Progress 05/01/12 to 03/31/13
Outputs
Target Audience:
Nothing Reported
Changes/Problems: Overall, our R&D plan was sound.R&D often involves paths that must be proven incorrect - frustrating, but educational, and eventually leading to a better product in the end.That said, we learned some new things during this effort. Lessons learned: Outsource as little machining as possible.Extensive delays in the machining of critical components – the rotor head and the reel drum in particular – delayed integrated flight-testing by at least two months. Future funding will purchase both a combination mill/lathe and a TIG welder – which in combination with the drill-press, table saw, band saw and numerous hand tools we now have, will allow us to do the majority of machining and assembly in-house in a fraction of the time required to go out-of-house, and at greatly reduced cost. Quick and inexpensive component replacement is important. Our next stage of development will involve extensive, nearly daily test-flights and extensive and nearly-daily equipment failures. In order to keep up the fast pace of testing, destroyed components must be replaceable quickly – in only minutes – instead of the hours or days previously required.For example, while the current blade designs worked very well, each wood blade cost more than $300 for both the raw wood purchase and the couple of hours of precision milling. Each blade then required two hours of hand sanding, at least an hour of epoxy and glue work, and two coats of polyurethane finish - all taking an additional two days to complete.Those blades would then be destroyed in only seconds. Similarly, the elevons required approximately four hours of hand-carving and sanding, precision drilling and assembly and then two days of polyurethane application.Connecting the servo required an hour of meticulous assembly of more than three dozen tiny components.While both blades and elevons worked very well, the construction and assembly time of both is non-sustainable for the pace of testing we will require in the next round of development. Both these components will be simplified in terms of construction and assembly, making their attachments much closer to a “snap-in” process requiring only minutes. Roll and pitch control. While the inherent design of the glider does keep it very stable, the first few seconds of flight off the aerie are in turbulent air (from the boat and aerie) which induces rolling motions in the glider. Hands-off launches and landings may well require a little more active control input than flight high above the ground.For that reason, the next set of tests will include gyroscopic control of both the glider’s roll and pitch for stability-control during launch and landing.Once the glider is in smoother air, the gyros will be turned off for stability flight experiments. Use Break-away connections wherever possible.Hand-testing early in this testing cycle employed a break-away bolt on the blades which reduced damage to both the blades and the objects they happened to strike.The final remotely-controlled flights required their removal to smooth the rotation of the rotor with the changes to the rotor head (from hinged back to teeter).The next blade connector design will again incorporate break-away bolts, as will the elevon connectors, and the rotor-head to glider-body connection.In this way we hope to reduce damage to all these components from the inevitable crashes. Servos require constant power. While servos will function fine in near-term future testing lasting less than thirty minutes (the approximate limit of on-board batteries), future long-term flight-surface controllers will require servos be replaced by some other electrically powered actuators – stepper motors, ball-screws, or hydraulic – yet to be determined. In this way, we will reduce the energy requirements at the glider (generated by stealing some torque from the blade to spin a small on-board generator). Hinged hubs/blades versus Teetered hubs/blades.Teetered hubs link the left blade to the right blade so as one rises the other descends – like a teeter-totter.The “fly-bar” connecting the two blades is a rigid piece of aluminum which limits imbalances and blade movements, and reduces resultant vibrations. However, teetering hubs are not usable beyond rotor sizes of about forty feet – which we expect our final gliders will need to exceed. Additionally, teetering hubs can accommodate no more than two blades, limiting the amount of total lift possible and reducing their use to lower altitude locations.Hinged hubs and blades can accommodate any number of blades (more than four would be unnecessary), allowing for more lift and use at higher altitude locations (such as the high-country of the American west or the Andes). For that reason, we believe hinged hubs/blades will eventually be a requirement for the Energy Glider. However, as we determined in this round of testing, the hinges connecting the blades to the hub must be extremely rigid, with absolutely no free-play. Our next round of testing will initially use that same teetering hub but will then advance to a newly designed precision-machined hinged hub and elastomeric blade connection to eliminate rotational vibration. Twisted versus straight blades.The auto-gyro effect is a bit magical.Once the blades are brought up to a certain RPM, the wind flowing through them accelerates the rotor to some steady-state RPM based on the drag the blades induce.Reducing the drag of the blades is critical to increase rotor RPM to the maximum attainable to create maximum lift – something we think we have come close to optimizing with our unique blade profile.However, only the outer third (or so) of the blades actually produce lift.The inner two thirds are driven by the wind flowing through them to spin the rotor.Before the last round of testing, we had postulated that by adding a twist to the blades, similar to that of wind turbines – and something neither commercially-available gyrocopters nor helicopters employ – we could increase the driving force of the blades while increasing tip speeds and subsequent lift.This proved true. Fine tuning of the design will continue in the next stage of development by also varying the blade profile from the root to the tip while experimenting with other twist angles. What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest? The results have not been disseminated to any organization other than NIFA for proprietary reasons. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Highest Wind’s USDA NIFA funded Phase 1 SBIR efforts significantly increased the development of the Energy Glider and placed Highest Wind in a good position for extensive flight-testing in our next cycle. The results of the Economic Viability Assessment were compelling. The University of New Hampshire launched its survey to look at the willingness of farmers to adopt a wind energy glider based on installation costs and utility savings. In total, 338 surveys were completed by farmers from all over America. The results indicated that there is significant interest in a wind energy glider system. Respondents were more sensitive to the value of electricity generated than to their farm income. Ideal locations to market a wind energy glider system would thus be areas with higher electricity rates and net metering. The size of state incentives is important; data suggests that many farmers would purchase wind energy gliders if their final net cost were $50,000 - $60,000 (possible in a number of states with current incentives). One third of the respondents would purchase a system if it generated $17,000 worth of electricity for a final cost of $75,000, achievable now, in six states with current electricity prices, current incentives, and the assumption of only a 50% capacity factor for system performance. The results support the development of the Energy Glider in terms of expected final price and the amount of electricity each system can produce. As electricity prices approach $0.20/kWh, Energy Glider systems will provide ROIs of less than seven years in most locations – even with no government incentives. Development Accomplishments: This effort ended on March 9th 2013. At that time the system included many improvements: a glider with a 13-foot rotor diameter – scaled from 8 feet in 2010; twisted angle of incidence blades with screw-adjustment for overall blade angle of incidence – compared to straight blades with shim angle of incidence adjustments; remotely controlled, servo-driven variable-angle elevons compared to fixed pitch elevons in 2010; a yaw-controlling tether attachment critical to smooth aerie/glider matings; aerie mating legs with matching glider landing legs compared to the crude aerie/glider mating of 2010; remotely controlled pitch-adjusting aerie landing cradle compared to the dangerous hand-adjusted pitch control in 2010; and an integrated 18kW reel/generator with pilot control panel, foot-controlled brake, reel speed control and computer-monitoring and session recording, none of which were yet developed or proven in 2010. Despite progress on the three major system components, development did not proceed as far as planned towards the collection of the power-curve data. Significant machine shop delays (for manufacture of critical glider and reel components) prevented complete system testing from beginning prior to the last month of our efforts. The Reel/Generator. Data collection for energy production from the reel/generator was achieved with people, cars, and bags of sand pulling on the tether, to simulate the speed and force of the glider. This glider-independent testing of the reel/generator section proved the feasibility of utilizing off-the-shelf golf-car motor/controller/differential components as the core of the ground-based energy production section.Even a man pulling the tether could produce 360 watts of power (about half a horsepower) – equal to that produced by any man on any dynamometer. A car pulling the tether at a peak speed of 15 mph produced a peak of 2.7kWs. The reel/generator therefore achieved the goals set forth for this effort. The Glider. Glider development started with suspending the glider from above, to eliminate crashes while testing blade designs, ideal pendulum lengths and weights, and elevon function. Suspending the glider required a redesigned rotor head with a non-rotating eye-bolt at the top of the head, from which the glider could be suspended. This required a change from the “teetering” rotor head successfully tested in 2010 to a “hinged” rotor head.This more complicated rotor head will provide many future advantages: allowing the rotor blades to be scaled up to unlimited sizes; making possible the utilization of three, four or five blades to provide more lift in thinner air; and the addition of real-time angle of incidence adjustments to the blades to enable jump-launch and other in-flight gross lift controls. To perform this testing, a structure was built on the boat from which a line suspended the glider in free air, ten feet above the boat. The tether pulling the glider down, kept the glider from flying more than a few feet above the suspended height. Together, the suspending line and the tether kept the glider from moving far enough to impact anything else on the boat. Unexpectedly, all test flights with the new rotor head showed what we thought was excessive blade imbalance.After working through numerous new blade designs over many weeks (and experimenting with various degrees of blade twist, which we were able to optimize despite the imbalances), and with increasingly precise balancing of the blades down to a single gram, we finally determined that the hinged rotor head itself was the source of the imbalance.The few thousandths of an inch of play inherent in the hinges attaching the blades to the rotor head afforded the blades enough wiggle-room at the tips, six feet out, to produce “shake” of the glider at any rotation speed.This shaking made elevon adjustments useless, and remotely controlled flight became uncontrollable. Despite all the advantages of a hinged rotor head, as time and money for the funded effort was running out, we were forced to revert to the teetering head we last used in 2010, resorting again to remotely controlled free-flights from the back of the boat. (Future designs will employ an elastomeric ,hinged blade which should eliminate the "shake" problem.) In hindsight, we should have implemented gyroscopic pilot assistance to keep the glider stable in a hands-off situation. But over-confidence in the glider’s inherent stability, demonstrated so well even when the glider was excessively shaking, distorted our thinking.The first integrated total system test in which the glider, aerie and reel/generator were all connected and data collection was implemented, ended in an immediate glider crash, due primarily to pilot error (over-control).The glider was destroyed beyond repair with too little funds and time left to rebuild another. Despite the lack of power curve data from the glider, tests with external forces pulling the tether show the glider design is effective. We are eager to continue flight-testing and resume data collection.
Publications
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