On small bikes, the magneto also powers up the lights and horn. The headlight dims radically at idle and you can pop bulbs at high speeds if the engine is 'tweaked' to give more than stock rpm.
Anyone running a magneto system carries extra bulbs, the power with rpm changes cook them fast, same for spark plugs ant the plug wire caps.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT'sCRWLR wrote:
I have an old BSA magneto driven scooter. It is neat.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT'sPaul Calman wrote:
On 02 Dec 2003 01:58 PM, CRWLR posted the following:
I've had plenty of experience with manual choke but I've never seen any kind of adjustable timing on a mag, although I have heard here and elsewhere that such things exist.
It all comes down to a basic operating difference between cars and aircraft. A car (or Jeep) basically runs at fairly low power settings ( like 30 or 40%) most of the time, but needs to put out high power occasionally, so there is a need for the adjustability. An aircraft engine will run at 100% power for several minutes during takeoff and climbout, and then throttle back to something like 75% power for cruise. It just doesn't need the adjustment. There are gains to be had by a variable advance but they aren't worth adding moving parts to the mags. In an electronic ignition it is as easy to include this feature as not, and that is one of the selling points for those systems, in addition to the more intense spark.
Taxi? Hell that is up near redline or at least cruise power for most aircraft engines. Generally we taxi at idle, or the lowest RPM that will move the airplane since any more than needed forces the pilot to ride the brakes, which is bad for them (they are not meant for sustained use). A traditional air-cooled aircraft engine has a huge displacement for its power output, with huge cylinder bores and a massive reciprocating assembly turning at a relatively low RPM. This is mainly imposed by RPM limits on propeller efficiency. Basically when the prop tips reach the speed of sound the efficiency drops way off, so the engine design is predicated on keeping the prop at its most efficient speed of operation.
Aircraft magnetos are totally self-contained units housed in their own cast aluminum cases, which in turn attach to the engine's accessory drive section and are turned (indirectly) by the crankshaft. They are held in place by the same sort of clamps that hold the distributor on your Jeep. They are timed when the engine is not running though, unlike an automotive system. A mag is no heavier than a typical alternator. An aircraft doesn't need a flywheel (except in some cases as a place to put a starter ring gear) since it has that big prop bolted to the crankshaft.
---------------------------------------------------- Del Rawlins- del@_kills_spammers_rawlinsbrothers.org Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website:
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