Sports Car Aerodynamics: Spoiler Alert!

Sports Car Aerodynamics: Spoiler Alert!


[MUSIC PLAYING] Say you like to draw. Specifically, say you
like to draw sports cars. What about the
spoilers in the back? Do they impact the
car’s performance? Or are they there just for show? OK, say we have two cars now. One has a spoiler,
and one does not. If they were racing under the
same conditions, same engines, and same route, the one with
the spoiler would actually win. What if we add a third
car with an airfoil? Which one do you think
will win the race now? Well, in order to understand
the differences that makes one car faster
than the other, let’s take a closer look at
the main forces, lift and drag, that are acting on the car. Lift and drag are forces
created as air flows around different shapes. Let’s look at a cross section
of an airfoil, or wing, to clearly show these effects. Air flows around
the wings smoothly, except at the tail end, where
there is some swirling air. The smooth, steady air
is called laminar flow, while the swirling air
is called turbulent flow. Laminar flow consists of
smooth, parallel lines, while turbulent flow
has chaotic swirls. Pressure is defined as
force divided by area. However, since we
are most concerned about the forces
of lift and drag, it’s easier to
write the equation as force equals
pressure times area. Pressure differences between
two surfaces of an object creates a force going
from high to low pressure because the pressures
want to equalize. Let’s identify the areas
of high and low pressure. The air travels
faster above the wing, creating an area
of low pressure. Conversely, slower air
on the bottom of the wing creates a high pressure area. The air flow above the airfoil
separates toward the back and creates turbulence,
impacting lift and drag. Now that the high and low
pressure areas are labeled, it is easy to identify the
forces of lift and drag. The high pressure area below
the wing and low pressure area above it creates
a force called lift. The high pressure area
at the front of the wing and a low pressure
area at the back creates a force called drag. Drag pushes the wing
backwards, while lift pushes the wing upward. If we take this same
airfoil and tilt it upwards, it creates greater
pressure differences and changes the area of the
wing that the pressure acts on. If you remember the
equation we talked about earlier, both the area and
the pressure affect the force. This is why it is important
to determine the best angle for the
airfoil to generate the optimal amount of lift
and drag for your application. Airfoils on cars use
the same principle, but are flipped upside down. And drag force is still
pushing the wing back, but the high and low pressure
areas have been switched. Thus, a down force
is created instead. Minimizing lift on a
vehicle is important, because it causes the
tires to lose traction. Less traction causes
bad handling and slower accelerations. Airfoils use a down force to
push the back of the car down. Let’s take a closer look at
these effects on sports cars. Say air is flowing
from right to left. The basic airflow around the
car would look like this. Air approaches the
front of the car, travelling in laminar flow. As it goes around
the car’s body, the air separates at the back of
the car, and parts of the flow become turbulent and swirl. The flow in the back is
an area of low pressure, while the shaded regions on
the front and bottom of the car represent areas
of high pressure. The pressure difference
between the front and back creates drag. And the pressure difference
between the top and bottom creates lift. Now let’s look at the
car with the spoiler. The airflow around
it is similar, but with key changes in
pressure differences. When the air hits the
spoiler, pressure builds up, causing a decrease in lift. The flow is then deflected
upward, which increases drag. However, the
advantage of less lift is greater than the
disadvantage of more drag, so the spoiler will improve
the car’s performance. Instead of using
spoilers, we can use an airfoil that decreases
lift without increasing drag. Air flows around the car. But this time a localized
pressure difference at the airfoil
creates a down force that doesn’t block the
airflow like the spoiler. Lift is decreased without
significantly increasing drag. In order to test
these principles, we built a small wind tunnel. Wind tunnels are usually large
and have a controlled current of air or smoke
moving through them. Here’s the set up. At one end is the nozzle,
where the smoke is introduced. Next to lies the test section,
where the object of study is placed. The fan in the back pulls
the smoke out the other side. When performing the
experiments we used lights to illuminate the test section. It is important to redirect
the light in the wind tunnel to create a good contrast
between the smoke and background. In this empty wind tunnel
you can easily see the flow. From the nozzle to
the test section, you can see the
smoke accelerating and flowing smoothly
through to the other side. Now let’s get down
to the fun stuff. We chose a 124th model
Porsche Carrera to test, because it’s a high performance
sports vehicle that I would like to own someday. Take a look at the streamlines. The smoke flows
smoothly over the front of this gorgeous machine, but
eventually becomes turbulent at the back of the car. Slow motion really captures the
path of the turbulent airflow. Let’s see that again. Nice. Next we try looking
at the effect of a spoiler on
the Carrera and how it blocks the flow over
the rear of the car to create a high pressure zone. Air flows over
the top of the car and eventually hits the spoiler. After hitting the
spoiler, the air is deflected in two directions. Some of it swirls
backwards, while the rest is redirected upwards. The redirected air leads
to a lower pressure zone behind the car,
which can increase drag. However, the deflected air
that creates the high pressure zone over the trunk
reduces the effect of lift with a down force. In other words, your car will
be able to accelerate faster and handle better. Next we have an airfoil
that demonstrates the effects of
pressure difference and their relation
to lift and drag. The smoke sticks to
the airfoil until it separates near the tail. The area under the
flow separation is lower pressure because there
are only small amounts of air there, which causes
the air above it to expand and fill the
space, creating turbulence. The slower airstream,
moving under the airfoil, creates a higher pressure zone. We can see a cooler visual
when the airfoil is tilted, and the effects of the air
flow become more pronounced. The flow over the
top of the airfoil expands into a bigger area,
creating more turbulence and low pressure zones, while
the bottom of the airfoil blocks a greater
area of the air flow, leading to high pressures. Drag and lift
change dramatically compared to the airfoil,
with the low angle of attack. You can experiment with
the effects of lift and drag by sticking your
hand out a car window and adjusting the angle. Now let’s get back
to the sports cars. Here we have a
Lamborghini Diablo for your viewing pleasure. It features an airfoil
on the back that acts like an upside down wing. This creates down force without
significantly impacting drag, because it allows the
air to flow around it instead of blocking the
flow like a spoiler. In slow motion you can easily
see the flow separating when it hits the airfoil, and
that the turbulence occurs further away from
the rear of the car, compared to the Carrera. Back to the drawing board. Let’s review what we’ve learned
about tricking out sports cars. We found that an
airfoil provides the best solution to decrease
lift and drag on your car. It looks cool, and will give
you better handling, faster acceleration, and
higher top speeds. Now we can clearly see that
if these three cars were to race along the same track
under the same conditions, the car with the airfoil
would win, because of superior aerodynamics. The one with the spoiler
would place second. Fun fact– at 130
kilometers an hour, F1 cars can generate
more down force than the weight of the car,
allowing them to theoretically drive upside down in a tunnel. Do not try that at home. [MUSIC PLAYING]

100 Replies to “Sports Car Aerodynamics: Spoiler Alert!”

  1. Not quite right, by this logic a massive spoiler and/or wing would increase acceleration further. But they merely increase downforce for traction at the cost of drag. At high speeds, where the spoiler does most of it's work, it could signifigantly reduce the top speed of a car while increasing grip for cornering. A lot if cars with epic air kits tend to not have amazing top speeds, exhibit viper ACR.

  2. Not 130km/h, teorectly one F1 can go up side down in about 180km/h but it depends the angle of his wings! Thank you for this great vid showing the air flow with wind tunnel images, it's very nice! And by the way: I love the design of 911 family, and diablo it's to me one of the most beutiful design of all super sportive cars! 😀 😀

  3. Ohh great… every ricer that watched this video is running up to Autozone as we speak, ordering a 747 wing for the trunk of their Civic.

  4. Wow, some ignorance on display in the comments section here. Just one example, rear downforce on a RWD car actually does improve acceleration at any speed where the downforce is effective. More downforce less tyre slip and yes the tyres do slip in a straight line, obviously the amount of downforce and power are relevant as to the amount of slip.

  5. a car wont accelerate faster with a wing only if you have a lot of horsepower and lose grip even in higher speeds. a car without a wing will also be able to hit higher speed because of less resistance which means in a lot of cases the car will accelerate slower but take corners faster

  6. There are many fundamentals in this video that you do not understand.

    In a drag race, the car without any rear aero would be the winner, due to increased drag on the other two cars with aero. Aerodynamic devices placed on the outside surfaces of a car will ALWAYS add drag, except for ones that take advantage of ground effect.

    Rear aero also does not increase acceleration, unless you are already moving at high speed and the engine produces enough power to spin the drive wheels without extra downforce. From a standing start, the spoiler cant do anything to help with acceleration as air movement relative to the spoiler/wing does not exist yet.

  7. I can't get past the horrible speech patterns of the narrator. When did people lose to ability to speak well, particularly when they speak for such a highly regarded school as MIT?

  8. Great theory but in racing there are too many variables, even two of the same car the HP varies by horses. If you had 4 cars the 3 you picked and a fourth that had the bottom completely smooth by putting plates to reduce turbulent air on the most inefficient part and that car will go faster than the other 3. You need more cowbell and real life. Less theory apply what's already known then add. You just took a huge useless dump on people that have no clue. adding a wing, takes HP to push thru the wind=down force=drag=less power to push the car. A car with a wing against a car with no wing of the exact same make will have a lower top speed cause of Drag. A wing does not work till it hits a velocity where it creates drag=downforce=hp to push thru the wind. Blah blah blah

  9. This video quotes MIT and wind tunnel testing but is full of fundamental errors. On a straight line infact the car with spoiler or wing is likely to be slower due to drag. And it will not aid acceleration – unless its a heavy wing and the car was originally struggling for traction lol. Plus the turbulent flow he drew on the inverted car wing is in the wrong side.

  10. For all the comments saying that a spoiler causes more drag and would slow down your acceleration. No that's not correct you are most likely getting spoilers mixed up with wings. While true spoilers cause drag they also reduce drag caused by high/low pressure (wind vortex) more then they create. Lowering the overall drag of the car and increasing the acceleration/mpg of said car.

  11. Correction !
    A spoiler or any other body parts that generate down force will slow down acceleration.
    in cars there are two types of Aerodynamics

    1st type of Aerodynamics is "less resistance"this will allows you to acceleration fast to a high top speed (also help the car get a good fuel efficiency)
    http://images.slideplayer.com/32/9831020/slides/slide_9.jpg

    but when you go fast you will need some down force otherwise you will loss grip/handling
    and this will happen ( https://www.youtube.com/watch?v=wJF06ZP7U2s )

    2nd type will be Aerodynamics that are made to get a better handling in corners (to act as a stabilizer so that you will not loss control)

    in the video the No:26 car would have been okay if the No:77 car was not in front of it !
    a good race/performance car will have both types of Aerodynamics
    race car drivers use slipstreaming

    No:26 was using No:77 to get more Aerodynamics of "1st Type"
    but with the elevation change in the race track only the No:77 had both types of Aerodynamics !

    with not enough air passing through/cutting the body No:26 became unstable at high speed
    and with the elevation change air got under no:26 and flip the car

    in a Drag race
    A big car like a "S Class" with no Spoiler will accelerate faster to the top speed of the car
    than the same "S Class" with a spoiler

    but in a circuit race for a example Nürburgring
    the S Class with the spoiler will be faster around the race track than the car with no spoiler
    because the car with the spoiler is more stable when turning and it can turn at a much more faster speed !

    Note: this explanation is oversimplified there are other forces at play
    like power to weight ratio, suspension, brakes, engine/drive train layout and rubber compounds and many more

    Tip : don't add spoilers to everyday normal cars !
    you are not going to go faster and you may burn more fuel !
    good suspension, brakes and good rubber will help you go faster with no weight reduction or power gain
    when you have good suspension, brakes, and rubber then you can get a spoiler that is made for your car
    then you move to weight reduction and power

    BTW suspension plays a big part in Aerodynamics and they need to be tuned

  12. WTF is this video explains everything wrong , spoilers at the back are mainly made to push the car down so the tires have better grip on the road and that the car doesn't fly away in the worst cases due to air drag. Jesus christ everyone looking at this video, that doesn't already know basics, will learn everything wrong, please delete this !

  13. So a separated turbulent pocket of air created by excessive wing angle is low pressure, but if you do it with a spoiler then that's high pressure? Get your facts straight.

  14. 0:20 now that is just wrong… if the cars could get to and over 150 mph or so, the spoiler would slow the car down… also, a spoiler could be badly engineered and not generate downforce at all, even slow you down.

  15. this is weard
    i think : the blue car = 1st the red = 2nd & the yelow = 3rd you got to do some reserch about the DRS in F1

  16. Uh, i thought increasing downforce only increases car control and at high speeds, not acceleration. I cant see why it would increase acceleration or speed at all, especially at a launch, as the air is stagnant at the time of a launch. Also, increasing downforce would require an increase in horsepower to reach the same speed a non spoiler car just by pure logic, so how would it help win that simulated drag race?

  17. This video is WROOOOOOONG!!!!!

    Spoilers are tradeoffs, if you have spoiler you will increase drag and decrease acceleration but you will have more downforce thus you will be better at cornering.

  18. It is only effective when u reach a certain speed , like 100km/hr. How it affects your car if you drive mostly in the city, does it increase fuel consumption?

  19. While the science is ok in this video besides the diagram at 2:30 (turbulent air on top!?) the logic depicted in the pictures does not match the content. The video is correct but only in extreme circumstances that these average looking depiction of cars will not experience. Most average modern cars even at their limits will not benefit from a spoiler if drag racing is your goal. Looking at the comments I can see this is an issue with many viewers.

  20. This video should be deleted.. It contains more misinformation than actual information. I can say that im truly glad that i study at another university than MIT.

  21. OH, AND FOR THE GUYS WHO ARE NAYSAYERS- SMOOTH AIR GUYS, SMOOTH AIR IS HOW YOU GO FASTER ! CAN YOU SAY "DRS" IN F1 ?!

  22. Ummm there shouldn't be turbulent flow over the upper camber of an airfoil, even at the back. If there is, you stallin.

  23. A lot is going on below, so I wanted to try to add a few information about the stuff we are talking about without adding more confusion.

    1. Downforce grows when you go faster and faster, at some curves F1 cars can not make the turn properly with 180 km/h but they can with 250 km/h.
    2. Coefficient of drag is around 0.7's at F1 cars but it's around 0.24's at Tesla Model S. So, as you can understand from that info alone, trade off between downforce and drag makes you faster if you calculate precisely. Drag can be a friend rather than a foe depending on what you have in your arsenal.
    3. There is no downforce in the begining for all three cars and there is an added weight for the cars which has spoiler and wing compared to the one without those. That means, in theory, the one with no wing or spoiler would make a slightly better start, and keep that until downforce starts to kick in. At some point when they reach to enough speed trade off between drag and downforce would start to pay off and while cars with spoiler and wing would keep on going with a pace, one without them would start to have issues because of the lift.

  24. Adding drag will not increase speed… It will make the car handle better, true but I believe your three car race analogy is incorrect.
    I didn't to college so don't take my word for it.

  25. The car the least amount of wind drag, meaning no spoilers will always win hands down. Spoilers are a rip off, and a scam.

  26. I have a migraine everytime I hear people say: "This car's aerodynamics suck." The aerodynamics of a certain object cannot suck unless it's a vacuum machine. There's only pressure, drag, forces, there's no "suck".

  27. For everyone saying this is wrong.. Spoilers reduce drag. It's not an airfoil. When properly designed a rear spoiler both reduces drag and creates downforce. (actually it just mitigates lift). The video is not incorrect, other than confusing spoiler with airfoil. They do not serve the same function.

  28. Very nicely explained! I`m looking for a wind tunnel like the one in your video. Maybe you know, where i could buy something? I do not want to make it by myself, have too much to do with my RC Cars..lol Best regards Martin

  29. Yo htf will speed increase with increase in downforce. Increase in downforce helps you break faster and corner better. It does not help you accelerate and gain high speed. The blue car would win, the red car would come second and the yellow car would come third in a straight line. If the race had been in a circuit full of turn no doubt the yellow car would win.

  30. Please stop commenting about things you don't know,I did research on this online and found out that spoilers indeed decrease drag and increase efficiency, an airfoil or a wing creates downforce and increases the handling of a vehicle,but a properly engineered spoiler gives better aerodynamics thus increasing acceleration and speed. Please don't mislead people by stating"facts" that you don't know.

  31. Doesn't spoiler create drag when generating downforce? Car with the spoiler would lose the race in a straight line. Did someone submit this as their class work? 😀

  32. You wrong buddy. Look at the Mclaren Senna. One of the fastest cars ever (around a track where the Aero assists in corner speeds. NOT straight line speeds) the Mclaren 720 is in actual fact faster in a straight line.

  33. “Here we have a lamborghini diablo for your viewing pleasure.”

    This one line has convinced me to subscribe, over all the useful information it was this one line alone.

  34. It's ok to simplify, but here you're going too far. It's full of serious mistakes, this is no more science.

  35. This wind tunnel of yours is total BS. You have NO data to show us, NO measurements just a load of incorrect BS about aerodynamics. Amateur hour central.

  36. I have a question , I seen this driver of an STI have a stock spoiler . This is the newer like 2015+ . They put on a rear roof spoiler that is kinda big and flings upward . Wouldn’t that stop or slow down the function of the stock spoiler . The air is being redirected upward instead of from the roof straight down into to spoiler . They whr getting props but was it for bs from ppl who do t know or am I just not knowing what I’m talking about . The rear roof spoiler was being turned upwards . 🤔

  37. on a straight downforce is not needed all that much. You need downforce if you are loosing grip – in cornering or in extreme acceleration. So if the cars are identical except spoiler type, the one with less drag wins. So the one without a spoiler.

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