Danny Fenton Posted March 7, 2019 Share Posted March 7, 2019 Okay so it was muted that some people might be slightly interested in an artf build I am doing for flying only comps this year. I had hoped to use my Hawker Fury but with very little time remaining before the first event I thought it prudent to put something together quickly. Queue the Seagull models Chipmunk. At 80" it is not as large as my Black Horse Chippy which is 85" but bigger than my Dennis Bryant Control line model which is 70" I started by fitting the motor and the motor mount. It is all very straightforward. Seagull suggest 8 or 9 cells LiPo which is crazy. I will go 5S with a 500kV motor. The 4258. this motor can give around 1200 watts, depending on how you prop it. 900 - 1kW will do me, I think a 15 x 10 should do it. I will let the pictures tell the story. it is all very straightforward stuff. Okay I lied, the first picture shows that you actually need to pack the motor out further than the travel of the adjustable bulkhead will allow. 145mm to the prop back plate from the motor bulkhead on the airframe. I added 6.5mm of SLECs finest ply, which brought the motor to 142.5mm a quick check of the cowl and this will be fine The spinner backplate needed the rear edge chamfered to allow it to sit flat on the prop backplate, due to the radius on the prop adaptor. I used this to check the cowl allignmet could be achieved, all is good. I will fit the cowl later. I then worked out where the speed controller was going, this is a HobbyKing 60/70A 1-8 cel, non BEC controller. I will be using a seperate BEC and a receiver pack. l will be trying one of Chris Botts tasty twin power feed circuit boards, with an FRSky receiver. Next up was the servos. I was going to use my trusty HK 5010 but then in a moment of madness splurged out online at Webbies and got some HiTec HS425BB and fitted the two in the fus, rudder elevator. there are twin feeds, one to each elevator, but a coupler means only one elevator servo. A nice touch would have been to shuffle the servos a bit so two could be used for redundancy. Cheers Danny Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 I then moved on to look at the tailplane and elevator. trying to lift it out the box made me realise that Seagull had dropped a clanger here surely? The tailplane and elevator weighed a massive 180g!!! So what to do.... day one of the build, motor mounted and two servos..... that was as far as I got before I modified the kit..... I scribbled around the offending item and started making a plan on paper. Can't remember the last time I did this, I use cad normally. Anyway a tailplane was duly manufactured. The kit one weighed in at 116g my replacement 32g..... so a very worthwhile exercise. It still needs covering but I cannot see that adding 84g!!! sanded while making this tailplane, which by the way was by making a 1/16th core and then adding medium 1/4 around the edges on one side. with some 1/8 ribs. this was flipped over and mirrored on the other side, before some careful sanding revealed a tailplane buried inside. Who'd of guessed Anyway that pic is actually a bit of a cheat, as the other skin isn't fitted yet, but it wont weigh much Cheers Danny Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted March 8, 2019 Share Posted March 8, 2019 You really show how it should be done Danny. Solid front end work, precision bolted, and looking ship shape, the motor as solid as it can be Using what is best of ARTF, then rejecting the tail, is a bold worthwhile move. That covering looks to be Cub Yellow. Following with interest. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted March 8, 2019 Share Posted March 8, 2019 ... subscribed, Danny. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 Thanks chaps Yes i made sure i had some Cub yellow Oracover before I started I will change the hinging in the elevator, and the flaps. Really dont like the fittings. I really mustnt alter this too much it needs to be a quick build so I can get back onto my Hawker Fury. Cheers Danny Quote Link to comment Share on other sites More sharing options...
Chris Bott - Moderator Posted March 8, 2019 Share Posted March 8, 2019 Come on Danny, keep up.. To be serious for a minute - mine is built straight from the kit. It needed lead up front so your weight saving at the rear should multiply up. We'll be able to do a direct comparison but I bet you just saved half a pound overall. Quote Link to comment Share on other sites More sharing options...
Jon H Posted March 8, 2019 Share Posted March 8, 2019 Im surprised the tail was so heavy. Is there not some hardwood or something important in the middle of it that your lighter version is lacking? You wouldnt want to build the super light edition and then find there is some important structural reason the original is so heavy. Interesting model, i have had enquires from customers about it so im interested to hear how it performs in the air...even with the vegan power plant Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 Yours does look lovely Chris Jon, reports from a guy Stateside that has flown his reports its a lovely flier. However the C of G (as usual with Seagull it seems) is way out, and needs bringing forward a fair bit. The original tailplane seems to have a lot of ply in it Jon, and includes a ply spar, and granted it is stiff. I could swat cricket balls with it! I know my structure looks light, but it is rigid, especially once the skins are on. This is more or less how Brian Taylor makes tailplanes. The thought of flutter did briefly cross my mind but its a Chipmunk and not meant to belt around the sky at mach 1 Chris wasn't it decided that the C of G should be around 115mm back from the leading edge? The paper instructions suggest 130mm and the online version 100mm so the US modeller felt safe at 115mm, and he reported it flew well at that. Cheers Danny Quote Link to comment Share on other sites More sharing options...
Jon H Posted March 8, 2019 Share Posted March 8, 2019 If they have carved the tail from a railway sleeper then thats fair enough. On the c/g thing, i have not flown one of these but have flown the Seagull Hurricane. I have also flown many YT models and on those all the forums were full of 'the cg is wrong' posts. In my experience the cg on all of these models is accurate but the rates they recommend are miles off and make the model way too sensitive, usually in pitch, leading to cries of bad c/g. I see it in youtube videos all the time too and its a bit like everyone crying that an overheated engine was lean. It wasnt lean at all, you just didnt cool the poor thing so it died! I usually ignore instructions and eyeball rates these days but always favour small movements. In general too little is better than too much. I dont know what the chord is but if 130mm is a 3rd of it then i would stick to that and bring the rates down. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 Okay the saga continues. Firstly I have been caught out with the tailplane incidence before so wanted to make doubly sure this one was right. feedback is that the model flies okay so I am going to stick with the incidence specified by Seagull. I set the fus on the bench and weighted it down so it wouldn't move. I didn't give a hoot as to the datum, I just wanted the fus to stay still. I fitted the original tailplane using a rubber band to hold it still, and took a reading on the incidence meter, -2. I then started sanding my tailplane support seats until the height was good, and the angle was the same -2 degrees. It came out well, though i should have used 1/8 balsa as the tailplane is a little thinner in profile than the original. It is probably slightly more accurate this way, although that was not the reason for the extra work. Final weight, less film, 44g Cheers Danny Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 Now do I add shrouds and rounded leading edges to the elevators "The devil most definitely is in the detail" Quote Link to comment Share on other sites More sharing options...
Chris Bott - Moderator Posted March 8, 2019 Share Posted March 8, 2019 130mm is 33% of root chord but that doesn't take into account the slight forward sweep of the planform. So it might be OK but then again I wouldn't go blindly with it, personally. I asked a number of folk who have other Chipmunk models in various sizes where their CGs were. Scaling from those, then 115mm seems more like it, especially for a maiden. Interestingly, Seagull appear to have ammended the instructions. This is now available as a PDF download saying 100mm. Quote Link to comment Share on other sites More sharing options...
Jon H Posted March 8, 2019 Share Posted March 8, 2019 Oh thats interesting. I tempted by one of these myself so i will give it a go with both given the opportunity. i just need to find the space thats all Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 The madness continues with elevator construction. The ones supplied by Seagull aren't sheeted in balsa, they are sheeted in lite ply! Same technique as the tailplane, 1/16th core with bits of "what I have lying around" to make the thickness. Cheers Danny Quote Link to comment Share on other sites More sharing options...
Braddock, VC Posted March 8, 2019 Share Posted March 8, 2019 If you remove it carefully you can re-use the covering material, may require a dab or two of balsa lock but that's ok too. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 I have a roll of Cub yellow Oracover to make good any bits. I am not into trying to re-use film covering Cheers Danny Quote Link to comment Share on other sites More sharing options...
Braddock, VC Posted March 8, 2019 Share Posted March 8, 2019 Waste not want not or, in jockonese, every mickle maks a muckle. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 I have left the parts alone just in case they are needed. Cheers Danny Quote Link to comment Share on other sites More sharing options...
Braddock, VC Posted March 8, 2019 Share Posted March 8, 2019 Better still! Quote Link to comment Share on other sites More sharing options...
Wingman Posted March 8, 2019 Share Posted March 8, 2019 Oh dear Oh dear! What a kerfuffle. It's a Seagull ARTF - they are all good flyers straight out of the box in my experience and almost Hangar 9 quality and it's to be used for flying only comps you say - it's a chipmunk so sedate to moderate flying is the order of the day and weight won't matter as regards a pound or so - looks to me like OCD is creeping in here or is it a guilty conscience for not building a competition model from scratch?? Edited By Wingman on 08/03/2019 21:14:52 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 The result of the thiner section and using medium balsa meant that the structure was a little too flexible. So I had to add the diagonal braces. The opposite side runs the opposite way, so between the two we have a crossed structure. This has stiffened the whole lot up significantly. If I really wanted to take it further I would use dope and tissue/nylon/silk as they impart even more strength. But as I am using film this is as strong as it will get. Iron on film adds nothing to the structures strength. 56g so far (original 180g) and each pin weighs a gram!! Cheers Danny P.S. There are some really sattisfying to produce chamfers amongst that lot Edited By Danny Fenton on 08/03/2019 21:19:48 Edited By Danny Fenton on 08/03/2019 21:20:56 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 You might be right ........ Shall I stop now, drop this in the bin, and accept 1/2 lb of lead in the nose? If it flies well at 11 1/2 lbs it will fly even better at 11 lbs Cheers Danny Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted March 8, 2019 Share Posted March 8, 2019 Woe Danny, this quality of work and logic is " top drawer " and read by many Don't be put off by trolls, just ignore Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted March 8, 2019 Share Posted March 8, 2019 If you were only going to save a couple or few ozs of nose lead then not worth the effort but at your rate you will be looking at a significant amount more than that so a job well done. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 8, 2019 Author Share Posted March 8, 2019 Thx guys, i won't go mad, but if you had picked the tailplane up you would have been shocked too. A hundred gram saved at the tail is several hundreds up front. If i can easily do bits and pieces to tidy the model up I will. Cheers Quote Link to comment Share on other sites More sharing options...
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