Well I actually got to the point where I got the fan and engine test rig mounted on my bench ready for the first test run!!
I made a quick video documenting it. This was after reading up loads from a old Aeromodeller annual I acquired through ebay which featured a really great ducted fan article by the legendary P.E. Norman. I was ready; confidence and excitement was running high!
After closing the needle valve on the engine, I filled the tank, opened the valve a little and wound the cord four times around the starter pulley (a metal cap from an old fuel tin) and pulled hard on it. First attempt it didn’t start. Increased the compression- no start. Third attempt after increasing the compression a little more; the engine burst into life!
I quickly adjusted the compression screw and screwed in the need valve, increasing the engine speed dramatically. But because the fan was’nt balanced well enough, the motor vibrated like mad
and small bits and pieces Laying around on the bench started falling off!
While all this was happening I tried to film the whole thing and stupidly switched my phone into camera mode instead of movie mode that I had already set it to! I got about 2 seconds of actual film. Later, after balancing the fan a little better, I set it up and tried again. Success!! I recorded about 3 sessions of the engine and fan running. Wow! It’s quite something to see a duct fan in action – even on a test rig. There were a couple of things though. Because of the vibration (a little more fan balancing to do), the comp screw and the needle valve would unwind making it difficult to see where the correct running settings were. This was later resolved by fitting a spring under the compression screw and some fuel tubing tight over the needle valve. Once I did this the engine ran perfectly. Now at last I had mastered starting the engine with a cord… but would it be so easy once the engine and fan were installed in the model?
plywood test rig with PAW 1.49 engine and home made fan. Very loud and very thirsty!
Well the big problem I found was that whilst there’s plenty of room in front of the engine to wind the cord when it’s bench mounted, there’s very little room and a little awkward around the hatch area once the engine and fan are installed in the model. Could I get my hands in to wind the cord? Could I heck! My first attempt took about 20 minutes of winding and pulling before the engine fired into life! I honestly don’t know how P.E. Norman did it….
I’ve managed to get 3 engine runs over two afternoons at the time of writing, which is not ideal. I seem to be experiencing a lot of engine flooding too, so maybe my method of starting is wrong. Ideally, what I would like is to be able to go to the field, fill up the tank and after 2 or 3 attempts start the engine and toss the thing in the air!
So It’s a work in progress. I’m re-looking at how to start the thing. Hmm… should I use an electric starter with a belt (bad idea) …or modify the pulley…? (better idea). Also how do I go about preventing the engine from flooding? Think I need to work on my start technique…
Watch this space!
Looks like a fun project!
I seem to recall photos of the RC ducted fan guys with rods attached to their electric starters, which they stick up the tailpipe and spin the engine with. Maybe it’s a hex key that engages a socket?
BTW, if you love balsa so much, why are you covering it with oil? 😉
Ha-ha! cant get too precious about things eh, – even balsa! I seem to have got the hang of it now, but there’s still a lot of work to do to get the plane to fly nice. Good fun though! Thanks for the comment:)