Proteus - an OpenSCAD slope soarer design

thingiverse

This is a fast, efficient slope soarer, NOT suitable for beginners.https://youtu.be/aQ_SdMxxsIY Update as of 19 January 2019: the Proteusv2https://www.thingiverse.com/thing:3366296 has more forgiving flying characteristics. Update as of 9 December 2019: Proteus Plus with 1.8 m span, PW51 airfoil and flaps:https://www.thingiverse.com/thing:3967057 Note: this Openscad design has a large number of parameters such as sweep, washout, dihedral and many many more. Adjusting these parameters will result in a corresponding outer shell being generated, but may result in some internal structures not being correctly positioned, or possibly puncturing the shell, e.g. increasing the dihedral will cause the ends of the main carbon fiber tube spar to be exposed underneath the wing. These issues are fixable but overall it is a lot of work to get that right for all possible parameters. Requires OpenSCAD version 2017.01.20 or later. Update 4 November 2017: Added ProteusFlyingWing.scad. This source file replaces CustomizableFlyingWing.scad and fixes an issue where increasing the noseLen parameter above 90 would cause the hatch to fail to fit properly. Note that fuselages generated with this new scad file will not fit the original hatch and vice versa. Default specs: Wing profile: MH-45 Fin profile: NACA symmetrical, 8% thickness Wingspan: depends on printer max z, 1040 mm for 200 mm, 1160 for 230 mm max z Root chord: 200 mm Tip chord: 130 mm Sweep angle (leading edge): 22 degrees Washout: 3.5 degrees Dihedral: 1 degree under each wing (2 degrees total) Flying weight: 560 g for 1160 mm span version (including 28 g of lead nose weight) Each wing is printed in 3 pieces, root, tip and fin. I have only uploaded the left-hand wing parts. Create the right-hand parts by reflecting them in the slicer. E.g. for Simplify3D, choose Mesh | Mirror Mesh | Mirror X (or Mirror y). The length of the root and tip pieces is set by the printerMaxZ parameter. I have only printed and flown versions where printerMaxZ is set to 230 mm. I have added stls for the case where printerMaxZ is set to 200 mm, for the convenience of people with printers limited to 200 in height, but I have not printed them. The hatch does not depend on the printerMaxZ parameter, all the other parts do, to some degree. The total span (including fins) of the Z200 version is 1040 mm. The only pieces I glue together are the nose to the rear fuselage and the servo guards to the wing (both with thick cyanoacrylate). The wing joints are taped, with fiberglass reinforced tape being used for the most important join between the root wing section and the tip wing section. The OpenScad code calculates the estimated CG position using code from rcwingcog@gmail.com:http://rcwingcog.a0001.net/V3_testing/?i=1 This CG position is used to place 2 small dimples at the correct balance position under the fuselage. Vitamins: 500 mm x 5 mm OD Carbon fiber tube spar:https://www.aliexpress.com/item/5pcs-5MM-OD-X-3MM-ID-X-600MM-Carbon-fiber-wing-tube-for-airplane-5-3/32242824992.html?spm=2114.13010608.0.0.dDXTx3 2 mm OD and 3 mm OD carbon fiber rod joiners:https://www.aliexpress.com/item/1pcs-Carbon-Fiber-Rods-Dia-1mm-2mm-3mm-4mm-5mm-6mm-7mm-8mm-10mm-11mm-12mm/32573564619.html?spm=2114.13010608.0.0.dDXTx3 Servos:https://hobbyking.com/en_us/hxt900-micro-servo-1-6kg-0-12sec-9g.html Servo extension leads:https://hobbyking.com/en_us/10cm-servo-lead-extention-jr-26awg-10pcs-bag.html Elevon linkages (these are too short for mechanical elevon differential - so use electronic differential, 2 pcs required):https://hobbyking.com/en_us/extreme-3d-1100mm-replacement-control-rod-1-pc.html Joining root wing section to tip wing section and holding servos in place:https://hobbyking.com/en_us/high-stength-fiber-tape-24mm-x-50m.html Elevon hinging (both top and bottom surfaces) and joining fins to wing tips:https://hobbyking.com/en_us/1-x-4m-roll-3m-blenderm-tape-hinging-tape-twin-pack.html Hatch latch: 3M™ Dual Lock™ Reclosable Fasteners (clear not black) Battery holder bracket mounting: 3M™ Dual Lock™ Reclosable Fasteners (clear not black) Joining wings to fuselage: PVC Tape (12mm) Nose weight: Lead fishing sinkers (1x 0.5 oz, 2x0.25 oz for the Z230 version) Weights: Root wing section (Z230 version): 81g Tip wing section (Z230 version): 44g Fin: 18g Elevon: 11g Fuselage (nose + rear): 105g Hatch:17g Total printed weight (less battery, servos, spar, joiners, tape, etc): 429g Control throws These are what I use for the glider version. They are likely to be too large for beginners and for the motorized version. All measurements relative to the trailing edge at the inner end of the elevons. Neutral: 1.6 mm of up elevon Elevator: -4.7 mm to +8 mm Aileron: - 10.8 to +16.5 mm In the tx mixer I set the elevator throws to be 45 % and the aileron throws to 100 %. I set the elevator to 20% exponential and aileron to 45% exponential. These throws are sufficient to allow a very fast roll, which is why either exponential or dual-rates are needed. Note, using too much up elevator in a loop will cause the glider to stall at the top of the loop and spin out, so be careful to fly it all the way around the loop to maintain speed (or reduce the maximum elevator throw). Print Settings Printer: Prusa i3 box frame Rafts: No Supports: Yes Resolution: fins, nose and fuselage - 0.2, wings - 0.24 Infill: S3D Fast Honeycomb, wings 4% at 72% extrusion width, to give 2.9% overall, fuselage 5% at 72% width Notes: Extrusion width: 0.4 mm (note infill is 72%, i.e. 0.29 mm), 0.48 mm for Polyflex nose Perimeters: 1 Top layers: 3 Bottom layers: 2 for all parts except wing root (3 layers) and servo guards which have 0 bottom layers. I use a 0.4mm nozzle. No fan for the wing sections, except for 50% fan for the last few layers (top solid infill). All parts printed in PLA or PLA+ except for the nose and servo guards, which I print in Polymakr Polyflex. Using white PLA(+) for the wing panels prevents the skin deforming in hot summer sunshine. I highly recommend using a flexible plastic for the nose piece since this greatly increases the chances that the plane will survive a crash unscathed. This is the case even if a wing tip hits the ground first, since in that case most of the damage occurs when the nose hits and the other wing tries to keep going. Polyflex is one of the easiest flexible filaments to print and is well worth the cost. I use Simplify3D and manually add small amounts of support as shown in the screen shots. I use automatic support for the wing root and then remove any support added to the wing spar tube using S3D's manual editing. The outer wing panel (ProteusLeftTip) does not need support. The fins need a small amount of support added manually under the trailing edge, as shown in the screen shot above. Note that the hatch is best printed on its side, with a small amount of support under the tongue: https://cdn.thingiverse.com/renders/3d/bf/6e/e7/57/7ddbe75d44a5aa6bae28178cb44c7549_preview_featured.jpg I experienced warping a the trailing edge of the wing root, so I added an oval hold down tab. I cut this off using a cutting disk on a Dremel style rotary tool (important -wear eye protection)! To avoid warping I use UHU Stick on glass on a heated bed at 70 deg C for the first layer, dropping to 50 C for the rest. Dropping to 50 C is important because otherwise the bottom layers of the print remain too soft, allowing the upper layers to warp them. I apply the UHU stick as a thin (single sweep) layer with the heated bed at 42 C. The glass needs to be washed clean between each print. Use glass at least 3 mm thick. Thinner glass will bend under the stress, especially with the wing root part, resulting in a warped print. Extruder temperature It is important that the extruder temperature is high enough to give good interlayer bonding. The optimum temperature varies greatly depending on the type of PLA. Low temperature PLA such as Diamond Age and Rigid Ink perform well in the 205 to 210 C range. Higher temp PLA such as the Chinese Wellhan brand need 235 to 240 C (despite the manufacturer's recommendation of 220 C max). To determine the optimum temperature I print temperature towers customized from https://www.thingiverse.com/thing:1298948. Because the PLA quality degrades the longer it is in the hot zone, it is important to print the temperature tower with speeds and layer times similar to the actual wing section. To achieve this, I print 2 towers at the same time, with 10% infill and no fan. Choose the highest temperature that prints well on the tower, but do not exceed about 245 C since above this temperature the PLA strength will degrade. Layer height: fins, nose and fuselage - 0.2, wings - 0.24. Extrusion width: 0.4 for PLA, 0.48 for Polyflex nose. I printed the servo guards in Polyflex with a 0.2 mm layer height. It is important to print at least 4 at once (2 mirrored in the slicer) to avoid the Polyflex staying too long in the hot end due to the low flow rate, which results in a lumpy surface finish. The dimples in the floor of the servo guards are meant to represent the sweep of the wing so you can tell easily which wing, left or right, a servo guard is shaped for. I use scissors to cut out a notch in the floor for the servo arm when it is in its most forward position and glue them on using thick cyanoacrylate. I also use thick cyanoacrylate to glue the nose to the rear of the fuselage, with 2 mm carbon fiber rods for alignment. All the other joins are tape, with 3 mm CF rods for the wing joiners. Cutting carbon fiber To avoid harmful carbon fiber (CF) dust in the air, I cut CF by hand with a fine hacksaw after spraying both the CF and the saw blade with water from a spray (atomiser) bottle. I start the cut on the under side then saw from the top so it cuts cleanly. I then use wet wet & dry paper to clean up the cut surfaces, and wet paper towels to collect the wet CF residue. Hatch The hatch is held to the fuselage at the rear using 3M Dual Lock. Cut 2 pieces the right length to cover the flat at the rear of the hole in the fuselage. DO NOT remove the backing that protects the adhesive just yet! Use a sharp knife to trim off the splines on the outer thirds of the top piece, leaving no more than the central third of the spines (otherwise too much force will be required to remove the hatch). Push the top and bottom pieces together and remove the backing from the top piece only and place the bottom of the bottom piece on the flat in the fuselage. Put the hatch on and push down at the back so the top piece of Dual Lock sticks to the hatch. Remove the hatch and rub down the Dual Lock so it is firmly attached to the hatch. Now remove the remaining backing material and replace the hatch pushing down at the back so the Dual Lock sticks to the fuselage. If the Dual Lock fails to stick to the fuselage when pulling the hatch off for the first time, spray a little CA glue accelerator on the fuselage and put some CA glue on the bottom of the Duo Lock before replacing the hatch. How I Designed This Inspired by http://www.thingiverse.com/thing:1659724 I decided to design a parametric slope soarer for 3d printing. In slope soaring, low drag and efficiency (the ability to convert height to speed and vice versa) are more important than weight. I therefore chose a moderately thin (9.85%), flying wing airfoil designed by Martin Hepperle, the MH-45, suitable for the Reynolds number range the slope soarer would fly in, of 100000 to 200000, and with good performance at the likely wing loading of around 30 g/dm. With a relatively thin wing and my desire to be able to use the wing for aerobatics, I used a carbon fiber tube spar. This also means the wings can be taped to the fuselage rather than glued, making it easy to replace damaged parts. I put the servos under the wing since drag under the wing increases lift, which in turn results in a partially compensating reduction in induced drag. This necessitated printing aerodynamic guards to protect the servos and linkages on landing. Ideally the servos would be in the fuselage and coupled to the elevons by torque rods, but that can wait for a future version. I was surprised how light and strong the printed parts are when printed with a single perimeter and Simplify3D's Fast Honeycomb infill. The weight of the infill is especially low as a result of specifying an infill extrusion width that is 72% of the perimeter extrusion width, combined with a 4% infill setting. The design is essentially monocoque, with the tensile strength all in the skin. The infill is so thin that it is somewhat flexible, but still prevents the skin from deforming too much under compression forces. The intent is that the infill acts a bit like the foam in a foam-veneer wing. I print the perimeters at 72% of the infill printing speed so that the pressure in the extruder stays constant between the perimeters and the infill.