|Apr 18, 2012, 08:40 PM|
Gemfan 9x45 and Naza Disk loading in atti mode
well, I got my gemfans. they are nice blade. very well suited for DJI 450 and 550. you do need to drill out the hub. hub diameter is similiar to DJI blade, but with carbon reinforcement, the blades are much stiffer and should be stronger. I used step drill to get it close and reamed the bore hole to .3135. tight fit on the motor. they needed very little balancing, and it was ready to put on.
One thing I noticed about puttng on the new blade were that my 450 and 550 both were bouncing around more in the wind. they were no longer solid anymore.
so, I did a quick and dirty experiment to determine the cause, most obvious being the diskloading.
my 450 were at 1.5kg, and 550 were at 2.6kg. both with 8" and flew well in wind. this is about 200sq in and 300 sq in disk area. 1.39sqft and 2.08sqft leading to 38oz/sqft and 44oz/sqft. both flying very well.
with 9" blade, same weight, my disk area is now 254sqin and 382sqin. 1,76sqft and 2.65sqft which lead to disk load of 30oz/sqft, and 34oz/sqft.
while hexa was more stable, it still was not as stable as the quad with 8".
so, to prove this test out, I added weight to quad and brought it upto 1.85kg, which brought the diskload to 37oz/sqft and now it was almost as stable as before. . I've brought the f550 to 2.9kg and also repeated the test. and it was same . (about 40oz /sqft) very stable.
so, at least in windy condition, naza really likes heavier disk loading in atti mode. I was in constant 5-10mph wind with gust that was higher. holding 1/2 stick or more in atti mode to keep it stationary at times.
well, received my graupners 9x5 and they are the best of the lot. smooth, quiet and motor is cool. one thing is that they do have bit less lift than gemfans, but on my hex, I am at 50% hover (2.6kg) which is fine. they have stepped 8mm with 5mm bore hole, which makes it easy to mount. (just drill out the 5 to 6, then it fits the dji motor perfectly.
also, i've also had first report of drilled out gemfan 9x4.5 failing in air. I am starting to be concerned about drilling out the bore to larger hole. I am very careful not to drill it out too much, but you are making them weaker. so, keep a look out.
for now, I am sticking to graupners for any mission critical flight.
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