Track Roadster Cd or Coefficient of Drag

Hey, Tim;

The Rover Al mill is a very good way to go. Std & trad hop-ups work well, as do the off-the-wall stuff that the hard-core-types like... . Some of the Rovers used a constant-velocity carb that, when used correctly, kicks ass all over the place. Using a v8 mill, you probably want to maximize torque, so's to go down the road at min throttle opening/load. You can also shoot for the-peak-torque-rpm-at-the-chosen-hiway-speed-&-gear-accordingly. You could consider adapting Cadillacs' 4-6-8 set-up to your sbc, but I'd opt for modifying the electronics to a simpler toggle-actuation-system. There's scadds of different things you could try - you'd grow old trying just ideas I have & have seen... . (Hey, I don't have the $$$, or I'd be trying them... ). You can also choose to run w/the throttle at near, or WOT, to minimize pumping losses. This would probably imply a very small engine w/the proper gears to load the mill at the desired speed. (Which is what we did w/the 50:50, & a couple of other similar-styled/thought-processed experimental cars. FWIW, one year, 'circa '75, on a mileage run up the West coast, two guys - [one did the body/chassis on 4 G-60's tires (BradleyGT) & the other guy did the mill (acvw 2cyl, ~800cc,dual port, long-rod-theory)] got ~ 80mpg. On carbs & points & gasoline. Tested at a EPA facility on their dyno, following their test driving protocols (well, *trying* to - they didn't have quite enough power to get to the proper speeds, so's they were running wot most of the time... ). Test driver stated that's the highest mpg they'd ever seen... . ) I've come to the conclusion that ports/head chamber - incl piston top/exh are quite important. & a lot of the "tricks" that even the factories do on their hi-po mills today as routine, are also needed to get where we want to be. The 50's & 60's tech, w/rare exception, doesn't cut it. Sorry, but it was a long-resisted & hard lesson for me to learn. I think the Mills are ok, but todays' stuff is designed better. Starting w/the old mill just means we have "an opportunity to upgrade"... . . & we work a little harder, & think a little deeper, so it can be done.

I forgot to mention a hi-mileage site that gets interesting - but these guys are beyond hardcore - my types!... . You'll really like the hyper-mileing technique... .
http://ecomodder.com

In the teens or very early 20's, Vosin (IIRC) did an aero sedan that was somewhere in the range of .30cd.(again, IIRC). It looked almost like a gondola from under a blimp. Fenders were flat from front to rear, & just below the beltline. Shaped somwhat like a football, if viewed overhead. I haven't thought about, or seen, pics of this is 10+ years, but once seen, not forgotten quickly. Which could be good or bad, depending... .

On the Coupe: yes, those are the same one(s). The front wheel spats help a lot w/the turbulence, but should've gone all the way over the front of the tire to maybe 15* up from the ground. Weather or not the wheel pant turns w/the wheel, or has a cut-out in it, al-la the original Tucker dream car, depends on how far back they go, + how wide the axle is vs the frame, & the turning radius required. Look at the late 70's->early 80's Top Fuel dragsters, as a lot of guys ran them for a bit. Would need to consider ducting in & out for the brakes.

On the glass, I should've said 3 dimensional, ie: curved both top->bottom & side->side. Yes, some pu or late model car/van/etc is usually used, & cut from the center. Really helps in the noise dept, & as a result of the wind spilling off easier, the aero benefits. Oddly enough, it seems that a whole lot of curvature isn't needed.

Also, think about the airflow. The front of the car is the most important, then the sides & then the back. However, the top & bottom kinda fall 'twixt the sides & back. Doesn't take much to hurt things. Something to think about: although everyone "assumes" that the teardrop is the most efficient shape (that may not be far off of the mark), & that that is the form liquid takes when it falls under gravities' force, hi speed pics show that is not the case. The front of the drop actually becomes concave from the air pressure acting on it. This doesn't mean that this is the form you want, just that things aren't as supposed, & that air flow doesn't act like we think it does, much less "logically", although it does act somewhat like a liquid, esp going around objects. FWIW. So, you need to consider your hi-pressure areas, along w/the lo-pressure areas, so you can utilize them for "free" pressurizing & evacuating purposes, if possible. Mother Natures' help, if you will. Easier to work w/it, than to fight against it, since fighting it costs you power to overcome w/brute force, = less mpg. .

Nice T. & very nice job on the mill & carbs. I'm thinking you're going to have trouble w/the carbs getting into alky. The issue seems to be when the carbs have alky in them sitting, not swilling it down. Moisture absorbs from the atmosphere - there's nothing you can do about it, & when not in use, the alky/h2o/(& maybe)+ noxious mix of 1000+chemicals known as gasoline eat the carb metal(s) + any seal not made of viton; not to mention the whole rest of the fuel system, which I think has to be made of either stainless steel or only a couple types of plastic to live long, = $$$. I know efi isn't "trad", but at least MegaSquirt *is homemade* - & it works, it's priced right, + you can dial-in both fuel & ign. For testing, repeatability is paramount - as is getting the best tune possible for the test of the fuel, so a self-learning/tuning device that compensates for damn near every variable is worth considering. Not to mention your time to get the tune right. Just something to seriously think about. This coming from a looonng-time efi-hater. The last couple of years have changed my opinion, a lot. This stuff was only a dream for me in the late 60's/early 70's, now it's affordable & it works! FWIW.

I'm thinking, since at least the mid-70's, that the best body lines I can see for aero, would be a very close copy of Jocko Johnsons' Dragster [Chet Herbert cams/Porting by Jocko Streamliner]('circa '55 ?). But actually driving that on the street would be suicide, at least here. But it sure would be a rush... . & what a way to go... .

The next best for me, but actually the true best in aero, would be AeroTech by Olds, mill(s) done by Jim Fueling. Swoopy & slippery doesn't begin to describe it.

Hope you can stay w/this project. You'll have some serious fun, & learn a lot. . Just know that: rules for mpg & usual thinking do *NOT* mix. Usual thinking is almost 100% wrong. Just a thought, fwiw.

Marcus...

 

I like the ideas of alternative fuels, car aerodynamics and improving MPG. I was an engineer. I can't help but think and say that you should be focusing on your current school project, graduating, and applying for jobs in case you don't stay in school.

 

All valid points,great ideas.I love that site with the ecomodder sprite, two trannys 65mpgs.Retired after250 thousand miles.There are many easy ways to get high mileage.It is when you throw in Traditional, functional, and attainable,is when you get the Master's Thesis.

 

I've always been sceptical of those maintaining that the raindrop shape is the most efficient shape for traveling through air. Gravitational force acting upon a "blob" of water gives the drop of water its shape. The air craft wing has its cross-sectional shape to create lift.
Arrows are pointed at the leading edge, not blunt. LSR cars are pointed at the leading edge, not blunt. F-1 cars are pointed at the leading edge. All these devices must gently open up a hole in earth's atmosphere, slip through that hole, and then let that hole gently close after passing through.
However, getting close to ground level, there is this problem of boundary layer that has to be dealt with. Belly tank LSR have little problem in this area, but flat bottom cars do. Imagine what speeds Jocko's car would have achieved had he incorporated "ground effects" skirting to move that boundary layer around the car instead of allowing it to drag under the flat bottom?
The SAE textbook, "Race Car Dynamics" by Milliken & Milliken is a worthwhile study, even for us hotrodders.
Thanks for posting this interesting topic.

 

BTW, the University of Saskatchewan School of Engineering in the '70s and '80s built and won numerous international competitions in fuel economy runs - later results in excess of 500 MPG. The vehicles were extremely light weight, single occupant, very flimsy and powered by an F-head 2hp Briggs&Stratton engine. They have the appearance of a cellophane belly tank on bicycle wheels.

 

Subsonic aero is well understood. F1 cars have terrible Cd. They are all about negative lift. At subsonic speeds we are talking some form of teardrop. BTW, raindrops are not teardrop shaped.

This is a great site on racing aero examples.

http://www.mulsannescorner.com/

 

Now we are getting somewere.Look at the cd of that teardrop. nice number. Now, what if our axle is shaped like that, and our drag link...and any other hiccup underneath.Now do the wheelpants help, or is air getting trapped under.Did we allow for air vents to extract that air out,while keeping the brakes,and the superduty roller bearings cool?How close are we to the louver guy?After all its mileage not speed,we are after.Mile after comfortable mile.

 

vD & Hoop make good points. I forgot to mention that the teardrop shape is obtained by a drop of liquid just before the point that it releases from what holds it. Changes quickly after it drops.

Shapes that are useful must be designed to the speed they are expected to run at, & for the medium they are expected to run in, & of course the use to which they will be put to. ie: a submarine is different from an F-18. Not a stupid comparison. Even subs are different, study an old U-boat (made to run primarily on the surface & sometimes cruise under water for awhile) to our current nuke-pwrd subs (designed to exist under water for month(s) at a time. & it'll out run the U-boat, too). Or a WWII PT-40/60 compared to a current destroyer. A car designed to run at ~60/70mph, or even 30mph, requires different shapes than a Bonneville 'liner. Not to mention different physical set-up.

Smooth underside really helps w/the aero drag reduction, but to get the most out of it, also requires that there be enough ground clearance, so's to allow clean airflow under the car, w/o the drag & turbulence from the road surface. To use road skirts & diffusion tunnels, you need very little clearance 'twixt the car belly pan & road surface, so's the air will channel through correctly. Two different reasons for two different styles. One can help the other, but sooner, rather than later, you're going to have to decide which will override the other, & to what extent. Jim Halls' ducted-fan Chaparral glued down well, but the skirts would tear-up/get-ripped-off quickly on the street. (Don't think I haven't been dreaming on how to incorporate *that* into a street car, since the 1st time I heard about it... )

Air trapped in the wheelpants depends on airflow possibilities through them. Verticle vents at the extreme rear edge, & inlets near the front &/or lower front lip by the tire would be a good start.

There was a very good book used by an extremely knowledgeable prof @ Western Washington State a # of years ago. AFAIK, he still does classes on this stuff. On a cross-country mileage trip, I got to meet him, & spent a couple of weeks competing w/a couple of the students in his program. Got into some rather interesting theory & practical application conversations. Our school did ok, considering what we had to work with. We probably got the most out the least, of anyone, & still did well.
Found the prof: Dr. M. R. Seal, book was by Walter H. Korff. Prized book for info.

One way to get through school & studies, is to apply the course-work to the car, using the car as a foundation to further your education. This will work if you don't spend yourself out of school, detract from your other studies, & have enough time for the rest of the schoolwork - 1st ! Hands-on is quite useful, but be careful.

(I did just this in the early 70's -> early 80's. More than one car, but primary was a 32 ford 5w, olds mill, etc. Goal was to get reasonably close to the 40's look w/an updated mill in the mid 50's. I got close, considering it cost ~ $1500.00, a bit less than $1./lb. The things I wanted to change didn't get done prior to selling it.)

Oh, & the aero sedan I mentioned might have been by Rumpler. It was done by a WWI aircraft mfgr. Never went anywhere.

Marcus...

 

sgtlethargic : you're absolutely right. I have been and will continue to focus on the matters at hand, but I can't help but get excited about this stuff, too! I've been looking around at jobs already (just in case), but I'm heavily leaning towards staying in for the Master's (I feel like in today's work force, it's almost not good enough to have just a Bachelor's degree, so I might as well get it out of the way quick). Thank you for the reminder, though; in all seriousness, I needed it

 

Marcus,
I hear you on the old school vs the new school drivetrain. Both of them definitely have their place, and I truly do love the old stuff, but it's hard to pull off highly efficient old school stuff- especially when the new stuff does it stock

Ecomodder site: I've spent a little time on there. That's where I found that Aero Model T and the teardrop aerodynamic template.

I checked out the streamlined bodies you mentioned a few posts up. That drag car is absolutely amazing. I want. I want bad.

Thanks for the tip on the glass. I would not have thought of that, and it would have given me fits for sure!

Also, thanks for the thought input on body shape. It helps to have more than one person say what I'm thinking/assuming so I don't feel crazy lol. I always wonder how the heck some of the new cars today have such a low Cd w/ how boxy they are, but I guess if you do your homework, you can get away with some of that stuff. I think concentrating on the high/low pressure airflow areas and making them work for you rather than hinder you is key.

You're right about the carburetors not getting along with ethanol. Like you said, ethanol in the carb is no big deal until the moisture collects in there and oxidizes stuff. If this was a long term goal for this car, I'd switch to a single carb (or EFI) and drive it frequently so the car isn't sitting for long periods of time w/out fresh fuel. I did make sure all my fuel system components were going to get along with ethanol, but like you said, the moisture will really cramp my style. This is mainly to help me understand the good and bad of alternative fuels (like if I even want to waste my time with them in the future lol). I'm remaining optimistic, though!

"Hope you can stay w/this project. You'll have some serious fun, & learn a lot. . Just know that: rules for mpg & usual thinking do *NOT* mix. Usual thinking is almost 100% wrong. Just a thought, fwiw."

I'll keep these thoughts in mind. Thanks again,

 

That last sentence may be the one of the greatest statements yet! Excellent point!

 

When you say cellophane, are you talking thin plastic sheets? Do you have any links for that? That sounds interesting...

 

That's a cool link. Question though: what's going on with the last cylinder on that figure? It's got a Cd of 1/2 the cylinder that's the second from the top. The air after separation point looks more erratic on the second cylinder, and R is to the power of 5 here instead of 7. What is the variable R?

 

rod1 - I like the way you think. Isolating every variable on the car's body and chassis and asking, "How can I make this better?" That's a great way to go about it. "Leaving no stone unturned" as they say.

 

Marcus,

Another thoughtful entry! Thank you! Regarding the belly pan and ground clearance, I was considering incorporating a similar setup to that of Lexus? I think that's who has it, but it's a self adjusting air suspension. Low to the ground on the nice smooth road, and supposedly pops up if needed. I wouldn't know; my pockets aren't that deep lol. I was also considering making channels in the belly pan with the Bernoulli's Principle in mind. Wide in front, neck down, then get wide again to the rear to create a venture effect and hopefully speed up the air and help eliminate turbulence. I think this would need some testing at least at a basic level before I started going to town with a sheet metal brake!

Regarding your advice to make school in some how or some way apply to the car: this is key. For anyone really. If you have no application for the knowledge, why learn it? A friend of mine taught me that years ago. Every school project was somehow related to his car, and he always did very well in school. I definitely look up to him for this.

I looked up the Rumpler aero sedan. That thing is pretty neat looking! Not sure if I would mimic anything on it, but it sure looks unique enough to be cool!

 

I've always wondered why the "streamline body" wouldn't work better when the trailing edge was leading instead, but I guess it doesn't. I'm an old sailor, we like our pointy ends forward! Gary

 

Reynolds number!

 

Well I feel like an idiot now! I kept thinking, Radius? But they already defined the diameter? LOL. My bad everyone. My bad.

 

Tim, go to www.wdm.ca/stoon/innovation.htm#tensor
then go to U of S Supermileage Car
then to U of S Supermileagecar artifact record

 

Sorry, it should read www.wdm.ca/stoon/innovation.html#tensor

 

Back to the original post: aside from the flat windshield, which early Ford body has the least amount of aerodynamic drag? How does the '23 to '25 body compare with the '27, the '29, the '31, the '32, the '34 (the most popular of the roadster bodies)?
RichFox appears to run a '26 -'27 "T" body. He may want to explain his reasons for that body choice.

Yes, I realize this discussion also involves fuel consumption. Any thoughts on the IC engine/hydraulic/accumulator drive experiments in Minnesota and Oregon on the '80s?

 

Here is the BSFC map of a 1.9L Saturn. The challenge is to be in the sweet spot.

 

It is not how you open the hole but how you close it. A great quote.

Posted using the Full Custom H.A.M.B. App!

 

Very cool! Thank you!

 

Excellent quote indeed! Author?

 

Very cool. Thanks for sharing.

 

I forgot to say the yellow (25), Green (50), blue (75) and red 100 = power levels.

http://ecomodder.com/wiki/index.php/Brake_Specific_Fuel_Consumption_(BSFC)_Maps#Saturn_1.9L_DOHC