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How rigging really works
We have developed a speedy rigging system for our larger bi-planes which is creating quite a stir of interest among large bi-plane enthusiasts. Our system uses recessed magnets in the upper wing panels, these lock the interplane struts firmly in their relative positions and then the wires are tensioned to load the struts using our quick release rigging grippers. Although not using magnets and quick release rigging grippers, the rigging principle is also how the full size aircraft works.
We have been asked by a few modelers if the magnets are strong enough to hold the upper & lower wings together, and on several occasions we have needed to explain the logic of just how a rigging system works. This has been encouraging to us, as we now realize that there is a need for some to overcome the thought that the interplane struts are in tension rather than compression. However, it was initially a concern of ours because of these possible thoughts arising in peoples minds. As a result of this, we did G force tests on the magnets and to our own surprise we discovered that the magnets themselves will withstand the tension forces of over 5G trying to pull the wings apart. This kind of situation never arises when the rigging is tensioned as can be seen from the info below.
The reality with fully working rigging is, that if the interplane struts were in tension, the whole thing would fall apart in the air as there would be nothing to accept the flying loads.
|Many people are a bit puzzled as to how
the rigging systems on Bi-planes & Tri-planes really works. In the
diagram (top right) the arrows are showing which way the forces are acting
within the rigging components themselves.
The blue arrows in the Interplane struts show that the struts are in compression, holding the wings apart. This compression is created by the flying wires (red) and the landing wires (green) being in tension as indicated by the black arrows, therefore trying to pull the wingtips together while the struts hold them apart.
The black wires between the front and rear struts serve to hold the wings in a pre-set non twistable or warpable position at their outer ends, therefore maintaining the twist stability.
All of this looks fine when the aircraft is not flying, now look at the forces during flight as explained below.
|Looking at the diagram (bottom right) it can be seen that
the forces acting on the upper & lower wings as indicated by the blue
arrows, is reasonably equal on each wing panel, therefore whatever
compression load the interplane struts were set at on the ground will only
increase in the air. This is because the red flying wires are being
directly subjected to the flying loads felt by the upper wing, while also
being indirectly subjected to equal flying loads from the lower wing via
the interplane struts. Therefore the lower wing is pushing its load up
through the struts, increasing the compression on the struts & adding
further tension to the already pre-tensioned flying
wires. From this it can be seen that the struts never see tension forces,
they are always in compression.
Click on the images to the right to see
our own rigging components
Also see this aircraft in flight on electric via the link below
Please Note; this aircraft is flying with the new magnetic struts & fully working quick rigging.