Great. Thanks for the clarificaiton. I always thought they just give
you a low number. Now I know at least they are honest albeit
misleading. So I looked up the C152 POH and the CAS stall clean is
actually 47kts (54mph). I should re-adjust my goal. I think a CAS of
40mph should be quite respectable for a little bush plane. And the
square of (54/40)^2=1.83 with the light weight should be able to
reduce the T/O run by half.

Anyone know what's the calibrated clean stall for a PA-11 Cub?

Jizhong
On Sun, 23 May 2004 02:01:56 GMT, Kevin Horton wrote:

On Sat, 22 May 2004 19:38:56 -0700, jizhonghe wrote:

I'm guessing for a certain design the stall speed is proportional to the
square root of the wingloading. The stock C150 is 10lb/ft^2 and stalls at
48mph, while, for example, it is 8.9 and 30mph for the Bushcaddy R120. So
if I trust the number, the wings for the Bushcaddy must be way more more
efficient than that of the C150. What's the deal here?

The airspeed of interest for this calculation is equivalent airspeed,
although that is almost exactly the same as calibrated airspeed at low
speeds and altitudes. But the BushCaddy stall speeds are almost certainly
indicated airspeeds, as kit aircraft companies rarely have the resources
to determine the airspeed position error. Indicated stall speeds are
almost always lower than calibrated stall speeds, so they like to quote
the lower number.

Bottomline - the BushCaddy might very well have an indicated stall speed
near 30 mph (there web site claims 32 mph, but it isn't clear whether this
is power off or power on), but the calibrated stall speed would almost
certainly be higher than that.

For example, the C182Q POH that I am looking at shows a full flap, power
off stall speeds of 38 kt IAS which equals 50 kt CAS. With flaps up, the
error is even larger - 41 kt IAS = 56 kt CAS.

Don't pay too much attention to quoted stall speeds unless you have
proof that they are calibrated airspeeds.