FAQ

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  • Technical
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  • General

A: In 2019 Jonker Sailplanes established JS GmbH as a marketing company to perform the sales and other administration functions in Europe. In addition agent borders in Europe were opened up improving accessibility between agents and customers. All JS sales in Europe are now made directly through JS GmbH and the customer.

A:  M&D is the TC holder of JS products in Europe.  A partnership agreement between JS and JS was signed in October 2013, agreeing that M&D will hold the design and production approvals on behalf of JS and will facilitate imports, handover and support of EASA Type Certified JS series sailplanes in Europe. 

  • JS2
  • JS3
  • JS3 RES
  • JS4
  • JS4 RES
  • JS5
  • RES System
  • Jet Sustainer System

A: The limit loads depend on the 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.

A: We have designed for 115kg, although the CS22 only requires a minimum of 110kg.

A: For an unloaded JS2 at 35.7 kg/m2 (7.3 lbs/ft2) 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/m2). 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.

A: Approximately 83 kg (176 lbs).

A: With the thinnest wings in its class, the JS2 wing requires many layers of carbon fibre to meet the design strength and achieve a safety factor of 1.725. Furthermore, to meet the structural requirements for the 18m, additional material is required.

A: No, 21m will be the max span.

A: Normally easy. We work towards plug and play and are very close to be successful. We manufacture in most cases both wingtips in any case, as it became clear that contest pilots order the other option a short while later.

A: The main wings tanks of all JS gliders are integral tanks and can be filled through the top filling hole. The JS2 21m tips also carry water. To fill the tips you require the JS tip filling tool, that plugs in the bottom of the tip. The outboard tips of all new models have the filling cap on the top surface an can be filled in the same manner as the main tanks.

A: JS2 main tanks 180l, tip tanks 34l

A: The rerouting of the electrical wiring has made it possible to incorporate a dedicated venting channel with the shortest route from the source of the air to the binnacle. The design intention is still to allow for the airflow to help with the cooling of the instruments while providing the pilot with demisting of the canopy in humid conditions. The demisting valve is operated manually in the same way as the JS3 (from the instrument panel with a push pull knob.)

A: The JS2 have 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 fill ports on the left skin of the fin. This allows the standard tail tank to be filled even after filling the main wing tanks. The pilot C.G. tank can be filled or drained independently.

A: The JS2 cockpit can accommodate a pilot of 1.96m weighing 120kg.

A: Standard batteries include two cockpit batteries, one engine one avionics plus an avionic battery in the tail. Third flat battery behind the seat is optional

A: The bug wiper winders are installed behind the back rest on the left and right side

A: Yes a fire warning system is a standard feature of the JS2

A: Yes, Solar panels are optional

A: Yes, strobe light in the fin is optional

A: The retractable/steerable tailwheel is standard

A: The limit loads depend on the 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.

A: We have designed for 115kg, although the CS22 only requires a minimum of 110kg.

A: In 15 m configuration and with a reference mass of 450 kg (992 lbs) the parameters are: a = +0.9547, b = -1.8498 and c = 1.4745.
In 18m configuration and with a reference mass of 500 kg (1102 lbs) the parameters are: a=0.9233, b= -1.6595 and c=1.2658
To enter these in the LX, go to the Setup Page, select Polar & Glider, and dial-in the three numbers and name the polar JS3 Rapture.

Min weight should be entered as 400 kg (this is equivalent to a wing loading of 35.7 kg/m2). 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.

A: Approximately 65.0 kg

A: With the thinnest wings in its class, the JS3 wing requires many layers of carbon fibre to meet the design strength and achieve a safety factor of 1.725. Furthermore, to meet the structural requirements for the 18m, additional material is required.

A: No, 18m will be the max span.

A: Normally easy. We work towards plug and play and are very close to be successful. We manufacture in most cases both wingtips in any case, as it became clear that contest pilots order the other option a short while later.

A: The main wings tanks of all JS gliders are integral tanks and can be filled through the top filling hole. The JS3 18m tip and JS1/2 21m tips also carry water. To fill the tips you require the JS tip filling tool, that plugs in the bottom of the tip. The outboard tips of all new models have the filling cap on the top surface an can be filled in the same manner as the main tanks.

A: JS3 main tanks 156l, tip tanks 34l

A: JS developed the cockpit air extractor in the JS models. The JS3 with its high wing does not allow cockpit extraction on the top surface. The extractor is moved to the bottom – the extraction is not as aggressive as the top, but the total drag a bit lower.

A: The standard oxygen storage tube is located in the fuselage centre section behind the pilot's left elbow designed for a Mountain High CFF-480 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, EDS O2D1-248-1P-F or EDS 02D1-480-1P-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.

A: The JS3 cockpit can accommodate a pilot of 1.96m weighing 120kg.

A: Standard 2 batteries with an optional battery behind the seat.

A: The bug wiper winders are installed behind the back rest on the left and right side.

A: Currently we do not have an undercarriage warning system, but install micro switches on the airbrakes and undercarriage as inputs to a flight computer that has warning logic.

A: The JS3 RES can be flown with 1 or 2 batteries up to MAUW. One limitation to consider is that the maximum weight with water ballast will not be exceeded, as the stall speed in this configuration must be below 80 km/h. The maximum theoretical weight is 426kg in 15m configuration and 495kg in 18m configuration. In 18m configuration a limiting factor is the weight of non-lifting parts.

A: The limiting factor is the ability to clear a 15m obstacle within 500m. Performance calculations using component data indicates that 500kg MAUW still meets this requirement. Flight testing is required to determine the actual limitation.

A: All components need to comply with the German consumer act requiring a 2 year warrantee. In addition we guarantee the batteries to 1000 cycles, without losing more than 20% of the original capacity. Batteries are protected by the Battery Management System, but care must be taken by the pilot to use and store the batteries in accordance to the manufacturer’s recommendations. Defective batteries will be repaired or replaced during the warrantee period by the supplier. Shipping costs to and from our German address is carried by the customer.

A: It will be limited weight self-launcher.  We will only be able to quantify the max mass after we have collected real data from flight tests – theoretically it seems that a take-off weight of 500 kg is an achievable take off weight to clear a 15m obstacle after 500m.  Soft short runways will be a problem for Electric gliders until the battery density is increased significantly (and this is slowly happening).

A: We plan to do the first flight in 2023. Plans are in progress to fast track this product, but priority will be given to the JS5.

A: The JS4 RES can be flown with 1 or 2 batteries up to MAUW. One limitation to consider is that the maximum weight with water ballast will not be exceeded, as the stall speed in this configuration must be below 80 km/h. The maximum theoretical weight is 426kg in 15m configuration and 495kg in 18m configuration. In 18m configuration a limiting factor is the weight of non-lifting parts.

A: The limiting factor is the ability to clear a 15m obstacle within 500m. Performance calculations using component data indicates that 500kg MAUW still meets this requirement. Flight testing is required to determine the actual limitation.

A: All components need to comply with the German consumer act requiring a 2 year warrantee. In addition we guarantee the batteries to 1000 cycles, without losing more than 20% of the original capacity. Batteries are protected by the Battery Management System, but care must be taken by the pilot to use and store the batteries in accordance to the manufacturer’s recommendations. Defective batteries will be repaired or replaced during the warrantee period by the supplier. Shipping costs to and from our German address is carried by the customer.

A: We plan to do the first flight in 2021.

A: Approximately 7000mm. With the outer wings removed the span is approximately 13.5m.

A: We expect the weight of the inner panel to be 80kg and the outer panel approximately 36kg.

A: The lifespan of the battery depends on multiple factors.. We tested all the cells (Samsung, Sony, LG) with a certain cycle (start-climb-cruise) and reached approx. 1000 full cycles to 90% state of health (capacity) with the Sony and the LG. So we expect around 1500cycles minimum to 80%. This can however be negatively affected by e.g. long storage with high or very low voltage, many charges at <15°C etc. There is an unlimited number of scenarios that we cannot test really but know the effects qualitatively. We are collecting battery data with our BMS and will read out the information so we can learn more about specific dependencies. Here you can help us in the future by sending us the read-outs. 

A: The charger is designed to charge one battery module outside of the fuselage but can charge both modules at once when charged inside the glider.

A:  There is basically no maintenance needed as with example the Lange System. If there is an anomaly, the cockpit instrument is going to register it via the sensors, isolation monitoring device and BMS. The data storage in the BMS can be read out at an inspection interval and sent to us, this would be inexpensive and informative. Also, I think it is better to know that something is done as inspection as opposed to zero inspection for the peace of mind of the customer probably.  There is storage for ca. 500 full cycles in the BMS.

A: It takes ±48s from system power up until full thrust.

A: A mandatory annual or 250 hours* inspection is required for issuing the Certificate of Airworthiness.
Life limits for MD-TJ42
Starts Hours Years
449 50 6

When these life limits have been reached, the MD-TJ42 turbine engine must be returned to the manufacturer or to an approved maintenance organisation so that the required maintenance activities or inspections can be performed.

A: Compatible with diesel fuel with added lubrication oil (2% 2-stroke oil).

  • JS 2
  • JS 3

A: The Certification process already started before the prototype construction started. With M&D’s design organization has been upgraded from an Alternate Procedures DO to a full Design Organization the certification process could be much faster. M&D may now propose the level of involvement during the approval, where the authorities had to be fully involved in all certification aspects with the “restricted” DO.

A: Although EASA plans to move away from the issue of many PtFs for gliders, the current maximum number is still 15.

A: The European variant, the JS-MD 3 developed by the Jonker Sailplane / M&D Flugzeugbau partnership, was awarded a Type Certificate by EASA (European Aviation Safety Agency) in July 2019. This variant was designed in accordance with the EASA CS-22 amendment 2.

A: Fatigue tests on composite structures, including wings, show that composite structures are less sensitive to fatigue problems than structures built from other materials. 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.

A: By now it is very clear that JS is a world leader in low speed aerodynamics. The T12 profile was specifically designed by Dr. Johan Bosman for the JS1 and JS3, and was the culmination of thousands of 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 at Delft University, and design assistance & confirmation were provided by Dr. Loek Boermans. It is more likely that future products from our competitors will be based on the T12 profile

A: Jonker Sailplanes are doing active research to minimize skin shrinkage, and hence working towards avoiding 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 the thick structural filler 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 composite 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 – and 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.

Our latest research shows a major reason for apparent shrinkage is foam expansion due to absorption of water if water is not completely drained and wings dried. We are consistently doing research on this topic with the NW University, and takes additional steps in the manufacturing process to seal the water ballast tanks. We are also investing the use of active drying fans to be used to dry wings out when now flown for longer periods

A: 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. The JS2 SL will be a new generation SL in our opinion. Great handling and performance is our goal.
The glider will be offered with a full redundant fuel injection system.
The fuselage and wing mould are completed. We started construction of the prototype in May 2020 and should be ready with the production line 3rd quarter 2020.

A:  We are in the process to develop the electrical systems for the JS3. In the near future the FES and a rear electrical propulsion system with limited self launching capabilities will be tested.

A: Electronic variometers operate using sensitive pressure transducers whereas mechanical variometers sense flow and so in theory there should be an effect on variometer performance if a single TE line is used as a both types. In practice the performance is not affected on the JS3 - 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.

A: Evaluation flights of JS gliders at our regional locations (Germany, Italy, Netherlands, East Europe, Australia, 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 M&D Flugzeugbau in North Germany or the Jonker Sailplanes Facility in Potchefstroom, South Africa for a tour and evaluation flight. Please feel free to contact us for details.

Purchasers of JS3 sailplanes are also encouraged to consider a visit to the Jonker Sailplanes Facility to inspect their glider, and test fly their sailplane in the southern hemisphere prior to ocean shipment.

A: We do not add VAT to the price of our gliders. For any European Union member state the aircraft is duty free but is subject to VAT (currently 19% in Germany). VAT payable is calculated on the CIF value, i.e. the sum of the value of glider and the cost of shipping and insurance.

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