I wanted to do a few real world hover tests with different prop sizes to satisfy my curiosity.
I tested 3 sizes of some commonly used props, the RCTimer Carbon 10x4.7, 11x4.7 and 12x3.8, all carefully balanced. There are other very similar props branded differently.
The 'copter is a carbon Tricopter, battery used is a new Turnigy 3300mAh 30C 3 cell. The motors are the very good Sunnysky x2212 980kv. Weight is 1046 grams (37oz) and the altitude above sea level here in Johannesburg, South Africa is 1500m or 5500ft.
The method was to take a fully charged battery, connect a BNB Products "Digital Power Recorder 50" inline, takeoff to 2m (7ft) altitude, hit alt_hold and let it hover in the same place for 90 seconds, then land. I then trimmed the log in the software to show only the first 60 seconds starting once the aircraft was stable. Not terribly scientific but enough to get some interesting data.
A summary of the tests:
|Average Watts||Average Amps||Average Volts|
First observation is that there is not very much in it, the 10x4.7's are about 3.1% less on the watts compared to the 11x4.7's and about 5% less compared to the 12x3.8's but there is noticeably less power with the 10x4.7's.
In fact, at the altitude I'm flying at I would not use the 10x4.7's as there really is not much power in reserve if you're coming down from a fast descent, it takes a second or two and 2m lost altitude to arrest a descent. It would be really bad with a payload.
I also expected the 12x3.8's to be lower watts than what they are, but this may be due to the larger surface area compared to the others and there must be more drag.
Here are the graphs: