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Star Wars Real-Engineered: Jet Bike
Tilting nacelle VTOL jet bike with 2 turbojets and 3 tail steering nozzles driven by 1 PF M-motor and 4 AA Batteries, 7-channel manual controls, 1 portable light machinegun, 1 portable RPG launcher, 1 Ejector seat (all spring-driven shooting), 1 Bionicle/Technic pilot, in Scale 1:10
About this creation
1 Preface for our “Star Wars Real-Engineered” mini-series

It is very clear that no one can make Sci-Fi movie without departing from existing scientific knowledge. However, it can be done in the clever way, like Stanley Kubrick’s “2001 a space odyssey”. Alternatively, it can be done unnecessarily raping very basic laws of Physics valid through the Universe - like in Babylon 5 or in Star Wars - serving the marketing needs of target audience. Our mission is trying to re-create the fanciest Star Wars-gizmos from Lego Technic using strict engineering point of view, based on current or slightly extended technology.

2 The Star Wars gizmo real-engineered: Aratech 74-Z Speederbike

Aratech 74-Z Speederbike designed by Ralph McQuarrie appeared first in “Return of the Jedi” in 1983. It is unrealistic even in “Hollywood science” standards: In 1981, George Lucas called several concept artists to design some rocket-powered personal vehicle for the new sequel. McQuarrie submitted such a mix of a chopper and a flying wingless goose that even Lucas felt distracted by its engineering inadequacy. But super-cool outlook ruled the needs of target audience and the design influenced dreams of several generations of young people about personal VTOL-crafts.

Figure 1: Aratech 74-Z Speederbike

From the several tons of MOCs modeling it, we just mention Kyle Peckham’s Minifig-scaled Speederbike because of its creative brick usage:

Figure 2: Kyle Peckham’s Minifig-scaled Speederbike

Currently there is no any military/commercial, really flying, jet-powered hover bike available even in prototype form. We will discuss the reasons of it later in the last chapter. Scale Model Addict’s Hoverbike shows in crystal-clear way, how modern concept artist think about hoverbikes: it is a bike minus wheels and some nozzles added. This specific design has the merit of at least having air intake and downward pointing (albeit small) nozzle. How stabilization/balance is maintained? How steering is solved? How gyroscopic torque of turbojet is neutralized? Where is the landing gear? How pilot’s leg is defended from hot jet blast? Where is any redundancy/rescue system? The standard answer for these questions is “The design has some hidden parts we do not show for patent reasons”…

Figure 3: Scale Model Addict’s Hoverbike

3 The closest real engineering solution: EWR VJ101 Jump Jet, 1968, Germany

The well-known AVB Harrier an JSF-35 are nice and practically useable VTOL jet fighters, but they require brutally expensive specialized jet engines with rotating nozzles, moreover they have far bigger dimensions than a jet bike, and cannot be downsized.

In our point of view EWR VJ101 Jump Jet developed in Germany in 1965-68 had the layout potentially useable to build real jet bike ever. Based on the original idea of Bell XF-109, it had 2 wingtip-mounted tilting engine nacelles containing 4 relatively simple and small turbojets, while aft of the cockpit there were another 2 vertically fixed turbojets for stabilization. After dozens of successful flights (including vertical-horizontal transitions), the project was cancelled not by technical, but financial reasons, in favor of the single-engine Harrier.

Figure 4: EWR VJ101 Jump Jet

4 Our design in Lego Technic: JB-1 Tilting Nacelle VTOL Jet Bike

*For considerable part of rendering and artwork, very special thanks to C BigBoy99899

Our JB-1 Jet Bike MOC is a piece of concept art, but it is strictly tied to real engineering principles:

Overview of JB-1 Tilting Nacelle VTOL Jet Bike
Figure 5: Overview of JB-1 Tilting Nacelle VTOL Jet Bike
See model in LDD

It is driven by the turbojet engine nacelles invented in my earlier Jetpack MOC. They are externally driven by electric motor and can be tilted +95°/-95° forward/back +20°/-20° left/right by 4 Z-shaped swingarms and 2 universal joints:

In flight view of JB-1
Figure 6: In flight view of JB-1
See model in LDD

Spring driven, shooting, auto-loaded, portable light machinegun and RPG-launcher are carried as armament:

Ground attack by JB-1
Figure 7: Ground attack by JB-1
See model in LDD

According to Pauler’s 4th law, no speedbike worth anything without a cute blondie posing on that. In engineering jargon this is called standard accessory, so we created her. Credit for her head goes to P. Andrei, but her highly poseable, rounded body is our latest development:

Girl posing on JB-1
Figure 8: Girl posing on JB-1
See model in LDD

Serving the need of senior MOCers, we put here her mother also. Weighed well over 150lbs, she really tests margin of safety in payload lifting capacity.

Her mother posing on JB-1
Figure 9: Her mother posing on JB-1
See model in LDD

Fortunately, Storm Troopers serving His Majesty of Palpatine, Emperor of the Mighty Galactic Empire are usually more light and can fit in the cramped cockpit of the light craft:

Left side view of JB-1
Figure 10: Left side view of JB-1
See model in LDD

5 Technical details of JB-1 Tilting Nacelle VTOL Jet Bike

*Please find further materials about current existing mini jet aircrafts and mini jet engines here

**In the forthcoming technical description, functional parts of JB-1 are referenced by numbers which can be found on technical drawings attached

***Parts of JB-1 are color-coded by their function:
- Yellow: Manual handles of working functions, Fuel lines, Combustion chambers
- Gray/Black: Static parts
- White: Dynamic parts
- Blue: Ejector seat
- Orange: Lubricant tank
- Dark green: AA Battery, Shaped charge

Functional overview of JB-1 Tilting Nacelle VTOL Jet Bike
Figure 11: Functional overview of JB-1 Tilting Nacelle VTOL Jet Bike
See model in LDD

5.1 Dynamic systems of JB-1

5.1.1 Drivetrain

Drivetrain of JB-1
Figure 12: Drivetrain of JB-1
See model in LDD

The main drawback of VJ101 was that it carried 6 engines in total, from which 2 were useless deadweight in horizontal flight resulting increased fuel consumption, reduced onboard space and payload, reduced fuel capacity and range. To avoid these cost-exploding factors:
- We opted for 2 turbojets with 2-stage ( (D10) axial + (D11) centrifugal ) compressors and 1-stage (D12) gas turbines placed in tilting wingtip nacelles. Drive of their (D1) main shafts is cross-linked for redundancy reasons with (D4) half axises running inside wings and (D5) half beveled gear set, quite similarly to how turboshaft engines of V-22 Osprey tiltrotor craft are interlinked mechanically. This is how we avoided the need of redundant duplicate engines.
- Cross-link half axises also drive (D13) tail steering compressor through a long (D6) driveshaft. This feeds pressurized air into rotatable tail steering cold air nozzles, which provide yaw- and pitch control both in vertical hovering and horizontal flight (a solution copied from Harrier VTOL). This how we eliminated the need for fixed vertical stabilization engine (and its duplicate) acting as dead weight in horizontal flight. The reduced weight of tail-mounted steering compressor still plays important role maintaining correct center Of Gravity (COG) of the craft, counterbalancing weight of pilot and armament.
- Unlike VJ101, roll control is NOT done by changing RPM of left/right engines selectively - as they have interconnected drive - but tilting nacelles aside asymmetrically. We rejected selective RPM-based roll control because RPM of turbojets is hard to change exactly and rapidly even with latest electronic control in adverse conditions (hovering low, in dust, partially ingesting exhaust gases).
- Engine RPM is controlled centrally by (D15) throttle pedals to change overall lifting force.
- Single (D9) PF M-motor drives the whole system via (D7),(D8) gearing with 0.33:1 gearing ratio. 4AA batteries in custom-built quadruple holder provide energy. We rejected using PF battery pack, because its bulky dimensions would kill the shape of the whole craft, but the price of it is the need for home-made wiring. In the reality PF M-motor would act as an alternator (albeit a little bit oversized) driven by turbojets, and there would be a jet fuel tank in place of 4 AA-batteries.

5.1.2 Engine nacelle attitude controls

Engine nacelle attitude controls
Figure 13: Engine nacelle attitude controls
See model in LDD

Each turbojets can be tilted independently by the corners of an eqal-sided triangle: inner corner is (D2) universal joint of engine drive, outer corners are supported by two (C5) crank arms joined with (C4) rotating/ (C3) sliding hinges to (C1) cross-boom of engine nacelle. Crank arms are actuated manually by (C7, C8) Z8+worm gear combo, connecting (C11) control handles at gearing ratio 1:8. Nacelle is centered between crank arms by two (C2) steel springs from ‘Shock absorber soft’, pulled on nacelle cross-boom. They also serve as vibration dumpers. This layout allows to changing attitude of engine nacelles independently from each other ±95° forward/back, ±20° left/right:
- Transition from vertical hovering to horizontal flight and back is made tilting nacelles forward/back parallel.
- Roll control in horizontal flight and emergency yaw control in vertical hovering is made tilting left/right nacelles forward/back echeloned:

Tilting right nacelle forward
Figure 14: Tilting right nacelle forward
See model in LDD

- Roll control in vertical hovering is made tilting left nacelle to left or right one to right.

Tilting right nacelle left
Figure 15: Tilting right nacelle left
See model in LDD

5.1.3 Rudder/Elevator nozzle controls

 Rudder Elevator nozzle controls
Figure 16: Rudder/Elevator nozzle controls
See model in LDD

Real VTOL jets usually use moveable vanes to control hot gas/ cold air blast used for stabilization/ steering. As controllable vanes cannot be built from TLG parts in reasonably small size, we opted for 3 tail-mounted steering nozzles fed by (D13) tail steering compressor with pressurized cold air. The top nozzle is fixed, but left/right nozzles can be rotated ±60° from cockpit by (C17), (C18) ruddevator ( rudder + elevator ) levers via (C15), (C15) drive shafts and (C19) universal joints. In default position, all nozzles are equally spaced at 120°, therefore their thrusts neutralize each other. E.g. at left yaw steering, left nozzle is rotated upward +30°, while right nozzle is rotated downward -60°. Upward/downward thrusts neutralize each other, and tail will move to right:

Left yaw steering by tail nozzles
Figure 17: Left yaw steering by tail nozzles
See model in LDD

E.g. at downward pitch steering, both left and right nozzles are rotated -60° downward, so they overwhelm upward nozzle, and tail is raised:

Negative pitch steering by tail nozzles
Figure 18: Negative pitch steering by tail nozzles
See model in LDD

Due to lack of space and simplicity, the Vee-shaped tail stabilizator surfaces are fixed, as yaw/pitch control is already solved with tail nozzles.

5.1.4 Fuel System

Fuel System
Figure 19: Fuel System
See model in LDD

Fuel system is only partially modeled, as there were no more space in stub wings besides drive/steering shafts for extending fuel lines. Custom built holder for 4 AA batteries consists of 2 circular endplates and 1 central bracing Technic cross-axle. Battery holder simulates jet fuel tank. Aft of it there is a lubricant tank also.

5.1.5 Retractable landing skid

Retractable landing skid
Figure 20: Retractable landing skid
See model in LDD

VTOL Jet fighters usually have wheeled landing gear, enabling them to take off/land as conventional jet aircraft in case of emergency or in high payload, long range missions. This is especially useful using “ski jump ramps” of smaller aircraft carriers/ landing ships. We had very clearly no space for wheeled landing gear in JB-1 Jet Bike. But we still wanted to provide some limited possibility for “jump starts”: when engine nacelles are not fully vertical positioned at takeoff to reduce the danger of hot gas ingestion, which can be lethal for BOTH the pilot and turbojets. Moreover the skid allows some limited crash landing capacity, when the craft cannot fully return from level flight to hovering due to control problems. As top speed of JB-1 is around 200 knots, landing skid is retractable to reduce its drag by (L3) worm gear + (L4) Z8 gear combo driven by (L1) knob via (L2) universal joint placed behind ejector seat.

JB-1 landed
Figure 21: JB-1 landed
See model in LDD

One can see from landed view that all armaments are detachable from their underwing pylons, and can be used as normal infantry weapons after landing.

5.1.6 Ejector seat

Ejector seat
Figure 22: Ejector seat
See model in LDD

Every military aircraft worth as much as it save the pilot in emergency, as new aircraft can be manufactured in matter of weeks, but it takes 20-21 years to manufacture a new pilot. Therefore we designed an extremely compact ejector seat (our first model with 45° backward tilted back part), propelled by (E7) 2×3 propellant springs disassembled from TLG part ‘Shock absorber extra hard’. Seat is arrested with compressed ejector springs by (E1) locking pin holding (E5) arrester hook. Pulling (E4) handles pivots (E3) lever, which pulls backward locking pin 0.5 studs via (E2) flange, It releases arrester hook, and the seat flies upward vertically. Back windscreen is broken up by (E9) parachute riser clamps, while forward windscreen and main instrument panel with HUD are upward foldable to clear ejecting path. Bionicle/Technic pilot is fixed to seat by (E10) safety belt made from TLG parts ‘Motorcycle chain’. As this belt cannot be tensioned very well, ‘Connector peg with knob’ connects back of the seat with spinal part of pilot for safe fixture.

Ejector seat deployed
Figure 23: Ejector seat deployed
See model in LDD

At top of the seat’s back, there is (E8) box for parachute, which has double lids opening up after ejection releasing parachute. Because of the limited space available, we had to omit survival kit, box of life raft, and personal defense weapon from seat.
We modeled mockup of the rescue parachute made from ‘Palisade brick, transparent’ and ‘String 30 cm’ parts in an auxiliary model. Of course, we do not want to build this structure for real, it is just “I can do more LDD than you”-showcase. It was tricky because string cannot be attached to anything in LDD, it can be positioned and built in copying it from clipboard together with other bricks.

Parachute deployed
Figure 24: Parachute deployed
See model in LDD

5.1.7 Navigation systems

Navigation systems
Figure 25: Navigation systems
See model in LDD

Despite limited space available, we tried to include navigation tools of light jets in JB-1. Besides, antennae, instrument panels, navigation- and searchlights, it is equipped with pitot tube, angle of incidence indicator, windscreen, wiper, oxygen bottles, fire extinguisher, canned food/drink, starter battery. Moreover it has 6 jettissonable IR flares/decoys to divert IR-homing missiles.

5.2 Armament of JB-1

Armament of JB-1
Figure 26: Armament of JB-1
See model in LDD

Because of its small size and light weight (around 800 lbs dry), JB-1 is not very steady firing platform, especially in hovering mode. In emergency, it can make dogfight and ground attack with its armament, but its primary purpose is to deliver weapons to a forward position. Therefore all armaments are portable and can be used as normal infantry weapons, after detaching them from under wing pylons.

5.2.1 LM-7 spring driven shooting, auto-loaded light machinegun with Cradle Grenade Launcher (CGL)

Animation of LM-7
Figure 27: Animation of LM-7
See model in LDD

JB-1 Jet Bike has very-very confined onboard space for weaponry even compared to an ultralight helicopter. Therefore, we had to develop new, more compact spring-driven, shooting, auto-loaded weapon from our previous MOCs (see Bionicle Gun Building Guide 2nd Edition ): (W22) Propellant springs are from disassembling TLG part ‘Shock absorber extra hard’. Projectiles are non-TLG parts as Lego does not produce reasonably small parts due children safety reasons, moreover ABS material is not enough heavy to be efficient projectile. Therefore 1.5×6mm projectiles are made from copper electric wiring can be found in any hardware store. Mass of the projectile is so small that it can fly stabile flight path even without spin stabilization because of the density and drag of air. Drum magazines are not very popular in modern automatic weapons (although they were used extensively between WWI and WWII), but building from Lego Technic, they provide much more compact and easily moveable ammo feed than box magazines or belt feed. Z-16 gear from TLG ‘Gear shift’ rounded by ‘Tire 24×7mm’ can hold 16 rounds. (LDD cannot draw the tire pulled on Z-16 gear, so we mock it with the red rubber ring as placeholder.). The weapon is equipped with optical sight, folding bipod and Cradle Grenade Launcher (CGL) shooting 8×53mm flying spigot type grenade with the help of 2 propellant springs.

Firing cycle of LM-7
Figure 28: Firing cycle of LM-7
See model in LDD

5.2.2 RPG-6 spring driven shooting RPG launcher

Animation of RPG-6
Figure 29: Animation of RPG-6
See model in LDD

The main difficulty creating any decent looking RPG launchers from Lego is the complete lack of thin long barrels with 1 stud inner diameter (probably due to children safety reasons). Any of such a barrel solution from TLG parts will result in nearly 3 studs outer diameter, which would look terrible. Therefore we invented pseudo-tube launcher. 2 stud / 1 stud diameter RPG is launched from among 4 parallel ‘Technic cross axles 12M’ spaced 1 stud vertical/horizontal gaping. This will result in reasonably sized launcher. Technically, real RPG launchers could be built this way also, but hot propellant gases would roast personnel to death. To create simple and compact launcher, our RPG has flying spigot type bolt: it flies out together with the projectile, leaving propellant springs behind.

Firing cycle of RPG-6
Figure 30: Firing cycle of RPG-6
See model in LDD

5.3 Dimensions of JB-1

- Length: 52.00 studs / 416.00 mm / 16.38 in, Real size: 4.16 m / 13 ft 7.68 in
- Span with engine nacelles: 35.00 studs / 280.00 mm / 11.02 in, Real size: 2.80 m / 9 ft 2.17 in
- Wing span without engine nacelles: 19.00 studs / 152.00 mm / 5.98 in, Real size: 1.52 m / 4 ft 11.81 in
- Wing chord: 5.00 studs / 40.00 mm / 1.57 in, Real size: 0.40 m / 1 ft 3.74 in
- Length of vee-stabilizators: 10.00 studs / 80.00 mm / 3.15 in, Real size: 0.80 m / 2 ft 7.48 in
- Chord of vee-stabilizators: 4.50 studs / 36.00 mm / 1.42 in, Real size: 0.36 m / 1 ft 2.17 in
- Distance between wing spar and vee-stabilizator spar: 22.00 studs / 176.00 mm / 6.93 in, Real size: 1.76 m / 5 ft 9.25 in
- Height with landing skid extracted: 21.00 studs / 168.00 mm / 6.61 in, Real size: 1.68 m / 5 ft 6.10 in
- Height with landing skid retracted: 15.50 studs / 124.00 mm / 4.88 in, Real size: 1.24 m / 4 ft 0.79 in
- Landing skid length: 19.00 studs / 152.00 mm / 5.98 in, Real size: 1.52 m / 4 ft 11.81 in
- Landing skid width: 9.00 studs / 72.00 mm / 2.83 in, Real size: 0.72 m / 2 ft 4.33 in
- Clearance under vertical engine nacelles: 3.00 studs / 24.00 mm / 0.94 in, Real size: 0.24 m / 0 ft 9.45 in
- Airframe width: 7.00 studs / 56.00 mm / 2.20 in, Real size: 0.56 m / 1 ft 10.04 in
- Engine nacelle diameter: 4.00 studs / 32.00 mm / 1.26 in, Real size: 0.32 m / 1 ft 0.59 in
- Engine nacelle length: 15.50 studs / 124.00 mm / 4.88 in, Real size: 1.24 m / 4 ft 0.79 in

5.4 Unsolved issues of JB-1

Our modeling of JB-1 was enough realistic to pop up some basic problems, which can explain, why jet bikes won’t swarm above your favorite Wal-Mart megastore on Saturday mornings – at least within your lifetime:
- The hardest problem of all VTOL jets is digestion of its own hot exhaust gases can immediately stop turbojets. AVB Harrier and JSF-35 blow a screen of cold air between engine air intakes and rotatable nozzles to prevent it (but they still not allowed to retreat during hovering). This solution requires expensive and bulky turbofan engine (or even more deadly expensive and bulky separate fan). As JB-1 has two very simple turbojets, it cannot hover low above one point, but it has to drift continuously to avoid exhaust gas digestion. Moreover it could make only jumpstart takeoff safely, but that requires wheeled landing gear instead of landing skid.
- We eliminated the need of duplicate engines in nacelles and the need of fixed stabilization engine cross-linking drivetrain of turbojets and tail steering compressor. But this requires high-tech, expensive drive shafts rotating at 30000 rpm. If they are armored, they are too heavy. If they are non-armored, they are the most vulnerable part of the aircraft (just like at battlefield helicopters with tail rotor shaft). Moreover bearings of cross-drive shaft will increase fuel consumption and maintenance requirement considerably.
Some special problems of our MOC:
- Ruddevator levers work reversed, but there were no space for reverse gearing.
- Z-swing arms of engine nacelles overstress the mechanical strength of Technic bricks. In the reality, it won’t be a problem as VTOL crafts are usually not built from ABS, but from duralumin and carbon-reinforced resin.

6 References

The enemy helicopter in the dogfight scene is my former Light Attack Compound Helicopter:

Light Attack Compound Helicopter
Figure 31: Light Attack Compound Helicopter
See model in LDD

The girl posing on JB-1 Jet Bike is my Standard Girl Model Scale=1:10. Credit for the head goes to P. Andrei, but the highly poseable, rounded body is our latest development:

Standard Girl Model
Figure 32: Standard Girl Model Scale=1:10
See model in LDD

Building instructions
Download building instructions (LEGO Digital Designer)


 I made it 
  May 12, 2016
Quoting Parrington Levens complexity!
 I like it 
  May 12, 2016
 I made it 
  April 22, 2016
Quoting Gabor Horvath Wow! It's amazing! I really like the animations! They helped a lot to understand, how the functions work! And the girl is beautiful!
 I made it 
  April 22, 2016
Quoting Oliver Becker So that's another great Technic- stuff with a big pinch of humor, Gabor! LOL I agree with NfP, but with these "special" pics you would have gotten more looks at this time for sure... ;)
Thanks. I did not wanted to shift into "parental guidance needed"-direction, but next time I will consider that. Women are definitely better like-generator than engineering...
 I like it 
  April 22, 2016
So that's another great Technic- stuff with a big pinch of humor, Gabor! LOL I agree with NfP, but with these "special" pics you would have gotten more looks at this time for sure... ;)
 I like it 
  April 22, 2016
Wow! It's amazing! I really like the animations! They helped a lot to understand, how the functions work! And the girl is beautiful!
 I made it 
  April 21, 2016
Quoting Nerds forprez Oh my. Why doesn't this stuff get more attention? I love it. Technicality plus Star Wars plus women? Count me in! Seriously though, love all the time and effort put in all this. Humor is a cherry on top.
Thanks. My feeling is that majority of public in MOCPages goes in different direction than my creations. I'm thinking about shifting into some more professional site, but still being uncertain about that.
 I made it 
  April 21, 2016
Quoting c bigboy99899 Another incredible work, awesome.
 I like it 
  April 21, 2016
Another incredible work, awesome.
 I like it 
  April 20, 2016
Oh my. Why doesn't this stuff get more attention? I love it. Technicality plus Star Wars plus women? Count me in! Seriously though, love all the time and effort put in all this. Humor is a cherry on top.
By Gabor Pauler
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LEGO models my own creation MOCpages toys shop Star Wars Real-Engineered: Jet BikeBionicle

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