Sorry to sound like a troll but liquid piston will go nowhere and Wankel engines simply have too many moving parts, all of which slide and rub. Although the weight is very low and the power high, they need lots of fuel and wear out fast and expensively. In a combat drone, they are perfect and in a Max, you would have to sit it forward of where a 277 would sit which isn't a big problem. Any weight savings would be offset by carrying lots of fuel |