Hello Tintrax

I fly only small autogyros very similar to yours. Mine all use code 5 polypropylene for hinging on both straight and delta hubs. I have never had the problem of flutter however, I do use a much wider hinge than seen on most small poly hinged gyros. It does make hinging slightly more rigid but this has had no effect on stability or performance. Its surprising just how rigid the hinges can be, I have in the past used thin titanium for the flex material which is considerably more rigid than poly and it has worked equally as well. In fact it was rigid enough to not require down stops on the hub !
This may be why I have not experienced any flutter as the more sturdy hinge prevents spanwise twisting effects. The rotors on my .10 size models have a chord of around 1.5 inches and are solid balsa with a hardwood leading edge.

The picture is of a few of my hubs with the widened hinge material. They are basically very similar to Jim Baxters excellent designs. I couldn't resist also throwing in an image of the carbon fibre hub I made, the thin flexible resin flapping hinge was later replaced by the thin titanium previously mentioned.

One question, did you put your blades directly on the to the tangs of your delta hub or did you still slightly negative shim them like you perhaps would on a normal straight hinged hub ?

Cheerio

Sean