lunes, marzo 25, 2013
Crowdfunding hope for human-powered helicopter project
By Paul Ridden March 23, 2013
Kenneth Huff and his team believe that rotor efficiency improvements will allow their design to fly using a fraction of the power needed by other Sikorsky competition contenders
Last September, the Gamera II team from the A. James Clark School of Engineering got so close to claiming the Sikorsky Prize of US$250,000 for human-powered helicopter flight that the American Helicopter Society must surely have been preparing to pull the dust covers off the safe and hand over the cash. Gamera II features a huge cross-shaped frame with enormous rotors at each of its four points, which are powered by sustained hand and foot pumping from a pilot at the center. It's a design that's been used by many of those attempting to nab the elusive prize (including AeroVelo's Atlas), but Georgia's Kenneth Huff has a rather more compact vision for success.
The project began in the spring of 2010, when Huff stumbled across some information about the Sikorsky competition while researching the building of an engine-powered single-seat helicopter that he was hoping to build after graduating from Middle Georgia State College.
"I am not sure how most people react to the question of human-powered helicopters, but I thought that it would be easy after reading about the competition," Huff told Gizmag. "I really didn't know what I was in for and after looking at Da Vinci III and Yuri I, I began to understand the nature of challenge."
A year later, he enlisted the help of two friends/fellow classmates (Neal Fischer, William Edwards) and requested a US$5,000 development grant from the College to work on a prototype and test the feasibility of building a human-powered helicopter that was much smaller than either Da Vinci III or Yuri I. At this point, the team had not come across the efforts of the University of Maryland's Gamera team, and AeroVelo hadn't yet embarked on its Atlas project.
Happily, the research proposal was accepted and work began on the first prototype. The aim was to develop a small coaxial human-powered helicopter that had the potential for reliable and practical recreational use, something that certainly can't be claimed for Gamera or Atlas. Banking on improvements in rotor efficiency allowing for a substantial reduction in the size of both frames and blades needed for lift, an additional grant in the spring of 2012 (along with a personal cash injection from Huff himself) allowed important design modifications to be made, along with the construction and testing of a new set of rotors.
The specs for the current prototype (and the next model) include a frame made of 6061 T6 aluminum, a 1:1 gearing ratio, and stacked rotors sporting a carbon fiber spar and S1223 airfoil with a weight of 15 pounds (6.8 kg) and total length of 12 feet (3.6 m). The total empty weight of the craft is 110 pounds (49.8 kg).
"The basic premise behind this design is that when the speed of an airfoil doubles, the lift quadruples," explained Huff. "We knew that we could reduce the area of the rotors by 75 percent when we doubled the speed. Take Yuri I for example, which had eight rotors all rotating at approximately 20 RPMs. If they had been able to double the RPMs to 40, then they could have eliminated six rotors or 75 percent of their rotor area."
"However, any aerodynamicist will inform you that drag also quadruples when the speed of airfoil doubles so there would be much more drag, which is completely true," he continued. "So we knew that our primary focus had to be to reduce the drag of the rotors (other teams are focused on reducing the power required by increasing the span of the rotor, which allows them to reduce the speed of the rotor needed to lift off of the ground). By using smaller rotors rotating at 60+ RPMs we knew that our rotors had to be as efficient as possible. So our efforts over the past two years have been to design the most efficient rotors that we possibly could without relying on previous designs or foregone conclusions about how a rotor should be designed."
Huff and the team now feel that they have developed one of the most efficient rotors ever designed, but have not been able to fully test it due to a lack of funds. They have another grant request in with the College, but impatience has got the better of them and they've headed to Kickstarter to both generate interest in the project and hopefully provide the cash injection needed to get their human-powered helicopter off the ground.
Though rotor testing has produced positive results, the simple aluminum frame topped by a pair of two-bladed rotors has yet to make it into the air. The maximum lift generated so far is 80 pounds (36 kg), while the minimum lift needed to get the craft to fly has been calculated at 240 pounds (109 kg).
"There is much more uncertainty about the feasibility our rotor design because it runs contrary to the design of all other successful human-powered helicopters," said Huff. "This uncertainty is compounded when coupled with the fact that we have been working on it for two years and have yet to have a successful flight. Furthermore, some aerodynamicists and human-powered helicopter enthusiasts may swear to the impossibility of our design but we believe that there is always room for improvement in any design and truly believe that practical human-powered vertical flight is possible and has the potential to one day be a recreational activity similar to hang-gliding, and we hope to prove it."
The developers are convinced that, with funding, the helicopter will be capable of lifting 300 pounds (136 kg) using 300 watts or less of power – a fraction of that needed by other Sikorsky contenders. Direction of the current model will be controlled by shifting the weight of pilot, but plans are afoot for a cyclic control system that should offer more precision.
Kickstarter backers can pledge support for the project in return for various rewards (including framed posters, a 48-page book or a brass S1223 airfoil cutout), or can take a giant leap of faith and promise $10,000 or more, which will secure a fully functional, full-scale replica of the finished helicopter.
In the event of another team beating Huff and friends to the elusive Sikorsky Prize – which requires a craft to stay in the air for 60 seconds, stay within a 10 meter (32.8 ft) square and rise to three meters (9.8 ft) at some point during the strictly human-powered flight – development on the project will continue.