The splitter and the wing -- with a very trusting passenger:
Here's a report on the day, with good news and bad.
The bad:
- I left my camera bag at home by accident. I'd wanted to shoot footage of the wing at speed in order to see evidence of vibration or stress and where it was located. I had the camera set up to shoot straight ahead, but the one that would have shot the wing itself was home on the kitchen table.
As a result, I don't have footage of the wing at work.
- Based on my initial 250# sandbag tests, I changed the rear mounting piece where the upright attaches to the tail. My new piece was thinner, but it had better lateral support. I tested it twice in a straight line with no one around me up to 135 mph twice, and everything looked fine. But on the first session out, the new pieces (which had a bend in them to keep the uprights parallel) started to bend further and flex down, in spite of a horizontal support between them that was supposed to keep that from happening. I spotted this after the first session and added some extra long bolt bridges to further triangulate the areas under stress. It worked all right, but I also damaged the wing while doing the repair -- I twisted the wing to move the uprights over for space to drill, and the short rear connector tube tore loose from its rib.
The track photographer got some pictures when I was giving Pelicanite bynbad914 (Tim) a ride. There's some interesting stuff in the pictures, where the speeds are about 120 mph.
In the first picture, you can see some burping distortion in the fiberglass hood. You can also see where the unsupported corner sections of the splitter appear to be bending down. You can also see the joining point in the center of the wing, where the part I damaged is causing uneven mating surfaces. (It's easier to see in a higher-resolution version of the photograph.)
In the second, slightly faster picture, you can see the front splitter bending down between the supports that run up to the bumper. You can also see the problems caused by the flexing base pieces below the uprights. The wing wasn't being held up equally on both sides, so it's twisting, slightly, in this picture.
At the end of the first day, I went to the local Home Depot and got the hardware to make spacers to simply replace the point where the metal bent. I also got some JB Weld to fix (somewhat) the damaged rear connecting tubes so the two halves of the wing would mate more evenly.
It was after dinner when I got the time to do the repairs, so I took the parts inside. I've never hammered and drilled in a hotel room before, and I was a little worried that I was going to get complaints from the neighbors. My approach was to turn on some TV programming (a Korean talent show) and the shower at the same time, and just hope that I was creating enough of a distraction to drill two quick holes and flatten out some steel. It only took a couple of minutes, but I felt like I was in a breaking-out-of-prison movie where I was going to be caught at any point.
The new base was heavier, but it held up fine all day on Sunday. Unfortunately, I don't have any high-speed pictures from the second day.
In any case, I'm seeing what parts of the wing and assembly should be made more sturdy in iteration 1.1 of the wing.
The good:
The wing itself showed no sign of stress, and I couldn't hear or feel any evidence of flutter at speed on the freeway or the track. From what I can see so far, it held up fine. When I do build version 1.1, I'll do an 'autopsy' on this one. But from everything I can see, it is plenty strong enough -- at least before time and fatigue start to reveal themselves. There were gusty wind warnings for Saturday afternoon, and there were still no signs of trouble with the wing.
Running without the wing, my best time was a 1:33.4. Running with the wing, my best time was a 1:30.4. The difference in driving was very noticeable. I'll see more clearly when I look at sector times in the data logger, but the comfort level through turn 1 (a 90-degree left), turn 2 (a 95-mph sweeper) and turn 8 (a 130-mph sweeper) were immediately noticeable from the first time I went out. With the wing, I was carrying about 200 more rpms through turn 2, flat on the gas through the entry and the exit, with far fewer corrections. In turn 8, where I wasn't brave enough to study the tach, the car was so well planted that I could go through it flat even on the first lap of a session when the tires weren't up to temp.
My top speed during a lap with the wing was 129.62. My top speed during a lap with the ducktail was 130.79. Both times were at the end of the front straight. This may not mark the full extent of the price of the additional drag, though, since I was probably entering the straight with more speed with the big wing, but still reaching a lower top speed before the braking zone for turn 1. When I go through the data, I'll try and pick a fixed exit point for turn 9 and see what the difference is from the finish speed in both configurations.
It's interesting to compare these times to the last time I was at Willow with the shorter wing. On the same tires and at the same track, the best I could do then was a 1:37 with no aero and a 1:33 with the wing and splitter. The tires I'm running are a full size down from my normal sizes. But they're Toyo Proxes RA1's, which have a long lifespan and should be good for this kind of testing. However, they're known to continue to get better as they heat cycle, which is part of the explanation for the improved times. I was also able to run race gas this time, which allows me to run a different programming map for my car's computer (I have a switch and a 'two chips in one' No Bad Days chip). Track surface conditions and driver inconsistency are also factors, I'm sure.
It's certainly all within my testing's margin of error, but there was a 4-second difference previously, and only a 3-second difference this time. Now, that could easily be misleading, since the track loses 1-2 seconds during the day because of accumulated heat and coolant/oil/tire rubber. But it could be that with my limited power that I've reached a point of diminishing returns with drag and downforce at the new wing size. It makes me want to test multiple wing sizes on the same day -- maybe make a 60-inch one, next, or another 70-inch wing but with a reduced chord length.
In terms of F/R balance, the car felt great, although there was some push to it. I'm thinking as a next step that the front splitter stays the same and maybe the wing gets reduced in size.
I also did some looking underneath cars and diffuser designs. There were two of the new Ford GT's at the event, but I didn't get a chance to look at their underbody stuff at all. I looked at some of the Vipers and the new Corvettes, but the most complete-looking package was on the Lotus Exige. I took some measurements with it of the height at the front axle down to the point where it changes its angle, about a foot ahead of the rear axle, and then where it angles up to the diffuser. One of these days, I'm going to take another stab at some underbody pieces.
One more picture:
It almost looks like the wing is doing
too good a job there, doesn't it?