Simon Chaddock Posted March 21, 2011 Share Posted March 21, 2011 My so far not very successful 18" 'Low Power Skyray' in the "Own Design" thread has prompted me make better use of the Depron in this compact and strong design to build one twice the size. Simple scaling up by a factor of 2 would mean 4 times the wing area but 8 times the weight, however it will still be made of the same 3mm Depron so the airframe should be only a bit over 4 times the weight. All the RC gear will be identical, the battery only 3 times , the motor and fan 4 times the weight.Overall I would hope the finished 36" Skyray will be a bit under 3 times the 6.25oz weight of the 18" version.Well that's the theory.The first cut. Those are big pieces of Depron. Just as well its light! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 22, 2011 Author Share Posted March 22, 2011 As I am waiting for HK delivery for the small Ray work on the big Ray is proceeding. The LH wing panel. It has a thickness/chord ratio of just 6.2%. Although built in a similar way to the small one it does have a balsa reinforced main spar. It has no ribs. Note the elevon servo cut out on the underside. The leading edge is 2 laminations of 0.8mm balsa. It weighs 1.04oz say 1.5 with the servo and elevon in position.The target for the bare airframe with both servos is 8oz. Apparently from what has been reported the surprise was not the Skyray's short service life but that it ever got into service at all.The prototype's maiden flight scared the Douglas test pilot so much he never flew a Skyray again. Not too surprising as just after take off it climbed at 45 degrees with the stick fully forward. Control only returned above 200knots!One of the pre-production aircraft was written off after an uncontrolled transonic 'pitch up' pulled 9.1g. As it was only stressed to 7g the wing bent and although the pilot blacked out he recovered enough to land it.Spinning needed special attention as the conventional recovery controls resulted in an inverted spin.All this meant that when in service the Skyray had quite a few placards dotted about the cockpit to remind the pilot of its flight envelope limitations. This might also explain why the pictures of RC Skyrays I have seen show them flying with reflex on the elevons. I imagine that with the CofG in the scale position things would become quite interesting. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 26, 2011 Author Share Posted March 26, 2011 I did a very preliminary test of the 110mm fan by simply bolting it in place of the 7x4 prop on my Wing Dragon which fortunately uses the same motor and battery configuration I intend to use of the big Skyray. It gave a good 12oz thrust. The next step will be to mount the fan at the end of a fuselage length duct (about 22") to how much thrust is then developed. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 27, 2011 Author Share Posted March 27, 2011 Both wings now complete with the 110mm 'plug' (a piece of soil pipe!) around which the fuselage duct will eventually be built. . Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 30, 2011 Author Share Posted March 30, 2011 The fan duct. Like the smaller one it is of planked construction. It weighs 1oz.Although built as a 'test' duct to check the thrust of the fan it is of the correct dimensions to be used in the 'flight' model as well.The 18" Skyray fuselage depth (67mm) was set by the 55mm ID of the duct with 6mm of Depron top and bottom.Rather than simply double everything up this duct is actually 6mm over size (116mm) and will have its two 3mm skins separated by 3mm spacers thus bringing the total to 134mm, hence the duct 'hoops'. At 116mm ID the duct has just over 11% more area than at 110mm so hopefully it will reduce the inlet losses a bit. The duct will be locally brought down to 110mm in the region of the aft mounted fan. This is Depron construction gone mad - building a drystone wall is starting to look rather attractive! Quote Link to comment Share on other sites More sharing options...
Erfolg Posted March 30, 2011 Share Posted March 30, 2011 Seems you are well on the way to success. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 31, 2011 Author Share Posted March 31, 2011 Some interesting testing. On the Wing Dragon the fan gave 12oz thrust. Interestingly the 110mm prop (4.4x7) with about the same pitch and only 1/8 the blade area still gave 8oz.This suggests that in free air at least the excess blade area of the fan is not particularly efficient and that its performance could be equalled with a 4 blade prop. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 1, 2011 Author Share Posted April 1, 2011 The fuselage centre section. As the skin is the same thickness as the smaller Skyray it has twice as many formers. It weighs 1.48oz.As before its rigidity will be greatly enhanced once the lower outer skin has been added.The rather more complicated nose section and inlet ducting will only be added once the fan has been installed and the actual thrust measured. If it proves to be below 10oz then that is as far as the construction will go - until I have worked out what the plan 'B' actually is! Quote Link to comment Share on other sites More sharing options...
Eck Posted April 1, 2011 Share Posted April 1, 2011 Quietly "lurking" and enjoying this blog - As with your other builds, it's a fascinating exploration of what's possible with the materials. Keep up the good work! Quote Link to comment Share on other sites More sharing options...
Erfolg Posted April 1, 2011 Share Posted April 1, 2011 Reflecting on your potted history, once gain I thought that the contrast of the official history with, reality. I remember the Skray as the worlds fastest aircraft, its ability at high speed climb to altitude, once again the USA showing its technical lead.I guess part of the handling issues will be down to the step change in performance. Just a few years earlier piston, propeller aircraft ruling the skies. Here we have one of the first delta aircaft, with a nose high landing configuration, the back end of the curve issues, not appreciated by most military aircraft. The tendency to rock, laterally at these high AOA.Maybe it was a little mis understood, being a step change from a Skyraider.Anyway I am looking forward to the first flight and you making the plan available. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 2, 2011 Author Share Posted April 2, 2011 I believe to a degree the handling difficulties were expected as nothing was allowed to limit its performance (50,000ft in 3 minutes) but perhaps not ideal for a carrier aircraft.The lower skin in place. It now weighs 2.1oz.8oz for the basic airframe still looks possible.Now to install (temporarily) the motor & fan to test the thrust. Edited By Simon Chaddock on 02/04/2011 00:13:26 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 4, 2011 Author Share Posted April 4, 2011 As in the small Skyray the motor and fan/prop will be mounted in the tail cone so that only this has to be changed to accommodate different motors, fans or duct exit diameters. The tail cone under construction showing its double skin tapering down from 116 to the 110mm diam of the fan or prop. Edited By Simon Chaddock on 04/04/2011 23:50:03 Quote Link to comment Share on other sites More sharing options...
Erfolg Posted April 5, 2011 Share Posted April 5, 2011 Simon Would it not be simpler to install one of the many HK fan units? They are are only about £16 A big Fan+motpr, or maybe just a smaller fan at about £12 with your own motor. When you make your plan available that will be my intention, as I am less than confident in making a good fan unit. Going well though, I will be interested in how it goes. At 36" dia. it is very possible to change fan units in experimentation. I do suspect that most of the DF's I see are designed for out and out speed as that is sought by the purchaser and hence high power is needed. The other aspect is that the low end handling is generally compromised, as the fan needs a certain speed to work well, if top end performance is wanted. The most successful from my wants point of view, was a Kysho F16, which had reasonable bottom end handling. Although a Fantom DF flies well at our club, being hand launched and with a wide speed range. As you will probably know there is no ducting just the fan unit.Edited By Erfolg on 05/04/2011 10:46:39 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 5, 2011 Author Share Posted April 5, 2011 ErflogYes you could probably squeeze that big fan in but I think at the price you quote you only get the fan & casing.The 36" Skyray is built for low power (150W) whereas that big fan is designed for a motor in the 2000W class and would need batteries to match. I am not sure running that fan on such low power would be particularly weight efficient. Some more testing. A 28mm 2600kV out runner with the 110mm (4.4 x 7) prop. Surprisingly with this prop it is slightly over loaded drawing 25A on a 3s but it certainly moves a lot of air. With a finer pitch I hope to get below 20A static.This will be compared against a 1500kV motor driving the 7 blade fan. Edited By Simon Chaddock on 05/04/2011 16:59:38 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 6, 2011 Author Share Posted April 6, 2011 The tail cone complete. It weighs just over 1/2oz. Ideally I would like the mounting to be designed in such a way both that both the motor,fan or prop can easily be changed. Its like looking down a piece drain pipe. Which of course is exactly what it is! Edited By Simon Chaddock on 06/04/2011 11:47:55 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 7, 2011 Author Share Posted April 7, 2011 The rather unusual motor mount. It is made of very hard 2.5mm balsa and 2mm ply Small Depron fairings will be added to produce produce a smooth 'tear drop' shape. The struts will be cut to length, sanded to a streamline profile and the whole assembly glued inside the tail cone. It now almost certain that I will use a prop rather than a fan as the new finer pitch (4.4x4.5) produces nearly 16oz thrust, about 25% more. If it gives anything like this figure when in the duct the big 'Ray' should have a sparkling performance. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 8, 2011 Author Share Posted April 8, 2011 The motor with the 4.4x4.5 prop fitted right at the end of the tail cone. This is now rather more of an EDP than an EDF. It weighs 2.3oz (66g)With so little to hold on to just a quick test showed it had not lost much thrust, if any, but boy is it noisy as the Depron seems to act as a sounding board. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 14, 2011 Author Share Posted April 14, 2011 Progress a bit slow as I have been drawing out the nose section fuselage formers and rather frightened myself.It may only be a quite modest 36" span but it is just a shade under 5 feet long. Its going to look enormous! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 17, 2011 Author Share Posted April 17, 2011 The nose section plan and the Depron formers. The two cut out formers will allow the cockpit section to be double skinned in Depron for extra rigidity.To give access for this inner planking only the very minimum of the external can be in place. Quote Link to comment Share on other sites More sharing options...
TonyS Posted April 18, 2011 Share Posted April 18, 2011 Simon, Fascinating stuff. EDP..... you've sparked off a whole new genre of flying Love the depron building. Looks very tidy. If you carry on like this the wing loading will be very small so should float down (s.t. the peculiarities of the design). T Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 19, 2011 Author Share Posted April 19, 2011 The nose section 'skeleton'. This is about as delicate as it gets.To avoid a 'banana' build the planks must be added equally both sides and their line carefully chosen to minimise any twisting loads on the flexible structure. It does get easier as the skin progresses, until of course the final plank which has to fit exactly all round!It will keep me busy for a few evenings. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 19, 2011 Author Share Posted April 19, 2011 The cockpit inner skin. It is a huge space. The 1500mAh 3s takes up less than 1/6 of the volume.At least it allows the battery to be moved about to position the CofG. Now the external planking can start in earnest.. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted April 20, 2011 Share Posted April 20, 2011 Simon With respect to the use of Depron you are an artist of the highest standards. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 22, 2011 Author Share Posted April 22, 2011 The planking progresses. At least the stiffness is slowly increasing as the planking progresses.Like this it weighs just under 1 oz. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted April 24, 2011 Author Share Posted April 24, 2011 At last the planking is complete.The nose section 'grafted' into the main duct. Its big!To create the inlet ducting quite a bit of the first two formers will be cut away.On paper at least the big Skyray should come out close to 16oz all up. Quote Link to comment Share on other sites More sharing options...
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