OSTIV Congress Day 1

Flytop-Competition — An Effective Method for Enhancing Safety in Glider Competitions; A. Ultsch

In the first presentation of the day, Alfred Ultsch discussed a proactive approach to flight safety in soaring. Instead of relying on regulations that react to past accidents, the discussed approach uses errors and shortcoming observed by the general soaring pilots in order to initiate safety improvements. That improvement process, however, requires specific training and preparation of the involved glider pilots. The need for specific training was highlighted in a study that used two different competitions. In either competition pilots could receive up to 6% extra points by recording safety concerns on index card. Based on those semi-anonymous feedbacks, the competition director took appropriate actions when feasible, e.g. providing longer tow ropes. Despite the positive reinforcement of extra points, the participation of the contest gliders was very clearly dependent on prior instructions and training about a proactive safety approach. The presenters are promoting and doing a similar approach with a two-day proactive-safety training in clubs. Supported by the experiment this training is imperative for a successful implementation of a proactive safety approach.

A Review of Contemporary Collision Avoidance Systems in General Aviation; C. Santel and U. Klingauf

C. Santel

To this day, collision avoidance is a challenge for general aviation including soaring. Unfortunately, see-and-avoid is not entirely reliable, as indicated by 21 mid air collisions in Germany from 1999 through 2011. New instrumentations, such ADS-B and FLARM, are a significant aid to the pilot by providing collision alerts. The presenter discussed a “human-factor model” that takes into account relative target size, search time, and other aspects, such as weather. An “instantaneous acquisition rate” allows the formulation of a “probability to acquisition” term. Based on this theoretical model, the presenter discussed ongoing research efforts to improve the performance of collision alerting systems that are suitable for the light end of general aviation, such as sailplanes. Primary issues are cost, weight, and power needs. In addition, improvement of the human-factor interfaces of those devices is the center of recent research in order to make them more effective. The goal is to develop design guidelines for the human-factor interfaces of low-cost collision avoidance systems.

Saw-Tooth Flight Performance of Motor Gliders with Retractable Jet Engine; G. Sachs, J. Lenz, and F. Holzapfel

F. Holzapfel

The presentation explored similar gains for motor gliders with retractable, small jet engines. Those engines have the advantage of providing significantly less aerodynamic drag and reduce the trim needs. Disadvantages are their relatively high cost and fuel consumption. A saw-tooth flight profile, that is powered climb followed by unpowered flight, can significantly extend the range of motor gliders with a retractable engines. In general, a saw-tooth profile consists of six phases: powered climb, engine cool down, engine retraction, glide, engine extension, and restart. Using an optimization approach, the conventional piston-engine driven motor glider can extend its range by a factor of approximately three in comparison to a cruise at a constant altitude. A similar analysis of the jet-motor glider indicates over twice the range using a saw-tooth flight profile rather than a constant altitude cruise. The analysis also indicates that jet engines with higher thrust levels have higher efficiencies of the saw-tooth flight profile.

Unique Performance Characteristics of Electric Aircraft; G. Sachs

Aircraft with electric propulsion have been around the 1970s. Unlike air-breathing engines, electric propulsion systems have only minor performance penalties with increasing altitude. A result typical for electrically propelled flight is that the speed for maximum range increases with altitude. Other issues for sustained electric flight are power storage and power generation through solar cells. The effectiveness of solar cells improves with altitude and varies with latitude. Apparently, at around 40 degrees latitude solar power seems to be at an optimum over the course of a day. Based on the solar information and the extended flight envelope, an optimized flight profile was found that maximizes range of sustained electric flight.

Note on Electric Propulsion Glider; F. Galvao

The presenter highlighted the advantages and disadvantages of electric propulsion for motor gliders. In general, advantages are low noise emissions, relatively cheap direct operating cost, the potentially “clean” power concept, and a high reliability of electric propulsion systems. Disadvantages are the relatively high cost and weight of batteries. Subsequently, the currently possible range of electrically propelled motor gliders is limited. In the presentation a low-cost electrical motor-glider concept is explored that uses a fixed propeller system, that is, it cannot be retracted. In soaring mode the drag penalty of the fixed propulsion system is very limited. A wind milling propeller-electric motor combination results in very little additional drag due to the very little internal resistance of a “free spinning” electric motor. This performance penalty could be accepted for the simplicity of the system. Additionally, the wind milling propeller-engine combination could be used to recharge the batteries, for example by extending the time in thermal after reaching cloud base. The additional energy stored in the recharged batteries can be used to climb above cloud-base level and, then, continue gliding flight from a higher altitude.

Flight Path Planning for the 2011 Green Flight Challenge; J. W. Langelaan, A. Chakzabartyy, A. Dengz, K. Miles

This talk was about the process of the winning team of the 2011 Green Flight Challenge. The winning design was able to move four passengers at over 200 mph over a predetermined course with an equivalent fuel efficiency of 400 person miles per gallon. This was accomplished with a design that used two Pipistrel G2 that were joined and has an additional center pod with the electric propulsion system. Despite the aerodynamically sub-optimal design, the subsequent Taurus G4 remained the winner of an overall field of 28 competitors and 4 actual aircraft that came to the actual competition in August 2011. One of the greatest challenges was the very tight schedule with a project start the previous April. Overall, the concept demonstrated the feasibility of electric flight for general aviation.

Note:
The senior authors have been requested to submit their papers to OSTIV’s quarterly, peer-reviewed, print and on-line journal Technical Soaring. The contact is Chief Editor Dr. Judah Milgram. Thus, soon you will be able to study the complete papers.