From Insectothopter to Delfly

In the 1970s, the CIA built the ‘Dragonfly Insectothopter’, the first insect-sized unmanned aerial vehicle, which flew just like a dragonfly, but was powered by a tiny gasoline engine on board. The test flights of the insectothopter were impressive, according to the CIA. However, further development stalled because of the difficulty of controlling crosswinds. Now, 30 years later, the most advanced ‘robo-dragonfly’, the ‘Delfly’, has been built by the MavLab of TU Delft’s Faculty of Aerospace Engineering (AE).
The Delfly Micro is a so-called Micro Air Vehicle (MAV) and measures only 10 cm from wingtip to wingtip, while weighing just three grams. The Delfly has an on-board camera that transmits images to a computer on the ground and is specifically built for operations in enclosed areas. Last year, a team lead by Robert Wood of Harvard University, got an even smaller fly-like MAV – 3 cm in length and weighing only 65 milligrams – airborne. However, it could only fly while attached to a ropelike tether that supplies power.
In contrast, the Delfly has a battery on board. According to Bart Remes, coordinator of the MavLab and a TU Delft (AE) graduate from Belgium, it is exactly this that makes the Delfly so special. “There are many small MAVs that are of the same size as the Delfly micro, but what makes the Delfly special is that we are able to deliver the power on board. And we can do this not only for its engine, but also for the camera on board.”
The objective is to develop the Delfly into an aircraft that can fly autonomously in closed areas. This is the main reason why the Delfly has a built-in camera. “For indoor-flights, GPS isn’t an option, because GPS signals are too weak in closed areas”, Remes says. “We therefore had to develop another sensor, and we decided to opt for an on-board camera.”

Obstacles
In order to allow the Delfly to fly entirely independently, some work still needs to be done. Remes:  “To fly independently the Delfly needs to know where obstacles are and be able to avoid them.” The Delfly should, in other words, be able to analyze its surroundings and act accordingly. “Currently this is our greatest challenge: to build software that can do this kind of analysis”, Remes admits.

The battery on board of the Delfly is however both a blessing and a curse: it allows the Delfly to fly via remote-control, but it also hampers the miniaturization process. “The problem is that the focus of battery industry is on volume reduction and not so much on weight reduction, which is important for us”, Remes says, while adding that he is however positive about the battery trends in the computer and laptop industry. “The production of ever lighter and more powerful batteries for laptops will help us to miniaturize the Delfly.”  

The Delfly Micro is part of the four-year Delfly program, which is a joint venture between TU Delft and the Netherlands Organization for Applied Scientific Research (TNO). The Delfly Micro is the third generation of its kind. Originally it was a project carried out by students in 2005: at that stage the Delfly measured an astonishing 50 cm in length. 

The next step in the miniaturization process is Delfly Nano. The wingspan of Delfly Nano will be 5 cm and it will weigh only 1 gram. But the ultimate goal is to go even smaller, Remes says: “In the future we hope to develop a MAV that is the size of a fruit fly.” Remes does admit however that it will probably take another 50 years to develop such an ultra small (about 3 mm long) MAV. 

“Everybody dreams of developing an insect like aircraft”, he says, “but the problem is that such a MAV shouldn’t only be able to fly, but also to fulfill other functions such as walking. Enabling all these different functions as efficiently as possible is what makes building such an MAV an enormous challenge.” Copying nature in this way is at least for now impossible, Remes concludes. 

Although the Delfly is indeed the smallest MAV in the world, there is a backdrop to the miniaturization process: unlike the Delfly II, the Delfly Micro cannot yet hover in the air or fly backwards. Choosing to prioritize the miniaturization of the aircraft was a conscious choice of the MavLab team: “Our strategy is to walk on the boundaries of what is possible. We’re first going to try to develop the smallest MAV possible. Subsequently we will improve it like we did with the Delfly I by developing it into the more advanced Delfly II.”

Robobugs
The Washington Post reported last year that a number of US government and private agencies are trying hard to develop these so-called ‘robobugs’ for spying. In addition, the American Ministry of Defence has earmarked millions in funding for a properly functioning MAV that is smaller than 7.5 cm from wingtip to wingtip.

Remes stresses that the main goal of the MavLab research team is to learn more about the aerodynamics of flapping wings. “The data generated through the development of the Delfly enables us to develop computer models that can analyze this specific type of aerodynamics”, Remes says.  Currently, such computer models don’t exist, because it’s impossible to carry out measurements on real insects. 

Remes indicates that as far he knows the toy industry currently benefits more from his our research than any other industry. He also says that any possible military applications can never be prevented: “We of course hope that in the future the Delfly will be deployed for saving lives.” This could be done by, for instance, using the Delfly to look for signs of life under the rubble caused by an earthquake. Inspired by the Delfly, the toy industry is currently developing toys with flapping wings. 

Unlike the CIA’s ‘Insectocopter’, the Delfly Micro is not meant for outdoor flights. Although outdoor test flights with the Delfly II have been successful, Remes argues that it’s not an objective of the program: “You can fly outdoors with the Delfly, but then, just as insects do, you have to use the wind to fly from one place to another.” Other projects at the AE faculty specifically focus on developing advanced outdoor MAV’s. Remes: “For now our main objective is to develop the Delfly into an autonomous indoor dragonfly-like MAV.”