“AFAIR, the only KTM scooters I've seen have been electric, but since 2T dirtbike sales (& racing) are much more of a sales focus for them, it does seem a natural priority at this point.”
When you have the only euro4 compliant (and euro5?) 2-stroke engine in the market, to leave it “useless” and produce – as every other maker can - electric scooters seems as not a good choice, unless you know some problems or issues (say, like “intellectual property rights”) of your 2-stroke technology.
This is why I keep asking the same question: “why KTM is not making / selling 2-stroke street legal motorcycles and scooters?”
You also write:
“As for the BRP/Rotax 2T 600 design . . . but they do feature amelioration of NVH, (like resilient mountings, something you could find in a Norton Commando ~1/2 a century ago)."
For an electric car the “resilient mountings” is not adequate: when the internal combustion engine operates to charge the battery, the NVH inside the car will be worse than in a conventional car powered by a 4-in-line engine (which also uses resilient mountings).
This is why AVL (and FEV) offered Wankel Rotary REM (Range Extender Module) for the electric car manufacturers.
You also write:
“What effort have you put into quelling the potentially noxious emissions (noise/fumes, etc) from your flyer, in terms of customer convenience/safety - not least, as well as per EU regs?”
First priority of the Portable Flyer is to fly.
The emissions and the noise are future issues.
On the other hand, the existing “Flyers” / JetPacks of Rossy, Zapata, Mayman and Browning have more than 50 (fifty) times lower mileage (about 1mpg) and unaffordable noise (supersonic velocity of the gas existing from the jet exits).
But even compared to the conventional reciprocating piston engines, the architecture of the Portable Flyer engines brings new “solutions” for better BTE (Brake Thermal Efficiency), cleaner exhaust, lower lubricant consumption, lower noise and lower vibrations:
The Pulling-Rod architecture of the OPRE engine gives some 35% longer piston dwell around the CDC (Combustion Dead Center), which means that almost all the fuel is burnt during the first portion of the expansion stroke (this is what Mazda claims with its SkyActivX (controlled HCCI) technology that brings to the gasoline engines similar to di Diesels fuel efficiency without the emission problems of the di Diesels).
(more at https://www.pattakon.com/pattakonOPRE2.htm
The same Pulling Rod architecture offers lower specific lube consumption, too, because the trust loads are taken at the cool side of the cylinder, away of ports and especially of “red hot” ports (i.e. wherein the scuffing of the conventional 2-stroke engines begins).
The same Pulling Rod architecture lowers the noise, too, because when the exhaust port opens, the pressure inside the cylinder is substantially lower: the more energy you milk from the fuel during the expansion stroke, the less energy remains in the exhaust gas to make noise.
Here it sounds and looks like HCCI:
The Tilting Valves of the Portable Flyer engine make “positive” the first half part of the scavenging (positive as, say, the way a desmodromic valve train closes the valves): at the opening of the transfer port the pressure inside the transfer passageway is high enough to push a lot of fresh charge in the cylinder; then the scavenging continues “positively” (back side of the piston, closed tilting valve, small “scavenge pump dead volume”) till about the BDC; then the scavenging continues and completes inertially (open tilting valve, communication of the scavenge pump space with the “crankcase” that communicates freely – though the open inlet ports - with the intake).
With direct injection (or TPI?) the OPRE Tilting seems capable of being greener than any conventional gasoline 2-stroke.
As for the vibrations: each OPRE Tilting is as perfectly balanced as the best V-12 engine. The two crankshafts counter-rotate in synchronization at zero phase difference (the tilting valves allows this symmetry, without sacrificing the breathing).
You also write:
“Will you have to run an annular safety ring around the perimeter of your prop-blades also, on safety grounds, & if so, will that assist or hinder, any useful pitch control methodology?”
The purpose of the Portable Flyer is to cover distances flying over 95% of the time at its “optimum” cruise speed, wherein the propellers are at their “optimum”.
For the rest of the flight (take off, landing, hovering) the propellers will not be at their optimum.
The drones also need variable pitch propellers.
Hopefully self-adjusting lightweight propellers will soon be available.