APC Thin Electric 9×6

9×6×2 · air · measured geometry

Chord & twist digitized from the real prop by UIUC. Sections are PropShaper's, not APC originals.

Checked prop. PropShaper's built-in blade-element model is regression-tested against this propeller's UIUC static and dynamic points. The tables below are the measurements. The curve in the studio is the model. They are drawn separately, and a run that uses a foil.tools polar is not part of that test.

Open this prop in the studio →

What the wind tunnel says

These figures are computed from the UIUC file, not from PropShaper's solver. Static thrust is T = C_T ρ n² D⁴ and power is P = C_P ρ n³ D⁵, with ρ = 1.225 kg/m³ (ISA sea level) and n in revolutions per second. Figure of merit is C_T^3/2 / (√2 C_P), the hovering-rotor definition. On this Volume 1 set it runs about 0.30–0.64. A helicopter near 0.75 is the wrong comparison.

Static at 6,108 rpm: CT 0.1160, CP 0.0513, figure of merit 0.54.
That coefficient is 410 gf and 41 W on one prop at sea level.
Geometric pitch speed at that rpm is 56 km/h. That is where axial angle of attack would be zero. It is not a recommended cruise speed.
Best measured efficiency is 69% at J = 0.57, 6,715 rpm (CT 0.0431, CP 0.0358). Peak efficiency sits toward faster forward flight.

Static measurement

apce_9x6_static_rd0987.txt. J = 0, so efficiency is not defined. Figure of merit is the hover number.

rpm	CT	CP	FoM
2333	0.1096	0.0541	0.47
2620	0.1095	0.0528	0.49
2901	0.1117	0.0526	0.50
3145	0.1121	0.0526	0.50
3476	0.1132	0.0525	0.51
3779	0.1137	0.0522	0.52
4079	0.1139	0.0521	0.52
4353	0.1141	0.0518	0.53
4667	0.1142	0.0515	0.53
4963	0.1145	0.0514	0.53
5251	0.1151	0.0514	0.54
5537	0.1158	0.0515	0.54
5841	0.1159	0.0515	0.54
6108	0.1160	0.0513	0.54
6415	0.1165	0.0515	0.55
6717	0.1169	0.0516	0.55

Forward flight, one run

The run whose rpm is nearest 6,108 is shown in full. apce_9x6_rd0991_6038.txt. Other runs are linked under it. Advance ratio J = V / (n D).

UIUC measurement at 6,038 rpm. Solid line is thrust coefficient CT. Dashed line is propulsive efficiency. This is not a PropShaper prediction.

J	CT	CP	η
0.109	0.1113	0.0528	23%
0.136	0.1096	0.0531	28%
0.157	0.1080	0.0532	32%
0.186	0.1059	0.0534	37%
0.215	0.1035	0.0536	42%
0.241	0.1012	0.0537	45%
0.265	0.0988	0.0537	49%
0.293	0.0960	0.0536	52%
0.318	0.0931	0.0536	55%
0.344	0.0901	0.0536	58%
0.370	0.0862	0.0532	60%
0.397	0.0813	0.0522	62%
0.424	0.0751	0.0501	64%
0.453	0.0668	0.0468	65%
0.476	0.0613	0.0444	66%
0.502	0.0554	0.0417	67%
0.533	0.0491	0.0387	68%

Other measured rpm

rpm	best η	at J	file
4003	67%	0.562	apce_9x6_rd0988_4003.txt
5000	68%	0.572	apce_9x6_rd0990_5000.txt
5013	68%	0.575	apce_9x6_rd0989_5013.txt
6015	68%	0.583	apce_9x6_rd0992_6015.txt
6038	68%	0.533	apce_9x6_rd0991_6038.txt
6701	66%	0.478	apce_9x6_rd0993_6701.txt
6715	69%	0.573	apce_9x6_rd0994_6715.txt

Geometry the studio loads

r/R, chord/radius and twist from apce_9x6_geom.txt. The geometry file does not record blade count. This commercial prop is loaded as two blades, which matches the three props the solver is checked against. Camber and thickness are PropShaper lofting defaults (slow-flyer families cambered, others near 2% camber), not the manufacturer's section. The hub starts as a conventional M5. Change it to your motor.

r/R	c/R	twist deg
0.15	0.141	31.67
0.20	0.147	37.59
0.25	0.183	38.78
0.30	0.207	35.90
0.35	0.218	32.07
0.40	0.223	28.50
0.45	0.222	25.81
0.50	0.217	23.58
0.55	0.209	21.66
0.60	0.197	19.99
0.65	0.183	18.58
0.70	0.167	17.29
0.75	0.150	16.37
0.80	0.132	15.46
0.85	0.114	14.30
0.90	0.098	13.40
0.95	0.075	12.02
1.00	0.051	10.61

Sources

UIUC PDB vol.1 (measured geometry)

UIUC Propeller Database, Volume 1, version 3, compiled by Gavin Ananda, 3 February 2015. Files were fetched 2026-10-09.
Brandt, J. B., and Selig, M. S., “Propeller Performance Data at Low Reynolds Numbers,” 49th AIAA Aerospace Sciences Meeting, AIAA Paper 2011-1255, January 2011. PDF.
Brandt, J. B., “Small-Scale Propeller Performance at Low Speeds,” M.S. Thesis, University of Illinois at Urbana-Champaign, 2005. The Volume 1 page says these online files include a wind-tunnel correction that post-dates the thesis, and that the online files should be used rather than the thesis tables. Thesis · correction note.

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