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

[drmiller100]

Originally Posted by 3-Wheeler

Hi Aerohead,


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.

hmmmm...... My thread about 100mpg car has a link to some pics.

my front outside width is 60 inches. Body is 32 at bottom, 38 in middle, 18 at top.

I am in the same boat as you and wondering what is the "right" thing to do. For now, I'm doing a traditional car style nose, but it will be a bit short to really get enough fairing outside the fuselage.

[jime57]

Originally Posted by drmiller100

hmmmm...... My thread about 100mpg car has a link to some pics.

And where is that thread? I can't seem to turn it up.

[drmiller100]

ecomodding central forum.
skip to last page and look for link to pics.

[jime57]

Found the pictures! IMO, with all those suspension parts handing out in the wind, you are definitely gonna need fenders all way out to tire outter edge. all those shocks, control arms, half shafts, etc. are an aero mess. Only thing you can do at this stage is to cover it all.

There were options, at one point, to do the front suspension differently, but with much more cost. On modern formula type race cars, the shocks and springs are internal to the central body and the load is transferred from the hub to the spring by a load rod and some bellcrank arrangement. And, as 3wheeler kinda intimated, the control arms themselves are streamlined. I think it is too late for that though, and not in keeping with the cost of your project. Interesting project!

[3-Wheeler]

Originally Posted by jimepting

.....On modern formula type race cars, the shocks and springs are internal to the central body and the load is transferred from the hub to the spring by a load rod and some bellcrank arrangement. And, as 3wheeler kinda intimated, the control arms themselves are streamlined.......

Yes Jim, you hit my example on the head!

To really make the cigar shaped body work, it has to be very narrow, similar to an Indy car, and all those appendages hanging in the breeze have to be in the form of airfoil shaped A-arms, with inboard shocks, and the wheels/tires with nicely done airfoils as well.

Once shocks and other members start going out there, well, you might as well just make the entire body shape cover the wheels as Aerohead suggested, but as Jim mentioned, the CdA will likely go up over something similar to an Indy car with skinny tires.

Jim.

[TEiN]

I think the bit that you guys may be missing is that given the choice, a clean-slate design, with the ability to choose an open-wheel design or a closed wheel design (when it comes to the race cars that you're using for examples), the open wheel design is *always* higher drag. It may be because of the necessarily wide tires hanging out there in the breeze (which may be mitigated somewhat on a low-drag eco-modder design with skinny wheels and tires), but open-wheeled raced cars have MUCH higher drag than their (all-other-things-being-equal) closed-wheel counterparts. Compare for example, Formula Atlantics with their closed wheel counterparts, C-Sports Racers. CSR's are much lower drag.

[Ragnarok Warrior]

It is hard to compare drag coefficients of race cars given their inherent purpose (handling vs. speed) because of the body parts that are their for downforce. I just read a book last week on Formula 1 design. Over the years the cars have changed because of the designer's schools of thought and partly because of the rule changes.

The OP was asking about one specific body design, assuming that the full body was already chosen. I would guess that unless you could design the fender flares to serve an aerodynamic purpose, such as directing the flow of air to where it is needed (the Nissan Leaf's headlights direct air around the side mirrors for instance) than a widebody would be the answer simply because of it's lack of protrusions, plus this would give you a bit more room to taper the front nose as well.

[jime57]

Originally Posted by TEiN

I think the bit that you guys may be missing is that given the choice, a clean-slate design, with the ability to choose an open-wheel design or a closed wheel design (when it comes to the race cars that you're using for examples), the open wheel design is *always* higher drag. It may be because of the necessarily wide tires hanging out there in the breeze (which may be mitigated somewhat on a low-drag eco-modder design with skinny wheels and tires), but open-wheeled raced cars have MUCH higher drag than their (all-other-things-being-equal) closed-wheel counterparts. Compare for example, Formula Atlantics with their closed wheel counterparts, C-Sports Racers. CSR's are much lower drag.

I really didn't miss the point, I was just commenting on where the guy stands right now since he seemed ready to take the next step. Though I don't have the actual CdA numbers at hand for a CSR vs say a Formula Ford, being somewhat similar in power and speed, I suspect that your conclusion is correct. Do you have any actual CdA numbers?

OBTW, even this example probably doesn't shed as much light as one would would hope because the wheels on Formula Fords, as most open wheelers, have no fairings.

[Big time]

Originally Posted by Ragnarok Warrior

I would guess that unless you could design the fender flares to serve an aerodynamic purpose, such as directing the flow of air to where it is needed (the Nissan Leaf's headlights direct air around the side mirrors for instance) than a widebody would be the answer simply because of it's lack of protrusions, plus this would give you a bit more room to taper the front nose as well.

So I thought.
But coke bottles look SO good.
Maybe the drag penalty for coke bottles isn't that bad after all?

[TEiN]

Originally Posted by jimepting

I really didn't miss the point, I was just commenting on where the guy stands right now since he seemed ready to take the next step. Though I don't have the actual CdA numbers at hand for a CSR vs say a Formula Ford, being somewhat similar in power and speed, I suspect that your conclusion is correct. Do you have any actual CdA numbers?

OBTW, even this example probably doesn't shed as much light as one would would hope because the wheels on Formula Fords, as most open wheelers, have no fairings.

Hey Jim,

My apologies: I didn't intend to infer you were missing "the point", just a bit of info that might not have been considered.

I don't have the CdA numbers... thought I could find them but after a few hours of searching, came up empty. I know that I had them a few years ago.

Also, the reason I chose CSR vs FA instead of CSR vs FF is because:
1) C-Sports Racers and Formula Atlantics are both high-downforce cars;
2) Formula Fords are non-downforce cars;
3) Many CSR's are converted from FA and the only real difference is open- vs closed bodywork;
4) CSR's and FA have very similar lap times;
5) Formula Fords are much slower.

At this year's SCCA National Runoffs, both CSR and FA fastest laps where right at 2 minutes flat, whereas the fastest Formula Fords were approximately 20 seconds per lap slower (i.e., "an eternity").