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New Foam Planes And CG's

Old 05-25-2015, 01:42 AM
  #1  
Karnsy
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Default New Foam Planes And CG's

Just got to thinking (first mistake) Why do some RTF & BNF foam planes come with cg already fixed. Example.... I have 3 or 4 Parkzone planes which have a perfect cg with recommended battery size and placement right out of the box. They all fly awesome and I did not add an once of weight. Then I have a couple other planes (FMS & Airfield) I had to add 3/4 of an oz to 3 full oz's. Why wouldn't they produce them all so they are easy to fly, not nose heavy or tail heavy right out of the box give or take battery size and placement ? Just thinking........
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Old 05-25-2015, 01:57 AM
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Rockin Robbins
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It's because not all companies are Horizon Hobbies. They actually prototype and test their planes extensively before they sell them! Seems like a no-brainer, and sometimes mistakes sneak through anyway, but actual design and testing seems to be the exception rather than the rule.

It's not that it is impossible to balance a plane. It's just that it is so nice not to have to.
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Old 05-25-2015, 02:35 AM
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Could also be issues with component vendors and availability/costs. The engineers, folks in R&D and testing can come up with an amazing product only to have it changed before release for various reasons.
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Old 05-25-2015, 03:16 AM
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Could be the cheap plane makers don't care.
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Old 05-25-2015, 03:51 AM
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Karnsy
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Thanks for the replies... I know as a newbie it is so nice to put a plane together and not have to worry about it. I wish they were all like that !
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Old 05-25-2015, 04:53 AM
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fhhuber
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even worse is when the recommended CG is wrong.

Great Planes Electrifly WWI series (appx 30 inch span +/-) ALL have recommended CG that is so far back that they are unflyable. 2 to 3 oz lead needed in the nose AFTER getting it to where they recommend.
Good thing I check by calculating correct CG as % MAC every time.
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Old 05-25-2015, 06:15 AM
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I lost a Goldberg Monster Pitts (38" wingspan) due to the manual not being very clear on the CG. In my noob seasons I balanced it, perfectly I might add, on the lower wing. Turns out it should have been the top wing. Total destruction.
Actually I just put that AXI 2820/10 out of the Pitts into a Stevens Aero Edge540 that I blew a bearing in today. Sure it's 1200kv on a 3 cell but with 45 degree hinges, it don't 3d well anyways. It will go fast though. And didn't change the CG!
Anyhow, it's a good thing that you are familiar with CG's. Check them often.
If they make this hobby too easy, what would constitute a good pilot?
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Old 05-25-2015, 08:30 AM
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Don't forget that not everyone wants same CoG .... they use different battery's, motors, some just like CoG different.

I agree that bit would be nice for factory to regulate build to recc'd CoG with recc'd gear ... but many don't.

Nigel
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Old 05-25-2015, 09:13 AM
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mclarkson
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I've been astonished at how badly some planes are designed and built with regards to their CG. Where the battery compartment isn't even close to where it needs to be. I know that not everyone works as diligently as Parkzone, but you'd expect it to at least be possible to get the battery in so as to balance the plane.

But, no. Not always.
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Old 05-25-2015, 11:37 AM
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Unless you use the EXACT SAME parts for servos, receivers, battery, esc and place then in the same position as the manufacturer did, you can not expect to have the CG be at the same or recommended location.
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Old 05-25-2015, 11:39 AM
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solentlife
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Originally Posted by mclarkson View Post
I've been astonished at how badly some planes are designed and built with regards to their CG. Where the battery compartment isn't even close to where it needs to be. I know that not everyone works as diligently as Parkzone, but you'd expect it to at least be possible to get the battery in so as to balance the plane.

But, no. Not always.
This does tend to be a Foam problem rather than one with Balsa / Wood ... where battery location is much more versatile.

It may be part of the mould set-up ... who knows ?

Skyartec Cessna 182 deluxe is the best I have ever seen for Battery and balance .... the battery box being a plastic affair set into the foam fuselage straddling the CoG .... so you can fit whatever LiPo will fit ... from lowly 1000 to 2200 .... brilliant ...

AND the battery box is available separately to fit to any other model ....

Nigel
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Old 05-25-2015, 10:03 PM
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Originally Posted by Rodneh View Post
Unless you use the EXACT SAME parts for servos, receivers, battery, esc and place then in the same position as the manufacturer did, you can not expect to have the CG be at the same or recommended location.
I have had RTF planes which refused to balance out of the box without the addition of lead.
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Old 05-27-2015, 01:20 AM
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Karnsy
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You know while we are talking about cg's I have a Great Planes cg balancer and I have a tough time using it. It is supposed to be simple but some of my planes that fly awesome show so nose heavy they slide off unless I hold them on. Also the wing on most my planes have a strong tapper at the at the beginning of the wing then slight. This is a difference of 1/2" in some planes which makes a difference. I am not sure where to line up the stem that goes against the wing. Some times I just don't trust it. Thus I kind of check the cg the old fashioned way, with my fingers.. hmmmmmmmm? anyone else feel the same or is this a beginners whoeeessssss?
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Old 05-27-2015, 02:28 AM
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I have a couple bladestruck 450 heli tail booms with pencils and the big tapered erasers jammed in them, plugged into holes in a board. This is used for the more accurate (new plane) work but still find myself using my fingers quite a bit. My foamies have notches pushed into them where my fingernails can locate. I have lost and seen too many other pilots lose planes due to missing this one basic preflight check. My hodge-podge array of batteries makes battery locating lines more of a rough estimate.
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Old 05-27-2015, 08:40 AM
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I have the Hobby King CoG machine .... it works but is a pain to get to point of balance. The pivot domes if you lock to the pins, do not pivot enough one way, but OK other. So you have to leave them sitting by virtue of weight. The model slides on the arms, the arms do not sit level under the wing.

So I often end up removing the arms and dome pivots - using the vertical pins in same manner as finger tips ! Then it works much better. But of course then you don't have the ruler to read of the mm distance.

Nigel
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