canards – Occam's Racer

My annual trip to the wind tunnel is coming up soon. I had originally planned to do just a single day of testing, but two cars became three, which became four. Now I’m at five. And that’s too many to test in one day.

So I’ll be headed to A2 on 5/18 for hatchback day, then to VIR to instruct for a couple days, and then back to A2 on 5/21 for fastback day. There’s room for a third car on the first day, contact me if you want to get in on this.

Hatchbacks 5/18

The first day will be my Veloster N and Andrew Rivers’ Honda CRZ. We are both testing canards and wings, and some other odds and ends.

I’ve tested canards on my Veloster twice now. The first time I was mostly concerned about the location of the canard. If you bought Wind Tunnel Report 01, then you know that location played an enormous role in downforce. The same exact canard produced anywhere from 11 lbs to 80 lbs of downforce depending on how high I mounted it.

The second time I tested canards I wanted to find out if I was getting downforce from the interaction between the canard and splitter, or was it just the canard itself? I was also able to test a CFD-designed canard from Verus, which didn’t produce a lot of downforce, but also had zero drag.

This time I’m testing canard edge treatment and size. The DIY canards I’ve tested on my Veloster have had a sharp outer edge, but I often see canards with a vertical outer edge, kind of a fence or Gurney flap. So I’m testing two different heights versus a plain edge. Then I’ll also increase the size of the canard to see if more area produces more downforce.

Finally, I want to see if I can get a mid-height canard to interact with the lower canard. On other cars I’ve tested, the lower canard does most of the work, while the mid-height canard seems to reduce the drag of the entire system. I want to see if I can make that happen on my car.

Andrew is doing some different canard experiments, seeing if there’s interaction between various front end components. I don’t want to say too much on this, as those are his tests, but they should be super cool.

Next we are both testing wings. I’m finally getting around to testing a MSHD wing, both as a single and dual element. I’ll bring along a 9 Lives with me as well, since that’s a popular benchmark, and easy to test as a single or dual element.

Because hatchbacks are weird, I also plan to test wing location. I’m fairly certain that higher is better, but I want to check forward and rearward locations, and how those affect front downforce. I also want to test bottom mounts versus swan necks.

Andrew is testing a Simon MacBeath wing with swan necks, and I’m very excited to see how that performs. He’s doing a sweep of angles and a couple different end plates. I plan to throw a MSHD on his car, just to see how they compare.

Andrew’s car looks great with all the aero, and I’m interested to see which hatchback will have better numbers. But no matter how it turns out, we’ll learn from each other’s experiments, and both of our cars can improve from that.

Andrew’s CRZ has very nice swan necks. The tube is a stiffener inside his DIY S1223.

Fastbacks 5/21

This is going to be an exciting day, because we can test wings on proper rooflines, not crappy hatchbacks. Pete is bringing his endurance racing 944, Raul has a BRZ, and AJ is bringing a C7.

As part of the wing tests, we will throw a mess of different end plates on the Porsche. I made an Open Call for testing end plates, but so far not that many manufacturers have joined the game.

Just the same, there are some really cool endplate designs we’ll be testing, with vents, 3D shapes, and other trickery. Even if endplates don’t make a huge difference, they are easy to change out and are visually interesting.

We may try the most radical end plates on two or three different cars, to see if there’s any difference. It’s worth checking out, but I kinda doubt it.

Raul’s BRZ will be the test bed for a few different wings including a PCI, MSHD, APR GTC200, and 9 Lives. I’m also trying to get my hands on a Verus high efficiency wing, and there’s a new nylon wing from Baero that might sneak into the tests if it can get through customs quickly. It has a familiar look, but with a lot more chord, and I have high expectations.

We have to fit many of those wings on the same trunk mounts, which is proving to be a bit of work making brackets. We also want to test wing location, and if setting the wing back a little further is better.

Raul doing the obligatory “is is strong enough?” test.

Raul’s car also has a splitter and so we plan to test splitter tunnels and some other front end stuff.

I’ll write up a report this summer, and probably jump on a podcast to talk about some of the results. Hopefully Kaan from the Blind Apex will come down to see some of testing firsthand, and we can recap that on his show with some special guests.

As usual I’m planning to rope AJ Hartman into participating, but also inviting Ido Waksman and Tim Miller, if their busy schedules permit. Michael Jui from Wing-Logic is also coming for the first day, and so it will be cool to finally meet him in person.

All said, it looks to be quite the party, and we are set to learn a whole bunch about our expectations, and that aero results are often not what you think. Subscribe to the blog if you haven’t already, you don’t want to miss the articles coming out of these tests!

Canards, also sometimes called dive planes or dive plates, are little winglets on the front bumper fascia. They are mysterious pieces of aero, because the shape, size, curvature, and mounting locations are all over the map. There’s no standardization at all. What they do depends on a combination of factors, and also who you ask.

I really like the explanation of dive planes on the Verus Engineering site: “Dive planes, also referred to as canards, allow you to shift the aero balance forward, possibly aiding you and your setup in balancing out a large rear wing or diffuser. Dive planes also help seal the sides of the car and help evacuate air from the wheel well, further reducing lift and drag in some cases.”

I love how much conjecture is in that description, and if you read between the lines, you’ll see that they might not help your car at all. I would sum it up like this: “Sometimes canards will make your car faster.”

The reason canards might make your car slower is because they are at the leading edge of the car, so they affect everything behind them. Airflow down the sides of the car, underbody, wake, and especially the rear wing could all be negatively affected.

Canards don’t have an airfoil shape, and so they create downforce through pressure, rather than suction. In Race Car Aerodynamics, Katz examines dive plates, and gives them a Cl of .03 and Cd of .01. That 3:1 lift/drag ratio is like a spoiler rather than a wing, which makes total sense all things considered.

You might use canards under the following circumstances.

If you have an older car that has the front tires exposed to airflow (Miata, etc), then canards can help deflect air away from the tires.
If you have a car with a flat bottom, canards may help seal the sides of the car via a vortex, which may help the underbody creates more downforce.
If you have a splitter and aren’t using spats or other tricks to extract air sideways, then canards can be beneficial when placed low on the bumper fascia. I’m going to dig into this one in more detail.

DIY canards

The Velsoter N bodywork has a lot of vents, swoops, and hard angles, so there aren’t a lot of options on the size of the canards, their shape, or where to mount them. Effectively, the bodywork itself dictates the dimension and locations of the canards.

The vents and bumper fascia elements make it difficult to mount canards. There were only three logical places to put them.

I made my canards out of aluminum street signs, which I get at the local recycler for cheap. I shaped them to fit the bumper fascia and curved them so they would fit where they would. All of the canards are identical in shape and curvature.

The top canard mounts just below the headlight. The headlight has a flat spot below and in front of it, and by putting a canard below that, I essentially increased the amount of planform area for free. (More area means more area for high pressure to form.)

Upper canard alone fits below the headlight and utilizes the extra planform area of the bodywork.

I placed another canard 5” lower than the top canard. It sits on top of the air curtain duct on each side of the car, so there’s no way to mount it any lower. I’ve several aero companies put their canards in this general location, so I figured it should work there.

The canards are duct taped on, because that works fine for wind tunnel testing.

I also placed one canard down on the bumper fascia as far as it would go. This was an audible call made by AJ Hartman during the wind tunnel test. I hadn’t planned to put a canard there, but I’m glad I did, the results were astounding. This is why you bring a professional with you to the wind tunnel!

Middle canard moved to the bottom position.

Test data

Recall that all of the canards are identical in size and shape, and so the primary thing I was testing was the location of the canards: top, middle, and bottom. It’s important to note that the car has a splitter and a wing, because canards will interact with both.

In the table below, front downforce is listed as a positive value, while rear downforce is negative. This is the normal see-saw effect of pushing down on one side of the car, the other goes up. But also, there may be some loss of rear wing downforce via turbulence from the canards. The Total downforce is obviously the two added together, and this is important when we look at Lbs of drag.

The next columns are drag, and if you divide the total downforce by the drag lbs, you get the L/D ratio, or how efficient the canard is. The top canard is the most efficient at 3.91:1. Finally the last column is HP, which is how much power is consumed by the canards at 100 mph.

	Downforce @ 100 mph			Drag
	Front	Rear	Total	Lbs	L/D	HP
No canards	0.01	0.05	-0.04	-0.04	0.89	0.04
Top only	15.18	-2.17	13.11	3.35	3.91	0.95
Mid only	11.13	-1.91	9.21	3.30	2.80	0.88
Top and mid	26.30	-4.08	22.32	6.64	3.36	1.82
Bottom only	85.61	-17.76	67.95	28.98	2.34	7.78
Top and bottom	100.79	-19.94	81.06	32.33	2.51	8.73

The top canard was the most efficient, probably because it’s mounted below the headlight where the extra planform area effectively adds to the canard’s surface area.

The middle canard has exactly the same drag as the top canard, but because it didn’t have the extra bodywork area to work with, it made less total downforce. The 2.8:1 L/D ratio is quite close to what Katz cites. When I look at canards from various manufacturers, they usually put them in about this location, but you can see it’s the least effective of all.

Using both the top and middle canard together was simply additive. Meaning, the data doesn’t show any effect of the canards working together to create more downforce than either one did individually. It makes me wonder why canards are usually mounted in pairs.

Take a look at that bottom canard, it made over 700% more downforce than the canard that was just 8″ above it. Drag also went up by a lot, but that’s an acceptable tradeoff for this much downforce.

Finally, I added the top and bottom canards together to combine the better L/D ratio of the top canard with the high downforce from the bottom. This gives just over 100 lbs of front downforce, and when matched with more rear downforce, would provide a lot more grip.

Discussion

I didn’t expect much out of canards, and I’ve often slagged them off as poseur junk. I was wrong about that. If AJ hadn’t prodded me to try the canard in the bottom position, I’d have missed some very useful information.

Canards aren’t an airfoil shape, and don’t create suction underneath like a wing does. The top surface is theoretically limited in the amount of downforce it can create via pressure to less than cL 1.0. But since the surface area of the canard and the angle of attack was identical in each position, then the canard itself can’t be making more downforce.

Suction is really the only way to explain a gain of this magnitude, and it’s not the canard that’s doing the heavy lifting, it’s the splitter. The canard must be extracting air from the wheel wells, and/or from the sides of the splitter, which is creating more suction under the splitter.

As a consequence of that, the bottom canard also makes so much more drag. Drag is a normal byproduct of downforce, but the canards in either of the other locations were much more efficient than the bottom.

One possible explanation is that when placed this low, the canard creates a much stronger vortex. Vortices take a lot of energy to spin up, and a bigger vortex makes more drag. Or perhaps it’s simply that canards are an inefficient way to create downforce, and drag increases at a higher rate than downforce? In any case, the location is obviously a very important factor in canard placement, and I’ve only played with one variable at this point, height.

Sometimes you see a canard with end plates, or a vertical outer edge. That kind of thing might help a canard create more local downforce, because it should hold more pressure on top of the blade. But this may not be ideal for the lowest canard, as the whole point of that one is to spin a vortex off the outer edge and suck air out from below the car. Or it might work better. Further testing is required.

It’s worth noting that you shouldn’t apply these downforce numbers directly to your car, unless you have a Veloster N with the same splitter and wing. If I’ve learned anything from this test, it’s that canards are finicky. About the only thing you can conclude from this test data is that height matters. And that’s only one variable that’s been isolated, with angle of attack, size, shape, fore-aft location, and wicker edge yet to be determined.

Before I sign off on this one, I’d like to go back to my statement that “Sometimes canards will make your car faster.” AJ recently stated in the Professional Awesome Technical Forum that canards have improved the L/D ratio of every car he’s tested in the wind tunnel. Well this is because he’s a professional aerodynamicist! He knows where to place canards, and what angle to run them at. The average aero enthusiasts buying appearance-grade canards and placing them where they look cool is a performance crap shoot. Good luck with that.

If you enjoyed reading this article, check out my wind tunnel report. It’s over 50 pages of similar data, but goes over many more pieces of aero, and to a much greater depth.

Tag: canards

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