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Poor (Flight) Performance

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Hi,

 

I was flying between Rio, Brazil, and El Alto, La Paz last night (around midnight zulu). I was using ASN for weather, and found that due to the temps being around ISA+26 to ISA+30 that the aircraft had incredibly poor performance. I initially cruised at FL320, but due to decaying airspeed (GW ~500,000 lbs), I had to descend. I ended up down at FL150, and approaching mountainous terrain. I evetually got her back up to FL360 to clear the mountains and reduce fuel consumption.

 

Does anyone else see such poor performance at these kinds of temperatures? At one point she was totally incapable of climbing above FL180.

 

How does this kind of performance compare to real-world? As it was the density altitude was some 3000 ft higher than normal due to the temperatures, but I'm not entirely sure how such high temps affect the engines. I felt the performance was too poor compared with what would be experienced IRL.

 

Anyone able to comment on this?

 

Best regards,

Robin.

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Hi,

 

I was flying between Rio, Brazil, and El Alto, La Paz last night (around midnight zulu). I was using ASN for weather, and found that due to the temps being around ISA+26 to ISA+30 that the aircraft had incredibly poor performance. I initially cruised at FL320, but due to decaying airspeed (GW ~500,000 lbs), I had to descend. I ended up down at FL150, and approaching mountainous terrain. I evetually got her back up to FL360 to clear the mountains and reduce fuel consumption.

 

Does anyone else see such poor performance at these kinds of temperatures? At one point she was totally incapable of climbing above FL180.

 

How does this kind of performance compare to real-world? As it was the density altitude was some 3000 ft higher than normal due to the temperatures, but I'm not entirely sure how such high temps affect the engines. I felt the performance was too poor compared with what would be experienced IRL.

 

Anyone able to comment on this?

 

Best regards,

Robin.

Hi Robin,

It sounds like your temps were a tad high for that altitude. I just did a quick check by looking at a MD11 REX plan between SBGL and SLLP. It shows temps at 30,000 feet -30c and 35,000 feet  -40c approx.


Geoff Bryce

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such a high temps at that flight levels are not realistic at all. You used ASN for weather, but maybe you used FSinn too for online flying? Just a guess, but If so, disable Vatsim weather. 

 

Anyway, you should found the reason for wrong temps


Zeljko Budovic

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Hi,

 

Thanks for your replies, but you mis-interpret the meaning of ISA+26. It means 26 degrees C warmer than ISA for that altitude. I had SAT of minus 30 to minus 26, which was in line with forecast for that area.

 

Best regards,

Robin.

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ISA+30 is very hot, equivalent to 45 deg C at sea level, and certainly will reduce engine thrust. Lower air density means less mass flow and so less thrust. Drag and lift will also be reduced. That certainly would affect climb performance.

 

 

Sent from my iPhone using Tapatalk


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'Cavok ok' will sort that problem enabling you to use your weather program.


Dave Taylor gb.png

 

 

 

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+26 ISA is pretty high, have you checked any prog charts for pressure activity causing the temps?


David Zambrano, CFII, CPL, IGI

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