I got the following: I have a copter tuned for 13 x 5 inch EOLO props, had some hardware accident, so I am waiting for new props, and decided to try 13 x 6.5 APC props.
I did a AUTOreTUNE, and was surprised that it kept the P and I quite similar to the previous tune, but almost doubled the D term.
Even so, the tune does not seem right, it got oscillations, and during the autotune procedure, there were constant (dying) oscillations. Overall feeling i had that it would be difficukt to tune well for this prop.
The main difference between EOLO and APC, apart from pitch, is the weight, EOLO is 14 grams, APC 34 grams.
Does propeller weight have an influence on how the copter/tuning/autotuning behaves?
If the inertia really has an influence, that would mean that copter would be much less responsive, i.e., changes in thrust requirements from FC would take more time to materialize… to compenate for this one would probably have to pump up P factor, not D, as Autotune did.
I never thought copter props had to be light… Will stick to lightweight ones from now on…
The APC propellers seem to be considerably more efficient than EOLO. I got 50 minutes hover time/slow flight time with my standard battery versus 45 minutes with EOLO, an increase of 11 %, which is considerable. (I fly till I have 3.0 V per cell). And that is considering that the copter is now 120 grams heavier due to heavier props and heavier prop mounting system. That is about 5 % extra weight!
I am not sure if this is due to the pitch or to prop quality. Ecalc suggests that there should be virtually no difference in efficiency between 13 x 5 and 13 x 6.5.
I also thought that flat props, i.e. low pitch to diameter ratio must be more efficient considering that most copter props are of this type, but this experiment suggests otherwise.
After that I tried a battery which has 50 % more energy and weight, i.e. added 550 grams. The surprising result was that the power (in Watts, not A) went up by 42 %, giving an estimated meager 6 % hover time increase…
So, hover time:
Prop Bat1 (1 kg) Bat2 (1.5 kg)
EOLO 13 x 5: 45’ 64’
APC 13 x 6.5: 50’ 53’
Got more interesting results…
Turns out that the range of the copter with 13 x 6.5 was greatly reduced, I barely managed to fly total 30 km real world, versus normal 36…40 km… But for hover and slow flying it indeed gave more time in real world flights.
With planes, a higher pitched prop usually could increase range but would reduce climbing, copters seem to have it the other way round, did not know that.
Also, I made some low air pressure tests, and discovered that at 44 kPA the copter began to fly much better. I had oscillations of less than 0.05 degrees compared to 0.2 degrees at 100 kPa, and the tracking of the desired versus real pitch and roll also became much better. I could not believe that… Now I did not do “stupid things” to test out copter behaviour under extreme maneuvers, but still… I have not observed any bad behaviour.
Which props are stiffer, the EOLO or the APC ? For me, I’ve moved to CF props for light weight and stiffness to get the best performance on my copters.
APC by far are much stiffer… The advantage of EOLO is their weight (14 grams versus 34). Also APC require special mounting hardware which is heavier, this adds another 10 grams.