The plane is modeled after the DeHavilland Twin Otter. Marius is from Vancouver, Canada, so probably sees these planes on a regular basis. The moniker "Baby Twin Otter" was chosen because it is not a purely scale model of the aircraft, but was inspired by it. The real aircraft is a Twin engined, piston powered amphibious float plane. In all these respects, the model is accurate. The model is truly enormous with a wingspan I would estimate at 2 meters. It is capable of sitting on its gear, although it was displayed on a raised platform to allow exercising of all the functions. Each float alone is bigger than any official Technic model ever made.
- There is so much scale detail in the model that I can't possibly explain it all here, but as an example take note of the tie-downs on the floats, the paddle, and the prop line on the fuselage. The wings have a mild dihedral and the wingtips are even washed out. If you don't know what washout is, go read about it and then imaging how hard this was to replicate. Marius built the wing with the front and rear spars intentionally misaligned and then used the cantilevered weight of the engine nacelles to twist the wing. The wing and body are built to show the accurate structural assembly (semi-monocoque)of a real aircraft including spars, ribs, frames, and stringers. There are diagonal struts which support the wing inboard edge and also very heavy struts and a cross brace for the floats. Although this is a studded model, many of the studs face outward or downward as required to create the shape and react the load.
- Flight Controls
- All of the flight controls on the aircraft are operable and match the function of the real aircraft very closely. They are even operated from the same locations in the flight deck as the real airplane. The flight deck can be seen in this picture.
- The outboard ailerons are operated from the control wheels (yoke type) in the flight deck. The pilot's and first officer's control wheels are bussed together. A pull-pull cable system runs from the flight deck to the ailerons which move in opposite directions (one trailing edge up while the other is trailing edge down) as they should. A spring system in used to maintain tension in the cables. Some of the aileron system can be seen in this picture.
- The rudder is operated from the rudder pedals in the flight deck. The pilot's and first officer's pedals are bussed together. A pull-pull cable system runs from the flight deck to the empennage where it drives the rudder. The empennage can be seen in this picture.
- The elevators are operated from the control columns (yoke type) in the flight deck. The pilot's and first officer's control columns are bussed together. A pull-pull cable system runs from the flight deck to the empennage which move the elevators in parallel (trailing edges in the same direction) as they should. The empennage can be seen in this picture. The elevator surfaces are mass balanced which reduces the amount of hinge moment required to move them.
- Trailing Edge Flaps
- The trailing edge flaps are operated from a lever in the flight deck. A motor drives the flaps aft and down in a Fowler motion by hinging them at a low point. The flaps drive until deactivated by reaching a limit switch (I think this is correct since there is no NXT servo to count revolutions). Note that the ailerons also droop and act as flaperons giving this aircraft full span flaps. The ailerons continue to operate in a differential manner as ailerons even when drooped as flaps.
- Both engines are motorized and the 3-blade propellers are operated by overhead throttle levers in the flight deck of the aircraft. The port and starboard engines have independent controls and can operate at different speeds, useful for directional control of the aircraft on the water since it does not have water rudders. The throttle lever actuates a push-pull (Bowden) cable which moves a rotation sensor on the wing. The signal from the rotation sensor is read by an RCX in the port side float which modulates power to the appropriate engine. Due to the RCX, the engines can operate at 7 different throttle settings. The engines are counter-rotating and even turn in the correct direction to eliminate a critical engine. Interestingly, a pilot of a Twin Otter came to the show and commented that the real Twin Otter does not have counter-rotating props, probably for commonality reasons.
- Variable Pitch
- The 3 bladed propellers of each engine are variable pitch and can have their pitch adjusted independently via overhead levers in the flight deck of the aircraft. The levers actuate a push-pull cable which moves a swashplate driving the prop pitch angle. This is a particularly complex mechanism since the cable cannot pass the plane of the propeller since it is spinning. The adjustment of the pitch angle is sufficient to allow reverse pitch. The nacelle with pitch mechanisms can be seen in this picture.
- Landing Gear
- The landing gear can be retracted into the floats via a lever in the flight deck. The landing gear is pneumatic and is sequenced. When extending the gear, the doors open first. The fully open door moves a valve which then deploys the gear. This sequence happens in reverse for stowage of the gear. A compressor in the tail provides the pneumatic power and has an air tank for storage. A pressure regulator is present which uses a spring and a pole reverser to shut off the compressor when a sufficient pressure charge is present. The landing gear can be seen in this picture. The landing gear has lock links which go on-center to lock the gear down and is capable of supporting the weight of the aircraft.
- Other Features
- Passenger Entry Door
- The passenger entry door is on the aft port side. It contains an air-stair and extends via a cable drum driven by a motor. There is a switch just outside the door to control its operation.
- Folding Wings
- The wings fold just past the strut attachment. This was a complicated feat since all of the outboard mechanisms had to disconnect as the wing folded, and reconnect when put back into position, as well as maintain structural integrity across the joint. Marius used a gear system which disengaged the inboard flaps (even though they are on the non-folding part of the wing) when the wing was folded to prevent the inboard and outboard flaps from losing synchronization.
Please join me in congratulating Marius on this phenomenal model which really does earn the title "EPIC"! Besides being an amazing LEGO creation, this model can also go a long way toward teaching someone how a real plane works and how it is built.