The big fear that is feeding the media driven drone hysteria is the thought of some idiot with a new flying toy, wandering into the path of a passenger airliner, followed by J.J. Abrams style fireballs and bodies falling from the sky. This gruesome scenario has really only been supported by people’s imagination, the media’s need for headlines, and lack of any real scientific data as to what would actually happen, should a rouge quadcopter make that million to one shot into a 9 foot basket moving 230 mph through the air.
So the smart folks at Virginia Tech’s CRASH (Crashworthiness for Aerospace Structures and Hybrids) lab have been working hard to answer these questions. Founded and directed by Professor Javid Bayandor, the team at the CRASH lab’s latest endeavor has been to build simulation models for turbofan engines, drone components, and basically smash them into each other to see what happens. From a Virginia Tech press release,
An 8-pound quadcopter drone can rip apart the fan blades of a 9-foot diameter turbofan engine during take-off in less than 1/200th of a second. The speed of drone debris thrashing about inside the engine could reach speeds 715 miles per hour. Broken blades also would create more fragments as the fan crumbles and warps the engine block housing, contributing to catastrophic engine failure.
(Simulation courtesy Virginia Tech CRASH Lab)
So there is little doubt that a drone of this large size would cause catastrophic engine failure. This sort of damage would be consistent with the type of damage that occurs regularly with a ingestion of a large bird. However thanks to FAA standards for aircraft engine design, the failure and detachment of a rotor blade is anticipated, and must be contained within the engine. Failure to contain a blade could obviously lead to other damages, from structural parts, to fuel tanks, electrical controls, or even death or injury. It has happened on older designs, such as Delta 1288, a MD-88 that failed and engine parts entered the passenger compartment, killing 2 (this was a 1963 designed engine).
While the FAA recognizes several categories of bird sizes, with the larger being flocking geese in excess of 8 lbs, there has not been any standard developed for objects that are not birds. What are the differences in materials? Of drone materials, which are the worst? Why would Virginia Tech study an 8 lb drone? I reached out to Professor Bayandor to ask him a few questions about their work. According to Professor Bayandor,
This is the drone size that one European country has sanctioned for their postal services to deliver packages to high altitudes. The work is not based on any organization’s request. We are able to model a variety of different drone sizes and models. We chose this model as a demonstrator, because it was one of the larger size commercial drones available that is capable of carrying large weights and reaching higher ceilings.
An 8 lb drone is not the type that one would get for Christmas and be used by a younger, less responsible person however. Without crunching the numbers, I suspect a smaller DJI Phantom sized drone at 13″ and 2.6 lbs would be more likely to be the first to actually get ingested into an engine. The Phantom seems to be the ‘go to’ drone for people first entering the hobby, and is most likely to be operated by those without any real knowledge of airspace or air safety.
Our plans are to study a full array of drone sizes, with different materials, weights, and configurations.
adds Professor Bayandor. Materials is also one of the topics that the CRASH team is studying. Currently, “The drone is composite, but the core is made of denser metal alloys.”. As we know, drones built from carbon fiber and alloys are not the only type we will see. Google has previously demonstrated a delivery drone in a wing form, made primarily from foam.
However, he adds, “In this early stage of the study, it seems that battery packs and on-board cameras can cause most damage. ”
I posed the question of what materials are likely to cause the most damage to the turbofan engine? Carbon Fiber tubes and plates, aluminum parts such as motor shells, circuit boards, LiPo battery packs? Professor Bayandor reports, “At this point, we are still formalizing our material modeling matrix, but the materials mentioned are among the general candidates considered.”