How to stop loosing power with altitude?

[norman_99 209]

G'day,I'm just starting to get into editing flight models, and was trying my hand at making a flyable Cessna 402C out of an AI model. I've got access to POH's and other data so started using these figures with AirWrench. My problem is I've managed to get the engines set up nicely at see level, with 39" MP and 2700 RPM producing exactly 325HP, which I can read from a test panel I'm using. But at 10,000ft, I only get about 260HP, yet the turbos seem to be working fine cause I'm still getting 39" MP and running at 2700 RPM. This isn't really possible, as with the same MP and RPM I should be getting the same HP, no matter what altitude I'm at.I've set the critical altitude to 12,000ft, so should be getting full power and MP up to that height, then both decreasing above 12,000. Is there a setting I'm overlooking or is there a problem with the turbocharging simulation within FS9? Either way, if anyone has any ideas or solutions I'd love to here them, and don't limit them to AirWrench, I'm open to any suggestions.Thanks, Michael

[norman_99 209]

So nobody else has ever had any problems with turbocharged flight models? Probably just something I've overlooked. Any comments would be most welcome.Thanks, Michael

[norman_99 209]

After a bit of playing around, I've found I had to lean the engines significantly to achieve the rated horsepower at the critical altitude. This is unrealistic, as the turbo's are feeding the engines with the same volume of air no matter what the height, and the reason turbocharged aircraft don't require progressive leaning in a climb to maintain power.Is there any section of the air file which deals with fuel flows related to RPM and or altitude that could have an effect on this? Again, any assistance would be appreciated.Michael.

[n4gix 4,947]

Do you have these entries set in the [engine] section of the aircraft.cfg file?

turbocharged - Boolean to indicate if the engine is turbocharged; 0 = FALSE, 1 = TRUE. turbocharged= 1max_design_mp - If a turbocharger is present, this value indicates the maximum design manifold pressure supplied by the turbocharger (inHg). max_design_mp= 36.5 min_design_mp - If a turbocharger is present, this value indicates the minimum design manifold pressure of the turbocharger (inHg).min_design_mp= 10

[norman_99 209]

Yes I do. It seems that the turbocharger is actually working, as I'm getting 39" MP up to 12,000 and it reduces as per the POH above that. This issue I'm now having is that in order to maintain power, I have to drastically lean the mixture. I should be able to obtain the same power with the same mixture setting at any height below 12,000 with leaning only required above this as MP starts to drop. Have you had any similar issues with turbocharged engines, or is this a limitation of FS9 I'll just have to live with?Thanks for yore help, Michael

[n4gix 4,947]

You might try increasing this value.critical_altitude= 14000If all else fails, cheat:fuel_air_auto_mixture=1

[norman_99 209]

Thanks for the reply. As far as I'm aware, increasing the critical altitude only increases the height at which max MP (and therefore max power) is available too. As far as enabling auto mixture, I guess it's a toss up between constantly leaning to maintain the power whilst climbing, or not using the mixture at all. Either way isn't totally realistic.I'm just surprise that I couldn't find much more on this topic in the forums, as it seems to be a fairly large flaw in the modeling of turbocharged engines.Michael