Very little mentioned about BKB in Nickel & Wohlfahrt's book .. only that tumbling (they call it "autorotating") could be started & stopped "at will" on the BKB.-can anybody finde short info about BKB1 stability in "Tailless aircraft" book\page circa 200-230?\
This also occurs on other low-sweep wings .. like Al Backstrom's "Plank".
It does not mean it is tuck-resistant .. rule of thumb: if it tumbles easily, it will tuck easily too.
Tucking and tumbling are related to low pitch damping .. not pitch stability.
Best remedies for tucking tendencies are lower aspect ratio (longer chord), and greater sweep angle.
Tucking rotation is most often caused by strong thermals or mechanical turbulence, and made worse by most weight shift gliders being attached to the main mass (pilot's body) with a hang strap.. so the pilot mass can be decoupled from the wing briefly during negative G loads.
If the pilot falls into the glider's air-frame hard enough, it can break something.
BTW, a hang glider buddy of mine has gone into a tuck situation multiple times, flying his high aspect ratio wing in very strong thermals .. but his glider is very strong and hasn't broken (yet), so it has always recovered quickly without needing to deploy the reserve chute.