What force does the drive need to open my window? What stroke length is required to achieve the desired opening angle?

These and similar questions inevitably arise when dealing with the retrofitting of windows and skylights with electric drives. We will show you formulas kindly provided by Fa. AUMÜLLER AUMATIC GmbH, Thierhaupten and perform a few example calculations.

Example of a tilting sash (middle drawing above)

The sash (i.e. the movable part of the window) has a width of 87cm and a height of 108cm. The double glazing consists of 4+4mm glass

We are looking for the sash weight. The formula is given above, with inserted values we get:

Sash weight = 0.87m * 1.08m * 8mm * 2.5 * 1.1 = 20.67kg

So the window sash weighs about 21kg. The "1.1" in the formula is a correction factor for the frame profile. Of course, it is always better if the actual sash weight is known.

 

We now calculate (as an example) the necessary driving force for a stroke length of 500mm according to the above formula:

Stroke/thrust force = 20.67kg * 9.81m/s² * 500mm * 0.54 / 1080mm = 50.7N

The actuator must therefore provide a minimum force of 50.7N. For tilt sashes, the required force is often quite low.

 

Assuming that we are looking for the stroke length of the drive and we know that the window must be opened at least 30°, the above formula gives:

Stroke length = √ (2 * 1080²mm * (1 - cos 30°)) = 559mm

The stroke length must therefore be at least 559mm. Of course, it is important to ensure that the drive has suitable brackets so that it can be mounted. So here we would probably choose a drive with 600mm chain length.

 

Now we are interested in the opening angle that results when a drive with 400mm chain length is used. According to the formula given above the result is

Opening angle = cos-1(1 - 400²mm / 2 / 1080²mm) = 21.3°

The opening angle will therefore be 21.3°.