Quote:
Originally Posted by Christ
I was just pondering this point earlier today and part of last night... I wonder though, if the ideal really should be 5:1 in ground effect, or if ground effect changes some part of the design?
In other words, if a body of revolution of L/D 2.5:1 were placed in ground effect without being halved, would the 2.5:1 fineness ratio still be most effective, or is that the most effective ratio for an airship-type vehicle?
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The research by the PhDs says that a vehicle with L/H= 5,@ zero-ground clearance has the lowest attainable Cd.
In "reflection".this produces a form with L/D= 2.5.This form also just happens to have Mair's 22-degree angle.Coincidence?
This form happens to look like an airship because airships are designed for low drag which is what this form delivers.
Below 250-mph,the 1/2-hemisphere nose is adequate ,with the rest of the body,a long tapering tail.(Teardrop ).
This was the premise of the Rolex-Big Ben template.
A shorter form suffers a Cd increase from profile drag.
A longer form suffers from increased skin friction.
You can clearly see this relationship in Hucho's table for ellipsoids.You can also see it in the table for sections.
There is always a point of minimum Cd where the curves for profile drag and skin friction cross.For 3-dimensional bodies this occurs @ L/D = 2.5.
In FLOW-IMAGES I attempted to provide enough examples of flow separation such that one could just look and see what happens when you go "off template."