JS3 high wing design – from our Aerodynamic Chief Engineer Johan Bosman

 Why did you select a high-wing configuration on the JS3?

Top performance sailplanes essentially must have the ability to climb and cruise better than its competitors. This implies that winning gliders have to be efficient flying machines at both low and high flight speeds which are, in many cases, contradictory design specifications. All parts, which contribute to the aerodynamic performance, must therefore be designed to operate at a wide angle-of-attack range (especially non-flapped sailplanes). One area that is influenced by this requirement is the wing/fuselage junction as it contributes significantly to overall drag.
If two aerodynamic bodies are combined, such as the fuselage and wing, the drag of the combination will be more than the sum of the individual drag quantities. The additional drag is caused by interference effects and is therefore called interference drag. Many aerodynamicists concluded that the junction interference drag is largely influenced by the location of the wing relative to the fuselage. These effects were hardly quantifiable by analytical approaches and research was for a long time limited to experimental work only.
Many factors contribute to the complexity of the flow around the wing/fuselage junction, such as super-positioning of the flow, asymmetric effects, circulation effects and viscous effects. Examples for the complexity of these effects: a mid-wing configuration has higher angles-of-attack at the root area due to the increased velocity component created by cross-flow effects from the fuselage. This is known as the alpha-flow effect and can cause significant separation problems on the top rear surface of the root section at higher angles-of-attack. Also, the wing span-wise lift distribution is compromised by the presence of the fuselage and has an adverse effect on the performance at slow speeds.
Many wing/fuselage experiments in the past suggested improved performance for high-wing configurations – current CFD analyses confirm these results. With the utilization of CFD, the effects of repositioning the wing can be studied and most of the detrimental effects associated with wing/fuselage junctions can have be alleviated. A significant advantages of the high-wing configuration is the increase in laminar flow in the root area. The geometry allows for laminar flow profiles closer to the fuselage with less overall interference effects which results in no flow separation and thus increased performance over the entire speed range.

Oil test on JS3 High Wing Design

● Does a mid-wing configuration not have the advantages of a smaller wing-area at high speeds?

Wing is always lower drag than fuselage. If you use the analogy that a larger fuselage increases the wing-loading, you might conclude that the bigger the fuselage the better the high speed performance…. no ways…

● What are the disadvantage of a high wing?

Only Attie suffers the disadvantages! The structural challenges increase significantly and different structural solutions had to be devised. At this moment the material structural limitations will not allow us to have wingspans exceeding 18m in the high position. It is also more complex to fit integrated bug wipers, as you can imagine. And it is also not good for inverted flying.

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Jonker Sailplanes