Landracing Forum
Tech Information => Technical Discussion => Topic started by: Chris Horoho on October 08, 2010, 09:21:15 PM
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on determining frontal area I understand it enough to be slightly confused but yet not
First if I come to a mild point of sorts (not quite but close) on a motorcycle streamliner would the shape of the vehicle profile from the front become the frontal area am I correct in thinking this?
Second say I go to a ball shape up front and slowly go to my profile shape would this then (the ball up front) become my frontal area instead of the profile?
sorry if these are rookie ?s I'm just doing a lot of research and this to me seemed a bit vague
Thank you
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frontal area is the amount of area as viewed from the front. Doesnt matter if the object has things forward or aft, if it can be seen from the front, its frontal area.
Another thing you should concern yourself with is wetted area.
Good luck and god bless google.
~JH
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that's kinda what lost me a bit before as someone told me if I went to a round front it would decrease my frontal area
This was said to not be as big an issue with subsonic vehicles (the example was a 747 isn't pointed (and yes i see this as well as the saying is its an airplane not a land vehicle but as I said I am just tryin to do research for a possible future build))
I understand the deal with drag and the goal is the get it as low as possible
again sorry I am prone to ramble
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that's kinda what lost me a bit before as someone told me if I went to a round front it would decrease my frontal area
They were misinformed.
It does change wetted area.
Points are good for supersonic.
Dont apologizes for rambling.
~JH
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that's kinda what lost me a bit before as someone told me if I went to a round front it would decrease my frontal area
They were misinformed.
It does change wetted area.
Points are good for supersonic.
Dont apologizes for rambling.
~JH
ok that i understand
and that have been what they meant and were just responding on short notice??
Thank you
now i have to figure out what style and design to stick with and model it up
so jonny you still have that MP or did you change it out
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It is basically a measure of how much air you have to move out of the way as the car passes, so the entire cross section of the vehicle as viewed from the "direction of the airflow" is your frontal area.
If there is absolutely no cross wind frontal area is the front view of the car.
If there is a slight cross wind the actual frontal area is the cross sectional area of the car seen from the direction of the wind. That is one of the reasons small cross winds can drastically slow a land speed vehicle down. The other is as the wind strikes at an oblique angle the air flow can change substantially and areas of the car on the down wind side of the car will change from smooth attached flow to turbulent detached flow which significantly increases drag.
One way to think of frontal area, is it is the smallest possible hole the car could pass through.
An easy way to get a good approximation of the frontal area, is to get well back from the car with a camera and take a picture of it at the same level as the axis of the vehicle.
Everything you see of the vehicle is frontal area.
Larry
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Chris and Hotnuts have it pegged.
Putting your object against a wall longitudinally and then shining a light on the shadow from the front is another handy visualization tool.
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ok lets add to this discussion a bit
lets compare the easyrider vs sam wheelers on Cd vs frontal area and wetted area and the calculations of required HP to achieve desired speeds
(http://www.rbracing-rsr.com/turbo/samwheeler.jpg)
(http://www.rbracing-rsr.com/turbo/aero_easyrider.jpg)
now this looks to be the where i get a little lost
the ez hook has a Cd at around .103
the easyrider is around .2
look to have similar frontal areas ??
this is why i get lost as the wetted area looks to be more on the ez hook then the easy rider??
and yes i understand these terms and designs but this just makes me not know if the design in my head for a liner is going to be any good (and no im not any good at sketching to get a drawing up i am more of a cad type of person lol sorry)
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the ez hook has a Cd at around .103
the easyrider is around .2
I would question these numbers. If one of these is an "estimate" it might be misleading.
Many times these numbers are arrived at by calculating drag based on actual runs, there are many factors that can skew this.
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As already explained, frontal area is simply the area of the hole you punch in the air. Cd is a measure of how slippery a shape is. With Cd you can compare different shapes to see which is more slippery. As a shape gets more streamlined the pressure drag will go down and the skin friction from the wetted area will then become the major source of drag.
CdA is the Cd times the frontal Area and tells you how well you are punching a given size hole for a given shape. You can have a larger area that is a more slippery shape than a smaller one. An egg and a sugar cube obviously do not have the same Cd but they have the about the same CdA. If you had to power these there would be more room for engine and driver in the egg but if you have a small enough motor and driver then a smaller egg-shaped sugar cube might be the better way to go.
Finding the best working balance of all the factors is the tricky, fun part!
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Woody is right. After posting I was thinking about the size difference of the two liners in question, size and shape is likely a major factor.
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Please explain "wetted area."
Thanks
Bob
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ok thank you
i do understand what you guys are referring to
the design i am pondering is going to have a frontal area of 4.8
i would only hope to have a Cd of .15 or better but would only hope
as that would put my goal and available HP about where they would need to be with a little HP in the bank as to keep it reliable
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Please explain "wetted area."
Thanks
Bob
wetted area is the area basically hitting the air or rubbing the air could be another way to explain it
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#1: Forever ban from your brain the concept of "frontal area". Until you do, you will learn very little about aerodynamics that will improve your vehicle over anyone else who still uses a term we stopped using in aerodynamics about 60 years ago.
#2: http://www.landracing.com/forum/index.php/topic,3900.msg51288.html#msg51288
#3: For a subsonic vehicle, drag is the wetted area times the skin friction coefficient plus all of that nasty stagnation and separation drag associated with blunt front and back ends.
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Think of frontal area as a full size cardboard cutout of your car. If you were to test this cutout (flat plate) in a wind tunnel you would get a CD around 1.0 and when testing the real car the CD is now reduced because of the energy recovery from the body (CD around .330 of this style car pictured). Frontal area is a measure of size and CD shouldn't change with scale. If you build an exact 20% replica of your car and tested it, the frontal area is reduced but the CD will be the same as the full scale version. When comparing car to car you really need to look at CDA (Coefficient of drag * Area). A jumbo jet has a lower CD then a car but because of the massive size there would be more drag force on the jet because of the area the force is acting on vs a car.
An example: Say you have 2 cars with different frontal areas but the same CD.
Car 1: Frontal Area = 22ft^2
Car 2: Frontal Area = 20ft^2
CD = .330 for both.
Car 1: CDA = 7.26
Car 2: CDA = 6.60
Car 2 would have less drag force and require less HP to go the same speed.
Click on the image to see it full size. Its not just a car as it appears small. It also illustrates frontal area.
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Frontal area is a measure of size and CD shouldn't change with scale. If you build an exact 20% replica of your car and tested it, the frontal area is reduced but the CD will be the same as the full scale version.
True if appropriate adjustments of fluid viscosity and/or speed are made. Tested at the same airspeed the smaller model will have a lower CD. The differences will be more apparent with lower CD forms.
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Frontal area is a measure of size and CD shouldn't change with scale. If you build an exact 20% replica of your car and tested it, the frontal area is reduced but the CD will be the same as the full scale version.
True if appropriate adjustments of fluid viscosity and/or speed are made. Tested at the same airspeed the smaller model will have a lower CD. The differences will be more apparent with lower CD forms.
I should have stated the obvious of a scale model tested correctly will have the same CD. Reynolds numbers, test speeds, and testing protocol is a whole other subject for another thread but thanks for keeping me honest.
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these responses are what i am looking for
Thank you
now the tricky parts to many different types of fronts
and sorta off subject but which would be better for air inlet to feed turbo and vent cockpit
front ram as the ezhook
or a set of tunnels?
or would cfd testing be better for seeing that answer through?
yes i do plan on loads of research as i have been doing but seeing the many ways people do these liners gives me mixed emotions?? on which route to follow
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#1: Forever ban from your brain the concept of "frontal area".
what an asinine statement!..... maybe not important if your building a 747! hey Blue you wanna take credit for designing the 747 also?
Chris, you want to do 3 things, 1st, make your "frontal area" as small as you can. 2nd, make your body as slippery as you can. 3rd never listen to Blue!....
Small and slippery is the most fundamental attention area for our vehicles
Kent
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.... :-D.....
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It seemed like an over generalization to say frontal area was old news but I'm not on this sight to make waves, I let Kent do all my waving for me!!! It does seem like it would take less effort to poke a small hole in the air (water) then a large one.
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hey Blue you wanna take credit for designing the 747 also?
[/quote]
lolol
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There is a stagnation point at the very front of torpedo shaped objects. An excellent place for an air intake. The EZ-Hook is using a good idea.
The frontal area and drag coefficient method is empirically based. In other words, it is an observed relationship. It is useful and our traditional way of looking at things. It is a simplistic approach to a complex problem. It does not give us much to go by when we want to look at a new idea. By necessity, the aerodynamic relationships were examined further and methods were developed that give us the means to arrive at fairly good shapes based on theoretical relationships. Testing is still very important, however.
The concepts Blue is describing are part of the more modern approach. His posts should be read carefully and considered. They have valuable information.
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It seemed like an over generalization to say frontal area was old news but I'm not on this sight to make waves, I let Kent do all my waving for me!!! It does seem like it would take less effort to poke a small hole in the air (water) then a large one.
One of the first things my friend Ken Mort said when he began helping me with the aerodynamic design was don’t worry about frontal area the design is much more important. Ken was one of the engineers (Stanford grad top of class) that ran 120 foot wind tunnel at NASA Ames and had much experience with full size aircraft and other aerodynamic body’s and has much practical experience. We have had some success with our design.
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We have had some success with our design.
I don't know what your talking about... :-D
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Small and slippery is the most fundamental attention area for our vehicles
Reduced wetted surface, as Blue emphasizes, is also a kind of "small". Are you suggesting that of two forms, both with wholly attached flow, the one with less frontal area but greater surface area will have lower drag?
(Or are you just saying "Blue bad, Kent good"?)
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I think what is being missed in Blue's comments is that small frontal area is not a be all end all solution, the real number is the product of CD and frontal area. Sometimes by making a body larger in places that are friendly to the air flow your CD drops so much that you gain more than building a smaller shape that cannot be made as slick.
If you make the body too small you get forced into shapes that cannot maintain attached airflow and rapid transitions that increase drag and wake area.
Sometimes you have to give up a little frontal area to gain a lot of reduction in CD.
Larry
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Don't get me wrong Larry I like what your saying, cause in kinda sounds logical. However you used the words frontal area 3 time and Blue admonished you to " forever ban from you brain" and I'm not going to use the rest of the quote because I'm starting NOW! I have already deleted that term from my program that helps me predict speed based on HP, CD, and that other term that I have banished from my brain. I think it may be time for Kent to jump in with some sooooothing words.
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I have herd Kent called a lot of things but sooooothing is a new one. :-D Come to think of it I can see him as a sooooothing balm. :-o Tony
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.....spell check......." a seeeeeething balm "
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Come on guys lets keep this topic serious. So I built a model of my new liner and I put a straight piece of coat hanger into the top of it and I ran it through the bath water a few times noting the deflection of the coat hanger. I build a bigger model and did the same thing and noted I had more deflection. What have I learned? And yes I carefully controlled the bath temperature.
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geo
yes i also wonder what I'm gonna call that required number i need to input into my formula that I've been using for the last 30+ years.... the other 2 "programs" i use also require a number.... it seems the formulas all need a dimension as to how big a hole the turd (soothing word) pushes through the air...hummmm what shall we call it?..... OH! hey! how 'bout "FA"..... nah maybe to close to the banned word... any ideas?
Tortoise.... YES to both yer questions :-D
Kent
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.....spell check......." a seeeeeething balm "
Never Kent :-D Tony
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geo...the "wetted" area went up..
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As I sit here in my bath, I'm thinking of Kent's Question as to what to call what was formally known as-------well, you know. I lack the education to come up with anything appropriate. Me thinks "turd" might not be universally accepted. There are other worrysome possibilities that could come out of all of Eric's Aerodynamicistic input into our little LSR world.
What if Marlo Treit becomes so intimidated as to stop his project, rethink his aero package and instigate a series of changes that put Jim Hume years behind schedule?
What if some day Blue's impute becomes so dominate as to require the SCTA to divide up the classes into two categories "Those Designed and recognised as being correct by Blue" and the antiquated old "intuitive, seat of the pants-gut instinct classes" Eric your original post stated you wanted to stir up some lively debate and so you have.
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The following are also "Blue's" comments...........
"""To be absolutely clear: I do not advocate outlawing anything"""
"""TEST! There is absolutely nothing I can tell anyone about their car that is better than the data they can get for themselves"""
""Keep it coming everybody, and be critical too. This is about safety and a broader understanding for everyone""
i remember when everyone told Ack he couldnt use "car" tires on his liner
and how it wouldnt work................
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I think I have a good idea what Blues' reasoning was behind 'forget Fa', ...I get ya buddy.
-however
Fa is a much easier concept for the non aero professional to understand and how affect its influence (make is smaller).
Fa does have an effect...maybe not as much as separated flow...but...ya know.
My problem is that I have never heard anyone discuss interference drag between the ground and the lower body surface. I would say these forces create a significant amount of overall drag.
Its one thing to design an airplane....but the interference drag created by the pressures off the ground add a new dimension that is misunderstood and NEVER discussed.
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Johnny, another Blue post about 3 yrs old....
"Preventing air from going under the car" is a combination of a good thing (negative alpha) and a bad thing (separation on the belly and tail). If you can do it without adding weight, add a belly pan with a diffuser at the tail to reduce the separation and increase the negative alpha even more. Then you can have the best of both worlds. Lowering the whole car makes the effect greater at the risk of separation. Where you go in height is more a function of how good your diffuser is at the tail and how much the extra drag costs you if you go too low and cause separation""
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ok
i understand that
FA and aero are 2 different things but i still want to use FA to get an understanding of twhat i need to bring to the table
i do understand that i can only go so small and still have good aero but i have an idea but unsure if it will work as of yet
and for another ?
i read an old post that stated the FA of a 2x3 oval was 6'2"
my calcs might be wrong but i thought the area of a 2'x3' oval was 4.8 and that is the size i am shooting for to be honest
but again i do understand they arent the same but using both will let me know what i will need in HP and such
thank you for the posts and please keep the tech up
just guys lets keep it clean and not fight
everyone has an opinion and all are welcome by me
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I'm always suggesting Carroll Smith's books, in TUNE TO WIN. there's a good chapter on aero and on pg 84 he gives some numbers
flat plate.. cd-1.5
round tube .60
aircraft structural teardrop tubing .06 :-o
JL222
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horoho...area calculations...
http://www.mathsisfun.com/area-calculation-tool.html
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horoho...area calculations...
http://www.mathsisfun.com/area-calculation-tool.html
yes i am getting a similar number from the length
and a tad dif formula but close
oval and ellipse arent quite the same but i am probably leaning towards an ellipse in design anyways ??
thank you
i have no clue where the other gentleman got his numbers from then
it was in an older post on here but no biggie
i am a tool maker/machine shop owner and am fairly advanced in trig and geometry that was why i asked
to see if i was seeing things or if i was correct on my calculations
Thank you
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Chris, start here: Aerodynamics For Racing and Performance Cars Hp1267 by Forbes Aird ($45~50)
A little hard to find but well worth it! :cheers:
For more info and math: :-D
Race Car Aerodynamics: Designing for Speed (Engineering and Performance) by Joseph Katz ($20~25)
or
Competition Car Aerodynamics: A Practical Handbook by Simon McBeath ($30)
For even more info and even more math: :-o
Aerodynamics of Road Vehicles: From Fluid Mechanics to Vehicle Engineering ([Proceedings] / SAE) [Hardcover]
Wolf-Heinrich Hucho (Editor) ($100)
All available at Amazon.
They all "mention" frontal area - but oh well! :?
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Chris, start here: Aerodynamics For Racing and Performance Cars Hp1267 by Forbes Aird ($45~50)
A little hard to find but well worth it! :cheers:
For more info and math: :-D
Race Car Aerodynamics: Designing for Speed (Engineering and Performance) by Joseph Katz ($20~25)
or
Competition Car Aerodynamics: A Practical Handbook by Simon McBeath ($30)
For even more info and even more math: :-o
Aerodynamics of Road Vehicles: From Fluid Mechanics to Vehicle Engineering ([Proceedings] / SAE) [Hardcover]
Wolf-Heinrich Hucho (Editor) ($100)
All available at Amazon.
They all "mention" frontal area - but oh well! :?
thank you
i will definitely be finding these and getting them when spare change is available
but thats just the fact of racing now isnt it lol
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Chris, start here: Aerodynamics For Racing and Performance Cars Hp1267 by Forbes Aird ($45~50)
A little hard to find but well worth it! :cheers:
For more info and math: :-D
Race Car Aerodynamics: Designing for Speed (Engineering and Performance) by Joseph Katz ($20~25)
or
Competition Car Aerodynamics: A Practical Handbook by Simon McBeath ($30)
For even more info and even more math: :-o
Aerodynamics of Road Vehicles: From Fluid Mechanics to Vehicle Engineering ([Proceedings] / SAE) [Hardcover]
Wolf-Heinrich Hucho (Editor) ($100)
All available at Amazon.
They all "mention" frontal area - but oh well! :?
thank you
i will definitely be finding these and getting them when spare change is available
but thats just the fact of racing now isnt it lol
Yep, check ,got 'em....some of them are about as relevant as a cook book for what we do, but at least they get you thinking.
I can hear a distant rumbling and I think it's Rex pulling his chair up to the computer to suggest Goro Tamai's book "The Leading Edge"...and it too is a weighty text but as I have said before ,do not attempt to operate machinery or complete difficult tasks after reading that book...it's not what you'd call a "page turner"
(http://t0.gstatic.com/images?q=tbn:ANd9GcTgwmN3vbbqr1UEHEUj-s9ckct4wIvZb5dgkH3cj-v7jMcbzHM&t=1&usg=__bol9R-lJq5tQnQ_s6Rbk5qDQC6w=)
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horoho...re ""oval and ellipse arent quite the same""
http://mathforum.org/library/drmath/view/55402.html
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Hot nutz
There has been quite a bit of discussion about ground clearance of a race vehicle and quite a bit of research and testing done…. Actually Denis Manning gave a presentation at the 2nd symposium of automotive aerodynamics in the late 70’s about ground clearance and angle of attack… his finding was getting the vehicle up off of the surface…. And he still uses his findings on #7… also the Wixon brothers found during the Cal Tec wind tunnel design testing of the HD XR road race fairings the center of pressure and stability increased when the back of the fairing was lowered to the ground…. Contraire to the forward to rearward upward rake found on current racing vehicles trends…. Without skirts it will suck air under the vehicle….. So to answer your question with a typical Blue response, Ford or Chevy? You decide your own answer….
Kent
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Goggles, your above post has to be best of the week!
I thot I was the only one beatin' up on Rex - for his spelling, damn engineers!
Couple of points, since Blew seems to be in the barrel these days. Don't know how you can dimensionally compare objects without reference to FRONTAL AREA.
Is CdA meaningless?
An amazing fact is 48 year old Bloo mentioned "WE" in reference to the "elimination" (my word) of the term frontal area in Aerodynamics. He said it had been ignored for 60 years.
That may be a record for IN-UTERO experience!
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horoho...re ""oval and ellipse arent quite the same""
http://mathforum.org/library/drmath/view/55402.html
http://www.spectrumanalytic.com/support/library/ff/area_calculations.htm (look half way down or so)
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horoho...re ""oval and ellipse arent quite the same""
http://mathforum.org/library/drmath/view/55402.html
http://www.spectrumanalytic.com/support/library/ff/area_calculations.htm (look half way down or so)
This wasnt meant to be a smartie responce just stating what ive been taught
An oval is 2 half circles with straight sides and an elipse is a circle looking at it at a 45 degree angle (or which ever angle to give set length)
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And to the fa not being needed i will say this and hope i dont stir up to many people
But you cant push a 747 on the ground to high speeds (even though fairly aerodynamic) with just 500 hp
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Chris, during lunch break a person can learn a lot by typing a subject like aerodynamics into a search engine and reading a little bit each day. There are some government sponsored sites dedicated to teaching teenagers about aero. NASA has one. Those are pretty good reading. A worldwide search will bring up the British web sites and there is a lot of info there.
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A big thanks to Dr. Goggles for getting a remark in on my favorite "aero" book, "The Leading Edge" ! Yes it is "challenging" reading and yes it is about cars that only go 50-60 mph, sun racers, but it addresses more of the details that we need to be interested in if we are going to build an efficient aerodynamic car than any other book I have seen. I have a copy in my shop, next to my bed and in the "reading room" and I re-read and review it all of the time. Maybe I need to stop reading and start building!!!
Just a comment on most of the present day cars that are running at the 400 mph area and also I include Marlo's car, if you look at them most of them are the same basic shape, some sort of pointed nose, a square cross section, long flat sides and some sort of shaped tail that closes out the rear of the car. Only the Spectre car, and Al Teague's (I know the spelling is wrong!) diverge from this general "formula". I think that the new car that is being designed by Rob and Woody (with help from Blue) is a true step away from the standard formula and I, for one, am wishing them the greatest success. Also if you look at the three leading motorcycles all of them are built along the lines that Blue is suggesting, not a flat bottom in the bunch.
Just a note on the Cd vs the "wetted area" conflict, I read an article in the magazine "Bernoulli" by the aero dynamisist for the JCB diesel car and he said that 75% of the total drag on that car was skin friction which is directly related to wetted area.
Rex
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horoho...re ""oval and ellipse arent quite the same""
http://mathforum.org/library/drmath/view/55402.html
saved link ,,thanks
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Rex, Is "Bernoulli" still in print? I loved that magazine, but it had sporadic distribution. Tony
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Tony,
I just received my latest issue of "Bernoulli" last week, 2 1/2 years after my first issue. Now that The Automotive Book Store in Burbank is closed you can probably only get it by subscription.
Rex
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With fast streamliners there are so many variables it's not easy to rate body shape by mile times
John Burk .
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I just received my latest issue of "Bernoulli" last week, 2 1/2 years after my first issue. Now that The Automotive Book Store in Burbank is closed you can probably only get it by subscription.
Bernoulli is struggling! My March issue arrived end of last month. All the staff tells me is, "It's coming next week!" Don't know if I will get all my subscriptions or not! Any back issues you can find are worthwhile reading.
A big thanks to Dr. Goggles for getting a remark in on my favorite "aero" book, "The Leading Edge"!
This is a good primer before trying to absorb all of "The Leading Edge": The Winning Solar Car: A Design Guide for Solar Race Car Teams - by Douglas R. Carroll ($50 - discount for SAE members.) An old(er) billiard instructor once told me there is a time to theorize and then you just have to bend over and shoot!
With fast streamliners there are so many variables it's not easy to rate body shape by mile times.
Cheese Louise, how many ways are there to go 200+, 300+ or 400+? Why just look at LSR! Balance all the factors and a brick with wheels can go 304+! :cheers: Too many (unbalanced) rules will always stifle innovation. Every safety rule written is based on an actual event and an overreaction by the governing body! In order to achieve a good balance my personal LSR design mantra is S³. Safety, Slippery and Small in THAT order but there is always more than one way to skin a water buffalo! [Of course the water buffalo doesn't like any of them! :-o]
That's my rant - for now! :-D
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Woody ... interesting perspective ... frontal area / coefficient of drag / different design arguments and then an open wheel roadster goes 304 ...
Joe
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Tony,
I just received my latest issue of "Bernoulli" last week, 2 1/2 years after my first issue. Now that The Automotive Book Store in Burbank is closed you can probably only get it by subscription.
Rex
Rex,
I believe the store just moved down the street a couple blocks. They had a nice little "Grand re-opening" about 2 months ago.
John
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Just checked Autobooks Aerobooks website . Looks like they're still in the same location as last time I was there. (Date on home page was today's.)
Address : 2900 W Magnolia , Burbank Ca. Phone 818 8450707
If you get there today (Sat) around noon you'll likely see Jay Leno hanging out.
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Fa is a much easier concept for the non aero professional to understand and how affect its influence (make is smaller).
Fa does have an effect...maybe not as much as separated flow...but...ya know.
Or, you could conceptualize your design around the goal of lowering the surface area to a minimum while avoiding separation. Surface area may be harder to calculate, but minimizing it is pretty straightforward even if you don't figure out exactly what it is.
The necked down fuselages in Costella's machines don't lower the frontal area, but they do drastically reduce the skin surface, as well as moving the center of pressure rearward.
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Woody ... interesting perspective ... frontal area / coefficient of drag / different design arguments and then an open wheel roadster goes 304 ...
Joe
With enough horsepower anything is possible.
Unfortunately this also is a reason that just because a streamliner went fast, doesn't automatically mean it was the best....or....even a GOOD design.
Consider factors like handling, visibility or what COULD of been (*speed).
It would be very interesting to see a group of dissimilar designs with the same power. I will bet peoples opinions would be different by the end of the test.
~JH
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Joe ..."""interesting perspective ... frontal area / coefficient of drag / different design arguments and then an open wheel roadster goes 304 ... """
now take that hp from roadster and speed and you get the drag number...
take the same from something streamlined such as any of the 300 to 400 mph streamliners...
then substitute back in the roadster hp....and see what mph pops up......
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I wonder how much having the rear tire in the middle of the nice curved shape like Ack's as opposed to on each side like a lakester would affect the seperation and how far out one would have to move the tires to lessen the tires influnce :?
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I think you guys need to put this in two categories. Bluff bodied and streamliners. A car/motorcycle (bluff bodied) is dominated by Invicid flow (pressure drag) and viscid flow (skin friction) accounts for very small percent of the overall drag (less than 10%). A streamliner will be affected by a much higher percentage of skin friction than a car, and wetted area is something to take into account. There might be some confusion about the two styles of cars and looking at FA or wetted area and who is right.
-A production based car is not a streamliner and vise versa so they might need to be approached 2 different ways. Also a production car is almost impossible to make smaller physically (see attached image). You’re kinda stuck with what you got so you can really only improve drag by improving how the air gets around it. Where a streamliner you can design how ever big or small you can.
I don’t know if that helps or not? A roadster is not the Ack or #7 and it seems like people are dumping all cars in the same category in this post and then there is confusion about who is right. My 2ct.
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Lots of hp doesn't help if you can't hook it up, thats why two streamliners that I know of that are being built will have wings.
JL222
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I think A2 has hit it on the head. Streamliners and roadsters, or Cameros in John's case, are completely different from an aero analysis stand point. A properly designed streamliner should have very little "pressure drag" and that would only be from the area of the boundary layer as it thickens to the back of the body and then recombines at the rear of the body. The rest of the drag for a streamliner would then be skin friction which should be the dominate drag on a streamliner. On a roadster or sedan, which is, as A2 has said, a bluff body the aero calculations depend on the frontal area and the Cd. The long runs of flat sides that many of the present streamliners is not as efficient at maintainling attached flow as the rounded shape that you see in Robs design.
Rex
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Low drag wings need to be long and slender , tapered , accurate , well mounted and at least 2 feet above the ground . Good downforce with slenderness requires an aggressive profile . NACA 63-021 (21% thickness) has good performance up to 12 deg and low drag . A long slender wing needs to be strong . The simplest wing is cnc milled aluminum . The 63-021 is symmetrical so only one setup is necessary . Anybody interested in making low drag wings can contact me , joyseydevil@comcast.net .
John Burk