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Fully Functional Foldable Bionicle Backpack Helicopter
With 2-blade, foldable Bell-main rotor, foldable variable pitch tail rotor, foldable 4-channel control levers, 2-cylinder engine, retractable landing gear, M-4 assault rifle, CGL grenade launcher, RPG launcher, Scorpion submachine gun (all shooting spring-driven), Bionicle pilot, in scale 1:10
About this creation

Figure 1: Bionicle Backpack Helicopter functions overview
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See model in LDD

1 Introduction

Designing functional foldable backpack helicopter for special forces is one of the toughest challenges both in real engineering and in MOC building. Real historic designs (you can find an excellent summary of them at Unicopter site
) from the very first Baumgartl Heliofly 357, 1942, Austria to recent GEN H-4, 2012, Japan usually preferred some form of rigid coaxial rotor with limited steering to eliminate the need for tail rotor. I also designed a sizeable Coaxial Personal Aerial Vehicle MOC earlier. Coaxial systems have the inherent disadvantage of higher complexity and doubling the heavy main rotor, which is critical if one has to hold it with shoulder, especially at hard landing. Therefore, the challenge was on to design more compact single rotor Bionicle Backpack Helicopter (BBH) with foldable but robust tail rotor. We achieved this placing the 2-cylinder engine and its fuel tank exactly under main rotor mast, so weight of the pilot is offset by the variable-pitch folding tail rotor reinforced with double booms and girder strut:


Figure 2: Bionicle Backpack Helicopter left cutaway view
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When BBH is folded, retracted landing gears serve as wheels of the ‘Granma’s shopping pulley’-like bag can be put in a large sized bonnet:


Figure 3: Bionicle Backpack Helicopter folded
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See model in LDD

2 Action screenshots of BBH

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


Figure 4: Bionicle Backpack Helicopter attacks Diver Delivery Vehicle in night raid
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Figure 5: Bionicle Backpack Helicopter takes off from Commando Hoverboat
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Figure 6: Bionicle Backpack Helicopter front view
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Figure 7: Bionicle Backpack Helicopter back view
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Figure 8: Bionicle Backpack Helicopter left view
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Figure 9: Bionicle Backpack Helicopter right view
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Figure 10: Bionicle Backpack Helicopter top view
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Figure 11: Bionicle Backpack Helicopter bottom view
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Figure 12: Bionicle Backpack Helicopter standby view
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3 Dynamic systems of BBH

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

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

***Parts of BBH are color-coded by their function:
- Yellow: Manual handles of working functions
- Gray/Black: Static parts
- White: Dynamic parts
- Blue: Harness/seat of pilot
- Red: Triggers of weapons

3.1 Drivetrain

The tricky part in designing drivetrain was that main rotor, engine, tail rotor transmission and cooling ventilator should be connected/reduced with minimal amount of gearing because of lack of space. Moreover, 2-cylinder, 2-stroke, air-cooled engine is placed directly beneath main rotor mast in vertical position. The solution was to use a ‘Z24 Crown gear’ (E7) to connect all four above, and allow reducing engine rpm for main rotor. It is used as both beveled and straight toothed gear. Tail rotor is de-clutched in folded position simply lifting up Z8 pinion gear (E9) from crown gear (E7).


Figure 13: Bionicle Backpack Helicopter drivetrain
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3.2 Collective blade pitch control

Because of the very limited space, we could not use the TLG part ‘Swashplate’ part with its bearing, gimbal and ball joints. Instead of it, semi-rigid rotor blades made from ‘Bionicle sword 16M’ are gently forced to keep zero degree pitch by a torsion spring (R2) made from ‘Rubber damper 2×1×1’. Swashplate (C1) here is just a plain plate with a hole in the middle, letting through main rotor mast (R9). Swashplate and can be tilted/lifted around main rotor mast by 1 central collective hinge (C4) and 2 corner-positioned cyclic ball joints (C2), while aligner pin (C3) prevents it rotating together with main rotor. Swashplate pushes blade pitch pushrods (R6) by their lower tip, increasing pitch of the blades by blade pitch arms (R5) against the force of torsion spring. Blade pitch rods are aligned by disc (R8). This is how we eliminated the need for large diameter bearing in swashplate.


Figure 14: Bionicle Backpack Helicopter collective blade pitch control
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See model in LDD

Collective control is done by a foldable lever (C10) incorporated with engine throttle (C14) held by right hand, just like at big helicopters.
Main rotor blades can be folded 90 degrees downward around blade folding hinges (R4). When blades are open, they are fixed by elastic blade locking sleeves (R3) made from ‘Rubber damper 2×1×1’. When blades are folded down, they are locked by folded control levers.

3.3 Cyclic blade pitch control

As usage of a centrally mounted yoke would be highly impractical at a backpack helicopter, cyclic control of main rotor is done by left/right cyclic levers (C15). Their combined movement can perform the same functions as a yoke, changing attitude of swashplate (C1) by cyclic ball joints (C2), while center of the swashplate is supported by collective hinge (C4) from the bottom, against the depressing force of torsion spring (R2) transmitted by blade pitch rods (R6). This mechanism is mechanically less effective than a real collective-cyclic mixing linkage, but performs its basic functions and it is more compact and simple (I hope that this time Henrik will understand it…).


Figure 15: Bionicle Backpack Helicopter cyclic blade pitch control
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3.4 Yaw control

A backpack helicopter cannot have yaw control pedals, therefore pitch of tail rotor is controlled with left hand holding foldable yaw control lever (C16). Yaw control is transmitted through a foldable linkage.


Figure 16: Bionicle Backpack Helicopter yaw control
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We can see summary of 4-channel controls on the next figure, performed by coordinated movement of left/right foldable control levers:


Figure 17: Bionicle Backpack Helicopter control schema
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3.5 Landing gear

In Hollywood movies, pretty female FBI superagents wear backpack helicopter, very-very BIG GUN and sexy high heel booties together with ease. In the reality, weight of a fully loaded BBH is around 80kgs +pilot +weapons, totaling up to 200kgs. It should be stopped and carried by human legs, even at bumpier autorotation crash landing… One can see that it is physically impossible. Therefore I designed simple, compact retractable landing gear carrying bulk of the weight besides pilot’s legs.


Figure 18: Bionicle Backpack Helicopter landing gear
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3.6 Harness

Pilot’s seat with safety belt has considerable size compared to a backpack helicopter. Therefore I designed it as a harness unit fast detachable from BBH, reducing its folded size. Moreover harness staying on pilot is useful carrying weapons, ammo, survival kit, field UHF radio as infantry gear.


Figure 19: Bionicle Backpack Helicopter harness
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4 Armament of BBH

A backpack helicopter is pretty useless, if it cannot carry small arms used by special forces: assault rifle, submachine gun, grenade launcher, RPG, spare magazines and grenades. Weapons should be portably fixed, and as close to main rotor mast as possible, to have minimal effect on Center of Gravity (COG). Even if a backpack helicopter is not a very steady firing platform, M-4 assault rifle and 160mm RPG can be fired during flight with trigger buttons placed on left/right cyclic levers (C15) for the sake of self-defense. Pilot has helmet display getting live picture from M-4’s optical sight enabling in-flight targeting. When BBH is folded, all weapons and spare ammo is removed for the sake of compactness, and pilot can carry them fixed on harness staying on his torso. All weapons can shoot, storing their energy with the help of 1×2 stud propellant springs disassembled from TLG part ‘Shock absorber extra hard’. As LDD cannot draw steel springs, we replaced them with similar sized and shaped ‘Corrugated pipe 2M’ parts in LDD models.


Figure 20: Bionicle Backpack Helicopter armament
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See model in LDD

4.1 M-4 assault rifle with CGL grenade launcher

M-4 is an assault rifle with 1.6×48mm barrel, rotating bolt made from TLG part ‘Rapier’, driven by 2 propellant springs, auto-loaded from 9-round box magazine for 1.6×7mm cylindrical projectiles. (TLG does not produce such a small parts because of children safety reason, but projectiles can be made from 1.6mm copper electric wire). Two halves of box magazine and projectiles are held together by rubber band when it is not loaded in the weapon (LDD cannot draw rubber band deployed). Auto loader arm depressed by advancing bolt uses the torsional flexibility of ABS parts to advance box magazine by its magazine catch into next position. M-4 has CGL cradle grenade launcher using 2 propellant springs and 1 round 8×63mm spigot-type grenade.


Figure 21: Firing cycle of M-4 assault rifle with CGL grenade launcher
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4.2 160mm RPG-launcher

16×72mm RPG-projectile is a self-contained unit, having a spigot at its end. It compresses 4 propellant springs held by trigger arm. Rear end of the spigot is held by ‘Rubber damper 2×1×1’ parts, when RPG is loaded. The portable launcher is merely 4 parallel launch rails, without any special mechanics. The reason of this ‘pseudo-barrel solution’ is that TLG does not produce any reasonable thin walled barrel part to prevent modeling working up-to-date weaponry… Technically, real RPGs could be made this way, but jet blast would roast personnel to death during shooting.


Figure 22: Firing cycle of 160mm RPG-launcher
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4.3 Scorpion submachine gun
Building shooting, auto-loaded pistol/ compact submachine gun in scale 1:10 from Technic parts is almost impossible, and has no practical relevance. It’s just show of building virtue to squeeze some very limited working from totally unsuitable TLG parts in such a small size.


Figure 23: Firing cycle of Scorpion submachine gun
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See model in LDD

5 Dimensions of BBH

Main rotor diameter: 39.00 studs / 312.00 mm / 12.28 in, Real size: 3.12 m / 10 ft 2.76 in
Main rotor disc area: 1194.59 sqstuds / 764.54 sqcm / 118.50 sqinch, Real size: 7.65 sqm / 82.19 sqfeet
Tail rotor diameter: 7.00 studs / 56.00 mm / 2.20 in, Real size: 0.56 m / 1 ft 10.04 in
Tail rotor disc area: 38.48 sqstuds / 24.63 sqcm / 3.82 sqinch, Real size: 0.25 sqm / 2.65 sqfeet
Distance between main- and tail rotor axis: 17.00 studs / 136.00 mm / 5.35 in, Real size: 1.36 m / 4 ft 5.51 in
Clearance under main rotor: 27.00 studs / 216.00 mm / 8.50 in, Real size: 2.16 m / 7 ft 0.98 in
Lenght: 30.50 studs / 244.00 mm / 9.61 in, Real size: 2.44 m / 8 ft 0.00 in
Lenght folded: 10.00 studs / 80.00 mm / 3.15 in, Real size: 0.80 m / 2 ft 7.48 in
Width folded: 11.00 studs / 88.00 mm / 3.46 in, Real size: 0.88 m / 2 ft 10.63 in
Height: 28.00 studs / 224.00 mm / 8.82 in, Real size: 2.24 m / 7 ft 4.13 in
Height folded: 19.50 studs / 156.00 mm / 6.14 in, Real size: 1.56 m / 5 ft 1.38 in


Building instructions
Download building instructions (LEGO Digital Designer)

Comments

 I made it 
  April 1, 2015
Quoting Jeremy McCreary Great engineering and very informative write-up, as usual, Gabor. Can we see the version with the pretty FBI agent in high heels? (We know you made one.)
You could, but only in adult version, as her skirt definitely will not fit between the control levers...
 I like it 
  March 31, 2015
Great engineering and very informative write-up, as usual, Gabor. Can we see the version with the pretty FBI agent in high heels? (We know you made one.)
 I made it 
  March 30, 2015
Quoting Nerds forprez He has done it again folks! Great job Gabor.
Thanks.
 I like it 
  March 23, 2015
He has done it again folks! Great job Gabor.
 I made it 
  March 23, 2015
Quoting Henrik Jensen Great to see you`re back with a new Backpack Helicopter. The project looks as thorough as what we have become used to from your hand. Simply amazing Work!
Thanks.
 I like it 
  March 23, 2015
Great to see you`re back with a new Backpack Helicopter. The project looks as thorough as what we have become used to from your hand. Simply amazing Work!
 I made it 
  March 23, 2015
Quoting Centurion Cone OH MY GOD!!!! YOU DID IT!!! how far do the guns shoot?
I did not test it for real, but I had some experiments earlier with similar sized non-TLG produced springs from extracted from pens: They can store much less energy than comparable sized rubber bands, just look definitely better.
 I made it 
  March 23, 2015
Quoting killswitch95 [DEMON] just amazing as ever man! i swear if you get the chance to actually build one of your creations, and it works, i would looks up to you as the "god of lego function"... im having a cheery day today haha
Thanks.
 I like it 
  March 23, 2015
OH MY GOD!!!! YOU DID IT!!! how far do the guns shoot?
 I like it 
  March 23, 2015
just amazing as ever man! i swear if you get the chance to actually build one of your creations, and it works, i would looks up to you as the "god of lego function"... im having a cheery day today haha
 I made it 
  March 23, 2015
Quoting c bigboy99899 Another superb project!
Thanks!
 I like it 
  March 23, 2015
Another superb project!
 I made it 
  March 23, 2015
Quoting Kain . Really don't know what to say here.Hmm, guess it's that good
I tested the main rotor in the reality and worked fine. Assault rifle and RPG were never tested in the reality, but I will publish them as separate model when I manage to test them.
 I made it 
  March 23, 2015
Quoting Polino zs again, again and again, you are the most admirable builder I have even seen. Fantastic job! Man
Thanks.
 I made it 
  March 23, 2015
Quoting Toa Nexal Wow. So this thing fits onto a basic CCBS (Hero Factory-style) torso? Or does it need a different torso base? It's somewhat unclear in your diagrams.
I simply used the 7×9 studs torso parts from LDD, I guess they are the standard one.
 I like it 
  March 23, 2015
Wow. So this thing fits onto a basic CCBS (Hero Factory-style) torso? Or does it need a different torso base? It's somewhat unclear in your diagrams.
Gabor Pauler
 I like it 
Kain .
  March 22, 2015
Really don't know what to say here.Hmm, guess it's that good
 I like it 
  March 22, 2015
again, again and again, you are the most admirable builder I have even seen. Fantastic job! Man
 I made it 
  March 22, 2015
Quoting Nick Barrett Impressive. Very thoroughly, and cleverly, engineered. You, sir, are Mr Helicopter!
Thanks. Unfortunately it is not very aesthetic: Technic bricks did their toll when all the necessary functions were incorporated.
 I like it 
  March 22, 2015
Impressive. Very thoroughly, and cleverly, engineered. You, sir, are Mr Helicopter!
 
By Gabor Pauler
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LEGO models my own creation MOCpages toys shop Fully Functional Foldable Bionicle Backpack HelicopterBionicle


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