Attie Jonker, JS Chief Engineer, explains:
The structural design of the JS1 Revelation was done
using normal engineering methods. Conventional
structures (such as the controls and landing gear)
were designed using traditional calculation methods,
with hand calculations for simple geometries and
laminate analysis for simple composite structures.
The more complex structures were designed using
modern FEM analysis techniques.
A combination of glass-fibre, aramid (Kevlar) and
carbon-fibre is used in the load bearing structure
of the JS1 Revelation. Each material is used where
it is most effective. The very thin wing section
(12.7%) posed quite a challenge for the designers,
especially in the wing root area where the maximum
thickness is only 100mm.
All structural design was according to the
certification standards set in CS-22 and with a
general safety factor of 1.725.
Finite Element Modeling (FEM) allows for the whole
structure to be represented as a wire frame of cells
or elements called “the mesh”. Loads can then be
applied to the mesh and the stresses calculated at
each point. The result is a colorful representation
of the stress condition throughout the structure.
This shows exactly where the structure needs
strengthening and where weight can be saved. The
figure below shows the stress condition in the front
and aft fuselage due to a load on the tail, and a
high-g pullout maneuver.
One of the advantages of using a full FEM model of
the sailplane for design purposes is that the
natural frequencies of the structure can be
calculated for avoiding flutter. This is especially
important with JS1 Revelation’s high VNE of 290km/h.
However advanced modeling and calculation
techniques do not substitute for structural testing.
The results of any model must be supported by
experimental data. The tail plane of the JS1
Revelation was first modeled using the finite
element method, then structurally tested, and the
results compared. A comparison between the predicted
and the actual measured deflection of the tail plane
showed a correspondence of within 0.5%, which
confirmed the validity of the FEM models and
FEM methods, together with structural
testing, have resulted in the JS1 Revelation having
a very light but extremely strong structure, at
least equal but probably better than any other
sailplane in its class.
Left: The symmetrical half-model CAD geometry of the
Middle: FEM mesh of the tail plane
Right: Structural static deflection test of the
Structural verification of the wing structural
stiffness : 6G wing bending