Simon Chaddock Posted September 8, 2016 Share Posted September 8, 2016 I have been thinking about this for, well, 9 months but I can resist no longer! The question I asked myself was not so much how much weight could be saved using Depron but how much would it weigh if it was simply made in Depron? First there is the question of size. At some point Depron needs significant reinforcing so it starts to loose some of its weight advantage. My experience suggested that 40" span is about right and has the big advantage (for me anyway) that it is then small enough that it can be built in one piece. Thus it would be 40/53 or 3/4 the size. That means it will only have 9/16 the wing area and given 'smaller' wings tend to be less efficient it is going to have to weight better than half the weight. The original came in at 71 oz so I don't really have a target weight except lower than 35 oz! So off we go with a light weight Depron Ballerina 'look alike' . First the wing. Basically 2 mm Depron skins and close spaced ribs with wide but tapered 1 mm balsa spar flanges flush with the wing surface to give maximum beam depth. That about as far as my thinking goes at the moment. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted September 8, 2016 Share Posted September 8, 2016 You won't go wrong with this one! Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted September 8, 2016 Share Posted September 8, 2016 ... wauw, Simon... what a surprise, here. Shame that I can't just 'copy' your wing design for the Bella as my fuselage is way to heavy... But, subscribed I am. Hakuna matata Chris BRU - BE / CTR Petitarina Control Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 8, 2016 Author Share Posted September 8, 2016 Just realised I have misspelt the title! It should be Petiterina with an "e" in the middle rather than "a". Perhaps a moderator could do the honours at some point. Next job is to shape a "rib master" The original wing section looks to be a standard 11.7% Clark Y. I have kept to Clark Y but in truth as the wing loading and chord come down a thinner section actually gives a better L/D ratio. By placing the spar flange within the wing skin means the ribs are 'simple' and have no cut outs. So 26 identical ribs in 2 mm Depron. Edited By Simon Chaddock on 08/09/2016 19:19:50 Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted September 8, 2016 Share Posted September 8, 2016 Hello Simon, If you don't mind, I don't think it's a 'pure' Clark Y as Peter's airfoil seems to have the flat bottom section starting closer to the maximum thickness and the Clark Y is more 'flat bottomed' than this one. Maybe he modified it a bit to have some better 'inverted' behavior than a 'standard' one... or this could be another part of my mental insanity... But I guess Peter will jump in & clarify it all... A question, if allowed. If you skin the wing with 2mm Depron and your tapered balsa spar is 1mm, how do you compensate the thickness difference, please? Or do you foresee your foam beam to be tapered the same as as your spar flange? 'Petiterina' sounds definitely better in my opinion, especially in French... Hakuna matata Chris BRU - BE / CTR Clark Control Edited By McG 6969 on 08/09/2016 20:28:18 Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted September 8, 2016 Share Posted September 8, 2016 Hi Simon Interesting project. The wing section is NACA 3414. PM me and I can send you a picture of that section. Clark Y is 12% thick, NACA 3414 is 14%thick, THis is also a bit closer to symetrical and or what is commonglt know as semisymentrical which Clark Y is flat bottomed. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted September 8, 2016 Share Posted September 8, 2016 Actually the section that you have drawn is closer to mind than Clark Y Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 9, 2016 Author Share Posted September 9, 2016 Peter Thanks for clearing that up. Thus using the Clark Y I will, albeit unintentionally, be using a slightly thinner section that is better suited to its lower Reynolds number! Chris The wing skin is made in 3 pieces When the Depron is added over the 1 mm balsa it does of course stand proud above the rest of the skin so it is carefully 'slotted' by 1 mm with a 2 mm wide needle file. Doing it this way, rather than cutting a notch in the rib, means it also accurately locates them as they are glued in. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 9, 2016 Author Share Posted September 9, 2016 The wing ribs glued onto the lower skin and the shear webs added. The spar as such will not be complete until the top element is added so it is all still pretty flexible. That is the next job. In fact the wing section follows the original pretty closely. It is truly flat bottomed which the NACA 3414 is not quite but at 14% it has exactly the same thickness to chord ratio. Edited By Simon Chaddock on 09/09/2016 14:02:52 Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted September 9, 2016 Share Posted September 9, 2016 To be perfectly honest the average person, including me, will not be able to tell the difference in perfomance and handling with most roughly similar airfoils and the old TLAR sections work pefectly well. TLAR THat looks about right also know as "Drawn round your boot sole." Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted September 9, 2016 Share Posted September 9, 2016 At that size it would fly perfectly well with a flat plate wing, but it's a bit infra-dig! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 10, 2016 Author Share Posted September 10, 2016 The top flange added along with the front top skin. It is now plenty strong and stiff enough to be handled so a 6 mm Depron leading edge is added and sanded carefully to profile. In this state the LH wing weighs just 0.91 ounces (25.8 g). So far so good so a start can be made on the LH wing - before I forget how it was done! The next stage is to cut out the aileron and fix in its servo. . Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted September 10, 2016 Share Posted September 10, 2016 That looks very nice. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 11, 2016 Author Share Posted September 11, 2016 Started thinking about the fuselage. I think it can be made entirely from Depron, probably 3 mm at least for the flat side panels and is might end up with more formers. It will look something like this. A 'soft' long stroke undercarriage is the best approach to reduce the shock loads and then to spread the forces over a large an area of the Depron as possible. The solution I evolved for my Depron Super Cub works very well. It uses acetate sheet side plates glued to the fuselage and carries a braced undercarriage made of relatively fine wire. With this method the wire itself is not fixed directly to the Depron at all The result is light, holds the wheel securely in line but allows considerable vertical travel. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted September 11, 2016 Share Posted September 11, 2016 Hi Simon, If you don't mind, there was a mistake - more than one, in fact - on the published plan of the Ballerina. Following Peter's original drawing and later remarks, the stabilisator plane should 'butt' against the last former (F10) and not leaving that small gap that you reproduced on your Petiterina drawing. It then brings the elevator joiner just on top of the fuselage at the extreme end of it. I don't think it is of extreme importance but 'originally' it was designed that way. I really like your acetate 'load distributor'. Very clever. At this tempo, your build will be maidened before I manage to finish my tailplanes... Hakuna matata Chris BRU - BE / CTR Tempo Control Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted September 11, 2016 Share Posted September 11, 2016 The other mistake (NOT MINE) was that the plan view taper starts at the trailing edge of gthe wing. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 11, 2016 Author Share Posted September 11, 2016 Peter and Chris Yes the drawings are a direct electronic copy of the originals so faithfully reproduce the inaccuracies but the errors are noted, thanks. My building tends to be of "make it up as you go along" technique so if something does not come out quite right it is altered regardless of what the plan may show. In fact I tend to use the plan only to mark out the components. The wing is actually built directly off the lower wing skin. The only time it was really used was to create the wing tip shape and to mark the ribs positions. I have decided to go for the 'silly' aileron option on the grounds the Petiterina is intended to be light so it might as well use the lightest possible option - a tiny direct coupled aileron servo. As the servo is so small the aileron is a bit shorter but has to be slightly broader to get the servo positioned within the wing skins. In the best model making tradition the aileron is literally cut out of the wing. A 6 mm Depron leading edge and the top skin added. The nose is then carefully sanded to shape and the servo horn 'inset' into the aileron. The outer will literally be a pin hinge. I must say I had forgotten just how tedious this is to do and I doubt it saves more than a few grams. It probably made sense with the Endurance where I wanted minimum drag but in this application I fear it is a case of "effort for efforts sake"! Edited By Simon Chaddock on 11/09/2016 15:33:37 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 12, 2016 Author Share Posted September 12, 2016 The completed RH wing with the LH one catching up. A test of the completed aileron. The Tx has been programmed to give 50% differential. Complete with the servo the half wing weighs 1.4 oz (40 g). About time to start the fuselage. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 12, 2016 Author Share Posted September 12, 2016 The fuselage bits. All 3 mm Depron. The sides are the good flat stuff, the formers are cut from 'aero'. All the curves have been marked from the the plan by the 'pin' method held up flat against a window. The 'parallel' section of the fuselage. Just the same as if it were in balsa! I guess it will end up slightly 'thin' as there are no fuselage doublers. As it looks like it will be seriously light., I have downsized the motor a bit to a humble Emax 2822 (1200kV). Turning a 9x4.7 slow fly. On a 3s it draws 11.4 A giving exactly 120W. Quite a conservative set up as the motor can handle up to 200W. We shall see. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted September 12, 2016 Share Posted September 12, 2016 Hello Simon, I think I'm close to get totally demotivated now. As opposite to what I wrote before, you will be maidening yours even before I 'start' the covering of my tailplanes... Doing great, sir. Hakuna matata Chris BRU - BE / CTr Motivation Control Edited By McG 6969 on 12/09/2016 20:58:37 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 12, 2016 Author Share Posted September 12, 2016 Chris Demotivation is not the idea at all! I have promised to build myself an EDF Comet and I want to get the Petiterina out of the way before the EDFs arrive from China. In addition the majority of this build is using build techniques I have done before - it saves a lot of thinking time! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 13, 2016 Author Share Posted September 13, 2016 Today I managed to get the motor and ESC installed in the fuselage. This allowed a short test to make sure it all still worked. Important when there will be very little (actually none!) access once the fuselage is complete. It demonstrates a good example of motor/air frame resonant frequency! The 20A ESC is placed in the bottom of what is likely to be the battery bay.. It has a 'fingered' heat sink that protrudes into the airflow so should get adequate cooling. Oh and by the way I have placed all the bits on the kitchen scales and .........lets wait and see! Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted September 13, 2016 Share Posted September 13, 2016 Please, don't worry, Simon. I'm not 'really' getting demotivated, but just had a 'dippie' when I saw your speedy progression. I know you're planning that huge Comet but then really wondering when your EDFs will be at home... Two things are sure by now: you love to burry your components into your fuselages and secondly, you must have a serious provision of 'finger-heat-sinks'... Hakuna matata Chris BRU - BE / CTR Funeral Control Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted September 13, 2016 Share Posted September 13, 2016 We all build at our own speed. I build fast because I am usually thinking about building the next model and want to get this one finished and in the air. Other people build much more slowly and because of that their building as far neater and better. Never, ever let what other people do bother you. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 14, 2016 Author Share Posted September 14, 2016 Putting bits in so not much actual building. The elevator (5g) and rudder (3.7g) servo mounted right at the back so they only need short direct links. The undercarriage wire formed with the acetate mounts. Actually redundant push rod wire which gives quite a bit of 'suspension' travel. The tail wheel uses the same principle but in a triangular arrangement. At last sitting on it wheels. The axle stubs are too long so will have to be cut off with a Dremel. Yes, even the wheels are made of Depron! Edited By Simon Chaddock on 14/09/2016 20:46:29 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.