Calculate PropRPM for Turboprop

[drnicolas]

I am trying to calculate the correct Prop RPM value with this formula

PropRPM = System.Math.Abs((Convert.ToInt64(JetN1.Value) * Convert.ToInt64(RPMScaler.Value)) / 65536

But, I am afraid the calculated value is much too high, should be about 1200 in Idle, but reads out as about 3400.

What is wrong ? JetN1 comes from 0898, the Scaler factor from 8c8

[Pete Dowson]

JetN1 comes from 0898, the Scaler factor from 8c8

You don't mention FS or FSUIPC version. In the FSX offsets list, offset 08C8 includes this note:

On turboprops this will give the shaft RPM, since there is currently no Gear Reduction Ratio available to fix values on such aircraft. I will fix this when I can.

There's a similar one in the list for FSUIPC3, but no hope expressed there. I'm afraid I've never found a way to "fix" it -- for FSX it was an item outstanding with Microsoft at the time they closed the FS department.

Would the ratio account for your discrepancy? You can find it in the Aircraft's CFG file I think.

Regards

Pete

[drnicolas]

o.k, this is different from the FSUIPC for prgrammers.pdf

As I understand you, 08c8 gives the turbines shaft RPM , not the PropRPM itself - is that correct ?

Can I derive the PropRPM with a constant factor from this ?

[Pete Dowson]

o.k, this is different from the FSUIPC for prgrammers.pdf

Ah, sorry, I think the currently issued edition is different. The problem of the Gear Reduction on turboprops was only brought to my attention after the last SDK update. In my copy it says this in the part for the scaler at 08C8

Engine 1 RPM Scaler: For Props, use this to calculate RPM – see offset 0898

(On turboprops this will give the shaft RPM, since there is currently no Gear Reduction Ratio available to fix values on such aircraft)

As I understand you, 08c8 gives the turbines shaft RPM , not the PropRPM itself - is that correct ?

That appears to be the case, for turboprops, yes.

Can I derive the PropRPM with a constant factor from this ?

It is constant for a specific aircraft. As I said, it is the Gear Reduction Ratio which should be found in the aircraft's CFG file. Search for "gear_reduction_ratio". I'm pretty sure it is named as such.

Regards

Pete