FREQUENTLY ASKED QUESTIONS
Q: Is the JS1 type certified?
A: The JS1-A and JS1-B were designed according to
the EASA CS-22 certification specification. The
South African Civil Aviation Authority (SACAA) Type
Certification was issued in March 2010 after
extensive work to show compliance with the
requirements of CS-22. Jonker Sailplanes is
currently working with the SACAA to progress towards
EASA Type Validation (a validation of the SACAA Type
Certification, so avoiding unnecessarily duplication
of the certification ground and flight testing).
With EASA Type Validation it is expected that all
signatories to the EASA-FAA bilateral will accept
the Type Certification, including the USA and
Q: The JS1 is designed under CS-22 to a safety
factor of 1.725. The static test on the website
appears to be carried out at ambient temperature
rather than the normal test at 54°C (129°F). Did you
carry out a further static load test at 54°C?
A: The JS1 is designed according to the CS-22
certification standard. For the aircraft type
certification Jonker Sailplanes had to prove that
all aspects of the standard were complied with and
the process for type certification took many months.
Officially observed tasks did include destructive
structural tests under specific environmental
Note that the static test referred to was required
in order to obtain authorization to fly the
prototype prior to the full certification tests. At
the time, the South African Civil Aviation Authority
required a number of documents, including design
documents, inspections, and partial tests. One of
the tests was a structural test to the ultimate
flying loads (at ambient temperatures and without
the safety factor multiplier). This test did not
override the type certification test - the
certification tests were done officially under
controlled conditions once the aircraft performance
was verified and the formal certification plan was
Q: What are the limit loads for the JS1?
A: The limit loads depend on glider weight. At 360
kg (793 lbs) the limit loads at Va are +8.0g /
-4.5g. At 600 kg (1322 lbs) the limit loads at Va
are +5.5g / -2.7g. For all glider weights the limit
loads decrease linearly from their respective Va
values to +4.0g / -1.5g at Vd.
Q: What is the service life of the JS1?
A: Fatigue tests on composite structures, including
wings, show that composite structures are less
sensitive to fatigue problems than other structures.
It may be possible to increase the service life from
the initial 3000 hours to 12000 hours, provided that
continuous airworthiness is demonstrated by an
inspection in accordance with the JS inspection
program at each 3000 hour interval.
Q: What are the max and minimum cockpit weights?
A: The min-max range is 70 kg to 110 kg (154 lbs to
243 lbs). The maximum cockpit weight can be
increased easily to 130 kg (287 lbs). Extreme pilot
weights can be accommodated by special weight &
balance of the glider. The JS1 has dual tail ballast
tanks and a brass tail wheel is available in place of
the Vesconite tail wheel.
Q: What are the polar parameters for the
LX8000/LX9000 flight computer?
A: For an unloaded JS1 at 35.7 kg/sq.m the
parameters are: a = +1.54, b = -2.81, and c = 1.85.
To enter these in the LX, go to the Setup Page,
select Polar & Glider, and dial-in the three numbers
and name the polar JS1 Revelation.
Min weight should be entered as 400 kg (this is
equivalent to a wing loading of 35.7 kg/sq.m). Empty
weight should be the actual empty weight of the
specific glider. Pilot weight (including parachute)
should be entered in the flight recorder menu.
Reading the relevant pages in the LX manual is
recommended. The calculations within the LX preclude
the need for another polar for the loaded condition
- the pilot simply adjusts the wing loading and the
polar is stretched accordingly.
Q: What is the weight of a 7.5 metre inner wing
A: Approximately 80 kg (176 lbs).
Q: Why are the wing panels this heavy?
A: With the thinnest wings in its class, the JS1
wings require a lot of carbon fibre to meet the
design strength and achieve a safety factor of
Q: Is it true that the aerofoil is based on one
of its competitors?
A: No. The T12 profile was specifically designed by
Johan Bosman for the JS1, and was the culmination of
many iterations. Of course the design methods used
are similar to those used elsewhere in the industry,
but the aerofoil itself is original. The profiles
were verified by Johan Bosman while at Delft
University, and design assistance & confirmation
were provided by Dr. Loek Boermans.
Q: I am sure you are aware of the shrinkage that
other manufacturers have with their latest models.
It is a real problem that they have yet to correct.
Will you have the same problem?
A: Jonker Sailplanes has taken measures to avoid
skin shrinkage, and hence avoid expensive wing
profiling within a few seasons. Specifically, the
carbon spar caps are bonded wet-on-wet directly to
the skins during the initial lay-up in the moulds.
This eliminates a thick structural filler (flox)
bond between spar caps and the skins, considered to
be the main source of shrinkage. The shear webs are
bonded at a later stage to the spar caps – so all
flox bonds occur between the shear web and spar caps.
The bond area has a high safety factor. There is
also no reduction in the foam thickness near the
spar - the bending strength is not affected as with
Shrinkage may also be caused by additional
cross-linking between resin molecules. Jonker
Sailplanes has invested in a post-curing oven to
enable extended post-curing before the sailplane is
finished in order to raise the cross-linking density
to levels where shrinkage is avoided.
Another possible reason for apparent shrinkage is
foam expansion due to absorption of water ballast.
Jonker Sailplanes takes additional steps in the
manufacturing process to seal the water ballast
Research work is being conducted in conjunction with
North West University students into optimising
post-curing processes and wing tank sealing
Q: Why does the JS1 have more wing area than some
of its 18-metre competitors?
A: The JS1 Revelation's wing is optimized for the
full range of conditions encountered in competition.
Jonker Sailplanes believes it is a given that
sailplanes must be able to run fast to hold a
competition lead, but we also believe that
competitions are very often won or lost on weaker
days. The JS1 wing provides outstanding climb
performance and, with its thin airfoil, also has
exceptional high speed performance. We feel that the
JS1 wing has the best balance between aerofoil
section, wing area and planform, and both low and
high speed characteristics.
Q: Is there a way for air to vent from the cockpit
to the tail boom, and from the tail boom out through
A: For models manufactured before 2012, the cockpit
pressure releases through the tail boom and exits at
the rudder control horn covers. For later models,
the JS Louvred Cockpit Air Extractor (patented) on
the upper fuselage just aft of the canopy is
standard, and the rudder control horns are closed
off with 'Cheetham' control horn fairings.
Q: Does the tail ballast water tank fill from the
top or from the bottom?
A: The JS1 has two tail tanks, the standard ballast
tank (which can be dumped in flight along with the
main wing tank ballast) and an optional pilot c.g.
tank to tune the weight and balance (which cannot be
dumped in flight). Both tanks have special
quick-connect fill ports flush-mounted with the skin
of the fin. Unlike other gliders, this allows the
standard tail tank to be filled even after filling
the main wing tanks. The standard tail tank can also
be filled via the dump outlet behind the tail wheel
if filled prior to the wing tanks. The pilot C.G.
tank can be filled or drained independently.
Q: Is the fuselage the same as some of its
A: As with any new design, the development of the
JS1 included (1) thorough engineering review of all
published technical literature pertaining to cockpit
design for crashworthiness and (2) benchmarking of
other competitive sailplanes representative of what
today's competition pilots require and expect.
Generally, the aerodynamic shapes of glider
fuselages have converged to optimum and are mostly
sorted out. The shape of the JS1 fuselage is
understandably influenced by several proven gliders
and the published literature.
The composite structure of the JS1 cockpit owes much
to the pioneering cockpit design methods and
research of several notable sailplane designers and
academics. To build upon this and ensure the best
crashworthiness, Attie Jonker and his engineering
team performed extensive materials tests, finite
element analyses, and loading to assure the
structure of the JS1 fuselage meets airworthiness
requirements and provides maximum protection to the
Q: Do you expect to have more clearance for the
landing gear doors?
A: The prototype landing gear doors originally
hinged open by about 90 degrees. The gear doors on
the series production sailplanes open wider to
further increase the ground clearance.
Q: What is the size of the standard storage tube
for the oxygen cylinder?
A: The standard oxygen storage tube is located in
the fuselage center section behind the pilot's right
elbow. Gliders up to serial number 015 accept a
Mountain High AL-180 cylinder or an Aerox AV54G
cylinder. Gliders from serial number 016 accept a
Mountain High AL-248 or Aerox CV54G in the standard
storage tube. A regulator with "radial" (as opposed
to "axial") outlet is recommended.
A complete MH system (EDS O2D1-180-1P-F or EDS
O2D1-248-1P-F) with cylinder, regulator, flow
controller, service line, cannula, and face mask is
available directly from Mountain High, from Jonker
Sailplanes, or from our regional JS agents.
For long duration or very high altitude flights
additional oxygen cylinder storage tubes are
available on a custom basis (example: an additional
additional Mountain High AL-415 in the baggage area
in front of the wing spars).
Q: What trailer options are available?
A: Cobra trailers are available for the JS1 from
Spindelberger. Contact JS for further information or
for information of alternative trailer suppliers.
Q: What is the difference between the trailer for
the JS1-A and JS1-B?
A: The trailer for the JS1-A has a larger fin to
accommodate the taller tail of the A model. The B
version glider fits in the JS1-A trailer, but not
Q: Will a JS1-B fit in all Cobra trailers?
A: No, the wing of the JS1 requires an F4 lift-top.
Please contact JS or Spindelberger if you require
Q: Can JS supply wing and fuselage dimensions to
see if the JS1 will fit in a second hand trailer?
A: Of course. Please contact JS directly with the
Q: When will the sustainer be available?
A: Development and certification of the jet turbine
sustainer is ongoing (see News section for the
latest information). Fuselages from serial number
013 onward have shipped (if customer requested) with
the sustainer engine cut-out and reinforcements
Q: When will the self-launcher be available?
A: Jonker Sailplanes is not actively working on a
self-launcher version at the moment. Feasibility
studies showed that installing a standard
self-launch unit in the JS1 fuselage would require
extensive structural modification to maintain the
strength and stiffness, and that with the structural
reinforcements the empty weight would be higher than
we judge reasonable for a competition sailplane.
However future studies continue to build up the
knowledge required for a self-launcher installation.
Q: Any plans for electric version?
A: Not yet, but when this technology is matured, we
will definitely consider it.
Q: Does the JS1 have an undercarriage warning
A: Currently we do not have an undercarriage warning
system, but can install micro switches on the
airbrakes and undercarriage as inputs to a flight
computer with the warning logic.
Q: Is it possible to have separate Total Energy
pneumatic lines for electronic variometers and
A: Electronic variometers operate using sensitive
pressure transducers whereas mechanical variometers
sense flow and so in theory there should be a effect
on variometer performance if a single TE line is
used for both types. In practice the performance is
not affected on the JS1 - there have been specific
comments from top international competition pilots
noting the quality of variometer performance.
However if a customer requests, then the TE line can
be split in the fuselage mid-section.
Q: Is it possible to test fly the JS1?
A: Evaluation flights of the JS1 at our regional
locations (Australia, Netherlands, United Kingdom,
Denmark, Australia, New Zealand and United States)
are absolutely available to pilots with sufficient
qualifications. Interested pilots are also very
welcome to visit the Jonker Sailplanes Facility in
Potchefstroom, South Africa for a tour and
evaluation flight. Please feel free to contact us
Purchasers of JS1 sailplanes are also encouraged to
consider a visit to the Jonker Sailplanes Facility
to inspect their glider, and fly their sailplane in
the southern hemisphere prior to ocean shipment.
Jonker Sailplanes is able to organise temporary
South African aircraft registration and SACAA
validation of a non-South African pilot licenses.