APC 7x8 Sport

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 !

After having tested the 7x7 Sport prop from APC, today it's the turn of the 7x8.

In order to look what a "more than square" prop can do!

The results are compared with those of the APC 7x7 Sport and the APC 7x6 Thin Electric:

Thrust coefficient:

Here we can clearly see that the prop is stalled in static.

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 N2826-1350, Kv 1350 - 51g,

- 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 7x8 Sport: