Flying Wings - why not?

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I have often wondered why we don't see more Flying Wings amongst us soarers, even outside competition. They seemingly offer a very high degree of efficiency due to their lacking the drag of a fuselage and tailplane and I would like to open a discussion about them if I may.

I have been designing my own gliders for some years, always with an eye to the aerodynamics, and lately have been studying available information on the Flying Wing.  Incidentally, it is almost impossible to buy a reasonably sized, and priced, flying wing glider these days and I have searched the mainland European suppliers as best I can. They just seem to be out of fashion for the moment.

Many years ago somebody discovered that you actually can make a straight, 'plank' wing fly without a tailplane if you curl up the trailing edge and pop a big lump of lead on the nose. The problem was that the lump of lead was always fighting the curl-up, one trying to nose dive the aircraft and the other trying to keep its nose up. This flying plank also needed a huge vertical fin to control the model and keep the Law of the Lever happy. The drag was therefore very high with this set-up until another bloke said 'why not sweep the wings back and put smaller fins on the wingtips?'. Bingo, it worked and the model really looked cool too.

Then the aerodynamicists stepped in and actually confirmed that the swept flying wing was in fact very efficient, both in and out of the wind tunnel. The amount of trailing edge curl-up, or reflex, could be drastically reduced and, like the delta wing, needed little or no dihedral. They explained that a normal aircraft flies with the centre of gravity in front of the centre of pressure or lift.  This will cause the aircraft to nose dive unless corrected by sticking a tailplane way back from the wing on the end of the fuselage.

But here is the interesting bit: The wing-tips of a flying wing are nearly as far back from its C of G as the tailplane is on a conventional aircraft. So by curling the tips up slightly you get the same stabilising effect but without the drag of a fuselage and a seperate tailplane!

Of course it is difficult to pack a load of passengers into a full-size flying wing but for radio control models it is an ideal configuration.  Using modern Eppler airfoils, like the E-186, the lift is excellent and the drag very low indeed. The only disadventage might be orientation when the model is very high up, but by painting a foot or so of the port wingtip with white enamel, followed by a coat of Humbrol Flourescent Orange, you won't lose track of it.

So there is my tuppence-worth and I would love to hear other viewpoints about the Flying Wing.  In particular what is present day thinking about the need, or otherwise, for progressively changing the amout of reflex or twist of the airfoil?  Is the airfoil shape speed dependent?

Finally, can somebody tell me how on earth do those Multiplex and Phase 3 foam models fly so well?  Their wing sections seem to ignore all the rules of aerodynamics when flying either fast or slowly!

Tim Costello, Dublin.