Naval Air System Command's Airship Advanced Development program office is the current source of information, advice, contract management, and development assistance for a number of projects related to airships. Among them is the Joint Chiefs of Staff (J-4 Mobility Division) investigation into the military utility of hybrid aircraft. Hybrids are lighter-than-air vehicles that never actually fly light. They operate free of one of the primary objections to "blimps"—the need for an agile ground crew to aid in flight termination (restraining it and adjusting ballast during the off-loading of passengers and cargo).
Lift for a hybrid aircraft is shared between helium and aerodynamics by shaping the envelope to resemble a lifting body. The lift ratio in one design is 70% static from helium and 30% dynamic from the air flow induced by forward motion. When coupled with proven air-cushion hover technology, the craft can operate from land and sea, independent of airports. Such a true triphibian would have much potential for the U.S. armed forces.
Attractive features of hybrid aircraft include spacious areas for crews and mission systems, a laboratory-like environment for electronics, and nearly unlimited electrical power for weapons, sensors, and countermeasures. In addition, review of the operational capability demonstrated in the 1930s, when small fighters resided aboard and flew from large rigid airships, has led to proposals for similar employment of unmanned aerial vehicles (UAVs).
The most surprising feature of non-rigid hybrid aircraft is reduced susceptibility and vulnerability to air defense threats and a huge improvement in crew survivability. Although they are gigantic, their radar and infrared signatures are less than those of transport-sized airplanes and helicopters. Nonflammable helium-filled airship envelopes have demonstrated remarkable resilience when subjected to live-fire testing. Unlike airships, airplanes often self-destruct when damage exposes the internal structure to the destructive dynamic air pressure that is a function of flight velocity. Airships exhibit a benign failure mode—they deflate slowly and float to the surface, which accounts for the historically low fatality rate of helium-supported non-rigid versions.
Hybrid craft could satisfy the Army's objective force goal to embark a combined arms team at its base, transport it over strategic distances while maintaining unit cohesion, and roll it down the exit ramp near the objective area ready for combat. (This capability could have produced dramatic results in Operation Iraqi Freedom.) The period from embarking to engaging the enemy anywhere in the world could be three to seven days—in spite of enemy anti-access measures that close airports and seaports. Surprisingly, the proposed stealthy "ghost ships" would offer greater comfort and survivability to their human cargo than current forms of global air transport.
A Hybrid Ultra-Large Aircraft (HULA) for intertheater lift may carry as much as 500 tons of troops and armor to distances of more than 5,000 miles at 60-90 knots, cruising at altitudes from just off the surface to 10,000 feet. Such giants require non-rigid envelopes with a volume of 25-35 million cubic feet. By way of comparison, the large rigid airships of the 1930s had a volume of about 7 million cubic feet. The largest non-rigid ship ever flown—the Navy's ZPG-3 in 1954—had a volume of 1.5 million cubic feet.
Other military missions being considered for smaller HULAs in the 30-ton lift category include:
- Extended range littoral and ocean patrols, with UAVs aboard to provide an over-the-horizon close-up look at targets of interest
- Resupply of naval forces afloat
- Employment of large aperture, low-frequency three-dimensional radar for force protection against cruise missiles and surface threats such as fast boats
- Insertion of special operations forces elements
These hybrids would have envelope volumes of less than 2 million cubic feet and be about the size of a football field.
An important combat mission application under discussion is a futuristic aerial gunship to follow after the Air Force AC-130. This hybrid "battle star" would offer mission periods measured in days and carry an expanded suite of multispectral sensors and armament, including directed laser weapons. It is predicted that the continuous overhead presence of a HULA would yield unprecedented levels of situational awareness, which is key to effective support of ground forces. There are no known physical or technical barriers to the use of air-to-air and air-to-ground missiles for self-defense.
Commercial applications of hybrid transports could include loading strawberries at two dollars per box near farms in the Imperial Valley of California and off-loading near Tokyo four days later at thirty dollars per box. Going directly from source to distributor would cut out much, if not all, of the intermediate handling that is necessary in transporting products to and from airports, seaports, and railheads. Costs are estimated at far less than heavier-than-air transport and only slightly more than sea transport that often takes weeks to cover the same distance.
The HULA's ability to embark and disembark anywhere has attracted the attention of those responsible for transporting hazardous waste because it must be carried via circuitous routes to avoid populated areas. United Nations officials are interested in the potential for accomplishing humanitarian missions, such as using "angel ships" to deliver food and medical care to remote areas of the world that lack modern transportation infrastructure. Further, some Department of Transportation planners—haunted by the specter of gridlock—see the hybrid as an attractive alternative to triple decking our freeways. Homeland Security, Federal Emergency Management Agency, and American Red Cross staffers are considering the potential for immediate disaster relief following accidents, earthquakes, and terrorist attacks.
Conclusions
Lighter-than-air hybrid aircraft designs have been explored for decades. The possibility for creating a magic carpet-like capability can be attributed to advances in technologies of materials, propulsion, control systems, avionics, and computer design tools. The confluence of these advances provides the basis for optimism regarding military and civilian exploitation of hybrid aircraft concepts.
Is this a mirage or an off-the-chart opportunity? Triggered by a Joint Chiefs of Staff initiative, with technical support from Naval Air Systems Command, the Department of Defense is in the process of determining the answer to that question.
Mr. Myers, a combat pilot of the Army Air Corps and Navy is president of Aerocounsel, Incorporated, in Gordonsville, Virginia. He is responsible for instigating reactivation of the Navy’s battleships in 1980.