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Reprise of the airship

Reprise of the airship

"Blimp Crashes Into West Side Apartment Building; Hundreds Amused"

That whimsical headline about sums up the real-life, great Manhattan airship wreck in the Summer of 1993. The sight of Pizza Hut's 160-ft "Bigfoot" blimp rearing out of control sent sunscreen-slathered urban professionals on a roof scampering for the stairwell.

An ignoble end for an aircraft with a legendary history and, according to some visionaries, a bright future. Although designers hope to enliven America's skies with airships doing everything from hefting cargo to guarding our borders, modern blimps are often little more than flying billboards.

Occasionally they break out of the corporate mold. For example, the Spirit of Atlanta, operated by Airship Management Services, Greenwood, CT, on behalf of Kroger Inc., Cincinnati, OH, flew a traffic management and security surveillance stint for the Atlanta Police Department during the Summer Olympics. The grocery giant donated use of its giant airship to the police for the duration of the Games.

The U.S. is experiencing something of a blimp renaissance. There are more new airship designs coming off drawing boards than ever before and designers have ambitious plans for their use, provided they can rise above a number of technical hurdles--and the reservations of potential blimp operators.

Hopeful hybrids. Maybe it is that vaguely childlike name that gives the more serious-minded pause. Bruce Blake, engineer and manager of Advanced Hybrid Aircraft, Eugene, OR, prefers the term "buoyant aircraft" for his designs. He insists the distinction is not trivial. The Australian-born Blake's new-generation aircraft bear some resemblance to blimps and share some features in common, but they are not blimps in the strictest sense.

Blimps are non-rigid airships (so-called because they lack a supporting skeleton, such as those possessed by von Zeppelin's great airships) that derive their lift aerostatically from lighter-than-air gas and have engines for propulsion. Blake's hybrids, while also non-rigid and equipped with helium-filled envelopes, generate a significant portion of their lift aerodynamically from wings. Blake hopes his buoyant aircraft will counter some of what he calls "the silliness" of current blimp designs: the need to devote precious payload to ballast and to maintain ground crews to get the things off and back down properly.

Advanced Hybrid's buoyant aircraft would not require ballast due to the weight of the gondola, engines, fuel, and wings and could operate from airfields without launch and recovery crews. The piston engines of Advanced Hybrid Aircraft's designs mount in a tractor configuration. The projected maximum speed is 80 knots compared to about 50 knots for a modern blimp.

This is all future tense. Advanced Hybrid Aircraft has yet to build a prototype. Blake says his company has completed designs ranging from the sporty Hornet LV (leisure variant) single-seat model for $65,000 to the four-engine Hornet AW (aerial work) hybrid for $1.2 million. Wind-tunnel models and radio-controlled subscale technology demonstrators do exist.

A niche filled, elegantly. While Blake's buoyant aircraft borrow from blimps, those designed by James Thiele, founder and president of American Blimp Corp., Hillsboro, OR, are quintessential, no-frills airships.

American Blimp concentrates on designing and building blimps that sell, a philosophy that has made it, by many metrics, the most successful airship concern in the world. There are more of the company's Lightship family of blimps flying than those of all other manufacturers combined. The model most people see tooling about in corporate colors is the 130-ft A-60+, powered by two 65-hp Limbach engines. Equipped with two 1,000W lamps inside a translucent envelope, Lightships provide a spectacle day or night.

Thiele, who has a degree in aerospace engineering from the University of Kansas, has found success in simplicity of design. The most advanced Lightship feature, perhaps, is the material of its envelope. Layers of proprietary plastic films, including DuPont's Tedlar, are laminated into a composite that provides UV protection and long service life.

The pilot adjusts a single air-filled ballonet inside the envelope using air scoops, fans, and vents to provide constant pressure as the surrounding helium expands and contracts due to changes in temperature and altitude. Use of a single ballonet simplifies pilot controls, eliminating the need to adjust trim for differences between multiple ballonets. The Lightship can have one ballonet because its gondola hangs from the sides of the envelope by external cables, a throwback to the very earliest non-rigid airship designs of the 1910s and 20s.

"Our philosophy is to use simple structures that work together well," Thiele says. "Design is what's important, not high technology." This has not prevented American Blimp from using high technology in pursuit of simplicity of design. The company enlisted the University of Toronto to develop a non-linear, fluid-dynamics-analysis software tool to simulate how airship designs will perform in flight. The code allows six degrees of freedom and, according to Thiele, enables engineers to perform complete design verification studies.

American Blimp has developed a more predatory version of the Lightship, its Spector series, for surveillance applications. The same characteristics that make blimps superb camera platforms for sporting events--stability, endurance, and relative quietness--make them equally suitable for patrol and observation missions. The Spectors have fully opaque envelopes and the gondolas can be modified for radar, powerful searchlights, generators, and extra fuel tanks.

Last year, American Blimp test flew its latest and largest airship model to date, the 164-ft Lightship A-150/Spector 42. This blimp, powered by two 180-hp Lycoming IO 360 engines, can carry a 1,373-lb payload--plus pilot and fuel. It can cruise for 17 hours at 24 knots. Top speed is rated at 52 knots.

American Blimp's Maryland-based Airborne Surveillance Group, which markets the Spectors, says the company plans to build airships able to carry two-ton payloads at altitudes up to 10,000 ft and remain aloft for 24 hours without refueling.

Treading softly. United States Lighter-Than-Air (US-LTA), Eugene, OR, is a veteran designer, builder, and operator of large, non-rigid airships. The US-LTA model 138S blimp, the Oregon Spirit, can carry 3,000 lbs of payload for up to 16 hours at 19 knots. The single Lycoming 300-hp pusher engine gives the blimp a top speed of 47 knots. Its centerline configuration takes advantage of the venturi effect produced by the airship's envelope in flight, as the propeller pushes denser air.

Ted Kruysman, a US-LTA pilot, prefers to dwell on those characteristics of the model 138S that make it a superb working aircraft--and a delight to fly. The pilot enjoys hydraulically assisted controls: control stick motion is boosted by hydraulic pumps and then transmitted by actuators to cables. These exit the rear of the gondola and attach to the rudders through a series of pulleys. "I can fly the airship with two fingers, if I want." Kruysman says. The control system can be operated without hydraulic assist, in the event of a system failure.

The Oregon Spirit has three large tail fins and the rudders are synchronized, making the airship quite nimble for its size. Kruysman says he can come about in two ship-lengths. Fore and aft ballonets enhance agility. The pilot adjusts the relative inflation levels of each to regulate trim, allowing the pilot to give the airship a level, nose-up, or nose-down attitude, as required by a particular mission or flight condition. In addition, the engine is reversible, enabling the model 138S to fly backward. The Oregon Spirit has demonstrated these capabilities with Kruysman at the helm during a number of atmospheric and oceanographic research flights for the Naval Research Laboratory, Washington, D.C., and the University of Washington, Seattle.

The airship's gondola, which seats six and can be modified to carry scientific instruments, is suspended by steel cables from nylon fabric curtains attached to the upper interior of the envelope. Kruysman says the arrangement produces a better ride than an external suspension system, since the curtains are located where helium is providing the greatest amount of lift, adding support to the gondola.

Goodyear Tire & Rubber Co., Akron, OH, claims the most advanced blimp as the flagship of its three-ship fleet. The model GZ-22, Spirit of Akron, is 205 ft long and carries up to 10 passengers. Shunning piston engines in favor of two 420-hp Allison turboprops, the GZ-22 has maximum speed of 56 knots. The tractor-mounted fans are ducted and vectorable for greater maneuverability during takeoff and landing. No mere hydraulic assist here: the GZ-22 has a fly-by-wire system controlling the four rudders on the X-shaped tail fins.

"The main improvements in the GZ-22 model--such as the fly-by-wire and vectorable turboprops--are designed make life easier for the pilot," said Joe Hajcak, senior engineer at Goodyear's airship operations. Hajcak, a pilot himself with 10,000 hours in blimps, says Spirit of Akron is the most maneuverable airship flying and, like US-LTA's Kruysman, boasts his ship has fingertip controllability. Such performance comes at a cost: turboprops are about four times more expensive than regular piston engines and suck down fuel at a greater rate.

In search of some backbone. Across the Atlantic, the ghost of Count Ferdinand von Zeppelin still haunts airship designs. The namesake company of the dirigible inventor, Zeppelin Luftschifftechnik GmbH of Friedrichshafen, Germany, has a rigid airship under development.

The latter-day Zeppelin LZ N07 features eleven triangular trusses attached to three spars running the length of the ship. This proof-of-concept demonstrator measures about 200 ft long and will carry over 4,000 lbs of payload. The gondola accommodates a crew of two and up to 12 passengers.

A definite advantage of rigid airships is that they can be made larger than their non-rigid counterparts and, in fact, have to be. Airships are streamlined in order to allow air to flow over the empannage assembly that includes the control surfaces. Thus, to make blimps larger, designers have to make the envelopes longer. A point exists where the ends of a long, non-rigid envelope will simply be bent upward by the lift-producing gas. A rigid framework inside the envelope keeps larger airships from assuming uncontrollable geometries.

Frames, generally made from aluminum, also provide support for useful dirigible features, such as gondolas, engines, control surfaces, and gas-filled cells. They also add weight that has to be countered with more gas, which means the volume of the envelope has to be increased to hold enough gas to produce lift.

Once this point is reached, however, volumes attained by increasing airship dimensions can result in huge amounts of surplus lift and impressive payloads. Rigid airships tended to be very large indeed: the Graf Zeppelin II, sister ship to Hindenburg, measured over 800 ft long, 130 ft wide, and had a payload of over 110 tons.

Zeppelin postponed a test flight last year, citing construction delays. The LZ N07 is now scheduled to fly some time this year. If the demonstrator proves successful, the company says it plans to develop dirigibles to rival those of the pre-war period that cast huge shadows over cities.

According to Mats Backlin, chief pilot for The Lightship Group, an Orlando, FL-based subsidiary of American Blimp, the airship's future is more likely to be found in modest envelopes. Backlin, who graduated from the University of Sweden with a degree in aeronautical engineering, went to Great Britain to design airships for Thunder & Colt. There, he developed the GA-42 hot-air blimp that supports a crew of two and features a fly-by-wire system that enables a pilot to control the blimp with a joystick.

While the GA-42 has won praise, Backlin says the airship suffered from a too sensitive envelope that tended to deteriorate after long exposure to sunlight. Seven were built, a fairly high production figure for latter-day blimp-makers. The company also produced a successful thermal airship that uses heated, pressurized air rather than helium to provide lift. However, Thunder & Colt, bought out by a hot-air balloon company, is no longer in the blimp business.

Nevertheless, today's airship designers are pushing the envelope--and filling it with more than just hot air.


Blue skies, bad weather?

Clouds are airbrushed sweeps on a blue canvas. A twin-engine turboprop practices touch-and-go landings. Piston engines whine in the distance. Across the field, the Hood Blimp drifts at tether like a vaguely impatient circus elephant. I hover outside the security fence, eager to climb aboard.

It is a sunny 5th of July and perfect flying weather at Beverly Airport in northeastern Massachusetts. Unless, of course, you are intending to fly in a blimp. A low pressure area in the region serves as an invisible damper on the blimp's ceiling. The Lightship A-60+ is leased by H.P. Hood Inc., a large maker of dairy products, and would not get high enough to perform its promotional duties.

Conditions do not improve by evening so the flight is postponed until the next day. The morning of the 6th is bright, a little breezy, and this time chief pilot Mats Backlin arrives accompanied by Terry White, his crew chief, and a number of lads dressed in red and white rugby shirts who look ready for a scrum.

One fellow climbs the tether tower and unlatches the blimp. Then the scrum begins. Some of crewmen keep the ship from drifting off by wrestling with nose lines. Others grab hold of the gondola and push it clear of the tower and guy lines. White conducts the whole operation with flight-deck-like hand signals.

Backlin and I climb into the small gondola and I take the right front seat. The Lightship has an instrument panel any private pilot would recognize, except for the helium and ballonet pressure gauges and ballonet inflation knob. There is only one set of flight controls: rudder pedals on the floor and elevator wheels on either side of the pilot's seat (it looks like he's flying a wheelchair). The Lightship is fly-by-muscle.

Backlin gets the OK from White and throttles up the 65-hp engines. The rugby team scatters. We roll forward a few yards and are soon airborne. The blimp climbs rapidly with a steep angle of attack. In minutes we are at 1,300 ft--and not getting anywhere. "Winds are 10 knots stronger than reported," Backlin tells me. "We'd better head back."

Landing is more exciting than take-off. The blimp is coming in 130 lbs heavier than Backlin would like. We had been fueled for a six hour flight and had only burned 20 minutes of it. The winds have picked up. The faces of the ground crew register concentration mixed with concern at our approach speed. We hit the field hard, bang the tail wheel, and roll a while before the team restrains us. The Lightship is land-by-muscle, too.

July 7th turns out to be perfect flying weather, blimps included. Backlin achieves an up-ship, where the blimp ascends vertically with no forward roll when released by the ground crew. My two-hour tour includes a spectacular Boston fly-by plus overflights of our publishing offices and my apartment complex. The fact it required three days to get me up in a blimp for two hours (with airplanes coming and going all the while) is rendered unimportant by the sight of our oval shadow falling over familiar ground.


Cyber Contact

For a wealth of information on airships of all descriptions compiled by Swiss enthusiast Roland Escher, visit his Airship and Blimp Resources page at: http://www.hotairship.com/index.asp

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