Do it yourself paraglider line measuring device

Note: This measurement device is not a proper replacement for having your wings regularly checked by an experienced inspector. There is more than just line lengths that effects your safety in the air. But having your own measurement device is fun and helps understanding the dynamics of paraglider line lenghts. And it is a great excuse for having a 3D-printer ;-)

The basic idea was to create a device that assists in measuring paraglider lines. The materials are all simple aluminium strips and profiles, cheap bearings, 3D-printed parts and screws. The equipment used are a saw, a machine drill (on stand), thread cutting tools (M3, M5), some files and a 3D-printer using PLA filiament. The 3D-printed parts replace the smaller, more complicated parts which are harder to make in metal.

There are two main parts, the riser attachment ruler with 5kg weight and laser target and the measurement ruler with the laser distance meter. The latter part is optional, but it greatly simplifies measuring. As long as the two parts are properly aligned and fixed, only pulling the weight and pressing the button is required. The art is finding the target while pulling 5 kg and keeping the line in place is no longer required. No corrections (apart from the riser-length) have to be applied to the measurement.

Links:

Riser attachment ruler

The upper half is made of two L-shaped profiles, with smaller L-profiles as riser end retainers at one end and the riser attachment rod at the other. The target plate is clamped on the larger profiles, making sure the exact line + riser length is measured. The clamp can be moved to the riser-line point, but this is not constant between wings. Below the profiles are two wheel trolleys which move in the lower half of the riser attachment ruler.

The lower half is an U-profile containing the two wheel trolleys. Two L-profiles in top of the profile and stops at the ends of the ruler keep the trolleys in place. The front end has a simple plate, the back has provision for the 5 kg weight pulley.

The upper half is 600mm long, enough for most risers. The lower half is 800mm, leaving 200mm range in line length.

riser ruler overview riser ruler part with riser attachment, target plate and weight pulley

Measurement ruler

The upper half is the measurement with a laser distance measurement device, a line attachment and a handle to pull the 5 kg weight. The construction keeps the line end and the back of the laser distance measurement device at the same distance of the target (and riser end).

The measurement ruler uses the same basic structure as the riser ruler. An U-profile contains a trolley, which carries the measurement part. The trolley is kept in place by L-profiles on top and stop plates at the ends.

The measurment part has two parts, independently replaceable. Handy if your laser device doesn't fit this cage. The line attachment bit construction allows both uncorrected measurements and exchange for an other line attachment type. The handle is for comfort. Using the whole hand to pull 5 kg is more comfortable and sustainable. Usually there are more wings to measure...

The measurement ruler is 1000mm long, which combined with the 200 from the user ruler should be enough for most wings. If not, longer U-profiles can be used. which only reduces portability. Ultimately one long profile could be used to contain both rulers.

laser ruler overview laser ruler part with laser distance 
    measurement device in cage, line attachment and the handle

A link to the 3D-printed parts. Complete description of the current version.

Software

The software to connect the measurement device to the spreadsheet is typically manufacturer dependent. Some more expensive devices can emulate a Bluetooth connected keyboard, but the cheaper ones require a special application.

To register the measured values a spreadsheet is a good fit, and a simple template is provided. In its current version it allows values for 12 to 15 line lengths per side/gallery and 3 or 4 risers. Some basic corrections are made for riser length (wing property) and break-line attachment point (rig property). This also depends on placement of the target plate. The riser-carabiner point seems a convenient solution.

Before use the manufacturers line lengths should be entered for your paraglider. The spreadsheet corrects for these and shows the the actual calculated line length, not the measured value. The sym column shows the length difference between this line and its opposite.

Another post-measurement correction is all lines. If all lines get longer or shorted by the same amount, this has, to an extend, no influence on the wing flying characteristic. Typical values are 15 mm for maximum differences between lines, but 50 mm for all lines at once.

The template spread sheet.

Inspiring video's and information online


fjkraan@xs4all.nl, 2019-05-25