Skip Higginbotham wrote:
> Mayf,
> Congratulations on your home and shop!!! Having done that a couple of
> times, I know how much fun it is. (-:(-: Would love to see it later on this
> month when we are there.
>
> Thank you for taking your time to take a stab at this problem. From your
> analysis and conjectural deduction, it would seem that covering/enclosing
> the upper half is the most important as it reduces the drag by about ?%
> (may be about 65% or so) because the free stream air now only interferes
> with the enclosure and not the rotating tire. The rotating tire and the
> shear between it and the enclosure have a drag loss but the fenderwell
> (enclosure) vents can reduce this some. We will add the vents like the
> sports cars do. How far down the tire should the enclosure go depends on, I
> suppose, the diameter of the tire.....or does it? As the tire surface
> airspeed approaches 0 (when the tire is contacting the surface, no
> slippage) drag also approaches 0. So the lower part (?%) can run in free
> stream air with little drag penalty.
> We are building enclosures for the rear tires on the "Rose" and results of
> this discussion will directly effect the amount of tire that gets enclosed.
> Right now I would cover 75% of the tire and leave the bottom 7-8" out in
> the open. Simplifies the fairing problem a lot! I'll see if my little mind
> can figure out the differential airspeed for the lower 8".
>
> How any of this would work in a fenderwell that is out of free stream air
> absolutely baffles me. But it might help some if the airflow in the
> fenderwell is significant and the direction can be established. Prolly need
> some tunnel time for this one.
>
> I have seen Cd for open tires that vary from .19 to .7.......anybody have
> some measured data?
>
> Skip (This is what makes this sport fun!)
>
Skip,
I would think there should be some info around for non-retractable aircraft
wheels; especially for some of the 'barrel racers'. Of course that is for the
whole shape, not nec. the rotating unit, but it should give some guidance.
I'm thinking of the bikes, and they have a 180 deg. limit on coverage.
The other factor for bikes is the chance to ease airflow past the fork legs
where
allowed.
I see non-streamlined bikes with no fender; wouldn't even a simple fender help?
There's a question; Is it better to treat the wheel as a stand-alone item and
try to ease the flow back from it, or try to use the wheel as a bit of 'fairing'
ahead of the lump that follows?
I know there is no one simple answer; bare, streamlined, etc.
Cheers,
Rick
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