notes

Stall Speed

In electric aircraft, the power system seems to be the most limiting factor in keeping things light. If you use a large motor you need a large enough battery and ESC to match. But, if you can keep your motor size to the bare minimum, now you can downsize the battery and the ESC, and cut some significant weight.

Let's do a quick bit of math to illustrate this.

You can estimate stall speed (in miles per hour) by taking the square root of the wing loading (in oz/square foot) and multiply that by five.

Let's use the FT mini Scout as a quick example.
The scout has about 1 square foot of wing area. We're ignoring some cutouts here for easier math.
24" wingspan x 6" chord = 144 square inches = 1 square foot.

My scout weighs just over 6 ounces with a 600mah 2s, so it has a wing loading of 6oz/sqft.
If we take the square root of 6 we get 2.45. Multiply that by 5, and you get an approximate stall speed of 12.25 miles per hour.

Now, imagine I stuck a 2000mah 2s on there instead. It weighs 2.6oz more. That would up my wing loading to 8.6 oz/sqft. making the stall speed about 14.7mph.