APC 8x6 Thin Electic (english)

This is a translation of my original article, please leave comments for any correction that can be made! my english isn't perfect at all !

Wind-tunnel test of the 8x6 Thin Electric from APC and comparison with the 8x6 CAM Slim from Graupner.

Only the results of the performance tests are given here, so as for the other tests by the way...

Three measurement runs were made, for the APC, wishing to obtain a picture of rotational speed effects on overall performances.

Unfortunatly and once again, the high pitch of the prop is limiting the max rpm achievable in the wind-tunnel. The three tests, at average rotational speeds of 6450, 7000 and 7600 rpm, are not very relevant, the variations in terms of thrust, power and efficiency are "drowned" in the margin of error.

Only one test was made with the Graupner, at 6500 rpm on average, speed that allows to go past the peak efficiency advance ratio, so giving a good picture.

Most of the time I'm using APC props, because I have many of them, that's not really favoritism, but...

The first conclusions are that the APC 8x6E at 10000 rpm gives the best of itself at airspeeds between 20 and 25 m/s, the ratio between rpm and m/s being proportional (5000 rpm --> 10 to 12.5 m/s), with an efficiency above 60 %.

Thrust coefficient:

Power coefficient:

Efficiency:

Extrapolations of thrut and power:

Below, charts for finding thrust, power needed and efficiency of the propeller according to flight speed and rpm.

IMPORTANT NOTE:

  Those curves are extrapolated from a single test, at the rotational speed indicated (ex: source test: Graupner 7x7SN - 6473 rpm). In the case of homemade test, the rotational speed isn't constant, it's the voltage that remains constant, the rotational speed increases as the prop "unload", in a similar way as what can be seen in flight.

The props are quite relatively sensitive at variations of their rotational speed, see the UIUC site. The following curves don't care about this!

The red curve "Réf." represents the test conditions.

The dotted red curve "Calc." represent a practical case, here:

- Motor: EMP N2836-1120, Kv 1120 - 80g,

- Voltage: 11,1V,

calculated by the homemade software.

Those two curve then show an increase of the rpm with speed.

The values are given for standard atmosphere, 0m height.

NOTE: "poussée" means "thrust", "puissance" means "power" and "tr/min" means "rpm" !

APC 8x6E:

Graupner 8x6 CAM Slim: