This really is an excellent forum. John, thanks, I am thinking that may have something to do with it. I had been lazy and said power as it's fixed pitch. Sycamore, that may be worth looking at if the opportunity arises, I certainly couldn't get a break at lower speeds nearer the erect stall.
Kebab kid, that's just brilliant! However my head hurts now
. I had thought the Heron would have an advantage with (presumably) a solid crank but the 2-/3-blade thing is very interesting.