RC Airplane Wing Ribs

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Arctic_Eddie
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Location: St. Petersburg, Florida

RC Airplane Wing Ribs

Post by Arctic_Eddie » Sat Dec 12, 2020 8:33 pm

I use the CAD part to import a list of airfoil points then connect them using the spline function. Thereafter, the shape is scaled up to the actual dimensions then include spar, server wire, and weight reducing holes and notches for leading and trailing edges. The CAM part is used to create the gcode file for cutting the pieces for a 4mm foam core and 0.75mm balsa cladding. The GrblMM post processor file will be used to cut the parts on a soon to arrive Sainsmart 3018 Prover with a 5.5W blue laser. Presently, they will be cut on a Bridgeport/Anilam CO2 laser. I've just posted a request for help on creating the Anilam post processor file. I like the QCAD/CAM approach as the job can be done with one program and customized to any CNC/laser machine.
:D

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Husky
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Re: RC Airplane Wing Ribs

Post by Husky » Sat Dec 12, 2020 9:38 pm

Interesting! Would be nice to see a few stills on that process .... 8)
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Arctic_Eddie
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Posts: 28
Joined: Sat Dec 12, 2020 5:23 pm
Location: St. Petersburg, Florida

Re: RC Airplane Wing Ribs

Post by Arctic_Eddie » Sun Dec 13, 2020 12:43 am

I have a test section with three ribs on a spar. It will be used to test wing covering, Monocote plastic film. I'll take a photo tomorrow and post it here. It uses the laminate method, balsa/foam/balsa, with skewed faces for angled spars. The ribs are for a wing with a tip chord of 300mm. The root chord section is 1000mm and will require the ribs to be cut in six passes. Each pass is 170mm long with the material advanced on the table by that amount after each cutting pass. Index marks are burnt at the material edge at the end of each pass and used to move the material to a reference mark for the next pass. The entire plane has a 2 meter wing span and is very similar to the new B-21 prototype. The airfoil is a Selig S3021 uses in gliders.

Arctic_Eddie
Active Member
Posts: 28
Joined: Sat Dec 12, 2020 5:23 pm
Location: St. Petersburg, Florida

RC Airplane Wing Ribs

Post by Arctic_Eddie » Sun Dec 13, 2020 8:28 pm

Here's an attached photo of a three rib section for Monocote testing. Since the leading edge is pulled back 35 deg, each rib has to have the outward balsa pulled back by a certain amount based on an angle of 35 deg and foam thickness of 4mm. The balsa pieces are the chord design length but the foam has to be 2.8mm longer. At assembly, the inward balsa is aligned with the front of the foam and the outward balsa aligned with the back of the foam. The foam outline is stretched in the x-axis in QCAD relative to it's center point, the spar. After gluing, water based polyurethane varnish, the excess foam at the nose and tail is trimmed with an Xacto knife while the remainder is removed with 100 grit paper on a sanding block. The V shaped notch on the front will be filled with a 1/2 in. piece of square balsa rotated 55 deg from square. This gives the minimum amount of sanding to achieve the airfoil shape. The slots at the back will be filled with a piece of 1/8 in. x 3/4 in. piece of balsa. A piece of tapered 3/8 in. x 2 in. balsa, aileron stock, will be the trailing edge. The ailerons will use the same material with hinges. The slots for the hinges will be cut into the 1/8 in. x 3/4 in. edge using a precision miniature table saw with a thin blade. The servo will be mounted on additional balsa blocks between two of the appropriate ribs.

The first test used 6mm foam but it was decided to reduce it to 4mm as the strength was far more than expected. The foam is hot wire sliced from 1/2 in. foam sheet from HD. The device for slicing, The Slabbifier, is also home made and designed using QCAD. The wire, 28 ga Nichrome 80, is heated to just the foam melting point using a 12VDC power supply and a DC PWM motor speed controller. Polystyrene foam board slices very well with a hot wire cutter.

PS
The board won't allow me to attached the JPG file of 800 x 450. It claims my post contains spam. I've used some symbols in the first version but have removed them. Without the photo, the description does not mean much.
Last edited by Arctic_Eddie on Mon Dec 14, 2020 11:04 pm, edited 2 times in total.

Arctic_Eddie
Active Member
Posts: 28
Joined: Sat Dec 12, 2020 5:23 pm
Location: St. Petersburg, Florida

Re: RC Airplane Wing Ribs

Post by Arctic_Eddie » Sun Dec 13, 2020 8:29 pm

Here's the photo. Now it seems to work if posted separately.
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AirplaneRibs3.jpg
AirplaneRibs3.jpg (112.65 KiB) Viewed 1644 times

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