[Stock][1.21] Moller Skycar with twin butterfly hinges, fully documented (image heavy)

[Torquimedes]

A pure-stock Moller Skycar model with pivoting nacelles, the culmination of many moons of iterative experimental engineering.  Because the inline cockpit most resembles the real Skycar, I was forced to shoehorn the hinge mechanism into the space inside a Mk1 structural fuselage.  This proved to be quite a challenge, restricting both the parts I could use and the space for them to move.  The axle assemblies comprise 72 of the 100 parts.

  
  

No need to switch control to the axles for transition, just tap a couple buttons in the cockpit and they smoothly rotate between vertical and horizontal.  And no docking-port camera jump which can be so disorienting while piloting a VTOL.  

Propulsion

Since the intakes on the nacelles are not attached to the parent craft, there is a circular intake hidden inside the nose.  Forward propulsion is provided by a Juno stuck to the aft end of the fuselage.  Lift is provided by an engine assembly hidden in the lower cockpit.  I surface-attached a girder to the top of the fuselage, then attached a Juno to the node on each end of the girder, and a third to the middle with a cubic strut.  I attached a fuel line hidden inside the cockpit canopy to the girder, and another from the girder to the central Juno.  Then I rotated and offset the girder engine assembly inside the cockpit until the Junos were just hidden. I shifted the girder fore/aft for VTOL balance per the RCS Build Aid mod.

 

Butterfly Hinge

The axle bearings are a pair of TR-2V stack decouplers.  Each has 8 thermometers canted outward at a 5 degree angle to make a slightly flanged socket for the axle.  This flanging makes it more tolerant of jiggles.  

The axle is another pair of TR-2Vs, attached by one node to one bearing, which requires the axle assembly to be constructed without the aid of symmetry.  Ejection force of all TR-2Vs is set to 0 for minimal explosiveness.  Four solar panels make up the wings of the butterfly in the hinge.  Two are attached to each end of the axle and overlap in the center.  In this configuration, if one end of the axle is nearer to the piston than the other, it receives more force until they are even again, keeping the two halves of the axle straight.  I’m using Z-fighting as a feature to damp out a lot of jitter.

The pushrods are a pair of LT-1 landing struts bound to action groups 1 and 2.  These begin in the 1 position, holding the butterfly against the bulkhead of a fuel tank which prevents rotation of more than 90 degrees.  When activated (1+2) one piston retracts while the other extends, smoothly rotating the butterfly through 90 degrees to hold the opposite side against the bulkhead.  

 

In flight the axles may move slightly, but this is by far the most stable butterfly hinge I’ve managed to build.  There is a delicate balance between enough spring tension to hold the butterflies in place, and overstressing and breaking the pistons.  

Nacelles

The hubs are cubic struts on the axle’s rotational axis, offset as far out as necessary to accommodate the nacelles.  The nacelles are composed of intakes and ailerons that visually approximate the pivoting ducted fans of the real Moller Skycar.  They are mounted on the hub at the end of each axle.  I omitted some more aesthetic bits to reduce part count in this tech demonstrator.

Flight control

All control surfaces are disabled except for pitch control from the tail.  Reaction wheels control yaw and roll.  In forward flight, drag torques the nacelles to pitch them up slightly against spring resistance from the pushrods.  The ailerons provide some lift based on this pitch, which increases with forward speed.  Parachutes in the nose and atop the tail provide a less explosive landing option when you run out of fuel.  Terrestrial landing is recommended.

Operation: Follow these instructions carefully, or the hinges will break.

1. Throttle to zero. Stage.
2. Press 1 to pressurize hydraulics.
3. Full throttle to lift off. Fly safe.
4. Press 1+2 at the same time to transition between vertical and horizontal flight.
5. Optional hover stabilization mode:
   1. Right-click the probe core on top of the tail and select “Control from here”.
   2. Engage SAS and select “radial out” mode.
   3. Control pitch as normal, but roll and yaw are reversed in this mode.
6. When all else fails, hit the ABORT button and extend the landing gear for a (relatively) safe touchdown.

 

KerbalX link

Mass 5.58t
Cost 63,521.0
Part Count 100
Built in KSP 1.2.1
Size 5.48 x 3.49 x 9.12
Ceiling 5 km
Cruise 60 m/s (135 mph)
Endurance 14 minutes / 74km

 

 

[Torquimedes]

I have been asked about the use of thermometers in the hinge, so I must give credit where it’s due.  @Majorjim! pioneered the use of thermometers that has enabled mechanical wonders.  When I saw them used with Oscars for an axle on @Bloojay VTOL Wasp, I realized a proper Skycar might be possible.  Then I set about designing the pushrod/butterfly assembly and breaking things until I made it work..

We all stand on the shoulders of giants.

Edited December 2, 2016 by Torquimedes

[klond]

9 hours ago, Torquimedes said:

iterative experimental engineering

breaking things until I made it work..

 Guys, we got another one!

 It was pretty awesome of you to take the time to make this posting with all the separate pictures and explanations.  I'm going to re-read it a few times.

 Working under the constraints of a replica really must have added to the total project time.  Not to mention dealing with small parts.  Hinge w/ hydraulic lever = hot!

[Majorjim!]

13 hours ago, Torquimedes said:

We all stand on the shoulders of giants.

We do indeed mate, we do indeed. There must be some long forgotten downtrodden guy right at the bottom of the pile! Awesome work and design skill here man, The mechanism is ingenious!

[Torquimedes]

I am humbled, gentlemen.  Thank you both.

I should also thank @EasyAce who asked if this was possible back in 0.90 when I first attempted this.

Deciding to use a Mk1 structural fuselage really constrained the width of the axle to the point where the smallest solar panels were the only viable choice for the butterfly wings.  I initially attached a couple panels to just one side but this had a lot of lateral wobble, even when I used dual pushrods to laterally distribute the spring force.  I was surprised that attaching wings to each side of the axle, which overlapped in the center with a single pushrod, eliminated most of that wobble due to the Z-fighting (mentioned above) causing the “butterfly wings” to act as independant suspension.  

After making the hinges work inside the Mk1 fuselage, I telescoped the fore and aft fuselages as far as I could into the cockpit to reduce the length of the craft and better resemble the real Skycar.  Since the cockpit already contains the hidden lifting engines, this resulted in a part density that makes it diffulult to see how any of it works.  This is why I documented a Careful Planned Dissasembly above (unlike all the rapid unplanned ones during development).  

I had planned to make animated GIFs illustrating each piece of the mechanism in action, so I learned how to create them for this project.  But after seeing the filesizes generated and considering the time it would take for people to load this page to see them, here’s a youtube instead.

People can add a butterfly to their mechanical toolbox and make great or goofy things, whichever is more fun.  Scale it up and add docking ports so the axle can hold controllable parts and the craft can be quickloaded.  Scale it down to wave flags on a parade float.

 

...Has anyone built Serenity yet?

 

[Bloojay]

Beautiful.

[Majorjim!]

On 12/05/2016 at 4:54 PM, Torquimedes said:

...Has anyone built Serenity yet?

I think so but not animated I am sure. Does it even have moving parts? I forgot the movie, saw it an age ago.

[Torquimedes]

13 minutes ago, Majorjim! said:

I think so but not animated I am sure. Does it even have moving parts? I forgot the movie, saw it an age ago.

She's a VTOL ship with rotating nacelles:

[Fearless Son]

6 minutes ago, Torquimedes said:

She's a VTOL ship with rotating nacelles:

According to the Serenity RPG sourcebook, those engines on the nacelles are hybrid air-breathing/rocket engines.  The big "abdomen" is the main rocket for interplanetary transfers.  

Of course, the book also admits that all the ships in The 'Verse "cheat" because they have fields that manipulate effective mass.  They can layer these fields in "bubbles" of different effects to say, create artificial gravity within a ship while also reducing the effective mass of the ship overall.  This is why they can get such good efficiency with relatively little fuel.  Said fields take a lot of power to generate, but very little power to maintain.  

Makes it hard to make a fully-functional stock Firefly.  

[Fearless Son]

On 12/1/2016 at 6:59 AM, Torquimedes said:

 

Torquimedes, I have to thank you for coming up with this butterfly hinge design using staged internal landing gear as pistons like that.  I always wanted a method to make stock engine nacelle swivels that worked on more than one axle simultaneously, and I never would have thought of this.