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Man versus Drone in Helicopter Dogfight
Foldable parasite/drone helicopters with Sikorsky X-2 type, 8-blade, steerable coaxial rotor, 6-channel RC-control, 2 30mm machineguns, 4 RPGs (all spring driven shooting), 1 Bionicle pilot/ or 2-channel RC moveable glass dome for cameras, in Scale=1:10
About this creation
1 Introduction and inspiration

Our Parasite/Drone Helicopter (PDH) MOCs are piece of concept art, but strictly tied to real engineering principles - unfortunately: The year is 2015, so we are in the future. The luckier and richer part of mankind kills and controls the much larger poor and desperate part with the help of drones, preventing them to take revenge fueled by aggressive ideologies. All major military powers pour tons of money developing drones, because of their numerous advantages. Contrary to human pilots, nobody cries for a drone shot down in action (except Treasury). Manufacturing another drone means more juicy orders and more jobs in military industry. Only brides will cry for their fiancées shot down by drones mistakenly identifying native wedding ceremony as fighting unit…

We want to reflect this military- and social paradigm shift in the Brick Universe with our PDH MOC designing both Drone and Personal versions based on our newly invented, compact, fully RC-steerable coaxial Lego Technic rotor:


Figure 1: Functional overview of PDH Drone version
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See model in LDD


Figure 2: Functional overview of PDH Personal version
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In real military engineering, there is mindblasting variety of newly developed drones, therefore we are focusing on showing just the most similar ones to our designs: foldable coaxial drone helicopters with reasonable size to carry machine gun containers or air-to-surface missiles:

SHARC is developed by University of Aachen, Germany and financed by EADS:


Figure 3: EADS SHARC

Its Chinese opponent is called YOTAISC X200:


Figure 4: YOTAISC X200

It’s totally different genre of rotorcraft than previous ones, but we mention
Hirobo Bit personal electric helicopter concept because its similarity in size and rotor used, moreover because its coolness factor:


Figure 5: Hirobo Bit

2 Action screenshots of PDH

*For considerable part of rendering and artwork, very special thanks to C BigBoy99899. I’m also very grateful for his modeling work creating mock-up of TLG Micromotor, improve styling of landing skid legs, and solving the mounting problem of Micromotors.

2.1 Drone version of PDH


Figure 6: Load master and technician from 101st Airborne load a PDH in Sikorsky S-129 SkyTank heavy battlefield helicopter
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The folded PDH is pulled up on the lowered cargo ramp with the help of internal cargo winch of SkyTank. Crew checks out the correct alignment of folded rotor blades, to prevent catching opening linkage of the ramp.


Figure 7: Folded PDH loaded on board SkyTank, left cutaway view
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One can see that the PDH occupies just the first half of cargo bay of the huge dropship.


Figure 8: Dogfight happened between Americans and Chinese at Oct 12, 2049, Siege of the Bund, Battle of Shanghai, WWIII
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While group of Sikorsky S-129 SkyTank heavy dropships of 101st Airborne approach the landing zone, two CHAIC WZ-19 light attack compound helicopters of the Elite 4th Helicopter Regiment of Beijing set up an ambush, hiding in a partially collapsed parking building. The surprised American heavy units start to drop PDH via bomb bay door to counter the attack. The PDH is just starting its turboshaft engines, and centrifugal force of spinning-up rotors will open folded rotor blades. The daylight darkness is due to nuclear winter.


Figure 9: Inflight refueling of PDH
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PDHs cannot re-dock into SkyTank in the air. Therefore surviving units return from South Asian Front above Pacific on their “own wings”, completing the 28-hour return flight to bases on Philippines with several inflight refueling. Crew fatigue is not a factor for a drone, in correct mechanical condition its endurance depends on fuel supply.


Figure 10: Left view of PDH
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One can notice that the nose of PDH is occupied by a huge RC-controlled rotating glass dome, which provides 0-360°°azimuth/elevation positionability for numerous sensors.


Figure 11: Back view of PDH
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As PDH has twin tail booms, there is a downward openable glazed clamshell door between them to provide better access to instruments and belly ammo magazines. As PF IR receivers are ridiculously incompact, they eat up all the space inside.


Figure 12: Bottom view of PDH
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Figure 13: Top view of PDH during desert landing
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Figure 14: Folded dimensions of PDH
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At 4° forward pitch setting of the rotor, neighbored rotor blades can be crossed, making the folded rotor more compact. At spinning up rotor, centrifugal force will open rotor blades. Landing skid is foldable, and it has elastic auto-open function: once the craft is dropped from the dropship, the skid opens.

2.2 Personal version of PDH


Figure 15: Front view of PDH
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Personal version has the smallest possible open cockpit, which can accommodate one person behind forward openable hinged windscreen. Space is so confined that there is no classic collective lever and yoke for control. Besides left/right yaw control pedals, which regulate throttle of left/right turboshafts driving lower/upper rotors selectively, there is an overhead control column for collective and cyclic rotor control and triggers of weapons. You can see a real example for this solution in GEN H-4 personal coaxial helicopter from Japan.


Figure 16: Left view of PDH
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Figure 17: Back view of PDH
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Against the Drone version, which has fixed twin vertical stabilizer surfaces, at personal version, they are moveable twin rudders. This is necessary because of correct yaw control of coaxial rotors during dead-engine emergency crash landing with autorotation. Rudders are connected into cockpit with pullrods.


Figure 18: Bottom view of PDH
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Figure 19: Top view of PDH
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Figure 20: Folded dimensions of PDH
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3 Technical details of PDH

*This part is technical and for helicopter builders with at least some experience. If you do not understand how do helicopter controls work, you can find an excellent summary at: www.aviastar.org

**In the forthcoming technical description, functional parts of PDH are referenced by numbers which can be found on technical drawings attached

***Parts of PDH are color-coded by their function:
- Yellow: Manual handles of working functions, Rotor blade tips, Ammo
- Gray/Black: Static parts
- White: Dynamic parts
- Dark blue: Seat of pilot
- Light blue: Control column
- Red: Triggers of weapons
- Orange: Lubricant
- Dark green: Shaped charge of RPGs, Battery


Figure 21: Left cutaway view of PDH Drone version
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Figure 22: Left cutaway view of PDH Personal version
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3.1 Dynamic systems of PDH

3.1.1 Main rotor

The world’s most widely used coaxial helicopter rotor is developed by Kamov. Its newest version can be seen on Kamov Ka-52 Alligator combat helicopter. Kamov’s rotor is a complex mechanical device performing many control- and automatic stabilization functions, which are performed by electronic tools at other helicopters. You can see an excellent animation about its working here.


Figure 23: Kamov’s coaxial rotor

In Lego Technic, we can model such a complex device with very strong simplification within reasonable dimensions. In two of my earlier MOCs I managed to model Kamov’s rotor retaining basic controls (collective, cyclic, differential collective yaw) in scale 1:10:
- Coaxial Personal Aerial Vehicle
- Ultralight Coaxial Attack Helicopter
However these coaxial rotor solutions and their drivetrain are not very compact for light crafts, which destroys aesthetics, moreover their controls are not very suitable for applying full RC control.

Therefore I turned towards modeling Sikorsky X-2-type coaxial rotor. It is more compact mechanically than Kamov’s rotor, having tubular coaxial rotor hub (created from 2 ‘Turntable 7 studs’, see parts (R6) above) which contains all rotor drives (R10), swashplates (R9), blade pitch arms (R3)/rods (R8) in its well-defended internal cavity. Moreover, its blades (R1) are more rigid and closer to each other. These result in more robustness, less drag and much higher speed than Kamov’s rotor. However, X-2 rotor requires much more complex electronic servo controls just to prevent breaking it, besides steering. I solved the X-2 rotor servo system with very strong simplification using 4 TLG Micromotors (C3-C6), while the original requires at least 10 servos or hydraulic actuators for steering and vibration dumping.


Figure 24: Compact 6-channel RC coaxial rotor of PDH
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The core of the idea of my compact X-2 type coaxial Lego technic rotor is that TLG part ‘Rapier’ is enough thin to move freely in standard 5mm Technic holes of ‘Turntable 7 studs’, moreover its rounded tip can slide in the side groove of ‘Wedge belt wheel’. Two of these 7-holed discs are used as (R9) swashplates to control eight (R3) blade pitch arms made from ‘Rapier’. Two of their holes are occupied by (R13) vertical diveshafts of the rotor, which have (R10) Z8 gears to drive upper/lower turntables by their internal gearing at gearing ratio 3:1. Swashplates can be moved vertically +/- 0.25 studs or tilted +/- 8°°in any direction around driveshafts. Attitude of upper/lower swashplates are synchronized by four (R8) trackrods occupying 4 of their holes. Lower swashplate has a 3 stud long (R12) tilting/lifting arm fixed in its 7th central hole, and protruding downward. Its lower end has a holder flexibly joining it to (C2) manipulator arm. Forward end of manipulator arm continues in (C7) overhead manual control column, while its rear end has 4 Z8 gears placed radially. These gears are rounded by 4 worm gears driven by 4 Micromotors (C3-C6). Suitable rotation pattern of 4 Micromotors can set the attitude of manipulator arm and linked swashplates necessary for collective and cyclic pitch/roll control.

3.1.2 Drivetrain

The disadvantage of the simplified X-2 rotor solution is that there is no space left for the differential collective yaw control used at real coaxial rotors. Yaw control is achieved with the help of the drivetrain: differential throttle/rpm setting of the 2 PF M-motors driving contra-rotating upper/lower rotors induces left/right yaw movement (this is the standard solution at small coaxial RC helicopter models).


Figure 25: Drivetrain of PDH
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3.1.5 Yaw control

Drivetrain-induced yaw control cannot be used at dead engine crash-landing, when rotors are in autorotation to save crew in Personal version. Therefore there are twin emergency rudders (C10) for yaw control connected to cockpit with trackrods (C13, C14). This emergency system is left out from the Drone version, as nobody cries for a drone.


Figure 26: Yaw control of PDH
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3.1.6 6-channel Coaxial Rotor Module and its Remote controller

For fellow MOCers with the motivation building physically more realistic, but compact rotorcrafts in the future, we prepared a separate sub-model in LDD about our compact coaxial rotor system and its RC console:


Figure 27: 6-channel Coaxial Rotor Module and its Remote controller of PDH
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3.1.7 Auto-open landing skid

When landing skid is folded, it deforms (S8) torsion spring made from ‘Rubber damper 2×1×1’, by the own weight of the craft. When PDH is air dropped, skid is automatically opened by torsion spring, and can be fixed in open position manually by (S3) locking pin.


Figure 28: Auto-open landing skid of PDH
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3.2 Armament of PDH

As PDH is not designed for high&hot conditions, it has relatively heavy armament compared to its small rotor diameter (although the 8-blade coaxial rotor allows quite high rotor disc loading ratio). Maximal armament can be carried only with the help of ground effect, in close-quarter combat. As both machineguns and 4 RPGs are portable and easy to remove, so armament can be selected flexibly for the given task. In case of emergency crash landing in enemy territory they can be used to heavily arm the surviving pilot. But pilot is also supported with a compact self-defense submachinegun placed behind the foldable back of seat.


Figure 29: Overview of armament of PDH
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3.2.1 Spring driven shooting MG-8 30mm machineguns

Our shooting MG-8 machineguns use 2 (W9) propellant springs disassembled from TLG part ‘Shock absorber extra hard’, while (W12) auto-loading arm is operated by the torsional flexibility of ABS parts. (W5) Flexible, disintegrating belts storing 35 projectiles in double belly magazines are made from echeloned series of ‘Technic beam 2×1×1’ parts connected with ‘Technic connector pegs with knob’. 3×15mm projectiles (30×150mm in real size) are not TLG parts, as TLG does not produce such a small parts because of children safety reasons, moreover ABS is not enough heavy to form reasonable projectile in such a small size. Projectiles are made from 3mm copper electric wire. They are fixed in cavities of belt with a tiny drop of molten wax, which breaks off easily under the shock of shooting. Belt itself breaks easily by the shock of shooting to prevent spent belt links hanging under the craft as a rope ladder.


Figure 30: Firing cycle of spring driven shooting MG-8 30mm machinegun
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3.2.2 Spring driven shooting RPGs

16×96mm RPG-projectile is a self-contained unit, having a spigot at its end. It compresses 4 propellant springs held by trigger arm. Rear end of the spigot is held by ‘Rubber damper 2×1×1’ parts, when RPG is loaded. The portable launcher is merely 4 parallel launch rails, without any special mechanics. The reason of this ‘pseudo-barrel solution’ is that TLG does not produce any reasonable thin walled barrel part to prevent modeling working up-to-date weaponry… Technically, real RPGs could be made this way, but jet blast would roast personnel to death during shooting.


Figure 31: Firing cycle of spring driven shooting RPG
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3.2.3 SM-10 compact self-defense submachinegun

There was 5×2×2 studs space left over between back of seat and IR receiver of turboshaft engines. The task was to squeeze something into that tiny space, which can at least imitate shooting. This is how this austere self-defense weapon was born.


Figure 32: SM-10 compact self-defense submachinegun
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3.3 Instruments and avionics of PDH
Most drones have rotating camera turret with wide angles of view, so the modeling challenge was there. I recognized that considering the largest glass dome TLG part with 8-stud diameter, there is not enough space in the turret for even Micromotors to move it. I had to figure out a solution, where 2 Micromotors and their IR receiver are placed outside the turret, and ‘7 stud turntable’ + central driveshaft combo transmits elevation drive inside the turret. Still the turret retains 0..360° degrees of freedom in azimuth/elevation movement:


Figure 33: Rotating glass camera dome of PDH, Drone version
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In the Personal version, a forward foldable windscreen with wiper, yaw control pedals and the very small central instrument panel occupy the nose. To model even the very basic flying instruments, we had to apply left/right side instruments panel also. Head Up Display (HUD) is fixed on overhead control column because lack of space.


Figure 34: Instrument panel of PDH, Personal version
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3.4 Crew/Accrual Systems of PDH

In personal version, we created a Bionicle/Technic pilot with 5-finger palms, pilot’s seat with safety belt and folding back, fire extinguisher, canned water/food. There was very clearly no space for even the smallest working ejector seat.


Figure 35: Crew/Accrual Systems of PDH
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4 Dimensions of PDH

- Main rotor diameter: 51.00 studs / 408.00 mm / 16.06 in, Real size: 4.08 m / 13 ft 4.53 in
- Main rotor disc area: 2 × 2042.82 sqstuds / 1307.41 sqcm / 202.65 sqinch, Real size: 2 × 13.07 sqm / 140.54 sqfeet
- Separation of coaxial rotor blades: 2.00 studs / 16.00 mm / 0.63 in, Real size: 0.16 m / 0 ft 6.30 in
- Clearance under main rotor: 19.00 studs / 152.00 mm / 5.98 in, Real size: 1.52 m / 4 ft 11.81 in
- Airframe width: 7.00 studs / 56.00 mm / 2.20 in, Real size: 0.56 m / 1 ft 10.04 in
- Airframe height: 11.00 studs / 88.00 mm / 3.46 in, Real size: 0.88 m / 2 ft 10.63 in
- Length folded: 42.00 studs / 336.00 mm / 13.23 in, Real size: 3.36 m / 11 ft 0.20 in
- Width folded: 17.00 studs / 136.00 mm / 5.35 in, Real size: 1.36 m / 4 ft 5.51 in
- Height folded: 15.50 studs / 124.00 mm / 4.88 in, Real size: 1.24 m / 4 ft 0.79 in
- height open skid: 21.50 studs / 172.00 mm / 6.77 in, Real size: 1.72 m / 5 ft 7.68 in
- Glass dome diameter (ver. Personal): 2.00 studs / 16.00 mm / 0.63 in, Real size: 0.16 m / 0 ft 6.30 in
- Glass dome diameter (ver. Drone): 9.00 studs / 72.00 mm / 2.83 in, Real size: 0.72 m / 2 ft 4.33 in

5 Unsolved issues

- Cyclic pitch and roll control of (C7) overhead manual control column is reversed. This was the price of integrating it with RC control.
- Rotor hubs are and blade pitch arms made from TLG part ‘Rapier’ are relatively weak, and do not allow to build any bigger diameter rotor in the current way. However in Minifig scale, this is just the average diameter of battlefield helicopter rotors.
- At the compressor of the right turboshaft, we have rotation directional error, as TLG part ‘Turbine’ has no mirrored part, and there was no place left for correct direction reverser gear.
- Suspension of turboshafts has only 6 studs, it may not withstand torque of PF M-motor and weight/recoil of RPG launchers.
- Opened landing skid cannot hold the enormous weight of PF Battery pack and 2 PF M-motors.
- Automatic locking of landing skid in opened position is not solved.
- Relatively large internal friction of turntables allows PF M-motors to turn rotors only at limited rpm.
- HUD should be placed on top of instrument panel instead of control column.

6 References

The Chinese CHAIC WZ-19 helicopter in the WWIII scene is my former Light Attack Compound Helicopter MOC:


Figure 36: Light Attack Compound Helicopter
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Building instructions
Download building instructions (LEGO Digital Designer)

Comments

 I made it 
  July 11, 2017
Quoting Stephan Niks This is so amazing: the idea, detail and the graphics: 6stars. When I have time I come back to read all the details
Thanks. Please check out my other MOCs, because this MOC already has a more developed version.
 I like it 
  July 11, 2017
This is so amazing: the idea, detail and the graphics: 6stars. When I have time I come back to read all the details
 I made it 
  November 18, 2015
Quoting Matt Bace Fantastic work once again! Your rotor hub designs continue to amaze me -- some very clever engineering there.
Thanks.
Gabor Pauler
 I like it 
Matt Bace
  November 17, 2015
Fantastic work once again! Your rotor hub designs continue to amaze me -- some very clever engineering there.
 I made it 
  November 17, 2015
Quoting c bigboy99899 Awesome work! Thanks for sharing with us!
Thanks. Very special thanks for your modeling help. Without that, I did not even start it...
 I like it 
  November 17, 2015
Awesome work! Thanks for sharing with us!
 I made it 
  November 17, 2015
Quoting Jeremy McCreary A fully developed weapon system for an imaginative scenario with a tremendous amount of thought and time behind it. The write-up could be a proposal for a production contract. Still trying to understand the rotor system. Intrigued by the right-hand controller interface.
Thanks.
 I like it 
  November 17, 2015
A fully developed weapon system for an imaginative scenario with a tremendous amount of thought and time behind it. The write-up could be a proposal for a production contract. Still trying to understand the rotor system. Intrigued by the right-hand controller interface.
 I made it 
  November 16, 2015
Quoting killswitch95 [SNRK] Such Technical, Very Detail, Much Functions... Wow... seriously though, always detailed, good stuff
Thanks.
 I like it 
  November 16, 2015
Such Technical, Very Detail, Much Functions... Wow... seriously though, always detailed, good stuff
 I made it 
  November 16, 2015
Quoting Stephan Niehoff Very impressive
Thanks.
 I like it 
  November 16, 2015
Very impressive
 I made it 
  November 16, 2015
Quoting Polino zs There is always something more than I can say ... becoz you are far beyond excellent! Your MOCs are not only professional, they all together make a landmark on this planet... Man, thanks for everything you bring to us ^_^
Thanks.
 I like it 
  November 16, 2015
There is always something more than I can say ... becoz you are far beyond excellent! Your MOCs are not only professional, they all together make a landmark on this planet... Man, thanks for everything you bring to us ^_^
 I made it 
  November 15, 2015
Quoting Rabbitdesign MB Again great storyline and flushed with technical details. A pleasure to read.
Thanks.
 I made it 
  November 15, 2015
Quoting Oliver Becker Your enthusiasm and your technical knowledge sparkle out of every pore of this MOC, Gabor! :)
Thanks.
 I like it 
  November 15, 2015
Again great storyline and flushed with technical details. A pleasure to read.
 I like it 
  November 15, 2015
Your enthusiasm and your technical knowledge sparkle out of every pore of this MOC, Gabor! :)
 
By Gabor Pauler
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LEGO models my own creation MOCpages toys shop Man versus Drone in Helicopter DogfightBionicle


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