Googled Sonerai stall speed and the results indicates may well fit the LSA category which requires stall to be 52mph or less. Somehow I always thought this design did not fit LSA criteria. Always liked the idea of a stretch 2 set up as as a single seat but with a LSP ticket....
It’s been done. Most LSA people want slower stalls than something meant to be a race plane, so it does not resonate with most. Lots want to go faster than LSA speeds so the plane is usually not configured to stay slow. I think the biggest problem is to make sure it hits the numbers, and not miss and make the project plane miss the mark.
You pretty much have to put a climb prop on the plane so it will not go faster. You can’t go for total performance. Forum member N8053H had a couple of threads on his. Hand prop, hand held radio, minimum paint job, leave wheel pants off will get the weight down.
There are a couple of certified plane STCs that do that. Remarked tach for the STC, but to gain the performance, you cheat and fly over new redline to engine TCDS listed redline. A regular airplane does not have the artificial speed wall though.
A prop in between the extremes is usually the best all around. I would hate to give up my climb performance and not get the cruise advantage. Trading for climb would at least give some advantages. It will also help sport/ aerobatics which is what would be more the focus, than speed.
You could set the "zero point" of the flaps and ailerons down 6-8 degrees at the trailing edge. Then you can add a "reflex" or "dive" position on the flap lever like the Maule and many competition gliders, where the flaps and ailerons come up 6 or 8 degrees. So when the flaps are in the officially "retracted" position, the airplane will meet the stall and cruise speed definitions of LSA. There may be times on a cross country flight where you wish to use the "dive" or "reflex" position, as appropriate for certain meteorological, astronomical, or biological conditions, which would in fact result in the aircraft flying for some distance with the flaps and ailerons 6 or 8 degrees higher than they were in the LSA-compliant neutral position.
Now this would come with a price of some extra time and effort and thought. The ailerons being lowered several degrees will result in it being easier to stall a wingtip in a low speed maneuver. Make no mistake, you're going to have to compensate for this somewhere else, whether that is in adjusting your approach and base-to-final turn speed, or adding vortex generators to the outboard half of the wing, etc. etc.
There will also be some new construction or design work to create the control linkages and monkey motion to make all of this work safely. Essentially a flaperon mixer of some sort.
And you are GOING to have to put differential aileron throw in to it, meaning that when you move the stick to the left the left aileron comes up a lot and the right one only goes down a little... or perhaps almost not at all.
The Sonex with the 3300 busted LSA speeds right off the get go. It was able to legally and correctly stay under the limits by Jabiru's RPM notations. IIRC, the older 3300 engine redlines at 3300 rpms, but cruise was designated 2700 rpms. So at 2700, the speeds would be under the max. This tactic would be more than appropriate for a self-built VW.
As far as I know, none of the Sonerai models use flaps or flaperons as designed. I also think the Sonerai II stall speed quoted on paper is an indicated speed likely far lower than the actual stall speed.
The original Sonerai II (not the Stretch model) is listed with an empty weight of 520 lb and a gross weight of 950 lb with the smaller engine. The NACA 64A212 (modified) airfoil on that 84 sq ft 4.15 AR wing is unlikely to do better than a max CL of 1.3, so my LAA spreadsheet gives a stall speed of a little over 58 mph. To bring the stall speed to 51 mph just by reducing weight you'd have to drop the gross weight down to 725 lb which leaves you only 205 for pilot and fuel *if* you can match that 520 lb empty weight. Possible, but not easy.
I'd suggest a stock, midwing Sonerai II, leaving out the front seat structure and fitting just a nylon cloth luggage compartment in it's place. Make a full-length canopy structure to cover the front seat but fit only a Sonerai I canopy over the rear cockpit. Use the absolute lightest 1835cc engine you can, Oratex fabric, light wheels, maybe a reduced-size fuel tank. Don't mess with flaps or flaperons or drooped ailerons, all of which would compromise the simplicity and handling of the original. Instead, set your gross weight at 750 lb and install full-span vortex generators to drop one or two MPH from your stall speed.