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Pico Stick (fusalage) c of g

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Steve Jeffery10/09/2012 10:01:59
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14 forum posts

Help please

I have put together a Pico Stick (the one with a fusalage) and the c of g is about 15 mm further back than it should be. It could be because I have added a 3mm carbon rod to the horiz. stabaliser or maybe because I cut the prop shaft down to bring the prop closer to the cowl, I have tried adding weight to inside the cowl but it needs 0.7 oz. On such a small park flier is this not excessive? Could I move the wings back to bring the c of g back onto the mark I have on the wing or do I stick with the excess weight?

I have put the battery and electronics as far forward as I can without cutting away foam

Thanks in advance

Radge10/09/2012 10:06:33
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Sorry, I'm a bit confused, is your balance point 15mm behind the recommended CofG?

Steve Jeffery10/09/2012 10:16:56
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Radge

Yes. I have marked the the recommended point (55mm) back from the leading edge on the wing and when it balances the balance point is 15mm further back

Biggles' Elder Brother - Moderator10/09/2012 10:51:00
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Its almost certainly the carbon rod in the tail - anyweight that far back is acting over a long moment arm and has completly disproportionate effect.

Moving the wings back? Now there is an interesting idea you don't come across everyday! Yes in principle it would work. It would of course shove your CoG a bit further back still but that should be minimal.

Assuming the wing is about, what er...120mm chord? Then 15mm is quite a way out. But if you could get it within say 5mm I'd give it a go. Deigners/manufacturers don't always get the CoG right and many are quite conservative - placing it on the forward side of uncertainty!

BEB

Bob Cotsford10/09/2012 11:06:09
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Moving the wings back really does go back to old time modelling, it's how we used to balance chuck gliders and rubber powered stick models. The carbon rod will be part of the problem but on a model like this the prop is actually a significant mass so that would also have had an effect on the CofG.

0.7oz? What's that, about 20gms? My PicoStick (I only know the one with a stick fuselage, I don't know what the 'fuselage type' one is) probably varies in all up weight by more than that depending on the battery size I use but as the wing carriers can be slid backwards easily enough so I'd go for that option.

 

BEB - not sure why you think moving the wing back would move the CofG back, you are moving the motor/battery and mass of the fuselage forward relative the the wing making the model more nose heavy - am I miss-reading your post?

Edited By Bob Cotsford on 10/09/2012 11:08:37

Biggles' Elder Brother - Moderator10/09/2012 11:43:51
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Yes you are moving the battery et al forward relative to the wing Bob - but the mass of wing (very very small true - which is why I said it would be "minimal" is going backwards in absolute terms on the fuselage. So there is some mass further back on the fuselage. But as we'd both implied the effect would be inconsequential!

BEB

Bob Cotsford10/09/2012 13:09:59
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I'm tempted to get into CofP>CofG movement (mainly to get it clear in my head0 but this isn't the place. I understand what you were getting at now, and yes, inconsequential is too big a word for a PicoStick wing!

Biggles' Elder Brother - Moderator10/09/2012 13:48:44
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LOL!

BEB

Tom Wright 210/09/2012 13:50:09
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The PS has a very low wing loading similar to many FF models) so a rearward cog is usually not a problem and can even improve LD but keep in mind that less elevator movement may be required.

Tom.

Edited By Tom Wright 2 on 10/09/2012 13:51:42

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