Hot Wings can probably explain more than me, but with a straight spar Fauvel wing sailplane, the pilot must sit very close to the spar. Adding an engine at the rear of the wing will allow a heavier pilot close to the spar, or an average pilot will have to move forward. But the balance becomes more critical, because both of the large weights (pilot and engine) are further from the balance point. Without changing the chord length of the wing, it becomes harder and harder to achieve good flying characteristics.
The span of the wing will not be the issue for Erkki, it will be the chord that may have to be enlarged.
Bille, you were just waiting for a chance to sneak that in there, weren't you? ;-) Thanks for sharing. I had a few occasions to interact with the naturalist and archaeologist Richard Leakey when living in Kenya, a great man who never seemed to let the loss of his legs in a plane crash in the 1990s even slow him down, let alone stop him. Cheers, Matthew
Earlier in this thread, someone mentioned wire braced aluminum tube construction. The Laird brothers used this in their aircraft, from just aft of the cockpit to the tail post. They didn’t use turnbuckles to adjust wire tensions, they used cycle wheel spokes, with 2” diameter rings in the center of the ‘X’. The threaded adjuster, which would normally be in the wheel rim, was in the central ring. The crooked spoke end, which would normally be in the wheel hub, was slid through a fitting in the corners of the fuselage bays. Light & strong & adjustable: Matty Laird was a clever lad!
There was one of HBA's most epic and glorious discussion threads, "Motorcycle of the Air", where most of those ideas were brought up and discussed. If you really want to go down the rabbit hole while "self-isolating", that 100+ page thread will definitely be the right vehicle to do so. One of our more talented HBA participants, FritzW, took hand sketches and ideas and napkin scrawls from several of the discussion participants, (myself and several others) and turned those sketches into the most magnificent digital renderings. Other participants (Sockmonkey, Delta, and others) did their own digital renderings and ideas, and further enriched that discussion.
The one you pointed out above was originally a hand sketch, based on the Backstrom Powered Plank flying wing, with a motorcycle "straddle" fuselage instead of the steel cage, and with the (problematic) Backstrom tip rudders changed to inboard fins mounted on removable booms. The original engine was to be a Briggs & Stratton V-twin, 25-30HP. Several other engines would be viable, but the Briggs hit the combination of reliability and price point.
Seriously, if you like any of this stuff, sit back, get a cup of coffee, and start looking through the "Flying Motorcycle" thread. Lots of great stuff, spirited discussion, and a lot of fun.