\label{cha:rams} In this chapter a first version of the RAMS characteristics is presented, based on similarity with existing aircraft. For an aircraft optimized for racing a reliability of one race day would be sufficient. However cost and sustainability factors do not allow this. The required reliability of the major components for the aircraft in race configuration could be set to equal about 75 hours of flight or one race season \cite{RBARmaint}. In after life, components could be replaced by more durable ones to allow for a longer maintenance interval and lower operational costs.
The following redundancy philosophies could be used. For electronic hardware passive and active redundancy and automatic fault detection and isolation could be used. One can avoid single points of failure and make use of diversity. For software N-version programming could reduce the chances of faults. Structural components could be designed according to the fail safe or safe life principle.
The aircraft is available when it is ready to perform the race mission. Operational limitations are daytime and meteorological conditions. With the to be installed flight instruments, the aircraft is capable of flying in ’Visual Flight Rules’ (VFR) \cite{FAAVFR}. During flight testing a maximum crosswind component will be determined wherein the aircraft is still able to land. The availability is reduced due to downtime before and between the races. Before the race, the aircraft needs to be assembled and certain maintenance activities need to be performed. The batteries need to be recharged or replaced. Downtime between races could consist of downloading the on board data, charging or replacing the battery and certain maintenance activities. Unscheduled downtime due to hardware or software failure could occur as well. To increase availability, use of fault monitoring, redundancy and line replaceable units could be considered.
Maintenance consists of scheduled and non-scheduled activities. For experimental aircraft, no maintenance regulations are stated. Maintenance intervals of certified aircraft are stated by the manufacturer according to CS-23 \cite{CS23} or at least an annual inspection is required according to FAR23 \cite{AOPA}. Typically for RBAR aircraft the heavy check interval is 75 flight hours \cite{RBARmaint}. CS-23 requires the issuance of an aircraft maintenance manual with instructions for personnel, which could also be considered for this aircraft.
Because of the novel use of electric propulsion in this race aircraft, focus should be placed on maintenance activities associated with the electric motor(s) and batteries. Electric motors require less maintenance since they are composed of less parts compared to combustion engines. Furthermore they are much simpler and cheaper in operation \cite{elecmaint}. An overview of electric motor inspection activities is given in \cite{elecmotormaint}.
Safety critical functions are functions intended to achieve or maintain a safe state \cite{safetyfuncdef}. Safety is the freedom from unacceptable risk of physical injury or of damage to the health of people, either directly, or indirectly as a result of damage to property or to the environment \cite{safetydef}. The following safety critical functions during regular aircraft operation are identified:
Protect pilot from environment (heat, electric circuits, fire, CO poisoning).
Protect ground crew from electric circuits.
Prevent battery thermal runaway.