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Is the JS1 type certified?

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 Australia.

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?

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 conditions.
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 approved.

What are the limit loads for the JS1?

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.

What is the service life of the JS1?

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.


What are the max and minimum cockpit weights?

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.

What are the polar parameters for the LX8000/LX9000 flight computer?

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.


What trailer options are available?

Cobra trailers are available for the JS1 from Spindelberger. Contact JS for further information or for information of alternative trailer suppliers.

What is the difference between the trailer for the JS1-A and JS1-B?

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 vice-versa.

Will a JS1-B fit in all Cobra trailers?

No, the wing of the JS1 requires an F4 lift-top. Please contact JS or Spindelberger if you require clarification.

Can JS supply wing and fuselage dimensions to see if the JS1 will fit in a second hand trailer?

Of course. Please contact JS directly with the request.


When will the sustainer be available?

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 pre-installed.

When will the self-launcher be available?

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.

Any plans for electric version?

Not yet, but when this technology is matured, we will definitely consider it.


What is the weight of a 7.5 metre inner wing panel?

Approximately 80 kg (176 lbs).

Why are the wing panels this heavy?

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 1.725.

Is it true that the aerofoil is based on one of its competitors?

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.

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?

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 other methods.
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 tanks. Research work is being conducted in conjunction with North West University students into optimising post-curing processes and wing tank sealing techniques.

Why does the JS1 have more wing area than some of its 18-metre competitors?

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.


Is there a way for air to vent from the cockpit to the tail boom, and from the tail boom out through the tail?

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.

Does the tail ballast water tank fill from the top or from the bottom?

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.

Is the fuselage the same as some of its competitors?

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 pilot.

Do you expect to have more clearance for the landing gear doors?

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.

What is the size of the standard storage tube for the oxygen cylinder?

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).