Olly P Posted November 10, 2012 Share Posted November 10, 2012 Lovely, really like the gatling cannon Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 10, 2012 Share Posted November 10, 2012 Been quietly watching this one - and as usual Phil.....lovely workmanship. Cant wait to see this beast thrown off the big rock :=) Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 11, 2012 Author Share Posted November 11, 2012 So with the forward fuselage complete bar the cockpit layup and canopy, I decided to move onto the other end and focus on the fins and tailplane next. Again, these would be veneered white foam structures, indeed the cores had been cut a long time back by Ron Broughton. The photo below shows one of the fin panels, symmetrical in section and cut in foam right back to the Trailing Edge. As previously mentioned, the fins were causing me some concern on a large PSS version of the A-10 without undecarriage, as the base of the fins sit well below the fuselage and even on a good landing, they are likely to catch and will drag with any forward movement upon touch down. I could foresee damaging not only the fins but also the tailplane and fuselage with any such landing loads. This is not an uncommon problem in PSS circles as undercarriage is generally only ever fitted to models with fixed gear - so any hanging items like wing mounted engine nacelles or weapons on wing rails need either to be designed to be dropped by R/C on the previous circuit to landing, or to knock off rearwards upon landing thus avoiding damage to the surrounding airframe. For the fins I could envisage the part of the fins protruding down being fitted on sliding ply surfaces, mounted on carbon rods and held with magnets, such that any landing impact on their leading edge radius would see them knocked off and clear of the tail, avoiding undue loading into the tailplane and rear fuselage. Edited By Phil Cooke on 11/11/2012 20:30:58 Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 11, 2012 Author Share Posted November 11, 2012 The first task was to veneer the fins both sides (again using the 0.8mm obechi) right to the Trailing Edge, then add a balsa Leading Edge and tip section, which were sanded to shape in 2D before work continued. Two fins on the A-10, so twice the work... The foam panel finished just at the point I would have drawn the sliding joint for the bottom section, so a 1/8" light ply face was added to the bottom face and sanded to profile. Fin bases were made in light ply, correct in 2D profile - these would later be filled in with soft balsa and sanded to shape. Now the interesting bit, here's what I had in mind. The sketch below shows the fin bolted to the tailplane at the correct incidence - you can see the intended ply faced sliding joints - and the 2 vertical 'steps' needed to be formed so that this can only be removed to the rear - with an inpact on the leading edge of the fin base. It was my intention to 'line' all these sliding joints and mating faces with light ply to aid operation and prevent wear. Edited By Phil Cooke on 11/11/2012 20:36:52 Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 11, 2012 Author Share Posted November 11, 2012 To aid accurate sanding of the balsa block infills, the ply bases were temporarily spot glued into position on the fin at the front and rear, the balsa was sanded to 3D profile and the fins were marked up carefully with the 2 new vertical faces before they were cut away. Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 11, 2012 Author Share Posted November 11, 2012 Having cut the sliding section away from each fin panel, additional material was removed to allow for the thickness of 1/8th light ply on all mating faces, this was added and once dry everything was finish sanded to profile. Heres a few photos to show the finished sliding sections, needing only the carbon dowels and magnets to finish this part of the assembly. The keenest of A-10 fanatics and scale modelling buffs will notice that the functionality requirement of these sliders means the rudder will have to be finished short compared to those on the full size, which has rudders running out to the bottom of the fin. This brings us on nicely to the next task... Cutting the working rudder and positioning a servo box in each fin will follow. Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 12, 2012 Author Share Posted November 12, 2012 Ok, so onto the rudders. With the fins already veneered this is all pretty basic stuff so I wont add too much detail... The fins were marked up with the rudder (hinge line) and a parallel line 1/4" each side of it to account for the balsa faces to be let in. Before they were cut away a servo box was also sized and positioned and marked on the inner surface of each fin. With the foam cut away to suit the balsa stock, the position of 3 hinges per surface was marked up and hard balsa blocks were let into recesses made in the foam - care was taken to ensure the hinge positions were bang on the centreline. Robart 'knuckle' type hinges are being utilised for rudder and elevator so a good balsa block is essential to secure them properly in the foam panels. With the blocks let into the foam pilot holes were carefully drilled for the hinges along the centreline - this would aid machining later once the LE and TE stock was fitted. Soft balsa was used to form the rudder leading edge and fin trailing edge and these were sanded to profile once the PVA had set. The base of the rudder was lined with 1/8th light ply for robustness and sanded to shape. The photo above shows the sanded parts during a trial fit of the hinges. Having agreed already where they were to be fitted, I made up 2 balsa boxes for the rudder servos and removed an equal volume of foam core to accept them. These were sized to accept a standard Ripmax servo mount/cover. A hole was made in the box to allow for servo leadout, this wiring would also need routing to a cavity where the tailplane is to be mounted, but more on that another time. The servo is positioned square to the hinge line at a short distance for simple, slop free control. The cover sits flush with the fin surface bar the blister, and will look just fine once everything is glassed and sprayed up the same colour. And thats it... The job was repeated ensuring a left and a right fin was made, leaving us with 2 fins finished pending only the tailplane mounting arrangement. But before we could do that, we would need a tailplane... Edited By Phil Cooke on 12/11/2012 20:55:38 Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 13, 2012 Author Share Posted November 13, 2012 Ok, so on with the tailplane – again, another white foam core veneered in 0.8mm obechi. Before the veneer, the core was made fit for purpose with some internals… Four 1/32” shear web spars were epoxied into the foam core material to give the tailplane sufficient stiffness along its span. Remember we are hanging 2 big fins off the end of the tailplane – and I wanted it to be robust, like the real A-10! As well as the spars, I modified the span of the core panel with balsa tips such that the tailplane would protrude into the fins by approx ½”. This was in an attempt to aid alignment each time it was assembled in the field. Epoxied in behind the balsa sub tips were two ¼” ply plates onto which were mounted captive nuts, to accept the fin bolts. These were carefully spaced and aligned to suit. On the centreline, the tailplane was fitted with 2 hardwood mounting plates, which would act as load spreaders for the tailplane mounting bolts, and a vertical ply plate into which the locating dowels (formed from 8mm carbon rod) would react. All this was fitted and made good before the veneer was applied in the same way as before using contact adhesive. Quote Link to comment Share on other sites More sharing options...
Olly P Posted November 14, 2012 Share Posted November 14, 2012 Lovely Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 14, 2012 Author Share Posted November 14, 2012 With the tailplane internals all complete, it was time for the veneer. The 2 elevators had already been cut away (as they had been cut integral with the tailplane in white foam) so these got the veneer treatment too. Once veneered, cavities were marked up on the tailplane and cut out for the balsa servo boxes - 1 servo per elevator positioned close to the hinge line on the underside of the tail. The elevators are pretty huge so Savox SC0252MG would be used here to give a confident pull under flight loads with no flutter risk. Again, just like the fins, material was removed to accommodate 1/2" balsa L/E and 1/4" T/E stock, but before that was added, pilot drilled, hard balsa blocks were epoxied into the cores to enable a robust mount for the Robart hinges, again, 3 per panel. Edited By Phil Cooke on 14/11/2012 22:40:54 Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 14, 2012 Author Share Posted November 14, 2012 The leading edge and trailing edge balsa stock was then added to the tailplane, as shown whilst the PVA was drying, and a similar stock was added to the front of the 2 elevators. Once dry, this was sanded to profile. Next, light ply end plates were added to both the elevators and the tailplane for robustness, once dry these too were sanded to profile. Hinge holes were drilled and tested. As all these flying surfaces are to be glassed none of the hinges have been glued in place as yet. The 2 location dowels were fitted in holes through the L/E and secured in the holes in the pre-installed internal ply plate. The extension leads (for the rudder servos) are shown routed from the end of the tailplane to the centreline where they will enter the fuselage. There is a cavity behind the ply end plate large enough to 'hide and retain' the servo connections so they dont get trapped or crimped between the tailplane and the fin when they are bolted up. Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 14, 2012 Author Share Posted November 14, 2012 With the tailplane and fin assemblies approaching completion, it was only right for another quick bench flight... Starting to look like an A-10 now! The next job would be the trickiest so far - to build up the tailplane mounts into the fins. Edited By Phil Cooke on 14/11/2012 22:48:40 Quote Link to comment Share on other sites More sharing options...
stu knowles Posted November 15, 2012 Share Posted November 15, 2012 Excellent thread Mr Cooke, some good leaning to be had here. Can I ask how you are cutting your foam, is it bow and templates or do you have something exotic?? Ref the tailplane core, are the 32nd spars let into the core or did you slice the core up and then rebuild it with the ply in place? Many thanks stu k Edited By stu knowles on 15/11/2012 13:26:38 Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 15, 2012 Author Share Posted November 15, 2012 Hi Stu, The foam panels that have been used in the build so far have all been cut with a hot wire bow around templates from the plan. I can't take credit for this foam work, it was done by Ron Broughton. Yes, you are right, my spar description was a little vague - the foam core on the tailplane was indeed cut into 5 parallel sections along the lines where the spars were to be placed, then glued back together using the foam beds as a guide whilst drying - this way the spars are full depth. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted November 16, 2012 Share Posted November 16, 2012 Really enjoying the build Phil, you are doing a super job on this. A friend at my club has built one of these and was showing it off the other week. Not quite as large as yours, but flew superbly. The flaps are undercambered it seems Cheers Danny Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 16, 2012 Author Share Posted November 16, 2012 Thanks Danny, still a long way to go of course, but we are getting there slowly. Thanks for posting the A-10 pics - that looks like a very nice rendition - I'm presuming EDF - is it designed by your club mate too? Looks the business! Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted November 16, 2012 Share Posted November 16, 2012 Hi Phil, I got quite a few shots but I dare say there are many great color schemes out there. Yes it is a home design, edf powered, I have some notes somewhere if you are curious, however when I last saw it at Ashbourne, Mr Whittaker was all over it like a rash, so a possible future featurrete. Cheers Danny Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 16, 2012 Author Share Posted November 16, 2012 As previously described it was important to set the tailplane incidence much flatter than that shown on the power plan, which had a huge amount of positive incidence fighting the down thrust from the engines. In fact for a PSS version I wanted the tailplane at zero degrees incidence and a datum line was carefully drawn onto the inner surface of each fin, checked, then double checked. I wanted the fins to slip over the end of the tailplane, to be located and positioned accurately each time it was assembled in the field, and for them to be bolted up tight against a ply load spreader. This required a balsa and ply box to be made for each fin, shaped carefully to suit the tailplane aerofoil section. It was basically a sandwich of 1/8" ply, 2 x 1/8th light ply and 1/4" balsa. The aerofoil section was cut into the balsa and light ply sheet leaving the ply as a backing plate - this is the load spreader for the mounting bolts. The box was dressed carefully so that they were a good fit over the tailplane at each end. Holes could then be drilled in the 1/8th ply to suit the captive nut spacing in the tailplane, and a third hole was drilled over size to accept the rudder servo wiring. Edited By Phil Cooke on 16/11/2012 23:14:32 Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 16, 2012 Author Share Posted November 16, 2012 Having checked the datum line once again on the fins, veneer and foam were removed to accept the balsa and ply boxes. The depth and flatness of this foam cavity was important to ensure accurate fitting of the box, and some time was spent fettling to ensure the correct fit. Further foam was removed to enable the rudder wiring to be fed from this position to the servo box already positioned outboard in the fin. The balsa and ply mount boxes were then epoxied in place. The balsa part of the box would later be sanded flush with the fin aerofoil section to complete the assembly. Quote Link to comment Share on other sites More sharing options...
David Gilder Posted November 16, 2012 Share Posted November 16, 2012 Have to say Phil, This is a real building masterclass your giving here! Enjoying every part! Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 16, 2012 Author Share Posted November 16, 2012 Sanding flush the 1/4" balsa section of the fin boxes effectively finished the fins and tail. Quite a bit of work, but a good, robust and repeatable fit was achieved at each end between fin and tailplane. Bolted up the alignment of each fin could be checked and a few final tweeks were made before these parts were put to one side awaiting final sanding in prep for glassing. With the tailplane, fins and rudders all complete, and with my wing panels still being manufactured by Barry Johnson at Foamwings, I commenced thinking about how to build a big pair of turbofans - PSS style. Edited By Phil Cooke on 16/11/2012 23:58:14 Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted November 17, 2012 Author Share Posted November 17, 2012 So onto the engines, a prominent feature on the A-10 for sure, from any angle! On a PSS design, my nacelles are not designed to carry powerplants, so they were built entirely differently to how shown on the original power plan - but of course, they must still look right to achieve the scale effect from the outside. My design would have to incorporate the characteristic blunt spinner at the front and the exhaust cone at the rear - whilst at the same time allowing air to pass through the nacelle in an attempt to minimise drag. The external shape of the nacelle and its L/E inlet lip was important to get right - twice - to form a matching pair! I wanted the nacelles to be removable for transportation and storage, at 1/6th scale they are easily big enough to get your arm in and I envisaged threaded dowels and wing nuts securing them to the fuselage mounted pylons. I sketched up some ideas and soon came out with a full-size plan using plywood, balsa and plastic vac-form components. Edited By Phil Cooke on 17/11/2012 10:22:53 Quote Link to comment Share on other sites More sharing options...
Matt Jones Posted November 17, 2012 Share Posted November 17, 2012 You make it look so easy! Enjoying the build Phil, keep 'em coming. Quote Link to comment Share on other sites More sharing options...
Foamie Dave Posted November 17, 2012 Share Posted November 17, 2012 Cracking job Phil ! Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted November 17, 2012 Share Posted November 17, 2012 Phil, have you considered blocking the engine nacelles? - you may find having them open INCREASES drag - a la "normal ducting". Fab work mate. Edited By Tim Mackey on 17/11/2012 11:44:36 Quote Link to comment Share on other sites More sharing options...
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