Quote:
Originally Posted by Engeu1
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1) the school bus foil is for back-soiling issues and would mitigate that issue at the expense of higher drag.
2) the rocketail adds frontal area.
3) the rocketail is lowering the drag of a rocketail-induced-larger -frontal area vehicle, compared to the unmodified tractor trailer. When the data is adjusted for the original frontal area of the trailer van, it is this drag that we'd be interested in.
- they use phenomena from axisymmetrical flow which does not exist for land vehicles.
- at flight conditions, crosswind, as it exists for road vehicles would not exist.
- statistically, a truck would always be driving in a crosswind.
- the rocketail cannot alter the total kinetic energy of the airstream ( conservation of momentum)
- it is the turbulent boundary layer ONLY! which can follow a disadvantageous pressure gradient, not the inviscid outer flow.
- since base pressure is governed by the local pressure at the line of separation, it follows that the rocketail is injecting faster, lower pressure air towards the wake, exasperating the base pressure, pressure drag, and overall total drag.
I don't know how rocketail's quanta were arrived at,but I find their claims quite dubious.
And they're comparing to a boat-tail that's not really an aerodynamic boat-tail in the classic sense of the word.
I'd like to see rocketail tested at NASA'a Palo Alto wind tunnel,where the Continuum Dynamics box-cavity was tested under SBA/ DARPA grant.
4) as to the other lateral vanes, they smell of the same thing Hucho commented upon.