The Flying Flea Saga Continues

CONTACT's picture

- Roy de Stadler, EAA Chapter 973 Krugersdorp

“The best-laid schemes o’ mice and men gang aft a-gley” - Robert Burns

I had thought my Flying Flea would have had its test flight early this year. In January the final inspection of the completed aircraft was conducted by our esteemed Life Member, Mike Spence, and pronounced fit to undergo the ground trials and test flight. The engine had still to be run in, however, and that was where my woes started.
Not with the engine itself, that performed well, but with my choice of propeller. A few years ago I had seen a prop with the pitch I wanted which had been used with a Rotax 503 ULDC, same as mine, and promptly bought it at a bargain price. The prop was designed for a 3.5:1 reduction drive whereas I am using a 3:1 ratio, but in ignorance of prop design I thought I would get away with it! Some very naïve thinking on my part and an indication of my total ignorance on the subject, and you are welcome to have a laugh at my expense!
Of course the engine could not deliver the power needed and the highest rpm I could get from the engine in a static test was 4200 to be compared with the required 6200 rpm. I consulted Pieter de Necker of P-Prop and he slimmed down the prop for me to the extent that he could safely go.

There was no guarantee of success of course, as he had to work within the geometric confines of the original prop. You cannot add wood to a prop, only remove it! With this modification the maximum rpm achieved moved up to 5200. The next resort was to reduce the prop diameter inch by inch, until I finally achieved the goal of 6200 rpm with the prop diameter reduced from 68” to 62”. It is interesting to note that in reducing the diameter I made a straight cut across the prop tip and that simply rounding the corners added another 100 rpm.
Interestingly enough, my prop now approximates the length and pitch of the prop on the Australian Flying Flea built by the guy whose plans I am using! So by a rather roundabout way I have somehow got to where I should be. The English call it ‘muddling through’, but I guess that is how the Experimental Aircraft Association got its name!
My sincere thanks go to Pieter de Necker who guided me through this process. It has been an interesting experience and I have done quite a lot of reading on prop design and now have some understanding of this subject and the sculpting of wooden propellers.
It now only remains for me to finish off the tips, balancing the prop in the process and to run a final test, but unfortunately I had to suspend work on the aircraft in May for personal reasons but will continue once I am able to again. So no guesses as to when my aircraft will take to the skies.