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"  Owners of the dirigible Lips prepare for a summer flight over the Vermont countryside. An inflated rudder juts to the left. (Photograph by Gina Levay) A heap of ripstop nylon, damp with dew, stretches 132 ft. across a farmer&amp;#039;s hayfield near Amherst in western Massachusetts. The predawn air is humid, still and cool--&amp;quot;Perfect weather for this kind of thing,&amp;quot; says one of the volunteers bustling around the lumpy shape. A large fan rips to life, drowning out the twittering of the birds and frogs, and the nylon gradually leavens, growing into a blob 70 ft. high. Experimental blimp builder and pilot Mike Kuehlmuss, standing in a makeshift cockpit of welded steel tubing, steps on a switch that shoots a jet of burning gas upward with a roar. With aching slowness, the watermelon-shaped envelope lifts off the ground, its jaunty black and yellow stripes and red tail fins bringing to mind a carnival jester. Nearby, a bearded, heavyset man in sunglasses and a polo shirt looks on anxiously. Dan Nachbar, owner of the blimp, splits piloting duties with Kuehlmuss; today, he&amp;#039;s overseeing the ground crew and fielding questions from the growing crowd of onlookers. Crew members hold the cockpit steady as Kuehlmuss straps himself into a bucket seat, salvaged from an old Toyota Corolla. He checks the instruments fastened to the frame in front of him: envelope temperature, fuel levels, compass heading, engine rpm. He triggers a blast of hot gas with the flick of a switch, then checks the view of the rear-mounted propeller, provided by a video camera designed for the back bumper of an RV. The burners ignite, and the cockpit levitates off the ground. At this point the craft is behaving like a conventional--if oddly proportioned--hot-air balloon. But then the 24-hp engine sputters into action and, with all the stateliness and grace of a passing cloud, the huge ship slowly rises and slides away into the sky. The Skyacht--the first of what its builders hope could be an entire fleet of recreational blimps--is on the prowl.  The Skyacht&amp;#039;s steerable 24-hp engine gives the blimp precise maneuverability. Designers hope to swap in a larger engine that could propel the airship as fast as 20 mph.  There is a new breed of recreational airship taking flight on the fringes of aviation. These blimps are intended for fun, not transport. The key innovation: substituting hot air for helium or hydrogen as a lifting gas. Hydrogen, the lightest element, is dangerously combustible. Helium, though inert, is expensive. If an airship uses hot air, as balloons do, you can just let the air escape at the end of each flight, fold up the envelope and store it. &amp;quot;I want to fix the world of the blimp,&amp;quot; Nachbar says. &amp;quot;Here you have a corner of aviation that has been dormant for decades, for generations. What we&amp;#039;ve come up with is a disruptive technology.&amp;quot; One hundred miles north up the Connecticut River Valley, one of the airship&amp;#039;s earliest and most creative proponents takes a decidedly different--and more laid-back--approach to blimp making than Nachbar and Kuehlmuss. In the 1970s, Brian Boland, 59, a lanky, bearded tinkerer, became one of the first in a new generation of hot-air-balloon enthusiasts and since then has racked up nearly 9000 hours in airships and balloons. Boland has made a hobby of designing hot-air blimps, and over the years he has created seven different models. On an early summer morning, Boland inflates his latest version at the edge of the public-use grass airstrip he owns and operates in the sleepy village of Post Mills, Vt. As the dawning sun touches the tops of the surrounding trees, a lumpy mass of fabric the size of a school bus trembles on the grass. First, a fan blows cold air into the unfurled ripstop nylon, causing it to rise like a vast, throbbing amoeba. Then a propane-fueled burner shoots flames into the quivering cavern of fabric, heating the air within. Over the next few minutes, the 76-ft.-long, bright-orange envelope gradually inflates. Because the weight of the basket pulls down the middle of the blimp, it takes on a double-lobed shape. With poetic simplicity, Boland&amp;#039;s wife, Louise, has dubbed the craft Lips. Its main virtue is not aesthetic, but practical. The envelope can be rolled up and stored in a bag small enough to load into the back of a compact car. Boland gives a yank on a 6.5-hp Briggs &amp;amp;amp; Stratton four-stroke engine, and the 36-in. wooden propeller buzzes to life. The noise of the motor does not diminish Boland&amp;#039;s experience. &amp;quot;Perceiving the world from above is a quieting sensation. Normally, quiet has to do with hearing,&amp;quot; he says. &amp;quot;The other kind of quieting comes from a change in perspective.&amp;quot; With a blast of propane, Lips lifts off the grass and sweeps into the blue sky. When Boland pulls on the inflated rudder, it mushes into a curlicue. This softness is a major shortcoming. Because the burner needs fresh air, the envelope can&amp;#039;t be closed and pressurized like a helium blimp. Without this overpressure to give the envelope its shape, Boland&amp;#039;s blimp has a baggy, down-on-its-luck appearance. The nose tends to dent at any speed higher than a few miles per hour. The highest wind speed he can operate in, Boland says, is &amp;quot;dead calm.&amp;quot; Otherwise, operators risk losing control, possibly crashing into trees, power lines or bodies of water. Boland enjoys taking his homemade blimps on tours over nearby Lake Fairlee, cruising the shoreline for the smoke of campfires. People are compelled to wave at the low-flying aircraft, and on occasion he sets it down to meet them. &amp;quot;We kind of invited ourselves,&amp;quot; he says of one such party-seeking excursion. &amp;quot;The campers wined and dined us. We didn&amp;#039;t fly home that time.&amp;quot; Boland disavows any hope that hot-air blimping might be the recreational pastime of the future. In fact, in the past 33 years, he&amp;#039;s sold only one blimp. &amp;quot;People call up from time to time and ask about buying one, but I end up talking them out of it, because of how poor the performance is,&amp;quot; he says. &amp;quot;It would be disastrous to get into it without having a lot of hot-air-balloon-flying experience.&amp;quot; When Nachbar, a former Bell Labs engineer, began his quest to build a quiet, easy-to-fly blimp in 2001, he turned to inventor John Fabel, a neighbor near the University of Massachusetts in Amherst. A specialist in efficient fabric-tension structures, Fabel quickly sketched out a design concept. Next, Nachbar called in Kuehlmuss, who was working at a nearby airfield as a mechanic. The craft made its maiden flight in October 2006. &amp;quot;You feel a connectedness with things when you get above the ground,&amp;quot; Nachbar says. &amp;quot;People fly without a destination or purpose, just going for a ride to soothe their souls. Pilots call it air therapy. And this is the ultimate air-therapy machine.&amp;quot; In the course of pursuing his aeronautical ambitions, Nachbar became acquainted with Boland. For years, Boland hosted an annual gathering of the Experimental Balloon and Airship Association. Each May, a small group of inventor-aeronauts from all over the United States converged on Boland&amp;#039;s airstrip for a weekend of drinking, barbecuing and airborne carousing. Boland no longer heads the association, and Nachbar says he regrets never having attended one of these events. Though Nachbar credits Boland for teaching him how to sew, he believes his fellow blimp designer isn&amp;#039;t seeing the craft&amp;#039;s full potential. &amp;quot;He&amp;#039;s an artist,&amp;quot; he says. &amp;quot;I&amp;#039;m an engineer. That makes a difference in how we approach problems.&amp;quot; The two rarely speak, and in private each refers to the other in politely skeptical terms. In order to overcome hot-air blimps&amp;#039; inherent bagginess issue, Nachbar and his team have devised a system of seven aluminum stiffening ribs that run from the Skyacht&amp;#039;s nose to its tail, with a steel cable running along the central axis of the ship. Spreading out the fabric like the ribs of an umbrella, the system adds substantial rigidity without adding much weight. It also allows the blimp to carry a large engine in its tail instead of hanging one inefficiently off the back of the basket, as in Lips.  Mechanic and designer Dan Nachbar takes the Skyacht for a spin. Pinpoint altitude control allows the pilot of a hot-air balloon to skim the grass. (Photograph by Chion Wolf) As the Skyacht takes its predawn spin over Amherst, its 24-hp utility engine seems inadequate. Where the Skyacht clearly excels is in maneuverability. Thanks to steerable thrust, it can virtually hover in place and rotate on its own axis. The ribs and cables, however, make the Skyacht bulkier and more labor-intensive to assemble than Lips. Nachbar insists that once the design and engine are perfected, the team will move on to refinements such as an easier-to-assemble rigging. Ideally, he says, it should take a crew of three as little as 2 hours to assemble and inflate a Skyacht from a package that can fit in a 20-ft. trailer. After more improvements, he hopes to obtain approval from the Federal Aviation Administration to sell models for about $150,000.  Boland has no such ambitions. It would be hard to imagine the FAA&amp;#039;s reaction to his ballast system. After setting Lips down on newly mown turf, Boland calls over to Louise to add ballast to the nylon bag hanging from the nose of the airship. &amp;quot;Four more beers,&amp;quot; he yells. &amp;quot;No, make that six.&amp;quot; She runs inside to the fridge and comes out with the requested cold ones. &amp;quot;They&amp;#039;re just the right weight,&amp;quot; he says. &amp;quot;Plus, you never know when you&amp;#039;ll need a beer.&amp;quot; With a roar of propane flame and a twist of the throttle, he putters off again into the cool morning air. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/flight/a3538/4278917/>