FLYING CARS
1. Introduction
‘Flying car’, ‘roadable aircraft’, ‘dual-mode
vehicle’ and other terms are used to describe the all-purpose vehicle that can
fly like an airplane and drive on the highway like an automobile. Make it
amphibious and we have the perfect all-purpose vehicle! Nevertheless, this
might be taking our ideas a bit too far.
It has long been the dream of aviation and
automobile enthusiasts to have a vehicle that will bring them the best of both
worlds. Many drivers stuck in rush hour traffic have fantasies about being able
to push a button and watch their car’s wings unfurl as they lift above the
stalled cars in front of them. Just as many pilots who have been grounded at an
airport far from home by inclement weather have wished for some way to wheel
their airplane out onto the highway and drive home. This yearning has resulted
in many designs for roadable aircraft since as early as 1906.
A designer of a flying car will encounter many
obstacles, including conflicting regulations for aircraft and automobiles. As
an automobile, such a vehicle must be able to fit within the width of a lane of
traffic and pass under highway overpasses. It must be able to keep up with
normal highway traffic and meet all safety regulations. It must also satisfy
vehicle exhaust emission standards for automobiles. Therefore, the wings must
be able to fold (or retract) and the tail or canard surfaces may have to be
stowable. The emission standards and crashworthiness requirements will add
weight to the design. The need for an engine/transmission system that can
operate in the stop and go, accelerate and decelerate environment of the
automobile will also add system complications and weight.
For flight, the roadable aircraft must be
lightweight and easy to fly. It must have a speed range at least comparable to
existing general aviation airplanes. Conversion from aircraft to car or vice versa
must be doable by a single person and the engine must be able to operate using
either aviation fuel or auto fuel. Ground propulsion must be through the wheels
and not via propeller or jet which would present a danger to nearby people,
animals or other vehicles.
2. Design
Approach
While
some people use the terms Flying car and roadable aircraft interchangeably, or
use the latter term to bypass the science fiction connotations of the former,
they are explicitly two quite different concepts. One wishing to design such
vehicles must first decide which approach is appropriate. The ‘flying car’ is
primarily a car in which the driver has the option of taking to the air when
desired or necessary. The ‘roadable aircraft’ is an airplane that also happens
to be capable of operation on the highway.
In
the past, most designs have actually been for roadable aircraft. They started
out looking like conventional airplanes but with wings and possibly with tails
that could be retracted or folded. Alternatively, they may be removed and towed
in a trailer when the vehicle is operated on the road. Several such vehicles
have been designed and built. A few, such as the Taylor Aerocar1 or the Fulton
Airphibian, have been certified for use in flight and on the highway. Both
types of vehicle have been sold to the public. The roadable aircraft is meant
to be primarily an airplane but with the capability of being driven on roads to
and from the airport. It must also be capable of getting the pilot and passengers
to their desired destination on the highway when the weather prevents flight.
As such, it is a vehicle primarily sold to licensed pilots. They would use its
on-road capabilities in a limited manner, and not as a substitute for the
family automobile for everyday trips to the supermarket. Typical
problems with such designs have been their poor performance both in the air and
on the road. Also, there has been in the past a reluctance of insurance
companies to write policies which will cover their operation in both
environments
The
‘flying car’, unlike the roadable aircraft, has proved to be more of a fantasy
than an achievable reality. A key element in the development of a successful
flying car is designing a control system that will enable a ‘driver’ who may
not be a trained pilot to operate the vehicle in either mode of travel. This
virtually necessitates a ‘category III capable’ automated control system for
the vehicle. This must provide a ‘departure-to destination’ flight control,
navigation and communication environment. Many experts feel that such a design
is possible today, but only at high cost. Ideally, if the ‘flying car’ is to
become the family car, it must have a price that is at least comparable to a
luxury automobile (preferably less than 25 percent of the cost of the cheapest
current four passenger general aviation aircraft).
Both
the flying car and the roadable aircraft concepts usually assume a
self-contained system capable of simple manual or even automated conversion
between the car and airplane modes. A third choice is the dual-mode design
which is capable of operation on the road or in the air but does not
necessarily carry all the hardware needed for both modes with it at all times.
One such vehicle was the Convair/Stinson CV-118 Aircar.Designed in the 1940s,
it combined a very modern looking fiberglass body car with a wing/tail/engine
structure that could be attached to the roof of the car for flight. This design
successfully flew, and operated well on the highway, but was a victim of high cost
and changing corporate goals for its manufacturer.
Another
decision facing the designer of any airplane/automobile hybrid vehicle is whether
to attempt to meet government standards for both types of vehicles. Unless one
wishes to go to the extreme of developing a very lightweight flying motorbike which
will operate under ultra-light regulations, one must meet FAR or JAR
requirements for general aviation category aircraft. On the other hand, there
is a choice when one considers the automotive aspects of the design.
Automobile
safety and emission control requirements necessitate structural and engine
designs that are heavier than one would ordinarily need for an aircraft. There is,
at least under United States law, a ‘loophole’ in the regulations under which
any roadable vehicle with fewer than four wheels can be classified as a
motorcycle and not an automobile. This allows those who wish to avoid the extra
weight and expense of meeting automobile design standards to develop a
three-wheeled vehicle and classify the resulting design as a flying motorcycle,
a vehicle that officially is an airplane in the air and a motorcycle on the
road. Motorcycles have very few safety or emission design requirements beyond
the specification of lighting, horn and engine muffler. Three-wheeled road
vehicles do have operational speed restrictions in the United States.
Another
decision that must be made is the extent to which the vehicle will meet the ‘luxury’
standards of automobile buyers that are not normally seen in general aviation aircraft.
Atypical modern American automobile lists in its ‘standard’ equipment package air-conditioning,
electric window controls and door locks, automatic transmission, CD/tape
players and similar items. None of these are usually found in most general aviation
aircraft and all add (sometimes considerable) weight to the aircraft.
3. Design
consideration
some of the specifications to be determined by the
design approach are:
Ø Range
Ø Endurance
Ø Rate
of climb
Ø Cruise
speed in air
Ø Cruise
speed in land
Ø Airworthiness
standards
Ø Automobile
safety and emissions.
Additional challenges to be noted are
·
The need to have acceptable in-flight wing
aerodynamics while being able to retract,
fold, or detach and stow the wing for road travel,
·
The need
to ‘rotate’ on take-off,
·
The need to find an engine/transmission
combination which could meet the conflicting
demands of ground and air travel,
·
The need for dual-mode control systems, and the
need to meet rigorous stability and
performance requirements in both modes
of travel.
The
design of a satisfactory wing is a dominant part of any roadable aircraft
layout. As a ‘car’ the vehicle must fit into standard roadway widths. The
resulting vehicle footprint (aspect ratio) is less than unity. This is regarded
as inefficient for an aircraft wing planform. A wing of reasonable aspect ratio
must then be capable of being extended from the body (fuselage) for flight and
somehow stowed for highway use. There are many ways to do this including
folding wings, rotating wings, telescoping wings, and detachable wings. These
could be stored in, under, or over the car configuration. Alternatively, they
could be towed behind the car. All such designs impose structural compromise and
weight penalties. The use of the wing for a fuel tank location would also be
ruled out.
The
take-off problem reflects the differing stability requirements of automobiles
and airplanes. Most modern aircraft are designed with a tricycle landing gear
arrangement with the rear or main wheels placed only slightly behind the center
of mass (center of gravity). This allows easy rotation in pitch to a reasonable
take-off angle of attack after ground acceleration. Placement of the rearwheels
in the optimum location for the main gear of an aircraft would result in a very
unstable car. It would have a tendency for its front wheels to lift off the
road at highway cruise speeds near the desired take-off speeds for the
aircraft. Cars are designed to minimize the likelihood of the wheels lifting
off the road at highway speeds! Some roadable aircraft designs have attempted
to solve this problem by having a conventional aircraft tail section that is
removed for road travel. This effectively moves the center of mass further
forward between the front and rear wheels. Others have employed a car type
suspension with wheels or axles that can be extended or retracted to give the
needed angle of attack for take-off.
Further
complications arise due to the need for the wing on the airplane to develop some
lift during the take-off run while the automobile must produce as little lift
as possible at highway cruise speed. Removing or retracting the wings for the
car layout will obviously solve most of the highway lift problem.
Aircraft
piston engines are designed to be run at constant rpm for long periods of time.
Automobile engines are designed to operate over a wide range of rpm and are coupled
to a transmission to make possible combinations of torque and power suitable for
a variety of operational needs. Aircraft engines must also be capable of efficient
operation over a wider range of altitude than car engines. Air-cooling is
normally used with aircraft engines while water-cooling is usually used for
automobile engines. Both a water-cooling system and a transmission system will
add extra weight not common in most aircraft designs. Some flying car designs
have proposed using separate engines tailored to each mode of travel. This is
on the assumption that two optimized engines may not weigh much more than a
single dual-mode engine and drive train, and that the improved efficiencies may
allow lower fuel consumption. Other designers have suggested the use of an
engine and transaxle from a small 4WD automobile with the drive for one set of
car wheels attached to the wheels and the other to the propeller.
The
extent to which the controls for flight and ground operation can be merged is also
a design concern. Do the in-flight rudder pedals become the accelerator and
brake pedals on the road? Does the car steering wheel, with a release to allow
it to move toward and away from the driver/pilot, become the in-flight control
yoke, or can a ‘stick’ replace the wheel and be used in both modes of travel?
Moreover, how are these controls coupled to the rest of the vehicle? Can a
fly/drive-by-wire system work in both modes or must the controls be mated to
two separate mechanical or hydraulic systems? Finally, there is the question of
‘roadability’. Beyond the question of tip-over angles (or ground loops during
taxi, take-off, and landing), this is an issue that does not normally face the
aircraft designer. The vehicle’s wheel placement and suspension system and even
the choice of tires must take into account the need for comfortable, stable
handling on the highway as well as be able to absorb the sudden shock of landing.
4.
design concepts
Some
of the conceptual, built designs are
Ø Convair
Aircar
Ø Taylor
Aerocar
Ø Moller
skycar
Ø Terrafugia-Transition
4.1 Convair Aircar:-
Figure: Convair Aircar
Attempts
at roadable aircraft have been made since the advent of the airplane itself.
Only fourteen years after the Wright brothers first flew, Glenn Curtiss tried
to develop a flying automobile. His design was exhibited at the 1917
Pan-American Aeronautic Exposition in New York. This vehicle was abandoned after
the flight characteristics were deemed unacceptable. George Spratt built the
first flying roadable aircraft by using an existing aircraft and adding a pivoting
wing. This simply allowed the existing aircraft to maneuver down the road
without side obstruction. Waldo Waterman was the first person ever to be
granted a patent on a roadable aircraft, the “Arrowbile” in 1937. The Arrowbile
was the first vehicle designed as a roadable aircraft that actually flew. This
gave other inventors hope in being recognized for roadable aircraft designs. A
few other designs were attempted afterward, but no real progress came until after
World War II.
The
huge success of airpower and confidence from WWII helped forward the advancement
of roadable aircraft. A milestone came in 1946, when Robert E. Fulton designed
a new concept. His FA-3-101 “Airphibian”
was the first to gain certification by an organized flight agency, the Civil
Aviation Administration. This opened the door for additional roadable aircraft
since it had been shown that a flying car could acquire certification. One of
these new innovators was Ted Hall, who became the closest to producing a
marketable roadable aircraft. He produced the Hall Flying Car, which flew and
was featured in Popular Science. He was on the verge of production when funding
fell through and the project fell to the wayside. Following this came another
strong contender in the field, the Convair Aircar, in 1947, which had the support
of a large corporation.
When
the cost of this project was determined to be uneconomical, the project was abandoned
and the future of roadable aircraft looked dim. Many people thought that if a
large company like Convair could not produce a viable solution, then no one
else would be able to, either.
4.2 Taylor Aerocar:-
Figure: Taylor Aerocar
Aerocar International's Aerocar (often called the Taylor
Aerocar) was an
American roadable aircraft, designed and built by Moulton Taylor in Longview, Washington, in 1949. It is the most
successful and probably the most famous "flying car" design to date.
Although six examples were built, the Aerocar never entered production.
Design and Development
Taylor's design of a
roadable aircraft dates back to 1946. During a trip to Delaware, he met
inventor Robert E. Fulton, Jr., who had designed an earlier roadable airplane,
the Airphibian. Taylor recognized that the detachable wings of Fulton’s design
would be better replaced by folding wings. His prototype Aerocar utilized
folding wings that allowed the road vehicle to be convertible into flight mode
in five minutes by one person. When the rear licence plate was flipped up, the
operator could connect the propeller shaft and attach a pusher propeller. The same engine drives the front wheels through a three-speed
manual transmission. When operated as an aircraft, the road transmission is
simply left in neutral (though backing up during taxiing is possible by using
reverse gear.) On the road, the wings and tail unit were designed to be towed
behind the vehicle. Aerocars can drive up to 60 miles per hour and have a top airspeed of 110 miles per hour.
Characteristics of Aerocar: Performance of Aerocar:
Crew: One
pilot
Maximum speed: 112 mph (172 km/h)
Capacity: One Passenger (2 total) Range: 300 mi (480 km)
Length: 6.55 m (21 ft 6 in) Service ceiling: 12,000 ft (3,658 m)
Wingspan: 10.36m (34 ft 0 in) Rate of climb: 550 ft/min (168 m/min)
Height: 2.18 m (7 ft 2 in) Wing loading: 12.5 lb/ft² (61 kg/m²)
Wing area: 15.6 m² (168 ft²) Power/Mass: 0.06 hp/lb (100 W/kg)
Loaded: 955 kg (2100 lb)
Maximum takeoff: lb (kg)
4.3
Moller skycar:-
Figure: Moller skycar
The Moller Sky car is a prototype personal VTOL (vertical
take-off and landing) aircraft a
"flying car"
called a "Volantor" by its inventor Paul Moller, who has
been attempting to develop such vehicles for forty years. The design
calls for four fans
encasing the propellers, which is safer to bystanders and more efficient at low
speeds.
The craft said to be currently under development,
the M400, is purported to ultimately transport four people; single-seat up to
six-seat variations are also planned. It
is described as a car since it is aimed at being a popular means of transport for anyone who can drive, incorporating automated
flight controls. It is proposed that in a model for the general public, the
driver may only input direction and speed. Piloting knowledge would be un-necessary;
however, training will be required.
Further, developers claim that by using eight
inexpensive Wankel rotary
engines - compared to jet engines, the vehicle's
price may eventually fall close to that of a luxury car ($100,000). The fuel
consumption is claimed to be 20 miles per gallon similar to that of a big car but
this has been calculated as unrealistic. According
to the developers, operation of a Skycar will produce as much noise as traffic
on a nearby freeway when taking off, and this will only last for a few seconds,
because it climbs so quickly.
The Skycar demonstrated limited tethered flight
capability in 2003 by hovering only. Scheduled
tethered flight tests, which were to occur in mid-2006, were apparently
canceled. Moller upgraded the Skycar's engines in 2007, and the improved
prototype is now called the "M400X". According to a 2008 article in the
media, a prototype is supposed to be flying in 2012, with certified versions
"a few years later".
Moller International's website claims that only
$100 Million has been spent in R & D at Moller International,
The company is also developing a more advanced
model called M600, with an intended capacity for 6
pasengers or a payload of about 2000 lbs (900 kg).
Operation
A Skycar is not piloted
like a traditional fixed wing airplane, and has only two hand-operated
controls, which the pilot uses to inform the computer control system of his
desired flight maneuvers. The Skycar's ducted fans deflect
air vertically for takeoff and horizontally for forward flight.
Rotapower engines
The engines
to be used are being developed by a separate Moller company called Freedom
Motors. They are Wankel engines they call
"Rotapower" which have a direct drive to a propulsion fan. Each fan is contained in Kevlar-lined housings with intake
screens to provide protection to bystanders. The
Skycar has four engine nacelles, each with two computer-controlled Rotapower
engines. All eight engines operate independently and, allegedly, will allow for
a vertical controlled landing should any one fail.
The
Rotapower Wankel engine would have the ability to operate on any fuel. Earlier Rotapower models used gasoline.
General characteristics
Capacity: Four passengers
Length: 19.5 ft (5.9 m)
Height: 7.5 ft (2.3 m)
Empty weight: 2,400 lbs (1088 kg)
Useful load: 750 lbs (340 kg)
Performance
Avionics
Computer control system.
Computer control system.
The
only flight demonstrations have been hover tests performed by a Skycar
prototype that for insurance reasons was tethered to a crane. The ongoing failure of the
Moller Company to actually fly an M400 led the National Post to characterize the Skycar as a 'failure’ and to describe the
Moller Company as "no longer believable enough to gain investors".
4.4 Terrafugia-Transition:-
Figure: Transition
The Transition is a light sport, roadable aircraft under development by Terrafugia, a small
start-up company based in Woburn, Massachusetts.
The Rotax 912S piston engine powered, carbon-fiber vehicle is
planned to have a flight range of 400 nmi (460 mi; 740 km) using
automotive grade unleaded gasoline and a cruising flight speed of 115 mph
(100 kn; 185 km/h). It does not come with an autopilot.
On the
highway, it can drive up to 65 miles per hour (105 km/h) to keep up with traffic. The
Transition Proof of Concept's folded dimensions of 6 ft 9 in
(2.1 m) high, 6 ft 8 in (2.0 m) wide and
18 ft 9 in (5.7 m) long are designed to fit within a
standard household garage. When operated as a car, the engine powers the front
wheel drive. In flight, the engine drives a pusher propeller. The Transition's layout, with folding wings, pusher
propeller and twin tail, is similar to experimental aircraft N8072 built by Dr. Lewis
A. Jackson in Xenia, Indiana during the 1960s.
The
experimental Transition Proof of Concept's first flight was successful and took
place under FAA supervision at Plattsburgh
International Airport in upstate
New York using FAA tail number N302TF. First customer delivery, as of March
2009, is planned for 2011.
General characteristics
Crew: 1
pilot
Capacity: 2, pilot and passenger
Length: 19 ft 2 in
(5.8 m)
Height: 6 ft 3 in
(1.9 m)
Empty weight: 890 lb
(400 kg)
Useful load: 430 lb
(200 kg)
@ 5500 rpm (continuous)
Propellers: Prince Aircraft
Company, four-bladed "P-Tip" propeller, 1 per engine
Cockpit width: 51 in
(1.3 m) at the shoulder
Fuel capacity: 20 US gal
(76 L; 17 imp gal)
Length on road: 18 ft 9 in
(5.7 m) with elevator up
Width on road: 80 in
(2.0 m) with wings folded
Height on road: 6 ft 9 in
(2.1 m)
Front wheel drive on road
Performance
Maximum speed on road: 65 mph
(105 km/h)
Fuel economy in cruise flight: 5 US gal
(19 L) per hour
Fuel economy on road: 30 mpg (7.8 L/100 km;
36 mpg)
Avionics
Glass panel; the proof-of-concept airplane includes:
Glass panel; the proof-of-concept airplane includes:
Dynon
Avionics EFIS-D100
Electronic Flight Information System with HS34 Nav and GPS Connectivity
Dynon Avionics EMS-D120 Engine Monitoring System
Garmin SL30 Nav/comm transceiver
Garmin GTX 327 digital transponder
Garmin GPSMAP 496 portable GPS.
Cost of this roadable aircraft will be around $200,000 US.
1.
conclusion
Ø
The flying car concepts will require some more
time to be in reality.
Ø
Roadable aircrafts design and development are
feasible.
Ø
Cost of roadable aircrafts play a vital role in
their success.
Ø The
success of roadable aircrafts will end uncertain weather, rising costs, and
ground transportation hassles on each end of the flight.
2. References
- “Aircraft Design Projects for engineering students” by Lloyd R. Jenkinson James F.
Marchman III.
- “Roadable
aircraft” a project report by Will Anderson, Et.all
- www.wekipedia.org
- www.images.google.co.in
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