Stall Speed vs. Weight and Altitude

[PA32]

Can someone explain how and why stall speed (TAS?) varies with aircraft weight and altitude? If you need equations to explain this, I can still handle algebra, but I have forgotten all of my college calculus! Thanks.

 

[RandomGuy88]

If your weight increases, then the amount of lift you must produce increases. But your maximum obtainable CL does not change. So for the same CLmax the heavier aircraft would have to fly faster, so the stall speed would increase.

The stall speed varies with altitude because the density of the air varies with altitude. At a higher altitude the density decreases so again, for the same CLmax you must fly at a faster speed to achieve the same lift at a higher altitude.