HISTORY manned

Manned Ornithopter Flights

Several manned ornithopters have made successful flights. The most successful to date were those constructed by Adalbert Schmid during World War II. They were the only manned ornithopters which were capable of making extended flights.

Often people think of ornithopters as a relic from the early days of aviation. I would like to present a different view. Successful flapping-wing flight actually requires more technology than the simple airplane. The current, rapid progress in this field means the ornithopter will see its greatest development in the future, not in the past.

It is important to realize that most ornithopter work is not aimed at producing a manned aircraft. Most ornithopter research deals with unmanned ornithopters that are the size of a bird or insect. There are many applications for small, unmanned aircraft.

Manned ornithopters may become a practical means of transportation in the future, but so far they are built simply because of the human drive to overcome a difficult challenge. It is why people climb mountains. For that reason, people who build manned ornithopters often try to use their own muscle power to flap the wings. It works a lot better if you use an engine.

Alexander Lippisch

Alexander Lippisch was one of the great aircraft designers of World War II. He designed the world's first rocket-powered fighter plane, the Me 163 Komet. Before the war, Germany was subject to restrictions on motorized aircraft, and Lippisch wanted to build an aircraft powered by the muscles of the pilot. He chose flapping wings because of their potentially greater efficiency compared with the airplane concept.

Lippisch constructed an ornithopter and began tests. A young pilot and athlete, Hans Werner Krause, was selected to fly this machine. Since a small engine could have done the job better, he didn't feel inclined to expend much effort. Lippisch promised Krause a vacation if he could reach a predetermined mark at about 250-300 meters from launch. The goal was achieved.

Although Lippisch declared the flight a success, some other people competing for the claim of first manned ornithopter have expressed their doubts. One argument is that the Lippisch ornithopter did not have enough wing area to fly on muscle power alone. Another problem is that the ornithopter was launched using an elastic cord. The cord imparted a certain amount of energy, which got the ornithopter off the ground and got it up to speed. It was common at the time to launch an unpowered glider in this way. After being launched, the aircraft can continue for some distance without losing any height. However, the aircraft speed would decrease throughout the flight as the kinetic energy is consumed. To demonstrate a truly "sustained" flight, we would need to show that the speed and height are both maintained for some distance. We simply don't have enough documentation to know if that was the case.

Lippisch continued his ornithopter research. He and his students in the 1930s constructed a whole series of engine-powered, unmanned ornithopters. The flapper designs were backed up by extensive laboratory testing and theory. One of these ornithopters had a 3 meter wingspan and weighed 1950 grams. Using a 4 cc petrol engine, it made flights up to 16 minutes. These ornithopters used small flappers in conjunction with larger fixed wings. This meant they didn't need as much gear reduction, so the ornithopters were easier to build.

At the same time, the Muscle Flight Institute under Oskar Ursinus was acquiring more information on human muscle power. They found that a person using arms and legs together could produce over 1 horsepower in a short burst. Also significantly, the athletes could produce the greatest amount of power when working their muscles at about 1.7 cycles per second. For ornithopters, the flapping rate is related to the size of the flapping wings. Lippisch's small-flapper configuration provided the best match between wing size and the required 1.7 cycles per second rate of muscle contraction.

Adalbert Schmid

Because his talents were needed in the war effort, Lippisch was not able to continue his ornithopter work. Therefore it was Adalbert Schmid who constructed the small-flapper manned ornithopter that seemed to follow logically from what had been done so far.

On June 26th, 1942, Schmid's ornithopter shown here made a flight of 900 meters at a constant 20 meters above the ground near Munich. This ornithopter initially relied on a tow launch and the muscles of the pilot.

However, Schmid went beyond the limitations of muscle-powered flight by putting an engine in this ornithopter. [Ref. 2] With a 3 hp Sachs motorcycle engine, the ornithopter was able to take off unassisted from the ground. Schmid's ornithopter may have used a dolly with wheels that could be jettisoned after takeoff. This practice was commonly used in early glider type aircraft and was also used by Lippisch for the Me 163. Schmid's ornithopter made a quiet 15-minute flight at about 60 kilometers per hour. Then a 6 hp engine was installed, increasing the speed to 80 kph. After these historic accomplishments, Schmid's work was interrupted by the war.

By 1947, however, Schmid had built a second ornithopter. This one, a modified Grunau-Baby IIa sailplane, was constructed with flapping outer wing sections. Using a 10 hp engine, this double-seater was capable of speeds estimated at 100 to 120 kilometers per hour. [Ref. 3]

Vladimir Toporov

Percival Spencer had proposed a four-winged ornithopter design, which would provide a smoother ride for the occupants of the ornithopter. He demonstrated the concept in 1960 with the world's first successful radio-controlled ornithopter. The proposed manned ornithopter was not built. In the mid-1990s, however, Vladimir Toporov tested a human-powered ornithopter with four flapping wings. The four-winged ornithopter design showed it is possible to greatly reduce the body oscillation, an important step toward a practical manned aircraft. Toporov's ornithoper is significant for another reason. With much greater wing area, and the much greater efficiency of the four-winged design, it is quite likely that this aircraft sustained flight with muscle power alone, rather than relying on the energy of the tow launch.

James DeLaurier

The use of an engine with appropriate gearing would enable progressively more of the wing area to be flapping. Birds get some lift from the body and tail, but the flapping wings are comparatively large. A team at the University of Toronto Institute for Aerospace Studies, led by James DeLaurier, constructed an ornithopter in the 1990s which had comparatively smaller fixed wing area. This ornithopter made a 14-second flight in 2006. It was assisted by a small jet engine, but the flapping wings did most of the work. [Ref. 4]

One of the problems encountered during this project was that the aircraft tended to bounce on takeoff, due to the flapping of the wings. The jet assist allowed a smoother takeoff and helped compensate for the added weight of a rebuilt undercarriage.

Todd Reichert

The University of Toronto Institute for Aerospace Studies followed its manned, engine-powered ornithopter attempt with a human-powered ornithopter called the Snowbird. The project was led by Todd Reichert. The human-powered ornithopter was designed to have a large wing area, in order to minimize the power requirement. It was powered by a leg-press motion, and only the outer portions of the wings were made to flap, thus addressing the need to match the flapping rate with the optimal rate of cycling the muscles. As with previous human-powered ornithoper attempts, the Snowbird relied on a tow launch. [Ref. 5]

I had suggested to Reichert that in order to document a sustained flight, he would have to measure not just the height, but also the speed of the aircraft, over time. These measurements are difficult to make, and Reichert went to great lengths to collect the required data. Unfortunately, the wing flapping causes a cyclical fluctuation in both the height and speed of the aircraft. That makes it a little harder to see the overall trend. But you can take the average height and speed for each wingbeat cycle, and still tell if the ornithopter has sustained flight.

Reichert, instead of averaging the wingbeats, chose specific points in time, which gave an inflated measure of flight performance. As a result, he falsely claimed that a 19.3 second sustained flight had been made. However, his own flight data show that the airspeed and the total energy of the aircraft were in fact decreasing overall for the 19.3 second interval he claimed as a sustained flight. Only for the first eight seconds, the total energy was increasing, and by 11 seconds the total energy fell back to the starting value.

Reichert also dismissed any prior claims of sustained flight. Even if there is some uncertainty in the prior claims, it cannot be stated with any confidence that Reichert was the first. The question of who made the first sustained flight from a tow launch is a thorny issue, which may never be resolved. But when a human-powered ornithopter finally takes off under its own power, that will be the true measure of success.

References:

1. Lippisch, Alexander. "Man Powered Flight in 1929" Journal of the Royal Aeronautical Society. July 1960.
2. Schmid, Adalbert. Weltluftfahrt, volume 1, issue 9, March 1950, page 195.
3. Lange, Bruno. Typenhandbuch der deutschen Luftfahrttechnik. Koblenz, 1986.
4. DeLaurier, James. Ornithopter Report for 8 July 2006.
5. Reichert, Todd and Cameron Robertson. Aircraft Overview: Snowbird Human-Powered Ornithopter. August 2010.