Originally Posted by
Genghis the Engineer
Yes. If you want a tailless delta that's efficient it wants to look something like a Horton or early Northrop, not a flexwing microlight.
That said, internal structural cleverness and use of fairings and simplified shapes certainly has potential to remove a lot of the easily identifiable profile drag generators in the way of cables, struts, pilots, etc... The best such at the moment is probably the P&M PulsR?...
https://www.youtube.com/watch?v=1RbDVS-0XTE
Which if nothing else, is very clever, and very pretty. Designed by the aforementioned Bill Brooks.
G
True - anything can be optimised, but you still have all those struts, wires and sticky-out bits. One of my prized possessions is a copy of "Aerodynamic Drag" by Dr. Sighard Hoerner*, and whilst the first half is a fairly typical analytical treatment of the fluid dynmaics (circa 1940s), the second half is a much more interesting practical treatment. It takes a basic aeroplane shape with "idea" shape features and then looks at the consequences of adding practical details like panel gaps, cowlings, gun ports, control horns, struts, wires, antennas, wheels etc etc and provides some rather good ways of predicting how they degrade the drag of the "ideal" shape. It's all based on empiricle methods - measurements of actual vs predicted drag for a range of aeroplanes. His examples are all 1930s/40s era german aeroplanes, and I am always amused when he refers to things like the Fiesler Storch or the Messerschmidt 110!
Anyway, in this book he offers some rather depressing guides on just how bad strut/wing interfaces and bracing wires are from a drag perspective. Even the PulsR commits what Hoerner rgards as "cardinal sins" by having V-jointed struts against he wing underside. Hoerner suggests that aeronautical performance stagnated until the materials and structural sciences allowed cantilevered designs which finally eliminated these performqance-sapping features.
Another thought is that these flex-wings operate at much lower speeds than the longeze (et al), so they fly at much lower Re with consequent need for much more wing area. That alone will increase both form drag and skin friction in comparison.
PDR
* my copy is one of the first print run - the one which he typed and typeset, added the hand-drawn diagrams and graphs, and then self-published because no technical publisher wanted it. These 1st editions are now rather rare (and no, I'm not selling it)...