View Full Version : Target Climb Rate?

March 8th, 2009, 13:17
Im getting a Target climb rate to high when trying to update my C-27 airfile with airwrench. Im stuck anyone please help as I have her switched from Jet to Turboprop as par to USCG aviation mechanics guide.

March 8th, 2009, 18:06
Correcting a flight model for an incorrect engine type can be a challenge, but AirWrench should be able to do it. Converting an old C-130 from jet to turboprop was one of the early 'problem child' test cases for AirWrench.

Things to check and verify are the horsepower rating of the engines, propeller diameter, N2 RPM, and prop gear ratio. If you're not sure of or are missing one of these, try to adjust propeller diameter, N2 RPM, and prop gear ratio so that the prop tip velocity is less than mach 1.

Climb rate is very dependent on weight, but more often than not, a rate of climb will be specified without ever mentioning what the weight was. An empty plane will climb a lot faster than a loaded one.

Climb rate will also vary considerably depending on the altitude. Just for reference, AirWrench is attempting to match the initial low altitude (sea-level) climb rate.

March 28th, 2009, 09:58
One of the sources that does have rate of climb vrs altitude (at a given weight) for many WWII fighters is "America's Hundred Thousand". One must bear in mind that such data was arrived at through flight test, and can be rather difficult to duplicate in flight testing in FS as well!

For supercharged piston engines, it is not always the greatest right at SL, The P-40 and P-51 come to mind as examples. Since we have a somewhat simplified way of modeling altitude performance of such engines, especially multi stage supercharging, the resultant effects we model will usually be quite close, but not right on.

Then of course it is revealing that the available test data of the era (WWII) will show significant variation depending on the source (ie mfgr and service test) so given that variability our best fit methods may be as close as we can justify.

Cheers: T.

April 4th, 2009, 20:50
Hello Fliger747,
I believe it is multi-speed rather than multi-stage supercharging that FS/CFS has trouble representing. The shift points of the supercharger sometimes end up as performance peaks of the FS/CFS aircraft rather than performance lows as they should be.

Performance tests also get a bit unreliable because the only documented tests may be of captured aircraft in unknown condition being tested by a group that does not have a great understanding of the intended operating parameters of the aircraft.

Hello Sparks,
I remember reading a really good description of the propeller tables from your site but still haven't figured out how to properly use the information in it to adjust climb rates.

- Ivan.