July 2020

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JULY 2020 WWW.PNWR.ORG 17 Figure 2. Effect of 911 Spoilers on Front and Rear Lift (Reference 1). Figure 3. Porsche 911 Steering Response in Emergency Stop from 90 mph in a Turn (Reference 1). An example of the effect of spoilers was dramatically shown in some early factory testing (Reference 1) where a 911 was driven into a corner at 90 mph and the brakes applied. Figure 3 shows the results with two runs done without spoilers and two done with spoilers. The results are quite dramatic with the spoiler equipped car requiring only a small turning of the steering wheel while the car without spoilers requires very large steering corrections to maintain stability. The end points of the traces show the significant advantage in stopping time, about one second, that was obtained with the spoiler. If a rear spoiler is used without a matching front spoiler, the attitude of the car at speed will be too nose high and cornering capability can be seriously reduced (see References 4 and 5). Flow Channels and Deflectors In addition to stabilizing spoilers, Porsche also uses aerodynamic deflector devices to guide cooling air and create vortex flows to assist cooling. An early example of this was on the 1973 and later 914 models, where the production cars have two spoiler flaps on the bottom of the car at the front edge of the engine compartment. These flaps, about a foot wide with tapered ends, extend down 2 inches to introduce higher energy air into the bottom of the open engine bay and assist in engine heat dissipation. These flaps provide a significant reduction in oil temperature on a hot day. The newer cars, with both front and rear engines, use front air intakes for radiators, air-conditioning condensers and brake cooling and often use air deflectors to assist getting the air to where it is needed. Front suspension members on the late 928 models have aerodynamic vanes mounted on them to help direct the flow. It is important that these vanes be left undisturbed or replaced if removed in order to maintain the original airflow and cooling concept for the car. The owner should also recognize that the use of aftermarket spoilers that disrupt airflow into the front vanes or flow channels for cooling should be avoided. Another example of a flow deflector is the small flap at the front of the sun roof that pops up when the roof is opened. These wind deflectors help minimize turbulence in the car with the sunroof open at higher speeds. In the case of the 911, the design of the deflector was upgraded in 1989 with the addition of a small additional flap in the center of the deflector that further improved flow over the car with the roof open. The aerodynamic design features and refinements built in to Porsche cars, particularly the models after the early 1970s, provide real benefits to the owner in driving stability and operating efficiency. It is hoped this short review will remind our owners to be aware of the importance of some of the aerodynamic features on their cars so they can be maintained to perform as originally designed. Any changes or modifications to the car should take into consideration the aerodynamic effects. References 1. R. White, "Porsche: The Cars and Weissach Engineering," Up-Fixin der Porsche, Vol. 5, pg. 309 Panorama. May 1978. 2. H. Burst and M. Preiss, "Airflow Tendencies- Aerodynamics of the Carrera 4", Porsche Christophorus Magazine, No. 217, May 1989. 3. L. Hamm, "What Do Spoilers Do?," Porsche Christophorus Magazine, No. 120, December 1975. 4. F. Schroeder, "Choosing the Right Spoilers," Up-Fixin der Porsche, Vol. 7, pg. 199. Panorama, August 1985. 5. R. White, "Adding Aerodynamic Devices to Earlier 911s," Up-Fixin der Porsche, Vol. 5, pg. 149 Panorama, June 1979.

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