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Hi Ernest,
Yea, I have taken a few lawnmowers apart in my time - I am not claiming any original thought on that one ;-) ... I seem to recall that lawnmowers run at around 3Krpm, I wouldn't like to be too close to one of those fly-wheels at 9Krpm !
Ideally, such an arrangement would be 'advance-less', ie set at a fixed advance, and be purely a battery-less backup - add steppers, micro-controllers and all the mechanical bits rather defeats the object of the exercise ... :-)
Another thought - if the 'ignition' magnet was cast in, say, the top (or left) half of the impeller, then one could cast many magnets in the 'bottom' (or right) half, then have a series of coils wound around formers which would be your alternator - being excited by the full-circle of magnets
I switched to electric lawnmowers long ago - no chance of forgetting to buy fuel ... age does this to us ;-)
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ernest Christley
Sent: 25 May 2011 04:11 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: New impeller design
Charles Davis wrote:
If an impeller were to be cast for this air-induction/super-charging application, and was tied-in to the e-shaft (key-way or similar) would it work to have a suitable magnet cast-in to the periphery of the impeller, so that two coils could be mounted, 180 degrees apart, to provide magneto-type spark to one set of plugs one coil per rotor at 180* for a 2-rotor, and 120* for a 3-rotor this sounds, to me, so simple that I am surprised nobody has done it before how good would it be to have a completely battery-independent ignition system for amateur-built aircraft ? maybe I should shaddup, & return to lurking
The system you describe has been working perfectly a lot longer than I've been alive. All I can say is, don't let your wife catch you pulling the flywheel off your lawn mower to power your airplane 8*) There is a magnet cast into the flywheel, and the coil is built around a C shaped stack of stamped steel. That flywheel could possibly handle the RPM of the eshaft (but I wouldn't dare bet anything important on it).
I think the only issue you'd have is modifying the advance. You could accept the "good 'nuff" compromise of a static 20* to 25* in exchange for the bone dry simplicity. Possibly driving just the trailing plugs as a dead generator backup. That, combined with a gravity feed system would make your engine electrically independent. Or you could try to design some sort of advance control. Maybe use a MegaSquirt and write some code to control a stepper motor that moves the pickup?
I'm currently trying to use the space between the engine and the gearbox mount plate to install a blower and a generator. I think that is enough multipurposing of a single piece of aluminum for now. However, at some point in the future I may need a new lawn mower. 8*)
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