Michael Baylis Posted June 16, 2009 Share Posted June 16, 2009 Now I'm getting a little down with these ARTFs. I've finished assembling my Tutor 40 and find that the CoG is 1.5cm too far back even with the battery rammed up against the firewall. I went to bed a little down but had a brainwave at 5am this morning (I know, sad), so I got the kitchen scales out and discovered that the all-up weight is down by 220g. As the battery pack only weighs 97g this to me seems a large amount to be down. I'm now having irrational thoughts about forgetting to add something to the plane. Yep, checked, the engine is on the front. So, I need to increase the weight at the front of the model. Would someone be kind enough to suggest some solutions? I remember reading about putting lead in to move the CoG forward. Can I buy lead weights from somewhere. Any suggestions of the weight of the weight I need? How do I secure it? Cheers, Michael Quote Link to comment Share on other sites More sharing options...
winchweight Posted June 16, 2009 Share Posted June 16, 2009 An alloy spinner to start off. These are as far forward as they can be and usually do the job. Or a heavier (higher capacity battery pack)? Quote Link to comment Share on other sites More sharing options...
Hamish Posted June 16, 2009 Share Posted June 16, 2009 Michael Can you move the engine forward before adding weight? Quote Link to comment Share on other sites More sharing options...
Snorbitz Posted June 16, 2009 Share Posted June 16, 2009 You can buy stick on car wheel type weights (from all the usual internet outlets) which are fine but i would reccomend you pop a bit of silicone sealer or similar glue to the edges just in case over time with vibration they wriggle loose. They start as low as 5g i think and go up from there. I wouldn't worrry so much about your all up weight though...it'll be different in almost every build you do and i'll be surprised if anyone has ever matched the manufacturers figures. There are so many variables that can effect it. Your CoG is important tho. IMO 1.5cm on a trainer isn't going to make that much difference i shouldn't think but the closer you can get it to the ideal the better and if anything slightly fwd is better. It might be a bit of a handfull as it is. Someone once said on here i think its like holding a tiger by its tail, and i can vouch for that description. You;ll know what i mean if you ever leave the ground with CoG too far back. I've experimented with my Boomerang Trainer and its not until you get miles off that problems start occuring. Hope this helps. Quote Link to comment Share on other sites More sharing options...
Russ Posted June 16, 2009 Share Posted June 16, 2009 You can buy a pack of lead weights specially for this purpose. Stick to anything never to come off! Available online or from your model shop. I had a Tutor 40 an excellent trainer, with an OS 46LA and I had to add weight to get the c of g correct. I then upgraded the engine to an OS 46AX (I needed more power to take off on our rough strip) and had to remove the lead as the c of g was spot on without any extra weight. Quote Link to comment Share on other sites More sharing options...
Michael Baylis Posted June 16, 2009 Author Share Posted June 16, 2009 The Engine is about far forward as I would like it to go. I didn't want to drill the mounting holes any closer to the end. The spinner is a good idea, didn't like the blue plasticy thingy anyway and I think the dedicated weights from the model shop will do, shame they are closed today. Thanks for you help guys. Quote Link to comment Share on other sites More sharing options...
Michael Hickman Posted June 16, 2009 Share Posted June 16, 2009 Michael I did noticed that on my last Tutor (my third) that I had much more trouble achieving the stated CofG. Previous Tutors I only need to move the RX battery pack. This time I added a second RX battery at the front of the radio bay and some "church roof" in the fuel bay, the total weight I needed was about 8oz (200g). I did ask at the club and everyone thought it was a large increse, but it flew OK. I have not weighed any of the airframes to compare, they all received front damage after a "sudden arrival", so i do not know if the earlier were naturally heavier at the front or the last one tail heavy. I assumed it must have been an odd "heavy tail" but now you seem to have a similar issue. Mike Quote Link to comment Share on other sites More sharing options...
Michael Baylis Posted June 16, 2009 Author Share Posted June 16, 2009 Michael, when did you buy you last Tutor? Beginning to sound like a design change that shifted the natural CoG backwards! However, it is comforting that you needed add 200g. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted June 16, 2009 Share Posted June 16, 2009 I saw some 'proper modelling' weights in the LHS, strange, they look identical to the wheel balancing weights I got from Kwikfit. A couple of quid got me about a dozen strips of 5 and 10gm weights. They're not lead any more, they look like plated steel, the inluence of health and safety no doubt, but they do the trick. If it's any consolation, my MiniPanic has about 100gm on the front bulkhead as there's nothing in front of that to attach anything to. The CMPro Cessna needed about 1 Lb of lead on the engine bearers, glass fus and ready built tail feathers, so there was now way it could be down to heavy handed building. Quote Link to comment Share on other sites More sharing options...
Michael Hickman Posted June 16, 2009 Share Posted June 16, 2009 Michael I am a "slow builder", putting it mildly, I think I bought it Feb last year, but only completed March this year. I bought a second hand Merlin at the club auction and flew that for a year. I know Irvine changed some things between number 2 and number 3, the tyres were more like foam on the earlier ones, although a little heavier I prefer the new tyre as the foam ones soon had flat spots if left supporting the aircraft weight for too long. I cannot say I noticed much else. The fuel tank on all three was different to the instructions, but I cannot remember any other inaccuracies. Mike Quote Link to comment Share on other sites More sharing options...
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