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View Full Version : Why does stall speed increase with weight?


Scutter82
30th Sep 2019, 20:02
I know that it does. And I can follow the maths to prove that it does. I understand that the increase in weight requires an increase in lift to counter. I understand that to increase the lift we have the option to increase v or CL (AoA). But why does the stall speed increase? Reverse logic suggests we will hit the critical AoA at a faster speed since I know the stall speed increases but my question is why? What am I missing? Every explanation on the web just explains that we need to increase lift because of the additional weight and therefore stall speed increases. I'm missing the jump between the two. Anyone got a nice simple answer?

rudestuff
1st Oct 2019, 17:03
A wing stalls at an angle of attack, not a speed - although straight and level we tend to talk about stall speeds.

A wing generates lift right up to its critical AoA, just before the stall. For any given aoa, for example 5° you already know that to generate more lift (because it's heavier) a wing must fly faster.

Well the same applies for 6° and 7° etc right up to critical AoA, and since the wing flies right up to the stall, the stall speed must increase too.

Kaillou
1st Oct 2019, 19:35
You have to consider that the stall speed is the minimum speed to maintain straight and level flight, as mention above. If you are heavier, then the minimum lift to maintain level flight will be higher and the only way that you can provide that lift without increasing the AoA is to fly faster.

eckhard
1st Oct 2019, 20:44
The important point is that for any given angle of attack, there will be a corresponding speed in 1g flight for a given weight. Therefore, at higher weights, every individual angle of attack will be associated with a higher speed. This relationship continues up to the stalling angle, which will also occur at a higher speed.

In other words, it’s not just the stall speed that increases - it’s every speed.