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An Essay by George Gregory



Overview of Roadable Aircraft



The idea of roadable aircraft has been around almost as long as powered flight. Beginning with the massive tri-winged Curtiss Autoplane in 1917 the idea of a dual purpose vehicle has fascinated aviators. Recent developments have sustained interest in the concept, and a crop of exciting new ideas have surfaced in recent days.


Where did it all start?

In 1937 Waldo Waterman created the "Whatsit" later dubbed the Arrowbile, and in 1945, Robert Fulton Jr. introduced the Airphibian, somewhat resembling a Stinson 108 with 4 wheels. This vehicle was eventually certified by the CAA and featured a car portion that detached from an airframe that was not portable and was intended to remain behind at the airport. Unfortunately, Fulton could not find a manufacturer and had to sell his idea to a buyer who shelved it.

In 1947 Theodore Hall's ConVair AutoPlane was unveiled, to be produced by Consolidated-Vultee. Like the Airphibian, the idea was to leave the airplane part at the airport; an attractive modern-looking automobile suspended beneath a conventional tractor aircraft. Public interest dried up, however, when the prototype crashed (fuel starvation, of all things).

Molt Taylor deserves credit for creating the first truly practical flying car, and shares the distinction with Fulton's Airphibian as the only other flying car certified by the CAA. He recognized that if the vehicle were completely self contained, that is, the airframe travelled with the car when being driven, a significant increase in usefulness was realized. He also improved the configuration by mounting a pusher propeller on the rear of the airframe, improving both the esthetics and aerodynamics of his creation. Molt Taylor almost got the Aerocar I to mass production: a Texas manufacturer (Ling-Temco) was set to produce the vehicle but Taylor failed to get the requisite 500 deposits to initiate tooling up; he only got 278, and the project collapsed.

A decade later Ford looked at the Aerocar, but the fuel crunch of the early 70's and the increasing flood of imported cars into the North American market caused them to drop the idea. His design is significant because he above all others tried to address the practical issues of utility and esthetics facing such a design and could be truly called the father of the roadable aircraft.


Why Roadables?

Anyone who has tried to travel VFR soon discovers how impractical it is. "Time to spare, go by air". Too many variables limit the effectiveness of a light aircraft for practical travel. Weather is probably the biggest problem; if the weather goes down, you either wind up cooling your heels in some motel somewhere, or you develop an intimate relationship with the side of a mountain. We all know of people who paid the ultimate price for pushing the weather. And if you arrive, fair weather or foul, someone has to come and get you, or you have to rent a car. Not very convenient. And IFR? That's an expensive airplane to maintain, and an expensive rating to get and stay current in. VFR is costly enough! With a roadable aircraft, if the weather's coming down you can land enroute and drive through the stuff. VFR flight becomes a practical way to get about.

Further, the idea of a true dual-use vehicle realizes a certain efficiency: one less vehicle to buy and maintain, no hangar to pay for (the family garage is just as good and it's there anyways!), daily use keeps the airframe dry and less subject to corrosion. A roadable aircraft extends the utility of an airplane, combining the speed of an aircraft with the daily usefulness of a car.


The Transportation Alternative

As a society we have become accustomed to efficient transportation. For short-haul travel, roadable aircraft fill the bill nicely. They may not be transcontinental travelling machines, but a vehicle that could produce doorstep to doorstep transportation at perhaps a third of the speed of an airliner becomes an attractive alternative, especially when you consider they can use smaller airports typically closer to your Aunt Mary's house.


Why Aren't the skies full of flying cars?

First of all, it is more work to learn to fly. Most people can do it, but it does take more effort and dedication for what is usually a recreational activity. Perhaps if Molt Taylor got the Aerocar I to mass production more people might have been inclined to learn... though as innovative as the Aerocar was, it still wasn't convenient enough. It could be awkward for one person to convert between modes, and then you had to trailer the detached portion. Further, the navigational infrastructure of the 1950's might have been overwhelmed if flying cars were numerous. GPS was still several decades away.

Manufacturing is a major problem. The costs associated with designing and certifying such a vehicle, especially these days is prohibitive. That is why the first successful roadables will probably be homebuilt prototypes, then kits, and maybe, just maybe if the idea catches on, a certified roadable aircraft.

And finally, militating against development are the stringent certification standards for automobiles: air bags, crashworthiness standards, pollution issues, and the like. This defeated Taylor's the Aerocar III: the regulatory bodies of the 1970's didn't know what to do with it. It presently resides in Seattle's Museum of Flight.


What's different now?

Things have changed since Fulton and Taylor first introduced their revolutionary vehicles. The litigeous nature of the American legal system all but killed light aircraft production in the late 80's and 90's and even though it is presently struggling back, the price of a new Cessna 172 is close to $200,000 CDN. The homebuilding movement flourished during this period and much innovation occured since homebuilt airplanes (or cars for that matter) are not subject to the same certification standards as factory built stuff. Composites, advances in airfoils and natural laminar flow, and innovators like Rutan, Whitcombe, and others were able to "push the envelope" in design and construction. Further, the recent advent of GPS and "Highway In The Sky" technology, the Small Aircraft Transportation System, and the NASA/AGATE GAP propulsion program have brought meaningful advances to small aircraft as a form of transportation.

Computers and the internet can't be ignored here, either. It has gotten so much easier to share information with other designers and enthusiasts, and of course there are computer programs to help the budding designer eliminate a lot of the guesswork and to examine different configurations and aerodynamic issues. Knowledge is growing exponentially.

The Ideal Roadable...would be homebuilt, probably of composite construction, convertable by one person in a few minutes, with a GPS - based navigation system, and if it were ever to be certified as a road vehicle, have three wheels (read motorcycle). It would have small, easily stowed wings replete with high lift devices to keep the landing speed down but realize a better L/D at cruise. It would be at least a two-place vehicle with enough room for groceries and/or baggage in an easily accessed area. Wherever possible components would do double duty: one engine, rear-mounted propeller, compact transmissions and PRSU's. It must be self-contained, probably what we would call an integrated unit for more convenient conversion, and at any rate able to take all components along for the ride regardless of the mode of travel.


Different Schools of Thought:

Roadable Aircraft

One thing that becomes soon evident is that there are several different schools of thought on what exactly the mission of such a vehicle should be. One group favours a vehicle that is primarily an airplane, but is street legal in a pinch, just to get through the weather, or to get to the airport. These vehicles are presumably not intended to be regular-use cars. In this group are Ken Wernicke's Aircar, a low- aspect ratio craft with an 8 ft wingspan and a chord of somewhat larger dimension. It features enormous winglets to improve effective aspect ratio, and a conventional aircraft tricycle landing gear with a tractor propeller. A large R/C model exists and has flown.

Palmer Stiles' CarNard is more like a Rutan canard, with high, asymmetrically mounted main wings when viewed from the front. The wings fold forward on top of one another for car mode, and the entire assembly sits on a tricycle landing gear. Evidently a flying model of this vehicle exists as well. Mark Kettering's 4-place design is another, an attractive twin-boom design with wings that fold straight up, and likewise sits on three wheels.


Different Schools of Thought:

Flying Cars

Others want a vehicle that has more utility as a car. Among these was Fulton's Airphibian. The airplane portion was left at the airport, the front section becoming a reasonably useful automobile. Around the same time came the ConvairCar, a conventional appearing vehicle featuring a removable aircraft section that attached to its roof. Again, the airplane part was supposed to remain at the airport, resulting in less utility as an aircraft. Cross-country usefulness is limited as you need to come back to retrieve the airframe portion of the vehicle. You can't take it with you.

Molt Taylor improved the concept with his Aerocar series, making the vehicle entirely self-contained; the wings and aft fuselage detached and trailered behind the car portion when being driven. In very recent years Taylor was working on a set of wings to attach to an already certified Honda CRX, a clever and legal way around automotive certification hurdles (the car part was already a certified vehicle that you bolted a separate, presumably portable airframe to). It required a separate, self-contained engine and would be fairly large to lift an entire automobile off the ground.

Roger Williamson has developed another concept with his Roadrunner design. The car portion sits in the front of the airframe and has a separate set of wheels not used at all by the aircraft. To drive, the nosewheel retracts so the aircraft bows forward, and the car part with its separate wheels drives out. The aircraft portion can then be folded up and trailered or left at the airport.

It's interesting to note that these successful examples (notable in that they are intended for more extensive road use) are all what we would call modular; that is, the airplane part is either left behind or trailered, and is not part of the automobile section.

Some more recent attempts are downright sexy. Labiche Aerospace has a proposed design that looks like a Ferrari with retractable wings that fold under the passenger compartment and a tail section and propeller that stow in/on the back of the car. Canards fold over the front hood for storage.

Branco Sahr has proposed the Advanced Flying Automobile, similar in concept, but with telescoping wings. Neither of these vehicles has flown to my knowlege, and would probably prove very expensive to build, but their elegance is undeniable.

Another is Aeromaster Innovations' Synergy vehicle, an attractive twin-boom pusher that is intended for kit production. They have gone so far as taking non-binding orders for kits and quoted a price of just under $40,000 (presumably in US dollars) for a kit sans engine, instruments, upholstry and glue.


Different Schools of Thought:

VTOL

A third category are the Volantors, VTOL type vehicles that are not automotive at all; they are more akin to a helicopter with ducted fans instead of rotors.

Paul Moller's Skycar fits into this category. Because of the high disk loadings, it requires a vast amount of power for takeoff and landing (about 1,000 hp) but somewhat less for horizontal flight as the ducts serve as annullar wings and contribute to the lift. One neat feature of the SkyCar is that it has a rather high wing loading in flight; a true VTOL it doesn't need big wings to keep the landing speed reasonable. It reaps the benefit of a better ride in turbulence and possibly a better lift/drag at cruise because of the higher wing loading. Moller intends the SkyCar for mass use: by using redundant onboard computers, fly-by-wire controls, and ballistic parachutes for safety, he anticipates eventual use by non-pilots. Hop in, tell it where you want it to go, and you're off. Whether this happens remains to be seen; but if it does, and he can tool up for true, automotive-scale mass production, it will truly by the most revolutionary vehicle ever produced. Building vehicles in those sort of quantities could make this most exotic of all vehicles actually affordable by virtue of the great numbers produced.

Xantus has produced a "low cost" tilt-rotor machine similar (but smaller) to the US Marines' Osprey, and a company called Millenium Jet is working on the Solotrek XVF, a single person VTOL featuring a pair of ducted fans suspended above the pilot, who straps the machine on like a jet pack. Their Duotrek is a two-place version that puts the occupants in a cockpit.


Design Considerations

One pet peeve I have is seeing some designs that don't take weight transfer into account. Airplanes are necessarily light on the front wheels; that's the last thing you want in a car. When driving, you have to have the weight more evenly distributed, because your control comes from the front wheels.

A number of designs recognize this; Palmer Stiles' Carnard achieves the weight transfer by folding the high mounted wings forward. The Synergy vehicle does likewise, but stows them on the side. Taylor's vehicles took the wings right off and trailered them, leaving the remaining weight of the car portion more evenly distributed between the four wheels.

A slightly different approach has LaBiche Aerospaces' offering, extending canards out of the hood area to provide extra lift up front. As well, the wings extend out and back for flight.

Weight should be kept fairly close to the ground, mandating wings that stow in a low position if possible; but then they must be somehow protected from road debris, gravel and the like.

Another issue is that of a truly durable suspension, but here personal philosophy becomes significant. As before, if you want something you can just drive occasionally, then a more airplane-like (read lightweight and simple) suspension not optimised for road use is acceptable. If you want something you can really drive on then you need things to be beefier, and probably closer to the ground, with at least marginally larger wheels. You can imagine what a pothole would do to an aircraft landing gear.

Where to put the prop? I think Molt Taylor had the right idea: put it in the back. It gives a more carlike appearance, and is more desirable if the craft is to spend any appreciable time on the ground.

Footprint is yet another thing to be addressed, again depending on what you want. It must be small enough to drive legally on public roads: for a true dual use vehicle it has to be small enough to park as well, and that means a driving size and height no larger than a small truck or van, about 6 feet wide by 16 feet long.


So here's my wish list for the practical roadable aircraft:

  1. Small, easily stowed wings with high lift devices to keep landing speed reasonable
  2. 20.5 lb per square foot wing loading.
  3. Durable suspension
  4. Usable, accessable luggage area
  5. Ease of entry/exit
  6. Weight transfer for driving mode: centre of gravity must be brought forward
  7. At least 2 place
  8. Cruise speed 150 or better, land around 70-80 mph
  9. Docile, conventional handling in car or flight mode
  10. Ballistic chute for entire craft
  11. Car-size footprint when in car mode
  12. Fail-safes for detachable components; i.e. engine won't start if wings aren't properly attached, etc.
  13. probably a 3-surface design.
  14. completely self-contained, and easily converted in minutes by one person

One thing that strikes me, the more I toy with the idea of Roadable Aircraft, the more I come up with something that looks like one of Molt Taylor's creations. It is not because I've set out to copy him, but in an evolutionary sense, as I've examined the compromises and shapes that the configuration dictates, it comes out looking something like Taylor's Imp. The exceptions are the canard to hold the front wheels, and perhaps an added bit of wing area. Personally, I think Taylor was a genius.


The Call

Sport Aviation has an abundance of talented individuals; builders, aerodynamicists, engineers. Why can't we pool our knowledge?

Talk about raising the RAA's profile!

In the 1950's one of the things the EAA did to raise awareness was to feature a homebuilt in Mechanix Illustrated. If the RAA endorsed the development of a TRULY successful roadable aircraft, it would have a profound effect on the visibility of our organization and be a shot in the arm for private aviation everywhere.

It must be a thing done by a group of individuals willing to build the thing as a group project, sharing information and cost between themselves; but ostensibly with the blessing of the RAA once its success has been verified.

You know what? I think it could be done. We just have to get started: it's a momentum sort of thing.


Contact

George Gregory may be reached by telephone at (604) 882-8016 or by email at -

gregdesign@telus.net




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