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The Following Article is from the December 2003 Issue of
the World and I Magazine by Science Editor, Glenn
Strait
Neither a blimp, nor a glider, nor a fuel-propelled
airplane, a new aircraft promises to translate gravitational
attraction into both lift and forward motion, capture wind
energy with a radical new wind turbine, and usher in the
era of fuelless flight.
Editor's introduction:
Thinking totally out of the box and utilizing private funds,
independent inventor Robert D. Hunt is pushing forward with
a project that could transform air transport in the twenty-first
century--if it proves successful. While Hunt's gravityplane
quite reasonably could have been conceived of in the twentieth
century, the materials and technologies for building it
may only be available now. Even today, the craft is pushing
the envelope, requiring the most advanced of lightweight,
fiber-epoxy materials and a radical wind turbine design
that has yet to emerge onto the commercial market. Hunt
envisions a craft that will control its weight and center
of gravity by balancing partial vacuum, helium, and compressed
air in interior chambers. The craft will rise when it is
lighter than air, and, when it is heavier than air, tilt
and glide forward, or float level and sink straight down.
All this is to be achieved through a computer-controlled
system of pumps, valves, piping, interior chambers, and
polyester-reinforced nylon balloons.
In this
aircraft, compressed air serves as a source of both power
and weight. The compressed air is produced through energy
captured from the high-speed airstream passing by the craft
as it glides downward. The energy capture is achieved by
two of Hunt's new vertical-axis turbines, which sit like
two counter-rotating eggbeaters atop the craft's center
section.
The concept
is simple, but the engineering is difficult. Every additional
mechanical component adds deadweight to a structure that
must weigh in as a lightweight if the craft is ever to fly.
Hunt is clear that a Cessna-sized gravityplane could never
fly. It would be too small. The weight of the aircraft structure
and machinery would overburden even the greatest possible
gravitational lift, which would be achieved if the plane's
interior were evacuated to hold a vacuum.
To fly,
then, the gravityplane must be big, gaining the advantage
of volume over surface area as its size increases.
Will the
gravityplane ever become a reality? Only a lot of engineering,
model making, and testing can decide. Hunt is betting that
he can make it a reality. Already a test module, a pod 100
feet long, is taking shape in a high-tech shipyard on the
outskirts of New Orleans.
In the following
article, Hunt writes directly about the principles, technology,
and developmental process of the gravityplane.
 any
people do not see the fingerprint of gravity in floating battleships,
buoys, and bottles. Yet a little thought reminds us that buoyancy
occurs because gravity exerts a greater pull on more-dense
materials than on less-dense materials. An air bubble in water
and a helium-filled balloon in air, for example, both rise
because of the force of gravity--because they are less dense
than the surrounding fluid.
Similarly,
it is easy to overlook the fact that glider aircraft can fly
only because earth's pull accelerates them downward as their
forward-moving wings produce a counteracting aerostatic lift.
The new gravityplane simply harnesses both forces of gravity--the
upward force of buoyancy and the downward pull of gravity
acceleration--so that it can rise into the sky using a gas
such as helium, and then glide downward like a glider using
the earth's gravitational pull.
Before shifting
into the glider mode, however, the aircraft must change from
being lighter than air to being heavier than air. The weight
change is achieved by drawing in and compressing air from
the surrounding atmosphere. This moderate-pressure compressed
air may be thought of as a primer load of potential energy
needed to initiate the downward glide through which the craft's
wind turbines will capture high-pressure compressed air.
Aboard the
gravityplane, high-pressure compressed atmospheric air at
about 1,500 pounds per square inch, or roughly 100 atmospheres,
is a treasure store of potential energy of both height and
pressure. The gravityplane is designed to take advantage of
both of these. The compressed air's weight (gravitational
potential energy of height) enhances downward glide speed,
while its pressure is a potential energy reserve, a fuel,
to run the plane's machinery. As the gravityplane operates
in a cycle of rising and falling (gliding), rising and falling,
it depends on high-pressure compressed air for changing between
the two modes, so it must always keep a minimal supply in
its tanks. In its original start-up, the gravityplane will
require an injection of high-pressure compressed air from
an outside source; or it may be able to capture its own high-pressure
air as it sits on the ground, if the wind is adequate to drive
its wind turbines (20 MPH or more).
More truly an airplane
 t
could be argued that the gravityplane will have a greater
claim to the name airplane than today's jet planes, which
take off with a heavy load of fossil fuel that their engines
burn throughout the flight. The conventional airplane uses
air for two crucial flight elements: aerodynamic lift and
forward thrust. In comparison, the gravityplane uses air for
four
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The gravityplane's inventor, Robert
D. Hunt (center), and his two chief associates at
Hunt Aviation, vice president Joe Chomko (left) and
president Gene Cox (right), announced the gravityplane
vision at the National Business Aviation Association's annual
convention in October 2003. Here, outside the convention,
they express their anticipation of a bright future for fuelless
flight.
crucial flight elements: aerodynamic lift, onboard
power, aerostatic lift (buoyancy), and ballast (weight distribution
within the craft).
In both the
jet airplane and the gravityplane, air flowing past the wings
yields aerodynamic lift. Here the similarity ends. Yes, the
jet airplane's thrust is from air, but that's only after the
air is heated and forcefully expelled by the fuel-burning
jet engine. The fuel provides the energy behind air's thrusting
force.
In the gravityplane,
highly compressed air is the fuel providing all the plane's
energy needs not met by gravity. Thus not only does the gravityplane
fly through the air like a conventional plane, it also gulps
in and captures huge volumes of the air. The plane will use
high-pressure compressed air to drive its internal system
of pumps and pipes, generate electricity, and power two outboard
turbines (used for vertical propulsion at takeoff and landing
and controlling the plane's direction).
The gravityplane's
wind turbines hearken back to windmills in the preelectric
era, when a windmill's spinning shaft would have been mechanically
linked to a mill wheel for grinding grain. In the gravityplane,
the wind turbines' spinning shafts are linked directly to
high-pressure air compressors for capturing compressed air
at 100 atmospheres. High winds from the plane's glide drive
the turbines. Through being compressed, air becomes the craft's
fuel and is readily converted to rotary motion when it is
released through a pneumatic motor. The rotary motion in turn
drives the plane's pumps and moderate-pressure compressors.
Just as water
is the pervasive component of the human body, compressed air
is the pervasive component of the gravityplane. The plane
maintains two separate confined-air systems: a high-pressure
system and a variable-pressure system. The high-pressure fuel
system is contained within a limited network of high-pressure
storage tanks and delivery lines. In contrast, the variable-pressure
system is coextensive with the entire interior of the plane's
two large pontoons, which are each subdivided into five great
chambers that can hold a vacuum. Operation of the plane will
require that the pressure of each chamber varies from perhaps
one-half to three atmospheres (7.4--44 psi). Each chamber
contains a partially inflated helium-filled balloon that expands
to fill the chamber under the partial vacuum and is compressed
to be nearly flat under the weight of three atmospheres of
air.
If the craft
needs to add weight, it pumps outside air through a moderate-pressure
compressor into the appropriate large interior chamber. The
compressor, of course, is driven by a pneumatic motor powered
by high-pressure compressed air. The spent fuel (the previously
high-pressure air) is simply added to the air supply in the
large chamber.
Follow the flight cycle
 nderstanding
the basic concept of the gravityplane, we can begin to grasp
the overview of its flight cycle and the way it manages air
for flight advantages never before achieved. By capturing
high-pressure compressed air during its descent, for example,
the craft naturally increases its weight and thereby increases
its glide speed. "Increased weight implies increased glide
speed" is a well-known principle of glider flight, but no
previous gliders have had the option of adding weight once
they were launched. With its full embrace of air as both fuel
and ballast, the gravityplane opens a new era of the high-speed,
long-distance glider.
Combining
properties of a glider and a blimp, the gravityplane must
rise or fall to be productive. Only in falling does it advance
forward, and only in rising does it gain the altitude it must
have if it is to fall fruitfully. When rising, the
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When executing a steep dive or floating
on water like a seaplane, the gravityplane will fold its
wings back.
craft gains potential energy that in its falling
is converted to kinetic energy of motion. This energy gain
is in direct relationship to the height attained.
If in its
ascent the craft fails to gain sufficient altitude before
the glide begins, then in its gliding descent it will fail
to store enough high-pressure compressed air to complete another
ascent-descent cycle. To complete the cycle, it needs to halt
its descent by pumping a partial vacuum into its chambers
so each is filled with its low-pressure helium balloon. Then
the gravityplane must rise again to an effective altitude,
carrying sufficient high-pressure air to run the compressors
that take in the air that allows it to become heavy enough
to fall again. The aircraft would normally land with a significant
load of compressed air--its fuel for later use, including
thrust for vertical takeoff.
While the
craft is on the ground or floating on water, its wind turbines
can generate power so long as the wind blows with a sufficient
velocity. This allows the supply of compressed air to be fully
charged after short flights that do not produce sufficient
compressed air to resume high-altitude flight. On the ground,
operation of the wind turbines also provides high-pressure
compressed air that can be used to produce electricity if
a pneumatic motor is connected to a generator.
Building the gravityplane
 reating
this radical glider-blimp hybrid stretches the imagination
of designers and engineers alike. It also challenges the most
advanced manufacturing facilities. How can we begin to construct
such a craft?
Once the basic
design plans are in place, the materials search leads to such
strong, lightweight materials as carbon fiber or Kevlar bonded
with epoxy resin. These will be used for constructing a rigid
frame and outer skin, and the helium bag in each chamber will
be made of lightweight, nonporous polyester-reinforced nylon.
Studies already completed for Hunt Aviation give the green
light for construction to begin. They show that a lighter-than-air
craft with internal chambers each occupied by a helium-filled
balloon can be built of these new ultralightweight materials.
A single layer
of Kevlar bonded with epoxy resin can cover an area of a square
yard while weighing as little as three ounces. Built up into
multiple layers, the Kevlar composite becomes rigid and strong.
The studies affirm the value of making a lightweight rigid
aircraft by coupling a Kevlar composite shell with a rigid,
carbon-fiber framework. Such a craft, the studies show, could
weigh as little as 16 ounces (one pound) per square yard of
surface area.
Realizing
the potential of the gravityplane requires that it be made
big. This size prerequisite is apparent from a property of
enclosed spaces that is well known by balloonists. Bigger
balloons hold more gas per square foot of surface area than
smaller balloons do. The gravityplane follows the same principle
even though it is more complicated, with its rigid shell requiring
a rigid frame and internal balloons as well. Calculations
show that to carry the same load, the gravityplane would need
to be about 50 percent larger than the 747.
Building a
craft that flies based on the gravityplane vision is the task
of years and a small army of experts. Hunt Aviation has already
assembled many of these:
Century Aerospace:
Bringing together experience from major aircraft manufacturers
of both large and small planes, including Boeing, Cessna,
Lear, Lockheed, and Rockwell, Century's design team will help
direct conceptual design of the prototype gravityplane. At
later stages, Century will be instrumental in the gravityplane's
certification process. The Mississippi
State University Aerospace Engineering Department: Faculty
in the department are conducting a nine-month evaluation
of the gravityplane's technological feasibility under the
title "Systems Analysis of the Hunt Aviation Gravity Powered
Airship."
United States Marine: A builder of lightweight
and strong vessels for the U.S. Special Forces, United States
Marine is in the early stages of building the first, 100-foot-long
pontoon.
Raven Industries: The main supplier of strong,
lightweight, high-altitude balloons to NASA, Raven will
supply the polyester-reinforced nylon gasbags designed to
go into the pontoons and wings of the gravityplane.*
The gravityplane
embodies so many new ideas and design concepts that testing
the concept requires starting with one part of it: the pontoon
(lifting body). Each plane will have two pontoons, but testing
begins with one. It will be 100 feet long by 20 feet in
diameter and have five internal chambers, each 20 feet long
and containing a polyester-reinforced nylon balloon. Both
the exterior and the dividing walls of the chambers will
be strong enough to hold a vacuum, and the entire unit must
be built out of materials that are of the lightest weight
possible.
As this
article is being written, engineers are finalizing plans
for a prototype of the lifting body to be constructed by
United States Marine within the next few months. The full-size
pontoon shell constructed of the lightweight composite materials
will weigh just 712 pounds, and the polyester reinforced
nylon collapsible gasbags plus the cell dividers will add
152 pounds. Thus the pontoon's total weight should be only
864 pounds. When that weight is balanced against the lift
provided by helium in its bags, the pontoon's net lift is
1,108 pounds.
Maximum
lift will be obtained by the use of a partial vacuum outside
the gasbags, allowing the helium within them to expand without
opposition from atmospheric pressure at sea level and expelling
air from between the gasbags and the pontoon shell. In this
way, the helium pressure within the gasbags can be lowered
to substantially below 1 atmosphere (14.7 psi).
Once the
pontoon is completed, it will be moved like a giant helium-filled
sausage on a string to a test site; there, it will be tethered
with lines connected to scales for measuring lift. The pontoon
will also be hooked up to umbilical hoses managing the flow
of gases (helium and air) into and out of the chambers.
When all is in place, every aspect of the pontoon's function
will be tested. Aspects to be tested will include:
- lift capacity
- filling the balloons with helium
- drawing a partial vacuum in the chambers
- compressing air into the chambers
- expelling air from a chamber through
downward-facing exhaust ports to produce upward thrust
- raising one end by adding air to the
end chamber and removing it from the other locking the
pontoon back and forth by alternately sinking one end,
then sinking the opposite end (the three central chambers
would remain constant)
These tests
will provide data that will be crucial for developing
the complex flight-control systems needed to manipulate
the gravityplane's constantly changing weight and weight
distribution. As the gravityplane flies, it will need
to constantly monitor and adjust each cell's lift characteristics
through the use of a computer program. This program will
be constructed from scratch, starting with the results
of the tests on this first module.
Manned but tethered
 n
the foundation of successfully testing and modifying the
first pontoon, we plan to build the first prototype gravityplane,
starting by building the second pontoon. The two pontoons
will be bridged together and fitted with wings and other
aircraft flight-control structures, such as ailerons and
a rudder. The bridge section will be fitted with a minimal
pilot's cabin, a wind turbine, and a small thruster-propulsion
turbine.
Although
the unit will be manned in flight, it will be tethered
to the ground at very low altitude (probably less than
500 feet). With both wings and pontoons, the prototype
will provide valuable data about the gravityplane's fundamental
premise that aspects of buoyant lift and aerodynamic lift
can both be beneficially incorporated into the same craft.
In many
ways, this tethered device may be considered a flying
wind turbine that employs both aerodynamic lift (like
a kite) and aerostatic lift (like a helium balloon). When
the wind is blowing, power will be generated and stored
as high-pressure compressed air within pipes inside the
pontoons. A portion of the compressed air will drive a
pneumatic motor that will power an electrical generator
to provide onboard power and charge the craft's batteries.
One option
will be to store so much high pressure (and hence heavy
air) that the gravityplane's weight will overcome the
combined upward force of the wings' aerodynamic lift and
the pontoons' aerostatic lift, causing the craft to sink
to the ground. Descent and landing could be controlled
more precisely by using the propulsion turbine powered
by high-pressure compressed air producing a downward thrust.
Likewise, the craft can practice vertical takeoff by downward
thrust that also reduces its weight as the air is exhausted
through the propulsion turbines.
After
the gravityplane passes all its tests and gains experimental
flight-class certification, it will take its first free
flight. Ascending and descending runs in the aerostatic
lift mode will eventually lead to the aircraft's initial
gliding descent, in which it will attain substantial velocity
of perhaps 100 MPH. The craft's relatively small size
will limit its maximum altitude and hence its maximum
speed.
Assuming
no insurmountable obstacles, the first prototype will
likely be followed by a larger, more complete model capable
of long-distance, sustained flight through the gravityplane's
distinctive series of cycles alternating between buoyancy-lifted
ascents and gravity-driven, gliding descents.
Bringing
the gravityplane into commercial operation as an alternative
to fossil-fuel-powered aircraft will require a decade
or more. The craft will be so different from any existing
flying machine that we probably cannot begin to imagine
all the forms it may take and the uses to which it could
be put.
For now,
however, dreams of future flights must wait. The next
step is clear: build and test the first pontoon.
On the Internet
Hunt Aviation
Video of fuelless gravity-powered flight
http://www.fuellessflight.com
Robert D. Hunt, the founder and president
of Hunt Aviation, is an independent inventor holding more
than 50 patents. Earlier in his career, he worked as a nuclear
designer for Newport News Shipbuilding, a division of Tenneco
Oil Company. |
