Bill of Materials
Blade to hub connection
For transportability I want the blades to be easily separated from the hub. I also wanted to be able to adjust their pitch. I decided to go with a 3D printed connector that consists of two parts. The “Elbow” and the “RootPlug”. You can simply click here and have them printed. If you want to modify the design or print them using a different printer you can find and download the design in many different format here. Simply click “Export” by right clicking on the “Elbow”-Tab:
Warning: Shapeways applied a “matte finish” to the parts that messes with the tolerances. The test print was fine but for the 4 production prints I had to scrape off some finish for the RootPlug to fit into the Elbow.
Things to know if you want to modify the Elbow
If you want to modify the design it might help to understand the purpose of the different features. Make sure to read the comments in the design:
Why are there two fins/levers on the elbow?
Why do the CrossRod and the wing spars overlapp in the RootPlug?
Why is there a tooth missing?
The Blades are hot-wirecut from EPP foam, strutted with two spars and coated with film for stiffness. If you do not want to cut the blades yourself you can go to a CNC foam cut service like flyingfoam.com and use these order details:
Foam Type: 1.3# EPP
EPP Color: Black
Wing Span: 24
Named Airfoil: fx63137sm
Basic Options 1.3# EPP: Basic Options 1.3# EPP, Qty: 1,
Tube Hole: Front/Rear
Front Hole Diameter: 0.2
Front Hole Location: 1.55
Rear Hole Diameter: 0.2
Rear Hole Location: 2.05
Spar Slot: None
Once you have your cores the assembly process is very simple:
- Glue in the spars (I used Elmer's Super Fast Epoxy – but any epoxy glue should do - but TEST to see if it melts the foam)
- Apply the film coating – There are plenty of videos on youtube on how to apply “covering to a foam wing”. I used Hangar 9 Ultracote following these instructions.
- Glue the short coupling pins into the RootPlug – these will hold the RootPlug in the Elbow via rubber bands.
- Glue the spars into the RootPlugs using epoxy glue.
The result should look something like this:
Notes on the picture:
- I made some blades orange and some white for no good reason
- If your blades and the film have the same width you will end up with uncovered ends because the film shrinks - no kidding...
- The little black pin will hold the blade in the elbow via bungee cord
Carbon fiber tubes
Order all your pultruded carbon tubes cut to length. If you need to cut them yourself please follow these instructions for cutting them with a rotary tool or a hand saw (some people take safety to the max :)
- Glue the two HubCross rods into the HubCenter
- Glue the four Elbows to the ends of the HubCross rods.
- ATTENTION The four Elbows must be oriented exactly in one plane – use a jig to hold them in position during glueing.
- ATTENTION The rods must go all the way through the Elbow end must end in the front plane.
- Glue HubStruts into the Elbows
- Add 2 bridle loops to each Elbow as connection points using Bridle Line.
- ATTENTION: Loop the bridle line around the Elbow! The fins are NOT designed to hold the entire tether force – they ONLY absorb some of the torsion forces from the blades.
- Add a loop of Shock Cord to each Elbow. These will be looped over the coupling pins when you stick in the blades.
Each Elbow should look like this now:
If you want to use your MAR suspended under a lifter kite like I did add bridle lines and the swivel:
ATTENTION: The red center line is VERY IMPORTANT. It absorbs the bending moments from the blades.
Congratulations, your MAR is ready to fly. You can see how to use it in this video:
Please let me know if you have any questions, problems or suggested improvements to the design.
Thank you and