For my senior design project at Drexel University, myself, and two mechanical engineering students worked on a project that would not only satisfy our graduation requirements, but would also fit with our love for RC aircraft and drones. Our project was to build an Autonomously Controlled Hybrid Rocket/Glider for Radiation Detection.
The problem we wanted to solve was to provide detailed information about an accidental exposure at a nuclear power plant. When an exposure is noticed, plant officials must contact local government within 15 minutes to notify them and recommend a plan for evacuation, if necessary. This rocket glider could be launched in under 60 seconds to an altitude of 1000 ft, and glide for 15 minutes in a circular pattern, while relaying radiation information to a base station. This would allow for the creation of a 3D visualization of the plume to accurately verify how much radioactive material was released, and where to focus immediate evacuation efforts.
While the project seems simple in concept, there were many constraints that had to be taken into consideration. Some of these were legal, such as finding a location and obtaining permission to fly an autonomous aircraft, or the amount of rocket fuel we could use. Others were physical constraints, such as the fact that a glider and rocket must have a drastically different center of pressure and center of gravity in order to fly correctly.
The main concept of this rocket glider was that we would have a rocket with spring loaded wings on the sides. The rocket would launch using two "G-40" sized rocket engines in parallel, providing a total impulse of nearly 200 newton-seconds. The delayed parachute charge would expel the rear portion of the rocket, removing the engines, one of the fins, and in total, about 600 grams of weight. The rocket engine compartment also served to hold the spring loaded wings back, and by expelling the rocket compartment, the wings would also deploy to glider position. This also shifted the center of gravity by 260 mm, making it stable for glider flight.
This video shows our progression of our scale prototyping phases. We begin by testing our engine ejection system. The next test was done with scaled balsa model to verify that our airfoil generates lift. By dropping the model straight down and having it climb out of the dive shows that it generates lift.
We then show our first rocket simulation, which utilizes the standard Barrowman Equations, which model the flight characteristics of the rocket. While it shows that the rocket should be stable, the Barrowman Equations could not account for the glider wings on the side of the rocket. This is why the following launches show the rocket climbing in a stair-stepping pattern. The rocket launches and is initially unstable, but as the fuel burns and the center of gravity shifts forward, the rocket becomes stable (when it flies horizontally, and then becomes over stable (when it turned skywards again).
After we defined our own modified form of the Barrowman Equations that can account for our wings, we were able to see a perfectly stable rocket flight.
Finally, we show a scale prototype rocket glider. It did not have electronics or controllable wing surfaces, so gliding was only controlled passively, by the dihedral we added to the wings to induce a spiral flight pattern.
After viewing the onboard cameras and datalogs from our flight controller, we were able to identify the four main causes of failure for the test. The first was that due to the impulse of the launch, the control surfaces of the tail fins fluttered so violently that the control horns ripped off. Secondly, our wings ended up deploying prematurely. The wings, at a meter long each, were not rigid enough and experienced fluttering. Since the wings were fluttering, they were not generating lift and the rocket began to tumble. After it began to tumble, the tube holding all of our electronics had been thrown from the aircraft.
Initially, we wanted to build our wings out of molded carbon fiber, similar to how remote controlled discus launch gliders are. Unfortunately, however, due to budget constraints, we had to revert to foam wings with a carbon core, which ended up being much weaker. Despite this, we had evidence to suggest that our flight control system was operating properly, and are confident that if we had stronger wings and fins, we could have had a successful launch.
Despite our failed launch, we were awarded an A+ for our project. According to our grading panel, even though our launch failed, the fact that we were able to analyze our launch, determine where the failures happened, and showed that our research was in fact valid, that we had earned that grade based on our research alone.
Please feel free to browse our 3 presentations, as they contain more images and videos of the project, as well as all of the data we produced.