A radio controlled helicopter was chosen as the vehicle platform for several reasons that demonstrate our philosophy of risk reduction and design simplicity. First, the aircraft's reliability has been proven, and replacement parts, as well as a large variety of parts for customization, are commercially available. Moreover, two Schluter Champion RC helicopters (0.61 cu. in. engines) were donated to the team. Although a custom-built platform may have been preferable if the team had more resources, the decision to use an RC helicopter avoided the substantial effort that would have been required to design and build an original platform. Finally, helicopter dynamics are well understood. Numerous mathematical models suitable for simulation and control design were readily available.
Only a few modifications to the aircraft were required.
The landing gear were rebuilt to accommodate a disk retrieval mechanism and
the fuselage was modified to support the sensor suite and flight computer.
Managing vehicle weight was a primary concern. For our helicopter, the maximum
takeoff weight is limited by the onset of the loss of tail rotor authority
to counter the main rotor torque. To increase the maximum takeoff weight,
we replaced the original two-bladed tail rotor with a four-bladed unit,
without changing any gearing. Determining our maximum takeoff weight (TOW)
was our first flight test, using a human pilot and loading the vehicle with
diving weights.
The maximum TOW for the 
cu. in. engine was determined to be
grams. The empty aircraft (i.e., without sensors, computer, disk
retrieval mechanism, and batteries) weighs 
grams.