Flying cars: Sky’s the limit but why has the concept not achieved take-off?

A number of us can thank a cartoon character from the future, George Jetson, for instilling our longing. Students of aviation history might look for inspiration to the Autoplane prototype built in 1917 by the flight pioneer Glenn Curtiss. And tens of millions of motorists who have been stuck in traffic jams stretching toward the horizon must also feel a need to know: Where are the flying cars?

It’s a dream that has reduced many would-be inventors to despair as they grasped the immensity of the engineering and design challenges rooted in the widely divergent natures of airplanes and cars. Cars must provide occupants with comfort, decent handling and braking and protection in the event of an accident – while complying with government air-pollution and fuel-economy standards. Keeping weight to a minimum is important, but a few extra pounds here and there can be tolerated.

Airplanes are quite a different matter. Weight is everything in a flying machine; weight determines the engine power and the wingspan required to get off the ground. Thus, aircraft make extensive use of lightweight materials that their designers fashion into the most efficient structures they can dream up.

Trying to reconcile the conflicting requirements of the two types of vehicles invariably results in a boatload of compromises that, some say, make the flying car a nonstarter. Yet, the dream lives on.

Ray Morgan, a consulting aerospace engineer in Simi Valley, California, knows a lot about efficiency and lightweight structures, having led a group that developed a series of prototype aircraft, cars and airships at AeroVironment Inc. Morgan has also studied flying-car design.

“In general, the idea that you are going to use an airplane for a car is just not realistic,” he said in a recent phone interview. “You are very likely to end up with both a bad airplane and a bad car.”

Promising prototypes

Over the years, flying-car proponents have explored all sorts of propulsion systems, including propellers, downward-facing lift fans and helicopter-style rotors. Several small companies are working on flying-car designs that they think will be the ones to finally crack the nut.

One of these, Terrafugia of Woburn, Massachusetts, has flown a prototype with self-folding wings and a pusher propeller nestled between two tail booms. The company is working on an advanced hybrid design capable of vertical take-off and highway driving using electric motors powered by batteries, along with a piston engine turning a pusher propeller during forward flight.

A start-up in Bratislava, Slovakia, called Aeromobil has a prototype with a pusher propeller for flight and drive shafts turning the front wheels when driving. Its wings pivot backward parallel to the fuselage when the craft is used in automobile mode.

It helps to put on an imaginary engineer’s hat when pondering the systems that would need to be on board a viable flying car. For starters, there must be an engine. And for weight and complexity reasons, it would be ideal for a single engine to provide power for flying and driving. Therefore, some kind of transmission must be devised to send power either to a propeller or to the driving wheels.

Wings, and how to stow them for highway travel, are another big piece of the puzzle.

“The heavier your vehicle is, the more wingspan will be needed to make the aerodynamic lift to fly it,” Morgan said. “Every time your weight goes up, due to adding systems peculiar to the car function, those wings must get longer. Or else you will need a more powerful engine, and your take-off and landing speeds get faster.”

The longer the wings become, the greater the challenge of getting them out of the way, so the flying car will fit the width of a highway lane. Building hinges or pivoting mechanisms into the wings reduces their structural efficiency and adds weight.

Even a flying car’s suspension system would require a fair amount of engineering. An automobile suspension is designed to withstand forces of about 2Gs as it smooths out the bumps in the road. Airplanes sometimes have bad landings, however, and their suspension systems must be built to tolerate 4G forces.

When Morgan prepared a study for the Defense Advanced Research Projects Agency on a rough-country "flying Jeep" concept, he envisioned adapting the long-travel suspension from a sand buggy. DARPA rejected the idea.

“I can’t say I’ve ever met a real military guy who thinks a flying-car-type vehicle is a good idea,” Morgan said.

Federal approval

Another looming challenge for a prospective manufacturer is clearing the hurdles presented by multiple federal regulatory agencies. A new aircraft must receive from the US Federal Aviation Administration what's known as a type certification, which approves the plane's design as safe and airworthy. Also mandatory is a production certification, which attests that the manufacturer has exacting quality standards in place and can build multiple airplanes identical to the approved prototype.

"It can take the better part of a decade to go through both of these approval processes for a new airplane," said Dick Knapinski of the Experimental Aircraft Association in Oshkosh, Wisconsin. "When the vehicle you're building is also a car, then you have to deal with the US Department of Transportation and the National Highway Traffic Safety Administration.

“The things you do to get automotive approvals add weight. Now, are you still within limits for the aeronautical side of the programme?”

Enthusiasts have a thing or two coming if they assume that one need only buy a flying car and point the nose skyward to soar above the dreary highways. Nobody gets off the ground without training and a pilot’s license, and no government agency will sign off on citizens’ routinely taking off and landing on public roads. That’s what airports are for.

A final impediment to swarms of flying cars filling the skies is the existing air traffic control system, which isn’t set up to keep track of low-flying aircraft that don’t have a flight plan and may impulsively change course.

“If this situation became reality, how many of those people would live to see dinner?” Morgan asked.

Despite this mountain of obstacles, there’s no reason to expect the allure of flying cars to wither. What child hasn’t imagined floating around the house a few feet above the floor, looking down on things from a new perspective? It’s a small leap from there to the great outdoors. And the march of progress may yet bring flying cars within reach.

NASA and the US Federal Aviation Administration are working on a GPS-based technology called an Automatic Dependent Surveillance-Broadcast, or ADS-B, receiver that would help multiple light aircraft coordinate flight paths and request changes. The proliferation of gasoline-electric hybrid drive componentry in the auto industry could also help get weight and complexity out of powertrains. Terrafugia is working on that idea.

© 2014 New York Times News Service

Flying cars: the past

Wizards and tinkerers have laboured to make cars fly since the early 20th century, with mixed results. Some designs had detachable wings and tail ends for highway cruising; others used mechanisms to fold the wings for driving. Here is a sampling of some noteworthy creations:

CURTISS AUTOPLANE, 1911 Glenn Curtiss, a pioneer in aviation and motorcycles, used a 100hp engine of his own design in his three-seat Autoplane, which used a pusher propeller for flying and road use, along with steerable front wheels. The Autoplane featured removable wings and tail, an aluminium body and a cabin heater. Financial backers could not be found, and the prototype performed only short hops, never a sustained flight.

FULTON AIRPHIBIAN, 1946 Robert Edison Fulton Jr, an architect, built four Airphibians. The lightweight, fabric wings and the rear fuselage were detachable and left behind during highway use. The Airphibian became the first flying car to receive government certification as an aircraft in 1950, when Charles Lindbergh flew one. Fulton flew and drove his Airphibians extensively, but the venture fizzled for financial reasons.

TAYLOR AEROCAR, 1949 The Taylor Aerocar went into low-volume production, and the surviving prototype resides in the Experimental Aircraft Association museum in Oshkosh, Wisconsin. The designer, Moulton Taylor, rejected Robert Fulton's idea of using removable wings and fashioned folding mechanisms for his machine, which attained government certification as an aircraft. The Aerocar sold for $25,000 and cruised at 100mph using a 150hp Lycoming engine.

ADVANCED VEHICLE ENGINEERS MIZAR, 1971-73 Henry Smolinksi, an aeronautical engineer, built a pair of these drivable aircraft. The Mizar was a wild mash-up of the wings, tail and rear engine of a Cessna Skymaster and a Ford Pinto. The Mizar used both a 210hp Continental engine and the Pinto's motor during the take-off roll; the car engine was then shut off. Smolinski and an associate were killed when a prototype crashed.

Flying cars: the future

TERRAFUGIA TRANSITION The ideal flying car might take to the roads and the skies with equal aplomb, but Carl Dietrich, a co-founder of Terrafugia in Woburn, Massachusetts, is unapologetic about the raison d'être of his company's Transition (photographed above). "We think of it as a street-legal airplane," he said. "It's an airplane that has the capability of driving safely on roads and highways and parking in a single-car garage."

As such, the target customer for the $279,000 Transition is someone who regularly takes trips of 100 to 500 miles and wants to be able to fly directly between local or regional airports, then drive to a destination unfettered by bad weather, traffic or speed traps.

Dietrich noted that one customer intended to tow his Transition behind a camper van: “They have their car, their plane, their house in one mobile package.”

The current version of the two-seat Transition has been in flight and road testing for two years, Dietrich said, logging multiple flights at altitudes up to 7,000 feet. Its fuel-injected, four-cylinder Rotax 912iS engine produces 100hp and runs on auto fuel, driving the rear wheels on the ground and a pusher propeller in the air. Cruising speeds are about 100mph in the air and about 70mph on the road.

The transition from car to plane – as the wings fold down – takes about a minute and a preflight check.

Terrafugia is taking $10,000 deposits for the Transition and hopes to start deliveries in the second quarter of 2016.

VAYLON PEGASE Infiltration, extraction, recognition and rescue may not be the first words that flying cars bring to mind, but Jérôme Dauffy, founder of Vaylon in Strasbourg, France, is taking a pragmatic approach to marketing the Pegase.

Though the Pegase (above) – which mates a paraglider with a lightweight, off-road vehicle – might seem to appeal to thrill-seekers, like climbers trying to reach remote peaks, Dauffy has played up its strategic capabilities to attract military and security business.

“The first market will be the military forces,” Dauffy said. “After, maybe the business market – for example, a surveillance company or humanitarian aid. Maybe researchers in the desert.”

The French military has shown intense interest, Dauffy said, and the prototype was on the defence ministry’s display last spring at the Eurosatory armaments trade show. Civilian availability is predicted in late 2015 or early 2016 at an expected price of $135,000.

Powered by the Rotax 912, the Pegase can reach more than 60mph on the road, take off in 50 to 100 meters and, driven by a pusher propeller, cruise at 40 to 50mph in the air, he said. The expected range in the air is about three hours with a ceiling of 10,000 feet.

Vaylon has built a functioning prototype, minus bodywork; a video shows it navigating dirt paths and sandy berms, then lifting off for a short flight and landing. Legal, on-road use will depend on whether Dauffy can navigate the dual certification processes.

AEROMOBIL In 1989, the Velvet Revolution deposed Czechoslovakia's Communist government. The founders of the Slovakian company Aeromobil – who grew up behind the Iron Curtain, dreaming of freedoms in the West – say their flying car offers the possibility of further liberation.

"Currently we are in the very same situation when it comes to traffic," said Stefan Vadocz, the company's head of communications. "We are trapped in traffic, and we think traffic needs a revolution."

The Aeromobil (photographed, above top) has been gestating since 1990, its design moving from a simple flying wing with vestigial wheels to what resembles a supercar with considerable flight capabilities. It “has all the characteristics of a full-fledged sports car and also full-fledged light-sport aircraft,” Vadocz said. “So there are no compromises.”

The most recent “pre-prototype” version 2.5, has had about 40 hours of flight testing, the company says. With a Rotax 912 driving the front wheels, the carbon-composite-and-fabric-skin Aeromobil has reached 100mph on the road with a range of up to 540 miles. Should its driver encounter traffic, he could find a flat, grassy field or airstrip and take to the sky, where the Aeromobil would have a ceiling of about 6,000 feet, a range of 430 miles and a top speed of more than 100mph.

The Aeromobil 3.0, which is to have a full-carbon body and an obstacle-avoidance and navigation system, is expected to begin road and flight tests in September, Vadocz said. – PETER SIGAL