Quote:
Originally Posted by Patrick
WRT #12):
Aircraft wing section coefficients are calculated based on the planform area, not the frontal area. So for a 6% section, you have to multiply the coefficent by 16.67 (100/6): 0.003 x 16.67 = 0.05 Cd based on frontal area. So the 0.103 found in the CalTech wind tunnel is only a 106% increase. For comparison, what were the Cds of the other bikes in the competition?
The GM Sunraycer was based on a 63-series wing section and AeroVironment claims that laminar flow was achieved up to the 30% chord maximum thickness.
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Patrick,I spent some time with my books and believe I understand the situation with Sunraycer which was described by Bart.
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With a 'flat plate' the transition from laminar to turbulent boundary layer would occur around 500,000.
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For a smooth body,if the pressure is decreasing in the direction of flow ( which is what is occurs at the front of Sunraycer as air accelerates towards the position of maximum cross-section ),this will have a stabilizing effect on a laminar boundary layer up to the first position of minimum pressure,which in the case of Sunraycer would be about 30 % of body length.
Then after the transition,the turbulent boundary layer helps hold the flow against the aft-body all the way to the trailing edge.
When looking at tables I had to be aware of if whether the author was discussing flat plates parallel to flow,perpendicular to flow,or bluff bodies in 3-D flow.
Also,when looking at wing performance,the following were mentioned as criteria which could affect:
* thickness ratio
* area
* aspect ratio
* taper ratio
* aerodynamic twist
* angle of sweepback
* section lift-curve slope
* effective lift-curve slope
* Jones edge-velocity factor
* section-moment coefficient about the aerodynamic center
* chord at any spanwise station
* air density
* air turbulence level
* air velocity/Mach number/local Mach number
*angle of attack
* roll
* side slip
* surface roughness
* camber
* vibration/damping/amplification
* unsteadiness
* frequencies/harmonics
* pitching moments
* interference
* induced drag
* waviness
* slipstream
* wing loading
* wing root
* wing tip
* slats
* flaps
* slots
* slits
* aileron
* blowing
* suction
* turbulators
* dive brakes
* compressibility
My head hurts!