Aero design question

[evolutionmovement]

In a heart beat! But where do you get drop tanks on the East Coast? I'm also still looking for an intact, but non-airworthy Cessna 150 fuselage to build a 3-wheeler out of, but running out of patience.

[botsapper]

Here's an interesting concept with plenty of the aero design criteria you are exploring. It's a PHEV concept but the lessons are put in place for you to study in your project.

AutoblogGreen

[jime57]

This is an immensely interesting discussion. botsapper asks some interesting questions related to realistic constraints on most such projects. You will probably have to start with some existing platform, otherwise the design and fabrication effort is huge. Reshaping of an existing car body can be done, and has been done by custom car folks for years. But it is expensive. The use of a portion of an existing platform and cutting away other portions, to be replaced with fiberglas, would be a fairly cost effective way to at least get some answers as to what works as an effective compromise.

It seems to me that the major questions are these: 1. do you want to design something conceptually with a clean slate and no compromises, or, 2. are you interested in modding something existing for a reasonable amount of money? (In the latter case, how much money do you want to spend?)

It seems to me that if number 1 is your objective, then the discussion can continue as to what functional shapes would be the "best" compromise for a 2 person, or 4 person, street legal auto. But note that VW has probably already done this work with their L1, I think that was the designation. And the Aptera is also a solution to this question. Both cars would probably be outside mainstream taste as "attractive" car shapes, though I like them both.

If conceptual only is the objective, then I suspect that lots of advanced aerodynamic modeling is in store. Some expensive design software would probably be required to have any confidence in the test shapes.

I'm just kinda thinking out loud and don't really understand exactly how you would proceed, but its interesting to contemplate.

[rkcarguy]

I want to sum up where I am heading with this and what I am after.
We can all agree that until some magic free horsepower fuel of the future comes along getting better mileage with the technology we have is the only option and is also a compromise.
Design and fabrication is what I have done for a living for many years. In the past I have focused on performance not mileage and built some pretty nasty cars. My latest build which is pretty much waiting for me to bolt it together is a 1963 MG midget that I auto-x. I got the chassis out of the blackberries at a friends house for $200, and spent a year building it up. I replaced all the MG running gear with a myriad of components, the rear end is a 87 RX-7 IRS narrowed 14" with posi, attached to coilovers which pick up a custom shock tower in the trunk. The front also has RX-7 hubs, spindles, and brakes with 92 prelude upper A-arms and aftermarket coilovers tied into another custom built shock tower. I stripped the body, cut out the stock fenders and rivited/moulded on fiberglass wide body fenders, which allowed fitting the car with 13x8 slicks. Originally I fitted it with a stock 12A rotary engine, it was very quick as it was under 1300#s. The rotary was a pig though and in the last few years parts have gotten harder to get and more expensive.....so I decided to swap....shoehorn..... in a japanese market nissan SR20DET. It has been quite a task. I had to notch and re-enforce the frame to clear the clutch slave, and purchased an aftermarket manifold so I could remount the turbo higher to clear the footwell. I did all my mods and changes, test fit everything, took it apart and fully welded and painted everything, and then our auto-x club lost it's places to race so it's just been sitting.
I really enjoy driving the car and thought "why do I need anything more than this to go to work and back?"
Being such a small light car should also yield good mileage.
I started considering building another one using D-mod prep parts which are more aero and not widebody, but that still left me with a convertable roadster type car which isn't very practical in this wet "evergreen" state.
My fascination with aero shapes goes way back, as a kid I was always amazed that I could take the lamborghini body and put it on 4 different slot car chassis's and that would always be the fastest one..
I am designing this one from the ground up built around the components I wish to use, because I don't have to compromise using an existing cheap steel chassis and put up with a production car that had to be designed to fit and perform for the general public.
Look at the front and rear view of the prius. The sides are pretty flat and there is not alot of curves on the sides. They focus on splitting the air over and under the vehicle, and I believe that often the curves or rounded shapes that deflect air to the side may cause more tubulance and drag, in the same way airplane wings have the turned up tips because swirls of turbulance off of the straight cut ends made the last few feet of wing in-effective.
I don't mind sitting on basically a padded floor leaned back at 20* if that's what it takes to get good mpg and as a bonus also enjoy a low CG for handling purposes.
As far as the aero design is considered, it may come down to just building it and go drive it. The aluminum nose shape can always be played with if the car has too much or not enough downforce.
I am still contemplating using the upper firewall dash and A-pillars from a Civic to ease the whole controls situation, but then that means a bolted steel/alum connection which may be more pain than it's worth.
Overall I'm simply looking to combine a few things together...
The sleekness and aero of a sports car/exotic
The efficiency and practicality of the lean burn VTEC engines
Lightweight materials and components(just get away from damn iron and steel)
A transmission that doesn't spin the engine at 3500 rpm on the freeway

[winkosmosis]

Can a homemade car be street legal? What about kit cars?

You should consider buying an old 1.6L Miata and getting 30mpg. They usually don't leak

[rkcarguy]

I already have a 1993 Civic Sedan with a B20B swap that gets 33mpg, and it's alot quicker than a miata too. I'm disapointed actually I thought the Miata would do better than that for mpg..

A homemade vehicle can be licensed in our state, I can chose 2 ways: taking the receipts for all parts materials etc and being assigned a vin for a custom built vehicle, or use parts from a donor vehicle, which will get scrapped, and then becomes the identity of the modified vehicle. I'm leaning towards the custom built licensing because then any exhaust I make would be the original and therefore not subject to our states bogus modified exhaust laws which they removed the sound limit and left it to the officers discretion(basically if your exhaust is shiny and aftermarket here's a ticket loud or quiet).
Building my own I would be subject only to the federal standards of 95 decibels or less.

[winkosmosis]

People on Miata.net say they get 30mpg with normal driving with the 1.6L. The 1.8 is worse. I get about 26mpg. Main problem with the Miata is the low gearing.


With your home built car, I hope you would use a catalytic converter, otherwise pollution will be much much worse. I believe a small 2 stroke scooter emits something like 10x the pollutants other than CO2 as a car.

[botsapper]

It is very good to learn that you are not only a grease-under-the finger-nails builder/fabricator but also a racer with a growing eco-heart. Your SCCA, Solo Series & MG club racing experience is also a great insight to your true car passion. Your thread general discussion may need to extend onto a larger scope for not only for an aero/ FE engine package but also one with great handling & performance dynamics. I suggest adding to your research. TTW - Motorized
I've have been studying TTW for some time because of it's hybrid driving dynamics & important smaller aero front profile. A racer enthusiast's joy of great driving experience with a great FE capabilities can use this as a great inspiration for the build.

http://www.youtube.com/watch?v=6cQETVQOYag

http://www.youtube.com/watch?v=7ITwD...eature=related

Crash tested too.

http://www.youtube.com/watch?v=S3ywadBp3wc

[rkcarguy]

Originally Posted by winkosmosis

With your home built car, I hope you would use a catalytic converter, otherwise pollution will be much much worse. I believe a small 2 stroke scooter emits something like 10x the pollutants other than CO2 as a car.

I will be using a cat and all emissions with the honda engine, they don't like running without them and also experience far longer warm up times. The stock cat flows pretty well, and I haven't noticed any gains in horsepower that were worth not having the cat. Typically you gain a little top end but at a loss of bottom/midrange power, it's something I only do for the track to keep the heat out of the engine when you're at WOT so much.

[evolutionmovement]

The Miata's big problems are the truly awful gearing—the high ratios way too short and the low ratios are too tall to just swap the rear end out. If I do an aero Miata project (it's 2 designs for a Miata, a tandem 2-seat Impreza IF I can make it look marginally attractive, and a cessna-bodied 3-wheeler I'm deciding between), I'm swapping the transmission with a 2nd generation RX-7. I believe you can swap the bellhousing and bolt it in, but I need to look into it better. From there, I'd be covering the undercarriage, building an external hood vent for the radiator, extending the rear bodywork into a Kamm/boattail type thing, and either building an aerodynamic hardtop or covering the passenger side of the cockpit over, removing the windshield, and installing a sliding teardop aircraft canopy over the driver's side. I'm just reluctant to only have a single seat vehicle.