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The Mercedes-Benz Flying Car
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Air drivetrain: 4 3-blade foldable propellers, driven by 4 L-Motors via RC of 2 SmartHubs, 4 foldable/Tiltable propeller arms driven by 2 M-Motors + 4 L-Motors via RC of 2 SmartHubs. Land drivetrain: RWD, 2-speed manual gear shift, rack & pinion power steering, front disc brake driven by 1 XL-Motor and 2 Servo motors via RC of 2 SmartHubs. Crew: 4 Bionicle/Technic figures, in scale 1:10.
About this creation
See this post also at Flickr

1 Introduction

The idea of the roadable aircraft (see Roadabletimes for their history) was born from the desire of „flying over the traffic jam”. 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/ propellers 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 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
In any retro-futuristic tabloid article, we will have flying cars all around within a decade, and they are promising this continuously since 1920. In 2018, we have 3 working prototypes, tons of media hoaxes, and 0 commercially sold crafts:

1. Terrafugia Flying Car, Woburn (MA), USA is a 2-seat ultralight airplane with side folding wings, pusher propeller, double tails and separate road- and aero engines. As it has excellent flying characteristics, it is the only flying car reaching FAA-certification up to date.

Figure 1: Road view of Terrafugia

However the price of it is reduced roadworthiness: theoretically, it can make 65mph on good quality road, but the high Center of Gravity (COG) of vertically folded wings, and large unfolded tail surfaces can make nightmare driving it in tight turns or in crosswind.

Figure 2: Flight view of Terrafugia

2. PAL-V from Netherlands is a 2-seat foldable autogiro with electronic controlled rear suspension of tricycle wheels to tilt the craft in road turns to maintain speed.

Figure 3: Road view of PAL-V

Retractable tail boom and rotor blades are folded into 2 pieces, which is a very demanding solution towards material technology. As it is an autogiro, not a helicopter, it still needs 50m/42yards space to take off.

Figure 4: Flight view of PAL-V

3. Aeromobil Flying Car, Slovakia is a 2-seat ultralight airplane with backward folding shoulder wings, single engine and pusher propeller aft double tail. It is still in research phase completing some road and air tests, but without real road/flight conversion on the spot. It is much more roadworthy vehicle than Terrafugia, maintaining better COG and crosswind-tolerance.

Figure 5: Road view of Aeromobil

It is done at the price of flying qualities: tail is too short and unfolded rudder/ elevator surfaces are too small. Moreover, the propeller has a long transmission shaft from the engine, and it is too close to control surfaces, causing strong vibration at the tail. Small control surfaces did their toll when Aeromobil had a non-lethal but serious accident entering wind shear during test flight.

Figure 6: Flight view of Aeromobil

Common disadvantage of all designs above that they are using fixed pitch propellers for simplicity, which cannot be feathered when they are fixed in road mode. This generates considerable unwanted drag.

We do not show here several personal multicopter projects:
- Ehang 184 octocopter from China, currently waiting for live field trial in Dubai,
- Urban aero X-Hawk double ducted fan craft from Israel, currently under field trial with life sized mannequins,
- Malloy hoverbike quadcopter from USA, currently under field trial with life sized mannequins.
These VTOL crafts often called “flying cars”, but they are not intended participate in regular road traffic on their own, so they cannot be considered roadable aircrafts.

In our earlier MOCs we already modeled:
- Roadable foldable helicopter-bike (2013)
- Roadable foldable airplane with 3-wheeled body and Vee-tail (2015)
- Foldable tilting propeller personal quadcopter (2018)
- Foldable tilting propeller octocopter/ tracked personnel carrier hybrid(2018)

2 Our Mercedes-Benz 1200FL (MB 1200FL) MOC

Our vision is that - as flying consumes at least 10 times more energy than land drive - any practically usable roadable aircraft will be used in 90% of the time as road vehicle, and it will make only short flights
- to avoid traffic jam/ emergency situations,
- to cross smaller water bodies,
- to access offices in high-rise buildings directly via helipad.
Therefore, our goal was to create a hybrid driven, tiltable propeller, 4-seat VTOL quadcopter, which can be folded in the dimensions of a full size car, with the most conventional 4 wheel RWD layout. So, it is capable to participate in regular road traffic without limitations. Our MOC is a piece of concept art, but strictly tied to real engineering principles, with the following aims:
- RC controlled air mode with 4 3-blade foldable propellers driven by 4 PF L-Motors,
- RC controlled transformation from hovering to level flight mode with tilting propeller arms driven by 4 PF L-Motors,
- RC controlled propeller arm folding driven by 3 LPF2 M-Motors into dimensions of a full size car with 4 wheel RWD layout, maintaining similar road abilities: acceleration, turning radius, maximal speed, stability of suspension,
- RC controlled land mode with RWD driven by PF XL-motor, differential, 2-speed manual gear shift, rack & pinion power steering and front disc brakes driven by PF Servo Motors,
- Modeling of the high performance hybrid power plant (turboshaft engine, generator, converter, rechargeable batteries, inverter) as non-working features,
- Modeling of ballistic rescue parachute and inflatable life raft as non-working features,
- Accommodation of 2 Bionicle/Technic figures (driver, bodyguard) in foldable seats,
- Accommodation of 2 Bionicle/Technic figures + baggage in luxury seats equipped with multimedia/video conferencing system and coffee machine as non-working features.
To complete these goals, our MOC contains 5686 bricks, yielding 13 RC power functions, 26 manual functions, and 50 non-working features, in scale 1:10:

Figure 7: Mercedes-Benz 1200FL functions overview
See model in LDD

Flying cars in the reality require very light materials with high tensile strength. Therefore our MOC – even if we tried our best to reinforce it – is well beyond the physical tolerance limit of TLG bricks, so its playability is almost nil. It serves as a digital demonstrator of an innovative concept.

3 Action screenshots of Mercedes-Benz 1200FL

Dieter Zetsche (better known as “Dr. Z”), head of Mercedes-Benz Cars in Daimler AG announced in 2024 that the company will celebrate 70th anniversary of issuing the legendary Mercedes-Benz 300 SL “Gull wing” with a big shot:

“Let the gull wings fly, guys!”

Figure 8: Mercedes-Benz 300SL

Mercedes-Benz 1200FL (1200KW hybrid drive, F=Flying, L=Luxury) was born as a prestige project to demonstrate the superiority of German technology and engineering over US car industry. As a result of protectionist policy of Trump administration against foreign car manufacturers and bankruptcy of Tesla in 2020, mainstream US car manufacturers were left without real competition. Encouraged by Trump’s federal ban of state-level emission regulations, they were turned back to stone-age technology solutions because that was profitable and convenient. As people had no other choice, they bought that. But Mercedes-Benz wanted to avoid US car import tax selling MB 1200FL as an aircraft and return to the high-end market of USA. MB 1200FL’s body was retro-futuristic looking as a tribute to 300SL. But inside, it was packed with the latest hybrid technology and space-grade materials, to prove that “King of cars and car of kings” is still built in Stuttgart, Germany.

Figure 9: Gull wing door open
See model in LDD

Because of the space grade gizmos built in, price tag of MB 1200FL equaled a 4-seat armed military helicopter, and supersport cars were cheap mass produced stuff compared to that. It quickly became symbol of status and unlimited power among billionaires and dictators. Victor Obranov, the psychopathic mass murderer dictator of Republic of Sowatia, was among the first customers. He stole the money received from EU for building network of children’s hospitals in Sowatia to buy it.

Figure 10: MB 1200FL escorted by 2 BattleBikes (animated)
See model in LDD

MB 1200FL MOC’s retro-futuristic body shape is dictated
- Partly by folded propeller arm layout,
- Partly by the very limited selection of large, curved windscreen TLG parts,
- Partly by weight saving: a large bubble canopy – which is compulsory part of all retro-futuristic concept cars - is hell in the summer because of the greenhouse effect, even using strong A/C unit. But in weight saving it is uncatchable.
- Party by space saving: We wanted to squeeze 4 Bionicle/Technic figures into the body, which are – against using ball joints - not nearly as foldable as real human bodies. So it really does matter if we have 1.5mm thin canopy wall instead of 8mm thick Lego bricks. Military hat of Victor Obranov and pony tail of his concubine, Natasha Grigorieva just touch rear windshield, in a car body, which is almost as big as a 1970s Lincoln Towncar…

Figure 11: MB 1200FL prepares for takeoff from helipad
See model in LDD

I got the idea of folding the propeller arms in the top part of mudguards from my father. He had an inferior East-Bloc made car called Wartburg in the old days, with relatively sizeable body and tiny 2-stroke engine. He could build in mudguards and smuggle quite an amount of home distilled-brandy from Hungary to Yugoslavia regularly.
Figure 12: Propeller arm opening sequence (animated)
See model in LDD

Instead of brandy, we designed there 4 300HP axial flux, brushless electric motors, powered by a 1566HP turboshaft-driven generator under the hood.

Figure 13: Hovering flight above dirt road
See model in LDD

The whole design process was “battle for square feet”: Which is the largest propeller disc area, which can be folded into the body of a full size car, using minimal number of load-bearing joints and hinges, to reduce structural risks of the design?

Figure 14: Low pass over lagoon
See model in LDD

Propeller disc area is vital because smaller area means lower hover efficiency and higher energy consumption. Moreover, as full size cars body has higher drag than a comparatively sized airframe, a simple quadcopter could not fly faster than 100KPH.
Figure 15: Tilting propellers from hovering to level flight (animated)
See model in LDD

Therefore, propellers are tiltable 38° forward to minimize air drag in high speed flight. But this further reduces effective propeller disc area to sustain hovering.

Figure 16: Level flight over the bay
See model in LDD

The next design trap is that steering and stabilization of quadcopters requires continuous acceleration/deceleration of fixed pitch propellers, to keep them mechanically simpler than helicopters. Therefore, energy consumption of steering & stabilization highly depends on propeller torque, which increases dramatically with size (and propeller disc area):
Figure 17: Level flight (animated)
See model in LDD

If the same propeller profile, from the same material, at the same RPM is doubled in size, it results in 4 times more propeller disc area (and roughly 4 times more lifting force), but as its mass increases 8 times, and rotational speed 2 times (but it effects torque on the second power), so torque (and energy consumption of steering & stabilization) will increase 8×2×2=32 times.

Figure 18: Night flight
See model in LDD

Therefore we tried to use the sleekest and lightest possible 3-blade foldable propellers: they are opened simply by centrifugal force, and they are closed as blades touch body during folding process.

Figure 19: Fully opened forward- and rear canopies
See model in LDD

The next design challenge was that although gullwing doors are very stylish – and relatively convenient with usage of lower foldable doorstep parts – their width is limited by folded propeller arms. So they are very clearly insufficient for 4 persons, even if the forward seats are forward/ backward foldable/ lockable. Therefore, forward- and rear canopies are openable to make boarding easier, but they are hard to use in rain shower or under thick snow.

There are all kinds of challenges in a dictator’s life: building up mafia-state, bombing kindergartens at rebelling regions with Russian-made nerve gas bombs, making complete fool from president Trump afterwards, but the hardest of all: how to handle concubine’s hysteria. Even flying cars can have flat tire sometimes (yes, the bullet-proof self-sealant is there, but somebody left a machete on the road…). Natasha quarrels about why they are shifting tire in a dangerous rural area infested with rebels. Victor tries to explain her that take off is not safe with flat tire, as it reduces safe clearance of propellers from the ground. Fortunately MB 1200FL has full size reserve wheel, lifter and tools in the bonnet, under a suitcase full with Natasha’s clothes.

Figure 20: Flat tire exchange
See model in LDD

It is more dangerous situation when in a sudden wind gush, left rear propeller hits smokestack of a concrete factory during “election campaign” tour. As quadcopters have no any redundancy in generating lift, and they are not capable of dead-engine crash landing (like helicopters using autorotation), MB 1200FL is equipped with BRS-type Ballistic Parachute

Figure 21: Launching ballistic parachute
See model in LDD

The parachute is stored in a container between forward- and rear seats, and it is automatically deployed in case of loss of lift through a jetissonable roof hatch with the help of 2 solid fuel rockets.

Figure 22: Ballistic parachute deployed
See model in LDD

It seems to be strange thing at the first sight that MB 1200FL is equipped with a life raft in its bonnet, which is inflated from a nitrogen pressure bottle automatically when submerged under water. But while normal cars rarely break down during flying above water bodies (maybe in “Lords of Hazard County”), it can absolutely happen with flying cars. The problem is the same as with Titanic: there is sufficient seating only for upper social classes. Victor Obranov forces the driver and bodyguard to stay in the deadly cold water with gun pointing. Natasha quarrels with him to shoot them instantly, before they get panic and capsize the small raft. Victor considers shooting all 3 of them, as he has prominent place in history appointed by God, while body guards and concubines are easy-to-replace rolling stock. A suitcase full with the latest Karl Lagerfeld-collection is worth to save anyway.

Figure 23: Deploy life raft
See model in LDD

The horrible cost and fuel consumption of MB 1200FL can be justified - even for stone rich customers - only if it can perform unique service, which cannot be done by any other vehicle. Therefore ThyssenKrupp AG developed a cantilevered landing deck, which can be installed in the facade of high-rise buildings.

Figure 24: ThyssenKrupp cantilever landing deck
See model in LDD

This allows MB 1200FL to perform Office-To-Office (O2O) service: Instead of taking the elevator to helicopter platform or to underground parking lot, then board into helicopter/ limousine, then taking the elevator again, MB 1200FL can fly directly from floor to floor between offices in high-rise buildings. For VIP customers, time saving and reduction of security risks of transportation can justify costs.
ThyssenKrupp landing decks can be installed with 8 floors (ca. 24m/ 80ft) vertical separation and 10m/ 33ft horizontal separation to allow safe landing even in bad weather or using ballistic parachute in case of failed landing. This way, a high-rise building with at least four 30m/ 98ft wide facades can have landing deck for each floors safely separated.
The landing deck itself is a 10m × 10m/ 33ft × 33ft gridded platform, supported by cantilever steel truss beams, with 1m/ 3ft 4in high wire mesh fence all around. The fence can be leveled by worm+Z8 gear mechanics driven by LPF2 M-Motor via RC of LPF2 SmartHub1 CH1. Platform surface is gridded and electrically heated for:
- Easier removal of rain and snow/ice,
- Counteracting vortex ring state, which can cause loss of lift at all rotary crafts during landing.
Leveled wire mesh fence is a safety measure capturing crafts sliding over the edge of the platform during failed landing: propeller blades and wheels can boggle in the wire mesh, preventing the craft falling down.
As at the facade of high-rise buildings high winds can make difficult vortices, a 10m × 10m/ 33ft × 33ft platform itself cannot give safe separation of propeller blades from facade surface. Therefore landing is helped by a crane-like manipulator nicknamed “Monkey catcher”. Instead of cables and hook, its tip is equipped with a head part, which is kept horizontal in any positions of the manipulator by a parallelogram linkage. At top of the head there is a large elastic suction cap, where vacuum is generated by a centrifugal vacuum pump driven by LPF2 M-Motor via RC of LPF2 SmartHub1 CH2. As the composite belly panel of MB 1200FL is completely smooth and flat, monkey catcher can grab it with the suction cap when the vacuum pump is working.
Monkey catcher can be erected up to 60° elevation by a “10/15 stud linear actuator” driven by LPF2 M-Motor via RC of LPF2 SmartHub2 CH1. It is also equipped with 2 “Assembly shock absorber extra hard”.

Figure 25: Difficult weather approach of landing deck
See model in LDD

So the only thing the autopilot of MB 1200FL has to do is to keep the craft in 60° descent glide path, and maintain 3m/sec constant speed of descent (which can be still taxing in bad weather). But extremely difficult deceleration/ hovering and danger of vortex ring state are avoided. Monkey catcher will grab the craft and decelerate it by its shock absorbers. Synchronized working of linear actuator will prevent bouncing back from the landing deck or sliding from it, even in strong crosswinds and vortices. Suction cup will release belly of MB 1200FL only when wire mesh fence is erected and locked around the deck.

Figure 30: Boarding at landing deck, fence deployed
See model in LDD

The Obranov Tower at Obranovburg, Sowatia was equipped with ThyssenKrupp landing deck under the supervision of Victor Obranov’s nephew, Arslan Obranov. He was able to complete his BSc in Structural Engineering only after the Dean of Faculty of Structural Engineering, at Victor Obranov University (VOU) of Sowatia was arrested and executed for treason. No wonder that Arslan forgot to design any additional wind bracing and vibration dumping installing the landing deck – it was simply welded into the facade. As a result, at landing of MB 1200FL, occupants of the building can have bumpy ride also.

Figure 26: Approach to landing deck (animated)
See model in LDD

ThyssenKrupp landing deck has 3 independent landing navigation systems:
- Monkey catcher is equipped with a small phased array radar, which reports back the relative position of the craft via data link to flight computer of MB 1200FL.
- If data link fails, there is an Optical Landing System (OLS) on monkey catcher, which is similar to ones used at aircraft carriers: the radar measures the relative position of the craft, and series of horizontal green lights (the “datum line” in marine slang) communicate the horizontal/ descent speed deviation from glide path, while 2 vertical rows of red lights (“meat balls”) communicate the vertical/ roll deviation from flight path. OLS can be observed from MB 1200FL by 4 propeller arm tip cameras rotated downward at landing.
- If radar and OLS fail, a large white cross painted on the deck and yellow tip of monkey catcher covering it can show the glide path visually.

Figure 27: On-board view of landing approach (animated)
See model in LDD

ThyssenKrupp landing deck is equipped with three 2.48m × 7.68m × 2.64m (8’1.57” × 25’2.17” × 8’7.87”) hangars with fireproof rolling gates + 2 personnel doors. Inside, there are 2 refueling stations - hanging from the ceiling on chains - supplied by 2 JP-1 jet fuel lines (in red). This eliminates the need of landing at the ground for refueling. As pressurized lines of highly flammable material impose extra risk in high-rise buildings, both fuel lines are secured by separate hydrants (in light blue) with numerous water/foam sprinklers, which can cross-support each other. At personnel doors, the Domina of Victor, and Inez, the Mexican maid of Natasha are waiting for the takeoff.

Figure 29: Hangars and refueling stations
See model in LDD

As 7.4m/ 24’3” land turning radius of MB 1200FL allows only very limited maneuvering on a 10m × 10m (33ft × 33ft) flight deck, the monkey catcher can be rotated left/right 20° around a 7-stud turntable driven by LPF2 M-Motor and Z8 gear via RC of LPF2 SmartHub2 CH2. This way it can help to orientate the landed craft towards/from side hangars.

Figure 30: Stowing MB 1200FL into side hangar
See model in LDD

Monkey catcher also plays important role lifting the craft before launching, to place it safe distance from facade of the building. The whole harem of Victor strongly hopes that the monkey catcher with suitable virus-infected software one day will drop MB 1200FL with Victor and Natasha from the deck: in Sowatia, only heir from the first concubine can survive. All other heirs get killed after transferring the power, to prevent opposition.

Figure 31: Launching MB 1200FL from flight deck
See model in LDD

The harshest the dictatorship, the more willing the opposition is to eliminate the dictator with homemade drones laden with gasoline + fertilizer explosive – being the air force of the poor (e.g.: Syria, Venezuela).

Figure 32: Formation flight with 2 Hoverbikes
See model in LDD

Therefore Victor Obranov’s MB 1200FL needs protective escort of Hoverbikes flying over the countryside.

Figure 33: Formation flight with 2 Hoverbikes (animated)
See model in LDD

The real problem arises when his concubine, Natasha gets bored and wants to drive a Hoverbike without any experience. One can see that the pilot is impaled: if he rejects the request, he will be executed. If Natasha gets wounded trying to fly it, he also will be executed.

Figure 34: Landed with Hoverbike escort
See model in LDD

It is hard to believe, but dictators are also ordinary men, just they fell love with themselves more hungry way. So sometimes they need a romantic ride in the countryside sunset with a beautiful concubine (or with the next, even more beautiful concubine):

Figure 35: MB 1200FL in sunset at the countryside
See model in LDD

To help this activity, MB 1200FL is equipped with left/right/center rearview cameras + 4 moveable propeller arm tip cameras + 7 LCD displays instead of conventional mirrors. No cameras can see rear seats any way, which are also separated from forward seats by their sizeable headrest displays. Moreover, because of lack of space, PF XL-Motor of rear wheel drive is placed just behind the rear seat, electrifying relationships there.

Figure 36: The main manual control system
See model in LDD

Operational ceiling of MB 1200FL depends on numerous parameters (air temperature, barometric air pressure, elevation). Generally, it can fly over 6000 ft elevation only in the winter, when cold air is denser, because of the relatively small rotor disc area.

Figure 37: MB 1200FL in winter flight
See model in LDD

4 Technical details of Mercedes-Benz 1200FL

*This part is technical. If you do not understand how multicopter controls do work, you can find an excellent summary at Wikipedia

**In the forthcoming technical description, functional parts of Mercedes-Benz 1200FL are referenced by numbers which can be found on technical drawings attached

***Parts of Mercedes-Benz 1200FL are color-coded by their function:
- Gray/Black: Static parts
- White: Dynamic parts
- Dark Blue: Folding seat of pilots
- Light Blue: Pressurized air ducts
- Red: Body plating, combustion chambers, fire extinguisher
- Orange: Ballistic parachute, inflatable life raft, battery dischargers
- Dark green: Batteries
- Light Green: Jet fuel lines
- Brick yellow: Jet exhaust pipes
- Light yellow: Manual controls

Figure 38: Mercedes-Benz 1200FL road mode cutaway view
See model in LDD

Figure 39: Mercedes-Benz 1200FL hover mode cutaway view
See model in LDD

Figure 40: Mercedes-Benz 1200FL hover mode cutaway view (animated)
See model in LDD

Figure 41: Mercedes-Benz 1200FL drivetrain systems overview
See model in LDD

4.1 Hybrid power plant

Design of hybrid power plant is based on engineering data published by Krossblade about the tradeoff effect between rotor disc loading and hover lift efficiency of rotorcrafts:

Figure 42: Rotor disc loading versus hover efficiency chart by Krossblade

- MB 1200FL has total rotor disc area: 39Sqm = 420SqFt
- We took rotor disc loading of Sikorsky CH-53 Sea Stallion heavy transport helicopter as technically certainly feasible one: 70KG/Sqm = 14.37Lbs/SqFt
- This will provide Maximal Takeoff weight (MTOW): 2730KG = 6026.5Lbs in the given rotor disc area
- According to Figure 42, Lift efficiency is: 3.15KG/KW = 2.35KG/HP = 5.187Lbs/HP given the selected rotor disc loading
- Dividing MTOW with Lift efficiency we get Requested power for hovering: 865.75KW = 1161HP
- According to Figure 42, Propeller downwash speed at hovering with MTOW will be = 20m/sec = 72KM/h = 44.7MPH. This is the maximum acceptable downwash in practice, not hurling away surrounding adults and 4 wheeled vehicles at takeoff/ landing.
- Requested power output for hovering at batteries (assuming 95% inverter efficiency and 95% battery efficiency) = 959.27KW = 1286.4HP
- Requested current of battery at 380V nominal voltage: 2524A
- Requested power output for hovering at turboshaft (assuming 95% converter efficiency and 95% generator efficiency) = 1063KW = 1425HP
One can see that even the most effective batteries in any realistic size/weight can provide such a power just for 3-5 minutes, not more. Therefore we need a hybrid drive, driven by a powerful turboshaft engine-generator combo called turbo generator. In turn, batteries will be relatively small sized, as they serve only as puffer between turbo generator and electric motors of propellers, because of two reasons:
- RPM of turbo generator cannot be changed so fast as quadcopter control requires,
- In case of turbo generator failure, batteries provide energy for crash landing.
We designed elements of hybrid power plant extending data of possible most similar existing stuff:

Figure 43: Hybrid power plant
See model in LDD

4.1.1 Daimler-Benz 1200KW (DB1200) Turboshaft

The next image is about introduction of MB 1200FL at Paris Motor Show, in 2024. One can wonder what the hell the bald old guy with distinct German beer drinking moustache is doing on the stage, besides regular cheerleaders dressed in angel costume? He is Dieter Zetsche, head of Mercedes-Benz Cars, known for unquenchable thirst for publicity, just demonstrating DB1200 Turboshaft engine for the Press.

Figure 44: At Paris Motor Show
See model in LDD

- Derived from engineering data of LHTEC T800-LHT-801
- Size: 0.56×1.04m
- Weight: 145KG = 320Lbs
- Maximum power output: 1166KW = 1563HP at 60000RPM
- Specific fuel consumption: 0.208KG/HP/HR = 0.459Lbs/HP/HR
- Idle race: 20000RPM
- Lubricant: Oil, 3KG
- Cooling: Air, 22KG/sec

Figure 45: Engine room view
See model in LDD

As we have 6 JP-1 Jet fuel tanks on board (modeled by 6 LPF2 SmartHubs) under seats with 6 × 65.5L = 393L total capacity, we can conclude that maximal hovering time on jet fuel at MTOW = 61min.

It is very hard to install turboshaft engine in a car body. The engine itself is smaller and lighter than a comparable piston engine, but has much bigger air inflow and exhaust outflow, which should be get through a heat exchanger called recuperator to improve efficiency. Piping eats incredible amount of space at the most inconvenient places (at front mask, firewall of engine room). Therefore we designed DB1200 with special Counterflow layout:

Figure 46: DB1200 Counter-flow Turboshaft Engine
See model in LDD

- Cold air (in light blue) enters at front wheel wells, and sucked in the engine at its middle.
- In recuperator, cold air is warmed by jet exhaust pipe manifold (in brick yellow) and by cooling external wall of combustion chambers (in red)
- Warmed air (in pink) is sucked by a centrifugal compressor at the forward of the engine.
- Compressed air turns backward, goes through jet fuel injectors (in light green) and turns into hot gas (light yellow) at combustion chambers.
- At the rear of the engine, there is an impeller type gas turbine, which is driven by hot gas, which turns forward leaving the turbine.
- Hot gas cools down (in orange) in recuperator, where it is turned backward again
- Jet exhaust (in gray) exits engine at its sides.
This layout allows the turboshaft + generator unit to be relatively short (comparable to a V8 + automatic transmission), and there are no protruding tubing through front mask or in the cockpit.

Figure 47: DB1200 Counter-flow Turboshaft Engine (Animated)
See model in LDD

- There are 4 muffled exhaust pipes, which can be used in road mode. Gas here enters in long secondary heat exchangers which are placed under the gullwing doors. Cold air streaming from front- to rear wheel wells cools down the exhaust, so it is not dangerous to bystanders anymore, when leaving vehicle before rear wheel, and noise is tolerable. But muffled exhaust pipes have high flow resistance.
- There are 2 non-muffled exhaust pipes protruding upward through hood. They are opened only in air mode (at 10 times more power generated). They release hot jet exhaust directly, so flow resistance is low, but noise and hot gas output of the engine equals with a comparable helicopter’s.

4.1.2 1200kVA Siemens generator

- Derived from engineering data of Airbus A380 generators
- Continuous rating: 1200kVA
- Power factor: 0.95
- Max. rpm: 60000
- Cont. output: 1140KW
- Voltage: 380V AC
- Cont. current: 3000A
- Phases: 3
- Nodes: 40
- Max. frequency: 20kHz
- Size: 0.4×0.48m
- Weight: 75KG
- Lubrication: Oil, 3KG
- Cooling: Air, by separate 4KW A/C unit

4.1.3 Zinc-Silver oxide rechargeable battery pack
(Data below should be doubled as there are two units)
- Derived from engineering data of Wikipedia
- Chemistry: Zn + Ag2O -> NaOH/KOH -> ZnO + 2Ag
- Specific energy: 130Wh/KG
- Energy density: 500Wh/L
- Net volume 16L
- Gross weight: 65KG
- Nominal voltage: 380V DC = 245 × 1.55V cells
- Capacity: 21Ah
- Maximal current: 1300A
- Resistance: 0.001 Ohm
- Waste heating power: 1.69KW at 1300A current
- Safety features: battery cell monitor/ load equalizer, battery discharger, converter line breaker, battery disconnector line breaker, inverter line breaker
We can conclude from the data that maximal hovering time on batteries at MTOW = 60sec, and the power required by cooling of 2 batteries + AC/DC converter + DC/AC inverter cooling is 4KW.

Figure 48: Bonnet view
See model in LDD

4.1.4 Axial flux electric motors

- Derived from engineering data of Yasa 750R
(4 units at propellers, modeled with PF L-Motors)
- Continuous torque 400Nm
- Maximum Speed 3250RPM
- Peak efficiency: 0.95
- Continuous power: 223.75KW = 300LE at 380V AC
- Winding stator rings: 3
- Permanent magnet rotors: 2
- Total weight 90KG = 198.7LBS
- Total volume: 21L
- Size: 320×320mm
- Coolant: 1.8L Oil, 60L/min

4.2 Air drivetrain

In the reality, AC outputs from (D20) inverter toward axial flux motors (D30) are controlled by (C1) flight computer via CAN bus line:

Figure 49: Air drivetrain
See model in LDD

In the MOC, 2 LPF2 SmartHubs provide RC control for 4 PF L-Motors of propellers. They are rather weak energy source, but foldable propeller blades made from ‘Bionicle sword 16M’ cannot tolerate very high centrifugal force.

4.3 Propeller arm tilting mechanism

For high speed flight, propellers should be tilted forward. In the reality, it is solved by 4 small servo motors. At the MOC, the problem is that PF Servo motors are too bulky to build them in propeller arms. Therefore we designed PF L-Motors in propeller arm roots, which can tilt them from – 6°..+38°. As L-Motors are not positionable correctly via RC, their rotation is limited by blockers placed propeller arms at -6° and +38°. Pull of propellers themselves can position arms to 0°.

Figure 50: Propeller arm tilting mechanism
See model in LDD

In the MOC, forward/ and rear tilting PF L-Motors can be controlled separately by 2 channels of an LPF2 SmartHub. The reason is that small tilting movements of propeller arms can help propeller arm closing considerably. An interesting TLG-specific design problem was how to create strong propeller arm tilting bearing within 3 studs diameter limit: Technic axle of propeller arm can be plugged into rotating part of PF L-Motor only 1 stud deep, and this is very clearly insufficient to handle loads on propeller arm. The solution was using TLG parts ‘6-shooter’ and ‘trigger of 6-shooter’ as (T3) heavy duty bearing.

4.4 Propeller arm folding mechanism

In the reality, there would be 6 servo motors to fold 4 propeller arms separately, left/right propeller arm cover plates. PF Servo Motor is so bulky that this was not an option for us.

Figure 51: Propeller arm folding mechanism
See model in LDD

In the MOC, the Z8+worm gear combos, which fold left/right propeller arms, are mechanically connected with driveshafts, so we need only 1-1 LPF2 M-Motors at forward and back. Folding of left/right and rear/forward propeller arm cover plates is also mechanically connected, and driven by single LPF2 M-Motor via driveshafts and Worm+Z8 gear combos. Longitudinal driveshafts serve also as pivot axis of lower doorstep part of gullwing doors (doors can rotate freely on that). This trick helped to save lot of space.

4.5 Land drivetrain

All of our previous design effort was invested into that we can say at this point, that MB 1200FL has the most conventional land drivetrain of a full size car, with fair road handling: 4 identical sized wheels, rear wheel drive with 2-speed manual gear shift and differential, rack & pinion steering, independent double wishbone suspensions.

Figure 52: Land drivetrain
See model in LDD

Because of the very powerful hybrid system, MB 1200FL does not really need more that 2 gears in in gear shift. It helps to keep gear shift assembly really small and simple. Space is needed in the bonnet by the components of the hybrid power plant.

Figure 53: 2-speed manual gear shift
See model in LDD

Pinion & rack steering is driven by a PF Servo Motor squeezed under the hood, between left suspension and turboshaft engine. Safety steering column has 2 universal joints.

Figure 54: Power steering assembly
See model in LDD

The only non-conventional feature in land drivetrain is that we tried to model servo-controlled front disc brakes in a very limited space. While braking of rear wheels can be easily solved by reversing RWD electric motor, there is very clearly no space left for any hydraulic system at front wheels like real cars (moreover TLG hydraulic parts are very bulky). But front brakes are more important than rear ones.

Figure 55: Front disc brake assembly
See model in LDD

We used a rather simplified mechanic system, which can simulate braking at least in the close to straight forward position of steering. (High steering angles allow only slow speed, which can be decelerated by rear brake alone.) (D43) TLG ‘Mini linear actuator’ driven by (D45) PF Servo Motor via (D44) driveshaft with 2 universal joints squeezes (D41) brake pads via (D42) linkage to (D40) brake discs very-very close to steering axis. This way even if brakes are on the non-steered part of the suspension, they have little effect on steering. As long as steering is close to straight forward position, it has little effect on braking. (D42) parallelogram linkage of brake ensures that braking has and suspension/springs have very little effect on each other. Of course it is only a compromised brake solution, moreover PF Servo motor of brake largely consumes one of the leg spaces.

4.6 Navigation systems

Navigation system is compound of components used at cars and light aircrafts, with some specialties:
- (N17) windscreen wipers are modeled as manual function with correct parallelogram linkage between them. They are installed on forward openable canopy.

Figure 56: Navigation systems overview
See model in LDD

- Body of a full size car has inferior all-around angles of sight/lighting compared to a helicopter airframe (no one wants to see or light the ground just beneath a car, while it is very vital at landing a helicopter). To overcome this difficulty, there are (N31, N32) rotate able camera + reflector mounts on tip of propeller arms used at landing and in “glass cockpit” functions. Their image is shown on (N18) middle console LCD displays and (N28) cabin roof instrument panel LCD displays.
- Instead of rearview mirrors, (N35) left/ right/ (N50) center rearview cameras are used, with (N14, N15, N16) LCD displays on dashboard.
- (N35) moveable rearview camera mounts together with (N36) moveable UHF aerial mounts are also used as locks of propeller blades in road mode.

Figure 57: Dashboard view
See model in LDD

It is a hard design question of all roadable aircrafts, how to combine controls of a car with controls of a helicopter effectively. At MB 1200FL, only the steering wheel and gear shift lever are mechanically linked to their subsystems, all other controls are fly-by-wire, which makes the transition easier:
- (C2) steering wheel, (C7) gear shift lever, (C8) servo hand brake work both in air- and land mode (in air mode, they are for slow taxiing on helipads/landing decks),
- (C10, C11) propeller arm tilting switches work both in air- and land mode (in land mode they facilitate easier propeller arm folding),
- (C9) switch shifts between air- and land modes,
- In land mode, the primary control is manual: (C14) pedals become brake and throttle, (C12) propeller arm folding switch and (C13) propeller arm cover switches are activated, (C3) pitch/roll steering column and (C6) hand throttle lever are inactivated,
- In air mode, (C1) flight computer becomes the primary controller and autopilot, manual controls are optional: (C14) pedals become yaw control, (C12) propeller arm folding switch and (C13) propeller arm cover switches are deactivated, (C3) pitch/roll steering column and (C6) hand throttle lever for collective control are activated. As steering column has double universal joints, it can be tilted up/ down (pitch control) left/right (roll control) without disturbing steering of front wheels.

4.7 Accrual systems

Figure 58: Back seats view
See model in LDD

While forward seats are rather inconvenient, as they have to be forward/ backward foldable/ lockable in a very confined space, rear seats are equipped with Old English styled luxury cushion, more convenient seatbelts, individual headrest displays, central videoconferencing & hi-fi system and coffee machine. Also they have much bigger legroom. The only thing we could not solve at back seats is headrests, because of the proximity of rear windscreen.

Figure 59: Accrual systems overview
See model in LDD

Besides the usual emergency kit used at cars (full size reserve wheel, lifter, toolset, medical kit, battery flashlight) MB 1200FL is equipped with a 2-seat life raft inflated automatically from the bonnet, when submerged into water. But this stuff is nowhere in importance compared to ballistic parachute: As MB 1200FL has relatively small rotor disc area, single turboshaft engine and 4 propellers only, it has very limited lift redundancy. Moreover it cannot make dead engine crash landing using autorotation, like helicopters. In case of turbo generator failure, it can hover only 1 minute on batteries. Therefore, it has to have absolutely failsafe and foolproof ballistic parachute rescue system, deployable between wide altitude and level speed limits, to get FAA-certified. Design of ballistic parachute is based on engineering data of original inventor and current market leader Ballistic Rescue Systems (BRS) Aerospace:
- Diameter: 15m/49’3”
- Area: 176.71Sqm/1900SqFeet
- Lines: 16 12m/39’4” Nylon ropes
- Descent speed at MTOW = 9.4m/sec = 34KPH = 21MPH
- Weight: 40.8KG = 90Lbs
- Booster: 2 solid fuel rockets with nylon extraction lines
Ballistic parachute can be triggered manually or automatically in case of electric motor overheating/ malfunction, structural failure of propeller arms, loss of propeller blades, etc. After triggering, working propellers are decelerated, to reduce risk of cutting/entangling parachute lines, when parachute is deployed from a destabilized, rolling craft.

Figure 60: Ballistic parachute booster rockets
See model in LDD

To reduce the minimum altitude of successful deployment parachute (ca. 40m/130ft), it is extracted from its container through jetissonable rooftop hatch by 2 redundant solid fuel booster rockets. They burn their nylon extraction lines before total burnout, allowing safe separation, and preventing them to damage opening parachute. One can see a strange circular surface sliding on the 16 main lines of parachute. It is a small braking parachute, which prevents opening the main parachute at high speed, holding the lines together by the force of air drag. This prevents ripping the main parachute deployed at too high speed. Under 100KPH/62.5MPH, in weakening air drag, brake parachute cannot hold lines together anymore, and main parachute is opened. BRS originally used an annular shaped brake parachute, but Mercedes-Benz developed its own spider-shaped one to avoid paying royalty to BRS, while the operating principle is pretty much the same. (It leaded to mutual lawsuits, being juicy chunk for lawyers.)

Figure 61: Descend on ballistic parachute
See model in LDD

Realistic working parachute is not a typical stuff, which is easy to build from TLG parts. Therefore we modeled the “wireframe” of it, using ropes and outer cables connected by Technic parts. The wireframe can be covered from the underside by the thin, sticky type of plastic foil used to wrap food in refrigerator.

4.8 Body structure

MB 1200FL MOC is built up very different way than other car MOCs, because it has to crowd quite an amount of stuff under its skin. We used ‘technic cross axle longerons + technic lever ribs’ load bearing space frame, covered by 2 layers of non-load bearing body plating (flat curved tiles on studded plates). Using the TLG standard Technic building technique (Technic beam longerons + cross axles covered by Technic panels) would waste much more space, moreover it would leave those nasty little gaps and holes on the skin.

Figure 62: Mercedes-Benz 1200FL light alloy tube space frame
See model in LDD

One can compare it with a welded steel tube space frame of a racing car, concluding that how much more framing is necessary building from Technic parts, just barely hold its own weight.

This post is continued here

Building instructions
Download building instructions (LEGO Digital Designer)


 I made it 
  August 10, 2018
Quoting Tom's MOCs Just as The Lego Group releases its kit for the (James Bond) Aston Martin DB5, here you come and completely upstage them! An ejection seat for the DB5? - Who cares! I'll take a Mercedes-Benz Flying Car, complete with parachute. But your MOC has almost 5 times as many elements as the DB5, so I fear I'd spend most of my remaining retirement building it. What I will do, though, is set aside an hour to study your extensive commentary - I always learn something from it. Thanks for spicing it up with the witty fictional scenarios, in this case about corrupt dictators and their must-have toys! Brilliant work throughout.
 I like it 
  August 10, 2018
Just as The Lego Group releases its kit for the (James Bond) Aston Martin DB5, here you come and completely upstage them! An ejection seat for the DB5? - Who cares! I'll take a Mercedes-Benz Flying Car, complete with parachute. But your MOC has almost 5 times as many elements as the DB5, so I fear I'd spend most of my remaining retirement building it. What I will do, though, is set aside an hour to study your extensive commentary - I always learn something from it. Thanks for spicing it up with the witty fictional scenarios, in this case about corrupt dictators and their must-have toys! Brilliant work throughout.
 I made it 
  August 9, 2018
Quoting Henrik Jensen WOW! What a mind blowing post here! So many details and technicalities in one single post, you certainly outdone yourself this time! Have to come back again to dig deeper.
 I like it 
  August 9, 2018
WOW! What a mind blowing post here! So many details and technicalities in one single post, you certainly outdone yourself this time! Have to come back again to dig deeper.
 I made it 
  August 9, 2018
Quoting Seaman SPb Fantastic work!
 I like it 
  August 9, 2018
Fantastic work!
By Gabor Pauler
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