Will personal air vehicles be a common sight in the skies by 2030? NASA and a handful of inventors believe the concept is fast becoming viable
The boy presses his face against the window and looks down to see if his friends are already at school as his mother follows the motions of the sidestick and gently banks the personal air vehicle - her "PAV" - towards the strip of tarmac reserved for pupils being "dropped off" by air.
His mother follows the guidance cues as the power automatically comes back and the fan makes its distinctive murmur in the spiral duct behind their seats. Their PAV touches down on the left hand of the school's three parallel landing zones and, after slowing to walking pace in less than 70m (230ft), she retracts its gull-like wings and rolls the vehicle to the drop-off point by the tennis courts.
Getting out, he pauses to watch her taxi to the departure point, extend the PAV's wings and take off in less than 50m, before climbing to the north for her commute into the city. Perhaps they could invent a six-seater so his family could take some of his best friends camping with them, he thinks idly.
Is this science fiction or, not withstanding the everyday terrors of parental driving around a school, a possible picture of urban life in the 2030s? According to NASA and a handful of entrepreneurs and inventors around the world, the PAV concept is fast becoming viable - technically and socio-economically. Unlike previous attempts to bring low-cost air travel to the masses with flying cars and similar concepts, modern PAV ideas embrace a host of enabling technological advances in avionics, propulsion, materials and design that seem to offer affordability and safety.
The leaders of NASA's PAV project are eager to distance it from the litany of failed hybrid aircraft/car and similar projects that have stigmatised the concept over the past 50 years. Although relatively successful, Robert Fulton's Airphibian of 1946 and the Moulton Taylor Aerocar never took off in the market. "We don't do flying cars," says Andrew Hahn, deputy vehicle sector manager at NASA Langley Research Center and deputy manager of the agency's recently inaugurated PAV work. The focus for the work is now on the "TailFan", a study concept within a class of vehicles dubbed Equipt (easy-to-use, quiet, personal transport).
As well as fighting several other NASA departments for funds, the fledgling project faces additional credibility hurdles, says Hahn, adding that "around here we're looked upon as wildmen". However, the TailFan has been formally established as a firm target for the start of NASA's PAV work, which is augmented by agency-supported research exercises on other external projects such as Barnaby Wainfan's Facetmobile and Jay Carter's CarterCopter. "We are not wedded to our design only, and we have been helping some of the little guys do something," Hahn says .
"The TailFan is our touchstone. That's what we are planning to build," says Hahn, who adds: "We are trying to execute a plan that in five years will have a flying demonstrator of an example of a PAV, and we think it is the best way to do it." Although essentially conventional in design, NASA's plan for the TailFan is based on a set of basic PAV principles, as Hahn describes.
User friendly
"Ease of use is number one. We're aiming it at people of fairly average capability and limited training. If they can't use it, then there is no point in doing it. We are looking for a rational transport system of the future, which, if not exactly car-like, then should be as close to the things we love about cars today. The big difference is it does not drive along on a road like a car, and that's where it gets a bit murky," Hahn says. The future PAV will have, however, the ability to taxi or "trundle", as this will enable the occupants to travel to and from a local landing area.
"It will be roadable in the sense of a golfcart. You'd never trundle it down the freeway or the motorway, but you could take it on the local streets and 'waddle' your way to a local country airport and then take off." This ability, argues NASA, will be the key to overcoming inter-modal delay, which Hahn says is "the Achilles heel of aircraft". The delay, in this case, concerns the usual hold-ups experienced by anyone transferring between airports and ground transport, as well as the delays involved in travelling to the airport itself.
The growth of the PAV concept could therefore be partially based on the gradual expansion of "air park" communities that are based around runways and dual-use roads and taxiways. Today's air parks are generally for the "retired or the wealthy, but we want it to apply to a much larger slice of the population".
To avoid the compromises that killed all the flying-car concepts of the past, NASA believes the PAV's "roadability" will have to be based on staying to a side-street speed limit of 40km/h (25mph) and keeping the vehicles to a maximum width of 2.6m. A separate electric motor would be used for ground movement, rather than thrust from the PAV's engine. Typical operation would be to pull out of a driveway, drive for 3km or less at under 40km/h to a community airfield, take off and fly about 160km (100 miles) at around 270km/h, land at another local field and finish the journey with another 3km drive to the destination.
Another key to success of the PAV will be its appeal to the mass market and its ability to generate the production numbers needed to bring the prices down to commodity levels. "We have to be careful what we say here. We're talking about transport and not entertainment," adds Hahn, who says that initially the performance targets are for a four-seater that is more akin to a high-wing Cessna single than a Cirrus SR-22. "When we offset performance it makes it cheaper," he says. "In the end we think there'll be a lot of shapes and sizes, but this will be the equivalent of a four-door sedan, only with two doors."
Target price for the TailFan is in the $100,000 range "to permit affordability in the transition market between the current low-production general aviation market and the high-volume production of a future PAV market", says NASA. The plan is to peg prices by adopting an aluminium airframe, rather than composites, which can be pressed into shapes using the mass-production techniques perfected by car makers. Aluminium is also recyclable, whereas composites are not, adds Hahn. The TailFan design also incorporates a radical skin-stiffened structure, reminiscent of the corrugated or ribbed metal skins pioneered by Junkers around 80 years ago.
Tackling cost
Cost is also tackled through the use of a ducted propulsor, powered by a liquid-cooled car engine - in this case the Chevrolet Corvette's LS1 V-8. NASA has put the engine through the US Federal Aviation Administration 150h endurance test specified for normal aeroengines, and is working with the agency on certification issues connected with using automotive parts. It also hopes that non-traditional suppliers, which might otherwise be afraid to come anywhere near the PAV arena because of understandable worries over liability, will be encouraged to explore involvement by adopting the American Society for Testing and Materials standards approach. "It has a track record of immunising manufacturers against frivolous lawsuits. That's the number one concern of suppliers," Hahn says.
Replace not repair
General Motors, for example, appears happy for the Corvette engine to be used for NASA experiments, but is believed to be showing no interest in allowing the engine to be used as a production powerplant for any PAV. However, for now NASA is more concerned about proving the concept rather than scouring the auto industry for a suitable replacement. "The real idea is to get the cost down. You're talking upwards of $45,000 for a [Teledyne Continental] IO 550 aeroengine, whereas this engine comes in a crate for $5,500. If we buy it in lots of 300 or more, that could come down to around $3,500, and that's the second biggest single unit cost factor in the aircraft," says Hahn.
The engine has to be rugged and extremely reliable for both performance and safety reasons. "We don't want 'tree-shade' mechanics opening up the bonnet to work on one of these," Hahn says. The concept is for the engine to be simply removed at a scheduled point, and replaced by a new unit with the original being sent back for "recycling". "We're talking TBR [time between removals] rather than TBO [time between overhauls]. We're taking it to the next level," he says.
The aircraft is designed to cruise at up to 170kt (320km/h) and land at less than 50kt. The use of the ducted fan propulsor is critical to the concept for several reasons, including low noise, propulsive efficiency over a wide range of airspeeds and altitudes, and the ability of the geared unit to convert the 4,000RPM of the Corvette engine into 280-300hp (210-225kW) of power. "The ducted fan is really critical, but no-one has produced a successful one for the kind of operating environment we're looking at," says Hahn. Previous low-speed ducts have been of fairly narrow chord, "but ours is close to 1:1", he says, adding that the agency is working on a low-noise design for windtunnel testing.
Touch and go
Another critical technology area is the development of a "haptic" flight-control system for the flight demonstrator. Haptic is defined as "relating to or proceeding from the sense of touch" and is similar to a self-playing piano, or a device that allows a user to interact with a computer by receiving tactile feedback. In the case of the PAV, NASA's plan is to develop a flight-control system that provides instant feedback to the pilot by applying a degree of opposing force along the X,Y and Z axes.
Originally developed for people with disabilities or learning difficulties, most haptic systems have benefited dramatically from advances in digital technology. Recent new uses include three-dimensional devices that can be used for surgical simulations, or remote operations of robotics. "It would provide instant feedback to the pilot as to what's going on. You can override it any time, so it allows you to fly a lot more safely than conventional flight controls. You also learn quickly and the idea is that you'd almost not know it was there at some point," says Hahn.
The system will be capable of managing the entire flight autonomously, but in reality would act "like a robotic co-pilot or like an instructor sitting beside you. If you're coming into land, for example, and you show no sign of pulling back on the stick, it will flare for you. If you become incapacitated and have not touched the controls for some time, it will waggle the wings to wake you up. If you fail to respond after a few attempts, it will declare an emergency and divert to the nearest airport."
Altering perceptions
The system is all about "perceived" safety, Hahn adds: "My wife would never fly in an aircraft piloted by me, but if she thought there was a system like this installed she'd be a lot more willing. It's all about perception." To reduce the expense and difficulty associated with training single pilots for current instrument flight rules (IFR) ratings, the system will also be designed to cope with automatic fight through marginal visual/IFR conditions. "We'd make it so you are not completely at the mercy of the weather," says Hahn.
More ambitious vehicles lay further out in the 10- and 15-year future. One project, recently moved from a 10- to a 15-year target, is the PAV Gridlock Commuter, an extreme short take-off and landing ring-wing vehicle. The chief design feature is a spiral duct that combines the natural thrust-vectoring capability of the Custer channel- wing design with the blowing control system used by the Lippisch Aerodyne.
The possibilities offered by PAVs extend far beyond easing commuter congestion, according to NASA. "While not flying cars, PAVs could create 'exurbs' by opening up rural areas for housing and business, much as cars created the suburbs by opening up the outskirts of cities," says Hahn. "With a daily reach of up to four times greater than cars, PAVs could allow the same economic activity as cities with only one-sixteenth of the population density. This means that oases of homes and businesses, serviced by community airfields, could flourish in rural areas as well as benefit from fast travel to larger towns and cities."
Should they succeed, PAVs could not only change the urban landscape, but also reseed the grassroots of aviation. The rest of the decade will be pivotal to both.
GUY NORRIS / LOS ANGELES
Source: Flight International
