Simon Chaddock Posted November 27, 2014 Share Posted November 27, 2014 Whilst 'steeling' my self to attempt to maiden the Q400 (unless I am very lucky it is unlikely ever to look as pristine ever again!) I noted I had a couple of 30mm EDFs in the drawer. Last year I had thought of building a Canberra with 55 mm EDFs but it would be pretty big so I eventually ended up building a Fairey Delta 2 with a 55 mm EDF right at the back. The question to be answered is how big would the Canberra be with 30 mm EDFs and just how light would it have to be. First I found a nice 3 view of a B2. Next to see the difference with the EDF right at the front or back of the nacelle. With the EDF as the tail pipe the inlet duct can be much larger (twice the FSA) which should reduce the duct losses but the airframe comes out rather large at 40" span and this would be for just 3 oz total thrust. With the EDF right at the front the exhaust tube is much smaller so can be the nacelle giving a span of just over 28". A 4 oz total weight seems rather more achievable at this sort of size. A plan view showing the proposed EDF installation. That exhaust tube looks awfully long and narrow. The first task is to design and build a complete nacelle to check what the actual thrust is. The result would determine whether there was any point in building the rest of the airframe! Edited By Simon Chaddock on 27/11/2014 17:10:39 Quote Link to comment Share on other sites More sharing options...
Tony Bennett Posted November 27, 2014 Share Posted November 27, 2014 i do love watching you build, it's an education in skill. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 2, 2014 Author Share Posted December 2, 2014 Using 22mm mandrel (a piece of plastic CH pipe) the paper tube is wrapped around it. The fan casing is 30 mm diameter so a short tapered section is required as well. This also made of paper around a specially turned wooden mandrel. The Depron outer skin will planked over the formers. The small 'cone' is an 'after body' that will be mounted in the duct just behind the motor to provide a smooth transition from the EDF annulus to a the smaller exhaust tube diameter. The nacelle completely planked and the mandrel removed. The mandrel will be retained to make the second nacelle. The after body installed in the duct with 3 litho fins. Hopefully the benefit in reducing turbulence behind the EDF will outweight the extra skin drag of the after body. The EDF installed in the front of the nacelle. The complete nacelle and EDF weighs 0.8 oz (23g). Next is to measure the thrust to see if the Canberra is a 'possible' or 'dead end'. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted December 2, 2014 Share Posted December 2, 2014 I hope you get a possible Simon John Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 5, 2014 Author Share Posted December 5, 2014 The Depron test stand. On (actually in!) the stand. On a 2s it delivers just a touch over 2 ounces thrust. But these Depron structures make wonderful sounding boards so quiet it is not! A total of 4 ounces thrust should give me a bit more weight to play with but the total current draw of 14A is likely to need a rather larger (and heavier) battery than I had originally planned for. I suppose it is to be expected. All EDFs are pretty inefficient and small ones even more so! . Quote Link to comment Share on other sites More sharing options...
Braddock, VC Posted December 5, 2014 Share Posted December 5, 2014 I wonder if there is any value, in the form of additional thrust, by reducing the clearance between the tips of the fan blades and the stator. Almost certainly it would reduce the noise levels simultaneously. Ideally the blades could be shrouded but, of course, this would mean the shroud would be subjected to significant centrifugal force and require balancing etc, second best would be to sleeve the stator with thin plastic, thin balsa or mirralite ply or even depron aiming for minimal clearance. Just thinking out loud..... Quote Link to comment Share on other sites More sharing options...
Braddock, VC Posted December 5, 2014 Share Posted December 5, 2014 Forgot to say, good choice in the canberra, one of my favourite planes, the full size being so versatile that even the usaf wanted it. Quote Link to comment Share on other sites More sharing options...
Braddock, VC Posted December 5, 2014 Share Posted December 5, 2014 Forgot to say, good choice in the canberra, one of my favourite planes, the full size being so versatile that even the usaf wanted it. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 5, 2014 Author Share Posted December 5, 2014 The 'generous' blade tip clearance is specifically mentioned in the instructions as apparently the whole fan 'expands' as the revs increase. Having examined a fan quite a bit of the hub is hollow so I can understand it would do this but why it should be done like this is a bit baffling. It is probably the reason that the fan is strictly limited to 2s, Those that tried 3 found a huge increase in thrust followed immediately by shed blades. The next problem is the wing section. It is recorded as being an RAE/D symm 12% at the root but so far I have not been able to find any details of it. The published RAE symmetrical sections are in the series 100 to 104 nominally 10% thickness with the maximum thickness ranging from 26% to 42% chord. The various sections of the Canberra wing shown in 3 views seem to indicate it had is maximum thickness well aft at about 40% which corresponds to the that of the RAE103 which is the fourth (D?) in the series. I am sure on such a tiny plane the thickness of the wing section will have a much greater impact on its performance than the exact detail shape of its streamline section so RAE103 it will have to be. Edited By Simon Chaddock on 05/12/2014 12:18:31 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 8, 2014 Author Share Posted December 8, 2014 The next task is to build an outer wing panel and then work out how to fix it to the nacelle. First printout the required wing ribs. The outer panel used ribs 4 to 9. With the out panel printed out to the required size the "D" box skins can be cut out. These skins a manipulated by hand to give approximately the require curvature. The shear web and ribs are glued in place on the lower skin. Once the top skin goes on the"D" box is rigid enough for the rest of the wing structure to be built from it. An unusual way of doing it that requires quite a bit of 'eye ball' to keep it all straight and true. Terribly time consuming but it seems to work well enough. It weighs 6.6g - which gives a construction rate of about an hour per gram! Edited By Simon Chaddock on 08/12/2014 01:21:53 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 9, 2014 Author Share Posted December 9, 2014 Next to 'fit' the wing accurately to the nacelle so it can be glued in place with the object of testing if the joint is rigid and strong enough without reinforcement of any kind. Somewhat of a trial to fit as on the Canberra the nacelle is slightly nose up relative to the wing datum. Structurally it does seem adequate as held only by the nacelle it was easily able to carry a 2oz (56 g) weight on the wing tip. As the dihedral joint is at the middle I have not yet decided whether to make the inner wing in two halves and 'insert' them through holes in the side of completed fuselage or to join the two halves first and then drop the wing into a big fuselage cut out. I can see advantages either way - which is why I have not decided! . In the mean time work has started on the other outer wing panel as I had already cut out all the parts whilst building the first. Edited By Simon Chaddock on 09/12/2014 00:49:44 Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted December 9, 2014 Share Posted December 9, 2014 I'm speechless! How do you manage to do it all. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 9, 2014 Author Share Posted December 9, 2014 I think I have come up with a third option which gives me the best of both the other alternatives. Build the fuselage in three pieces! The middle part of the fuselage (it is a true parallel tube between the wing leading and trailing edge) can then be built 'on' the wing centre section. In this way it will be much easier to run the wiring and install the battery box as the build progresses. To save weight the Canberra will be a 'bank and yank' so there will only be the elevator servo wire to run forward which in turn means the fuselage tail section will have to be completed before the middle section. The whole nose section will have nothing in it and thus be no more than an aerodynamic fairing. One day I might actually build a plane where everything can can be put in at the end and taken out again - but I haven't yet! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 11, 2014 Author Share Posted December 11, 2014 It gets a tedious now just building more of the same fiddly bits. Got this far. That is a 24" rule. At least the wing is recognisably Canberra shaped! Next is to join the wing centre section to the nacelle to finally confirm the strength and rigidity of the glued joints. I shall then divide my time building the centre section of the fuselage around the wing (interesting) and building the other nacelle (tedious!) although I have not yet got the replacement EDF (from Hong Kong). Just out of curiosity I started counting up the individual pieces of Depron. Nacelle 28, wing outer panel 27 each, centre section 26, giving a total so far of 108. Probably twice that in the completed airframe. Edited By Simon Chaddock on 11/12/2014 01:04:20 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 12, 2014 Author Share Posted December 12, 2014 With the nacelle glued to the wing centre section a modest start is made on the centre section of the fuselage. As hoped it is built up from the wing centre section which makes it much easier. I now have to start the second nacelle. As with all these very light planes virtually the whole plane has to be completed before the battery position can be even roughly set but I hope it will be under the box spar. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 14, 2014 Author Share Posted December 14, 2014 Upper planking on the centre fuselage. The underside is left open. It will only be planked after the installation of the wiring, radio and battery. The formers for the second nacelle. The centres have to be cut out very accurately for them to be able to pass over the paper thrust tube but still be a close fit to be glued in place. The formers cut out for the rear fuselage. It will be built as a half shell over the plan. The solid first former is temporary and will be removed to save weight when the rear fuselage is completed. Edited By Simon Chaddock on 14/12/2014 12:01:34 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 15, 2014 Author Share Posted December 15, 2014 With the formers held in place with temporary keel strips the half shell can be planked. Lifted from the plan the temporary keels strip can be removed. And the other half formers glued on. With just skin and formers this type of construction is about as light as it can go. The next challenge is to fit the single elevator servo in such a way that it can move both elevator halves in the dihedral tail plane but with minimum weight. Quote Link to comment Share on other sites More sharing options...
Toni Reynaud Posted December 15, 2014 Share Posted December 15, 2014 Silly question maybe, but the wings are at present open construction. Are you going to skin them in thin Depron, or use film of some sort? Quote Link to comment Share on other sites More sharing options...
Andrew Price 2 Posted December 15, 2014 Share Posted December 15, 2014 Lovely aircraft, full sized and this model is looking fantastic - another successful build on the way. Unlike the Q400 the Canberra looks as though it may well fly!! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 15, 2014 Author Share Posted December 15, 2014 Toni The open panels (and only the open panels!) will be tissue covered. Its under half the weight of even 2mm Depron. The Depron "D" box is plenty strong and stiff enough so the rest of the wing is just 'aerodynamic fairing'. No dope of course but water shrink and then 'set' with a very light spray of clear acrylic. The planking complete on the rear fuselage. It weighs 7.8 g (just over 1/4 oz). Now to make & fit the tail feathers and the tiny 2.5 g elevator servo. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 16, 2014 Author Share Posted December 16, 2014 The top over the rear fuselage cut away to seat the 3mm Depron sheet tailplane. The tiny 2.5 g servo just fits on top of the tailplane and within the fuselage. Appropriately trimmed the cut out is replaced. The elevator servo horn protrudes to allow individual links to each aileron half although the RH link will have to pass through the base of the fin. Slowly getting there. Edited By Simon Chaddock on 16/12/2014 22:21:20 Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted December 16, 2014 Share Posted December 16, 2014 Delicate work Simon, looking good John Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 18, 2014 Author Share Posted December 18, 2014 As the servo are going to be several inches from their surface I was concerned that the push rods were going to add significant weight given that the servos themselves only weighs 2.5g. So I built a 5" long test push rod using 2 mm x 1 mm hardwood strip with an acetate clevis and horn along with a pin (literally!) hinge. It weighs just 0.38 g!. Using the same principle the elevator uses a 'divided' push rod. Under test. Seems to work ok and it is very light. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted December 18, 2014 Share Posted December 18, 2014 That elevator set up looks good Simon. When I tried to deal with a similar dihedral tailplane on a Supermarine Swift, I used a similar approach. However the pushrod wasn't central to the fuselage line and so the connection to one side was almost straight and the other was cranked. In practice I found that instead of the pushrod maintaining a direct push/pull, it tended to deflect sideways and cause unequal movements in the two halves of the elevator. The answer was to locate it with guides to prevent it from deflecting, but the way you've done it looks far better than my attempt. Edited By Colin Leighfield on 18/12/2014 09:58:06 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 18, 2014 Author Share Posted December 18, 2014 I think some benefit comes from the fact that the twin push rod is rigid, that is the rods are physically joined together just before the servo clevis but of course the loads are very light as the servo doesn't have much torque anyway! A bit of a fiddle mounting the fin with a slot just big enough to clear the push rod. Compared to the fin the rod has a rather complex motion. Hopefully I can soon start fixing all the bits together as at the moment it looks a bit like a aeroplane graveyard. Quote Link to comment Share on other sites More sharing options...
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