Simon Chaddock Posted October 9, 2013 Share Posted October 9, 2013 Some time ago I built a plane that had 4 LiFe cells built into its wings. They were charged in-situ. A sound structural solution allowing the plane to carry 60% of its all up weight as batteries, Electrically the set up worked fine but the widely distributed weight did result in some stability issues which were never completely solved. Its difficult flight characteristics meant its absolute endurance (1 hour) was never tested. As an experiment I replaced the LiFe cells with Li-ion. Of identical proportions they have 3 times the capacity, 3.7V instead of 3V and are 5% lighter. Fantastic on paper but the downside is a maximum of just 1.5C. For electric endurance (1+ hour) the battery is not actually required to deliver more than 1C so the LI-ion limit is not actually a problem. My current Endurance plane uses a 5000mAh 2s LiPo and flies on 1A so the battery is only required to deliver 0.2C. The battery weighs 7.3oz. Nine 3000mAh Li-ion cells arranged in a 2p3s arrangement would give the same voltage, weighs just under 8oz and have a capacity of 9000mAh. If a plane carrying it could be made to fly on 1A the ultimate duration would be.....silly! There is little practical point doing this but I am curious to see if it can be done. Past experience suggests the plane would fly better with its cells concentrated in the fuselage. Conventional tubular cells can be arranged efficiently in a triangle and stacked 2 deep would conveniently give the required 2s3p arrangement. A section of triangular Depron fuselage to test the battery layout. There has to be some way to insert the cells as they should be charged individually. A single cell sized hatch would be a possibility. Having decided the battery arrangement looked promising the full fuselage in 6mm Depron. The formers represent the battery compartment. The wing and tail surfaces will be mounted on top of the fuselage with a 70W out runner in the nose. Will it work? I have no idea - yet! Quote Link to comment Share on other sites More sharing options...
Martian Posted October 9, 2013 Share Posted October 9, 2013 another great idea I'm sure it will work, nothing can be done unless you try Quote Link to comment Share on other sites More sharing options...
Erfolg Posted October 9, 2013 Share Posted October 9, 2013 Is there a record that you are using as a comparison? If it is a personal challenge, I do not know what to think. The confusion I am experiencing is partly down to my own experiences. When we all flew of a bungee, I think 3 minutes was a typical flight without lift. Every flight was about achieving the 10 minutes (from memory) slot time, used in competition. So 20 minutes was a one in possibly 50 or probably more launches of the bungee. Retrospectively I now see that my devotion to winch launching, was just a device to improve on my limited flight duration, without any increase in skill. When I returned to modelling, it was by motorising my gliders. At first I felt pretty chuffed, my skills had really increased, I could do 20 minutes easily off one Lipo. If the aim was to use the motor once, I really could get the model to a dot in the sky, in 30sec. and then easily achieve 10 minutes. Yes I really had become that good. I then motored one of my biggest models, using a Mammoth Lipo to get the CG right, without lead (Pb). Now 45 minutes was easily achieved. I was now that good. Then the penny dropped, this duration flying was boring, had more to do with my motors and battery combinations, than me. I seldom fly gliders now, increasingly my models are sports planes. My thrust is, as a technical challenge what you are doing is very personal, in some respect vague, in that you are satisfying your own target. Perhaps some electric duration record is needed, to provide a firm goal! But if this approach and challenge, shakes your tree, and gets what you want, who am I to comment! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 10, 2013 Author Share Posted October 10, 2013 After some thought I decided the best solution to removing the cells was to hinge the complete nose. This will allow the cells to loaded like a torch and swinging the nose down would actually make the contact with the cells. The elevator servo will use external pull/pull wires. There are 3 sets of spring contacts for the negative end of the batteries. Each cable is actually soldered to the top of each spring so no current passes through the spring steel itself. The individual cables are joined to a larger one which is taken forward to the nose section. The radio will be in this area as well. The cells in place standing just proud of the join ready.to be compressed on their contact springs by the nose when it is in place . The nose will containing the motor and ESC. Quote Link to comment Share on other sites More sharing options...
Martian Posted October 10, 2013 Share Posted October 10, 2013 looking good Simon ,is no piece of depron safe from your furtive imagination Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 12, 2013 Author Share Posted October 12, 2013 The nose section hinged onto the fuselage. .The Blue Wonder motor is buried under the Depron rings. The nose lifted to show the battery access. The triangular plate is just visible on the rear face of the nose that makes contact with the positive end of the batteries. With 3 Depron 'cheeks' added to match the diameter of the spinner, a lot of sanding and some lightweight filler. Now to start thinking about the wing. Quote Link to comment Share on other sites More sharing options...
Martian Posted October 12, 2013 Share Posted October 12, 2013 that is starting to look really nice, by the way Simon can you show me a pic of the adapter for the motor shaft to prop please Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 12, 2013 Author Share Posted October 12, 2013 Martian These neat driver/spinner units used to be stocked in 3 sizes by Giant Shark (when they were Giant Cod) but are no longer available. This is the small size (32mm). The prop driver itself has a hex body that fits the nylon(?) folding prop unit which takes takes normal 6mm root blades. The blades are retained by conventional folding prop type screws. The fact the blades are held in plastic does limit how much torque/speed can be safely used (and maybe the reason they are no longer stocked) but these light and beautifully streamlined units are ideal for my purpose. Quote Link to comment Share on other sites More sharing options...
Martian Posted October 12, 2013 Share Posted October 12, 2013 thanks Simon they certainly look good how is the hub retained onto the motor shaft ? I expect there are poss alternatives maybe HK Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 12, 2013 Author Share Posted October 12, 2013 It is a standard collet type that tightens on the motor shaft as the nut is done up. The HK 'small' is almost identical but note it is not clear what size root blade it takes (5mm?) and is drilled for a 2.5mm motor shaft. I guess to limit the size of motor that can be used. HK only seem to stock blades larger that I would be confident to use on this hub. ps Giant Shark do now have the small and medium units in stock but for a 2.1mm motor shaft and a range of smaller diameter blades as well. Quote Link to comment Share on other sites More sharing options...
Martian Posted October 12, 2013 Share Posted October 12, 2013 Ah thats a blow I've got a couple of brushed motors I want to use but they are 3mm was planning on using 8x6 props ,is it poss to drill them out by half a mill ? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 12, 2013 Author Share Posted October 12, 2013 On my real light weight planes I usually specify 2 mm prop adaptors simply because they are smaller and lighter and drill them out to 3mm but I do it on a lathe to ensure the hole is concentric and true. You do have to be careful not to drill into the threaded part of the adapter as a 3mm hole is likely to be close to the minor diameter of the thread. The motor shaft may have to be shortened to get the adaptor to seat fully home. This was exactly what I did on my Depron Fokker V25 as the 2805 motor had a 3mm shaft. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 12, 2013 Author Share Posted October 12, 2013 Back to the Super Endurance The wing utilise the 15" tip sections of the Battery Wing but will have a new 10" inner panel to give a 50" span. The new wing will have a single centre dihedral break. The inner panel spar. A balsa/Depron/balsa sandwich 3mm thick. The balsa spars are deeper towards the root. The spar is inserted into the skin to give maximum depth. The inner panel spar and lower skin glued to the tip with the new ribs added. The spar joint is reinforced by 1mm balsa plates glued each side of the top and bottom balsa flanges. The left and right inner panels are completely symmetrical so 2 of each component was cut out at the same time. The other wing inner panel should be a quicker build. Quote Link to comment Share on other sites More sharing options...
PatMc Posted October 12, 2013 Share Posted October 12, 2013 Posted by Martian on 12/10/2013 21:06:21: Ah thats a blow I've got a couple of brushed motors I want to use but they are 3mm was planning on using 8x6 props ,is it poss to drill them out by half a mill ? Are you sure they're 3mm ? IIRC brushed 540 - 600 size motors generaly have 3.2mm shafts. Edited By PatMc on 12/10/2013 22:28:43 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 13, 2013 Author Share Posted October 13, 2013 The left wing complete, the right in progress. The wing panels joined and resting on the fuselage to see what it looks like. Not exactly elegant but it is intended to be an efficient weight lifter. The batteries make up over 50% of the total flying weight of 15oz. Tail feathers next. Quote Link to comment Share on other sites More sharing options...
Martian Posted October 13, 2013 Share Posted October 13, 2013 Are you sure they're 3mm ? IIRC brushed 540 - 600 size motors generaly have 3.2mm shafts. pretty sure but i'll remeasure by the way they are 480 brushed motors Quote Link to comment Share on other sites More sharing options...
PatMc Posted October 13, 2013 Share Posted October 13, 2013 480 motors are generaly the same shaft size as 400s - 2.3mm. Quote Link to comment Share on other sites More sharing options...
Martian Posted October 14, 2013 Share Posted October 14, 2013 measured again they are 3mm ,used a micrometer which is in thou but placed against a steel metric ruler and yep 3mm Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 15, 2013 Author Share Posted October 15, 2013 Tail feathers added and fixed in place. At least initially the wing will be retained with rubber bands as with such heavy batteries the wing position will be very sensitive to achieve an acceptable CofG. Quote Link to comment Share on other sites More sharing options...
Piers Bowlan Posted October 15, 2013 Share Posted October 15, 2013 I like the nose hinge idea for battery removal (I might copy that!). What are you using to stop it hinging in flight? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 15, 2013 Author Share Posted October 15, 2013 Piers I thought about this for some time. I was concerned that any motor vibration no matter how small might temporarily break the battery contact despite the contact springs on the negative end of the batteries so I went for the old favourite - rubber bands! The Depron has some local reinforcement and the bands are quite tight (I have a huge supply so they will be replaced each flight) but the advantage is it will keep the nose held down under positive pressure no matter what which a positive latch will not. The other benefit is the nose will 'give' if the landing is less than perfect! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 17, 2013 Author Share Posted October 17, 2013 Complete showing the temporary wing mounting. The big 6mm Depron pad over the wing is to prevent the bands damaging the wing, particularly the very fine trailing edge. It will need more bands to carry the full battery load but once the correct wing position has been established the wing will be permanently glued in place. The all up weight is as I hoped almost exactly 15oz (425g) which gives a wing loading of 6.2 oz/sqft. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 18, 2013 Author Share Posted October 18, 2013 It flies. The wing proved to be in the right place so it was glued in position with gives a rather neater installation. The prop has been changed from a 7.5x4 to a 9x5. A rather boring video of its second flight (the first with the glued on wing) The next is to establish the minimum power it can fly on and then to bench test the batteries at this level to see how long they can supply it. Quote Link to comment Share on other sites More sharing options...
Martian Posted October 18, 2013 Share Posted October 18, 2013 nice job Simon. are you going to try and fly it just on the point of stall ? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted October 18, 2013 Author Share Posted October 18, 2013 Martian Minimum power speed (minimum sink) is usually just a bit above stall speed. With a relatively thick wing section (12%) the problem is the drag rises pretty quickly with speed so not only must you fly at the required speed but also maintain it accurately. Not easy to do from the ground! Quote Link to comment Share on other sites More sharing options...
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