Aerodynamics and Relationship to Speed

I believe some members have run cars at Santa Pod and are thinknig or may think of doing it in the future.  Well some time ago (i think Ben_cab)  was interested in running faster and I mentioned the underside of the car.  While at the time i didn't have any real evidence to support my comments only personal theory. I have investigated the potential improvements in Drag coeficient,  and the relationship to power and speed.

Obviously you need to get the Golf through the air with as little amount of drag or wake as possible as 30 - 50% - 80% engine power used just trying to push the Golf through the air.

So weight off, grille blocking, wipers off, panel gaps taped, underside, smooth, tyre wind deflectors.  

Parts  Percentage of Total Drag
 
Cooling package (including radiator, intercooler, oil cooler, etc)  33.4%
 
Exterior  31.7% (this is on a .29 Cd car)
 
Front wheels  13.1%
 
Rear wheels  6.9%
 
Floor  6.9%
 
Rear Axle  3.1%

Engine  3.1%
 
Front Suspension 1.4%
 
Exhaust  0.7%
 


The links below may be worth a look.

http://autospeed.com/cms/A_2455/article.html

http://autospeed.com/cms/A_2456/article.html

http://autospeed.com/cms/A_2160/article.html

http://autospeed.com/cms/A_2455/article.html


It may be worth thinking about?

Grant Parkers Golf MK1 [quickest over 0-60 2.6 seconds and 10 second quarters] also has brick type aerodynamics .

Cheers……

Yeah it is a quick time, but hasn't he fitted a more Aero front end? Front and Rear wheel deflectors?  From the pic its certainly looks like it. Not including anything underneath which i can't see.  The golf shape isn't the best starting block obviously, but everything can be improved,  and just because its bad, doesn't mean you can't do anything.  Its not about huge spoilers as these are for drag and down force, but subtle ways to cut through the air. as his Golf shows.

Regarding wheel deflectors these few cars show the subtle improvements car manufactures use to cut through the air.  small 2mm thick, 25 -35mm plastic boards to defuse the air before it gets to the tyre, and yet not big enough to create front or rear end lift or wake out the side i.e. drag.







The golf seems to have a metal plate to smooth air over the front arch perhaps? Including the improved mk2 bumper aerodynamics, and angled side sill near the rear wheel deflecting air down from directly hitting the tyre.  Wouldn't suprise me if he isn't grill blocking aswell,  especially if he only uses it for QM.  

Lets be honest if you want to go really fast the mk1 isnt the car to use.

100% agree

But as we are on a MK1 forum and Mk1's run the QM its a good place to post a topic on shaving tenths off times

well we will see how much time i can shave of by removing bits of bodywork while at the pod for vw action

did a 14.5 with no rear seats so lets see what we can take off

bonnet
hood
bumpers
back box
rear seats
passenger seat
parcel shelf
door cards


before you say it bonnet all the mk1 escort guys run without them apparently ill get scene points for that  

Not really worth trying to make the mk1 aerodynamic, it already has an optimised rear hatch angle of 30 deg. which is the most effective aerodynamic feature in a hatchback car. The mk1 golf was a benchmark in aerodynamics because of this! 8) It also has good vortice control with the sharp boot side edges 8)  

You can add wheel spoilers and smooth underfloors and whatever else, but they wont make much difference unless the whole rest of the car is fully optimised.

We're talkin short overhangs, roof curvature,  similar bonnet/screen angles, and air flowing easily through the engine compartment. These things would be difficult to change on a mk1, and if you did it would probably look nothing like a mk1. :?

There's not that much you can do specifically for the aerodynamics but this will help:

Lowering - reduces frontal area and the amount of air under the car
Use GTI spoiler - I have done back-back runs with/without, adds 0.2s if not fitted
Remove mirrors

If you're serious about it, put the drivetrain into a Mk1 Scirocco, these are around 4" lower than the Golf even before any lowering, etc.

before and after with the spolier paul was that just because one of the pod marshalls had to retreive it from the strip last year    

bens_cab said

before and after with the spolier paul was that just because one of the pod marshalls had to retreive it from the strip last year    

Lol

Phataz1 said

You can add wheel spoilers and smooth underfloors and whatever else, but they wont make much difference unless the whole rest of the car is fully optimised.

But i don't think you can do much without changing it from being a Mk1 as you say, but wouldn't the rest help?  Even if you left the profile of the car and simply removed the weight and extra bits?

Blocking off the rear valance could be effective without the overall change in anything visible, as its very untidy under the back end. its like a parachute!  Your right about the 30 degree angle of the hatch, but on the cab, the rear side windows have a very big step to the roof on the leading edge to the air, piece of trim would sort that out with duct tape

I would still be inclined to make a simply panel out of black 2mm plastic board and cable tie it to the grill to reduce the air flow into it.  seems popular in the US for drag running. Even if you take it off straight away after the run…

well hood down windows down skid lid on no rear seats or parcel shelf remove the bootlid thatll make the air flow straight through the car

I would have thought a cabriolet was more aerodynamic with the hood up ?

Don't they do less MPG with the hood down ? Same as having the windows down .

chudd said

I would have thought a cabriolet was more aerodynamic with the hood up ?

Don't they do less MPG with the hood down ? Same as having the windows down .

I think so Chudd

I would have thought it is better to keep the air "attached" to the car(hood up), than detached, turbulent and creating a bigger wake.  The air will get real messy once it goes over the windscreen otherwise.

These 2 articles below, with pics discuss attached and detached air in a car (its not indepth language, but idiot or Emm proof )

Content from the article:
Cars with gently sloping rear windows ? often hatchbacks or coupes ? allow the airstream to remain attached right to the rear of the car, so producing only a small wake. The transitional curve between the roof and the hatch needs to be gentle if the airflow is to remain attached, and the angle of the hatch to the horizontal is also critical. It?s important to note that while it may look ?obvious? to the eye that the airflow remains attached across a coupe or hatchback?s rear, wool tuft testing needs to be carried out to prove this.

What happens at the back of the car is extremely important in determining total drag, rear axle lift and, to a more limited extent, front axle lift. In many cases, the flow at the back of the car is more important than the flow behaviour at the front

http://autospeed.com/cms/A_109778/article.html?popularArticle
http://autospeed.com/cms/A_108677/article.html?popularArticle

As Emm said aero at the back is probably the area most likely to be improvable on the Mk1.  Always remember a few years ago I was doing race car aero for my dissy, I found wind tunnel data for Vauxhall Novas and the work Vauxhall did to verify the rear lip spoiler on the SR.

Of course these things can make a difference, it's just at what cost…unless it's all C/Fed up.

Doubt its worth it.  Plough the money into getting power down tbh.

Air flow doesnt have to stay against the surface of the rear profile for the best aerodynamics. You can also create 'delayed wake' with use of a spoiler which gives the same effect for a hatchback, but it has to be in the right place and the right shape, so not one of those full on picnic tables

It basically delays the turbulant air swirling back and causing the vacuum behind the car.

Another major drag factor in many cars is the mirrors as paul c said. Removing these and fitting a windage tray or GTI spoiler are probably the best things you can do.  Things such as taping up gaps are not worth doing

Like said, if you have enough power, aerodynamice doesnt matter lol :mrgreen:

taking my hood off is a weight thing  

if i did lose the hood and boot lid surely the air will go straight through the car causing less drag

anyway to the above question my car seems quicker with the hood down and the wind deflector up perhaps its just a noise thing i dont know :wink:

Yeah i agree do the power thing with the cash and the aero mods for free with cheap or free fabricated parts!  You certainly won't go quicker with 40hp less with simple added aero mods.  but if you spend the money to get the power and then add the aero mod improvements to get the tenths off the time. (amongst all the other stuff you need to get right)  I mean all things being equal like the best start and the best gear change and the best power that can be afforded,  the rest is cheap little 1% improvements.

Regarding the removal of the bonnet and the boot lid.  Yeah its difficult to say whether the weight saving will be outweighed by the shocking air flow over and around the car.  Initially you will be quicker with less weight.  But i would have thought that as the speed builds and the force needed to push an increased drag and wake car,  you may expend more power trying to push the car through the air at the end, than you gain off the line…



Interesting to think about it though. (if you are a little sad like me )

I still think hood up but it would be great to see some back to back runs.  however i suppose its so hard to be consistant  with so many variables.

I think the bonnet thing will make for faster times - as well as the weight reduction, you'll get a better cold air feed. Aerodynamics only really become significant at higher speeds - which ben doesn't achieve! (only joking mate).

Thanks Paul

I know its only a discussion and general runs but its good to hear what you all do or think of in the area other than just POWER!   

power is probably the least important aspect of going fast - its mostly down to weight (or lack of it!)