Just for Justin: Working 6-blade foldable main rotor . Working 6-blade foldable main rotor of Sikorsky MH-53J with electric drive, 2 turboshafts, collective and cyclic dual controls in cockpit. Scale=1:20 . *Visit my Lego helicopters blog also
I was pretty impressed by Justin Davies recent MH-53J Pave Low III MOC, which has 6-blade foldable main rotor using double gimbals to model some limited functionality of a helicopter's main rotor. I started to think about whether this superb airframe design could be supported with fully functional main rotor. I quickly pulled toghether in LDD the following draft. Its scale is roughly 1:20 (Lego Technic figure scale), but it could be a little bit downscaled, as I left some reserves for downscaling.
2. List of working functions of my MH-53J styled main rotor
1. 6 aerodynamic SNOT blades with 40 studs lenght, made of fairing tiles supported by 32+8 studs long technic axle spars. These type of blades are pretty heavy, so I had to reinforce blade folding jacks, being more thick and less realistic looking. But ABS material of jacks has somewhat smaller tensile strenght than real ones made of forged titanium, they would simply break off without reinforcement by the weight of heavy blades. At my earlier helicopter models I experimented with spar-and rib structure blades covered with 2in duct tape skin. These blades are pretty light and strong, and old jack would be sufficient for them. Just duct tape is not quite a regular lego component, and LDD cannot show it. So I present my MOC with heavy blades just for the show and for TLG diehards, but light blades are much-much more practical.
2. Collective and cyclic pitch control of blades, NOT using the TLG swashplate part (which has erroneous design). Swashplate here is just a tiltable/liftable flat plate. Lower end of blade pitch control pushrods are siliding on that. Elastic counter-pitch springs made of rubber dumpers 2 part press down blades to zero pitch angle, pushing their control pusrods to the surface of swashplate. Control rods are sliding vertically inside the yawing jack of blades, this solution saved lot of space, thats why rotor hub can be so compact.
3. Yawing hinges for blades. There are no flapping hinges, but in original MH53-J rotor, most of flapping vibration is dumped by flexibility of blades also.
4. Advanced blade folding jacks: they are easy to disengage, pulling out 3 blue colored locking pins per blade. Disengaged, they allow more degrees of freedom to fold blades: 0..-135 deg horizontal, +90..-90deg vertical, and +90..-90 deg axial rotation. I seriously modified the construction of the real MH53-J jacks, because Lego rotor blades are more bulky, and their folding is more difficut task. So blade root, the folding jack, and the blade can rotate separately axially in disengaged position.
5. Armored upper shield plate
6. Main rotor is connected with dual controls in cockpit with compact collective/cyclic input mixing linkage
7. Integrated cockpit with dual 5 channel controls (pitch, roll, yaw, collective, elevator flap) with instrument panel and working ejector seats plus technic figure replacement pilots
8. Electric drive by a PF M sized motor through reduction gearing
9. Transmission shaft for tail rotor with correct gearing ratio to main rotor. Tail rotor has 4 blades with variable pitch.
10. Modeling of turboshaft engines with electric driven moving 2-stage compressors, gas generator- and power turbines, movable jet blast deflectors (this reduces IR-image), 8 combustor heads, fuel line.
11. Movable elevator surface connected with pitch component of cockpit controls
- The whole rotor assembly has 106 studs diameter
- It is 12 studs tall (with armor plate at the top)
- Blades are 40 studs long, their chord is 6 studs, and they are 1.25 studs thick.
4. Color codes of parts:
- Red: Connections to existing airframe structure/ OR parts cannot be placed in LDD correctly, because it cannot draw rubber block parts distorted.
- Blue: Blade folding jack locking pins/ ejector seats
- Gray: Dynamic parts
- Yellow: Working cockpit controls
- Green: Pilots body