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Not a different aerofoil just twice the size :) ) it has a carbon fibre core for stiffness, its tricky to print so i've had to design custom supports and print all 3 blades at once like this (see attached) with a brim base support, this is just the outer section of the blade.
The tuning of rotational speeds with the generator for the design output is difficult and requires some maths. There is always a temptation to over do the gear ratio and try to spin the generator faster resulting in an increase in torque the turbine cannot overcome. The big advantage of the HAWT is rotation speed, I had the MkII spinning in the 1200-1400rpm range in 5m/s wind speeds which is insane, a 2:1 gear ratio doubles that and the output is good for such a small (1/2 meter) diameter turbine with little generator torque to overcome. The torque on the MKIII NEMA23 is huge!!! and therefore i'm using a 1:3 epecyclic reduction gearbox meaning I will have to spin the turbine faster and i've focused a lot of effort on making the bearing alignment and stiffness better to enable these higher RPM's. Bearing alignment and reducing flex in the shaft is important for overall efficiency, perhaps look at bearing alignment and try to reduce shaft flex for reduced mechanical drag, this will help out on start up and power output.
On the MKII if you slightly change one of the aerofoils to be out of alignment with the other two the rotation speeds for a given wind speed drastically reduces and this might also be true for the VAWT as the attachment to the centre rotor looks difficult to setup and align, perhaps try and take some measurements of the angles and ensure everything is nicely aligned? I use a RPi to measure RPM so I can do back to back tests using a fan and try and find the sweet spot of all the different things you can tweak?
I hope this helps in some way, let me know how you get on?