Quote from: sanjayrai55 on September 14, 2014, 09:06:19 PM
Iyer sir. Measurement imho is the only way. Just use a voltmeter

But sir, for that many of us have test rigs

The question was directed in the context of some issues that had come up, wherein one without a wattmeter etc. and without experience to make a reasonably accurate guesstimate, could predict, thus helping him or her to select a suitable prop for the given motor for the given model

That's so true...
But most of them who do not have test rigs do rely on freely available thrust calculator.  And that's the only way out... Use specs and calculators
By the way Rai sir thanks for your inspiration I do have a test rig now... 
Will post pics soon

Quote from: K K Iyer on September 14, 2014, 10:12:36 PM

Hope you agree that 'selecting a suitable prop' is a subset of 'How much power is required' and 'pitch required'

Precisely the questions i tried to address in my first Tech Talk - for precisely the same audience!

Glad we are on the same wavelength!

If it makes you feel happy! Your happiness is paramount.

Otherwise, I don't. It certainly is not the same. In one case you talk about optimum prop selection. In the other, analysis of what is happening in prop rpm drop under load. If the first answered all questions, the second was never needed.

OK, here's an actual example of yesterday.

I had 2 old (in age, not use) 3300 mAh Turnigy Nanotech 30-50 C Lipos.

Just made a new model, aerobatic, 1.3 Kg. Wanted 350 Watts, and used a 3536-1250 KV with a 10*7 prop.

On testing with the old batteries, they gave 270 Watts @ 32 A, and 9.1 V

Then tested with a new battery. Got 560 Watts @44 A and 12.2 V

Massive difference

The old batteries are not puffed excessively, and all cells are in balance, and charge till 12.55-12.56 V

Just died from old age - however the important point is how the voltage can drop under load, especially on old batteries, and the importance of measurement (I did not measure thrust and RPM, did not need to in this case.)

And yes, the maiden was successful    Will be posting that log soon