First fan blade tests


Initial tests had promise, but still work to do. 

Before the world championships, I was so close to getting my fan blades ready for racing. In the end, I managed to test a 4 bladed fan on the spring balance and got 90% of the thrust i was getting with 6 standard hascon blades as I have been running all season.

After making 6 blades, i am reasonably confident in the manufacturing process, which is complex, but if you follow the steps, reliable. The manufacturing needs its own blog post, but suffice to say, it is approximately 8 hours of labour and £30 materials to get to a trimmed blade ready to install… The injection moulded, glass filled nylon blades we use as standard really are excellent pieces of engineering…

In any case 400Lb from the hasconwing blades was less than i was expecting, based on my models and experience. I put this down to the fact that since the thrust fan in the F2 was spinning slower than design, since we were in 5th gear, the blades had to be pitched up further than optimum, more like paddle streamer blades. My model estimates that the max lift coefficient of the blades in this condition was 1.4, which is close to stalling for this blade section. I might be able to get more thrust using a fan with more blades, or speeding it up so i can take some pitch off.

The 4 blades i tested in the craft have issues in themselves, primarily the leading edge had a large bump due to the parting line on the mould. Since the blade skin is in carbon/ kevlar, it is difficult to sand the bump back flush. The bump on the leading edge means the blades will stall early. Additionally the foam in the leading and trailing edges of the blade caused the skin to wrinkle up, however the effect on performance shouldnt be much compared with the leading edge issue.

I plan to make another batch of blades, with some tweaks so i can fix these issues, and i will re-test the blades, hopefully wth 6 available

Posted in: Fan design, Featured, General, Racing Diary on October 5th by admin


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