Originally Posted by
Downwind Lander
Let me put it this way.
If you compare the power requirements and the cruising speeds of Rogallo wing a/c and the Long EZ, there is a big discrepancy.
If you take a good look at these two, it seems obvious why - but because it "seems obvious", it doesn't follow that the conclusion is correct.
Protecting myself with the Edward Debono "Po" concept, here is a Po suggestion: rip the wings off a EZ and nail them on a microlight - quickly glossing over the fact that there are control surface issues, with a few tweaks, how much better/worse would it do?
The microlight would never get fast enough to use the longeze wing at its efficient operating point, and would have a much higher stalling speed than is permitted for microlights.
As GtE says, the low speeds can de-emphasise the drag issues to some extent (especially the form drag), but for a given AUW a lower speed means either more wing area ( => more form drag, more skin friction) or a higher lift coefficient (=> higher induced drag which increases with the
square of lift coefficient) or both. You can partially mitigate the form drag increase by reducing the aspect ratio, and you can mitigate the induced drag increase by
increasing the aspect ratio (by the square of the Cl difference) but clearly you can't do both.
Flying slowly without external help (vectored thrust etc) is inherently draggy - look at all aeroplanes designed to fly at low speeds and you see highly cambered surfaces, ofterm with slattery-flappery assistance and/or external bracing to improve structural efficiency to keep the weight down. So you either need a very complex variable geometry setup (multi-slotted, area increasing flappy-slatty stuff) that you can tuck away to remode for higher speeds, or you need lots of area to generate the lift at the lower speeds. Or both.
PDR