I saw this a couple of years ago, its a pretty nice rotary engine. As others have pointed out, rotary engines have their challenges but their advantage in weight and torque still makes them a good choice for aircraft.<p>The "secret sauce" that the Liquid Piston folks bring to the party is the upgraded rotor shape. It doesn't need apex seals like the old Wankel version did. The news here is that they had reduced their experimental work into an actual functional engine. Unlike the Wankel, their cylinder design would really support a compact multi-rotor engine but presumably you could gang them together on the same crankshaft if you really wanted to.<p>Other than the UAV and possibly the paramotor market I'm not sure where these guys are going to find customers though.
For those wondering how it works, here's a visualization: <a href="https://www.youtube.com/watch?v=0e785YnDmq0" rel="nofollow">https://www.youtube.com/watch?v=0e785YnDmq0</a>
It might be fairer to compare to a state of the art piston engine. Brief googling finds a DeNardis 40cc engine weighing 11 lbs and producing 7hp. Still impressive though.<p><a href="http://www.denardisengines.com/40cc.html" rel="nofollow">http://www.denardisengines.com/40cc.html</a>
Pretty informative video about rotary engine dis-advantages. <a href="https://www.youtube.com/watch?v=v3uGJGzUYCI" rel="nofollow">https://www.youtube.com/watch?v=v3uGJGzUYCI</a>
This article/company are misrepresenting the truth. Once you add the carburetor, a starter (watch the video, they use a drill to start the engine, obviously real small engines have pull starters, which add weight.), the exhaust, intake manifold, etc. This engine is much heavier than 4 pounds.<p>This is almost the equivalent of me saying I've invented a 3 pound airplane, which is nothing but a carbon fiber tub. You just have to add wings, engines, cockpit, etc. etc.<p>It's a small engine, yes, that's nice. But don't blow it's carbon emissions up my ass and expect me to believe the hype.
0.75hp/lb is better than the 0.1625hp/lb engine they replaced with it, but doesn't seem so revolutionary compared to the power-to-weight of existing engines:<p><a href="https://en.wikipedia.org/wiki/Power-to-weight_ratio#Engines" rel="nofollow">https://en.wikipedia.org/wiki/Power-to-weight_ratio#Engines</a><p>Even the well-known Mazda rotary is slightly better at 0.92hp/lb, and various aviation engines have higher power-to-weight ratios still.
This is another take on the rotary/Wankel engine. Mazda and many others have tried to develop durable, efficient versions of this type for decades, with only limited success.
This is potentially very interesting for medium sized drones that need 12+ hour endurance, as lithium ion/lipo batteries just don't have the energy density of gasoline... Even when you lose 50% to heat in a typical internal combustion engine the kilojoules per kilogram is so much greater in a liquid hydrocarbon fuel.
When I read it was 70 cc I was a little taken aback. In Italy there are a ton of people moving on scooters (mopeds) that are limited to 50 cc. It's true that they can't have more than 1.5 hp of power, but that's the law not the physical maximum for a piston engine.
A video with a slightly different design, including hollow cylinder head:<p><a href="https://vimeo.com/163543761" rel="nofollow">https://vimeo.com/163543761</a>
Clickbait. It's a 4 pound engine that makes 3 horsepower. Impressive, but the article says the 40 pound engine makes 6.5 horsepower. Also, one costs $50 and the other probably $50,000. And no information given about the 4 pounder.