Quote:
Originally Posted by Otto
We'll just have to disagree on optimum fineness ratios. My 3.33:1 comments based on Zedan et al, Bruce Carmichael, Heinrich Hertel, and Dr. Hoerner's books, all in my library, based on tests of optimum fuselage pod shapes, etc., i.e., bodies of revolution, not air foils. Also measured proportions of shark, tuna, etc.. per Hertel. That's my story and I'm sticking to it.
Motorcycle pie plate efficacy depends on speed and crosswind gradient--the faster the less effect from a given crosswind. You knew that.
The pie plate on a stick trick might work pretty good on a motorcycle, since the basic essentially concave shape of an unfaired motorcycle is so bad to start with. Easy to test. Actually, those crude windscreens on unfaired Harleys reportedly help somewhat, and have some of the aspect of pieplate on a stick, just not so far out in front. A serrated edge on the pieplate might also help--makes little vortices that may counter-rotate each other and dampen turbulence. At least, that's part of the theory of serrated trailing edges on new jet engine nacelles, said to be quieter than conventional.
We won't know until we try it. Can the motorcycle mod guy be talked into this? A simple coast-town test might tell the tale.
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Otto,I'm okay with disagreement,I certainly do not "know it all" and I mean no disrespect to you nor messengers Zedan,Carmichael,Hertal et al.
And I'll digress and share what I've run across and we can see if I've missed the boat on some fundamental.
I believe that Hoerner along with every Fluids text cites Prandtl's work which includes Airship bodies.
My data reflect that for length/diameter ratios of 2.5:1-2.8:1,Cds of 0.04 are realized for a frontal area drag coefficient.
An airship with 5:1 scores an overall Cd 0.05 and the higher value is attributed to greater skin friction overwhelming the diminishing form drag.
The airship Los Angeles of even greater L/D has Cd0.071.
The data clearly appear to demonstrate a trend toward increasing drag as L/D increases beyond 2.8:1.
In Hucho's text in Fig 4.117,at the top of the table appears "Body of revolution optimized for low drag" with a sub-0.04 Cd.
This data is from reference 4.85.
Reference 4.85 is Hucho's contribution to Gino Sovran's(GM Research Labs) "General Discussion........................." which cites reference 4.3.
Reference 4.3 is 'Prospects for numerical simulation of bluff-body aerodynamics,' in Sovran's "Aerodynamic Drag Mechanisms of Bluff Bodies and Road Vehicles",1978.
Which would mean that the sub-0.04 form is generated from CFD.
From the Journal of Fluid Engineering,Sept 1980,Vol 102,they admit that modeling of 3D lifting bodies surface singularity methods to calculate potential flow are flawed by incompleteness of ability to model near wake flow,something MIT finally achieved with the Navier Stokes Equation in 2009.
The Journal says" Although one can learn something of the fundamentals of bluff body flow by studying isolated axisymmetric bodies this family of shapes has only limited relevance to the land vehicle problem."
My question about Zedan's form,would be :
(1) Is it real and was it developed in a windtunnel at critical Reynolds number with turbulent boundary layer?
(2) Mair's boat tail research arrived at a maximum tail angle of 22-degrees to prevent flow separation ( and Mair's own research does not include skin friction of the body ).The sub-0.04 shape in Hucho's book has the max cross-section occur at 42% of length and ends with an included angle of 41-degrees.Does Zedan's form have a tail with as radical an architecture?
(3) Is the performance of Zedan's aftbody sensitive to,and completely dependent upon the exacting architecture of the forebody?
(4) If so,would the utility of Zedan's form be of only limited value and basically represent an academic curiosity?
I'd like to see the form if you could post it.
I've tried to follow Bonneville,the HPV competition at Battle Mountain,Man-powered Subs at David Taylor Tow Basin,EAA,NASA,etc.,so far I just keep seeing the same old fluids stuff.