Eric Robson Posted February 14, 2022 Share Posted February 14, 2022 4 hours ago, kc said: I knew there would be a good reason! I suppose your way is somewhat like laminating - bend one layer and then attach the other layer. I think it would be possible to counteract that by saying wood is pretty good under compression but fails in tension - so attaching the wide balsa might help prevent failing in tension and also prevent some joints springing open. In the end both the 1/8 and the sheeting are bent just as much. But whatever works works! Are there any other published RC designs that are as lightly built as those by Ivan Pettigrew? I have not noticed any. I think Einstein said ( or was it one of my flying pals... ) that not only do light planes crash less but they crash lighter too . I don't know if the plan was published kc but this one is 8ft span for rubber power and only weighed 4lb. It would be nice for modern electrics but more work than I would like to take on. Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 15, 2022 Author Share Posted February 15, 2022 (edited) Added some of the upper fuselage formers tonight. As I seem to be getting through my stock of 1/16" balsa, I decided to use 3/32" and adapt Robins rib system for the upper formers where they will not be seen. Seems to have gone really well so I may adopt this as a standard approach. Certainly saved lots of balsa as I barely used 1/2 a sheet, so that means less weight too. The front 3 formers are 130mm wide. The solid front formers are the rear of the cockpits, the rear solids are the tailplane support formers so I need strength there. Added some bracing between the tops of the formers which will help when it comes to supporting the join for the upper 1/16" sheeting. Edited February 15, 2022 by Andy Gates Quote Link to comment Share on other sites More sharing options...
kc Posted February 16, 2022 Share Posted February 16, 2022 You are making great progress Andy. What exactly is Robin's rib system? It looks as though it involves cutting the smaller ones from the waste of the next larger one, but maybe there is another way? Maybe a join? Or are they lapped to get the grain in the best direction? Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 16, 2022 Author Share Posted February 16, 2022 Each of the arches are 2 pieces of wood which have been cut separately from the same piece of sheet in such a way that the outer cut of one provides the inner cut for the other. Hardly any waste at all and uses far less balsa. Strength seems pretty good too as the way I have cut it - the grain runs corner to corner. I will take some better pictures when I get home. Robin has a thread on RCG as eye4wings about cutting ribs to save balsa. I will add a link on my website later for you. Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 16, 2022 Author Share Posted February 16, 2022 Here goes as promised, picture of one of the arches showing the 2 piece construction. 1 Quote Link to comment Share on other sites More sharing options...
kc Posted February 17, 2022 Share Posted February 17, 2022 Andy that explains it well, and all those joints on the 1/8 framing look very accurate. If you have any tips on how those close fitting diagonals etc are made then I would be interested. Do you use just a scalpel, or some sort of balsa chopper ( guillotine ), a sanding jig or just a sanding block and patience? The speed of your build suggests you use cyano for these joints or is it PVA and more patience? The link on your website shows the rib method and I found there is more about Mini Waste Wings here. I am not sure how he controls washout or wash in though! Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 17, 2022 Author Share Posted February 17, 2022 Wash in or out would be controlled by jig I would imagine. I will be adding a small amount of wash out just to stop the tips falling away too easily at the stupidly slow speeds I sometimes fly - probably not required but I will add it. Still deliberating with myself about the wing incidence - more research required. With 5 Ivans models, I have had plenty of practice at making the joints fit well. My first (Chipmunk) was not so good as I had not got a technique to cope with it. My method is to sort the top and bottom runs then add the uprights. I normally fit a central one first and work my way out. All this is done by pinning the wood to a board (with the plan over the board covered with laminating film / cling film / covering backing depending on the glue used). The pins are not through the wood but either side to hold the wood against the outline on the plan. The wood for the uprights is initially over laid on the top and bottom strips. The top angle is sorted with a combination of scalpel / sanding block. The lower end is marked on the over laid strip of wood with a sharp scalpel erring on the over size. Once cut the sanding block then adjusts the final fit. The cross braces follow a similar pattern to the above, BUT I now only fit the cross braces to the top and bottom strips. Initially I was trying to fit cross braces to the top and bottom strips and the uprights, for me one too many accurate cuts to make a good job of it. I also now try to glue the whole joint in one hit rather than in a piecemeal fashion (I use thin CA for the framing job as I am not that patient). I found that doing it bit by bit did not give such a strong glue joint as it is CA on CA rather than CA on bare wood. My glue use depends on what I am doing and sticking. CA for framing jobs, if it is a CA on CA joint I opt for something like the "Brush & Nozzle" thicker glue as it is a bit stronger. Sheeting normally PVA as it gives time to adjust the fit to suit. Also works well on wetted balsa. Sometimes I combine the 2, tacking sheet in place with CA while the PVA joins dry but I have to be very accurate with the CA for this to work. Anything involving plywood, Basswood, Spruce I use PVA or for high stress jobs (undercarriage) epoxy. Sorry to be so wordy but I hope this helps. Quote Link to comment Share on other sites More sharing options...
kc Posted February 17, 2022 Share Posted February 17, 2022 (edited) Thank's Andy - I think that is all information that may be useful to many. The rather traditional stick construction method that is not used much now. Pat Mac once showed a handy gadget for cutting verticals to length to meet the longeron. I thought that was probably the secret! I realised that by building the frame over the plan that you save the trouble of marking then cutting a sheet fuselage side to exact size and then making another the same. No doubt the frame first method is a timesaver. One thing not mentioned is the classic method of building the second frame over the first. I never found that worked well for me! Edited February 17, 2022 by kc Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 17, 2022 Author Share Posted February 17, 2022 I always build the second frame over the first frame, I just add another layer of plastic over the first frame and build on top. At least that way both frames are identical, even if the frames are wrong - they are both contain the same error. Did a little more tonight, and then did my first "put all the bits together" motivational picture. Not really enough space in our dining room to show it properly, but it is wet and windy outside. 2 Quote Link to comment Share on other sites More sharing options...
kc Posted February 17, 2022 Share Posted February 17, 2022 That's looking very promising! You probably will have it ready to fly by the time these gales cease... Building one frame over the other probably went wrong for me due to parallax! Quote Link to comment Share on other sites More sharing options...
Trevor Posted February 18, 2022 Share Posted February 18, 2022 Coming on very nicely Andy. When building those fuselage frames, I sometimes work my way along adding an upright, then the next diagonal, then the next upright, etc. I find this makes getting a good fit with the diagonals a lot easier - once you get a good dry fit for the diagonal in one corner (say the top), the other end is trimmed to rest neatly on the bottom longeron. Then finally the end of the diagonal is sanded to align with the drawn position of the next vertical strut. I hope that makes sense! Trevor Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 18, 2022 Author Share Posted February 18, 2022 Makes perfect sense Trevor. Strange how we all do things slightly differently. I did add some side sheeting after the photo last night, not ventured outside to look how it went yet. Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 20, 2022 Author Share Posted February 20, 2022 Moved on a bit. Side sheeting came out pretty good. Added the motor mount and cowl to the fuselage Rear formers arched to clear the elevator pushrod Servos fitted for rudder & elevator Tail wheel mount / cover 2 Quote Link to comment Share on other sites More sharing options...
kc Posted February 21, 2022 Share Posted February 21, 2022 Plenty of progress Andy. Is that front cowl glued on or is it removeable? Can you fit the motor through the cowl? Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 21, 2022 Author Share Posted February 21, 2022 Front is fixed and will merge with the framework when the sheeting is added. Motor does indeed fit through the front, even if I need to go up a size which I doubt I will. Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 25, 2022 Author Share Posted February 25, 2022 A little more progress has been made. Motor fitted to the mount. Aileron servo mounts made and servos fitted. Finally cores made for fin and rudder 1 Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 27, 2022 Author Share Posted February 27, 2022 Sheeting this weekend after flying. First front upper cowl.. and outer panel leading edge sheeting to complete the D-box, with packing under the trailing edge for some washout Quote Link to comment Share on other sites More sharing options...
kc Posted February 28, 2022 Share Posted February 28, 2022 There are lots of interesting details on your model Andy. It would be interesting to see a photo of the completed fin & rudder showing whether it's sheeted on top of the framing or not. The elevator horn and joiner looks unuusal ( i.e not a commercial item ) so how do you ensure it won't come loose on the joiner? Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 28, 2022 Author Share Posted February 28, 2022 (edited) For those who are wondering where KC saw the image of the elevator joiner, it is on my website as I did not consider it as anything different. The horn is cut from 2mm glass reinforced plastic sheet, the joiner is 2mm hardened steel. The steel was roughed up and the hole in the GRP horn was drilled to 1.9mm. This meant the horn was a press fit onto the shaft and the horn was then glued with thin CA which has wicked its way under the horn with some persuasion. Then an epoxy fillet was added on either side to make sure there is no movement. It was bent to shape after everything had dried or set. This system is more than sufficient for my Pitts which exerts much more stress on the elevator system than this machine ever will. Back to a recurrent theme, because it is being built light, it will fly slower, which will mean the control surfaces will not have to work very hard against the slip stream so the systems can be lighter. Fin and rudder will follow the pattern of the tailplane and elevators, 1/16" core with a frame around the edges on both sides and "ribs" on both sides. No sheeting for the outsides of fin, rudder, tailplane or elevators at all. Keeps it light? Edited February 28, 2022 by Andy Gates Quote Link to comment Share on other sites More sharing options...
kc Posted February 28, 2022 Share Posted February 28, 2022 Thanks for the explanation Andy. Before I asked the question I had a good think which produced some ideas on what could be used as a sound elevator horn/joiner arrangement on any model. I came up with 1. a two piece piano wire joiner with arms bent up then inserted together and soldered into a brass tube to form the horn. 2. a flat steel joiner going into a slot in the GRP ( that's what I thought I was looking at in Andy's photo ) the flat steel being less likely to rotate than a rod, also more area to grip the balsa. 3. a normal piano wire joiner going through a brass strip to form a horn and reinforced with bits of brass tube bent up to give flanges to increase soldering area. Silver soldered. 4. Hammering the piano wire to form a flat to go through a slotted hole in the horn rather than a round hole to avoid any possible movement. Might produce metal fatigue at a crucial point though. 5. a forked pushrod avoiding joiner and using 2 horns. I would rather favour 5. for security or 1. for a neater look. As you can see Andy did something quite different and it's his model! Quote Link to comment Share on other sites More sharing options...
Trevor Posted February 28, 2022 Share Posted February 28, 2022 I often use option 1, but epoxy the brass tube onto the two part piano wire joiner. Trevor Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted February 28, 2022 Author Share Posted February 28, 2022 I often use option 3 with no brass reinforcement. GRP system seems to work well for me on lower stress situations. Not too sure I would use this on a highly aerobatic machine or a high speed one. Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted March 1, 2022 Author Share Posted March 1, 2022 Arrr! I goofed. I added the upper central sheeting prior to fitting the undercarriage blocks, now rectified thank goodness. Quote Link to comment Share on other sites More sharing options...
kc Posted March 1, 2022 Share Posted March 1, 2022 We have all done that sort of thing! But it seems to be going well otherwise. One further idea for elevator joiner occurs to me - By soldering another small bit of piano wire alongside the joiner and drilling another hole right alongside through the horn, the horn would not rely on the glue to hold it from turning but would function even if the glue fails. Too late now but just an idea. Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted March 3, 2022 Author Share Posted March 3, 2022 Quite a bit more done but nothing really to show for it. Wing LE sheeting and strip fitted, strip has had its first sand to rough shape. Upper central sheeting completed too. Upper trailing edge completed out to the ailerons. 1st cowl cheek added. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.