2*WL/rho*Cl*sin(theta) = R (turn radius - sustained)
First, yes, Stoney knows his stuff and doesn't give bum steers. Thank god for that because the last thing this place needs is another bullsh*t thrower. I'm still sick of hearing Thrash ragefully emote (i.e., devoid of fact or reason) against the Spixteen.
Second, the equation above is a simple expression of what drives Radius - Wingloading lives in the denom and high is bad. That's quite clear.
However, this powerloading deal is critical, too, since sin(theta) approaches max as bank angle theta approaches 90. While sustaining a 90 is out of the question, it takes excess power to overcome the increased in lift-dependent drag required as you bank. Thus, as noted in a previous post here, yes, powerloading is also important since it determines your max bank.
I also think Stoney's practical consideration for the P-51's eminently "loadable" airframe (all that range is achieved by a combination of the low drag afforded by the lf wings and airframe design PLUS a whopping fuel load) is also valid - .i.e., you MIGHT see a P-51 at the lower edge of it's WL range but then, monkeys MIGHT also fly from my butt. Generally, people fly with a significant proportion of fuel. They get nervous when it gets low - even if low in a 51 isn't nearly the same as low in a 109.
