solentlife
We all go through it : small prop, high KV and then what battery to use. Or a sedate parkflyer with low KV, big prop and ?? battery.

Would anyone like to suggest a rough and ready rating for KV vs Battery Cell number ? Lets keep it in the generalised parkflying realm ?
I'll fly anything if I can launch it ! Youtube : solentlifeuk
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solentlife
Some time ago ... when I was part of the Need for Speed group on another forum - I used a spreadsheet to enter values found by various combos of kv / battery / prop. The results showed that a factor could be produced to use for various types of flying.

Factor made up of KV x Battery Cell number x Prop Diameter x Prop Pitch. Depending on the final result desired - the relevant factor was used to decide setup.

Lets take a Polaris .. usual here is 2200 KV, 3S, 6x4.

This leads to a factor of 2200 x 3 x 6 x 4 = 158400

Now we take a sunday flyer Piper Cub ... 1100 KV, 3S, 7x5 >>>>>>>>  factor 115500

Next my Tiger Moth .....  500KV, 5S, 13x6 >>>>>>>  195000 ... this can actually be reduced to 4S if necessary.

Interesting to see if anyone else has any 'formulae' they use as rough guides ?

When I look to change a prop size or battery combo - I use the factor I found for successful flight and use that to determine ther change. If a flight has been marginal - the Tiger Moth is example where 12x6 gave sufficient power, but needed to keep above average throttle ... the factor showed me what NOT to drop below.

I tyhink we all in our own ways have 'personal' ways to decide things ... as I say - would be interesting to hear others ... 
I'll fly anything if I can launch it ! Youtube : solentlifeuk
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Wildthing
My formula is touchy feely 😃 , 
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