Quote:
Originally Posted by Bicycle Bob
Creating induced drag is the purpose of wings, with as little form drag and surface drag as possible. So, if you align a wing with the airflow, to eliminate induced drag (as in the Vomit Comet going over the top to produce weightlessness) you have a pretty well streamlined shape, with low enough form drag that the unavoidable surface drag is a significant part of the whole.
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Bicycle Bob,when I posted last,I was shooting from the hip without my references with me,as is common for me.I got into Theory Of Wing Sections and found your airfoils.There was also a NACA 0010-35 that had Cd 0.035 @ a couple degrees each side of 0.At some time one of the pop sci magazines did an article about modern airliners and tossed around numbers as low as 0.002.-------------- In Schlichting's Boundary Layer Theory,he was big on NACA 63(4)-021,as it is a laminar flow wing,but it doesn't score numbers as low as the 66 series airfoils.--------------- Where I really missed the boat,is with Mair's numbers.I enlarged his graph and added resolution to the data points,and when extrapolating out to a full boattail,his body of revolution scores on the order of Cd 0.0225.---------- This conflicts with Hucho's portrayal at Cd 0.04.Perhaps the art reproduction in the book is off.I don't know.---------------- Going back to Aerodynamic Drag by Hoerner,the lowest drag he publishes,is for the ideal teardrop,at Cd0.04,which might take form as an airship or wingtip tank.A basic fuselage scored Cd 0.06.A 12% fuselage got Cd 0.066.15% fuselage got Cd 0.05.Gee Bee R-1 I estimate at Cd 0.044.37% teardrop Cd 0.04.Mair body of revolution with prolate ellipsoid nose an full 22-degree boattail an 39.6% dia/length = Cd 0.0225.---------- The best float I could find was Cd 0.056.Flying boat hull Cd 0.063.Torpedo Cd 0.35.50-kg bomb Cd 0.11.------------ The wing sections are slick,but its two-dimensional flow and packaging kinda weird.--------- I don't know what to make of Mair's form(secret-sauce streamlining).--------- If we take Cd0.04 as the minimum for three-dimensional flow in free-flight,at a fineness ratio of around 2.5 to 1 we get 5-to-1 due to ground-effect mirroring and Cd 0.08.Adding wheels,Cd jumps to 0.13.Fairing in the wheels and we get back to Cd 0.10.the theoretical minimum.I don't know if Ernie can break Cd 0.10.If you introduce any angle of attack,then induced drag eats into overall drag,and at 200-mph,which I think was Ernie's target,would stability not be a problem if lift is varying as the square of the velocity?