Peter Miller Posted January 5, 2016 Share Posted January 5, 2016 Yes, well, some people have a funny ideas about what does look right! The only numbers I do is working out the basic wing area for the engine size that I want. And even that is TLAR. Abot 55" span, 11" chord for somewhere aorund the 550 sq incches. Just right for a .40 FS Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted January 6, 2016 Share Posted January 6, 2016 At least Dr. Eifel did use his best TLAR-meter on his TLAR-board... Happy towering Chris BRU - BE / CTR Tower Control Quote Link to comment Share on other sites More sharing options...
kc Posted January 6, 2016 Share Posted January 6, 2016 Actually I was referring to the Edsel car - one of Fords most controversial designs and a commercial disaster. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted January 6, 2016 Share Posted January 6, 2016 ... but then maybe you omitted the Corvair, kc... ... I thought I wrote Dr. EIFEL ... not Edsel... Chris BRU - BE / CTR Corvair Control Edited By McG 6969 on 06/01/2016 11:47:48 Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted January 6, 2016 Share Posted January 6, 2016 Actually few American cars of that era looked about right!!! All teeth and chrome and fins. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 6, 2016 Author Share Posted January 6, 2016 Posted by Peter Miller on 06/01/2016 11:48:17: All teeth and chrome and fins. Sounds like some of the women I know! BEB Quote Link to comment Share on other sites More sharing options...
kc Posted January 6, 2016 Share Posted January 6, 2016 Back to aeromodelling! A thought occurred to me that if the lipo eventually needs to go way back then to avoid this the servos could be put through the fuselage right at the tail end. Some people like that anyway. Quote Link to comment Share on other sites More sharing options...
kc Posted January 7, 2016 Share Posted January 7, 2016 BEB looking at your method of calculation ....whilst going throught the first bit I came across this "the centre of the engine is 0.245m forward of the aircraft's CoG. So the moment created by the engine is: Me = 0.36 x 0.345 = 0.0882Kgm." Seems to be a misprint? Should be 0.245 instead of 0.345? So this got me thinking - if I found a tiny error could there be any other errors in the calculations? BEB's theoretical calculations goes against my experience/rule of thumb/ feeling that if replacing a glow with electric then the Lipo front needs to go further forward than the glow firewall did. I started building my model on that basis- a 165 gram motor at the nosering and a 4S3000 lipo 320 gram immediately behind the motor. My halfbuilt fuselage worried me that my rule of thumb might be wrong and BEB's theory seemed to say I was wrong. A days thinking suggested a practical test but I didnt have an OS40 FS or a completed ballerina to hand! But a very crude balance - just a 2ft plank of wood balanced on a alloy T section with an OS 40SF less silencer ( 360 gram) plus a tank at 295mm on one side and a Turnigy 3548/ 6 ( 165 grams) again at 295 mm with a Zippy 4S3000 ( 320 grams) right behind it just balanced! Very crude and certainly not that accurate but my practical test showed that my motor plus Lipo should balance instead of an OS FS 40 surpass. Well that is if a 40SF two stroke is about the same weight fore and aft as a four stroke! The weight of a plastic spinner altered it either way. Edited By kc on 07/01/2016 20:01:23 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 7, 2016 Author Share Posted January 7, 2016 Yes - "0.345" is a typo for "0.245" - but the result is correct! ie 0.36 x 0.245 is indeed 0.0882. This has happened because I did the original calculations on paper and then typed them in. In the process of inputing them I accidently typed a "3" instead of a "2" - but the result stands. I have checked the calculations again, and while I'd be the first to admit that its very easy to make a small slip, I can find no error. What surprised me was not that the battery didn't have to go in front of the firewall - my TLAR was telling me that because of the very long nose the model has - it was just how far back it came out to be! But the result isn't that strange when you consider that my motor plus ESC weighs in at 0.282Kg. This compares with Peter's OS 40 at 0.36Kg. In other words my motor and ESC are 78% the weight of Peter's engine. That's very high for an electric set up. Bear in mind Peter has no other significant weight - the tank is not that much - so it isn't really surprising that the battery ends up only just in front of the CoG - we have very little to "make up" on! For folks with significantly lighter motors and who are perhaps placing their ESC's further back, I would advocate redoing this calculation with their own figures to check, their battery will have to be further forward than mine, but I'd still be very surprised now if it came out to be ahead of F1 BEB Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 7, 2016 Author Share Posted January 7, 2016 Posted by kc on 07/01/2016 19:32:58: a Turnigy 3548/ 6 ( 165 grams) again at 295 mm with a Zippy 4S3000 ( 320 grams) right behind it Yes but your motor is only 0.165 - against mine 0.222+ESC (=0.282)! 70% heavier! BEB Quote Link to comment Share on other sites More sharing options...
kc Posted January 7, 2016 Share Posted January 7, 2016 I am going to suggest that with BEB's motor ( including ESC studding about 120 grams heavier than mine ) practical experiment predicts he would need to have the centre of his 3000 lipo at more like 100mm in front of CG rather than the 57mm he calculated! Edited By kc on 07/01/2016 21:07:50 Edited By kc on 07/01/2016 21:09:33 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 7, 2016 Author Share Posted January 7, 2016 Time alone will tell kc! BEB Quote Link to comment Share on other sites More sharing options...
kc Posted January 8, 2016 Share Posted January 8, 2016 I started by wondering that if nobody else had spotted the typo then maybe nobody else had really read through the formula either. I went on to think that if an Excel spreadsheet could be produced then everyone could just fill in their motor & lipo weights and instantly have BEB's calculations done for them. A moments thought told me that producing a spreadsheet might not allow for all the variables so a simple practical experiment would be quicker! The fact that my experiments gave a different result to BEB's formula suggests that the unknown factor is the position of the greatest weight in a glow motor ( possibly right at the front) compared to that of an electric motor (probably right at the rear) Maybe one needs to know the precise balance point for each component for such a calculation to work. Actually time will not really tell because every model is different in construction. Peter used an extra servo behind CG for throttle, presumably well fuelproofed all the front, used solarfilm not 'tex, may have had a lighter sheets of balsa etc etc. So exact comparison would not be possible unless the original were re-engined. What everyone should deduce is that the variables are so great with electric conversions that provision needs to be made for a wide range of Lipo positions just to avoid using lead. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted January 8, 2016 Share Posted January 8, 2016 Hi to all, I think BEB is right with his approach & calculations. And I believe kc is right too considering that there are too many "unknown factors" and approximations - ie CG of different components in the formula, different personal types of construction, etc.) - to achieve an 'universal' guidance. As a beginner, I'm considering using a 3 & 4S compatible motor (lighter than BEB's powerplant) and starting out with a 'sedative' 3S. So I must try to remain as 'flexible' as possible in my approach and if I make a motor mount at 40-50mm in front of F1 & a cutout in F1 for the Lipo in 3S, there would be plenty of room to bring the battery backwards for 4S... Does this sounds silly? Happy guestimating Chris BRU - BE / CG Control Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 8, 2016 Author Share Posted January 8, 2016 kc - with the greatest respect I think you are slightly missing the point of my analysis. I did not set out to find the battery position, nor would I claim that the analysis tells us that a 3000mAh battery will have its centre 57mm in front of the CoG! My objective was to answer the question: "Do I need to modify F1 if it is left in the position in the design? Because, if I do, I need to do so before I start building the fuselage." Now if I had got an answer that suggested that the battery might not have to go through F1, but only just, then I would probably alter F1 anyway - because I can't be that certain in the accuracy of the result - there are assumptions and approximations being made. But the significance of the result I got is that it suggests that the battery will be no where near F1. Now I night be a bit out fore-and-aft (as I said originally 10-15% easily) but I am very confident in that basic result ie: I do not have to alter F1, but I do have to alter F2. That was the point of what I was doing, not to fix the exact point of the battery, that can only be done when I balance the model once built. Given I got that result - all I am suggesting is that others might like to consider a little before automatically modifying F1 and leaving F2 unmodified, because that way that they might be creating a problem for themselves down the line if they find the battery position is considerably aft of where they have assumed it to be, which would appear to be likely. BEB Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 9, 2016 Author Share Posted January 9, 2016 Well I went to bed last night with great plans. I was going to get into the shed early and make a good start on the Ballerina as rain was forecast! A day of biulding accompanied by the radio - bliss. However Mrs BEB revealled to me this morning that she too had plans - and they involved me. We all know that in the contest of competing plans - our OH's plans always have priority! So it was about 5:00pm before I finally got into the shed - then I had a lot of tidying up to do from the end of the last build! But at least I have made a start. As I've said elsewhere, I like to start with the fuselage. First job is to glue on the ply doublers: I am very prone to silly errors - aren't we all! And the classic one here of course is to make two left's or two right's rather than a mirror image pair. To protect myself from this trait I always lay out the fuselage sides as mirror pairs as above. To fix the doublers I use a contact adhesive. Some folks successfully use PVA here - but the slight problem with that is that if you are not careful the wettness of the PVA can curve the balsa. The way to avoid this is to weigh the parts down and leave them until they are completely dry. The advantage of contact adhesive is that you don't have this problem. Being solvent based there is no water content. But the disadvatage is its a "one shot" process - i.e. you get one go at putting the two parts together then they are stuck. If you slightly misalign them - tough. For the last 3-4 models I've built I've being using Evo-Stick Timebond: This is handy stuff. It allows you to carefully place the two parts together and as long as you don't press them together you can adjust and tweak them to get the alignment just right. Once there, you simply press the parts together firmly and - instant bond. Next up I marked the postions of all the formers on one of the fuselage sides and identified the appropriate formers: Some of these formers will require some work! F2 will have to have the top removed, and possibly that square tank cut out deepened. F1 can be left more or less as is regarding generally shape, but I will need to fit 4 M4 captive nuts for the studding. So rooted out the required nuts from my stores and some M4 studding: So, that's as far as I got - not much I know, a bit dissapointing, but at least it's a start. Should be able to sort those formers out tomorrow and maybe get them into place on the fuselage side, then it will be into the jig to bring the fuelage together. BEB Quote Link to comment Share on other sites More sharing options...
Chris Barlow Posted January 9, 2016 Share Posted January 9, 2016 I was wondering when you were going to stop chatting and start building! A frustrating start but definitely underway now. Quote Link to comment Share on other sites More sharing options...
Lindsay Todd Posted January 9, 2016 Share Posted January 9, 2016 not come across Time Bond before, will certainly get hold of some sounds very good stuff. Linds Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted January 10, 2016 Share Posted January 10, 2016 Ah you've started then I can't take the fumes from contact adhesives or I would use it myself, like the idea of stud mounting though. John Quote Link to comment Share on other sites More sharing options...
Chris Barlow Posted January 10, 2016 Share Posted January 10, 2016 BEB did you notice the additional doublers at the tail end as well? (or have I dreamt them) Quote Link to comment Share on other sites More sharing options...
AVC Posted January 10, 2016 Share Posted January 10, 2016 Good starting BEB! Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted January 10, 2016 Share Posted January 10, 2016 Hi BEB, Fine for you to finally get into the starting blocks. I just hope that you are not intended to stop 'chatting' now... One question though: I was planning to use M3 for my short motor studding (length 25-30mm). Is it too thin? Is it better to go the M4 route? Thanks again for your advice on my blog. Happy starting Chris BRU - BE / CTR Studding Control Edited By McG 6969 on 10/01/2016 09:21:26 Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 10, 2016 Author Share Posted January 10, 2016 Hi Chris, its a very short stand-off that we have, as you say only 25-30mm. I would think M3 would be OK, I'm using M4 for two reasons: 1. I do have a bit of a heavy motor that is going to be whacking out a fair bit of power! 2. I only had that, or M5, in stock! (That's the real reason! ) BEB Quote Link to comment Share on other sites More sharing options...
kc Posted January 10, 2016 Share Posted January 10, 2016 I was going to mention the rear ply doublers. If they are to be used they should go in whilst the fuselage is apart. If omitting them then F10 will be too narrow which affects the line of the fuselage ( don't ask me how I know this...). I would suggest cutting slots for snakes before gluing in place. And then they become handed as well. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted January 10, 2016 Share Posted January 10, 2016 Hi BEB, Thanks again for answering. As my crossmount holes are 3mm, I'll stick to the M3 version then. Do you need some? I have been adding some 'building projections' to my post, so while your glue is curing, could you please have a visit for comments/remarks? Cheers Chris BRU - BE / CTR Advice Control Quote Link to comment Share on other sites More sharing options...
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