Craig Spence Posted October 13, 2009 Share Posted October 13, 2009 Hi all, I have just bought the CMPro Quest 50. I am really strugling with the centre of gravity, it sais 95 to 105mm from the begining of the wing (root). I have just glued loads of lead to it and its still off by about 10 to 15 mm, my old instructor said to just keep putting it on until the CofG is correct but I think its too much, anyone advise on this. The model is specd for a 46 two stroke or four stroke equivilent, I am useing an Irvine 53 which has the same dimensions and weight as a 46. Could the CofG be wrong in the manual?, I really dont want to keep adding weight, I think this plane was built around a four stroke in mind. Everything is moved as far forward as possible as well with no effect, the wing is very far forward as well ie very close to the engine and its a wept back wing if that makes sense. Is this common to put so much weight on this type of model. Cheers all, feedback very much welcomend. Quote Link to comment Share on other sites More sharing options...
Bruce Richards Posted October 13, 2009 Share Posted October 13, 2009 How much weight exactly have you added? Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 13, 2009 Author Share Posted October 13, 2009 Hi Bruce, I really couldent tell you, I dont have scales and I dont buy the fancy lead from the model shop lol!, its old strip lead about 3 to 4 mm. To give you an idea of how much ive put on. Ive glued two layers of lead on the firewall under the engine mount and one layer on the under carriage underneath the firewall. Cheers Bruce. Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 14, 2009 Author Share Posted October 14, 2009 Ive just been given some good advice from my father although it doesent solve this problem. He said to keep adding weight (but dont glue it yet) bit by bit until yo get the desired effect then take all the small bits and weigh them up, once you have the weight you can put one whole piece on it opposed to loads of little bits. Quote Link to comment Share on other sites More sharing options...
Bruce Richards Posted October 14, 2009 Share Posted October 14, 2009 That sounds like good advice. Sorry I can't help much further as I do not know the model. Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 14, 2009 Author Share Posted October 14, 2009 Hi Bruce, thanks for the help anyway. Quote Link to comment Share on other sites More sharing options...
Stefan Hafner Posted October 14, 2009 Share Posted October 14, 2009 Hi What is the chord of the wing as usually the CoG should be around 1/3 of the chord length from the leading edge. I would suggest that you try to get the balance right, preferable nearer the forward location to start with, after all, you can always take some off at a later date. Remember, if you strat tail heavy the first flight may be the last Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 15, 2009 Author Share Posted October 15, 2009 Hi Stefan, sorry could you elaborate on what the chord of the wing is, its not camber is it, (shape?). Ive now got the CofG just in front of the rear mark, however there is a over 1lb of weight on the nose of my plane, im thinking of taking it down a race track to do circuits lol. Do you think it will still fly?, also after doind a bit more research on forums people have been useing the measurement of 110 to 130 mm opposed to 95 to 105 mil. Il take it flying and reduce the weight if I feel I can on the field. Quote Link to comment Share on other sites More sharing options...
Stefan Hafner Posted October 15, 2009 Share Posted October 15, 2009 The chord is the linght from the leading edge to the trailing edge of the wing. In the case of the Quest with a tapered wing this will obviuosly change alonng the span of the wing, so i would assume the CoG location is measured at the root. I think it should fly fine, especially if people have been flying with it even further back, might just be a bit more sensitive to elevator inputs, but if in doubt take it to your club and ask some of the more experienced guys to help. Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 15, 2009 Author Share Posted October 15, 2009 I have assumed the same thing however the instructions are not vey specific. I have always took the CofG from the root of te wing, can you take it from the tips if the wing is tapered (swept back). I hope it flys fine I really cant afford to loose this at the momnet, I will be getting help from my old instructor. Cheers for the help. Quote Link to comment Share on other sites More sharing options...
Bruce Richards Posted October 15, 2009 Share Posted October 15, 2009 Are you sure the measurement is not back from the LE rather than forward from the TE?Edited By Bruce Richards on 15/10/2009 20:23:07 Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 15, 2009 Author Share Posted October 15, 2009 Hi Bruce, yeah its back from th leading edge, it shows it on the diagram, however the instructions are poor. After watching some videos on you tube it looks quite heavy taking off anyway, I think im gonna have to suck it and see but I would rather much like it to be lighter as I have a feeling its gonna come in for a landing at 100mph. Imused to this anyway from my old plane. I think when money permits Im going to get a 60 four stroke and put it in and remove a little lead. For now im going to take it flying and remove lead if I feel I can at the field, alot of people are saying they are going up to 130mm back from the leading edge as opposed to the instructions of 105mm. Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 18, 2009 Author Share Posted October 18, 2009 Hi all, ive flown the plane now for two days. I was right and so was my instructor, the CofG was well off, you dont need much lead up front at all. However it was a strange type of landing and I dont feel the plane tracks that well, others think its great, but it feels a bit off. any thanks all. Quote Link to comment Share on other sites More sharing options...
inspector9566 Posted October 18, 2009 Share Posted October 18, 2009 Hi Craig I recently had a bad crash with one of my fav models a home made proto that i bought s/h from another club mate i had lost the c of g and used this web site http://adamone.rchomepage.com/cg_calc.htm very easy to use and got it spot on hope this helps Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 18, 2009 Author Share Posted October 18, 2009 Hi inspector9566, thanks very much for the help there, very much appreciated. I will try hat website later on, just to see if im flying behind or in front of what it should be, should be interesting lol!. Thanks. Quote Link to comment Share on other sites More sharing options...
inspector9566 Posted October 18, 2009 Share Posted October 18, 2009 no probs Craig it got me out of a bind but a 1lb of lead sounds a bit excessive. let us know how you get on. Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 18, 2009 Author Share Posted October 18, 2009 Im going to recheck it tomorrow now but as for re-maidening her on the new CofG (if need be) it will have to wait for a couple of weeks. Cheers. Quote Link to comment Share on other sites More sharing options...
Former Member Posted October 19, 2009 Share Posted October 19, 2009 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 19, 2009 Author Share Posted October 19, 2009 Hi all, just spoke to one of the fellas at my local model shop about this problem and I gave him the measurements of the root, tip and full length and he came up with a different measurement all together. 164mm from the leading edge of the wing, thats 30 mm extra than what people have been useing on the internet and the manual (which is very wrong sais 95mm to 105mm. I think this is going to be going on for a little while yet lol!. Also something that came to my attention when I was flying it is that it is slightly moveing to one side, I thought this could be the thrust angle but after being reccomended to do a wing balance found out that the wing is off balance. This will be rectified with some screws or shot (any tips). Eric I had a brief look t that thread and its the same method which the bloke at the shop uses, well see how it performs with the new CofG and wing balance. Many thanks all. Quote Link to comment Share on other sites More sharing options...
Adrian Smith 1 Posted October 20, 2009 Share Posted October 20, 2009 Hi Craig, sorry to be a bit tardy in answering your Quest 50 problem but have been on me hols. Anyway I have a Quest 50 and it flies beautifully the way it's not set up by trial and error. First, disregard the instruction book. My CG sits at 110mm from the leading edge where the normal measurement is taken. I have 3.5 ounces of lead in the nose and the grunt is powered by an OS 46AX using an 11x6 APC prop. Trust me it will do all you want on that and more! Best of luck, Adrian. Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 20, 2009 Author Share Posted October 20, 2009 Hi Adrian, this is what I really wanted, someone with first hand experience, questions, questions lol!. So whats your plane like on the glide or tick over on the CofG you are useing?, what have you found the stall characteristics to be like?. Not that im able to but can you prop hang the model, harriers, whats its abilities if your ability is good?. Have you got the same undercarriage on it?, I had a hard landing and it broke the wood underneath, I now have one from carbon copy on it. Does she pull out of loops? mine does at full thrittle were deciding if its torque or wing balance at the mo, at full throttle she flys straight as an arrow, the wing balance is off slightly which will be corrected with shot or some pennys lol!. Did you manage to fit the 300 fuel tank in OK?, I used a 260 which fits better for me. So Im useing an Irvine 53 with the same dimensions and weight as a 46, with a 12-6 prop, do you think an 11-6 or 11-8 would be better?. When I flew it last the CofG was about 120mm is this OK or a bit tail heavy?. The fella at my shop doing the calculations sais 164 as a ball mark but its nearly half the wing lol!. Feedback appreciated, many thanks. Quote Link to comment Share on other sites More sharing options...
Andy Gates Posted October 20, 2009 Share Posted October 20, 2009 Beware of judging CoG by the manner in which a plane pulls out or executes manoevers.Incorrect trimming can create all sorts of weird reactions. An incorrect thrust line on the motor (no down thrust for instance) can make a plane pull out even with a correct CoG. One other comment Craig, try and solve one issue at a time with one solution.Doing 2 or 3 things at the same time may solve the issue but you will never know which of the solutions was the one required and you may create other problems. Not only that if the solution causes problems then you only have one thing to put back. Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 20, 2009 Author Share Posted October 20, 2009 Thanks Andy, on the day I go down I will be doing things one by one, fine tuning with my instructor. Cheers. Quote Link to comment Share on other sites More sharing options...
Adrian Smith 1 Posted October 20, 2009 Share Posted October 20, 2009 Glad I was of some help. Firstly one thing I forgot to mention was that my Quest has between 1-2deg side thrust using washers, but I have no downthrust. In answer to some of your questions - given that the wing loading is very light this makes the glide characteristices of my model excellent. I haven't prop hung but harriers are fine. I still have the original U/C which seems ok but I did reinforce the U/C slots with 1/32 ply just to be safe. I used the original tank but it was a fiddley job I must say. As far as the prop goes it depends what you want to do. For out and out aeros use 11x6 -8 as long as you are on a glass strip that is very flat, otherwise you might need a 12x5 to get you off the ground easier I but lose out a little on the aeros as the prop unwinds in the atmoshere.As far as CofG at 120mm, I haven't tried mine there as I found a happy solution at 110mm. Hope that helps. Adrian Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 20, 2009 Author Share Posted October 20, 2009 Hi Adrian, yes very helpfull, Im going to go out tomorrow and buy a book lol, ive been meaning to do it now for a while but it will just help as a reminder untill ive soaked up all the info. I had problems with the retaining nuts on the engine mount but still managed to get two washers under one of the mounts to get the side thrust. I also got th down thrust as well. I think after what you have been saying about the glide on your model I may put a little more lead up front but well see when I stall test her on the next flight. That what happened to me with the undercarriage on mine was unfortuate but it has worked out very well the new UC is great and lifts the wing a little making take offs a little shorter. My patch is riddled with holes and isnt the smoothest so good take offs and landings have to be a must or you will damage your plane lol!. The tank was far too much hassel for me lol!, the bolts were too long and even after shortening them it was still difficult, so I jacked and put a smaller tank in lol. As for the prop, my patch is also on a hill lol, so I think ill have to stick with the 12-6 untill my confidence grows with it, it takes a good distance before it gets sucked off the ground lol. Did you have any issues with the wing balance?, mine s droping the left wing when I balance it. Cheers. Quote Link to comment Share on other sites More sharing options...
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