Calculating the required

stroke lengths and forces

Specifying the space required on the window is equally important to the selection of the right drive as the calculation of the required stroke and of the force that needs to be generated by the drive.

The required opening width of the window can be calculated based on the specification of a desired opening cross section or opening angle and based on the window dimensions of sash height / width. Depending on the type of drive and type of installation selected, this opening width will be equivalent to the drive stroke. The opening width that can be achieved with scissor drives and spindle drives that are installed on the side depends on the drive stroke and installation measure x. It is, thus, definitely possible to achieve large opening widths with small drive strokes.


Compressive force / tractive force
The compressive / tractive force indicates the force of the drive that is available to open and close the window. The drive must be selected such that the specified drive force is greater than the required force that results from the sash weight and any wind / snow loads that may have to be considered.

FDrive ≥ Freq = FG + FW + FS

FDrive: Force generated by the drive
Freq: required force
FG: Weight force of the sash
FW: Wind force
FS: Snow force

The weight force FG is calculated by multiplying mass with gravitational acceleration. The calculation uses the simplified formula given below

FG [N] = sash weight [kg] x 10 [m/s²]

Simply put, we can deduce that: 10 kg ~ 100 N

The wind / snow force is calculated by multiplying the wind / snow load [N/m²] by the area on which the load acts vertically. One factor that needs to taken into account is the installation position of the window. For instance, the wind force generated at a facade window is markedly higher because the entire area of the window is subjected to the wind load as an attack surface. The attack surface in roof-top windows is the projection surface of the window that is situated vertically to the wind load. This surface becomes smaller with a reduction in roof pitch.


Roof-top window

Sloped roof-top window

Facade window

Additional loads with increasing or reducing values may have to considered depending on the weight and installation position of the window.


When calculating the required weight force, you need to take into account that the drive will not have to lift the entire weight of the window because the window is usually supported on one side. Lifting, therefore, requires only half the amount of force.

Locking force
The locking force of the drive guarantees that the window sash will be pressed firmly against the frame, thus ensuring that the window seals tightly. As a result, the required force also depends on any wind loads to which the window may be exposed.

Project planning aids that will help you