I did a bit more on this stuff. The inconsistency was to do with the
power available and power required. The Autocourse article has
unreasonable values even though it states "Power at road wheels". I
don't believe a motor that dynos 90hp can generate 86hp at the road
wheels. Once scaled back, everything looks reasonable. It looks like Cd
= 0.48 for the TR2 and 0.58 for the TR3. In Jabekke trim, the Cd =
0.43, but with frontal area reduction CdA was 32% less. I don't know why
the TR3 should be that much different from the TR2. The only major
difference is that the TR3 test was for a hardtop car, while the TR2
tests were for a soft top with top and sidescreens erected. I'd think a
hardtop would be better. The numbers are supported by the top speeds.
The TR2 went slightly faster with 10 fewer ponies.
BTW, the numbers that are posted on the Mayfield site come from a DOS
program called CarTest. There is no telling how reliable those numbers are.
I've attached a copy of the spreadsheet and realize it will not go
through to the FoT list.
Randall wrote:
>> Unfortunately, the numbers were
>> not consistent from road test to road test. For example, why could a TR2
>> with
>> 85hp go 108mph and a TR3 with 100hp go only 100mph. The frontal area is
>> 15.5 sq ft.
>>
>
> Is that with the stock windscreen, or racing screens? My mirrors probably
> add another 0.1.
>
>
>> The drag coefficients ranged from 0.47 to 0.63. I believe 0.52
>> would
>> be a good number.
>>
>
> Same problem, the car can be reconfigured for measurable changes in Cd.
> Spats, tonneau cover, etc. I believe tires start playing a role in overall
> drag at higher speeds as well and of course several different tires were
> supplied.
>
>
>> I can share the spreedsheet if anyone is interested.
>>
>
> Sure, I'd like a copy.
>
> Thanks,
> Randall
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