Our world is certainly not left wanting for free sources of energy. The sun vomits an absurd amount of energy upon the Earth's surface constantly-- up to a thousand watts per square meter during the daytime; the planet's mantle writhes with heat energy, up to 4,000 degrees Celcius; and a tremendous supply of energy saturates the entire planet in the form of gravity. The difficulty has always been in finding ways to capture such energy usefully. Solar panels have had some success snatching up sunlight for conversion to electricity, geothermal installations use the earth's heat to create power, and hydroelectric plants tap the potential energy of gravity. Currently a Nevada-based aviation company is exploring another creative way to utilize gravity as a power source-- combining some very old ideas with some very new ones-- to produce an aircraft concept which might one day tote people and cargo great distances without the need for fuel. The project is called the GravityPlane.
The idea sprung from the brain of Robert D. Hunt, a theoretical physicist and inventor who founded Hunt Aviation to develop his patented "gravity powered hybrid aircraft" concept which operates on the principles of buoyancy, aerodynamic lift, and gravity. It uses a cycle of climbing and descending to maintain its lift and forward speed, mimicking the behavior of the bodies of warm and cold air which make up the weather.
In order for the GravityPlane to become airborne, gas bags inside a pair of rigid, zeppelin-like structures are filled with helium from storage tanks inside the vehicle. This causes the aircraft to become lighter-than-air, and it rises from the ground. Compressed-air jets on the sides of the craft add further propulsion, pushing the vehicle skyward and decreasing the craft's overall weight by releasing the stored air which acts as ballast. Once the craft reaches the altitude where the helium is no longer lighter than the surrounding air-- theoretically as high as ten miles up-- it is unable to climb any further. Some of the stored compressed air is then expanded into the dirigible areas, decreasing the buoyancy effect of the helium and starting the aircraft's descent phase.
As gravity pulls the plane towards the earth, the long wings are moved to the swept-back position to reduce wind drag, and air turbines mounted on the top of the craft capture some of the forward momentum and use it to drive air pumps which can refill the on-board compressed air storage tanks. In this gliding mode, the aircraft achieves aerodynamic lift for a gradual descent at high speeds, and can travel in this configuration for about 400 to 600 miles. At the end of the gliding phase, the wings are redeployed. The compressed air can once again be forced out through the compressed air jets, pushing the vehicle upwards and increasing the vehicle's buoyancy to lighter-than-air once again, beginning the cycle anew. This process can be repeated as many times as needed to cover the required distance.
If the concept ever leaves the drawing board and becomes a prototype, it will be massive. Much like the zeppelins of old, the volume of helium needed requires a very large gas bag area. But hypothetically, this design could allow the aircraft to travel practically any distance with no fuel. It would expel no polluting gasses, and it would be virtually silent. It would also have some interesting features for such a large craft, including vertical take-off and landing (VTOL), and the ability to set down on land or at sea. Additionally, its buoyancy would allow it to hover in the air if needed, even in the event of total power loss.
Considering the GravityPlane's simplicity, its environmentally friendly propulsion, and its freedom from heavy and expensive fossil fuels, this concept could completely revolutionize aircraft design in the coming decades if it proves viable. And using non-flammable helium means that a Hindenburg-style disaster is not a risk. Can Hunt Aviation deliver the sparkling, rigid-airship future that zeppelins promised us so long ago? Time will tell.