alex nicol Posted June 22, 2020 Share Posted June 22, 2020 I need to add around 350g of nose weight to balance out my latest airframe. In order to add as little as possible I was thinking of melting some lead down and adding it to the spinner. Can anyone advise if this is feasible and if so what should I watch out for. The model has a 75mm (3" aluminium spinner on the end of an ASP 1.80fs. I understand some balancing may be required and there could be an element of flywheel effect. Thanks in advance Alex Quote Link to comment Share on other sites More sharing options...
Ernie Posted June 22, 2020 Share Posted June 22, 2020 Well, Alex? My opinion is that its a NONO, Just too much to go pear shaped. BUT, An old friend of mine, a very accomplished modeler (he talked me through my first wobbly loop) regularly filled plastic spinners with lead shot and epoxy..never saw one go wrong ernie Edited By Ernie on 22/06/2020 09:09:15 Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted June 22, 2020 Share Posted June 22, 2020 No never Just my opinion You save 10gram adding 340gram to the End of a spinning crankshaft Just no Quote Link to comment Share on other sites More sharing options...
alex nicol Posted June 22, 2020 Author Share Posted June 22, 2020 Hi Ernie, Thanks for your response, if lead shot/epoxy in a plastic spinner worked the aluminium/lead combo is theoretically possible. Ideally there will be someone out there who has tried this and can advise. Alternately it'll need to be a 'suck it and see' approach. Cheers Alex Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted June 22, 2020 Share Posted June 22, 2020 Taken from Mick Reeves' website pages: We recently fitted a steel disc weighing 1 kg on Jims engine shaft, ahead of the prop. To achieve the same effect with ballast on the firewall, it would need 1 1/2 kg. Quote Link to comment Share on other sites More sharing options...
Brian Cooper Posted June 22, 2020 Share Posted June 22, 2020 I saw this practice done once way back in the 1960s. . . It didn't end well. Leaving aside the issue of finely balancing this kind of arrangement, basically any increase in "G" loads puts an excessive amount of force on the crankshaft. So any aerobatic manoeuvres will be a cause for concern. . Indeed, even a bouncy landing could impose 4 or 5 "G" on the thing. Eventually, the crank will bend, fatigue and/or break. The one in the 1960s broke the crankshaft while being revved up in the pits. Happily nobody was in the way when it let go...... and it went a long way. Keep in mind the adage:: "If it CAN happen, then it ruddy well WILL happen" ..and then ask yourself if you would fly in it if it was full size. Frankly, having seen what a heavy, broken crankshaft, complete with its propeller can do, (and how far it can go) I would personally throw someone out of the Club for adopting this dangerous practice. B.C. Quote Link to comment Share on other sites More sharing options...
alex nicol Posted June 22, 2020 Author Share Posted June 22, 2020 Apologies Gents, I should clarify, if the spinner idea is a go the actual ballast required will be in the region of 250g as opposed to 350g if bolted to the firewall. My other alternative is to shape some lead strip and fit it inside the cowl just behind the spinner ring. (Model has a non detachable balsa cowl) Quote Link to comment Share on other sites More sharing options...
Jon H Posted June 22, 2020 Share Posted June 22, 2020 How heavy is the model? If the 350g is less than 10% of the overall weight then just ignore it. Filling spinners with lead is a really bad idea. Bolting great big weights to engine crankshafts is also not brilliant as any imbalance will ruin the engine bearings in short order. I have to confess, i dont understand the hysteria related to adding ballast to a model. The thing needs to balance to fly, and it needs X amount of ballast to balance...so just add the ballast and fly it. Why such a fuss? My big Sea Fury is 23 lbs, and 2 of them are lead. The engine/spinner were about as heavy a combo as was available short of a radial, the batteries/servos etc were as far forward as possible, and i built a new elevator that was lighter than the original. That left me needing 2lbs of ballast under the engine to make it balance. I ended up with a 23lb 80 inch WWII fighter with a laser 360v for power. Would i want to be any heavier? not really, would i want it to have any less power? not really, does it go like a scalded cat? ohhh yes :D Quote Link to comment Share on other sites More sharing options...
Keith Berriman Posted June 22, 2020 Share Posted June 22, 2020 Alex I was once in your predicament and solved it by fitting the Rx battery in the engine bay is this an option Quote Link to comment Share on other sites More sharing options...
brokenenglish Posted June 22, 2020 Share Posted June 22, 2020 I would prefer the 350g on the firewall! Edited By brokenenglish on 22/06/2020 10:14:12 Quote Link to comment Share on other sites More sharing options...
perttime Posted June 22, 2020 Share Posted June 22, 2020 Is there anything else in the model that can be moved forward? I'd prefer not to add weight to a component that is spinning rapidly. Quote Link to comment Share on other sites More sharing options...
alex nicol Posted June 22, 2020 Author Share Posted June 22, 2020 Gents, Thanks for your experiences/opinions. I think I'll go for fixed non spinning ballast epoxied and glassed to the inside of the cowl as far forward as possible. (I've no desire to create anything that may be at risk of parting company with the airframe Cheers Alex Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted June 22, 2020 Share Posted June 22, 2020 Just to show what even a slight problem can cause: Way back I had a conntrolline model with a Kiel Kraft plastic spinner which had a screw on front cap, which was very light. The nose cap came off in flight and removed one propellor blade.The imbalance instantly removed the complete engine,tank and bearer assembly which departed across the flying field and very luckily missed the spectators. 250 Grams!!!! The men in white coats will be coming along soon!! Quote Link to comment Share on other sites More sharing options...
Nigel R Posted June 22, 2020 Share Posted June 22, 2020 Any possibility of screwing some sheet lead onto the engine mount? That might gets it half way between firewall and prop. Quote Link to comment Share on other sites More sharing options...
alex nicol Posted June 22, 2020 Author Share Posted June 22, 2020 Admittedly I had doubts about the spinner weight, hence the original reason for asking the question. With regards to things departing airframes, many moons ago (early/mid 70's) I flew a lot of control line combat where mid airs and motor departures were common place (this was pre engine tethered to bell rank rule) The distance and damage a 15 sized engine could go/do never ceased to amaze. Quote Link to comment Share on other sites More sharing options...
alex nicol Posted June 22, 2020 Author Share Posted June 22, 2020 Hi Nigel, It's quite a neat fitting cowl with not a lot of clearence around the mount. It looks like I'm just going to have a look just now to see what I can do. In short the battery is as far forward as I can get it and the ballast will be as far forward as I can get it and remain firmly fixed and behind the prop. Cheers Alex Quote Link to comment Share on other sites More sharing options...
Geoff S Posted June 22, 2020 Share Posted June 22, 2020 I'm sure I've seen extra heavy prop nuts advertised specifically to get ballast as far forward as possible. I nver thought it a good idea, mostly because of the damage it could cause to bearings but the thought of an actual crankshaft's breaking hadn't occurred to me. Anything flying off the front of a running engine/motor could be very dangerous. It's amazing hw high G forces can increase even at apparently modest rpm. About 40 years ago I was involved in the design of short range radio telemetry for aero-engine temperature and stress measuremnt (by short I mean millimetres!). The housing for the electronics (which were epoxy potted) were about 350mm diameter and rotating at around 7000rpm IIRC. We were dealing with 25k g! Amazingly the only things to fail were the inter-module and transducer wiring. On my current build, which will certainly need lead, I'm intending to screw it to the cowl. I've made sure the cowl is very securely attached. Geoff Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted June 22, 2020 Share Posted June 22, 2020 Many years ago(You are old father Wiliam!!!!) I designed a small scale model of the Taylor Monoplane with an OS20 Four Stroke. That had a circular intake in the cowl and I cast a lead ring to fit right at the front. That worked. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted June 22, 2020 Share Posted June 22, 2020 Like Peter I made a nose weight for my ESM Hurricane by adding lead shot to some slow setting resin and pouring it into the front of the cowl which had a waxed beaker pushed into the engine shaft hole. The lead / resin mix formed a nice ring around the front inside face of the cowl. Quote Link to comment Share on other sites More sharing options...
Keith Berriman Posted June 22, 2020 Share Posted June 22, 2020 What size Rx batteries are in the model can you put some bigger cell batteries in ?? AA to say 2/3 cell or Sub C Quote Link to comment Share on other sites More sharing options...
alex nicol Posted June 22, 2020 Author Share Posted June 22, 2020 The deed is done, 3 bits of 2mm lead sheet formed into shape and epoxied upfront inside the cowl. once it dries I'll glass over it just to be sure thanks to all Alex Quote Link to comment Share on other sites More sharing options...
Jon H Posted June 22, 2020 Share Posted June 22, 2020 Posted by alex nicol on 22/06/2020 14:29:33: The deed is done, 3 bits of 2mm lead sheet formed into shape and epoxied upfront inside the cowl. once it dries I'll glass over it just to be sure thanks to all Alex Dont make it too secure. You need to be able to get it off if you want to adjust the balance after the model has been flown Quote Link to comment Share on other sites More sharing options...
alex nicol Posted June 22, 2020 Author Share Posted June 22, 2020 Hi Jon, Thanks, I'm already there, the majority of ballast is fixed securely and I have some wheel balance weights on self adhesive strip that'll let me adjust the balance point between 25 and 30% of chord. So fingers crossed that should suffice. Cheers Alex Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted June 22, 2020 Share Posted June 22, 2020 Just remember that the lead is attached to the cowling and don't try a test flight with it removed. A very experienced modeller was caught out this way and the results weren't pretty! Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted June 23, 2020 Share Posted June 23, 2020 Remember too that on an heavy arrival, the lead will continue the journey 10ft further on than the cowl area. Quote Link to comment Share on other sites More sharing options...
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