ozplane wrote:Bimbling along in the Wonderplane yesterday there seemed to be quite a lot of thermic activity. It has a fairly high wing loading of about 14 lbs/sq ft and does "punch" through the bumps quite well. However I know nothing of flex wing microlights and I wonder how they cope with these conditions with what I suppose are much lighter wing loadings?
At first approximation gust response is a function of speed over wing loading. So the Flexwing loses on wing loading (low) but gains on speed (slow). However, they have an added achiles heel, which is that having no rudder they have to have high directional stability (provided primarily by wing sweep) that tends to cause significant yawing excursions in turbulence.
They compensate somewhat however by pendular stability - basically the CG is a long way below the wing, and pilots are trained to hold onto the bar and damp out the motion using the weight of the trike. It works, but you end up with somewhat tired arms (even more tired if you're daft enough to actually fight the motion, rather than gently easing it steadily back to wings level). But also anybody "in the know" never flies a flexwing lightweight in summer thermals - load the tank up full, put a big "boss bag" full of water in the back seat if you haven't got a passenger, and also trim fast - as whilst the "g" response to vertical gusts will go up a bit, faster reduces the directional stability and thus the yawing (and through secondary effect, rolling) excursions a bit and makes the flying experience rather less comfortable.
But, executive summary - yes, flying flexwings on thermic summer days is somewhat hard work compared to 3-axis microlights or light aeroplanes.
G
I am Spartacus, and so is my co-pilot.