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Product Design

Rotor Bug Strikes Again (Tech Trends Feature)

31 Jul, 2008 By: Kenneth Wong

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Sportcopter builds up, tears down autogiro designs in SolidWorks.

Jim Vanek was bitten by the rotor bug when he was a kid. He watched his dad, Chuck Vanek, build rotor-powered aircrafts, commonly referred to as gyroplanes. Their workshop often was littered with foam, wood, and sawdust when a new craft was in development. At the time, the only way to determine whether the rotor blades would clear the tailfin or if the cockpit would comfortably seat a pair of passengers was to build a full-scale mockup. Jim Vanek knew, as a given, a number of those models would be built and destroyed in the process.

After his father's retirement, Jim Vanek became the principal rotorcraft builder for Sportcopter, the family business that's been in operation for nearly 50 years.These days, he relies on 3D CAD, so his shop floor is comparatively tidier. The creation and destruction of his mockups take place largely in the digital space on a computer screen.

Sportcopter II
Some folks might have wondered if Vanek was tempting fate when he chose to fly his latest creation, the Sportcopter II (SCII), for the first time on September 11, the ominous anniversary of the 2001 terrorist attacks. But Vanek had confidence in his flying machine because he had flown it countless times inside another machine — a PC loaded with SolidWorks and COSMOSXpress. In the computer, he'd worked out the geometry, the mechanical operations, the weight, the lift, the tensile strength, and the rest of his engineering concerns.

"We've built many aircrafts in the software that we probably will never build in the real world," said Vanek. "Look is often 90% of what we sell. We scrapped a lot of ideas inside the computer just because of how they looked."

Figure 1. Designing the Sportcopter II in SolidWorks 3D software, the makers were able to determine the angle of the tilted rotor head that provided clearance for the blades.

In the early phase, he was exploring at least 10 design alternatives for the SCII, pinned to a 4' x 8' whiteboard. "I'd start with a sketch, then give it to [design engineer] Evan Dagle," he recalled, "and he'd turn it into a finished 3D model. Then we'd start pushing and pulling it to figure out the weight and the materials."

The criteria Sportcopter used to eliminate some of the designs included construction costs, materials costs, and the amount of time required to build the craft. Studying the different designs in SolidWorks, Vanek could determine the amount of plies, composite cloth, and glass needed for the fuselage and the frame, so he was able to estimate the cost.

The most preferable design was one with a tilted rotor head, which meant the blades would rotate at an angle (Figure 1). By animating the motions of the blades, Vanek was able to ensure they would clear the rear of the craft.

"Since we could move the rotor head around," he said, "we could get an understanding of the distance [the blades] travel."

The 2D drawings automatically generated from the 3D model of the SCII also made it into assembly instructions for the buyers.

Autogiro Airplanes

The birth of the autogiro aircraft, or gyroplane, is usually attributed to Juan de la Cierva, a Spanish nobleman who had the brilliant idea to combine an existing aircraft frame with a windmill rotor (see: gyroplanepassion.com). The craft's flight power comes primarily from a free-spinning rotor and aerodynamics. Soon after a video clip of the Sportcopter II's debut flight appeared on YouTube.com/, someone posted a frequently asked question about gyroplanes: "What if the engine goes out?" The test pilot who submitted the clip responded, "The main rotor blades are not powered — they are autorotating, so if the engine were to fail, you can glide and land safely."

Through Thick and Thin
Before building the machine, Sportcopter's engineers ran stress tests on the nose wheel, the suspension system, the rotor head, and other critical components using COSMOSXpress, the design-validation tool embedded in SolidWorks.

"In some of the complex parts, because we were trying to make them really light, it was helpful to see where the stress lines were," Vanek recalled. "Eventually, we began to see how to reshape those parts by adding or taking away materials."

Vanek wishes he could run SolidWorks on the Macintosh, but the software currently isn't available for that platform. SolidWorks' press office clarified, "Currently SolidWorks has no plans to add a Mac version of its software to its product portfolio but is constantly reassessing that decision based on customer feedback. To date, the demand for a Mac version has not been high enough to warrant it."

The chassis of the SCII was "cut from a single chunk of material, then molded into shape," said Vanek. "We provided [the machine shop] with the solid model of the body. They sliced it into two halves."

Green Commute
Sportcopter plans to sell its latest craft for $90,000–$120,000, depending on whether the customer purchases it as a kit or a fully finished

Figure 2. The Sportcopter II is an autogiro plane, which flies primarily with a self-rotating rotor and aerodynamics.

model with desired options. Though gyroplane flights currently are confined to hobbyists, Vanek doesn't see why these lightweight, fuel-efficient aircraft could not be used for short aerial commutes of roughly 350 to 400 miles. (Sportcopter's gyroplanes are equipped with engines, complemented by rotating blades and aerodynamics. According to Vanek, "The rotors are not powered in flight but are pushed through the air by the pusher engine" and the craft is "more fuel efficient than a helicopter." [Figure 2].) From a private helipad or a rooftop, this type of craft could easily take off and land, bypassing the need to wade through airport security checkpoints.

"Some of the machines are very simple. It has an engine and a rotor, so you just start the rotor by hand, taxi the craft, and fly," said Vanek.

On the other hand, models such as the SCII are sophisticated enough to include an autopilot mode, which allowed Vanek's 12-year-old son to land the craft by himself once. It seems that another generation of Vanek has been bitten by the rotor bug.

Editor's note: The above article includes corrections to the original version, which appeared in the August 2008 edition of Cadalyst magazine.