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At Last, Flying Cars?
ColdWetDog writes, "OK, we've all whined about the fact that we are now firmly entrenched in the 21st Century and no flying cars. So it is gratifying to see that our good friends at DARPA are finally going to do something about it." The project is called Transformer TX. "The Government's envisioned concept consists of a robust ground vehicle that is capable of configuring into a VTOL air vehicle with a maximum payload capability of approximately 1,000 lbs. ... Technologies of interest may include: hybrid electric drive, advanced batteries, adaptive wing structures, ducted fan propulsion systems, advanced lightweight heavy fuel engines, lightweight materials, advanced sensors, and flight controls for stable transition from vertical to horizontal flight. ... Like all DARPA projects Transformer TX is unlikely to succeed at all. Even if US Marine rifle companies one day do ride to war in handy four-man sky jeeps rather than cumbersome choppers or Humvees, that doesn't necessarily mean flying cars for all any more than Harriers or Ospreys did."
Unless someone develops a low energy input, low mass anti-gravity mechanism, flying cars are never going to be commonplace, merely niche vehicles.
The why should be obvious: it takes a lot of energy to get one in the air. Even standard small prop aircraft gets middling mileage, and earns points only by its ability to fly in a straight line. However, it needs a lot of room for take off and landing.
Hence, a practical flying car needs to be VTOL, which is by its nature very energy inefficient.
Luke, help me take this mask off
There's no fundamental problem in building a modest-size VTOL craft. Many have been built. The fuel consumption and cost will be high, but for the military, that's OK.
The big problem back in the 1950s was stability. Now that unstable aircraft are routinely computer-stabilized, that's far less of a problem. It's going to need a jet engine. Piston engines don't have the power to weight ratio needed. That's what runs up the cost. A basic problem with jet engines is that they don't get much cheaper below small bizjet size. That's why general aviation is still piston-powered, despite Williams, etc.
It's not going to be a pure-thrust VTOL, like the Harrier. That takes so much engine power that it's only feasible for fighters, which are mostly engine anyway. Ducted fans, maybe. Successful ducted-fan aircraft have been built, and with modern stabilization, there are several robotic ducted-fan craft. With better stablization, the fans can be pulled in closer to the body, making for a much more compact craft.
There's a new Israeli ducted-fan craft, the AirMule, which is currently in early flight test and can hover tethered.
A big problem with single-engine VTOL aircraft is that they fall like a rock if they lose engine power. Aircraft can glide and helicopters can autorotate, but VTOLs can do neither. Ejection seats are indicated.