Johan Bosman, JS Chief Aerodynamicist, explains:
Aerofoil design is the key to the overall
performance of a sailplane, so the design process of
the JS1 Revelation started with development of the
main wing aerofoil. Attie Jonker together with an
NWU final year student had conducted wind tunnel
tests on one of Attie’s aerofoil designs. Combining
the wind tunnel data together with new technology
and research on techniques that might help climbing
performance, then after making hundreds of
iterations made with the XFOIL program, we ended up
with the JJB44 main wing aerofoil.
we send the coordinates to Loek Boermans at TU Delft
for a check up. His comments weren’t all bad, but he
made some significant recommendations.
had very low profile drag, but would lack low drag
at high lift coefficients due to laminar flow that
extended too far aft on the upper surface. Using the
aerofoil at low Reynolds numbers would also be
detrimental to overall performance.
After several hundred iterations later working with
the aerofoil and considering Loek’s recommendations,
we have ended up with the T12 aerofoil used in the
JS1 Revelation today. By careful design we have
managed to maintain very low profile drag, but also
enlarge the laminar drag bucket for low drag at high
lift coefficients as well.
To optimize climbing in
turbulent thermals the T12 does not have the typical
flat top Cl-Alpha curve at high lift coefficients.
Maximum thickness/chord ratio 12.7%
14% camber changing flap
Low drag with extensive regions of laminar flow
Laminar to turbulent transition on the lower
surface occurs at 93% where artificial
transition is applied for negative flap settings
Transition on the upper surface occurs at
approximately 65% for a 0° flap setting and 2°
angle of attack
The top surface is smooth at 13.5° with almost
70% laminar flow
Fluent 2D calculation (with new transition models)
of T12 aerofoil, showing turbulent kinetic energy as
the flow moves over the aerofoil. The long laminar
flow region on the lower surface is clearly visible.
Although aerodynamically optimised, there are
structural challenges using such a thin aerofoil. At
the time the T12 aerofoil was the thinnest main
aerofoil used on modern sailplanes.
decision was made to use the thin aerofoil,
consistent with the JS motto of “no aerodynamic
compromise”. The aerodynamic performance gain is
worth more than the manufacturing cost and
The aerodynamic design of the wing root is very
challenging as this is turbulent flow, rather than
the laminar flow over most of the wing.
a new root aerofoil in conjunction with the
wing/fuselage junction design, which reduces
separation problems at the trailing edge and optimised overall drag.
Six different aerofoils are used in the wing for
maximizing the performance of the glider. All are
derived from the main T12 aerofoil, optimised at
each spanwise station for the specific chord length
and Reynolds number. The wingtip aerofoil is
designed with an ample lift reserve to help handling
characteristics and avoid any tendency for wing