New in SEOW 3.1.0: TAS -> IAS Conversion

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IV/JG7_4Shades
Posts: 2201
Joined: Mon 08 Jan 2007 11:10 pm
Location: Perth, Western Australia

New in SEOW 3.1.0: TAS -> IAS Conversion

Post by IV/JG7_4Shades »

Thanks to II/JG3K.Brandle's exhaustive researches, it became clear that the SEOW Mission Planner was actually allowing commanders to order aircraft to fly at unrealistic speeds. How? Well, let's get some background information.

The MP reads a maximum speed value for every different aircraft type from the Object_Specifications table (Speed field, measured in metres per hour). As compiled, this Speed field contains a representative maximum flight speed for the aircraft in clean test mode - this is a True Air Speed (TAS) - gleaned from a variety of sources. Advanced SEOW users are free to change these Speed values as they see fit.

However, prior to SEOW3.1.1, I had expected that speeds encoded in the mission files were also TAS speeds. Therefore I had written the MP to specify flight speeds to each waypoint as TAS. It seems that this is WRONG! :shock:

In fact, the speeds encoded in the mission files are Indicated Air Speeds (IAS), which are always slower than TAS, and slower by an increasing margin as altitude increases. The net effect of this is that commanders were specifying IAS speeds based on a range of speeds appropriate for the faster TAS range.

From SEOW3.1.1 onwards, the MP automatically applies a flat correction factor to the TAS maximum speed before presenting speeds to the commanders for adjustment. The correction factor is set in MP-Configuration.php:
$TASIASFactor=0.75;
Now, commanders can be assured that all aircraft speeds in the MP are expressed as IAS speeds. Of course the flat correction factor is a gross simplification - we could build altitude-dependent correction factors and altitude-dependent maximum speeds into SEOW, but this might not be worth the effort. Any feedback?

Cheers,
4Shades
IV/JG7_4Shades
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Hitcher
Posts: 117
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Location: The Red States

Post by Hitcher »

As long as the base speed presented to the mission planner as he/she creates waypoints are reasonably accurate, I think we are good for now. Building altitude-dependent correction factors and altitude-dependent maximum speeds would be a luxury that only those involved with coding can determine the worth of, in my opinion.

I think it may be time to push Brandle into the coding business. He has the time, the interest and the ability. Wouldn't that be something? :wink:
Hitcher
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