Hi Kloner,
First off, do not be scared, it doesn't bite. Looks crazy but its really simple you will see. This will help you. The link provided gives you access to the specs of all the props APC makes. Check out the E model. The raw data seems confusing but if you concentrate only on the column Pe (which is propeller efficiency) you can determine the actual speed at which your prop will be the most efficient. This is the airspeed you can conduct testing at for a given RPM' of course. Do not forget that you will unload in the air so 8000 RPM on the ground will likely be around 8500 RPM in the air. Lets' look at the chart for an 11 X 7 E prop at 8000 RPM. You quickly discover that the props' max efficiency is at 55.7 MPH. So in level flight, when you are turning approx 7000 RPM, are you flying at a speed close to 55.7 mph. If so, this is where you will make your longest flight i.e. use with most efficiency the your Lipo battery and be the most efficient at trading mah for mph. Notice that above 70 MPH, the prop efficiency is negative which means that the prop is actually slowing down the plane (aerodynamically, it is called the Brake mode...). You do not want that! From this and your telemetry, you can put together a winning prop combo! So here is the link:
http://www.apcprop.com/v/downloads/PERFILES_WEB/datalist.asp
11x7E.dat 04/19/12
====== PERFORMANCE DATA (versus advance ratio and MPH) ======
DEFINITIONS:
J=V/nD (advance ratio)
Ct=T/(rho * n**2 * D**4) (thrust coef.)
Cp=P/(rho * n**3 * D**5) (power coef.)
Pe=Ct*J/Cp (efficiency)
V (model speed in MPH)
PROP RPM = 8000
V J Pe Ct Cp PWR Torque Thrust
(mph) (Adv Ratio) (Hp) (In-Lbf) (Lbf)
0.0 0.00 0.0000 0.0963 0.0553 0.367 2.889 2.875
2.4 0.03 0.0499 0.0917 0.0534 0.354 2.792 2.736
4.8 0.06 0.0983 0.0872 0.0515 0.342 2.692 2.602
7.3 0.09 0.1457 0.0829 0.0496 0.329 2.591 2.474
9.7 0.12 0.1930 0.0791 0.0476 0.316 2.489 2.360
12.1 0.15 0.2338 0.0733 0.0455 0.302 2.380 2.187
14.5 0.17 0.2759 0.0688 0.0435 0.288 2.271 2.053
17.0 0.20 0.3165 0.0644 0.0414 0.275 2.164 1.923
19.4 0.23 0.3554 0.0623 0.0408 0.270 2.130 1.860
21.8 0.26 0.3928 0.0601 0.0400 0.266 2.093 1.795
24.2 0.29 0.4287 0.0579 0.0392 0.260 2.050 1.727
26.6 0.32 0.4630 0.0554 0.0383 0.254 2.001 1.655
29.1 0.35 0.4957 0.0529 0.0372 0.247 1.945 1.580
31.5 0.38 0.5269 0.0503 0.0361 0.239 1.886 1.503
33.9 0.41 0.5564 0.0477 0.0349 0.231 1.823 1.424
36.3 0.44 0.5838 0.0450 0.0336 0.223 1.756 1.343
38.7 0.46 0.6091 0.0422 0.0322 0.214 1.684 1.260
41.2 0.49 0.6326 0.0394 0.0308 0.204 1.608 1.176
43.6 0.52 0.6540 0.0365 0.0292 0.194 1.525 1.089
46.0 0.55 0.6734 0.0335 0.0275 0.182 1.436 1.001
48.4 0.58 0.6903 0.0305 0.0257 0.170 1.342 0.910
50.9 0.61 0.7042 0.0274 0.0237 0.157 1.240 0.817
53.3 0.64 0.7134 0.0242 0.0217 0.144 1.133 0.722
55.7 0.67 0.7171 0.0209 0.0195 0.129 1.020 0.625
58.1 0.70 0.7129 0.0176 0.0172 0.114 0.900 0.525
60.5 0.73 0.6968 0.0142 0.0148 0.098 0.774 0.424
63.0 0.76 0.6607 0.0108 0.0123 0.082 0.643 0.321
65.4 0.78 0.5860 0.0072 0.0097 0.064 0.506 0.216
67.8 0.81 0.4236 0.0036 0.0070 0.046 0.366 0.109
70.2 0.84 -0.0010 0.0000 0.0044 0.029 0.228 0.000
Have fun!
Rodge
