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JamesIceland

Temperatures and PMDG777

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Hi there

 

I have the latest beta of Opus installed and have no problems getting the winds/temp data into the T7 for higher altitudes which is great. However, at lower altitudes and flying in the tropics as I have been for the last couple of flights there seems to be too high outside air temperatures (more than 8 degrees c) up to and even above say 24,000ft and I'm finding that vnav is going haywire on ascent but more on descent - the aircraft accelerates rapidly as it meets the hot air. This only happens when the temp changes from being minus x degrees to suddenly plus x degrees. I have to disconnect vnav and manually input vs speeds to combat the weather changes. Without opus on and clear skies it was fine. Any idea how I can get the temp profile correct on ascent/descent to avoid this?

 

Many thanks

 

James

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Have you put in an assumed temp where possible for your aircraft sim (e.g. in the NGX FMC Perf page), which you can get from your GRIB report (OpusWeatherReport.txt or Upper Atmosphere weather report window), for cruising altitude, ensure you don't omit the minus sign if appropriate.

 

Cheryl

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Hi Cheryl,

 

I did do that actually and it didn't make a difference. I will try again later to see if I can fix it. Interestingly I tried a similar flight (tropics) using Opus but this time with the Airbus X and it was all fine. Something about the PMDG in combination with Opus seems to be off so not sure if this is a PMDG thing or Opus thing. Will investigate further. Whilst I do, any thoughts on the really high outside temperature indicated in the T7? 

 

James

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OK, thanks for the feedback. The temperature targets we inject into FSX are not dependant on the aircraft type as far as OpusFSX is concerned. We don't have the 777 to test with here.

 

Cheryl

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A reminder about high temps and the possibility of confusing your SATs with TATs ...

 

Ambient temperature = SAT (Static Air Temp) = OAT (Outside Air Temp)

 

SAT = Static Air Temp ... i.e. what the air temp would be if it were static (or when your airspeed is zero).

 

TAT = Total Air Temp ... the effective air temp taking into account your airspeed.

 

The TAT is a calculated value, it is calculated within FSX or the aircraft sim and is always warmer than the SAT due to compressional heating of the air molecules. The air has to be slowed down to be measured and hence gets heated. Hence the TAT is dependent on your airspeed (actually the square of your airspeed as a Mach number) and also on the ratio of specific heats of the ambient air (i.e. how dry or moist the air is - which effects air density - which determines the number of air molecules being heated).

 

At the typical airliner cruise speeds (0.75+ Mach) a TAT of 20 to 28 degrees warmer than SAT is perfectly normal.

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Thank you...I sheepishly admit that is a mistake I think I've made. I do also think the 777 is very sensitive to temp/wind changes as I've just watched it climb to cruise and on reaching around 22,000ft the wind changed direction and temp dropped and the aircraft reached overspeed very quickly. As this issue is limited to the 777 I'm going to assume that this is where the issue may lie and it may well be with my current lack of knowledge on the aircraft at this point...you live and learn! Opus still my favourite add on by the way!

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Thanks for your comments.

 

Don't worry, you are not the first person to make this mistake and most probably not the last one either!

 

I assume from your initial post that you have an OpusFSX beta  3.31.0 (2 Sep) onwards, we introduced anti wind shift measures within the Sim Friendly GRIB Data processing, that together with entering an assumed temp in the T7 (as you have) will hopefully minimise wind shift and perhaps overspeed problems.

 

Regards

Cheryl

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Thanks Cheryl, great service as always. It's my passengers I feel sorry for. Until I figure it out they're in for a bumpy ride!

 

James

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