Load Spectrum Development for Unmanned Aerial Systems Airworthiness
Unmanned aerial systems (UAS) are vehicles that are remotely controlled by human pilots typically from a ground station, or fly independently based on automated systems. These vehicles have been typically used for military applications, although they have a large potential for commercial and/or civil applications.
With the introduction of UAS in the National Airspace System (NAS) for commercial and civil applications, these vehicles become regulated under the Federal Aviation Administration (FAA), which requires airworthiness certification of all aircraft to grant them authorization to operate in flight. Unmanned aircrafts vary significantly in size, configuration, and application, making it impractical to describe them as a single type of aircraft. This makes it currently impossible to designate a type certificate for them and no special class has been designated for them by the FAA.
Currently, UAS aircrafts are regulated under the Special Airworthiness Certificate within the experimental category order 8130.34. This certificate is given to vehicles that are assembled without supervision, quality control of a production certificate holder, and do not have a type certificate. However these special vehicles are in condition to operate safely. UAS vehicles with issued experimental certificates can only be used for purposes of research and development, crew training, or conducting market surveys (14 CFR 21.193) and cannot be used for compensation or hire. Operational limitations only allow flight of the UAS vehicles within the line of sight of an observer, during daylight hours, and when other aircrafts are not in the vicinity.
These limitations make necessary the development of standards for UAS to regulate them under a standard airworthiness certificate and open up the UAS to commercial/civil applications market. Load Spectrum is currently one of the various unknowns on UAS, and research is needed to show the differences between UAS and commercial aircraft design criteria. With this differences identified, future standards can be developed for UAS with these distinctions in mind.
Currently the majority of General Aviation Aircrafts are successfully designed to CAR 3/FAR 23 loads criteria, and several of the existing UAS airframe designs are similar in weight and performance to that of a General Aviation Aircraft (GA). However, the loads and flight spectrum assumptions may not be the same. The focus of this research is to identify the critical differences between UAS airframes and GA aircrafts that relate to the current regulatory airframe design requirements, to provide the regulatory authorities with the technical information necessary to start the development of standards for UAS standard airworthiness certification.
A major reason for the loads and flight spectrum assumptions to be different between GA and UAS systems is that pilots and passengers usually avoid high maneuvering and gust g loads. While these high loads occasionally occur, pilots take action to alleviate the load and discomfort. The UAS pilot would not experience the discomfort from gusts or high g maneuvering and might continue to fly in those conditions exposing the airframe to more severe loads and cycles than CAR3/FAR 23 intended.
Currently the majority of General Aviation Aircraft is successfully designed to CAR 3/FAR 23 loads criteria. With the limited pooling of the UAS manufactures and their products associated with the research it can be said that several of the UAS airframe designs are similar in weight and performance to that of a General Aviation Aircraft (GA). However the loads and flight spectrum assumptions may not be the same. For example airframe geometries, V tails and push props may have a significant affect on fatigue. How different geometries are currently categorized for general aviation aircraft will need to be defined for UAS airframes as well.