Simon Chaddock Posted May 8, 2023 Share Posted May 8, 2023 The existing, for time being, XPS Skyray has reasonably scale proportions except it has over size inlets. A feature required by the 3x4 three blade prop inside the fuselage. In reality the inlets are quite small. So I wondered if I made a bigger but little or no heavier airframe I could transpose everything over from the smaller Skyray and keep scale inlets. This process would have the advantage that I would not "gain" another plane as I have simply run out of storage space! My idea is to use 3mm Depron rather than the 5 mm XPS which would go some way to limiting the weight of the larger airframe After doing some sums I decided that a 36" span would be big enough to achieve what I was after. It would represent a 138% increase over the 26" span of the XPS Skyray and giving it nearly twice its wing area. The 36" Skyray is going to have to be built 'light'. First job is the duct. As the motor and prop are right at the back there is only an inlet duct. Printed in 8 sections using LW-PLA, single wall & 'vase' printed'. The parts are designed to fit each other and are simply glued together. The new duct along side the the 26" Skyray for size comparison. The bifurcated inlet is lofted to give a smooth changing profile, The duct weighs 36g. So far so good. 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 12, 2023 Author Share Posted May 12, 2023 The fuselage which includes the wing roots is built around the the virtually full length inlet duct. Each formers are divided along the centre line and has to be carefully fitted so when glued in it fully supports the duct but does not distort it. Definitely "building in Depron" using techniques not that dissimilar to balsa.😉 In this state it is fairly delicate. Only when the Depron skin is complete does it become a full monocoque structure. In needs no further reinforcing. The large holes are not just for lightening (actually they only save 2.5g!) but should allow the aileron servo wires to be installed through to the cockpit area even when the skin is complete. Still some way to go. 6 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 15, 2023 Author Share Posted May 15, 2023 Adding the 3mm Depron skin panels to the fuselage underside. Loads of pins! By hand forming the skin panels it is possible to get them to fit close enough over the frame that simple pins hold the joint surfaces in place over the formers. At least in Depron they are easy to push in. The holes that are left are so small even alight paint coat completely covers them. Note the ends of each panel only cover half the former to give the end sections a surface to start from. The more complex shapes of the end sections will require multiple narrower 'planks' but the forming and pinning process is the same. So far it certainly feels light. 2 Quote Link to comment Share on other sites More sharing options...
Eric Robson Posted May 15, 2023 Share Posted May 15, 2023 I don't use pins on my builds Simon I use UHU Por like a contact adhesive, works for me. Nice build as always. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 15, 2023 Author Share Posted May 15, 2023 Eric I am using Technicqll. It does not work as a contact adhesive like POR does but in 24 hours is does dry rock hard so unlike POR a Depron joint can be sanded smooth using 120 grit paper. A useful feature on a planked double curved surface.😉 Quote Link to comment Share on other sites More sharing options...
martin collins 1 Posted May 16, 2023 Share Posted May 16, 2023 9 hours ago, Simon Chaddock said: Eric I am using Technicqll. It does not work as a contact adhesive like POR does but in 24 hours is does dry rock hard so unlike POR a Depron joint can be sanded smooth using 120 grit paper. A useful feature on a planked double curved surface.😉 Which one in their range are you using Simon, i has a quick look and nothing jumped out as a possible? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 16, 2023 Author Share Posted May 16, 2023 martin Its in the yellow 70 ml tubes. Polyvinyl Adhesive. Foam safe This Ebay supplier is the cheapest for two tubes. As I have observed before it costs as much as the foam 😲 but fortunately you don't use that much doing simple joints so the weight penalty is very modest. If the joint surfaces are in really close contact and the glue is fully hard the joint is a strong as the foam so a simple 'edge to edge' butt joint is as a good as a single piece. The down side is once fully set you can't get it apart again without damage. I have been "saved" many times by being able to 'prise apart' a POR joint even after several days.😉 2 Quote Link to comment Share on other sites More sharing options...
David P Williams Posted May 16, 2023 Share Posted May 16, 2023 Lighter fluid is the thing for separating POR joints, even old, long set ones. Just brush along the joint and the POR softens. Might be worth a try on your other stuff. Quote Link to comment Share on other sites More sharing options...
Eric Robson Posted May 16, 2023 Share Posted May 16, 2023 2 hours ago, Simon Chaddock said: martin Its in the yellow 70 ml tubes. Polyvinyl Adhesive. Foam safe This Ebay supplier is the cheapest for two tubes. As I have observed before it costs as much as the foam 😲 but fortunately you don't use that much doing simple joints so the weight penalty is very modest. If the joint surfaces are in really close contact and the glue is fully hard the joint is a strong as the foam so a simple 'edge to edge' butt joint is as a good as a single piece. The down side is once fully set you can't get it apart again without damage. I have been "saved" many times by being able to 'prise apart' a POR joint even after several days.😉 Thanks Simon, I was going to ask you which type, but I've had a busy morning. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 17, 2023 Author Share Posted May 17, 2023 The fuselage underside is fully skinned as well as the more complex planking around the air intakes. Lots of pins again! it is getting to the point where the EDF (actually its a quad motor and 3" prop) needs to cut out of the small Skyray and installed at the back of the 36" Skyray fuselage. 4 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 19, 2023 Author Share Posted May 19, 2023 The quad motor, printed mount and 3x4.5 three blade prop extracted from the small Skyray. Glued onto the end of the bigger Depron Skyray duct. The duct is the same diameter on both the Skyrays but on the bigger one the inlet and exhausts are scale size. The top skin is also complete as far as possible to allow access to run the motor and elevon wires. Once the motor is tested in situ (always test at every stage!) the next task is to build the nose/cockpit section. 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 22, 2023 Author Share Posted May 22, 2023 The nose section is planked as a half shell over the plan When lifted from th eplan the othe half of the formers are added. When all the planking is completed the nose section is simply glued on. The nose cone is printed. It feels remarkably light. 4 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 25, 2023 Author Share Posted May 25, 2023 A bit more progress. The fin, top skin and printed cockpit framing added. The ESC and Rx transferred from the small Skyray installed. Note the solid 'magnet' wires passing through the formers from the ESC to the motor right at the back. For the same amp capacity they as about half the weight of the normal multi strand silicone insulated wire. Yes its a 35 meg Rx!😲 Its long aerial passes down the fuselage spine and up the fin. It can easily be withdrawn should I want change it over to 2.4. Time to start on the wings. 5 Quote Link to comment Share on other sites More sharing options...
MattyB Posted May 26, 2023 Share Posted May 26, 2023 Wow - super impressive stuff Simon, well done! PS - What is that square thing sticking through the side of the fus - ESC heatsink? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 26, 2023 Author Share Posted May 26, 2023 Yes. A fingered heat sink like that, particularly in the airstream can dissipate many times the heat of a flat plate. On a cold day directly after the flight the heat sink is cold to the touch. Of course Depron is a wonderful insulator and with little or no air movement things inside the cockpit warm up quite quickly. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted May 31, 2023 Author Share Posted May 31, 2023 The wing construction is a bit unusual, just top and bottom skins and shear webs. All in 3mm Depron. The wing section itself is entirely controlled by the shear web's dimensions. First the leading edge shear web. The actual leading edge will be 6mm Depron glued on and sanded to profile. All six shear webs. The 6th shear web carries the elevon. The top skin glued in place and the 6 mm leading edge added. The forces required to bend the skin meant it was a two stage process. Simple weights could be use for the skin over shear webs 2 to 6. Only when that was fully set (24 hours) could the skin be brought on lo the leading edge web and be held in place with many spring clamps. This type of construction does rely on the glue drying truly rock hard, foam safe Technicqll in this case. The bare wing weighs 31.2 g. The servo and elevon will be fitted before the wing is attached to the fuselage. The other wing is WIP. 4 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 4, 2023 Author Share Posted June 4, 2023 Still quite a bit still to do and the final fiddly bits take time but the wings are now on . As a 'single piece' plane it looks like a lot of Depron. Battery compartment next which hopefully will end up somewhere under the cockpit canopy! 4 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 10, 2023 Author Share Posted June 10, 2023 With the final bits of the fuselage skin added a start made on the cockpit, battery box and some paint.. The underside has had a light coat of white 'match pot' emulsion overall but I have run out of masking tape to complete the grey upper surface! 3 Quote Link to comment Share on other sites More sharing options...
MattyB Posted June 11, 2023 Share Posted June 11, 2023 How do you paint your Depron models Simon? Foam roller, brush or airbrush? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 11, 2023 Author Share Posted June 11, 2023 MattyB Nothing fancy just a series of paint brushes. As the artists brushes in particular are very soft I do thin the emulsion a bit with water. The painting now more or less complete. The inlets will have red edges. The decals are next to go on and I am also waiting for some small magnets to secure the rear of the cockpit. It weighs 530g (18.5 oz) with a 1500mAh 3s. It has a wing area of 6.06 sqft giving a wing loading of just 3.03 oz/sqft. 5 Quote Link to comment Share on other sites More sharing options...
MattyB Posted June 12, 2023 Share Posted June 12, 2023 Very very impressive. How does that compare to the earlier smaller version? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 12, 2023 Author Share Posted June 12, 2023 MattyB The smaller version had just over twice the wing loading. Still quite modest but then a delta will always have a lower than normal wing loading. My reason for building the bigger one was more for 'appearance' by using light weight and a small fan to allow scale size inlets. However I do fear the power to weight ratio of the big one will be a bit low. An underpowered delta is risky as although the lift remains over a wide range of AoA the drag rises very quickly. With insufficient 'spare' thrust even a gentle manoeuvre can cause it to simply stop flying. We shall see.😉 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 13, 2023 Author Share Posted June 13, 2023 Now with the markings on Need some really calm weather for the maiden. 3 Quote Link to comment Share on other sites More sharing options...
Trevor Posted June 13, 2023 Share Posted June 13, 2023 Looks great Simon. Good luck with the maiden. Trevor 1 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 14, 2023 Author Share Posted June 14, 2023 Well it does fly, just about, but it is seriously underpowered. The flight was limited to just a circuit and a ridiculously slow into wind glide landing all done on the basis of "quit whilst you are ahead". The ESC will have to changed to allow a 4s battery. Some surgery will be required to do this on an otherwise undamaged just finished plane. 😟 Such is life. Quote Link to comment Share on other sites More sharing options...
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