MOSAIC/Sport Pilot 2.0?

Should we try for a sport pilot-eligible design?

The new Sport Pilot rule announced in 2024 allows sport pilots (or private pilots exercising their sport pilot privileges) to operate certain aircraft without a medical certificate. The previous gross weight limit was eliminated and the clean stall speed was raised to 59 knots (68 mph).

So should we design this airplane to meet that stall speed requirement? If our current design has a stall speed with flaps of 58 mph, it appears we may not be far off. Let’s see what it would take to get there. This should be pretty straightforward since we exclude the effect of flaps in the calculation.

First, let’s calculate for 68 mph.

$$ \scriptsize q_{V_{S0}} = \tiny \frac{1}{2} \scriptsize \rho V^{2}$$

$$ \scriptsize q_{V_{S0}}= \tiny \frac{1}{2} \scriptsize (0.002377 \text{ slugs/ft}^{3})(68 \text{mi/hr} \cdot \frac{5,280 \text{ft}}{\text{mi}} \cdot \frac{ \text{hr}}{3,600 \text{ sec}})^{2}$$

$$ \scriptsize q_{V_{S0}} = 11.82 \text{lb/ft}^{2}$$

Using the same equation we did previously, but excluding the flap term, we find the new lift coefficient:

$$\scriptsize C_{Lmax} = 0.9 \left( c_{lmax} \cdot \cos{\Lambda_{c/4}} \right) $$

$$\scriptsize C_{Lmax} = 0.9 \left( 1.47 \cdot \cos{(3.7)} \right) $$

$$\scriptsize C_{Lmax} = 1.32 $$

Now, substituting this into the lift equation,

$$\scriptsize S_{ref}=\frac{L}{qC_{Lmax}} $$

$$\scriptsize S_{ref}=\frac{2,080 \text{ lb}}{11.82 \text{ lb/ft}^{2} \cdot 1.32 }$$

This is about 12 additional square feet of wing, or a 10% increase. We suspect this may tip the scales against making the plane sport-pilot eligible while still meeting our performance targets, but we’ll proceed with the original design and decide after we have some estimated performance figures.