Over the past several months, I’ve tested eight different spoilers on my car. I could test more, but I’ve reached a point where I would rather install something permanently and move on to other things, leaving this spoiler project behind. Hence this Spoiler Roundup. Let's meet the competitors:
|Straight Gurney flap|
|Sinusoidal Gurney flap|
|Commercial lip strip|
|20° board with slot|
|Hellcat. I want this one to win only because I enjoy saying "Hellcat."|
Which one should I use, if any? That depends on a few things, including my goals, my design limitations, and how much I want to permanently alter the car.
I’ve left out the spoiler + fins tests
since they weren’t much different from the spoilers alone.
|Positive change on each axis shows reduction in drag or lift.|
Are these reasonable? Well, they seem to be, just comparing them to the pressure changes. I haven’t had a
chance yet to install the ride height sensor I purchased a couple months ago,
and unfortunately I don’t have an easy way of measuring drag changes on this
car. But I did perform some coastdown testing recently and verified that
the expected change in drag from adding the Hellcat spoiler (+15% or so) correlates
with the change in magnitude of acceleration (+13-14%) I measured in that test.
That suggests that this method of estimating drag and lift changes is good
enough for comparison since the calculation was fairly close to reality for one of these spoilers. Bigger spoilers or steeper angles generally decrease lift and
increase drag more than the smaller ones, as expected. Check.
Go try this on your own car, with whatever modification you're interested in investigating. You will be amazed at what you
can learn through testing.