Dumb question?
 

Sorry if this is a dumb question - I'm new to this... but I was just wondering if, rather than extending the back of the car using a Kammback arrangement, anyone has tried modifying the shape of the car by adding a raised and curved roof?

ie if I have a flat topped station wagon, if I could somehow raise and reshape the roof to make it better fit the teardrop template, could the increase in frontal-area be compensated-for by the more aerodynamic shape..?

Has anyone tried anything like this or is it a non-starter? Just wondering! :rolleyes:

Another question: My Golf estate, on a particular downslope will take 35 seconds to slow (when put into neutral) from 50mph to 40mph.

My much lighter and shorter Perodua (Daihatsu Mira) will, under the same conditions, slow down in 14 seconds.

I wonder how much of that is because of the greater mass of the station wagon, or could it be that the wagon has that much better aerodynamics?

(There basic shape is not that much different really)

TIA!

Welcome!

there is a thread in the last 2 weeks about adding to a roofline.
Might look for that.

Non-starter. It adds so much frontal area that you have to push more air out of the way when driving. It only works if you're losing attached flow on the top of the vehicle, and this only very rarely happens on very boxy vehicles.

However, I always encourage people to tuft test their own cars to see the flow in real life. It helps you get a better understanding of it :)

Kingsway,
It isn't a dumb question and we are all new to this...even those of us with years of involvement since there is still a lot to know.

The coast down test I would think is more due to momentum and vehicular weight than aero drag but an easy way to test is another test from say 70 to 50 and see if the trend follows or deviates from that you have already found.

Just an aside...some makers here (Australia) use "vanes" (curved metal plates attached to the wagon at the rear corners and roof) to alter airflow.
The idea is to keep the rear window clear of dust in the country but there is no reason why you cold not adapt the same mechanics to alter the aero of your VW.

Peter.

I don't want to crap on your ideas but I recall a thread that basically disproved those as aero aids. If they're not extensively tested and meticulously engineered they will probably just add drag. Carry on! :thumbup:

Ah, okay I will try it at from different speeds and see if that makes a difference.


Re the curved deflectors for dust control - I know exactly what you mean!

I've lived and worked in Central Africa, where most of the roads were un-tarred and most of the then very popular Peugeot 404 station wagons had them to help with the dust problem. I also have a gut feeling that such a thing ought to be possible for reducing that vacuum at the back of the car - but without a wind tunnel, or some fancy simulation software, I'm guessing it would be almost impossible to get it to work effectively.

Thanks for your replies! :)

Four words: Best settled by experiment.


(The roof-thing, the deflectors are for keeping the rear clean, not improving aero.)

Hey there,
i asked the same question a few weeks back, and there was another before me some 6 months back, have a read of the thread below, and one of the posts also links to the other thread.
http://ecomodder.com/forum/showthrea...bad-20460.html
Lots of discussion, but the likely conclusion is that even if you improve the form and reduce drag, the increase in frontal area will probably offset this resulting in no net gain or possibly even a loss. I haven't burried the idea totally yet, but just put it aside for now as food for thought.

Read the post.

They were never intended to be aero aids or reduce drag.
They were meant to deflect clear air onto the rear screen to stop the build up of dust. In that regard they worked well.

I agree they will add drag if not suitable engineered.

Peter.

Hi guys, I am just about to embark on an experiment to see if the dust deflector on the back of my station wagon ( 1991 subaru legacy ) makes any contribution to the overall aero of the car. I'm hoping the added drag it imposes is significant enough to make removing it a smart move. Time will tell. Anyone else tried this to see if it made any difference?