Aerodynamic Streamlining Template Overlay for ZX2?

[alohaspirit]

I getcha

[aerohead]

Originally Posted by Tygen1

So heres the results.

Spoiler was set to 30 degrees, with an angle of interception to the roof of approximately 13-14 degrees

Conditions: 30 degrees F, 30.17 Baro, 33% Humidity, Winds NNW 9mph.
No wind on route, unless noted, road is surounded by trees. Starting Speed Was 70mph, then coasted down to 30mph. Runs were started in the same place, unless noted, going each direction, road is not flat. All runs ended in approximatly the same place as well.

First Coast Down Run going West with Spoiler:
West, 53.7 sec.
East, 1.00.2
West, 54.6
East, 1.00.3
West, 59.6
East, 1.00.2
West, 57.4

Now without spoiler going East to start:
East, 101.1 sec.
West, 102.2 (tailwind, enough to blow a flag by the road)
East, 101.5
West, run spoiled by someone deciding to park in the road
East, 103.4
West, 59.4
East, 102.6
West, 55.0 (started and ended in a different spot due to "traffic")

Now with Spoiler again.....wait....whats that sound, thats the sound of the spoiler getting ripped off at 65mph, should have put on more tape! Made two runs without knowing it was off, then drove under a street light and noticed it wasn't there. The next half hour was spent in the dark looking for it. Ran out of time and couldn't finish. Either way, these next two numbers are without bias, because I thought the spoiler was there and it was not, but I did have a lot of flapping tape
East, 1.00.1
West, 55.7 (started in the same place as noted above)

With some creative droping of highs and lows to account for the inconsistancies I get 58.06 sec. with Spoiler and 60.41 without spoiler. It would seem the spoiler did not help in this configuration.

Edit: Some notes after some pondering.... I believe the West bound times are as inconsistant as they are because I did not have land mark to reach 70mph by and therefore had an inconsistant start point and because it was a bit hilly, the ending point on the West Bound coast down was an up hill. So we could just drop out those times and just look at the East Bound times. If we do that we get a 1.5 longer coast down time with the spoiler vs. 2.35 as I calculated it before.
I also noticed that quite a bit of dust had accumulated under the spoiler, in just one hour of driving. So this leads me to believe that it just increased the size of the wake.

I believe the next steps will be some tuft testing to see what the air is doing on the trunk lid and I'd like to try a horizontal extention to see what effect that has. Also need to try and find a better road to test on.

waiting on some feedback from you fellas...

Tygen1,I know you're working with what you've got and we all appreciate you testing and sharing .
And not to create work for you but let me throw out the following and see what you think.
First,your temps are just within bounds for what SAE would recommend so that's okay.
Second,SAE recommends that the rest road have no more than 0.50% grade.I think those hills are beating you up!
Third,if you will "start" your paired return run in the opposite direction where you "finished" the original pass,you'll be covering the same surface for both E-W runs and "cancel" any uphill/downhill the car might have seen.

The dust behind the spoiler is a GOOD sign! It means that the separation is behind it.Your original wake is as high as your roof.
Your tuft test should NOT indicate attached flow in front of the spoiler.There will only be an attached vortex trapped between the back edge of the spoiler and the top of the roof with a sideways tornado spinning in between.
It's this vortex which is giving you the drag reduction.

[Tygen1]

Is it not acceptable to just look at the runs from one direction and ignore the other?
I will try to find a better road that has minimal grade and retest this spoiler.

[MetroMPG]

If all you're searching for is a relative difference, then one-way coast down runs are OK.

In other words, it's OK if you're not trying to quantify anything like drag or rolling resistance.

You're only trying to see if there's a repeatable, detectable difference between set up "A" and set up "B", so it's fine.

[aerohead]

Originally Posted by Tygen1

Is it not acceptable to just look at the runs from one direction and ignore the other?
I will try to find a better road that has minimal grade and retest this spoiler.

For an "official" coastdown you would be required to work with your back-to-back paired runs with each direction reflected,which theoretically would cancel any grade effects of the test road.
But as Metro mentions,you can definitely see a 'trend' if doing back-to-back runs,same piece of road,all same direction,with and without mods,as close together as you can on same day.

[cfg83]

aerohead -

Originally Posted by aerohead

For an "official" coastdown you would be required to work with your back-to-back paired runs with each direction reflected,which theoretically would cancel any grade effects of the test road.
But as Metro mentions,you can definitely see a 'trend' if doing back-to-back runs,same piece of road,all same direction,with and without mods,as close together as you can on same day.

For the majority of us, I think this is the best way to look at it. Don't make the claim that it is having exactly effect X. Simply claim that there is a delta-Y effect. Because we don't have access to the hard tools (wind tunnels) that the big boys do, we have to make do.

CarloSW2

[aerohead]

Originally Posted by cfg83

aerohead -



For the majority of us, I think this is the best way to look at it. Don't make the claim that it is having exactly effect X. Simply claim that there is a delta-Y effect. Because we don't have access to the hard tools (wind tunnels) that the big boys do, we have to make do.

CarloSW2

I totally agree. My eyes cross when I look at the SAE Coastdown protocol and I have to get up and walk around some before I can go back to ponder it any more.Truly daunting!
The resolution and accuracy for data aquisition that they require leaves me weak in the knees.
"Trends" are plenty okay with me.

[catchonfire]

Can anyone point me to instructions for doing this overlay on my own?

[cfg83]

catchonfire -

Originally Posted by catchonfire

Can anyone point me to instructions for doing this overlay on my own?

I use a super-old paint shop pro (PSP) program :

1 - I have a black/white version of the template.

2 - I go to tirerack to find good side views of cars by capturing the "View [wheel] on vehicle" picture. This won't work on a lot of pre 1990's cars.

3 - I re-size the template to match the height of the car image.

4 - I use the "Paste as transparent selection" option in PSP to overlay the template onto the car.

You need to have a paint program that does transparent pastes. That's the key. I also prefer the tirerack images because they are very clean, aka no background, and have no perspective distortion.

Hope that makes sense,

CarloSW2

[aerohead]

Originally Posted by catchonfire

Can anyone point me to instructions for doing this overlay on my own?

catchonfire,the lowest tech solution,and the one I'm forced to use,is to actually photocopy enlarged images of vehicle and template at same scale,tape the template over the vehicle photo where max roof camber positions line up,then actually take a straight pin and pierce the template through to the image below.
When you separate the two,light will shine through the pinholes,revealing the template trend line,and a french curve can be used to 'connect the dots.'
It's dirt simple,requires no computer and can be accomplished with a few simple drafting instruments.
I work in 11" X 17" scale.For better accuracy,you can photo-enlarge to a greater scale and just tape the paper together.
It's kinda Fred Flintstone technology but it will get you to the party.