Original URL: http://www.theregister.co.uk/2008/05/04/green_flying_cars_overloaded_with_granola/

Added green burden could ground flying cars for good

Get off my flying car, hippies!

By Lewis Page

Posted in Science, 4th May 2008 07:02 GMT

Analysis Regular readers of the Reg will be familiar with the many obstacles that lie between us and our long-desired flying cars. Unfortunately, rather than any boxes being ticked off on the checklist, it rather appears as though yet another has been added. More and more, people seem to expect their already difficult enough flying car to be green.

An example of this cropped up last weekend with the annual Electric Aircraft Symposium taking place (where else?) in San Francisco. The event is run by the CAFE Foundation, the same volunteer non-profit group that handles NASA's rather cheapskate Personal Air Vehicle (PAV) annual tech prize programme. Many luminaries in the PAV world were at the electric flight symposium. (NASA formerly had a PAV programme of its own, supposed to produce a working "Tailfan" aircraft by 2009, but is was cancelled in 2005.)

The Taurus Electro during tests in the Czech Republic

Even less like a flying car than before.

PAVs are a (somewhat) more realistic version of the flying car concept. Rather than a miraculous, silent, hover-capable wingless machine, all you get is a very advanced light aeroplane. It can take off after a very short run, yet is still quiet enough not to upset people nearby.

Hopefully, the PAV can fold its wings and drive about on roads like an ordinary car. Best of all, it can more or less fly itself, even in very crowded airspace and bad weather - presumably with the aid of a very advanced automated air-traffic-control infrastructure.

All this might allow PAVers of the future to take off from a handy little airstrip-layby at the end of their street, happily zoom through nil visibility conditions along with tens of thousands of other PAVs, and descend to land on a short strip at the mall or the office carpark.

If the PAV was as safe in use as existing aircraft, this would all be much less dangerous - both for fliers and people beneath - than ordinary ground vehicles are. (People might not appreciate this last point, of course, as they would be more inclined to notice rare deaths from the odd PAV crashing though a roof - probably quite slowly, hanging below an emergency parachute - than the routine slaughter among drivers, passengers and pedestrians today.)

That leaves a lot of new stuff to be invented, of course. Automated, higher-volume air traffic systems are at least on the drawing board; but quiet, short-takeoff, roadworthy self-flying planes certainly aren't. The best that's likely to be available soon is the excellent-looking Terrafugia Transition, which offers only one of these things - road mode. And the Transition certainly isn't green, getting a measly 25 miles per gallon, though at least it can use unleaded fuel (most light aircraft still can't).

But sadly, the talk among the PAVers in San Francisco at the weekend was all of adding a green-tech hoop to jump through along with all the rest. The annual PAV challenge, indeed, has now wandered further yet from the original NASA flying-car programme and is now re-branded as the General Aviation Technology Challenge - with, of course, a Green Prize starting in 2008.

Much was made of the new electric glider option from Pipistrel - the company which won the last PAV challenge - for instance, described by CNET in visionary terms:

The first batch of two-seater aircraft to fly on electricity rather than fossil fuels could reach more than a dozen buyers by year's end... that's a step closer to a gridlock-free future when relatively ordinary folks will hop to work in small, carbon-neutral planes... [the] Taurus Electro can climb to 6,000 feet after taking off on a 30-kilowatt motor. Recharging the glider's lithium-polymer battery is meant to take about as long as powering a cell phone. Depending upon the weather and skills of the pilot, the glider can travel 1,000 miles in a day.

Whoa there. The Taurus Electro is indeed an impressive piece of kit, and hats are deservedly off to its Czech developers. But it's a glider. The battery is flat after the 6,000 foot climb - you might get 1,000 miles after that by chasing thermals, but this is not a viable way of getting to a destination - you'll be landing essentially at random, the way gliders tend to do. The Taurus isn't even vaguely aimed towards a flying car future - though it is green. Assuming you have access to some green electricity, anyway.

Much has also been made lately of Boeing's long-delayed but ultimately successful effort to prove that a motor-glider airframe can fly straight and level with one person aboard - though not climb - driven by hydrogen fuel cells alone.

It's perfectly true, of course, that adding a battery to the fuel cell can give you climb power, much as the battery or ultracapacitor in a fuel-cell car allows it to get up hills and overtake. The San Francisco conference was full of people planning electric/hybrid planes and gliders of one kind or another. CNET even tell us that there might soon be "a light aircraft that would fly on a battery at 15 kilowatts per hour" - though we'd hazard a guess that the manufacturer didn't actually say that.

The trouble with this is that all you get is a somewhat worsened motor glider. This kind of gear offers no serious potential to be roadworthy, and very little chance of powering or perhaps even lifting the super-autopilot systems and actuators that a flying car would need. Most of these planned aircraft would be doing well just to get into the air and stay there.

Ultimately the engineering realities of practical aircraft are well understood. Flying cars are difficult enough to achieve using nice energy-dense fossil fuel powerplants - indeed the problems are sufficient to have kept the idea totally marginal to date, though we continue to wish we had enough money to own a Terrafugia Transition. But a green flying car, with its power-to-weight ratio slashed - that's not just marginal, that's outright silly.

Let the road car industry work on green tech for goodness' sake, people. They're the ones who aren't bound hand and foot by aviation's strict safety standards; they're the ones who have a comparatively easy technical feat to achieve, with the issue of weight so much less pressing. Frankly, the motor industry are the ones - compared to aircraft in general, let alone general aviation - causing the pollution and carbon emissions, the ones wasting expensive, imported crude oil as though it was going out of fashion.

Let's not hang another millstone round the flying car's neck before it's even born. Let's get it working first, or at least get the roadable light aircraft working first - and make it green later, when doing so would actually matter. ®

Bootnote

Caveat: As the CAFE people point out, there's always the chance of something surprising out of left field. Such as miracle ultracapacitors, able to store 100 times more power than batteries of the same weight - and deliver it as fast as you like. As it might be, when spinning electric ducted fans at maximum thrust for a quiet, vertical driveway takeoff before moving to a less power-hungry forward flight mode... it's a lovely dream, anyway. We wouldn't mention it, but Lockheed seems to be getting caught up in the excitement to some degree.