we start the second engine as then both T2 probes will have air flowing over them. But it’s really not that big of a deal. I have no problem entering it before starting engines. However if that doesn’t work for you it would probably be because you have anti ice on. I have no idea if they have actually simulated this but when we turn our anti ice on in the real jet it will always delete any flex temp and not allow a flex takeoff.

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13 hours ago, Matthew2312 said:

From what I’ve seen an engine needs to be off to enter a flex temp in the sim. Not how the aircraft actually works as our procedure is to only enter our flex temp after we start the second engine as then both T2 probes will have air flowing over them. But it’s really not that big of a deal. I have no problem entering it before starting engines. However if that doesn’t work for you it would probably be because you have anti ice on. I have no idea if they have actually simulated this but when we turn our anti ice on in the real jet it will always delete any flex temp and not allow a flex takeoff.

Ive tried with engines running and engines off, while also having anti ice off and still can't get the temp to enter. Do you mean just have 1 engine off and 1 running?

 

Could this be a bug?

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  • Developer

The preconditions for entering a flex temperature are:

  • Both throttle levers in IDLE or SHUTOFF position
  • Weight on wheels for more than 60 seconds, so you have to wait even after loading
  • Indicated airspeed below 65 knots

The flex temperature can be between -99 and 99 degrees Celsius or the equivalents in Fahrenheit if that's selected in the EFB.

Entering -100 degrees resets the flex temperature to the outside air temperature.

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