## 2 Materials and Methods  
### Description of Original RPA. ALO project  
The selected RPA for this work was chosen from the Project ALO (in Spanish, Avion Ligero de Observacion--lightweight reconnaissance plane) that is an RPA developed by INTA (in Spanish, Instituto Nacional de Tecnica Aeroespacial--National Institute of Aerospace Technology) which can provide real-time reconnaissance, surveillance, and target acquisition information by means of interchangeable, steerable TV and FLIR (forward-looking infrared sensor) cameras. The images can be sent in real-time to the ground control station (GCS) where image processing capabilities are provided. In a typical mission performed by ALO, the RPA is transported to the launching site in the transportation vehicle that also plays the role of ground control station, Figure 3. The whole RPAS is transported on a single vehicle (Unimog size), which provides great mobility and transport capabilities, allowing missions from non-prepared locations. Assembly and installation of the RPA can be accomplished in less than 30 min without the use of special tooling. After loading the waypoints on the on-board computer, the UAV is launched from a hydraulic or pneumatic launcher. The RPA will fly the programmed mission over the surveillance area transmitting, in real-time, the images captured by the camera and relevant telemetry data, such as, position of the RPA, speed, fuel consumption, revolutions per minute (rpm) of the RPA engine, or altitude. In case of detecting any possible target, activity, or area of interest, the pilot located at the GCS can take manual control of the RPA flying around the selected point. When the mission finishes, or whenever decided by the pilot, the RPA can return autonomously to the launching site and the recovery will be performed by means of a parachute. Furthermore, for mission evaluation, the whole mission is recorded and can be replayed on a video monitor where the all the main flight parameters are displayed. ALO RPAS Description  
The ALO RPA could perform reconnaissance, surveillance, and target acquisition missions at a distance of up to 50 km from the GCS for a maximum of 60 min. Nominal observation speed of the RPA is 70 km/h. To carry out an operation, the RPAS was divided in the Air Segment (RPA + payload + spare parts) and the Ground Segment (GCS + transportation vehicle + launcher + tools and spare parts). Specifically:  
* Air Segment:
* Steerable TV and FLIR cameras
* Spare parts to guarantee 1 week of deployment with 3 missions per day
* Ground Segment:
* Transportation vehicle  
Figure 3: Completed ALO (Avión Ligero Observación) system: Control ground station, rubber bungee launcher, and aerial aircraft. * Hydraulic or pneumatic launcher
* Maintenance tools
* Spare parts  
The specific design features of the engine and aerial platform provides the RPA with very high climbing rates and a wide range of flight speeds: The UAV can reach the area of interest at a high speed and then decrease the speed down to facilitate recognition and identification of targets. Figure 4 shows an ALO RPA in the launching pad and Table 6 states the main features of the RPA regarding dimensions, weights, and performance values. To understand the RPA architecture, the main parts are:  
* The RPA is a conventional V tail fixed-wing aircraft made of reinforced fiber glass. The airframe can be easily disassembled in parts: fuselage, tail cone, and wing. The tips of the wing can also be disassembled. This modularity improves maintainability and allows and easy transportation of the RPA. The main components of the airframe are:
* Fuselage: Made of epoxy resin and fiberglass layers. The fuselage is a non-divided compartment without bulkheads or internal structural elements. This feature gives ALO the possibility to accommodate a wide variety of payloads and avionics equipment. * Tail cone: Fiberglass layers enclosing a core of Rohacell(r). Very simple union with the fuselage. * Wing: The wing is a sandwich structure made of fiberglass layers and Nomex(r).