Thursday, July 26, 2012


Most LEGO websites are flooded with vehicles of positive superheroes: Batman, Spiderman, X-Man, Y-Man, Z-Man, Whatever-Man… However equipment of bad guys are heavily underrepresented. Therefore, hereby we represent to MOCers community Bad Guys Escape Helicopter (BGEH). Both in Hollywood movies and in the reality bad guys/gangsters/dictators/politicians escape on their personal helicopter when moment of justice/revolution/NATO-bombing/IRS comes. So it is absolutely the first item on their shopping list spending stolen/taxpayers money.

BGEH is a twin engined, 4-seat, armed executive transport in 1:20 scale (Lego Belleville/Playmobil figure size) made of 1718 bricks featuring:
-          2-blade, semi-rigid Hiller-Bell type main rotor with folding blades
-          2-blade variable pitch tail rotor
-          Variable pitch elevator surface
-          Aerodynamic rotor blades with spar-and-ribs structure
-          6-channel twin controls connected into cockpit: cyclic pitch/roll, yaw, collective pitch, engine throttle, elevator
-          Twin M-motor electric drive
(all these features above are packed into a self-contained Light Helicopter Module)
-          Powered cargo ramp
-          Powered rescue winch
-          Four-barrel, belt-feed rotary gun in nose turret trainable with joystick from cockpit at -21..+26/-30..+30 degrees
-          Magazine with 100 rounds of ammo
-          Windscreen with mechanized windscreen wipers
-          Swing arm-mounted, lockable side doors
-          Lockable cockpit doors
-          Folding rear seats
-          Fully faired airframe
-          Battery pack loadable into emptied cargo space
See model and building instructions in Lego Digital Designer (LDD): BGEH With Guide
2.Basic idea
2.1.Building BGEH was inspired by work of several excellent MOCers:
(This part is technical and for heli builders with at least some experience. If you do not understand something, see: about basics of how helicopters work)
SgtPepper set up the mark for high-end Lego Technic helicopter modeling with his Aerospatiale Alouette II (about real, see: ) in 2008 with almost photo-realistic modeling of airframe in scale=1:14 (see: But it is also very functional with electric drive and 4 channel controls in cockpit.  Unfortunately it uses 2-blade main rotor instead of the original 3-blade with Lego swash plate drilled through allowing it sliding on main rotor axis for collective controls.

It is interesting because Wojtek already developed functional 3-blade rotor in his Aerospatiale Gazelle (see real ) in 2006, in scale=1:14, electric drive, 4 channel controls in cockpit (see ), but its fenestron (ducted fan) tail rotor left unfinished.

One of the finest fenestrons in Lego Tech heli industry can be seen at Samrotule’s Eurocopter Dauphine (see real ), 2003 in a some what larger scale=1:10, electric drive, 4 channel controls in cockpit,  (see: )
The closest model to my concept is Steph77’s Bell UH-1 (see real ) from 2012. He maintained reasonable material requirement using scale=1:18 (Lego Tech figure scale) at the price of less exact airframe. But he managed to model one of the mechanically most complex types of rotors, the Hiller-Bell, with electric drive, 4 channel controls in cockpit (see: )

In terms of airframe, I owe much inspiration to Darkenski’s Eurocopter EC145 (see real ) from 2011, in scale=1:18, electric drive. It has no real controls, but its creator met the challenge to model a modern heli airframe using large amount of composite materials and many CAD-designed curved surfaces  (see: )

2.2.Building BGEH was inspired by the following real helicopters:
There are 2 generations of German-originated helicopters with so high versatility that they are used „from tank attack to heart attack” (in roles from anti-armor to medical rescue) worldwide. I wanted to create similarly versatile and modular craft.

MBB BO-105 from 1967 (see ) was twice as expensive as contemporary light helicopters with the double capability.

MBB-Kawasaki BK 117/Eurocopter EC145 (see / ) from 1999. I was especially amazed by the Kawasaki-built version, which can have gun turret under the nose.
2.3.Innovations and advancements of BGEH compared to contemporary models:
(In the forthcoming technical description, functional parts of BGEH are referenced by numbers which can be found on cutaway drawings)
GOAL 1: First Lego heli with functional 6 channel twin controls: The models shown above had all 4 channel twin controls (2 cyclic, 1 collective, 1 yaw control). I added 5th channel of engine throttle  control by rotating knob (29) on collective lever (28) and 6th channel controlling tail elevator surface (86) by pitch component of yokes (30) position, just like in real helicopters.
GOAL 2: First Lego heli with aerodynamic rotor blades: In my vision, putting a studded bar in the airflow is funny, but only until you play with Duplo. I simply got fed up with that Lego cannot support us with reasonable rotor blades and come up with my solution: A structure of blade spar (50) and ribs (51) covered with duct tape, assuming that decals - which are regular parts in many Lego sets - could play more important role as cover of aerodynamic surfaces.
GOAL 3: Fully faired airframe: The usual, gridded-style look of Lego technic models looks nice at cranes, heavy machinery and early helicopters, but it is ridiculous at modeling streamlined, curved forms of modern heli airframes made of composite materials. So I decided that I will maximally utilize Lego Technic fairing panels to eliminate gaps, holes, steps, facets, etc. But the price was that I could not tie myself strictly to model an existing helicopter. Instead I created a mix from MBB BO105, Kawasaki BK117, and Bell Jet Ranger, but strictly adhering to real engineering principles.
GOAL 4: Put engines where they really are: Even at models with scale 1:14..1:10, Lego Technic electric motors are usually put „somewhere” in the airframe, and engines are fake. This has negative consequences: e.g. at Steph77’s UH-1, battery went in place of engines, so electric motor went in place of controls before main rotor mast, thus controls went into passenger deck, thus passengers most probably went into the sea. Therefore I tried to incorporate electric motors (61) in place of turboshaft engines.
GOAL 5: Windscreens and glazing: Most technic models usually do not have any windscreens or glazing. This is pretty OK. for a bulldozer, but modern helicopters with large curved, one-piece windscreens get a distinctive „burnt-out scrap” look without glazing. Fortunately, introducing Star Wars and other themes in Lego resulted in variety of windscreen and canopy elements we can use with some tricks in Technic.
GOAL 6: Modularity: At first, this seems empty marketing slogan, as Lego by default is modular. But it means that all stuff necessary for a twin engined electric helicopter with  6-channel twin controls in cockpit are incorporated into a self-contained Light Helicopter Module (LHM), with which you can build wide variety of helicopters.
GOAL 7: Reasonable materials requirement: I reduced the scale from 1:18 (Lego Tech figure scale) to 1:20 (Lego Belleville/Playmobil figure scale). As material requirement changes in average third power of the scale of the model it has definite positive effect on reducing costs. Even if whole BGEH consist of 1718 bricks, the LHM - which contains all vital parts of a helicopter – is made from only 628 bricks, avoiding any rare or exotic parts. 1090 bricks are spent on airframe, auxiliaries and armament… I paid the price of re-scaling in that I had to develop compact, simplified, but still functional structure at main- and tail rotors, which was challenging.
3.Light Helicopter Module (LHM)

See model in LDD: Light Helicopter Module

The purpose of LHM is to pack ALL FUNCTIONALITY (except battery) of a twin-engined, electric driven  Lego technic helicopter with 6-channel twin controls in cockpit into a self-contained unit made of 628 bricks. With its help, you can create helicopter from almost any light land/sea vehicles, replacing their roof with LHM, if they have at least 10 studs long × 9 studs wide × 9 studs tall internal space to accommodate cockpit and controls. To support this, creating LHM I intentionally avoided using any exotic/rare bricks: material requirement of core components can be found at almost anyone’s brickshelf. Let’s see its functions more detailed:

See dynamic systems in LDD: BGEH Dynamic Systems

3.1.Main rotor

To understand why building a compact Hiller-Bell type main rotor was a big challenge, we have to see through types of helicopter rotors very shortly:

3.1.1.Bell-type rotor

We show an example of the most simple helicopter rotor at SgtPepper’s Alouette II: Rotating part of swash plate (black) is directly linked to variable pitch rotor blades with pitch rods and ball joints (marked with red and yellow). Usually, between these rods there is a small scissor-jack keeping rotating part of swash plate aligned with main rotor mast, while still enabling swash plate lower/raise vertically on main rotor mast for collective control. Static part of swash plate (grey) is linked to:
-          its rotating part with a large diameter bearing,
-          to main rotor mast with a central ball joint, which can also slide on main rotor mast
-          to collective and cyclic control rods (dark grey and black) with ball joints

SgtPepper used here the Lego Technic swash plate part, which has several problems:
-          It is bulky (6×6 studs) resulting large rotor hub with 8 studs diameter and 13 studs tall
-          It is not designed to serve as swash plate, but to tilt rotor as one monolith unit around main rotor mast, which is practically unworkable and misleading. A real swash plate has ball joints of both static and rotating part in one plane

-          Moreover, it cannot slide easily on main rotor axis so poor MOCers have to drill it enabling collective control, which is not really Lego-compatible move.
The same functionality of Bell-rotor can be achieved with much more simple and compact structure, if we omit Lego swash plate. The example is my earlier model, the oTo Helichopper ( rubber band (8) acting as a torsion spring gently forcing blades into zero degree pitch relative to each other. Thus red pitch rods jacking on yellow hinges are pressed down to swash plate. Swash plate here is a flat, non-rotating plate can be tilted and lifted around main rotor axis by sliding cardan-hinge. A 6-hole disk fixed to main rotor axis drives pitch rods, whose lower tip slides on swash plate, thus we do not need any bearing. When swash plate is lifted or tilted, pitch rods will increase blade pitch from zero against the force of torsion spring. Rotor hub has 3 studs diameter and 5 studs height (all the extra stuff outside this are to make blades foldable). Quite a difference.
The general advantage of Bell-rotors is simplicity, the disadvantage is lack of any automatic stabilization, so it is very demanding on piloting skill or requires difficult avionics
3.1.2.Hiller-type rotor
A somewhat more complex rotor using Flybar stabilizator (as an example, see my earlier Light Assault Helicopter model: ). Flybar (grey rod) is a pendulum-like device fixed with cardan-hinges to main rotor axis transversal to rotor blades. It tries to keep its original plane of rotation because of its gyroscopic torque in case the helicopter is tilted by disturbances in airflow. Changing the cyclic pitch of rotor blades through control rods, it counterbalances tilting. In Hiller system, the pilot can shift only the plane of rotation of flybar with collective and cyclic controls through the swash plate, and only the flybar controls main rotor blade pitch. It has the advantage of increased stability over the Bell-rotor, its disadvantage is less responsive control.
3.1.3.Mixed Hiller-Bell rotor
Thus, there is a mixed system called Hiller-Bell, which results in stable AND responsive, but mechanically more complex rotor. We show Steph77’s UH-1 as an example: here BOTH flybar and rotor blades are linked to swash plate with rods and ball joints to mix manual input from pilot and gyroscopic torque of flybar in blade pitch control. However, there is a nasty difficulty: swash plate makes relatively big vertical movements in collective pitch control compared to fine correction movements of flybar. Thus, while blades are connected with swash plate with simple straight rods (black) flybar can be connected with swash plate only with a complicated jacking mechanism (light and dark grey) compensating vertical swash plate movement and aligning rotating part of swash plate to rotor blades. This is the weak point in Lego Technic where minimal cross-section of any parts is 1 stud: both for main rotor mast and small jacks, which are at least 5 times thinner in reality. So the rotor hub will be quite bulky: 9 studs diameter and 14 studs height.
At BGEH I created simplified Hiller-Bell main rotor with lifting flybar: swash plate (39) is a flat plate with a hole in the middle letting through main rotor mast (45). It can be tilted in any direction by cyclic swing arms (38) and pushrods (24), and lowered/lifted by collective lever (18). Flybar (40) is lowered/lifted together with swash plate, because 2 rollers built in flybar hub (43) roll on that. Flybar can be tilted in any direction around main rotor mast (45), which has an ½ Bush closely rounded by flybar hub components. This solves centering flybar on main rotor mast. Leading slides (41) and leading swing arms (42) keep flybar strictly transversal to rotor blades, but allow its all necessary tilting and lifting movements. Plane of rotation of flybar hub (43) is influenced:
-          Partly by manual cyclic and collective input from swash plate (39) through rollers.
-          Partly by gyroscopic torque of flybar masses (40).
Blade pitch rods (44) are linked to flybar hub (43) offset from its centerline, so they are mixing manual - flybar torque input in proportion 60% - 40%. This solution eliminates the need of complicated jacking mechanism between flybar and swash plate consisting of small parts. Therefore, main rotor hub can be more compact: 8 studs diameter and 7.25 studs tall.  Blade pitch rods (44) change the pitch of blade locking sleeves (46), which nest the inner end of blade spars (50). Rubber tie (48) acts as a torsion spring gently forcing blades into zero degree relative pitch. This way, rollers of flybar hub (43) are pressed down against swash plate surface (39) through blade pitch rods (44). When swash plate is lifted or tilted, it will lift/tilt flybar against the force of torsion spring, and flybar will increase blade pitch from zero through pitch rods. Blades can be folded into storage position around blade folding hinges (47) disengaging end of blade spars (50) from blade locking sleeves (46).

3.1.4.Aerodynamic rotor blades
Rotor blades are the most controversial part of my design. I simply got fed up with that Lego cannot provide us reasonably aerodynamic rotor blades. They introduced specialized rotor blade component at set 8046 in 2010 but they put studs in the middle of it making it pretty ridiculous.

Building bigger blades from studded plates and flat tiles gave trouble to every MOCer. E.g. SgtPepper wrote that blades of Aerospatiale Alouette II were too heavy, even using 2 instead of 3…
Therefore I created structure of blade spar (50) made of the longest Technic rod (32 studs) part and blade ribs (51) 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.
-          Most duct tapes are 48mm (2in) wide, so they can be applied to 3 studs (24mm, 1in) wide blade ribs in 2 strips: Strip A is stickled first by its half-line to trailing (rear) edge of the blade, and bent forward gently to ribs. Strip B is stickled second by its half-line to leading (front) edge of the blade, and bent backward gently to Strip A and ribs. This way sticking upper and lower half of cover can be avoided by the elasticity of the tape.
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.
-          They are cheap and comply children safety rules as long as they are not enough big that kids can strangle each other with that
-          Larger areas of cover can be stickled together from smaller standard parts
-          Duct tape material technology made serious improvement in recent years using high tensile strength plastic foils, water-resistant glues, sticky surfaces renewable with simply washing it with detergent, stretchable foils keeping their shape, etc.
-          Combining decal covering with stiff/elastic rod structures would provide excellent modeling tool for real world’s welded steel/Dural tube structures covered with glass/carbon fiber reinforced resin: e.g. most racing cars, rigid wing aircrafts, hovercrafts, light ships, etc.
-          Mildly curved surfaces e.g. windscreens of cars/planes could be modeled with ease
(And Dear Lego Guys, when you will design the next “bionic eye” part for future Godzilla/ Tyrannosaurus/ Alien/ Lady Gaga sets, can you accidentally use the shape of NACA 712A315 aerofoil, thanks.)
3.2.Tail rotor
It is a simple two-blade construction, where blades (67) have the same structure as main rotor blades. Blade pitch rods (66) are connected with an assembly which has 4 ears (65) and can slide on tail rotor shaft (120) left and right changing blade pitch. This slide is controlled by pitch control lever (63) which forces a roller (64) in the gap between the ears (65). Tail rotor is protected from hitting the ground by a Bell Jet Ranger-style vertical stabilizer surface.
3.3.Transmission and engines
Main rotor is geared to tail rotor at 36:100 ratio in two-step reduction gearing assembled from Z12 and Z20 conical gears (111, 112). Two M-sized electric motors (61) are geared to main rotor 1:1. This is because M motors already have built-in reduction gearing, and two of them have enough total torque to drive main rotor 1:1. (But, in case of using motor without internal reduction gearing, gearing ratio can be changed to 36:100 easily just switching the Z20 conical and Z12 half-conical gear with each other at the motor.) Motors are connected with main rotor reduction gearing through short (2 studs) cross-axles, which have two Z12 half conical gears, this leaves 1 stud gaps between main rotor assembly and engines. It is usual gearing layout at real battle helicopters (e.g. AH-64 Apache), because the distance between engine and main rotor reduction gearing prevents single explosive shell taking out both of them in the same time. At LHM, I use this 1 stud gap to lead control rods of yaw (23), elevator (87), 2 engine throttles (26, 91) lead through from forward to back side of main rotor in a compact way. Without the gap, it would be troubleful.
(Note: handles of functionally working controls are built in yellow color in the model.)

With the trick described above, I could solve all controls with control rods avoiding usage of control wires. SgtPepper at Alouette II and Steph77 at UH-1 used wires for yaw control, as the real aircrafts use them. I also used them at my previous model oTo Helichopper but their usage proved very troubleful in Lego Technic. Parts made of ABS easily twist and bend when control wires are correctly tensioned making them loose and useless.
3.4.1.Channel 1-2: Cyclic pitch/roll
Tilting twin yokes (30) are synchronized by roll synchronizer rod (30) and pitch synchronizer shaft (124). It will change position of lower cyclic control swing arms (131), which transmit control through ball joints (108) to lower cyclic control pushrods (130). These will rotate cyclic swing arms (21) through cyclic control hinges (132). Cyclic swing arms will push/pull upper cyclic control rods (24), which will tilt swash plate (39) through its swing arms (38).
3.4.2.Channel 3: Yaw control
Yaw control pedals (31) move yaw control sliding block (121), making lower yaw control rod (123) sliding forward/backward through slide (122). This moves small yaw control swing arm (126), which is fixed on a cross-axle in the cushion part of the left pilots seat together with medium yaw control swing arm (127). It moves vertical yaw control pushrod (129) through ball joint (128). It moves upper yaw control swing arm (22) through yaw control hinge (133). The swing arm moves upper yaw control rod (23) through a ball joint. Upper rod (23) will transmit yaw control to the tail to tail rotor pitch lever (63).
3.4.3.Channel 4: Collective pitch
Raising collective control lever (28) will rotate it around its pivot (125), pulling downward a 2-part collective pushrod (18, 109). It will raise collective lever (18) rotating it around its pivot (20). Collective lever (18) will lift swash plate (39), and flybar (40), which will increase blade pitch collectively.
3.4.4.Channel 5: Engine throttles
Turning throttle control knob (29) on collective control lever (28) will rotate lower throttle swing arm (107), which will move upper throttle swing arm (89) through a vertical pushrod and its ball joints. This swing arm will turn engine throttle pivot axis (135), where there are two smaller swing arms (25, 107) fixed on its both ends. Small swing arms will move upper throttle control pushrods (26, 91) both for left and right engine. Pushrods move engine air intake nozzles (60) for throttle control.
3.4.5.Channel 6: Elevator pitch
Vertical elevator pushrod (101) is linked to lower swing arm of right yoke (131) to receive pitch component of yoke’s movement. Pushrod (101) will move upper elevator swing arm (88), which moves upper elevator pushrod (87) through a ball joint. Pushrod (87) transmits elevator control to tail, changing pitch of elevator surface (86).
I tried to create streamlined, faired and lightweight airframe, maximally utilizing Technic fairing panels and flexible rods, and Star Wars windscreen elements
4.1.Windscreens and wipers
Windscreens are made from part „Screen bowed 4×8×2” connecting them with part „Fric/stump with crosshole” to Technic airframe structure. Windscreen wipers were inspired by Darkenski’s EC-145. There wipers are static and do not follow lines of windscreen very well.
Therefore, I placed a mechanics for them from two Z16 gears at the front edge of head instrument panel, which ensures correct movement of elastic wiper arms.
4.2.Cockpit doors
They are the weakest part of my design as I could not find any glazing matching their shape. Part „Gate 4×8” has correct size and half-rounded shape, but it is not available in transparent color. Part „Door for wall element” available in transparent, but it is too long. Of course I could cover cockpit doors with transparent duct tape any time, just like rotor blades, but it would be too easy solution without challenge. To compensate my reluctance, I equipped cockpit doors with lock, inner- and outer opening knobs (82, 117), and rear view, truck-style side mirrors (118) (they are used to check rotors and rescue winch crane during flight). (Note: at top corner of doors, there should be part „angle element 0 degrees”, just LDD could not match it with flexible frame, even using flex and match tools. Pity. In the reality, of course it is not an issue.)
4.3.Side cargo doors
See model with doors open and blades folded in LDD: BGEH Doors Open
In the reality, most helicopters have side cargo doors backward sliding on rails. However, this is a trap in Technic, as minimal thickness of any door built from more parts is 1 stud. So it will create a very nasty and disproportional 1 stud step on the side of a 9-11 studs wide cabin as we can see it at Darkenski’s EC-145:
Therefore, I placed 8×11 stud sized side cargo doors on 6×2 stud, L-shaped swing arms (57), which can rotate 180 degrees: when they are in forward position, doors are locked, PERFECTLY IN LINE with cabin wall, and cushioned top of swing arms serve as arm stands for back seats. When swing arms are backward, they extract side doors from cabin wall 2 studs and move them backward 10 studs. Each cargo doors have two „train windows” and between them there are latch-type door locks with inner and outer opening ears (99)
4.4.Cargo ramp
Light and medium sized helicopters usually do not have lifting cargo ramp, just 2 streamlined „clamshell doors” made of glass fiber reinforced resin. However, modeling clamshell doors in Technic is troubleful as we can see in Darkenski’s EC-145: there are quite a gaps around door where poor rescued guy and its casevac can fall off in sharp turns…

Therefore, I decided to build a two-piece, liftable, powered cargo ramp, which is mechanically more challenging than clamshell doors, but it can be faired easier with existing Technic panels. The ramp consists of two jacking pieces, the larger lower (71) and the smaller upper (72) part to better follow streamlining of the end of the cabin. Ideally, ramp should be lifted by a separate electric motor, but even the smallest type of Technic motor is too bulky and heavy for this – we have not enough space there. Therefore lower shaft of tail rotor reduction gearing (112) is extended backward and continued in an universal joint (113). This transmits drive to a ½ conical gear (114), which can slide on a short axle, forced by lift drive clutch lever (116) and pushrod (73). When the pushrod is pressed backward (accessible from left rear seat), gear (114) is connected with lifting gear and axis (115), which has ramp lifting hinges (74) at its right and left ends. Rotating 2 hinges pull 4 swing arms of ramp parts (75) through 4 pushrods (76) and ramp is lifted. Ramp lock rod (95) has a hook catching the left hinge (74), locking ramp in closed position. Pulling ramp lock rod to the left (accessible from right rear seat), the hook disengages, and ramp parts go down in line with cargo space floor by their own weight.
The big challenge in building this was that lifting mechanism could be 1 stud wide on both sides to preserve 7 studs × 6 studs maximal cargo gauge using the ramp. The maximal cargo size can be loaded with ramp lowered is 7 studs wide × 6 studs tall × 24 studs long. Such an oversized cargo can be fixed to hooks (140) on ramp floor. When ramp is lifted, main cargo area can still accommodate cargo 7 studs wide × 7 studs tall × 11 studs long, as side doors have bigger maximal gauge than the ramp.

See model with empty deck in LDD: BGEH Empty Deck
4.5.Rescue winch
It is nearly the same story as cargo ramp: powering it would require a separate electric motor, but there is not enough space for that. So winch gets its lift/lower drive connecting left/ or right ½ conical gears (92) placed on spool axis with a swing arm to forward stage of tail rotor reduction gearing (111). This device eats only 1 studs space on main cargo space roof. Rope is lead from winch to crane arm (93) between throttle control rods (91) of right engine, which has rollers to drive rope. Crane arm (93) can be rotated 90 degrees above cabin roof to reduce drag when it is not used.
4.6.Toilette module

Most bad guys/gangsters/dictators/politicians consider themselves immortal gods, or at least semi-gods who can do anything without any consequences. So they won’t eat, wear, drink what ordinary people do. And they will not use public restrooms… Therefore a decent personal helicopter should provide all these amenities on luxury level. Toilette module is a lightweight structure can be easily fixed and removed from main cargo space floor including toilette (54), hand wash basin (53), cabinet (52), entrance door (98). On the outer wall of the module facing towards back seats (56) has LCD TV (55) (made from part „train window”, whose back is covered with parts „container door”), intercom (100) and A/C unit (96). When toilette module is installed on cargo space floor, it locks left cargo door in closed position. So one cannot suddenly open it revealing the „big man” in desperate need… Toilette outer window has darkened glazing, but it is still the toilette with the greatest view on the face of the Earth.
4.7.Folding back seats
The primary motivation behind torturing and massacring ten thousands of innocent people - regularly made by bad guys - is to accumulate enough money and power to hunt down most expensive girls and top models. (e.g. Kaddafi’s amazon bodyguards, Silvio Berlusconi’s unga-bunga parties, Saddam’s lovers, etc.). Or, hunt down not-so expensive girls, after lot of alcohol (e.g. Dominique Strauss-Kahn). A personal aircraft – as a symbol of status and power – can be an excellent device for womanizing activity if it provides discrete environment (e.g. Catherin Hepburn and Howard Hughes in PYB Catalina hydroplane in the movie Aviator). Therefore, back seats can be folded backward to create double bed releasing locking handles (58) and flipping down locking ears (59). Still with this help, life can be a boring routine for bad guy’s girlfriend aboard BGEH: morning – poison gas bombing of a rebel mountain village, noon – skiing in Swiss Alps, evening – cocktail party with celebs in Hamburg. To create some excitement, lid of toilette (144) is foldable and toilette paper roll (145) is rollable, providing excellent battlefield for women’s hysteria.
4.8.Placement of battery pack

See model with battery loaded in LDD: BGEH Battery Pack Loaded
Lego Technic battery pack is too bulky and heavy to build in fixed somewhere in the airframe in scale 1:20. It would totally destroy styling. But BGEH can carry it as cargo when cargo deck is cleared. I will wait with integration of battery pack into the structure until Lego develops more compact, light, higher capacity and rechargeable Li-Po battery pack. This way, they could reach at least the technology level of cheap mass-produced Chinese mobile phones…
4.9.Fuel tanks
In the reality, kerosene fuel of turboshaft engines is stored in the 2 large hollow spaces (2×7×11 studs) of cargo deck floor and lower cargo ramp floor can be filled trough cap (139).
4.10.Landing skid
In most Lego Tech heli models landing skids are parallel with plane of main rotor disk area. However in the reality, cabin and rotor is put on skids somewhat backward tilted to make autorotation crash landing easier. I used  3.75 degrees backward tilting on skids (35) at BGEH. Moreover, it is important, because rear end of cargo ramp can touch ground, when lowered in level with cargo deck floor. This makes loading and unloading easier.
Sooner or later, moment of justice/the good guy/revolution/the next bad guy comes for every bad guy, when survival depends on BGEH. Don’t repeat the mistake of Fantomas, who built a jet-powered, flying Citroen DS-19, but forget to put there any armament. Pity.
5.1.Four-barrel 12.7mm(0.5in) rotary gun in nose turret

See gun turret in LDD: Nose Gun Turret
This gun is modeled after the Russian diminutive of the famous American M61 Vulcan 6-barrel rotary gun, which was used in Mil MI-24 battlefield helicopters. It is little bit oversized for a light helicopter. I paid the price of it in limited arcs of fire (-21..+26 degrees vertically and -30..+30 degrees horizontally), but creating it was challenging. Belt of 12.7mm (0.5in) ammo is modeled with motorcycle chain parts (Note: In LDD, this type of chain cannot be twisted, but it tolerates that pretty well in reality). To save space, I omitted parts of gun behind its rotor (151): bolts, springs, catches, etc. Gun turret can be controlled with joystick from cockpit through laying pushrod (152), which rotates trunnion directly. Training is made by training pushrod (153) rotating training lever (7), which drives training transmission gear (105) through rotating axis of trunnion. Gear (104) rotates training gear of gun (105). Behind fixing hardpoints of turret (154) there is a magazine for belt of 100 rounds (106). Belt is extracted from magazine by extractor gear (155) and received at gun by receiver gear (5), which is driven by gun rotor (151). This type of gun has firing rate of 4000 shots/min in the reality, so it can empty the whole magazine in a 1.5 second-burst, but I had no more space for magazine, and motorcycle chain is not very compact.
5.2.Six TOW missiles
TOW stands for Tube-launched, Optical-targeted, Wire guided anti-armor missile developed by Hughes Aircraft in 1971 and continuously improved since that. Its advantages are relative cheapness and accessibility. As it is re-engineered and manufactured by Iran also, it is an everyday commodity on illegal weapons market for bad guys. As the missile is controlled during its flight by electric signals traveling on a double piano wire spooling down from a coil, it is relatively safe against Electronic Counter Measures (ECM). Disadvantages are limited range by wire (max. 3750m), limited speed to prevent tearing the wire (187m/sec in average) , limited armor piercing (630 mm) by 3.1 kg HE warhead, and the biggest one: launching platform has to keep target in line of sight during whole flight time of missile (max. 20secs) being an easy target itself for AA guns. Its semi-automatic optical guidance requires a gyro-stabilized periscope sight (15) with an ocular (85). At helicopters it is usually placed at cockpit roof, this way at least the cabin of the helicopter can be behind some cover during targeting. Modeling the missile launch tubes (80) in scale 1:20 was not an issue, as their real diameter (0.15m, 6”) matches pretty well with 1 stud diameter-tube parts.
Missile weapons can be attached to retractable side weapons consoles (79) on both sides. When they are employed, they lock side cargo doors in closed position, but cargo deck is still accessible through cargo ramp.
5.3.Two Hellfire missiles
Hellfire is a more modern and potent fire-and-forget weapon with semi-active laser homing produced by Lockheed Martin. Thus, it is much more hard to access for bad guys. I included it because of modeling challenge: the missile is launched from short rails, and I wanted to solve it as it is. The key was „Tacho 8”, an 8-winged stabilizator-like part (161), which has small T-hooks at the end of wings. These hooks can go between rails of „1×2 plate with rail” parts (162) in the reality, even if LDD cannot handle this. The difficulty was that rails had to be spaced in a distance, which did not match any standard Lego part size. Therefore, I hanged assembled rails with parts „1×1 plate with holder” on 4-stud cross-rods named „Lightsword” (165). This way, gap between rails can be freely adjusted to safely hook missiles (97) by T-hooks.
6.Dimensions of BGEH:
Main rotor diameter: 69 studs/ 552mm/ 21.73” in real size: 11.04m / 36’ 2.36”
Main rotor disc area: 3739.28 sqstuds/ 0.239sqm / 370.93sqinch in real size: 95.72sqm/ 1029sqfeet
Tail rotor diameter: 16 studs/ 128mm/ 5.04” in real size: 2.56m / 8’ 4.72”
Tail rotor disc area: 201.06 sqstuds/ 0.013sqm / 19.94sqinch in real size: 5.147sqm/ 55.33sqfeet
Distance between main- and tail rotors: 39 studs/ 312mm/ 12.28” in real size: 6.24m / 20’ 5.51”
Height: 25.25 studs/ 202mm/ 7.95” in real size: 4.04m / 13’ 2.95”
Cabin size: 11studs/ 88mm/  3.46”wide × 12studs/ 96mm/ 3.78”  tall × 44studs/ 352mm/ 13.86”  long in real size:  1.76m/  5’ 9.25” wide ×  1.92m/  6’ 3.54” tall ×  7.04m/  23’ 0.98”  long
Largest loadable cargo size (with lowered cargo ramp): 7studs/ 56mm/  2.20”wide × 6studs/ 48mm/ 1.89”  tall × 24studs/ 192mm/ 7.56”  long in real size:  1.12m/  3’ 8.07” wide ×  0.96m/  3’ 1.77” tall ×  3.84m/  12’ 7.09”  long
Minimal storage space of BGEH with folded blades, without armament: 15 studs/ 120mm/  4.72”wide × 26.25 studs/ 210mm/ 8.27”  tall × 73 studs/ 584mm/ 22.99”  long in real size:  2.40m/  7’ 10.43” wide ×  4.20m/  13’ 9.25” tall ×  11.68m/  38’ 3.54”  long
7.Unsolved problems and shortcomings
- There is only one collective lever/throttle control for 2 pilots, so one of them should be left-handed: This was not because technical limitations, but I wanted to keep 9 studs internal gauge of cockpit. Wider cockpit can be done with twin collective lever.
- Cyclic and collective controls are interlinked: changing collective pitch will influence cyclic pitch also and should be compensated on yokes. This is because there was not enough space for 4 dislinker levers in the already crowded controls housing. It is the price of the 1:20 scale.
- Tail rotor is too close to main rotor and too close to ground, and disturbs usage of cargo ramp: Bell Jet Ranger-style straight tail boom should be replaced with angled tail boom and universal joint on tail rotor transmission shaft, even it will increase minimal storage size.
- There are no flapping hinges and yaw dampers in main rotor. BGEH is already too big and too heavy using semi-rigid rotor.
- Correct gearing ratio between main- and tail rotor should be 10:100 instead of 36:100
- There are no centrifugal clutches between engines and main rotor gearing, which would prevent stalling engines destroying inertia of the autorotating main rotor.
- Gearing ratio of cargo ramp lift and rescue winch is insufficient: both of them should use clutchable worm drive, but there was not enough space for that.
- Cargo doors can flip-flop in rotor downwash when their swing arms left half-open: there was not enough space left for secondary swing arms securing it.
- Cargo ramp tends to jam at lowering, when there is not enough weight on that
- Cockpit doors have no glazing.
8.Building guides
See building guide: BGEH With Guide
Complexity of BGEH put guide-generating algorithm of LDD on hard testing. This algorithm most probably starts from center of gravity of the model, and seemingly tries to group similar parts in each others proximity into sub-modules. Also it seemingly checks collisions of sub-modules during assembly at some level, but no fully. However, the fully faired design confused up it totally:
- First, during 370 steps, it builds all the internals of the helicopter, then puts it aside.
- Second, it builds up the „empty skin” of fairing elements in more than 200 steps.
- In the final, 618th step, it tries to pull the whole „skin” on internals in one step, just like a robe, which is funny, but totally impractical. You may use the building guides of sub-models (e.g. LHM) instead of this.
The idea of this twin-engined, twin-controlled helicopter is born on the same day as my twin sons – Daniel and Szilard – so I recommend it to them.
10.To be continued…
My next Lego Technic heli has 6-blade main rotor with 148 studs (1.18m, 3’10”) diameter. So stay tuned…