Model 3 Spoiler Analysis?

Discussion in 'Model 3' started by Cypress, Nov 20, 2018.

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  1. Cypress

    Cypress Active Member

    PNW
    Has anyone looked at what impact the spoiler has, if any?

    Does it really only help with downforce at higher speeds?

    Does the Model 3 show less efficiency with the spoiler?

    Hard to find good videos and images really showing what the spoiler looks like. And I haven't seen any in person. Wonder if it adds to the look and style of the car in a positive way? But are there downsides?
     
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  3. bwilson4web

    bwilson4web Well-Known Member Subscriber

    You might want to read about Kammback which is an aerodynamic trick to reduce drag. It creates a vortex behind the car that give the effect of a tapered after-body:


    Here is a video showing the effect in production cars:


    In words, the air passing over the top of the car reaches the spoiler with velocity decreasing and pressure increasing. But trailing below the lip about 2 feet behind the car, there is a horizontal vortex (aka., circular air flow.) This pulls the air behind the spoiler down which continues to slow down and increase the pressure behind the car ... reducing the aerodynamic drag.

    Bob Wilson
     
  4. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    I'm not an engineer, and I certainly don't consider myself to be any sort of expert on this subject. I wouldn't even begin to know how to try to apply a quantitative analysis to the question.

    However, my understanding is that a spoiler, or at least the one on the Model 3, is intended to reduce drag at the back of the car. If that is the case, then that indicates it should increase energy efficiency... not reduce it.

    Presumably a wind tunnel test could determine if the spoiler reduces turbulence behind the car, and if it reduces turbulence then it should reduce drag, in theory. But whether that theory always proves true in practice... I don't know.

     
  5. Cypress

    Cypress Active Member

    PNW
    While interesting videos, as a mechanical engineer working in Aerospace and having designed major trailing edge control structures for large aircraft, and as having worked on various vehicle racing teams, I really didn’t need an aerodynamics lesson.

    A spoiler, is intended to “spoil” the airflow to reduce lift at high speed. Or to produce downforce at high speed to keep a car on the road.

    This generally produces additional drag. It is possible that Tesla designed their “spoiler” to help improve efficiency as per your videos, but then it would be a misomer to call it a spoiler.

    This is why I am curious if anyone has done an technical comparison for the TM3P with and without the spoiler to determine what impacts it may have on various performance metrics at speed.

    Or is it purely cosmetic?
     
  6. bwilson4web

    bwilson4web Well-Known Member Subscriber

    Sorry, I didn't see your work experience in the original post. I agree the aircraft spoiler is significantly different to the terms use in automotive practice.

    Personally, I would call the auto body mounted 'spoiler' a type of vortex generator. In this case the vortex has a horizontal axis, normal to vehicle motion. The Kammback generated, trailing vortex is an aero-trick to increase after body, trailing pressure.

    I would probably use a roll-down test to measure the effects. As for test vehicles, our Prius Prime is close.
    [​IMG]
    Water noodles can be easily trimmed to eliminate the rear 'spoiler' edge. Held on with 'blue' masking tape with cardboard boxes trimmed for a 'trunk.' Then use roll-down tests to measure the effect.

    Would that experiment work for you?

    Perhaps you have a car that the same experiment might be done? If it doesn't have a 'spoiler', a cardboard version attached with blue masking tape might work.

    Bob Wilson
     
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