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Old 06-19-2020, 10:56 AM   #121 (permalink)
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WAG

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Originally Posted by MeteorGray View Post
As noted before, I also have observed variations in the TPS (throttle position sensor) screen of my Scan Gauge when at WOT using a throttle-stop device. These variations seem to depend on on road grade and wind speed and direction, ie, the engine load.

For instance, at a consistent WOT pedal position, I found that my Scangauge reported TPS values from 26% at 70mph to 28% at 75mph. This was during an uninterrupted 10 minute WOT run over a stretch of approximately level and approximately north-south oriented road with a wind that the weather bureau reported was 10mph from the northwest. I was going approximately south at the time, so it was essentially a tailwind. I attribute the range in speed to imperceptible road grade and wind direction-and-speed variations. The only surprising thing to me was the 2% TPS variation. This is obviously something other than a mechanical throttle position being reported by the gauge on its TPS screen.

As part of the same test, I turned the car around and drove in the opposite direction, ie approximately north, which then put the wind as a headwind. On that run, which was only a minute or two so did not see as many road or wind variations, I recorded a speed of 65mph at a TPS of 27%.

This kind of puzzled me, since I didn't see why the throttle position value would change with these variations in load when I know that the throttle is being held in exactly the same position, mechanically speaking.

So, I must conclude that the throttle position sensor screen is not reporting the actual throttle position per se, i.e. mechanically speaking. I think in my drive-by-wire Mazda3, the TPS value is actually a calculated derivative, probably resulting from a combination of such computer-read sensors as the throttle sensor on the throttle pedal, the mass air flow sensor that measures the volume of air going into the engine which is used to determine the load for the proper engine settings, and whatever else the engineers felt useful. Just a WAG.

As noted before, I quit looking at the TPS value on the gauge because it is not useful in trying to measure the precise mechanical throttle position, which does not change with load. I just take it on faith that when the throttle is being held at WOT by the throttle stop, the actual throttle position does not change with load. The speed does change with load, of course, but not the mechanical position of my throttle pedal. What the computer is doing with that mechanical pedal position obviously is up to the engineers and what their design dictates.

Incidentally, I also looked at the LOD (engine load?) screen during my tests, but it gave values that ranged widely that seemed even more useless to me.

The world of computers has passed me by without even a courteous honk.
That's a very thoughtful 'WAG' !

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Old 06-19-2020, 03:14 PM   #122 (permalink)
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HP to the salt

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Originally Posted by j-c-c View Post
My suspicion on the vette on the flats, there is a lot of effort there to gain rear DF with the least amount of drag within the rules, being getting HP to the salt is difficult at high speeds with OEM body shape. My guess, drag reduction was the lesser goal.
1) it's not unusual for many of the cars to experience wheelspin, even at the 8-Mile, for the power-to-weight ratios they have.
2) if the car gets sideways, it's aspect ratio, as a crude wing, can increase by an order of magnitude.
3) in 2014, a 1991 Corvette, which had been two ahead of me at DARKO, got sideways at the finish at World of Speed,at 231-mph, going airborne about ten feet in the air, doing a reverse-half-somersault, landing on its roof. The car was trashed, and driver shook for over a half hour afterwards, brought to tears by the event.
4) all those capping plates on the Vinson car give it a bit of weather-vaning capability, and if the driver is quick enough they can get the parachute(s) out in time to save the car.
5) the 'Bonneville' spoiler also helps the pilot chutes to find clean air for rapid chute deployment.
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Old 06-19-2020, 03:42 PM   #123 (permalink)
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Eroding clay method

Looking at the closeup photos, something came to mind.
It appears that the clay introduces an artificial roughness which by itself would alter Reynolds number, directly effecting the point of separation, as with VGs.
Not only the performance of the wing ( turning vane), but also any of the Insight's body covered or behind it.
Technically, this would have to be sorted out.
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Old 06-19-2020, 03:53 PM   #124 (permalink)
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testing protocol

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Originally Posted by JulianEdgar View Post
A good example of aerodynamic modification testing.

Modification:

Diffuser wing



Intent:

Working with full undertray, change wake pattern to reduce drag

Mock-up:

GOE222 wing extrusion with plywood endplates, attached to rear diffuser with aluminum angle.

Test:

Throttle stop testing, 30 per cent throttle, top speed in km/h, Breadalbane straight, New South Wales, Australia. Weather: 13 degrees C, light head wind, 26/5/20, 8.30am

Results:

No wing - 100
1 finger upper gap - 100
2 finger upper gap - 100.5
3 finger upper gap - 99.5
4 finger upper gap - 100.5

Conclusion:

Makes no difference to drag

Outcome:

Remove mock-up.
Please forgive me if this has been covered elsewhere.
It takes 30-miles (48-Km ) of continuous driving at 50-mph ( 80-Km/h ) before all lubricants and dynamic rubber structures reach equilibrium, steady-state conditions.
If all testing follows this pre-test condition, then we're a-okay, as long as all other possible variables are accounted for.
If not, we're introducing number of variables which are not accounted for during measurements, which remain unknown quantities, and are certain to influence measured data and conclusions.
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Old 06-19-2020, 03:56 PM   #125 (permalink)
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Please forgive me if this has been covered elsewhere.
Spoken like a true gentleperson.

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