Aero ideas revisited, not discussed before

I bought the Kaira rear wing. It was shipped over to California...where it sits while the body kit makes its slow boat journey across the ocean... Then it'll all be freighted to me, and perhaps I can tell u some firsthand news about it! I'm about to DIE to get it! lol

 

The reason they probably didnt do much with the undertray is one of cost vs weight. They did do a very good job of tucking everything up and making it quite flat though, better than most by a long way.

There is an aerodynamic advantage with air dams, but they need to be very close to the deck to be really effective, within the zone of 3/4" to 1- 1/4", might not be all that practical for the road as it will get wiped out on speed humps and drains. Air dams should be roundish in profile from above

Still the more air you can cut off from going under the car will be an advantage, and controlling it on the sides with skirts, and letting it expand better with a rear diffuser at the end of the undertray will assist.

Hard to say about the rear wing, they are aero mods meant to provide downforce on the rear of the car, just as well profiled dams will do on the front. The actual angle depends on the shape or crossection used for the wing itself. If you can get me a closer look that would be an advantage, perhaps...

If it has a flat side that is an unequal shape that will always try to suck to the opposite side, if its equal both sides in shape, its zero lift is at zero degrees angle of attack (AoA), where it has no influence except by adding to drag, but there is another feature of them I will get to later. That said, the AoA depends very strongly on the airflow off the car going around it, which unless you can find wind tunnel smoke streams is a bit tricky to predict

The end plates just make it more efficient by around 20-30%, but they do so by adding area, therefore drag.

I think most of these devices are purely for looks, and have very little effect on the aero drag of the car, except that more than a few I have looked at will probably add to it. So if you are in it for the looks, dont worry too much about the rest, you can be reasonably sure the designers of the kit didnt either

Ideally if you were interested in the drag signature I would look for aero kits that are smooth without protrusions or unnecessary holes, well rounded front dams that will hold some air in front of them with a lip, and tend to push air up over the car and out to either side. Thats why rounded profiles (from above) are an advantage

Side skirts just contain the air under the car from influencing airflow out from under the sides, but the flutes in the body of the Prius on each side already contain that mess of airflow close to the road quite well, and hold it close to the road where flow will be more turbulent. Skirts are all about reducing pressure under the car, that tends to leverage the forces of airflow to keep the car on the road.

I would try not to mess too much with airflow over the roof, its best for airflow to maintain contact with the roof all the way to the back of the car. If airflow breaks contact with the roof it will go turbulent and add to drag and more suction behind the car, requiring more fuel at a given speed. Critically this isnt a place where you want the leading edge of the hatch to be a poor fit and deflect air up, if anything it would be better slightly down by a few mm. If the air has a habit of breaking contact easily there, you can excite the airflow with turbulators that will increase pressure and maintain airflow contact to the body.

A spoiler will tend to attract flow from some distance in front of it, and tend to push it out flat over the back of the car. Since its a Kamm back design, Im a bit unsure if thats a good thing or a bad thing, and the only way to really find out is on a rolling road in a wind tunnel, but I think I would err on the side of it being a very moderate improvement. But the something same is probably achieved by the rear spoiler lip on the end of the stock tailgate.

hope that helps ..

 

Luis, at Carson Toyota, has been "the man" and has hooked me up with 95% of everything I've bought so far. I just bought the wide window visors by Interial, but I had to get the from Jin at Kyoei... I locate most of the Japanese items, then Luis has people that get them for me and ship them over. I had an entire crate with a Fledermaus body kit and wheels all shipped over on the boat together. I bought a hood spoiler from Ikki-81, as well as a rear hatch spoiler from them, but am having trouble with them supplying those items... (manufacturing problems, Ikki says. Some of them are 'breaking', whatever they mean by that.). I paid Carson a total price for the cost of all that stuff, which included shipping. They shipped the wing over by itself, for some reason, instead of waiting to send it in the crate, so it would have had its own shipping charge, but I have no idea what that was, since Carson is handling all that for me. I just knew the minute I saw it online (accidentally "bumped into the picture") that I HAD HAD HAD to have it. It was what --- $1200, or something around that? I'm not into the whole carbon fiber thing, so didn't get it in carbon fiber. But if you like the wing, GET IT!!! I'm a strong advocate of GETTING IT! Since you're just looking at all this stuff, I will let you know that I also ordered the Valenti LED tail lights, LED signal mirror covers, folding mirrors, and I've bought a Beat-Sonic shark fin antenna, Bellezza curtains, PriusChat foglights, Lexus emblems to replace the front and back Toyota emblems (long story...lol), a Garson D.A.D. steering wheel brooch to replace the Toyota emblem..., Lexus velour seat towels (to protect the leather), Mbro LED turn signals, and various other things I can't think of right now. I am getting the price to buy these coilovers that Fledermaus has on their website picture of their Prius, cause I want that same stance that they have. Link to coilovers:

(http://www.rs-r.co.jp/e/script/itemsearch/index.html?Prius&ZVW30&shock)

Of course, I'll have to get tires for the new wheels... Still haven't looked into that, but I gotta get the kit installed and all the painting over with before I want to take it to have the coilovers and wheels done. Have had WAY too many wheels and tires oversprayed in the past to go thru that with these new wheels.... Oh, and I'm gonna put a larger wiper on the back. I'm trying to find a custom headlight place that will do them just the way I have in my mind with the Audi-ish LED lights clear across the headlights. Thinking about replacing the horn with a LOUD one, cause I'm on the Interstate with nearly all driving I do, and nobody can hear the horn on the car. Don't know what I'll do if IKKI doesn't let me get that hood bonnet and the rear hatch spoiler/visor. I had REALLY counted on those. Well, that's about all I can think of at the moment, but that's the main things anyway...

 

If you want the wing for looks, great, not my thing, but to each its own. If you want to improve efficiency, not so great. You really think if something so simple could improve the mileage, that Toyota would not have already done it? Really, think about it. They could have done it for cheaper than any aftermarket company. A company that designed the car in a wind tunnel, and added wheel rings to the previous version when they found it made a difference, would have missed adding a wing if it helped?

The fact is that in nearly all applications a wing adds drag. Yes, even in most race applications. Then why have them you say? Because they also push the tires down to the ground, increasing tire grip, which is pretty important. The aero hit they take is worth the better handling they get thru the corners. Or the fact that they don't turn into an airplane wing at speed. That is why they are adjustable for different tracks, depending on straighwaways compared to cornering speeds. It is said that the average F1 car gets so much grip from its wings that it could actually drive upside down at speed.

So if you like it, go ahead. But know that you likely have wasted your money on it, it will likely cost you more in gas, not less. And that people will almost certainly point and laugh.

 

Oh and for the undertray, with a major manufacturer like Toyota they also have to have concerns about the serviceability of the car, you can't make it take 3 hours for a simple oil change. And also you have to be able to evacuate the heat from the engine bay and you have to be able to do that even driving across death valley at 115 degrees, or across the center of Australia without overheating or coming close to it.

Know that anything simple, cheap and legal, Toyota has looked at it.

 

It also has to work driving across Death Valley on a hot day.

 

Toyota used this Prius extensively for promotions, note the front lip spoiler

 

Spot on.

The flip side though is that general solutions might be optimized to local conditions. The best example I can think of is owner installed radiator block in cold weather.

 

Talking about aero --
I was wondering today about fan use in the passenger cabin set to non-recirc mode. Power is spent turning the fan, but I imagine the fan as holes in the frontal surface area of the car that lets air pass through. There is also a system advantage, since the air cools the traction battery.

Any opinions ?

 

does anyone still do that with a modern car?

 

2011 Chevrolet Cruze Eco Drive: Chevy Cruze Review
"First, Chevrolet optimized the Eco’s aerodynamics by inconspicuously paneling off more of the upper grille than on other Cruze models and by adding motorized shutters to the lower air intake to close it off during high-speed cruising."

Obviously this is to reduce aero drag, but in cold conditions (colder than the Bay Area where you live) blocking helps warm up the engine faster. Which reduces the amount of gas used in the warmup phase and enables the car to enter ICE-off operation sooner.

 

I thought you meant more like the pieces of cardboard held on with cloths hanger wire I remember as a kid. Not the automatic ones like the Eco or I think a Bently model or two does that as well. Back then it was done more for driveabilty issues than airflow -- I think, it was a long time ago. We are talking the 70's and such, where there were still carburated cars around, and the computer processing wasn't what we have now. So people in cold areas would have a tough time with their cars in the bitter cold, where it just took too long to get the engine warm enough to run properly -- or to put any heat in the cabin. Plus the emissions standards had just come out, '74 maybe, and the manufacturers really had a tough time meeting the requirements at first.

 

I have seen front grill infills in fibreglass aero kits

 

Ack.. That looks gross to me.. But maybe it is just me?

 

what does that do to the cars engine cooling?

 

no, it looks gross!

 

while I agree its not the best look, but note beauty is somehow in the eye of the beholder, the top grill isnt the only air entry point to the radiator system.

 

Heck yeah. Search 'grill blocking' in this forum for hundreds if not thousands of posts on the subject.