Instructions - ABS Maxi Cub

Transcription

1 Instructions - ABS Maxi Cub Version Nov 2012 As noted in the post on Thingiverse, these instructions are to be used as a guide only. While every endeavour has been taken to ensure they represent the model as constructed, variations in build sequence and method are easily conceivable. All persons using all or part of this information for any purpose at any time do so at their own risk. Specifications: Wing span: 1410 mm (55.5 in) Wing chord: 150 mm (6 in) optional 200 mm (8 in) Wing COG: 52 mm (34%) Wing area: sq in (2.35 sq ft) Wing loading: 14.7 oz / sq ft OAL: 900 mm AUW: 980 grams (34.5 ounces) Servos: 2 x 5 gram

2 Step Notes Parts - 2x straight wing joiners 2 x angled wing joiners - 15 degree. 4 x wing spars each side of the main section, 2x wing spars for each of the poly sections plus the left and right wing ends. 6mm square hollow carbon rod, glued with epoxy 3mm carbon tube, fitted and drilled to suit. Centre section 760 mm Poly sections 336 mm Overall length 1410 mm The images posted here are of the first version of the wing, which was strong enough with the number of spars fitted, but the balsa plates were distorted by the pressure from the shrink wrap. I added the additional half spars for spacing as well as an additional piece of balsa sheet to get the finish you see below, which was a consistent and smooth wing profile. Fit balsa nose strip, cover edges with 1mm balsa sheet, sand and fit.. super glue works well for this application, but you do use a bit of it. Cover and seal with adhesive heat shrink film. Print Settings (Feed rate / travel rate / layer ht / shells / infill) 80 / / 1-2 / 10% Print and assemble fuselage 80 / 100 /.2 / 4 /

3 sections, threading parts on from smallest to the largest. 20% Spacing between sections going from the rear to the front are approximately 80, 95, 75, 80, 146, and 100mm. I tried to thread the sections on so that there was no apparent stress on the rods. Fuselage OAL (nose cone to tail) is 755 mm Print and fit the tie down brackets at 50mm and 210 mm from the rear of the nose section to the front of the cross brace. Some drilling of the tie down bracket holes is required to suit the angle of the fuselage tubes. I have used 4mm solid CF rod for this fuselage as there is some flex. Gluing with epoxy is a must for these parts. Print and mount the battery and electronics holder in place before securing the last fuselage section and the nose section. 80 / 100 /.1 / 2 / 10%. There is no external support required for this part if printed in the orientation as saved. There will be some small tidy up required as the inner edge of the upper surface will sag. This is not material to the performance of the part and cuts down print time significantly.

4 Print the ABS tail section and tail fin bracket, drill the guide holes for the control rods, sleeve the openings with plastic tube and glue in place. 80/ 100 /.2 / 2 / 10% Be sure to fit this part with an angle of incidence between 2 4 degrees to the main wing. An easy way to do this is to locate the fuselage on a level surface, using your iphone measure the angles of incline for both the tail plane and the wing mounts. Drill and fit the push rods, before glueing in place. Print and fit the tail wheel bracket. I have used the same 15 mm sheet metal fasteners with washers. 40 /40 /.2 / 4 / 20%.. is a fine print.. set speeds to very low. Fit the axel and retain with a touch of super glue. The wheel is nominally 32mm dia. Print the ABS nose section. This design has a little excess material on the face to allow it to be sanded down to suit the angle of the engine (3 5 degree downward and left cant). 80 / 100 /.2 / 2 / 10%. Increase HBP temp from 115C to 117 if lifting occurs. NOTE: The engine mount section will break if the engine is not secured with >30 mm fasteners, which penetrate the two internal layers of this part. For safety, I have intentionally broken the engine mounting block off, secured with epoxy and then fastened with >30 mm metal screws when mounting the engine.

5 Print the stabiliser, elevator, tail fin and rudder. 80 / 100 /.2 / 2 / 20% Recommendation to use these parts as templates for 3mm foam board cut outs as it saves around 55g in weight. For foam board parts, reinforce the lower section of the rudder and the centre of the elevator with.08mm aluminium sheet and glue in place. Print the landing gear. Secure with 4 x 20 mm metal screws after drilling pilot holes. 60 / 80 /.2 / 3 / 80% Cut and fit a single piece of CF rod to your desired wheels and secure with axel collars. Print and drill the tie down brackets out to suit 5mm CF rod. Thread and glue in place. 60 / 80 /.2 / 3 / 20% Print the tie rod ends, drill out to fit and spot glue with super glue.

6 Print the wing mount brackets, drill and glue 4 / 5 mm CF rod in the forward hole and 3 mm tube for the aft brace. 80 / 100 /.2 / 2 / 20% Overall width, 66 mm. Assemble the tail fin, rudder and stabilisers, add control horns, thread mm steel rod through the tail section and adjust servos for zero loading at the neutral position. 80 / 100 /.2 / 3-4 / 20% I located the speed controller on top of the extension piece on the battery holder and the receiver underneath to give clearance for the pushrods from the wiring. To save weight I have used metal ends on 2 mm carbon rod for the pushrods, secured with heat shrink tube and a spot of super glue Mount the motor and electronics using a combination of adhesive Velcro and hot melt glue. Test for correct operation and freedom of movement. Secure the battery by threading a Velcro strap through the

7 slots provided in the housing. Print and glue the battery cover and mounting blocks in place after trimming / drilling as required. Use the locking catch from the donor fuselage battery cover to secure this battery door. Drill a 1.5mm hole in the fuselage section adjacent the unhinged end of the battery cover and secure screw with super glue. 6 inch wing - Fit the wing mount bracket and secure with a cable tie over the forward cross brace onto the fuselage section. For the mounting blocks - 40 /40 /.2 / 4 / 20%.. is a fine print.. set speeds to very low. Increase feed rate to 60 / 60 for the battery cover. 8 inch (200mm) wing Optional wing mount, also located further aft on the fuselage, with the rear bracket flush to the section fuselage section. This version has the forward bracket at 48 mm from the centre of the CF rod to the rear face of the nose bulkhead. You will also note two sections of 8mm balsa as cross braces to reduce tail wag. NOTE - Using this version of the wing mount will produce a more docile plane when using the 8 (200mm chord wing), it also reduces the amount of lead required to balance the plane once completed.

8 I have loaded a six to eight inch wing mount adaptor to allow this wing mount to be used for both wing variations. Print settings 3 shells,.2 mm layers Glue or cable tie these blocks in place for as desired. In this configuration, I required less than 5g of ballast mounted on the forward face of the tail section to achieve a slightly nose down balance when using the (37g lighter) Turnigy D2826 motor. Cover the fuselage with adhesive heat shrink film. Lastly, weight and balance. The wing chord is 150 mm, with the COG at 52 mm from the leading edge.

9 Motor selection The rule of thumb for a trainer is that you need 50W 75W per pound. A model with an AUW of 980g (2.16 pounds), would require 162W of power. For this version you could use an E-Flite Park 480, which is a motor suited to planes with an AUW up to 990g / 250 Watts, fitted with a 10 x 7 prop. Spec: Type: Brushless outrunner Size: Park flyer Bearings or Bushings: One 4 x 9 x 4mm Bearing, and One 4 x 10 x 4mm Bearing Wire Gauge: 16 Recommended Prop Range: 10x7 to 12x6 Voltage: 7.2 to 12 RPM/Volt (Kv): 910 Resistance (Ri):.08 ohms Idle Current Continuous Current: 20A Maximum Burst Current: 25A (15 sec) Cells: 6 10 Ni-Cd/Ni-MH or 2 3S Li-Po Speed Control: 20 35A brushless Weight: 87 g (3.1 oz) Overall Diameter: 35mm (1.40 in) Shaft Diameter: 4mm (.16 in) Overall Length: 33mm (1.30 in)

10 An alternate would be the following motor from Hobby King, with a 3S battery a 6 x 4 inch prop, which is also suitable for up to 980g. D kv Outrunner Motor Specs: Rpm/V: 2200kv Shaft: 3.17mm Voltage: 2S~3S (7.4v to 11.1v) Weight: 50g Watts: 342w Max Current: 34A ESC: 40A Suggested Prop: 7x4(2S) ~ 5x5 (3S) Mounting Hole Bolt Circle: 16mm or 19mm Both motors would suit a 40A ESC, which includes some margin to ensure they run cool. Servo 2x 5g micro servos required. Update to the wing design to follow with a further 2 servos required to operate the ailerons.

11 Battery For this application the following battery works well, giving around 15 mins of mixed flying per charge. Turnigy 1300mAh 3S 30C Lipo Pack (AUS Warehouse) Spec. Minimum Capacity: 1300mAh Configuration: 3S1P / 11.1v / 3Cell Constant Discharge: 30C Peak Discharge (10sec): 40C Pack Weight: 123g Pack Size: 73 x 34 x 23mm Charge Plug: JST-XH Discharge plug: XT60 The design as configured will accept up to a 2100 mahr LiPo battery.

12 Additional guides... Applying Heat Shrink. Film is convenient to use, and adds more strength to the structure than tissue or silkspan. This covering is commonly used over balsa wood, although it can also be used over fiberglass, and even foam (low temperature film only). There is some skill to applying heat shrink plastic well, and this photo tutorial will help you develop that skill. First, you will need a part that has been sanded smooth. I prefer 800 grit sandpaper as the final finish. If the final finish is not smooth it will show after covering, do not think that you can hide it! A good sanding job is a critical piece of getting a good covering job. Second, make sure to remove that sanding dust. The dust particles get trapped under the covering and result in imperfections and bubbles. You will also need to remove dust from your work area, or perform the covering in a cleaner room (e.g. unused guest room in your house). A tack cloth from the hardware store is essential for cleaning the balsa airplane parts. Wipe the whole airplane down with the cloth; get into all the crevices that you can. Also use a vacuum cleaner with a brush attachment to remove dust. The wipe with the tack cloth again. You will also need to wipe down your work surface and tools. It's also a good idea to wash your hands before after cleaning the model and before starting to cover. You get the point: the cleaner, the better. OK, now you're ready to cover! You'll need the covering material, scissors, a sharp blade, a covering iron, heat sock, and a metal ruler to cut trim pieces. Our demo piece is an outer wing panel. Place the panel on the table, and measure and cut a piece of covering at least 2 inches bigger than the part. For wingtips, make the excess about 4 inches, as you'll need to hold on here during the wingtip sealing. Don't forget to remove the clear plastic protective backing from the film! The covering will first be tacked down at a few places around the frame, then it will be sealed at all the edges, then shrunk tight. The recommended sequence for tacking is shown below on the left. Click on any of these thumbnails to enlarge.

13 For a wing or other flight surface, you'll generally cover in two pieces, bottom first. For a fuselage, four pieces work well. Look closely at the numbered sequence of covering pieces, and at the overlaps. These overlaps should be around 1/8 inch. This sequence will help ensure that seams are less visible. When covering the fuse, if you need to use multiple pieces along the length, start at the back of the fuse and work your way forward, so that the seams face to the back. A word on the covering iron temperature. These films have an adhesive that is activated at one temperature. A higher temperature is required to shrink the film after tacking it in place. The covering iron has a dial with generic settings. For the old Hobbico iron and Ultracote covering in these photos, 1.25 works for tacking and 2 works for shrinking. Of course, this will vary from iron to iron and covering to covering. Read any directions that came with your roll of film to see what temperature they recommend. You can purchase a covering iron thermometer, but you could just estimate the correct temperature this way: cut a

14 small piece of the covering, place it adhesive side upwards, on the face of the upturned covering iron. If it begins to change color slightly, that's a good temperature to start tacking. It the film wrinkles a lot, try that setting of the iron for shrinking. If the films melts or vaporizes, that's way too hot! With your iron at the lower temperature, begin tacking the film. Use the tip of the iron to tack a spot about 1/4 to 1/2 inch diameter at one corner of the frame (labeled "1" above). Let the corner cool for a couple of seconds, then gently pull the covering towards the opposing corner ("2"). This pulling is essential to make sure that the covering ends up moderately tight, minimizing the shrinking that is need later. Don't pull so hard that you break the airframe! After tacking at corner "2", proceed to pull-and-tack around the airframe, till all eight (8) labeled spots are tacked: Note that if you don't like how a certain spot is tacked down, you can reheat that spot and gently pull the covering up, then reposition and stick it back down again with more heat. There are lots of wrinkles at this point, but that's to be expected. Now seal all the edges except the wingtip. The best way to do this is tack at the midpoints between all the previously tacked 8 points, e.g. halfway between 1 and 5. Then seal the entire length between 1 and 5. Repeat the rest of the way around the frame. Don't seal over the edge of the frame yet, just on the surface. Now you're ready to tackle the special case of the wingtip. It's special because it has compound curves, i.e. curves in more than one direction at once.

15 To make the film go around these curves, the film has to become very stretchy, so we must apply more heat. Turn up the covering iron temperature to the "shrinking" setting. Pull the covering tight over the tip, and begin to iron it in place. Work slowly from the center to the front, then from the center to the back. Move along just a few millimeters at a time. Stick the covering just over halfway up towards the topside of the wing. The middle photo below shows the covering pulled tight where the tip meets the leading edge, note the wrinkles. The next photo shows the same are after the covering is ironed is place, note the lack of wrinkles. It's the iron's heat that allows this to happen. If you find yourself exerting a lot of force on the covering (and risking a break in the airplane structure), then turn up the heat! Here is the tip after the covering is completed ironed around it. We'll trim the excess covering with an X-acto or single-edge razor blade:

16 Now turn the iron back down to the lower tacking temperature, and let it cool for the next steps. We'll start to trim the excess film. First use a blade to remove right-angled pieces from the corners of the frame. Then start to trim along the edge, leaving enough to overlap as in the "wing section" diagram above. Rest the cutting hand on the edge itself, use that as a guide as you cut. If you work slowly you can get a fairly straight line (it does not need to be perfect, as it will be overlapped later). For the trailing and leading edges, overlap a bit more more than half the thickness of the edge. See the photos on the right below: Now seal the overlaps to the wood. Go over the entire structure, making sure that it is completely and securely sealed: leading edge, trailing edge, wingtip, and inboard edge. Now cover the topside of the wing, using the same procedure. Again trim the overlaps using the frame as guide; this time, put the blade itself on the frame, using the frame as your ruler to get a straight cut.

17 Now that both bottom and top are covered and all the edges sealed, it's time to begin shrinking the covering. Put the heat sock onto the (cool) covering iron. You will be running the iron over the entire surface of the covering, and the surface will have small scratches if not protected. Turn the iron on, and let it heat up to the "shrinking" temperature. Now start gliding the iron over the bottom surface. Do not press down onto the wing! The iron should be barely touching the surface. Start the iron at one end of the structure and move it in slow circles. As a guideline, move in 2 to 6 in circles, about one circle every couple of seconds. The speed that works will depend on the iron temp and the covering brand. Do not leave the iron over one spot, as you can burn a hole in the covering! You'll see the covering change color slightly, wrinkles will form and disappear as you move the iron. As one area begins to look tight, drift slowly downwards to the adjacent area.

18 Keep moving down the entire wing until the whole bottom covering looks tight. You will probably need to go back to a couple small areas and re-shrink. When the bottom is done, flip the wing over and do the top side. And now we're DONE! Also check out our 'how-to' on making multi-color trim schemes from heat shrink covering. Motor selection guide motor selection.pdf With thanks and all credits to the original authors of these documents.