Quote:
Originally Posted by JulianEdgar
You completely missed my point. I don't know why I am bothering, but...
1. Honda Insight Gen 1 - attached flow over rear window. (Tuft test your own car if you want to take issue with that.)
2. Measured pressures:
3. Draw in the force vector for -80 on the hatch. (Pressure forces act at right-angles to the panel.)
4. Resolve the vector into lift and drag elements (use the triangle of forces - engineering 101).
5. Note that attached flow is, in the case, causing drag (and lift).
As I said, if you think that pressure drag can be caused only through separation, you are making a very basic mistake. |
1) on the Insight, the trailing edge of the backlight is 24.5mm below the AST-II profile. Okay according to Buchheim et al.. No argument from me. Check!
2) so your measurements reflect those of a 'streamlined' roofline. Check!
3) whether or not each discrete resultant possesses a horizontal component will be reflected in the coefficient of drag.
4) the lion's share of drag will be determined between forward and rear stagnation point.
5) if the body is to be three-dimensional, capable of containing occupants, we must live with the consequences of resultants.
6) the final analysis is Cd.
7) if the Insight is capable of Cd 0.09, and it's Cd 0.25, then, by definition, the Insight has Cd 0.16 designed in.
8) this is what I've been interested in since 1973.
9) this is why I went to college.
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10) and then the big, ugly question rears its head. Even if we make all these measurements, what in the world do we do with them, which gets us to Cd 0.09?
11) Hucho told us in 1987.
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QUESTION :
at what velocity were the Insight measurements obtained? I've been adjusting all your values to 70-mph, as other automotive messengers are reporting figures obtained at 70-mph.
Second question. In other reporting, forward stagnation pressures = to local density altitude / station pressure are indicated, normalized to SAE standard = 101,327-Pascals.
When I adjust the 50-mph and 43-mph data to 70-mph, none the stagnation pressures indicate even a fraction of that.