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Christchurch, New Zealand
The test rig.
2 degrees up nozzle seemed to work best – note cooling ducts running over top of pump
The impellers are simply superglued to the shaft – quick and easy way to secure them. Grub screws don’t hold strongly enough in the plastic.

Note the screw guides at the 4 corners – keeps the unit centered when assembled.

Intake grates help prevent debris get in… I probably should have fitted one earlier! I’m surprised at how well it operated with so many blades missing. I didn’t really notice anything was off other than top speed dropping slightly. Crazy. These impellers were printed in ABS – PLA is a lot harder so I will try them in PLA next. At 1mm thick I may need to thicken and reinforce them.

So, its quick. Still porpoising slightly. I’ve worked out that 0 degrees upward trim isn’t very good. 4 degrees up is too much and it porpoises. 2 degrees seems to work rather well. I still need to play a bit with the CG to find what works best. No doubt the tuning will change again once the lid with decorations is put on so I will need to get those on sooner rather than later.

It likes to spin out on the corners still – not sure if that is because of the smaller diameter pump providing less downward force? Perhaps I need to go to a lower exit velocity pump that provides more downward suction? What about varying the pump intake throat? Perhaps its the front strakes that provide too much grip at the front, but no additional grip at the rear.

Leave your thoughts in the comments.

Hopefully next update comes out next weekend 🙂

Post Author: Jotham

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