As progress continues in both the automotive and aviation fields, interest in
vehicles that can be used in both areas continues. Automobiles are becoming
lighter in weight, more efficient in propulsion, and more aerodynamic in shape.
Airplanes are becoming easier to fly, more efficient, and easier to navigate.
While the Interstate highway system is expected to provide a convenient
means for travelling between many areas during the next 20 to 40 years,
there will still be many other areas that remain hard-to-connect and/or require
long driving times. Furthermore, congestion on metropolitan freeways
continues to grow, so the 'cross-town' commute between suburbs calls for
problem-solving.
The main purpose of the Dragon aircar is to provide a single vehicle for
personal and business door-to-door transportation. In addition, the
recreational value as a sport vehicle is appealing to many of us.
The underlying theme of the aircar is to trade off the high cruise speed of
the fast small aircraft for quicker and more convenient trips by reducing the
time lost in changing from automobile to airplane and vice versa. Likewise,
the aircar trades off the typical automobile's capacity for airplane
components. A typical round-trip day trip with a radius of 420 miles to
destination is figured to take the same time via Dragon aircar cruising at
140 knots as with a 200 knot airplane or 400 knot airliner, due to the time
savings for conversion from road to air and vice versa. The figures are in a
spreadsheet and chart at *Trip Time Comparisons.
For a comparison with driving six days a week for a maximum usage, using an
aircar would save 4 hours per trip, times 300 trips = 1,200 hours per years.
This allows for week-end recreational flying, maintenance, and weather,
assuming that the pilot is instrument rated. Assuming a load factor where
40% of the trips are by the pilot only and 60% include a passenger, for a
factor of 1.6, this gives 1,920 hours per year. Figuring the value of the users
at about $100 per hour, the savings amount to about $192,000 per year
(less maintenance such as engine overhaul) as compared to driving. From this,
one should subtract maintenance such as engine overhaul and the difference
in fuel costs. Maintenance such as engine biennial overhaul may be estimated
at about $40,000. One may assume a fuel cost of $3 per gallon for aviation fuel or
premium automotive fuel, fuel burn rates of 2 gallons per hour while driving
and 7 gallons per hour for flying. This results in $6 per hour for driving and
$21 per hour for flying. Fuel costs for driving would be 10 hours at $3 per hour,
or $30. Fuels costs for flying would be 6 hours at $30 per hour, or $180.
The difference would then be $150 per round trip. The annual fuel cost
difference would then be $150 times 300 trips, or $45,000. This would then
result in a net savings of $192,000 - $40,000 - $45,000 = $107,000.
The value of the time savings would quickly provide recouping the investment
in leasing or buying an aircar in about two years.
The underlying benefit of business opportunities should also be considered.
The aircar may replace the automobile to a large degree, saving on that expense.
The ultimate benefits are that the aircar provides: an increased radius of travel
for business; or shorter workdays to provide more personal quality time; or
more time for vacation travel. You can figure out the times for your trips and
see how much time you would save if you used an aircar instead of only driving
your automobile. You can work out the cost comparisons for an aircar versus
a combination of a car and a plane. Needless to say, there are many obvious
side benefits to having an aircar instead of constantly switching from car to
airplane and vice versa. The pure recreational benefits of using an aircar are
a bonus. Development and production of the "Magic Dragon" aircar is
considered to be a viable enterprise that would satisfy a niche market and
provide a profitable venture for an extensive period of time. Ultimately, this
may involve several thousands of aircars in use within several years.
The StrongMobile is considered to be a viable candidate for the flight trainer
market, even without any road drive, because it can provide a introduction
to flying with a familiar setup similar to a conventional automobile.
HISTORY
Development of the Dragon has been ongoing for forty years in several phases.
The Road Runner
During the author-inventor's pilot training, he envisioned a better lightplane,
called the "Road Runner", that featured:
- wings folding into the
body;
- a ducted fan based on the
Stipa "barrel plane", as reported in NACA TR 292,
to eliminate engine and propeller torque effects, reduce the risk of injury, and
eliminate the need for propeller pitch control; - four-wheel landing gear to
improve ground handling;
- simplified flight controls
with full-span flaps integrated with elevator trim; and
- spoiler ailerons to
eliminate the need for rudder control.
RASer
The RASer (inventor's initials), was designed originally in the late '50s as a
lifting-body aircar (
RASer and other roadable airplanes, officially called "autoplanes" by
the
no parts need be detached at any phase of operation. This criteria then
required that the wings be small enough to be included with the road vehicle.
Previous aircars, such as the Ford/Stout Skycar, the Waterman Aerobile, the
thereby increased the required time for a conversion operation. RASer was a
vectored slipstream design; the stub wings relied on fan exhaust for lift.
The *Coanda 1910 was the first thermojet airplane, using a compressor and two
burners mounted on the sides.
The Stipa "barrel plane with ducted fan propulsion solved propeller stowage.
The Nash Airflyte automobile design inspired the front air intake and covered front wheels
The vectored fan-stream design was later seen to be too risky due to the
potential for engine failure at low altitude, such as landing or take-off, and
subsequent catastrophic loss of lift with little potential for recovery. Also, the
aircraft landing gear mounting was found to be unsuitable due to weakness and
the design had inadequate brakes for highway use.
Originally, the engine purchased was a
It was similar to that used in the Tucker "Torpedo"; it was the key
to that
car's performance. The manufacturer no longer supports that engine;
however,their O-335 may be used. A concern is that the road mode operation
calls for extended periods of idling that may foul the spark plugs.
Construction on a prototype RASer was begun, but abandoned due to extensive
relocations, time constraints, and the aforementioned design deficiencies.
StrongMobile
The RASer was then modified in 1963 with conventional swing wings as
an undergraduate Aeronautical Engineering Airplane Preliminary Design
project. The inventor's Instructor was the late Edgar Lesher, who held
world speed records for lightplanes; he advised the class to "distort the
specifications". The specification chosen to be distorted came from my
background in
numbers by making the airplane roadable. The figure below shows the
preliminary design sketch for the project. The design was to have had a
road drive via a power take-off from the aircraft engine with a Dodge
Flexidyne transmission and lightweight, light duty differential gear by V-Plex.
At full power for take-off, the jet exhaust was calculated to be about 250
m.p.h.,
giving a boost to the wingroot lift, thus retaining the RASer's vectored lift
notion.
A small model of the StrongMobile
was built and displayed at the
Experimental Aircraft Association's National Convention in 1965.
The StrongMobile design was tested in the CalTech Guggenheim wind tunnel
as shown above. The tests showed that the aft fuselage-body and tailplane
interfered with each other and created a nozzle effect; this was cured by
re-designing the aft fuselage to provide more up-sweep towards the tail;
this also makes for a more stable reflexed fuselage airfoil.
Improvements to the 1/12th scale wind tunnel model were mainly removing the
wheels and smoothing over the wheel wells, similar to the retractable concept.
The Cal Tech technicians also removed the wheels and filled in the wheel wells
with clay and tested again; with the streamlining, the lift/drag ratio was 8:1,
which is quite acceptable by airplane standards. The lower portions of the
wheels will remain exposed for the initial engineering prototype, although the
wheel-wells may be more streamlined with retractable "slipper" covers
The model had a simulation of an engine cooling exhaust augmenter nozzle;
this cowling design showed separation and was changed.
Other improvements increase the L/D, such as eliminating the engine cooling
exhaust duct drag, increasing wingspan, and re-contouring the turtleback to
reduce interference with the tailplane. Testing the current design is required.
The design was patented with US Patent 3,612,440,
The design was then put on the back burner, so to speak, as a result of
the vanishing lightplane market that was influenced by liability litigation
and the fuel crunch. The inventor continued to refine the design with
several design improvements. The rear end was changed to include a
convertable bumper fairing that provided a degree of crashworthiness.
The large single dorsal fin was replaced with dual fins, a "pi"-tail.
The biggest change was to enlarge the wing surface area to accommodate
the added weight of changing the design to use automotive suspension
and drive train. The solution was to add folding wingtips and stow them.
The wing flip-tips further reduce the induced drag and improve the design.
The design was re-named "Magic Dragon".
After 2001, the inventor built two more models of the Dragon design.
A 1/12th scale tether model showed that the stability and
center of mass were OK.
A ½ scale model was built and displayed at the
After a barn was built to shelter construction, the full-scale mock-up
was built.
Its design incorporated the folding tailplane concept for better stability.
A great deal of time was spent on studying an electric hybrid version; however,
inputs from folks attending forums and exhibits overwhelmingly favored using
a conventional mechanical road drive, so the design was changed accordingly.
Also, there were objections to using the fan while driving, so a clutch was
conceived for disconnecting the fan.
You can view or download the original 1973 development
report,
27 pages, as a Microsoft Word 7 file at: * Strongmobile
Development Report 700k
and/or the updated reports * SDR31
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