The Piper Super Cub PA-18 was built from a Hanger 9 ARF kit originally manufactured and sold between 2002-2003. This is a 1/4 scale model giving the model a wingspan of 100". It is pre-built and covered and required the final installation of radio equipment and motor system.
This particular model was built modified to be used for a sailplane tug. Its size and power system were determined based on the desire to tow sailplanes up to and larger than 4 meters in span with all up weights of 10 lbs to 20 lbs.
The initial work completed was the installation of an electric motor system and speed control. The Eflite Power 160BL motor was used in combination with a Castle Creations HV110 speed control and a 10s 6000 mAh set of Lithium Polymer batteries (two 5s 6000 mAh pack connected in series). This system is rated to approximately 2500 watts, depending on battery configuration and propellor used.
In static tests on the workbench it was found that the model had a continuous current of approximately 61 amps at full throttle, which is well within the abilities of the motor/speed control/battery set-up that has been used.
After completing the motor and speed control installation the radio and flight control systems were installed. JR equipment was the choice for this system, using a JR R1221 2.4GHz 12 channel receiver with a total of 8 servos for flight control.
The servos that are installed include JR DS8231 servos for the wing surfaces (ailerons and flaps), JR DS8411 servos for the elevators (a servo for each elevator half), a JR DS8417 servo for the rudder, and a JR DS 9411 servo to actuate the tow release.
Two independent battery packs are used to provide power to the flight control systems because of the large size of the model and the number of servos used. The batteries for the flight control system are 3s 2100 mAh Lithium Polymer batteries that connect to an individual Castle Creations programmable BEC for each pack. The Castle Creations BEC's are both programmed to an output voltage of 6v. These then feed into the JR R1221 receiver, which has inputs for 2 battery supplies.
The motor system batteries and flight control system batteries are independent of eachother to prevent loss of control of the aircraft in the event of a motor battery failure or low voltage situation.
To use the Super Cub as a sailplane tug required installation of a tow release and reinforcement of the bulkhead near the trailing edge of the wing. A Ben Diss Tow Release was choosen for installation and it operates by the simple use of a metal pin connected directly to a servo on the retract control.
The tow release is placed near the trailing edge of the aircraft on the upper fuselage, in the case of this model it is forward of the trailing edge by about 2". This placement seems to be useable from flight testing completed over the past few weeks.
The Piper Super Cub has been able to tow scale sailplanes up to and just larger than 4m with all up weights of 15lbs-20lbs. The most recent testing showed the current motor and battery configuration was able to tow sailplanes of this size up for 3 full height tows to an approximate altitude of 800'-1000' before needing to be recharged.
The photographs were taken recently and show the Piper Super Cub towing a 1/4 scale Schweitzer SGS 1-26 B (Moskal) with a wingspan of 3.2m (126"), it has an approximate all up weight of 12lbs-14lbs.