Aerodynamics

The blue X with the giant red wing was cute. As silly as the snorkel is that wing would be a bit much for street use.
 
carl said:
that wing would be a bit much for street use
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The other day I was out running errands and saw a young kid driving a stockish Honda with a ginormous rear wing mounted on the trunk. So big it stuck out by at least 6" on each side, and it sat well above the roof line. And not just any wing, but one with a bunch of very garish "styling" added to the upright mounts, end plates, etc. I had to laugh, but I shouldn't have - I was young once too. Thankfully they did not sell stuff like that back then.
 
I saw a article about a time attack car that was built for a series allowing pretty much anything done to the cars. A team of various engineers got together to build it with a goal of setting the all time fastest laps. It looks a lot like the hill climb car posted earlier, with huge wings and tons of aero. But in this case all of the aero was designed by a F1 aero engineer, and it has been fully tested and refined. So it actually works despite looking like a comic book car.

Here is a pic:
I00000Aak4RTykbI.jpg


Some interesting specs:
Total weight fully loaded plus driver is about 2600 lbs.
Power is almost 1200 HP to the rear wheels (from a 4 cyl "VW" engine).
Front engine, rear wheel drive based on a 968 Porsche tub.
More than half of the total downforce is generated by the floor and rear diffuser (55% if I recall). The rear wing is another 25%. And the front wing, etc make up the rest (20%). I never would have guessed those percentages.
They gave some of the other aero data from their testing, but I don't recall the details.
 
Dr.Jeff said:
I saw a article about a time attack car that was built for a series allowing pretty much anything done to the cars. A team of various engineers got together to build it with a goal of setting the all time fastest laps. It looks a lot like the hill climb car posted earlier, with huge wings and tons of aero. But in this case all of the aero was designed by a F1 aero engineer, and it has been fully tested and refined. So it actually works despite looking like a comic book car.

Here is a pic:
View attachment 29387

Some interesting specs:
Total weight fully loaded plus driver is about 2600 lbs.
Power is almost 1200 HP to the rear wheels (from a 4 cyl "VW" engine).
Front engine, rear wheel drive based on a 968 Porsche tub.
More than half of the total downforce is generated by the floor and rear diffuser (55% if I recall). The rear wing is another 25%. And the front wing, etc make up the rest (20%). I never would have guessed those percentages.
They gave some of the other aero data from their testing, but I don't recall the details.
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Note that the front splitter/spoiler/tray (whatever) forces air under the car.
 
gene cooley said:
Note that the front splitter/spoiler/tray (whatever) forces air under the car.
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I've been noticing several race cars with large front splitters that seem to angle up slightly like that. I wasn't sure the reason, but wondered if it was needed to keep the leading edge from biting into the tarmac. :D
However it's likely a part of the undertray aero? The article had some discussion about the car's bottom...apparently that was a huge aspect. Note how the side rockers extend out to be part of that.

Then the rear diffuser is also worked into the floor. Here is a rear view:
gallery-1468431435-968timeattackrear.jpg


The development of the complete aero package started with super computer computations in CFD. Then models for testing. Back to the CFD, more tests, etc. After the third complete redesign they finally made a full size and began testing that. I believe they said it has been a three year process just for the aero.
 
Great video. ;)
The open discussion reminds me of conversations you can get at some of the industry trade shows; you'll meet top experts like him at those shows and can engage in asking questions with extremely knowledgeable answers/explanations. Very informative, even if I don't always follow all of it 100%. :oops:
Especially in this case, I had difficulty understanding some of what was said simply due to their accents and the audio quality/background noise. But it is clear that he really knows his stuff, and the details of small nuances in aero design are amazing. :cool:
 
I saw another interesting item on the subject of aerodynamics. The car maker Koenigsegg is known for making cars that go very fast. Top speed seems to be a focus for them, so aerodynamics is certainly a speciality of theirs. The latest in their designs is intended to be the fastest car they will ever produce, supposedly capable of exceeding 300 MPH! And that's a street car (technically).

But the interesting part is they have designed two versions of it; one for maximum top speed (low drag coefficient), and one for track use where top speed has to be compromised for the sake of cornering capabilities (high downforce). So they will offer it with or without the wings, splitters, louvers, etc, to make the difference. Those changes result in the track version having over 3000 pounds of downforce, while the speed version has only 330 pounds at best. That is a HUGE difference.

Koenigsegg_Jesko_2_Together(1).jpg
Koenigsegg_Jesko_2_Together(2).jpg
 
How bad it would be fron aspectvof aerodynamics if rear bonnet (one piece) would be made of some kind of mesh?
examples in photo
8B09B253-9BDD-46D8-89A2-6C0F9541DBCA.jpeg
38CB8693-1CE0-42AF-9D4F-AC23B4AFEDA3.jpeg
 
From what I understand, the smoother a surface is the better the air flows over it. But in this case there are LOTS of other variables at play, so no idea. It might also matter what the surface under the rear section is like (i.e. a flat sheet there too).

However the open mesh cover will allow a LOT more hot air out of the whole rear section of the car. To me that would be a bigger benefit than any small loss of aero might be. There are some factory "supercars" with mesh engine covers to allow heat escape. I imagine they found it was worth any tradeoffs.
 
I have met Steve and seen his work. He's very good. He is spot on about the 'systems' aspect of aero. When the average person looks at an aerodynamic device they normally think of what it does in terms of downforce, when its individual function might be air management downstream. The dive planes you see on the front corners of some racecars are typical. I see lots of racers add these to their cars thinking they produce additional downforce. And they do to some extent. These date back to the 1960s when they were used to prevent front end lift on GT40s (and other cars). Today, on serious racecars (Prototypes and GT3s and 4s) they are employed to control airflow over the front wheel opening. Their purpose is to create negative pressure at the front wheel opening to draw air out from the brake ducts and from under the front splitter. Those little dive planes provide a small amount of downforce but contribute significantly to the efficiency of the front splitter.

Another glaring example is the defusers you see under the rear of many cars. These create little downforce by themselves but their actual function is to draw air from under the floor of the car increasing the Bernoulli Effect. Thus without a splitter and full belly pan the defuser does little to nothing. Also, considering the systems aspect of aero, the rear wing can help the efficiency of the defuser and the defuser the efficiency of the rear wing.
 
This is an interesting topic but odd in view of the fact that our Xs are horsepower deficient. 100 pounds of downforce would probably pull my X to a stop!
Steve makes the best point, it's all about the total effect. I wonder how an F1 car would handle if there was a total ban on aero on them. Would they go back to the cigar shape of the 60s?
 
Dan Sarandrea (Phila) said:
Wow, haven't heard that name in AGES! I remember these: https://www.techopedia.com/definition/2155/bernoulli-disk-drive It's the big one in the pic below.
Bernoulli_Cartridge.jpg
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HAHAHAHA!!!

You have no idea. :D

In my first career out of school (I am on my 3rd for those counting) I was partner in a company that sold tech products into both the defense industry and commercial industry. We were one of first companies to sell the original Bernoulli drives. And yes, I still have a hard time separating the two.
 
I have done some crude testing by filming a number of strings taped on one end on the engine cover and rear trunk cover and left to move freely on the other end. The intent was to "see" airflow off the back edge of the roof and over the rear end of the car. At over 120 km/h, ALL the strings were either flying vertically or pointing toward the FRONT of the car, indicating strong turbulence and airflow curving back and pointing towards the rear glass, just as it does on most convertibles. Unless I am mistaken, this is drag, which is theoretically harmful. But this also indicates that air is moving upward from the engine compartment, which is good for cooling. My question is: what is the use of the ducktail if very little airflow seems to be going over it? Would a roof deflector à-la-Stratos be useful in "bending" the airflow downwards over the rear end of the car?
 
More important: How fast do you need to be going to make any use of all this superstructure?
 
The thing you need to understand about automotive aerodynamics from a downforce/lift perspective is that they don't do much under 100 mph... Not much use on a street driven car... I'm sure there are gains to be had as far as cooling/airflow goes, but most factory add-on aero just causes drag....
A ducktail is somewhat effective on a coupe/fastback shape. On a car like an X/19, with a sharp roof/ rear window transition, that air is nowhere near that ducktail. Most effective wings are large and high enough to be in the 'clean' air, over any turbulence from the edge of the roof...
 
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I agree with the turbulence theory over the trunk lid, here is a still pic from a video I took at 120kph of short wool threads taped to the lid and the edge of the engine cover of my track X to test a small boot lip spoiler. The threads moved around a bit, but quite often pointed forward rather than backward. I then did similar tests with a higher spoiler with string on higher posts. It looked like it may be a bit more effective, but still of doubtful benefit. I did go ahead and
Snapshot - 25.png
Snapshot - 35.png
fit a spoiler mainly just for looks, as expected, it has made no difference to track times.
 

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