Decreasing Vy with increasing density altitude
I'm currently flying in areas with high temperature differential to standard atmosphere and I am struggling somewhat with a solid climbout at high density altitude airports (7000 - 10000 ft), especially since they are often in challenging topology. I thus want to max out the performance of my Cherokee.
I'm aware that Vy decreases with density altitude, and Vx increases, until they meet at the absolute ceiling. Of course, I also lean for best performance during runup and accelerate in ground effect before climbing. But the initial climb rates I'm getting are a bit of a crap shoot before finding the right IAS for Vy -- and this in the critical initial climb phase.
So how much do Vy and Vx vary with altitude? The Cherokee POH doesn't include data about that. Any theoretical pointer, rule of thumb, or actual performance data would be helpful.
From my own experiments, for the Cherokee Warrior II at medium weight, the Vy changes from 78 kias below 3000 ft DA to about 75 kias at about 5000 ft, and to about 72 kias at 8000 ft. Does that sound about right?
Last edited by Zonkor; 22nd June 2013 at 20:43.