The team has tested many different configurations for our retrieval aircraft. We have already developed a system to reverse the thrust of the aircraft so we can land with a very steep glide-slope, however the remaining challenge was to find a suitable take-off method. The take-off method must:
- Have steering control during ground run
- Be capable of taking off from grassy or sandy terrain
- Be capable of taking off in less than 15m
- Have enough clearance for prop during take-off and landing
- Not impact the endurance of the plane by adding too much weight or too much extra drag
- Be as simple as possible
Twin-tractor Hercules with belly-skid
The first configuration tested was a twin-tractor Hercules delta-wing with a belly-skid. The aircraft was quite heavy and not efficient in cruise. The belly-skid did not provide adequate clearance for the props and many props broke during landing.
Gladiator belly-skid with single, rear, pod-mounted pusher
The next approach was a gladiator with a belly-skid and a single rear, pod-mounted pusher prop. (The gladiator is a smaller, higher aspect ratio version of the hercules). The rear pod-mounted pusher would cause a forward moment pushing the belly-skid into the ground and meant take-offs from sand weren’t possible.
Spring activated ‘leap-frog’ system
A torsion-spring from a bike rack was used to rotate the plane up and into the air. A prototype was developed, however the significant extra complexity, added weight, risk for stored spring energy, and difficulty timing the motor to activate at the right time meant that we did not continue further development.
Grim Reaper with large belly-skid and single, forward-mounted puller prop and rudder
The large belly-skid provided enough clearance for the prop, but could not take-off in sandy terrain. The rudder allowed good steering control.
Skywalker with wing-wires
The wing-wires helped the plane stay level during take-off. The fuselage protects the prop from ground strike during take-off, and the blown rudder allows for good steering control. However the skywalker airframe is not the most efficient design, and a significiant ground run was required.
Gladiator take-off from rails
It was thought if we could raise the gladiator airframe to a high enough pitch (ie > 60 degrees), then the plane could take-off directly with-out any ground run. We tested this several times, and while a successful take-off could be achieved it was not very reliable.
Gladiator XXL with deployable undercarriage, twin forward mounted puller prop
This plane could take-off in a short distance from a variety of terrain, and differential thrust could have been used to give good steering control. However, the twin-prop configuration resulted in inefficient cruise.
Grim Reaper with deployable undercarriage, single forward mounted puller prop, and rudder
This plane achieved efficient cruise of 180W at 20m/s with 1kg of battery. The plane could take-off in a very short distance from a variety of terrain, and the rudder allowed for good ground steerage. Modified high-torque servo-less retracts were used which allowed the plane to land on its belly and then raise itself up on the ground.