Spa Francorchamps race weekend was as usual a good proving ground to test low downforce aero package to be adopted at Le Mans.
We take opportunity to review here Rebellion R13, primary actor competing on LMP1 privateer title.
Interesting to see how they will perform at Le Mans, competing with Toyota hybrid TS050.
It is known that Rebellion R13 is built around Oreca 07 chassis, and Gibson GL458 engine.
At first look the car from outside has same philosophy as the Oreca 07, but there are several changes from front to back creating different airflow management on external aerodynamics as well as cooling.
Rebellion R13 rear fender is more conventionally designed with very slender and vertical leading edge. Oreca 07 in fact has a very unique concept of slanted front volume of rear fender, so to grant an optimized shape to control airflow without separation when small lateral flow build up due to car slip angle.
Side edge of front splitter adopt a continuos and wider top surface up to maximum width, without the vertical end plates that normally terminate on the spoon skirt. This make sense considering left side of the picture depict the low downforce configuration, demonstrated also by the single dive plates on front fender.
Comparison Rebellion R13 (left) vs. Oreca 07 - details of front splitter edge (low downforce version) and rear fender leading edge
Rebellion R13 (left) vs. Oreca 07 - details of front splitter extremities. Low downforce (left) and curved skirts with end plates.
Splitter bottom side, facing the front wheel, is a very sensitive area to control the high pressure zone and vortex that is created inside the wheel. Vertical strike is used to guide the flow so to blow it where is desired rather than leave it free to develop in an uncontrolled high vorticity zone
Rebellion R13 - details of vertical strike underneath front splitter, facing front wheel.
Front keel, turning vanes under nose, wheel drum fairing are also components revised on Rebellion R13. Those elements are design to direct the flow coming from splitter trailing edge, diverging it alongside improving underflow pattern and feeding rear diffuser with cleaner airflow.
Rebellion R13 (left) vs. Oreca 07 – Complex turning vanes system to guide flow coming from front splitter
Detailed view of the three vertical turning vanes in the front-side area of side pod. This channel, between inside fender cusp and tunnel intake need to guide the flow around the high velocity low pressure surface of side pod, reducing drag and avoid separation.
Vertical span of the second and third vanes are so to create a tapered equivalent surface with less wetted area and blocking effect.
Rebellion R13 – barge boards on sidepod at tunnel entry
Rebellion R13 engine type Gibson GL458 is based on LMP2 version with capacity increased from 4.2 L to 4.5 L. This has changes the heat rejection figure with consequent need to improve cooling. Internal flow, heat exchangers position and size have been designed accordingly.
On top of side pod is visible the air duct to capture fresh external flow and direct it inside the tunnel.
Rebellion R13 - Cooling duct on side pod top surface