The Wingspar
Here we would like to show you how the load carrying spar is installed into the wing. The installation procedure described here comes from the time of wooden wing and spar construction and takes construction issues already encountered during those days into account. All current Schleicher aircraft spars are constructed and installed using these procedures.
Fundementally
The wingshell and the wingspar have different roles to fulfill in a wing. 90% of the bending loads are carried by the spar and 10% by the wingshell while 100% of the torsional loads are carried by the wingshell.
Wing bending
Wing torsion
The Installation sequence
Our construction procedure calls for pre-fabrication of the complete spar. It consists of upper and lower spar caps made of rovings, separated by a shearweb. This highly stressed part can thus be controlled easily during each construction phase. The completed spar is then bonded into the open lower wingshell:
After all the remaining interior wing components have been installed, the upper wingshell is bonded onto the lower wingshell. The two wingshells are bonded together at the leading edge, along the spar and at the hat-shaped rear spar. The bonding material is shown here in blue.
The decisive advantage of this construction method is that there is no bonding material inside the wing spar itself and consequently none in the main shearforce area. If, despite all possible care, a small void should occur when bonding the spar to the wingshell, it would have no effect on the overall strength of the wing since since the wingspar, taking 90% of the bending load, is completely intact.
And this is how the whole process looks during production
The lower wingshell is finished.The small depression in the sandwich where the spar will be installed later is clearly visible:
The pre-fabricated wingspar is ready:
The bonding material is applied onto the lower spar cap:
The wingspar is placed onto the wingshell:
Surplus bonding material is pressed out on the right and left sides of the wingspar and can be removed:
The wing and spar in cross-section:
