What is more aerodynamic: a wider body or bulging fenders/fender flares?

[botsapper]

My kids drive F1 aerodynamics guru Adrain Newey's Red Bull X2010 for hours. His valuable championship knowledge and real-life practical experience unleashed him on a 'no rules' prototype. His creativity came to 'life' in Gran Turismo 5. The design encloses the driver on a narrow covered-fuselage, and covered the wheels. Sucker fans & active wings gives it ultimate low-speed traction and as well as low drag top speeds...in the virtual world! At least the ideas are intriguing.
Red Bull X2010 S. Vettel - Hangar-7

...and the ubiquitous aero template was made in 1937! SIA Flashback – The Arrowhead Teardrop Car | Hemmings Blog: Classic and collectible cars and parts

[aerohead]

Originally Posted by 3-Wheeler

Hi Aerohead,

OK, I am going to ask a nit-picky question here....

So a car with wide spaced wheels and thus covered with an appropriately wide body will, for it's resultant frontal area, have a lower Cd.

So far so good.

However, the counter response to this is....

Make an appropriately sized 1) "cigar-shaped-fuselage" and cover the vehicle occupant, and 2) make proper sized airfoils for the appendages hanging outside the main fuselage, such as wishbone suspension members and wheels/tires.

I would think that this second vehicle, while having a higher Cd overall, would also possess a lower frontal area, and thus come away with an overall lower aero drag component than the "one-piece-body" shape.

Now my "discussion" above makes the assumption that this "body shape" is optimized for a single occupant, who is also the driver of the vehicle. I am not talking about the "new" VW 1L that has side-by-side seating and thus forces a wider body shape to the wind.

The width of the cigar body is, let's see, about 27 inches wide.... I had to measure the one that's in the basement right now....

I simply can not imagine how a car with a track width of let's say 60 inches, and a body that also is wide enough to cover this same width, and has a Cd of let's say 0.10 is going to ultimately have a lower overall drag component than a cigar shaped body with width of 27 inches and all external appendages covered with airfoils, with a Cd of let's say 0.15??

It may be that our responses to the main question above need to be qualified a little better to avoid over-simplifying the answer.

Just my opinion.

Jim.

Jim,it's a good question.And I don't have a vast library to draw upon.
Mercedes did publish in the 1950s that when they enclosed their Gran Prix racer,even though the frontal area jumped,the overall drag factor (CdA) went down.
When So Cal Speed Shop wanted top performance,they enclosed their So Cal belly tank lakester inside a fully-enclosed streamliner body of greater frontal area.The car wrecked at Daytona Beach and was never raced again so we don't have a lot of numbers there.
GM's Firebird-1 scored a very mediocre Cd with it's rocket-ship,open-wheeled styling.Typical SUVs today have lower drag.
The 1987 OLDS AEROTECH started life as a March INDYCAR of approx.Cd 1.20.When they lost the wings the drag dropped to around Cd 0.57.Without wheels these bodies are Cd 0.25.By enclosing the car inside the long-tail AEROTECH body,the drag drops to Cd 0.19.
Matt Llewelyns(sp?) Sylph,which registered Cd 0.11( I think Michael Hackleman reported it even lower) in the Guggenheim tunnel at Cal Tech in model form would be an example of a 'lakester'-type form of low drag and frontal area.So your logic is dead on!
The thing for me is to look beyond the MPG euphoria Hucho warns about and consider safety,
Virtually every fatal auto accident I've ever witnessed involved side impact.
Without an enclosing side body,there is virtually zero crumple-zone to absorb kinetic energy of an impact and even with side-curtain airbags you can still sever the brain stem.
I thought about this with my mini-hypercar and elected to go with a fully-enclosed body with ample side pod protection.
I really like open wheel design,it's just that I can't trust Barbie and Ken to drive defensively.
So it's a safety prejudice I get trapped in.
The 'pumpkin seed' body might deliver only Cd 0.11,maybe better.That seems like a decent compromise for safety sake.

[3-Wheeler]

Originally Posted by aerohead

....The thing for me is to look beyond the MPG euphoria Hucho warns about and consider safety....

Hi Aerohead,

Your argument about safety is well taken! This is something I think about as well in a well streamlined body shape.

However, anyone who rides a motorcycle is exactly in the same situation. I have a motorcycle license and have ridden motorcycles for years.

To add to this "safety" discussion, a man in a large SUV *thought* he was safe by virtue of this large vehicle, until a motorcycle coming the opposite way lost control, did a classic "high side", the motorcycle flipped high into the air, and went right through the SUV windshield, taking the roof off the SUV with predictable results to the driver.

Two months ago, I was on the way home and saw, what remained of a small compact car after a truck driver pulled out in front of the small car. The truck driver was shaken, but OK, and the small car driver, who hit the truck head-on was killed, even though air bags and such were involved in the new car.

Such is life! We have no guarantee's and yet I still ride a motorcycle and drive an extremely small Honda Insight. No, when it's my time, I will go peacefully with no regrets.

I am only slightly more concerned driving a narrow three wheel motorcycle on our roads.

Jim.

[jime57]

Well said 3-Wheeler. Anyone who goes for the adventurous side always make this choice. Something interesting or lots of sofa time. My sofas last a long, long time;-)

[Shepherd777]

Originally Posted by aerohead

Mercedes did publish in the 1950s that when they enclosed their Gran Prix racer,even though the frontal area jumped,the overall drag factor (CdA) went down.

When So Cal Speed Shop wanted top performance,they enclosed their So Cal belly tank lakester inside a fully-enclosed streamliner body of greater frontal area.

I completely agree. This is why I designed my aero semi truck this way. Here is a quote from my web site:

One can see by these fiberglass pics that the rig does not have the traditional look of a other class 8 rigs. Other Class 8 rigs slope-in the hood starting at the firewall under the "A" pillars. Then they highly swoop the wheel wells over the tires and then drop-off the swoop in front of the doors. This "old-school" automotive design is based on 70-80 year old automotive theories and mind-sets.

One of the best examples of those old-fashioned designs is shown by the pic below on the left of a 1941 Willys. Obviously, contemporary Class 8 trucks don't have the pointy nose like the Willys. They just cut-off the point of the hood and have that big, dumb, square diesel truck radiator as part of the body! At least back in 1941 they got it right and placed the radiator inside that pointy nose. They ducted the radiator engine cooling air through that lower horizontal lower body grill. So all other modern Class 8 trucks took the best part of the 1941 Willys design and destroyed it, by cutting off the pointy, aerodynamic front end, and exposed those big, dumb, square radiators.

This rig is based-upon the more modern 21st. century design of a Bullet Train. After all, if you were building a new design Class 8 rig, and you wanted superior aerodynamics and fuel savings, what would you base your design upon? A 70- 80 year old design, or a 21st. century design that travels up to 350mph on a bullet train???

[3-Wheeler]

Originally Posted by Shepherd777

I completely agree. This is why I designed my aero semi truck this way. Here is a quote from my web site:

One can see by these fiberglass pics that the rig does not have the traditional look of a other class 8 rigs. Other Class 8 rigs slope-in the hood starting at the firewall under the "A" pillars. Then they highly swoop the wheel wells over the tires and then drop-off the swoop in front of the doors. This "old-school" automotive design is based on 70-80 year old automotive theories and mind-sets.

One of the best examples of those old-fashioned designs is shown by the pic below on the left of a 1941 Willys. Obviously, contemporary Class 8 trucks don't have the pointy nose like the Willys. They just cut-off the point of the hood and have that big, dumb, square diesel truck radiator as part of the body! At least back in 1941 they got it right and placed the radiator inside that pointy nose. They ducted the radiator engine cooling air through that lower horizontal lower body grill. So all other modern Class 8 trucks took the best part of the 1941 Willys design and destroyed it, by cutting off the pointy, aerodynamic front end, and exposed those big, dumb, square radiators.

This rig is based-upon the more modern 21st. century design of a Bullet Train. After all, if you were building a new design Class 8 rig, and you wanted superior aerodynamics and fuel savings, what would you base your design upon? A 70- 80 year old design, or a 21st. century design that travels up to 350mph on a bullet train???

Hi,

I'm going to throw something into the mix that is not so obvious....

"If we go to an extreme with the mentality of covering protruding wheels from our vehicles at any cost, then we should do the same thing with airplanes currently sitting at the airport".

Discussion:

1) Let's look at an airplane with a tadpole configuration..... The wheels are mounted about 3 feet from the bottom of the fuselage and without any covering, breaking a fair amount of wind. Let's further say that this amount of air drag needs to be dealt with.

a) Do we make small pants to cover the wheels?

b) Or do we (now get this), extend the bodywork all the way down to cover most of the wheels, and resultantly make the fuselage longer to accommodate the huge rise in cross-section? Note: we are not even addressing the weight gain and increase in skin friction from doing this!

The above conversation is an extreme point, but something that is being missed in this entire thread.

At what point do you simply add "pants" to exposed wheels/tires, or make the entire structure of the body shape larger to accommodate the protrusions?

I think there IS a rule-of-thumb for this effect, but no one has addressed it yet.

My three-wheeler, with a primary body with of 27 inches, and tires that stick out to the sides, at 60 inches, I believe is beyond the threshold of expanding the body shape to accommodate these "extensions". And I have already provided some basic math that shows this point fairly well.

The airplane example above is also in this same realm. No one would think to extend the bodywork to cover wheels...... wheels that extend away from the main shape that far.

I agree that as the main body shape is made larger relative to the track width, at some point it makes more sense to extend the bodywork to cover the leading tires. And when we look at the "bullet" train shown above, it makes perfect sense to cover the wheels with the body shape, since the body shape is already the same width (or wider) as the track width. This makes sense because it's so obvious!

No, a rule of rule-of-thumb for this breakpoint would be helpful to all who are eager to read topics such as this one!

But I don't think that a body shape that is fully, one-half the width of the tire tracks is at this point. Can we be a little more scientific than just "speculating"? Let's see some math or at least some nice pictorials showing why your design merits "automatically" covering the wheels with a body shape.

Developing a rule-of-thumb for anyone designing road going vehicles with different body-width to track-width ratio's would be very helpful.



Another consideration is what happens to the clearance between the main body and wheel pant, when the wheel is turned 30°, as in the example below... It appears that if a very streamlined pant is utilized, then either the wheel needs to be moved out, OR the body needs to be narrower. If this is not possible, then truncating the pants may need to be improvised.

It's obvious that if the body is another couple inches wider per side, there may be no option but to make the entire structure the same width as the tires, unless someone has other ideas....



Yet another option is keeping the pant "secured" (non-rotatable) and making cutouts for the wheel to make turns, similar to the front wheels on most cars. Obviously higher drag, but still gives the option of not having to drastically increase frontal area to cover the wheels, with much longer body shape as well. Slightly less unspring mass too.



Another way to allow getting the outboard wheel closer to the main body is to allow the rear of the wheel pant to pivot as shown below.... Just an idea, but could be useful.



Rule of Thumb:

3-Wheeler Design ----------
Track Body - Ratio Wheel -- Math
Width Width ------ Pants
-60 --- 27 - 0.45 -- Yes -- Post #22 and CAD Dwg

Bullet Train (estimated) ----
Track Body - Ratio Wheel -- Math
Width Width ------ Pants
-48 --- 80 - 1.67 -- No -- See picture above

Jim.

[drmiller100]

>>>>Developing a rule-of-thumb for anyone designing road going vehicles with different body-width to track-width ratio's would be very helpful.

I agree. My build is 60 inch outside/outside, with the body 36 inches wide. Therefore, the fenders add 12 inches on each side - obviously NOT worth putting separate fenders on.

At some point, there is a break even point. My guess is the break even point is the distance between the tires and main body.

Your car OBVIOUSLY needs separate fenders.

[Shepherd777]

My aero rig tractor is 100" wide on the outside of the steering tires, 86" wide behind the steering tires at the firewall, and the skirts over the drive tires are 102" wide. Talk about your typical Corvette coke-bottle look! From a plan view, anyways.

I supposed I coulda made it pointy in front and put wheel pants over the steering tires, but I figured the bullet train configuration would be more appropriate. And it woulda looked like an 80,000 lb. Plymouth Prowler the other way. Which is not too bad come to think of it, as I love how the Prowler looks.



So what makes perfect sense in the configuration of 3-Wheeler's rig, would not make sense in someone else's Ecomodder rig.

One size does not fit all, in this case.

[3-Wheeler]

Originally Posted by Shepherd777

....So what makes perfect sense in the configuration of 3-Wheeler's rig, would not make sense in someone else's Ecomodder rig.

One size does not fit all, in this case.....

Ah, so now we're getting somewhere!!!!

You hit the nail on the head!!!! (smile)

When this thread was first started, there was a "cookie cutter" statement made that basically said, "just make the body width the same as the tires and you'll be at your optimum".

Well, this may be the case in certain situations, but as we have seen, there ARE circumstances that differ from this, and that is why I tried so hard to make a point of it.

Shepard, you just summed up this thread better than I could while using many more words. Thanks.

Jim.

[aerohead]

Originally Posted by 3-Wheeler

Hi Aerohead,

Your argument about safety is well taken! This is something I think about as well in a well streamlined body shape.

However, anyone who rides a motorcycle is exactly in the same situation. I have a motorcycle license and have ridden motorcycles for years.

To add to this "safety" discussion, a man in a large SUV *thought* he was safe by virtue of this large vehicle, until a motorcycle coming the opposite way lost control, did a classic "high side", the motorcycle flipped high into the air, and went right through the SUV windshield, taking the roof off the SUV with predictable results to the driver.

Two months ago, I was on the way home and saw, what remained of a small compact car after a truck driver pulled out in front of the small car. The truck driver was shaken, but OK, and the small car driver, who hit the truck head-on was killed, even though air bags and such were involved in the new car.

Such is life! We have no guarantee's and yet I still ride a motorcycle and drive an extremely small Honda Insight. No, when it's my time, I will go peacefully with no regrets.

I am only slightly more concerned driving a narrow three wheel motorcycle on our roads.

Jim.

I myself am okay with whatever transpires.I made it through combat and everything beyond that is overtime.
I'll be taking calculated risks and will have to be satisfied with what is.
If you're going for something like Matt Van Leeuwen's 'Sylph',this would be something I'd have no issues with.
'just want everyone to understand the risks they face.