Quote:
Originally Posted by gumby79
Am I understanding correct?
1)
If there's no change in frontal aera the a-b comparison will both be skued the same amount? Making the % of change an acaccurate a-b test. But the actual CdA # would be illegitimate.
Eg. Leave the Headache Rack on for ab cap test (the red part ) because it adds 15*2" of surface. 114*2" aera.79*2'
This shot is from a slightly elevated angle making the increase look larger. The lower bar is below the cab . Ecept in the center its 1/2"T ×6" W above. With ~ 7°pinch for & aft . The 3"W ×1/8"T is dead flat to the air.
The plan is for this to have an air curtain affect. To settle the disturbance from the cab/ cap gap. A less functional more aerodynamic design,has been suggested by many people , would be to eliminate this cab protection feature.
2)the Dodge advertised CdA (have you beenable to locate one yet?not me )compaired to the DARCO naked. Would this yield a value to the amount of skue?
I think the anwser is :
A) there is a variant from tunnel to tunnel so not comparable
3)
The removal of the headache rack (red part ) would alter the %of blockage resulting in a different skue ? A naked test could not be compaired to a headache rack test(different Aera/skue)? |
* The large frontal area creates local acceleration of the airflow to velocities which exceed the 'infinity' velocity of the tunnel (76-mph).
* This 'super-velocity' causes a thicker boundary layer on the truck,tunnel floor,walls,and ceiling,which chokes the flow causing buoyancy effects which can't be eliminated.
*It's this buoyancy effect which trashes all the data.
*There is absolutely no way to know how much the 'actual' values are being skewed.
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*With a constant frontal area,none of the coefficients can be trusted,and even with A-B-A testing the absolute numbers cannot be trusted.We'll only be able to see 'trends'. Which I think will still be valuable on their own.
* To complicate things,if you remove the headache rack,whatever numbers are produced must be taken in light of the lower frontal area.
*We can only say that the 'observed' overall drag went up or down.
*But that's valuable data in itself.
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* There are some published Cds and frontal areas from Dodge.I'll try and dig out what I have.
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*A 'naked' Cd from Dodge,compared to a 'naked' Cd at DARKO would be valuable.It WOULD infer an amount of 'skew'.
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* There IS a tunnel-to-tunnel variation in coefficients when a standard NACA-profile calibration model is tested from location to location.A number of tunnels have been evaluated,and a standard deviation has been established.
*Unfortunately,both the A2 and DARKO are too new to have been included.Same for Gene Has' new rolling floor tunnel.
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*As to the cab-bed gap,I'm gonna try and test,sealed,and 'normal' to measure any difference on the T-100.2-years ago,the smoke blew over the gap as if it wasn't there.I'd like to know what difference it makes.