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Fearless

Speed at Cruise Altitude

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My current IAS at FL200 is 159kts | 183mph; 206kts GS

Head wind 14kts. Aircraft at MTOW.

manifold pressure: 30.2 in Hg | 1703 RPM| 

Throttle at 77% | Props at 52% | Mixture at 30%

Using Bernt’s FDE.

Running very smooth but certainly cannot get max cruising speed.

How are the results above?


Regards,

 

Fred Fleuren

 

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12 minutes ago, Fearless said:

Running very smooth but certainly cannot get max cruising speed.

Which speed are you looking to max during cruise? You appeared to refer to three. Indicated, true, or ground speed?  What is your TAT/OAT?  Do you have a valid reference chart for FL 200 at various TAT/OAT?

Edited by fppilot

Frank Patton

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Former USAF meteorologist and ground weather school instructor; AOPA Member #07379126

There is no limit to what a man can do or where he can go if he doesn’t mind who gets the credit! - Benjamin Jowett

 

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Greetings Frank,

Thanks for that. Found the performance tables from the C421C POH and the current IAS is pretty close.

OAT is 20F

Edited by Fearless

Regards,

 

Fred Fleuren

 

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Just checked the RW POH values at MTOW at FL200. 

1700RPM, 30.0MP = 205ktas. 

edit. Temp is lower than standard but not much. Since you departed at MTOW I assume you've got a bit lighter at FL200.

At FL200 159kias = 216ktas but the IAS/TAS ratio in FSX/P3D doesn't exactly match RW data and deviates even more if temp differs from ISA. 

Edited by FDEdev

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No. Just edited my above post.

Btw, you will not get max cruise performance with such low RPM and MP settings.  For max cruise you need 1900RPM and 32.5MP (225ktas at ISA)

Edited by FDEdev

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Much appreciated all.

I did make a slight adjustment in the aircraft.cfg file prior to listing the results above namely increased the prop diameter from 7 to 7.6 as per POH and prop thrust scalar to 1.17 as well as engine power scalar to 1.1

Edited by Fearless

Regards,

 

Fred Fleuren

 

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