Question MOSAIC, LSA, and your Piper

We were talking about this yesterday on an editorial email thread.

Using *just* gross weight as the line would be appropriate for production aircraft, but then you'd have things like a 1650-pound Lancair considered a LSA...and that's an airplane that a Sport Pilot should not be flying.

Using *just* stall speed, you're risking bringing in things like the Cessna 185 I mentioned a few posts back.

Using stall speed plus horsepower or stall speed plus gross weight would do a better job than just one of the above options.

At the end of the day, I think it may be difficult to convince the FAA to revise the proposal in a wholesale manner, so perhaps advocating for just a small increase in Vs1 (and leaving everything else as is) may be the most effective path.

I wonder if they could raise the stall speed (59 kts?) and put in a horsepower limitation? Maybe 250 hp? That would still allow some pretty nice 4 seat aircraft and keep things on the calmer end of the scale.

Calculating KCAS Vs1 stall speed with modern Piper POHs.
We'll use a PA-28-181 Archer III for an example.

1A. Determine Vs1 by consulting the "Stalls" item in "Normal Procedures," Section 4. Note that this is given in knots indicated airspeed (KIAS). Some POHs do not list stall speeds here. In this case, it is clear that the Vs1 of the Archer III is 50 KIAS (45 KIAS + 5 knots for flaps up).


OR

1B. Determine Vs1 by consulting the "Power Off Stall Speed" chart in "Performance" Section 5. Again, Vs1 is shown as 50 KIAS.


THEN

2. Use the chart "Airspeed System Calibration" (usually Figure 5-3) in the "Performance" Section 5 to convert KIAS to Knots calibrated airspeed (KCAS). 50 KIAS corresponds with 57.5 KCAS on the chart. Note also that this is where the solid "0 degrees flaps" line begins.
Thus, the Archer III's Vs1 is 57.5 KCAS.



 

The public comments that I've seen on the docket so far seem to indicate strong support for raising the 54 KCAS Vs1 in order to include more aircraft. The risk here is inadvertently bringing in things that a sport pilot doesn't have much business operating (e.g., an early Cessna 185 actually has a lower Vs1 at 56kcas than most Cherokees). 

Interesting thought on the STC. Perhaps something to the effect of "Amends operating limitations. MTOW 1,950# when operated by a Sport Pilot. Vs1<=54kcas at 1,950#."

An alternative to raising the Vs1 limit or a paperwork STC would be to just permit operations at a weight less than MTOW, where the Vs1 would be 54 kcas or less. For the early Cherokees (140/150/160/180), that's right around 2,100 pounds. 

My former Cherokee 180B (same airframe as a 140) could thus have been operated by a Sport Pilot as long as I was only taking one passenger... which is part of the proposed regulation anyhow! The empty weight was 1283, so even with full fuel (300), there's still room for 517 pounds of pilot, passenger, and bags. 

Maybe someone could come out with an STC limiting the Cherokee 140 to the 1,950 lbs gross which would make it legal.

Eric, that may be true for the Pacer/Tri-Pacer.

Unfortunately, there are few Cherokee 140s which were originally certificated with the 1,950-pound gross. Most all are 2,150 pounds. 

Nearly the entire PA-28 line is excluded, which is a shame as they are about as simple to fly/land as you'll find in a four-seater piston aircraft.