Electric driven combat helicopter-motorbike transformer with all working gear shift, brakes, 4-channel helicopter controls
About this creation
*Visit my Lego helicopters blog also
** See all pictures in better quality at Flickr
***See model and building instructions in Lego Digital Designer (LDD): Here
Figure 1: Two Battle Rotorbikes finish off enemy assault transport at May 23, 2049
In most cartoons and sci-fi, some form of personal flying-killing machine is a must buy-item in the shopping list of superheroes/ninjas/empire storm troopers. Unfortunately, these machines are very far from physical reality, usually trying to fly without any kind of wings or with pizza-sized rotors. To prevent sudden death of poor hero guys by free fall, we created Battle Rotorbike for them.
Figure 2: Battle Rotorbike in Urban Warfare Close Support (UWCS) duty at May 13, 2049
It is a model of a turboshaft-powered combat helicopter-motorbike transformer made of 1194 bricks in scale 1:10, featuring: Working functions for road mode:
1- Electric drive with 1 PF M-motor and 2 AA-batteries integrated into main frame,
2- 2-speed manual gear shift (1:0.43/neutral/1:1.12),
3- Bowden-operated double disc brakes forward,
4- Pedal operated drum brake rear,
5- Spring suspension and steering,
6- Adjustable double headlights,
7- Adjustable rearview mirrors,
8- Moveable windscreen wiper.
*See road mode model in LDD: Here
Figure 3: Overview of Battle Rotorbike in road mode
Working functions for helicopter mode:
9- Semi-rigid Bell-type main rotor with swashplate and collective/cyclic controls,
10- Aerodynamic, foldable main rotor blades with spar-and-ribs structure covered by decals,
11- Twin legged main rotor mast, backward tilt able at 64 degrees, equipped with rotor mast locks, transmission clutch, Center-of-Gravity (COG) shift compensator,
12- 2-blade, variable pitch ducted fan (Fenestron) tail rotor integrated into rear wheel rim connected with yaw control pedals,
13- 3 independently trainable weapons consoles (front wheel axis left/right and central one) lay able with steering
14- Steering column brake to block steering torque generated by recoil force of guns at left/right weapons consoles,
Figure 4: Overview of Battle Rotorbike in flight mode
1- 12.7mm (0.5in) 4-barrel Gatling MG on left console with rotating barrels, moving belt feed and rotary ammo drum,
2- 32mm (1.26in) 4-barrel Gatling grenade launcher on right console with rotating barrels, moving belt feed from linkers and projectiles, rotary ammo drum,
3- 5 rotary launchers (left console:1/ right:1/ central:3), all with 6 unguided rockets with 80mm (3.15in) AP or HE warheads,
4- Pilot figure from Bionicle elements,
5- Nitrogen displaced hydrogen peroxide-driven rescue jet pack with 30 secs flight time to save pilot,
6- Main rotor blade detonator to clear jetpack launch path,
Figure 5: Right side of Battle Rotorbike in flight mode
7- Dashboard with indicators, starter key, and triggers of weapons,
8- 12V battery imitation, lubricant tank, suspension adjustment gas bottles,
9- Pitot tube, angle of incidence indicator, GSM and UHF aerials,
10- Hinged windscreen to follow movement of central weapons console
11- Navigation/indicator lights,
12- Internal structure of turboshaft engine ( auxiliary model )
Figure 6: Front view of Battle Rotorbike in flight mode
2.1.Building Battle Rotorbike was inspired by the following vehicles:
The idea of the roadable aircraft (see Roadabletimes for their history ) was born from the desire of „flying over the traffic jam”. For my generation, the Star Wars-trilogy gave another push with empire troopers zooming among woods on jet bikes. Departing from an „airfield” with average size of 5×2.4m/17’×8’ rounded with other vehicles, road signs, traffic lights, lantern masts, air cables and other nice&sweet stuff requires excellent VTOL (Vertical Take Off Landing) capability. Done by an aircraft foldable into the dimensions of a full size car… The engineering challenge is incredible:
-Even ultralight aircrafts usually have 8-10m/26’-33’ of wing length/rotor diameter to produce sufficient lift, so if rigid/rotary wings are used, they should be foldable, which is risky and requires high-tech materials.
-If smaller ducted fans are used for lift to save space, it has two disadvantages: 1. The higher the speed of air downstream, the less fuel-efficient it is. 2. The craft is not able to make controlled dead-engine crash landing. So the nasty FAA (Federal Aviation Administration) won’t certify it – and they are right: Designers of such crafts usually recommend ballistic parachute for crash-landing. But if you deploy it from a destabilized, rolling craft, flying low, it is merely an invitation to your funeral.
-Sizeable wheels, suspension, chassis providing reasonable road safety are just too heavy to fly or they should be made of expensive composite materials
-Ideal placement of COG (Center Of Gravity) and wheel layout is very different between road vehicles and aircrafts, which can be bridged with complicated folding wings/tails/landing gears
Answers to the challenge include some expensive media hoaxes ( Moller), unmanned military drones ( Urban aero), but recently 2 FAA-certified crafts ( Terrafugia and PAL-V ).
Battle Rotorbike is a tribute to the Dutch guys creating PAL-V, a roadable 2-seat autogiro, solving tremendous engineering challenges with 10 years of hard work:
-Electronic controlled rear suspension of tricycle wheels to tilt the craft in road turns to maintain speed
-Retractable tail boom and rotor blades folding into 2 pieces – a risky solution requiring aerospace materials, careful maintenance and expensive spare parts.
But, as it is an autogiro, not a helicopter, it still needs 50m/42yards space to take off instead of the 5m/17’ we have in the traffic jam.
Figure 7: PAL-V
With all the respect to their work, I do not think that roadable aircrafts will ever be economically viable in civilian/commercial use: you can get far better separate car and aircraft at lower price. Moreover, they require excellent piloting skills and careful maintenance because of their complexity. In my vision, the only area they can succeed is law enforcement patrolling and special operations forces, where time of transition between air and road is critical. So, costs of mechanical complexity and excellent piloting skill can be justified.
Battle Rotorbike is also a tribute to the pioneering work of Marine Turbine Technologies LLC (LA) (see MTT home page ) creating 420R, the first road-legal turboshaft-powered bike. Without the power of Rolls-Royce Allison C250 or LHTEC T-800 turboshafts squeezed into a motorcycle frame with engineering magic, wheels will never lift from the ground…
Figure 8: MTT 420R Turbine bike
2.2.Previous model versions
Battle Rotorbike is based on my earlier model, the oTo Helichopper a helicopter-chopper hybrid created as alternative model of 8051 Racing Bike.
Figure 9: Overview of oTo Helichopper
In this model I explored basic principles of combining light helicopter and motorbike, but it has serious limitations because of material constraints dictated by set 8051. It had no separate drive for rear wheel and tail rotor, so real wheel has to be lifted to use it as tail rotor, which is troubleful at landing. Conceptually, this had backward tilting mast-behind-pilot layout, which allows pilot to stay onboard during road-air transition, but results in inferior mass distribution, allowing only small engine and light armament, and uncompact shape in road mode. Moreover, tail rotor was too close to main rotor mast, requiring considerable part of engine power to counteract main rotor torque because of short arm of force. I eliminated these disadvantages designing current model in LDD from scratch, where material limitations are lifted, and layout was changed to rotor mast-before-pilot. What Battle Rotorbike is inherited from previous model almost unchanged is the compact semi-rigid Bell-type main rotor and decals-covered folding rotor blades, which were tried and well proven in reality.
3.Functional parts of Battle Rotorbike
*This part is technical and for heli 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 Battle Rotorbike are referenced by numbers which can be found on technical drawings attached
***Parts of Battle Rotorbike are color-coded by their function:
- Yellow: Manual handles of working functions
- Gray/Black: static and dynamic parts
- Light green: pilots limbs, nitrogen tank
- Dark green: fake battery
- Red: sliding/friction part, lubricant tank, weapons trigger
- Orange: CNG fuel tanks/AA batteries
- Dark blue: armor
- Light blue/dark brown: explosive charge
- White: plastic covers or domes/hydrogen peroxide tank
*See partial model in LDD: Here Figure 10: Main rotor assembly
Helicopter-motorbike hybrids require extremely compact main rotor hub and tilt able rotor mast to maintain reasonably low Center of Gravity (COG) in road mode. This is a challenge because there are not really small mechanical parts in Lego - need by heli rotors - out of children safety reasons, and there are not really good specialized rotor parts (e.g. Lego swashplate has to be drilled up centrally to perform its real function because of its erroneous design, moreover its not very compact). Therefore I simplified further the simplest possible type of main rotor, the 2–blade semi-rigid Bell, to get it fit into 7 studs height × 5 studs width × 3 studs deep space with all its controls and gearing included. Let’s see, how it works: at the top end of main rotor shaft there is a (S9) flange, and (S10) cross-axle can rotate in that. Cross axle rotates together with changing pitch of right blade (shown actually half-opened) when blade is fully opened turning it around (C32) blade pivots, and end of (S12) blade spar is plug into (C33) blade locking sleeve. Changing its pitch, left blade can rotate around (S10) cross axle together with its (S7) spar, (C32) pivots and (C33) locking sleeve, but not entirely freely: (S6) 2×1×1 rubber block is placed on (S7) left blade spar, but end of (S10) cross axle is also plugged into that when left blade is opened. This way, (S6) rubber block acts as a torsion spring, gently forcing blades to 0 degrees pitch relative to each other, so they will not generate any lifting force. However, upward movement (C31) blade pitch flanges and (C29) blade pitch rods can give positive pitch for rotor blades trough (S8) blade pitch catches against the force of (S6) torsion spring. (C29) blade pitch rods can slide up/down in holes of (C30) rotating drive disc to preserve their correct attitude relative to blades. Lower end of (C29) blade pitch rods slides on (C28) swashplate. This is just a plain plate with a hole in the middle letting through main rotor shaft. But it can be tilted in any direction around main rotor shaft by (C27) swashplate hinges, (C26) cyclic control rods and (C5) cyclic control horns, forcing (C29) pitch control rods moving up/down cyclically, resulting in pitch/roll movement of the craft by asymmetric lift force. (C28) swashplate can be also lifted 0.5 studs parallel to main rotor shaft by (C43) collective control rod and (C42) collective control horn, resulting in increased pitch of both blades collectively against force of (S6) torsion spring, which gives bigger symmetric lift force. (S18) rubber block fixes collective control rod in any given position to preserve collective pitch setting. With this solution, I could avoid using the troubleful and bulky Lego swashplate. When pilot leaves craft in emergency using rescue jetpack, rotating blades would decapitate him/her. To prevent this, rotor blades can be detonated before leaving, pressing (C44) detonator button, which will detonate (C45) charges placed in (C32) blade pivots by radio signal. As soon as pivot bolts are exploded, blades will fly off by centrifugal force and jetpack can be started.
3.1.1.Twin legged rotor mast
Rotor mast-before-pilot layout gives favorable mass distribution, allowing large amount of weapons at the front of the craft to counterbalance pilots and engines weight. But, it has two disadvantages: 1. Pilot cannot stay on the craft while rotor mast is tilted, 2: Rotor mast has to have twin legs as pilot has to look it through when opened, and saddle and fuel tanks have to fit in its middle when closed. So I created a rotor mast where two (S14) rotor mast legs, (C26, C43) pitch control rods and (D4) main rotor transmission shaft are grouped in two 3×1studs groups, 3 studs apart from each other to left/right. (D4) transmission shaft gets its power input from (D3) half bevel gear and transmits it upward to (D5) Z8 pinion gear, which drives main rotor shaft’s Z24 gear. Main rotor can be disconnected from drivetrain in road mode pulling upward (C12) main rotor transmission clutch.
This clutch has important role at autorotation crash-landing in case of engine failure. Battle Rotorbike most of the time performs its duties in „Dead man’s zone” (combination of low speed an altitude where autorotation will not work – e.g. among the houses of a densely populated slum). This zone can be reduced 2 ways: 1. It has high-inertia rotor system: rotor blades are relatively thick and heavy, in the reality they even have depleted Uranium (U238) weights at their yellow tips. 2.Main rotor can be disconnected from drivetrain with (C12) clutch from rest of drivetrain performing „dead man’s zone”-critical autorotation crash-landing. This has the advantage that main rotor does not drive back drivetrain and tail rotor, but the big disadvantage is that yaw control is lost because of stopping tail rotor. Outside „dead mans zone”, normal autorotation can be performed, where main rotor drives tail rotor and yaw control is maintained.
Main rotor mast can be tilted from +8 to – 64 degrees around (D22) cross axle.
Main rotor mast is locked to main frame in open position by (C11) rotor mast locks. Additionally, top of main rotor mast is locked to (S17) pivot placed on reinforced frame of windscreen. Frame rotates with steering, but (S17) pivot is exactly on the upward projection of (S5) steering axis, so it can fix rotor mast regardless of steering. However, fixing rotor mast on (S17) pivot is adjustable from +8 degrees forward tilt to -3 degrees backward tilt during flight time with (S51) knob of Center of Gravity (COG) shift compensator. Why it is necessary? Most battlefield helicopters carry bulk of their armament at left/right sides of the main rotor mast, because this way COG shift of the craft is minimal when all ammo is fired. In Rotorbike, we cannot do this as left/right placement of weapons would exceed standard motorbike gauge, loosing the advantage of driving in narrow gaps in road mode. Moreover, side placed weapons can hit the ground at high speed tilted turns causing accidental explosion. So, we had to place all weaponry on the forward fork, where they are counterbalancing weight of pilot and engine placed at the back of rotor mast. But when all ammo is fired, COG of the craft will change considerably affecting flight stability badly. But pilot can compensate this tilting rotor mast some degrees backward during flight.
3.1.2.Aerodynamic rotor blades
Rotor blades are the most controversial part of my design. I simply got fed up with that Lego cannot provide us reasonable helicopter rotor blades. Putting studded bars in the airflow is funny, but only until you play with Duplo. Recently, Lego introduced aerodynamic heli rotor blade component in 2012 at their 9396 Rescue helicopter set, but it is too big and too heavy to use in Battle Rotorbike. Therefore I created structure of blade spar (S7, S12) made of the longest Technic rod (32 studs) part and blade ribs (S13) made of „Bionic eye” part covered with duct tape. These blades are aerodynamic, strong and lightweight even at large size. They are still very far from a patented NACA (National Advisory Committee for Aeronautics)-aerofoil section, but they made their effect. When I prepared the open-air photos of my earlier model oTo Helichopper, there was medium wind, and blades did what they are proposed to do with annoying flipping-flopping. However, duct tape is not quite a regular Lego component, but decals are already well-known technology for Lego being part of many sets, so they could be used as structural stressed skin components of machines instead of just being decoration.
3.1.3.Opening sequence of main rotor
*See partial model in LDD: Here Figure 11: Main rotor open sequence
Main rotor mast in its closed position lies around the engine sitting on its top of with (S16) cross-rod of (S15) main rotor mast frame. Folded blades are sitting behind (S19) holding ears of (C15, C41) yaw control pedals. It is opened in the following steps:
STEP1: Lift rotor blades from behind (S19) holding ears and fold them 90 degrees
STEP2: Connect end of (S7, S12) blade spars into (C33) blade locking sleeves, and press (S6) rubber torsion spring on the end of (S10) main rotor cross axle.
STEP3: Fold down (C5, C42) cyclic and collective control horns 90 degrees.
STEP4: Lift rotor mast forward up 72 degrees
*See partial model in LDD: Here Figure 12: Tilting main rotor mast
STEP5: Lock (C11) rotor mast locks.
STEP6: Connect (C51) COG shift compensator to (C17) rotor mast pivot on reinforced windscreen frame
STEP7: Engage (C12) main rotor transmission clutch
*See partial model in LDD: Here Figure 13: Tail rotor assembly
The main difficulty of creating tail rotor is that rear wheel and tail rotor hub spinning on the same axis but with separate drives, which requires coaxial running parts. However in Technic we have almost complete lack of coaxial parts. The key to the solution was (D25) Z16 running gear from Lego gear shift. It has a circular cavity with catches interrupting it. (C58) blade pitch rods of tail rotor made of ’screwdriver’ parts protrude into this cavity and caught by catches, so they can drive (S22) tail rotor hub, which anyway runs freely on (D11) rear wheel axis between driving rings (S21). This is how tail rotor and rear wheel can be driven separately by separate transmission shafts. (D25) running gear can slide 0.25 studs to the right on (D11) rear wheel axis, increasing pitch of (S23) tail rotor blades with the help of (C59) pitch control arms. When (D25) running gear is sliding left, air drag of tail rotor blades forces them back to 0 degrees pitch. Pilot can slide (D25) running gear with the help of echeloning movement of (C15, C41) yaw control pedals. Their echeloning movement is ensured by (C52) echelon arms catching flanges of (C53) echelon fork. Yaw control is transmitted from this through forward/backward movement of (C54, C55) yaw control rods. It turns through (C56) flange (C57, C21) pivot arms. (C56) flange compensates up/down movement of rear fork. (C21) pivot arm pulls/pushed (C22) yaw control pushrod, which turns (C23) yaw control swing arm, which moves (D25) running gear right/left.
*See partial model in LDD: Here Figure 14: Drivetrain
(E1) PF M-motor drives (D1) turboshaft transaxle, which drives (D23) Z12 half-beveled gear. It drives (D22) Z12 bevel gear and main rotor mast pivot axis. Then it drives (D3) Z12 half-beveled gear of (D4) main rotor transmission shaft, which drives Z24 main rotor shaft gear through (D5) Z8 pinion gear. Engine is geared to main rotor at 1:0.33 rate. Moreover (D22) rotor mast pivot axis drives (D14) Z24 crown gear, which drives (D15) Z20 bevel gear and gear change axis. This axis can slide 0.5 studs left and right (Left:Gear1, Center:Neutral, Right:Gear2), moved by rotation of (C49) gear change over catch, which protrudes into the gap between (D15) gear and (D2) gear shift disc. The catch is fixed on (C55) rotating part of yaw control rod, which can be rotated by (C16) gear shift pedal +/- 45 degrees. Catch is fixed in any given position by a Z8 fixer pinion gear rotating on D21 rubber block with strong friction. In Gear 1, (D15) Z24 bevel gear drives (D16) Z24 half bevel gear, in Gear 2, it drives (D17) Z12 half bevel gear. Both (D16, D17) drives (D19) half bevel gears of transmission shaft, and then finally (D11) rear wheel axis. In Gear 1 engine is geared to rear wheel axis 1:0.43 ratio, in Gear 2 1:1.12. (D18) Z24 bevel gear, (D7) Z12 half bevel gear, (D8) transmission shaft, (D9) Z8 pinion gears pair, (D10, D11) Z12 half bevel gears pair, (D24) sliding pinion gear and (D25) running gear of tail rotor transmission are driven only in Neutral and Gear 2, but not in Gear 1. This is because when moving on rough terrain in Gear 1, rotating tail rotor could be damaged by stones and bushes, so it is stopped. Tail rotor is driven in road mode when driving fast in Gear 2, but - as tail rotor blades are automatically set to 0 degrees pitch without yaw control input by their air drag – it does not necessarily generate any yaw force. At Vertical Take Off (VTOL), gear shift is in neutral, rear wheel is stopped and tail rotor is spinning. It is also possible to make „jumpstart” Short Take Off (STOL) in Gear 2, when both rear wheel, main rotor and tail rotor is open, driven and controlled. This can save considerable amount of fuel at takeoff, if there is at least 50m/42yards space for it. Engine is geared to tail rotor 1:0.6. Main rotor is geared to tail rotor 1:2.
LHTEC T-800 turboshaft engine is modeled with (E1) PF M-sized electric motor placed on the end of main frame. This positioning has two advantages: 1. Length of the engine will not increase wheelbase, which would affect steering badly, 2. Eliminating the need of long exhaust pipes. However it affects Center of Gravity (COG) of the craft badly: engine is far back from main rotor mast, so it hast to be counterbalanced by the weight of armament placed forward. Moreover, engine placed high will increase height of COG, which affects riding in road mode badly: it is more difficult to keep bike balanced, and large gyroscopic torque of turbine rotor makes tilting bike in high speed tight turns hard. Electric motor is feed from two (E4) AA-batteries integrated into main frame. AA-batteries model high pressure bottles of Compressed Natural Gas (CNG) fuel in the reality. Besides that we have there (E10) fake 12V battery and (E5) lubricant tank. Moreover, we prepared an auxiliary model to present the internals of T-800 turboshaft engine:
*See partial model in LDD: Here Figure 15: Internal model of turboshaft engine
To build a functional model of a turboshaft in the size of PF M-motor (3 studs diameter × 6 studs length) was quite a challenge, because Lego produces kindergarten-level parts for turbines. (E21) part ’turbine’ is an exception, but it is not very compact, and it took some time to figure out how to build it in a functional model. There was a help that some turboshafts use centrifugal compressors, which resemble half bevel gears we used anyway to build 3:5 reduction gearing. Air (marked with blue arrows) flows in through (E12) intakes into (E15) first stage centrifugal compressor, which is fixed on (E11) output shaft. (E15) serves also Z20 half-bevel gear of reductor. Compressed air flows between first and second stage through (E22) air ducts. It is compressed further by (E23) second stage centrifugal compressor, which runs freely on (E20) power turbine shaft, which is connected to output shaft through (E16, E17, E19) Z8 reduction gears. Due to lack of space, (E20) power turbine shaft and (E17) reductor shaft have no normal bearings. They have (E18, E20) sliding rings surrounding by other components as bearing. (E30) combustion chambers protruding between (E23) second stage compressor and (E25) gas generator turbine prevent power turbine axis falling out from engine backward. Air flows from (E23) second stage compressor into (E30) combustion chambers, where it is mixed with fuel from (E28) fuel injector system, combusted and getting hot (marked with red arrows). Then it drives (E25) gas generator turbine and then finally (E21) power turbine. Both (E23) second stage compressor and (E25) gas generator turbine run freely on (E20) power turbine axis, but (E25) gas generator turbine has (E26) friction wheel, which drives back (E23) second stage compressor trough (E27) friction gear (it is made from part ’voodoo ball’ because it was the only matching thing in diameter) and (E24) Z12 half-bevel gear. Due to lack of space, stator vanes and stator parts of first- and second stage alternators to generate electric power/starter motors are omitted.
*See partial model in LDD: Here Figure 16: Brake systems
Battle Rotorbike has pretty conventional forward double disc brake, operated by (C38) brake lever trough (C25) brake Bowden cables. Rear wheel has even more simple (C46) drum brake operated by (C53) brake pedal trough (C48) pullrod. The tricky thing is why we need (C4) steering column brake? As barrel axis of guns placed on left/right weapons console do not intersect with steering axis, recoil force of the guns will generate unwanted steering torque, which is impossible to counteract manually. Therefore, (S5) steering axis has (C55) brake disc pressed by (C54) brake shoe when (C4) brake lever is pulled. This lever also serves as a safe for (C6, C7) triggers of guns: you cannot fire them until steering column brake is not activated.
(C20) stander seems pretty small compared to open-rotor dimensions of Battle Rotorbike. However, as main rotor has high inertia, if engine spins in idle race driving main rotor at 0 degree pitch (no lifting force is generated), gyroscopic torque of main rotor can stabilize the standing bike, even without using stander.
*See partial model in LDD: Here Figure 17: Frame geometry
In general, even light helicopters have pretty much bigger dimensions than biggest cruiser bikes, so it was hard to make a compromise. Battle Rotorbike has to have large wheels to accommodate weapons and tail rotor. Therefore I reduced model scale to 1:10 from original 1:6 scale of Lego motorcycle wheels. This resulted in wheels with 0.5m/ 1’7.68” radius in real size. This way Battle Rotorbike has a road size between a large police cruiser bike and a compact car.
I had to use pretty steep head angle (19.5 degrees), because forward fork is elongated upward into reinforced windscreen frame, which supports main rotor mast through (S17) pivot. Additionally steeper head angle allows more space for weapons on the center console. With rake offset of 2 studs, this head angle results in pretty small positive trail (0.08 studs). Smaller positive trail makes tilting such a big bike into high speed sharp turns more difficult, but results in reduced wheel flopping. This is vital at autorotation crash-landing, when wheels can be hit hard touching the ground: with big positive trail, front wheel would totally flop immediately (it is impossible to hold it manually) resulting in top down flipping disaster of the craft.
*See partial model in LDD: Here Figure 18: Armament
Left/right weapons consoles are trained around front wheel axis. Axis of firing barrel of (W4) 12.7mm (0.5in) Gatling MG (Left console) and (W2) 32mm (1.26in) Gatling grenade launcher (Right console) intersect with front wheel axis, therefore no training torque is generated by recoil forces. This is not true in case of laying torque: as guns are left/right sides of front wheel, they recoil will generate steering/laying torque, which is blocked by (C4) steering column brake activated before firing. Placing two pretty heavy guns on front wheel axis means two problems: 1. Unsprang mass of front wheel assembly increases tremendously, which makes steering and riding difficult. 2. Training mechanism of guns should work invariably regardless spring travel of front fork. I opted for this solution because springs in forward fork can help absorb serious recoil force of the guns. Training mechanism is resolved the following way: from breech block of the guns, a ’screwdriver’ part protrudes backward into the grooves of (W7) training worm gear. If worm is turned, it will train guns. Worm is fixed to (W8) training axis, which has (W11) half-bevel gear. It can slide on axis when it moves up/down with spring travel. (W11) is driven by (W12) half-bevel gear and (C9, C35) training cranks placed below steering grips. Both guns have rotating barrels and (W6) belt drive sprockets. As they rotate during firing, they pull down (W3, W5) disintegrating ammo belts from (W9, W10) rotary ammo drums placed behind overhead projectors. Belt links are ejected from the guns down and outward to prevent rear wheel driving on them when firing in road mode.
Training center weapons console is made by a single worm gear mechanism placed in forward fork head. This serves also for training overhead projectors, because they are used not only in road mode, but in air also to illuminate/blind targets on the ground.
As firing (W1) rocket launchers does not generate serious recoil force, they can be fired with (C37) trigger without activating (C4) steering column brake. Launching rockets would generate hot jet blast wave backward, which could seriously burn pilot’s legs. Therefore, there are water plugs in rockets nozzles to dim and cool blast wave at launch, resulting in a steam jet. As pilot has to wear hot steam resistant suit because of rescue jetpack anyway, this is not an issue.
Aiming of guns and rocket launchers is done with (N14) head up display fixed on reinforced windscreen frame.
*See partial model in LDD: Here Figure 19: Dashboard
Designing dashboard the main difficulty was that I had to squeeze instruments and indicators of a helicopter and motorbike in a confined space (legs of opened rotor mast make it even more confined). Moreover I had to place navigation equipment, which are not very usual at bikes: (N1) Pitot-tube measuring air speed, (N2) angle of incidence indicators vital for autorotation crash-landing, (N4) UHF aerial. Besides that we have the usual stuff from police cruiser bikes: (N5) windscreen wiper, (N7) police signal flashlights, (N10) rearview mirrors and indicator lights. Therefore I placed indicators of engine status on windscreen frame. These are partially covered by open rotor mast legs, but they have to be read less frequently. Windscreen and its elastic wiper arm can hinge up and down, following the training of the center weapons console.
*See partial model in LDD: Here Figure 20: Rescue jetpack
All military aircraft worth as much as they can save the pilots in emergency, because new aircraft can be produced in couple of days, but it takes 19-21 years to produce a new pilot… As Battle Rotorbike works most of the time below safe parachute bailing altitude, in a densely populated, crowded urban environment, scattered with roofs, chimneys, lantern masts, air cables, aerials, etc. where parachute ropes can catch anything instantly, we need something more compact rescue device. The solution is hydrogen peroxide-propelled jetpack (you can find an excellent summary about its history at Wikipedia). Until this point all experiments are failed to use it as practical personal flying device because of its short flight time (around 30 secs) resulted by low specific impulse of hydrogen peroxide (H2O2) propellant. But as a live saving device, it is promising because of three reasons: 1. It is dead simple compared to other rocket engines, 2. It will not explode if it gets hit, as hydrogen peroxide is a highly corrosive, water-like fluid, but not an explosive. 3. Hydrogen peroxide will decompose in the presence of silver (Ag) catalyzer into steam (H2O) and oxygen (O2) increasing its volume 5000 times, resulting in a 740C°temp steam jet. It is still less hot than 3000-5000C° jet of other propellants. Therefore cheap common structural materials will tolerate it without additional cooling and heat shielding of pilot is way simpler (a steam resistant suit is sufficient). How does it work? Whenever Battle Rotorbike reaches critical status, the pilot primes jet pack opening (C17) pressure valves, so the inert nitrogen (N2) displacer gas from (E6) pressure bottles can pressurize (E7) hydrogen peroxide tanks (without priming, they are not under pressure). Then pilot detonates main rotor blades pressing (C44) detonator button to clear flight pathway of jetpack. Then (E32) throttle is opened by (C19) arm, so pressurized hydrogen peroxide through (E31) flexible tubes can flow in (E33) reactor, which contains a grid of silver catalyzer. Generated hot steam flows through (E8) insulated pipes towards (E9) steam nozzles. Jetpack is controlled by (C18) control horns, which rotate throttle+reactor+steampipe+nozzle unit around (S2) ball joint, changing the attitude of nozzles relative to Center of Gravity of the craft. (E31) flexi tube is not connected on the drawing to (E32) throttle because LDD cannot bend it so sharply, but in the reality it is not an issue.) We can see an example of the launching process of jetpack in the following figure:
*See partial model in LDD: Here Figure 21: Lt. Will Moody detonates main rotor blades and lifts off with his jetpack after a SAM all but annihilated the back of his Rotorbike. June 18, 2049
4.Dimensions of Battle Rotorbike
Main rotor diameter: 66.00 studs / 528.00 mm / 20.79 in, Real size: 5.28 m / 17 ft. 3.74 in
Main rotor disc area: 3421.19 sqstuds / 2189.56 sqcm / 339.38 sqinch, Real size: 21.90 sqm / 235.37 sqfeet. Considering 12kg/sqm (2.4lbs/sqfeet) maximal rotor disc area load for safe autorotation crash-landing, maximal takeoff weight without ammo is 262.8 kg / 577.58lbs.
Tail rotor diameter: 8.00 studs / 64.00 mm / 2.52 in, Real size: 0.64 m / 2 ft. 1.18 in
Distance between main- and tail rotors: 18.50 studs / 148.00 mm / 5.83 in, Real size: 1.48 m / 4 ft. 10.24 in
Height of main rotor: 31.75 studs / 254.00 mm / 10.00 in, Real size: 2.54 m / 8 ft. 3.94 in
Safe clearance under main rotor: 29.75 studs / 238.00 mm / 9.37 in, Real size: 2.38 m / 7 ft. 9.65 in
Minimal storage space with folded blades:
- Height (without aerials): 24.75 studs / 198.00 mm / 7.80 in, Real size: 1.98 m / 6 ft. 5.91 in
- Length (with guns): 43.50 studs / 348.00 mm / 13.70 in, Real size: 3.48 m / 11 ft. 4.92 in
- Width: 13.00 studs / 104.00 mm / 4.09 in, Real size: 1.04 m / 3 ft. 4.92 in
Wheelbase: 27.00 studs / 216.00 mm / 8.50 in, Real size: 2.16 m / 7 ft. 0.98 in
Wheel diameter: 12.50 studs / 100.00 mm / 3.94 in, Real size: 1.00 m / 3 ft. 3.35 in
Rake offset: 2.00 studs / 16.00 mm / 0.63 in, Real size: 0.16 m / 6.30 in
Forward fork length: 9.00 studs / 72.00 mm / 2.83 in, Real size: 0.72 m / 2 ft. 4.33 in
Trail: 0.09 studs / 0.69 mm / 0.03 in, Real size: 0.01 m / 0 ft. 0.27 in
Rear fork length: 13.50 studs / 108.00 mm / 4.25 in, Real size: 1.08 m / 3 ft. 6.50 in
5.History of Battle Rotorbike
5.1.Developement of Battle Rotorbike
MTT LLC submitted proposal of oTo Battle Rotorbike for „Flying Jeep” tender of DARPA in 2016. First, it was completely rejected, being very far from the tender specification of roadable aircraft carrying 4-6 soldiers capable of move on rough terrain.
Figure 22: Flying Jeep tender of DARPA
However, after the Big Budgetary Crisis of 2022 causing the fall of second Clinton-administration, military budget was cut back, all running DARPA-programs were halted or cancelled, and the less expensive oTo Battle Rotorbike got free way in 2024. MTT developed first prototype for law enforcement market in 2027, having lighter chain drive at both rear wheel and tail rotor:
Figure 23: First prototype with lighter chain drive and 3×6 unguided rockets
But, DoD was concerned about the vulnerability of chain drive for enemy AA gunfire, which was not an issue in original law enforcement duty. Drivetrain with transmission shafts was considerably heavier, destroying flight performance and mass distribution balance. This issue was resolved when MTT gained access to the more powerful (1370 shp) military version of LHTEC T-800 turboshaft. In the second prototype issued in 2031, the extra power allowed to carry 5 rocket launchers instead of 3 (with 30 rockets instead of 18) to counterbalance additional weight of reinforced drivetrain. After successful official trials of second prototype in 2033, MTT received a contract to deliver 330 units for field trial all kinds of special ops forces. Later series were modified from using JP-1 jet fuel to Compressed Natural Gas (CNG) fuel. In the era of raging oil shortages and skyrocketing oil prices, CNG enjoyed safe domestic supply from rapidly expanding shoal gas wells.
5.2.Operational history of Battle Rotorbike
Battle Rotorbike slowly infiltrated in law enforcement duty in pre-WWIII years, and gained some popularity for its useful role resolving the Carnegie Hall Hostage Crisis in 2042.
As the historic old Huey heli became the symbol of Vietnam War in last century, Battle Rotorbike became the symbol of the nuclear inferno of South East Asian Front in the three year desperate worldwide struggle between USA and China for the last oil reserves of the Earth. 100000 acres of burnt urban rubble fields, blasted with radiation from nuclear fallout, totally collapsed infrastructure, flocking herds of enemy aircrafts darkening the sky made Battle Rotorbike vital for survival there.
Figure 24: Dogfighting happened at Oct 18, 2049 between Chinese gunship and Battle Rotorbike at Siege of Skyscrapers, Battle of Shanghai, WWIII: Lt. Will Moody from 101st Airborne cornering a high-rise building to avoid heavy fire of the gunship and trying to take it down shooting through the windows. Heavy overcast is due to nuclear fallout.
Figure 25: Rotorbikers patrol from unknown unit taking out pillbox of Peoples Guard, Outskirts Shanghai at Aug 11, 2049. Popular support of desperate Chinese defense caused staging American losses. That’s why Battle of Shanghai considered as Stalingrad of 21st century
6.Effect of Battle Rotorbike on popular culture
Appearance of Battle Rotorbike in law enforcement duty quickly resulted in its debut at Hollywood in pre-WWIII years. Google Time Warner financed the sequel of the famous movie E.T.: The aging Elliot gets divorced and becomes drug addict. E.T. decides to return to the Earth to help out his friend, but evil FBI-agents immediately start to hunt down him. E.T. escapes to the landing spaceship with the help of a stolen Rotorbike in epic aerial chase, and returns with a mighty space fleet to take revenge on Earth. The movie produced banging $50 million loss - almost causing bankruptcy of Google Time Warner - because targeted audience totally disregarded character of E.T. as a bloody man-eating monster.
Figure 26: Poster of contemporary movie from pre-WWIII era: a nasty fail
Battle Rotorbike got its role at one of the biggest blockbusters of the re-population era after WWIII, producing $550 million for MGM-Fox. It was a remake of the historic musical „Miss Saigon” into WWIII scenery, preserving nearly the same characters.
Figure 27: Blockbusting nostalgic romance from the re-population period after WWIII
7.Unsolved problems and shortcomings of Battle Rotorbike
1- There was no place left to put centrifugal clutch between drivetrain and engine. This way main rotor has to drive dead engine during controlled autorotation crash-landing, eating up rotor inertia, which is critical for survival.
2- Main rotor is geared to the tail rotor 1:2, and to the engine 1:3. In the reality both gearing ratios are beyond 1:10, but limitations of space in mainframe prevented using higher gearing ratio.
3- Unsprang mass of front wheel assembly increases tremendously because of the guns, which makes steering and riding difficult.
4- Placement of the engine behind main frame results in increased height of Center of Gravity. This – together with the high gyroscopic torque of the engine – makes riding very difficult in tight turns.
5- Tail rotor transmission shaft and yaw control rod are too bulky, blocking considerable amount of air flow from tail rotor. Specialized torque tube part from Lego could resolve this problem.
6- Main rotor mast and blades are not lockable in folded position, they just lay atop the vehicle, and this should be corrected.
Thanks to my wife Cathy, not divorcing me because of 30 days creation and documentation of Battle Rotorbike. Moreover thanks to my 11 months old boys Dani and Szilard not climbing onto the keyboard before saving (which they tried 268 times).
Battle Rotorbike brand name „oTo” comes from the name of Otoe American Indian tribe. This Sioux-originated tribe originally resided at Great Lakes but in 1884 they were deported in Oto Reservation Nebraska.
Role of Chinese gunship was played by my earlier Bad Guys Escape Helicopter model:
Thanks for the picture. I have seen this until this point only in 4-rotor version. There are several problems of these enlarged dual/quadcopters:
1. Small diameter, fast spinning rotors have very low efficiency
2. Therefore, this type of vehicle cannot lift above groud hovering effect (5-7m height), which is well below parachute deploying altitude
3. There is no autorotation glide mode at such a small rotors. Consequence: one engine out - you are very dead.
4. Moreover, even rotors are small, the vehicle cannot fit in standard motorbike (even compact car) gauge.
Because of these reasons, I intensionally selected folding main rotor with largest possible diameter within the given vehicle size. Rotor diameter - means your life!