Paul Hartley Posted December 8, 2016 Share Posted December 8, 2016 Simple question regarding an electric conversion of a IC model. I assume that the C of G position on an IC model is determined with the model empty of fuel, but otherwise fully built. This would then give it a (safe) slightly nose down balance when fuel is added and ensure that as fuel is burnt off the model never ends up with a rearward C of G. If then doing an electric conversion which generally will leave the C of G in the same position all the time (ignoring the slight variation of different battery weights), should you just ensure that the C of G of the built and battery fitted model is at the designed point or slightly forward? Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted December 8, 2016 Share Posted December 8, 2016 Exactly Paul, the C of G remains where it is marked. There is in truth, not a huge feeling of difference between a full or empty fuel tank, though the model feels lighter in the later stages of the flight, and as you say, we balance for the worse scenario, an empty tank! Quote Link to comment Share on other sites More sharing options...
Andy48 Posted December 8, 2016 Share Posted December 8, 2016 I would beg to differ. I am increasingly finding that I really have to fine tune the CofG on planes designed for IC and running on electric. Mostly using the CofG on the plan seems to be OK, but with nearly all my planes, that fine tuning moves the CofG back slightly, with the only difference being in the flare out on landing which is much improved. I have not found a plane where the CofG moves forward, but several where moving it back slightly improves low speed handling. I suppose you can tweak it more accurately with electric as the weight remains exactly the same each time, whereas with IC one ends up with a slightly varying weight each flight. Quote Link to comment Share on other sites More sharing options...
Geoff S Posted December 8, 2016 Share Posted December 8, 2016 The CoG of an electric model should always be checked with a fully discharged battery shouldn't it? Geoff Quote Link to comment Share on other sites More sharing options...
Former Member Posted December 8, 2016 Share Posted December 8, 2016 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted December 8, 2016 Share Posted December 8, 2016 No matter where we balance the C of G, it still remains in the same place on the model on this planet, at the centre of gravity Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted December 8, 2016 Share Posted December 8, 2016 Welcome to the friendly forum Quote Link to comment Share on other sites More sharing options...
Former Member Posted December 8, 2016 Share Posted December 8, 2016 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Mike T Posted December 8, 2016 Share Posted December 8, 2016 You should always stick them on with non-permanent adhesive. That way, if you find your CG is 'out', you can relocate them easily to correct it... Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted December 8, 2016 Share Posted December 8, 2016 Posted by Andy48 on 08/12/2016 13:13:54: I would beg to differ. I am increasingly finding that I really have to fine tune the CofG on planes designed for IC and running on electric. Mostly using the CofG on the plan seems to be OK, but with nearly all my planes, that fine tuning moves the CofG back slightly, with the only difference being in the flare out on landing which is much improved. I have not found a plane where the CofG moves forward, but several where moving it back slightly improves low speed handling. I suppose you can tweak it more accurately with electric as the weight remains exactly the same each time, whereas with IC one ends up with a slightly varying weight each flight. Most designs seem to set the CoG a smiggen forwards of optimum - I guess they do that to make the maiden more predictable, leaving it to the pilot to trim it back to his level of capability Quote Link to comment Share on other sites More sharing options...
Former Member Posted December 8, 2016 Share Posted December 8, 2016 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted December 8, 2016 Share Posted December 8, 2016 You should always make sure you have a good supply of CoG's. HK used to do them by the bag full, which was very handy if you found that your model didn't have one, or that the one pre-fitted was unsuitable. But they only seem to be available in the International Warehouse now - personally I blame BREXIT. I suspect there will be import duty on CoG's soon. BEB Edited By Biggles' Elder Brother - Moderator on 08/12/2016 23:00:49 Quote Link to comment Share on other sites More sharing options...
iqon Posted December 9, 2016 Share Posted December 9, 2016 They have restocked the uk warehouse, but the price has gone up.. Quote Link to comment Share on other sites More sharing options...
Andy48 Posted December 9, 2016 Share Posted December 9, 2016 Posted by Biggles' Elder Brother - Moderator on 08/12/2016 23:00:14: You should always make sure you have a good supply of CoG's. HK used to do them by the bag full, which was very handy if you found that your model didn't have one, or that the one pre-fitted was unsuitable. But they only seem to be available in the International Warehouse now - personally I blame BREXIT. I suspect there will be import duty on CoG's soon. BEB Edited By Biggles' Elder Brother - Moderator on 08/12/2016 23:00:49 Pleased to see that retirement is having a positive effect. Quote Link to comment Share on other sites More sharing options...
DH 82A Posted December 9, 2016 Share Posted December 9, 2016 If using old COG's, make sure you check the "use by" date. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted December 9, 2016 Share Posted December 9, 2016 Posted by DH 82A on 09/12/2016 11:29:47: If using old COG's, make sure you check the "use by" date. And whether they are imperial or metric CoGs BEB Quote Link to comment Share on other sites More sharing options...
iqon Posted December 9, 2016 Share Posted December 9, 2016 Have they got to be CE marked now.Only ive still got some old ones left Quote Link to comment Share on other sites More sharing options...
The Wright Stuff Posted December 9, 2016 Share Posted December 9, 2016 Are people still using mechanical COGs? We should all be using electronic ones, now. They can be adjusted in flight by pressing a button on the Taranis! Quote Link to comment Share on other sites More sharing options...
Don Fry Posted December 9, 2016 Share Posted December 9, 2016 No, the CG is on the main spar, and if not the designer did a complete redesign of the wing so it would be on the spar in the final version. Quote Link to comment Share on other sites More sharing options...
iqon Posted December 9, 2016 Share Posted December 9, 2016 I hear the new CG`s are adjustable and you can move them 5mm either way and secure in place when happy Quote Link to comment Share on other sites More sharing options...
maurice northcott 2 Posted December 9, 2016 Share Posted December 9, 2016 A number of years ago I assisted Pyramid Models to develop a moveable C of G. These have been on sale since then. Change your C of G without adding extra weight, just move it around to suit. They are still on the Pyramid Models website...... Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted December 9, 2016 Share Posted December 9, 2016 I thought EASA were planning to ban movable C of Gs due to safety concerns raised by the European Parliament. In future, it seems that a re-certification process will need to be followed, involving full aerodynamic calculations, computer simulation, wind tunnel testing and compulsory CE marking of its position. Edited By Martin Harris on 09/12/2016 14:39:38 Quote Link to comment Share on other sites More sharing options...
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