BT Tech Rear Aero Spoiler!!

Brian

How far up the glass from the bottom edge does the spoiler measure?

Wayne

 

This sounds interesting, but would someone explain how this works? I think I basically understand the airfoil effect, and how wing and splitter spoilers are basically inverted airfoil/wings. I believe this spoiler is a lid spoiler and hyo silver was talking about a roof spoiler. I suspect both work on the same principle, which I can't seem to visualize.

Also, can you give some details such as lift/drag ratio (or is it downforce/drag ratio)? I expect this to have little effect both to drag and downforce at low speeds, and to make a significant difference at high speeds. Is that correct?

Where is the downforce applied to the car? Is it relatively distributed or toward the back where the spoiler is located? If it is to the back, isn't this sort of imbalanced?

Does the spoiler affect rear visibility at all? Or is below the portion of the rear window which is transparent?

 

I don't profess to be an expert on this, but I will attempt an explanation. Brian, or anyone else, please correct me if I'm wrong.

Because of the shape of the prius, air flows faster over the top of the car than it flows under the car, and generates lift, just like an airplane wing. It's not enough to make it fly, but it is enough at higher speeds to make the steering feel lighter, and to increase the sensitivity to cross winds.
The spoiler adds a bit of drag, slows down the air, and reduces the lift. My intuition tells me it's not a matter of adding downforce, but of reducing lift to let the car's weight keep it on the road.

I can't quote lift/drag ratios, or say how the centre of pressure changes with the location of the spoiler. I would guess that the spoiler might appear a little thicker through the rear view mirror, and that mileage would be slightly affected. But, if you spend much time at highway speeds, particularly in a windy place, these trade offs are more than welcome.

 

That seems to make a lot of sense. Now you have me wondering... at what speed can I safely rotate to take off? I'd LOVE the idea of a flying Prius!!!!

 

Brian, in the flurry of messages since your announcement, you may have missed my request to post a photo of just the device.

It's hard for me to visualize what it looks like when I see it in the photos you have posted.

 

Sorry, I don't think you'll see any flying Prii anytime soon. Unless of course they're pink and you've had too much of a good thing. :lol:

 

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Interesting. When I was trying to visualize how it worked, all I could see was that it would slow down airflow and I discarded that as a useful mechanism for a lid spoiler to use, since that seems like drag penalty is pretty high to gain downforce compared to a wing or splitter spoiler. I guess I neglected the possibility that it may have a worse downforce/drag ratio, but still be a useful tradeoff.

Brian, how about a photo from the interior through the rear window to see how it affects visibility/looks from the inside?

 

How fast do you have to drive before the car starts experiencing body 'lift'? I had understood anecdotally was around 90mph and higher. Basically, you have to approach race-track speeds.

 

Very true... I used to own a C152 and I would push down on the yoke to keep it on the ground until 80 knots. The I would pull back and takeoff like a fighter pilot. Only did that a few times.

 

How much pressure is exerted on an airfoil that is doing a lot to hold the car down? Is even really tough superglue going to keep it in place?

What kind of under-car additions would work to equalize the pressure and lessen the lift?...

 

yeah, I'm thinking there isn't enough pressure exerted at 55 mph that you couldn't hold it on with Blu-tak.

If people here start gluing thing on, I just won't believe it. This is a group of folks who pride themselves on 60 mpg, and their going to take an MPG hit for this? Seat of pants dynos are sooooo cool.

 

OK, I mis-interpreted one of the previous posts and thought downforce was an important aspect of this part doing its job. Lots of downforce would probably need a welded-on part.

Since I think, IMHO, that the car's main problem is being blown off course due to aerodynamics, I'm willing to look into an effective solution for that. Early adopters should post freely... :mrgreen:

 

That isn't the only think this part is supposed to adjust.

My car was rocked by a (not that big) truck going by.

Supposedly this part is going to help with the shimmy when a larger, faster vehicle is passing you.