Aerodynamics discussion

[diss7]

Originally Posted by dradernh

4: If you can use a 15" wheel, use it; however, please do tell us which 15" wheel will accomodate the AP Sprint Kit's 325mm/12.81" rotor/caliper combo

Here you go.
http://www.ft86club.com/forums/showthread.php?t=50693
I started out exploring 16's, and then started realised 15's would fit.
That 15" is a 4 stud off my ae86, but I've since found a 5x100 watanabe 15x6 + 35 fits, but needs a 25mm spacer.

I'm looking to use a 15x8 +10. Which sits inside the bodyline just. Any further in and it fouls on the tie rod end ball joint. Bloody hard finding a 15x8 in 5x100. And I'm not keen on getting custom ones made unless I know they'll definitely fit.

While my 86 was on the hoist today, and armed with some more difuser knowledge, I had a closer look at things. One thing my mate pointed out (who will be doing my fab work) is that my diff, subframe, and even the lower control arms are all higher than the floor; even while the suspension is fully unloaded on the hoist. So will mean a super smooth path and entry to the diffuser.





This subframe and diff are all raised as high as they can go. This will all end up in the race car. The exhaust on this car is 3", the race car will have a 2.5" But Simon pointed out that he'll only need to notch the subframe about 5mm for the smaller exhaust to be higher than the floor and diffuser.
But he's more of a fan of side exiting the exhaust.

So this is looking quite promising.

[dradernh]

Originally Posted by diss7

...my diff, subframe, and even the lower control arms are all higher than the floor; even while the suspension is fully unloaded on the hoist. So will mean a super smooth path and entry to the diffuser.

Excellent; you've a great deal of flexibility then.

Thx for the info on the Watanabes - which tire will you be running?

[diss7]

Originally Posted by dradernh

Excellent; you've a great deal of flexibility then.

Thx for the info on the Watanabes - which tire will you be running?

I already bought some 17" slicks, but have not see them as the stock oiling system is not upto that level of grip. They're 240/610-17, Michelins; the same tyre toyota racing New Zealand are using on the tr86.

If going 15, I'll use the same slick I use on the ae86 which is 200/580-15 kumho s700. I have a spare set of these also, ready to go.

[atledreier]

Old thread, but i'm interested in actual figures for how much lift I'm getting at certain speeds with a stock, or close to stock setups? I've read through this thread but could only find a CL value that doesn't give me actual numbers in Newtons for a certain speed. (I think, I'm a novice at aero).

[Shankenstein]

Originally Posted by atledreier

Old thread, but i'm interested in actual figures for how much lift I'm getting at certain speeds with a stock, or close to stock setups? I've read through this thread but could only find a CL value that doesn't give me actual numbers in Newtons for a certain speed. (I think, I'm a novice at aero).

Typically, the lift is related to the velocity^2 and your frontal cross-section area.



where
L = lift force
rho = density of the fluid (air)
v = free-stream velocity (vehicle speed or localized speed over a wing, etc)
S = frontal cross-section area

In reality, you're looking at a dynamic density and localized velocities... but let's keep it simple.

If you needed a ballpark number, here's a horribly inaccurate estimate:
S = body + tires + side mirrors
= ( (51" - 5") x 70") + (2 x 9" x 5") + (2 x 7" x 5")
= 3390 sq in = 23.5 sq ft

[tahdizzle]

42

[Shankenstein]

Originally Posted by tahdizzle

42

Now we just need to find out what the question was...

[kavanagh]

I just realized I've already been following the aerodynamic thread mentioned in your signature that I was afraid of jumping into:


If you think you're nerd enough, join in the discussions about Suspension and Aerodynamic modeling!




It must be time for me to dig into the suspension one.


Wish me luck!

[atledreier]

Reason I ask is that there's finally some good tools to put cars into a good commercial racing simulator called Assetto Corsa. I am doing the '86 platform and need as accurate data as I can get my hands on. :-)

[Malt]

@plucas

Given that you've done loads of aero testing, in your opinion is there any benefit to these TRD parts or are the purely cosmetic?

This fills the gap between the rear window and the trunk lid.


How about the TRD style lip spoilers?

[7thgear]

question in rear wing location




wings mounted far back away from the rear axle, and wings mounted as close if not over the rear axle


the far back mounted wings, do they not act as a lever.. making the axle the pivot point, and therefore lift the front of the car?


and hence it would theoretically be better to have the wing directly over the rear axle to reduce this


(but obviously impractical due to the roof being there and all that clean air stuff

[Shankenstein]

Originally Posted by 7thgear

the far back mounted wings, do they not act as a lever.. making the axle the pivot point, and therefore lift the front of the car?

and hence it would theoretically be better to have the wing directly over the rear axle to reduce this

Think about it in terms of big booty betties... 200 lbs of her downforce is either sitting on the front area of the trunk lid or back at the bumper support.

The required support from the ground is still 200 lbs. How that force is distributed (front-to-rear) will definitely be affected by leverage. Chassis deflection, suspension geometry, squishy bushings, and other things will prevent the car from acting like an infinitely rigid member (Call 1-900-Mix-a-Lot!).

In the motorsports world, they use aero leverage as a tool for balancing the car. Typically the rules restrict wing placement... but when the rules are loose (like hillclimb), you'll see some really innovative aero designs.

[Gunman]

When you can move the wing back, you can get it to help drive the diffuser, so you gain downforce not only from the wing itself, but the increased efficiency of the diffuser.

[plucas]

Originally Posted by Malt

@plucas

Given that you've done loads of aero testing, in your opinion is there any benefit to these TRD parts or are the purely cosmetic?

This fills the gap between the rear window and the trunk lid.


How about the TRD style lip spoilers?

The window filler probably doesnt do much. Might reduce a little drag but doubting it. I would ventue and say it is cosmetic.

Lip spoilers work well. It will make more downforce than wingless/spoilerless trunk. It will make less downforce than a proper wing. It should also have less drag that both wingless truck and a proper wing.

Sorry I missed this question until now.