Prop Decouple Question...TAS vs IAS in C-130 Technical Posted May 5, 2010 I appreciate all the thoughts but I'm still not sold...I want to understand why the prop at 10,000ft requires less force (i.e. lower IAS) to generate -6,000pds of torque in order to decouple vs. a higher force at 1,000ft. That doesn't make sense to me because there are less air molecules turning the prop towards -6,000pds the higher you go. Wouldn't a consistent force (i.e. IAS) instead of the speed through an airmass (i.e. TAS) be more relevant? Also I'd agree that the prop knows density altitude, but what density altitude tells us is that the higher the density altitude the more TAS is required to achieve the same amount of power/lift...aka the prop is less effective. We fly off IAS because stall speeds directly correlate to IAS not TAS which is corrected for density altitude. Keep the ideas coming...I really want to get a handle on this.