Newbie and CG balancing

[PapaC]

Got my self a Volantex Phoenix s 1600, build was smooth and it is all hooked up to the radio gear with a 2s 2200 battery, as I understand things before the maiden flight I should balance the plane on the CG marks.

 

With the 2s battery as far forward as it can the pheonix is still very tail heavy, to get it to balance on the CG marks i had to add about 100g of weight is this normal to have to add this much ballast or is this correct so larger sized batteries can be used?

Also should it balance level or should it be slighty nose or tail heavy to make flying "easier"?

[GrumpyGnome]

Slifhtly nose down. Add the weight - you can always remove it gradually if necessary.

 

Do some research first as manufacturers balance points are often way our...

[Murat Kece 1]

I use a larger battery rather than adding weight..

 

[Ernie]

hi PapaC,     If you ever build a short nosed WW1 model, you'll need to raid the roof of York Minster to find enough lead to get a sensible balance point. GET IT RIGHT. Too far forward and the result will be like chewing a toffee with the paper on. Too far back and you won't even taste the toffee

ernie

[PapaC]

Thanks all for the advice so far, all good thoughts

 

4 hours ago, GrumpyGnome said:

Do some research first as manufacturers balance points are often way

 

Is there a general rule of thumb for all planes or does it differ based on the design, wing shape position etc?

 

[Ernie]

Probably about 1/3 back from the leading edge for a simple parallel chord wing, but it's critical, so don't chance it.

ernie

[Shaun Walsh]

Have a look through the reviews here:

https://hobbyking.com/en_us/volantex-742-7-phoenix-1600-epo-composite-r-c-glider-pnf.html

A number of complaints about motors burning out but in some cases it's not clear whether they were using a 2S or 3S battery. Given the motor is 1400 KV the prop fitted may be too big for a 3 S battery causing the overheating problem.
There is one comment about moving the CG 8mm rearward and it flying OK.

[Martin Harris - Moderator]

Years ago, the BMFA News published a simple to use nomograph which I’ve used successfully on a number of occasions. I don’t know if anyone has an electronic copy?

 

The published CofG should really be a range of positions within which the handling will be acceptable.  Where a point is marked on a plan will be the designer’s best guess at a good starting point (or in the case of some ARTFs an arbitrary guess/error!).
 

The position of an acceptable CofG depends on many factors - primarily the mean chord (this takes into account wing taper and sweep), the effectiveness of the tail (area and moment arm) and personal taste so there’s no “one fits all” solution although it will often be within the 25-33% range on a trainer/sport/scale type platform.