Motor calculation

The table hereafter gives the main parameters calculated at various speeds for the XXS "Hi-tech" equipped with the WES 5-2.4 motor, a 1/7,5 gearbox and a 23X12 propeller. It should be noted the good agreement between calculated and measured values for motor current and voltage.
You can download this table in an Excel file format to use it for your own needs. Thus you will be able to determine in advance whether a given motor is suitable for your model plane.

Any motorisation with:
- An electrical power to mass ratio between 30 et 60 W/kg,
- A thrust to mass ratio between 1/3 et 1/2,
- An air speed to stall speed ratio between 2 et 3,
should satisfy any indoor's needs.

For example, the downloadable Excel F1319_3e.ZIP file gives theoretical data for the Faulhaber 1319-03 motor with a 8,5/1 gearbox on the XXS. Calculated data are very close to those given by the WES 5-2.4 motor.

For more information on WES products, click here
For more information on Faulhaber motors, you can visit the Micro Mo site (US) or Minimotor site (Switzerland) which gives specification for all Faulhaber motors as well as many information on coreless motors.

XXS "Hi-tech" model plane

MOTOR: WES 5-2.4

Propeller WES: 23X12 (9X4.7)

Gearbox: 7,5/1

ELECTRICAL DATA:

Unit

Propeller speed:

rpm

2200

2400

2700

3000

3200

Power at propeller shaft:

W

1,7

2,2

3,2

4,4

5,3

Propeller shaft torque:

mNm

7,5

8,9

11,3

13,9

15,8

Gearbox efficiency:

0,85

0,85

0,85

0,85

0,85

Motor shaft torque:

mNm

1,2

1,4

1,8

2,2

2,5

Motor torque constant:

mNm/A

2,24

2,24

2,24

2,24

2,24

Calculated motor current:

A

0,52

0,62

0,79

0,97

1,11

Measured motor current:

A

0,52

0,63

0,82

1

1,2

Velocity constant:

rpm/V

4200

4200

4200

4200

4200

Armature resistance:

Ohm

2,5

2,5

2,5

2,5

2,5

Calculated motor voltage:

V

5,2

5,8

6,8

7,8

8,5

Measured motor voltage:

V

5,3

5,7

7,2

8

8,8

Calculated electrical power:

W

2,7

3,6

5,3

7,6

9,4

Calculated efficiency:

%

63

61

59

58

56

AERODYNAMIC DATA:

Flight mode:

slow cruise

cruise

take-off

short take-off

45 deg. climb

Plane mass:

g

122

122

122

122

122

Electrical power to mass ratio:

W/kg

22

30

44

62

77

Calculated static thrust:

g

34

40

51

63

72

Thrust to mass ratio:

2/7

1/3

3/7

1/2

3/5

Wing loading:

g/dm2

5,8

5,8

5,8

5,8

5,8

Stall speed:

m/s

2,3

2,3

2,3

2,3

2,3

Air speed (at propeller):

m/s

4,4

4,8

5,4

6,0

6,4

Air speed / stall speed:

1,9

2,1

2,4

2,6

2,8

Notes:

- Velocity constant: Velocity constant equals no load speed at nominal voltage divided by nominal voltage.
- Torque constant: Torque constant equals stall torque divided by stall current.
- Armature resistance: Armature resistance equals nominal supply voltage divided by stall current (at nominal voltage).

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