Trouble finding prop size
 

I'm using a Tacon Bigfoot 160 with a Turnigy Sentilon V4 100A 5-12s HV Bulletproof Speed Controller w/RPM Sensor

and 8 Cell battery on a 15 pound model whats the largest prop i can use

I used this calc program.

http://ecalc.ch/motorcalc.php

I used an 8s battery 8000mah, 20x12 APC E prop and it calcs 76 amps, 344 ounces of thrust.

I figure about a 10% plus or minus to real world numbers. You would need a watt meter to keep from letting the magic smoke out.


Buzz.

You can do some simple checks to answer your own question. What is the minimum ground clearance you need; this will determine the maximum diameter. Now you need to pick the pitch that will keep you within the maximum current ratings of your ESC and/or motor. That is where you need the watt meter so you can test with different amounts of pitch.

"whats the largest prop i can use"
One that loads the motor to no more than 2700W.