Three inventors are trying to get their plans up in the air. All have taken the familiar blimp and done strange things to it to create hybrid airships capable of lifting heavier loads at lower costs than can be done with conventional blimps or helicopters.

Each of these inventions has a different shape, is in a different stage of development and uses a different method to overcome weaknesses of other aircraft.

But the prime market for all of them appears to be the lumber industry -- making it possible to haul away felled trees without the cost and waste of building roads for huge trucks.

A 1978 study for the National Aeronautics and Space Administration by Booz Allen Applied Research in Bethesda estimated a need for more than 1,000 heavy-lift airships just for logging use worldwide, and the three inventors have listed other potential uses, including transportation of heavy construction equipment and delivery of factory-built houses.

The airships are:

The Cyclo-Crane, invented by Arthur Crimmins, president of Aerolift Inc., which has its headquarters in Tillamook, Ore., on -- what else -- Blimp Boulevard.

* The Cyclo-Crane looks like a blimp with four T-shaped wings and engines coming out of the middle of the balloon and a circular band for a tail. The pilot and passengers occupy a cabin suspended from the balloon body on cables, and the payload hangs underneath the cabin from separate cables.

By the way, the blimp body and wings rotate left to right for reasons that will be explained later on.

* The Magnus LTA, invented by Frederick D. Ferguson of Magnus Aerospace Corp. of Ottawa. The LTA looks like a manta ray carrying a ball on its back. Passengers and crew ride in the front of the "ray's" body, and the wings curve upward to hold the ball, which is a balloon. Some payload can be carried inside the "ray's" body; the rest would be hanging on cables underneath the craft.

By the way, the balloon rotates front to back for reasons that will be explained later on.

* The Piasecki Heli-Stat, invented by Frank Nicholas Piasecki, president of Piasecki Aircraft Corp. of Sharon Hill, Pa. The Heli-Stat not only looks like a blimp with four helicopters attached underneath, it is a blimp with four helicopters attached underneath.

By the way, the Heli-Stat will be flown by one pilot in the left rear helicopter's cockpit, where the company says he will have "an excellent view of the suspended load hanging from the center." Flight engineers will occupy the cockpits of the three other helicopters.

Crimmins began AeroLift in 1979 to develop a lighter-than-air, heavy-lift aircraft. The company is publicly held, has a staff of 20 and is listed on the Vancouver Stock Exchange.

Crimmins had worked in marketing and service With Bell & Howell Co.'s electronic instrumentation division for more than 10 years, then in sales and marketing with All American Engineering Co. in Wilmington, Del. He describes himself as a "technical peddler."

"What really started this was the revolutionary invention of the Aerocrane by Donald Doolittle in 1972" at All American Engineering, Crimmins said. He described the Aerocrane as somewhat resembling the Cyclo-Crane, in that it had four helicopter-like blades coming from the center of a balloon body. But in this case the plane of the blades was horizontal, rather than vertical.

"They got Navy contracts, built models up to 50 feet [long], but never got it in the air because it was too small" to fly, according to Crimmins. Doolittle was the company's president for engineering, while Crimmins' job "was to see where the company should be in five years, so to speak.

"I saw the very significant need to move large trees out of the forest," he recalled. "We tried long and hard to get the Aerocrane working -- to find someone to give it financial support." Crimmins and Doolittle left All American in 1976 to work on the Aerocrane in Australia, Brazil and Canada. They hold Aerocrane patents in those countries.

In 1978, Crimmins came up with the Cyclo-Crane. Why not Doolittle? "Sometimes a little bit of an outside look will help" an idea, Crimmins said. "It's a little bit like a ping-pong game with ideas," in that he and Doolittle would bounce their ideas back and forth. The break came when a Princeton engineer said that putting the Aerocrane on its side would eliminate a problem known as the Magnus effect. "Suddenly, a blackboard picture of the whole system flashed in front of me," Crimmins said.

According to Crimmins, the Magnus effect refers to what happens when a sphere is spinning so that the axis of the spin is 90 degrees to the direction of travel: The spinning of the sphere produces lift and drag, which causes the flight path to curve. It also lets a good curveball pitcher baffle otherwise champion batters. "My solution was to put the axis of rotation on a horizontal, rather than vertical, basis," he said.

"It turns out that the Cyclo-Crane is a different vehicle than the Aerocrane," according to Crimmins. He said that All American is challenging the patent that was granted for Cyclo-Crane last November, charging that it infringes on an Aerocrane patent.

Doffing his inventor's hat for his marketing hat, Crimmins looked for a way to sell the Cyclo-Crane to the logging industry. He claims that "there's no incentive for U.S. firms to reduce the cost of timber harvesting" because of U.S. Forest Service regulations. "Therefore, I decided to find a country that doesn't have the same rules, and that turned out to be Canada," he said.

Working through the Forest Engineering Research Institute of Canada, which he said is roughly analogous to the research and development arm of the U.S. Forest Service, Crimmins attracted the interest of -- and $4 million in seed money from -- four major Canadian forest-products companies: MacMillan Bloedel, Pacific Forest Products, BC Forest Products and Silver Grizzly Logging.

All that Crimmins had to show potential investors was "an 8 1/2-by-11 sheet of paper with one drawing on it made in my den on a drafting machine I bought for $15 at a garage sale," he said.

The first working model of the Cyclo-Crane -- a 50-foot device -- was flown in a blimp hangar in Lakehurst, N.J., in 1979, Crimmins said. A larger working model was destroyed by unexpectedly heavy winds, but tests began last October on its successor.

Previous lighter-than-air vehicles, including blimps and airships, need to release compensating ballast when they pick up loads, and add ballast when they release loads, Crimmins noted. "This makes them pretty lousy as cranes," he said. "We carry twice the load at a quarter of the cost of a helicopter -- a process improvement factor of 8."

As the Cyclo-Crane's airfoils rotate, the wings change their angle of attack in each rotation (up to 13 a minute) so that the wings on the top and bottom are creating lift while those on the side are not producing thrust. The blades attached to the wings act as a large propeller because the assembly is rotating, increasing efficiency.

When the Cyclo-Crane body is rotating at top speed but the vehicle isn't moving relative to the ground, the airspeed over the wings is equal to the maximum air speed of the vehicle, but the Cyclo-Crane does not attain this speed until the wings are realigned and the rotation stops.

AeroLift is trying to find more money, possibly through another public issue, Crimmins said. His company is talking with the Forest Service and the Department of Defense. He said that there is substantial overseas interest.

Before the first Cyclo-Crane is built for sale, "We have to get some more money," Crimmins said. "It's a couple of years down the pike, at best." He estimated that first deliveries couldn't come before 1986 or 1987. The company is planning to begin production with vehicles that can carry loads of about 16 tons and that will cost about $5 million. So there is the Cyclo-Crane, designed to overcome the Magnus effect, but the LTA uses this same phenomenon, which is why its producer is called Magnus Aerospace Corp.

According to Norman J. Mayer of Alexandria, who retired last year from NASA as a consultant on lighter-than-air vehicles, Magnus Aerospace's LTA works this way: The ducted fans at the end of each wing are pointed straight up to lift the vehicle off the ground, and then are tilted forward to move the LTA forward through the air.

Simultaneously, the balloon sphere is rotated about its horizontal axis. (Because the direction of rotation is opposite the direction of travel, there is a pressure differential that creates aerodynamic lift, according to material from Magnus.) Mayer added that the fans would be realigned again when the pilot wanted to bring the vehicle to a stop relative to the ground, for example while a payload was being attached.

Ann Dempsy, Magnus Aerospace Corp.'s director of communications, said that Ferguson holds "a vast majority" of the privately held company, and that outside investors include Canadians. The company has 30 employes.

"We expect production to begin within two years," Dempsy said, adding that Magnus probably would start with a 16-ton version, the same size as the prototype, which has not been test-flown and won't be flown for another two years. She said that Magnus defines the potential market as that set out in the Booz Allen study.

Piasecki is a pioneer in the development of the helicopter. He founded and headed the research group that designed the second successful helicopter to fly in the United States. The group became Piasecki Helicopter Corp., which he sold to Boeing, and which now is known as Boeing-Vertol. Then he started Piasecki Aircraft Corp. and received the first patent on the Heli-Stat in 1961.

According to Mayer, the recently retired NASA consultant, the Heli-Stat relies on the helicopters to lift the payload and position the aircraft, while the helium in the balloon lifts the dead weight of the aircraft.

The Heli-Stat is being built under a Navy contract and funded by the Forest Service. The current version of the airship, which began ground testing last week, will be able to haul a 24-ton payload. Later versions could be produced to haul up to 200 tons, the company indicated.

The current Heli-Stat is 343 feet long, and the company says this makes it the largest aircraft in the world.

The company also points out that using surplus helicopters and a 20-year-old blimp to build the Heli-Stat is a major factor in keeping the project costs low.