Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 01-05-2012, 02:30 PM   #21 (permalink)
Master EcoModder
 
Join Date: Oct 2008
Location: Mid-Atlantic
Posts: 491

OurInsight - '06 Honda Insight
Thanks: 170
Thanked 69 Times in 44 Posts
Quote:
Originally Posted by TEiN View Post
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").
No offense taken

I had a thought. Both the Aptera folks, and the University of ??? team that won the X-prize both apparently had strong thoughts that seperate body and wheel fairings was a more aerodynamic way to go, since they built to that plan.

To me it seems a little misleading to compare really good aero stuff, like CSR, to any open wheel car. The open wheelers without the wheel fairings are going to be a lot worse than the same vehicle with good fairings. So, I'm not sure that this is a productive line of reasoning.

I also did some searching for CdA numbers and came up empty handed for time being.

Interesting

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 01-05-2012, 02:32 PM   #22 (permalink)
Master EcoModder
 
3-Wheeler's Avatar
 
Join Date: Dec 2008
Location: Southern WI
Posts: 827

AlienMobile - '00 Honda Insight
Team Honda
90 day: 80.05 mpg (US)
Thanks: 94
Thanked 558 Times in 191 Posts
Quote:
Originally Posted by TEiN View Post
....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.....
TEiN,

Did you miss the spot in the middle of post #15 where I mentioned using airfoils to cover the skinny tires/wheels?

I still think the CdA of a cigar shaped body with properly done "exposed and airfoiled" wheels is lower than widening the entire bodywork to match.

I guess my mistake was mentioning the word "Indy" car in my statement above. We jump to the conclusion of downforce and so on. Not my intent here. Remember, we are looking for maximal aero efficiency.

No, the only point in referencing an Indy car is that the fuselage is "cigar shaped", but obviously we are more concerned with a "round at the front" and a "tapered tail" in the design of our fuselage shape.

Let me point out some quick math: Let's calculate the CdA of two prototypes.

Fenders covering wheels, and at 60" width
Assuming the height of our vehicle is 36 inches, then the frontal area is 15 sqft
Optimum body shape Cd = 0.10
CdA = 1.5

Cigar Shaped Body with Airfoiled Wheels
Assuming cigar body width of 27" and height of 36 inches, then frontal area of body is 6.75 sqft
Airfoils over wheels are 12" wide by 24" high; frontal area is 2 sqft x 2 wheels = 4 sqft
Optimum body shape Cd = 0.10
CdA of body .675
CdA of wheels 0.4

So far the exposed wheel vehicle has a lower CdA... However, this only applies to a cigar body width of 27". You're mileage may vary.

There will be an interaction between the cigar body and faired wheels, so let's subtract something for this... make the CdA 10% bigger to accomodate CdA = 1.18

Also, air compression under the wider vehicle will also take it's toll, so can it be fair to add %5 to it's CdA, due to this effect?

The overall length of the 60" body shape will need to be longer to still reach a Cd of 0.10, so this vehicle design will need to consider this....

To me the cigar shape with faired wheels comes out ahead of the enclosed wheeled vehicle, just based on the math above..... Less frontal area, and shorter overall length for same Cd.

Jim.

Last edited by 3-Wheeler; 01-05-2012 at 03:00 PM..
  Reply With Quote
Old 01-05-2012, 06:08 PM   #23 (permalink)
Master EcoModder
 
Join Date: Oct 2008
Location: Mid-Atlantic
Posts: 491

OurInsight - '06 Honda Insight
Thanks: 170
Thanked 69 Times in 44 Posts
A great starting place for a new design might be a late model Formula Ford, with all the inboard springs/shocks and streamlined suspension arms. Fairings to the front wheels wouldn,t be much of a challenge. Then one could chop off the body and frame just behind the driver and convert the rear to some sort of rear single wheel drive. It might even be possible to add a tandem seat and a canopy.

An engine/drive train doesn't immediately come to mind, but the whole thing might work with a good 125cc motorcycle setup.

I believe that Formula Fords are required to have mild steel tube frames, so fabrication wouldn't be all that difficult.

The advantages of a "3-Wheeler" is that one can then register it as a motorcycle - in some states at least. Is that where the screen name came from
  Reply With Quote
Old 01-05-2012, 09:44 PM   #24 (permalink)
Not wearing pants
 
Join Date: Jun 2008
Location: GP, Oregon
Posts: 60
Thanks: 223
Thanked 6 Times in 5 Posts
Quote:
Originally Posted by 3-Wheeler View Post
TEiN,

Did you miss the spot in the middle of post #15 where I mentioned using airfoils to cover the skinny tires/wheels?

I still think the CdA of a cigar shaped body with properly done "exposed and airfoiled" wheels is lower than widening the entire bodywork to match.

I guess my mistake was mentioning the word "Indy" car in my statement above. We jump to the conclusion of downforce and so on. Not my intent here. Remember, we are looking for maximal aero efficiency.

No, the only point in referencing an Indy car is that the fuselage is "cigar shaped", but obviously we are more concerned with a "round at the front" and a "tapered tail" in the design of our fuselage shape.

Let me point out some quick math: Let's calculate the CdA of two prototypes.

Fenders covering wheels, and at 60" width
Assuming the height of our vehicle is 36 inches, then the frontal area is 15 sqft
Optimum body shape Cd = 0.10
CdA = 1.5

Cigar Shaped Body with Airfoiled Wheels
Assuming cigar body width of 27" and height of 36 inches, then frontal area of body is 6.75 sqft
Airfoils over wheels are 12" wide by 24" high; frontal area is 2 sqft x 2 wheels = 4 sqft
Optimum body shape Cd = 0.10
CdA of body .675
CdA of wheels 0.4

So far the exposed wheel vehicle has a lower CdA... However, this only applies to a cigar body width of 27". You're mileage may vary.

There will be an interaction between the cigar body and faired wheels, so let's subtract something for this... make the CdA 10% bigger to accomodate CdA = 1.18

Also, air compression under the wider vehicle will also take it's toll, so can it be fair to add %5 to it's CdA, due to this effect?

The overall length of the 60" body shape will need to be longer to still reach a Cd of 0.10, so this vehicle design will need to consider this....

To me the cigar shape with faired wheels comes out ahead of the enclosed wheeled vehicle, just based on the math above..... Less frontal area, and shorter overall length for same Cd.

Jim.

I missed it...

The suspension and half-shafts contribute zero?
  Reply With Quote
Old 01-05-2012, 10:01 PM   #25 (permalink)
Master EcoModder
 
3-Wheeler's Avatar
 
Join Date: Dec 2008
Location: Southern WI
Posts: 827

AlienMobile - '00 Honda Insight
Team Honda
90 day: 80.05 mpg (US)
Thanks: 94
Thanked 558 Times in 191 Posts
Quote:
Originally Posted by jimepting View Post
A great starting place for a new design might be a late model Formula Ford, with all the inboard springs/shocks and streamlined suspension arms. Fairings to the front wheels would'nt be much of a challenge. Then one could chop off the body and frame just behind the driver and convert the rear to some sort of rear single wheel drive. It might even be possible to add a tandem seat and a canopy.
That's why I liked the original VW 1L so much.... The tandem seating keeps the body width to a minimum and the length of the overall shape is utilized.

Quote:
Originally Posted by jimepting View Post
An engine/drive train doesn't immediately come to mind, but the whole thing might work with a good 125cc motorcycle setup. I believe that Formula Fords are required to have mild steel tube frames, so fabrication wouldn't be all that difficult.
Wisconsin state regulations for frame materials mandates steel construction. No fiberglass or carbon fiber that I know of.

Quote:
Originally Posted by jimepting View Post
The advantages of a "3-Wheeler" is that one can then register it as a motorcycle - in some states at least. Is that where the screen name came from
Yes, a three-wheel vehicle is known as a class #2 motorcycle here in Wisconsin. The requirements to get the vehicle road legal is that all salvaged items should be requisitioned from DOT road going vehicles. And no, ATV's are not considered a legal source of parts. I've had numerous discussions with my state inspector regarding this.

My handle is indeed based on the tadpole configuration.

Jim.

Last edited by 3-Wheeler; 01-05-2012 at 10:09 PM..
  Reply With Quote
Old 01-05-2012, 10:06 PM   #26 (permalink)
Master EcoModder
 
Join Date: Dec 2011
Location: Boise Idaho
Posts: 842
Thanks: 39
Thanked 89 Times in 69 Posts
Years ago I built a DSR from an old Van Diemen FF race car.

basically took the front suspension and chassis, and put a snowmobile engine in the back with a chain driven live axle, then put aluminum body panels over it.

Truly, hideously ugly.

weight 770 pounds wet, no driver, with 150 horsepower engine with a CVT clutch. Used it for mostly autocross.

Won every race it ever entered except a couple of hillclimbs.

Some notes: Some chassis are brazed. The Van Diemen was which is HORRIBLE to modify.

Big drivers don't fit - cockpit is small.

The chassis are light, but really not very strong, and really not very safe compared to other designs.
  Reply With Quote
Old 01-05-2012, 10:06 PM   #27 (permalink)
Master EcoModder
 
3-Wheeler's Avatar
 
Join Date: Dec 2008
Location: Southern WI
Posts: 827

AlienMobile - '00 Honda Insight
Team Honda
90 day: 80.05 mpg (US)
Thanks: 94
Thanked 558 Times in 191 Posts
Quote:
Originally Posted by TEiN View Post
I missed it...

The suspension and half-shafts contribute zero?
Yes, the suspension tubes add a little bit, but are very low. I would however, go to the bother of adding foam/fiberglass airfoils to them.

I my design, there are no half-shafts, and the vehicle is rear-wheel driven.

But if there were half-shafts, they could be enclosed in a foam/fiberglass housing that moves up/down with them if the air drag was considered a big deal.

Imagine how sleek the Aptera could be if the seating were tandem instead of side-by-side as it is now?

Interesting side note: has anyone noticed how the first Aptera's had rear wheel drive, and the newer versions have front wheel drive and half-shafts? Are they anticipating the Aptera to be driven in snow at some point? Not sure, but seems to be a possibility.

Jim.

Last edited by 3-Wheeler; 01-05-2012 at 10:27 PM..
  Reply With Quote
Old 01-05-2012, 10:17 PM   #28 (permalink)
Master EcoModder
 
3-Wheeler's Avatar
 
Join Date: Dec 2008
Location: Southern WI
Posts: 827

AlienMobile - '00 Honda Insight
Team Honda
90 day: 80.05 mpg (US)
Thanks: 94
Thanked 558 Times in 191 Posts
Quote:
Originally Posted by drmiller100 View Post
.....Some notes: Some chassis are brazed. The Van Diemen was which is HORRIBLE to modify.....
Very interesting company here ! ....

State of Wisconsin regulations, at least from two years ago anyway, does NOT allow any *main* structure to be brazed.... only welded joints are allowed. A non-structural member can be brazed however.

I'm not a brazing expert by any means, but the requirement seems to be saying that to achieve really good brazed joints requires more skill and is harder to come by, than let's say oxy-acetylene or TIG welding. Just a guess on my part.

Jim.
  Reply With Quote
Old 01-06-2012, 12:09 AM   #29 (permalink)
Master EcoModder
 
Join Date: Oct 2008
Location: Mid-Atlantic
Posts: 491

OurInsight - '06 Honda Insight
Thanks: 170
Thanked 69 Times in 44 Posts
Quote:
Originally Posted by 3-Wheeler View Post
Yes, a three-wheel vehicle is known as a class #2 motorcycle here in Wisconsin. The requirements to get the vehicle road legal is that all salvaged items should be requisitioned from DOT road going vehicles. And no, ATV's are not considered a legal source of parts. I've had numerous discussions with my state inspector regarding this.
Bummer. That probably means you can't find a way to get inboard suspension approved Never came on any DOT vehicle that I know of.

How far along are you currently?

Last edited by jime57; 01-06-2012 at 12:15 AM..
  Reply With Quote
Old 01-06-2012, 02:55 PM   #30 (permalink)
Master EcoModder
 
3-Wheeler's Avatar
 
Join Date: Dec 2008
Location: Southern WI
Posts: 827

AlienMobile - '00 Honda Insight
Team Honda
90 day: 80.05 mpg (US)
Thanks: 94
Thanked 558 Times in 191 Posts
Quote:
Originally Posted by jimepting View Post
Bummer. That probably means you can't find a way to get inboard suspension approved Never came on any DOT vehicle that I know of.

How far along are you currently?
Jim, what about using inboard motorcycle shocks, for example. Remember that they are still DOT approved. They would just be mounted on the INSIDE of the frame instead of the outside. No difference really. Thinking outside the box helps!

I welded up one frame, and did not like the distortion, so I cut it all apart and welded it a second time. Much better on weld distortion, but still not really happy with it, so there it sits. I am pretty picky however, so it makes sense.

Besides, this is about the same time that I bought the Insight and found out how much gas sipping potential it has

Jim.

  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com