Paul Williams Posted April 21, 2013 Share Posted April 21, 2013 Hi all, I purchased a Sbach 30cc from hobbyking some time ago. I built it with a zenoa 38cc and all looked well till I flew it. The first time out, although balanced to the book, c of g was miles out it was tail heavy and flew awful. I removed the tail wieght and things improved it was now very stable and landed without stalling. Trouble now is it flys with its tail low to the nose and almost harriers all the time. Its impossible to land without hitting the tail wheel first. A friend has sugested the thrust line is wrong I fitted the engine mount straight onto the already fitted firewall which looks ok you can see clearly there are some angles built in. I guess what I am asking is what could cause it to fly with the tail hanging low? I have guessed the CoG to be a third of wing width where it meets the fuse and its very stable just pulling its self out of a dive without any input to elevater. it does need a lot of up stick to fly inverted, all showing CoG to be nose heavy. Quote Link to comment Share on other sites More sharing options...
Rich too Posted April 21, 2013 Share Posted April 21, 2013 Doesn't sound like the cog is correct? If it was nose heavy it would need down elevator inverted? Sounds tail heavy..I just maidened my Pulse and I had to trim in up elevator because it is nose heavy - I knew it nose heavy when i checked the cog (tried moving the battery as back as possible, but I have a heavy Zenoah 23 up front. Rich Edited By Dickster on 21/04/2013 15:46:36 Quote Link to comment Share on other sites More sharing options...
crispin church Posted April 21, 2013 Share Posted April 21, 2013 I have guessed the CoG to be a third of wing width where it meets the fuse dont guess do it and always check the measurements with cog calculator thats a big heavy model not half a kilo foamie Quote Link to comment Share on other sites More sharing options...
Andy Green Posted April 21, 2013 Share Posted April 21, 2013 I think the only way to know for sure as to what is going on is to hold it securely and run an incidence meter over it, and make adjustments then. Until you know what is going on it will be guess work. Andy Edited By Andy Green on 21/04/2013 20:04:16 Quote Link to comment Share on other sites More sharing options...
Rich too Posted April 21, 2013 Share Posted April 21, 2013 also, if it was nose heavy it wouldn't fly with the tail down, would it? personally in the past 30 odd years i have always marked the correct cog position and checked with the fingertip method - i bought a great planes fancy bit of kit years ago but never got on with it - and it has never failed me, and work from there...Rich Quote Link to comment Share on other sites More sharing options...
Simon B Posted April 21, 2013 Share Posted April 21, 2013 My dad's 30e Sbach was massively tail heavy too. Seems to be a pattern with these. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted April 21, 2013 Share Posted April 21, 2013 Totally agree Simon. I have a GoldWing Sbach gorgous looking model, couldn't wait to fly it. When I did, what a dissapointment. Although it was set up as per instructions, it handled like an absolute pig! The maiden was the shortest ever! 2mins of shear terror - I had a real 'tiger by the tail' - very tail haeavy, "roller-coaster" wasn't in it. I was very lucky to get it down in one piece. Everything shifted forward, CoG forward of the recommended position, I tried again. It was better, but still not good. Some lead added to the nose - by now the CoG something like a wopping 1/2" forward of the front of the recommended range. Expo on the elevator upped to 60%. Tried it again - it flew like a dream! Dead straight, virtually no "push" inverted. Sits well in the air. So you can "tame" the Sbach - I'm delighted with mine now - but I think you have to be prepared to disregard the instructions and follow your own instincts on this one. BEB Quote Link to comment Share on other sites More sharing options...
Simon B Posted April 22, 2013 Share Posted April 22, 2013 Interesting. I'll let Hobbyking off the hook then, as I just put it down to cheaper manafacturing. Quote Link to comment Share on other sites More sharing options...
Mondeoman Posted April 22, 2013 Share Posted April 22, 2013 My Goldwing 30cc DLE Sbach has just had it's first flights, CG set as per the manual, (came out dead on with no juggling batt' position or adding weight), flew superbly, did'nt even have to give a single trim click!!, one of the best knife edgers I've encountered. Verdict, fantastic quality and ditto flyer. Quote Link to comment Share on other sites More sharing options...
Paul Williams Posted April 23, 2013 Author Share Posted April 23, 2013 Posted by Mondeoman on 22/04/2013 13:56:57: My Goldwing 30cc DLE Sbach has just had it's first flights, CG set as per the manual, (came out dead on with no juggling batt' position or adding weight), flew superbly, did'nt even have to give a single trim click!!, one of the best knife edgers I've encountered. Verdict, fantastic quality and ditto flyer. what would realy help is the measurement you used when the plane flew well guys. I have also noticed after closer inspection the firewall has only 1 deg of down thrust built in I am guessing this is not enough. BEB your story is very simular can you tell me the final figure and check if you have down thrust built in? Quote Link to comment Share on other sites More sharing options...
Paul Williams Posted April 23, 2013 Author Share Posted April 23, 2013 Andy Hi thanks for your post, I live up in manchester mate. I have a incidence meter but no information on the figures so using it is worthless at the moment. Is there a standard setting? Quote Link to comment Share on other sites More sharing options...
Rich too Posted April 23, 2013 Share Posted April 23, 2013 I don't see how it can be nose heavy if you are having to input lots of "up" when inverted. However, having said that, with that big lump up front (bigger than the rec motors?) i would be surprised if it wan't nose heavy. One poster on HK said the his flew great with the cog in the middle of the wing tube. Rich ps whats the auw? Edited By Dickster on 23/04/2013 13:02:39 Quote Link to comment Share on other sites More sharing options...
Paul Williams Posted June 12, 2013 Author Share Posted June 12, 2013 Well I think maybe some one has found the problem, I mentioned I had fitted a Zen G38 engine thinking a bit more power would only help !! Well I was wrong the G38 weighs in at 2k which is twice the 980g of a dle 30 or rcgf 30 the result was extra weight on the tail to balance all this added up to a very overweight aircraft which flew terrible at low speeds. I take it all back Hobbyking I need a wing loading lesson and a new light weight engine. Any one wanna buy a G38 just run in? Quote Link to comment Share on other sites More sharing options...
Mark a Posted June 12, 2013 Share Posted June 12, 2013 I maidened my Slipstream Sbach on Monday. The model was secondhand and fitted with a JC28 petrol engine. I set up the C of G 130mm back from the leading edge right on the wing tube and it didn't fly to bad seemed slightly tail heavy. Will be moving batteries further forward and trying again once the weather improves. Quote Link to comment Share on other sites More sharing options...
Paul Marsh Posted June 12, 2013 Share Posted June 12, 2013 Posted by Paul Williams on 12/06/2013 16:13:32: Well I think maybe some one has found the problem, I mentioned I had fitted a Zen G38 engine thinking a bit more power would only help !! Well I was wrong the G38 weighs in at 2k which is twice the 980g of a dle 30 or rcgf 30 the result was extra weight on the tail to balance all this added up to a very overweight aircraft which flew terrible at low speeds. I take it all back Hobbyking I need a wing loading lesson and a new light weight engine. Any one wanna buy a G38 just run in? Really the G38 is such an obsolete, heavy engine, and only good for trundling models, or WWI. The LMA use them. I had a G38, but had no power, comparingly to a new 30 odd cc petrol engine of smaller capacity. They're reliable, but things have moved on... Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted June 12, 2013 Share Posted June 12, 2013 Glad you sorted out the problem paul. Still think there is some thing else to be learned here. Had a model years ago, that flew like a dream, with CoG as per drawing, but with the tail hanging low. Moving CoG forward made no differance. Flew well but looked wrong. Any suggestions ? Quote Link to comment Share on other sites More sharing options...
Paul Williams Posted June 20, 2013 Author Share Posted June 20, 2013 Just to round off this post I have now fitted a RCG 30cc engine to the Sbach and flew it yesterday. What a difference I take it all back Hobbyking the CoG was set on the wing joiner tube about 125mm back and the plane flew fantastic. Loads of grunt and perfect low speed behaviour you never stop learning in this hobby and this has been a lesson I will not forget . For those who are considering a Sbach go for it just keep the AUW within spec !!!! Quote Link to comment Share on other sites More sharing options...
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