Magneto

On 29 Nov 2003 06:48 PM, Kevin posted the following:

About the only thing they have going for them is that they generate their own power. A modern electronic ignition produces a better spark, is plenty reliable for ground use, and has no points to wear out. The mags I have worked on (aircraft) do not have any provision for an automatic advance, and are fixed to fire at the same number of degrees before top center under all conditions. This is okay on an aircraft which runs at the same RPM for hours on end, but not so good for an automobile in traffic. Other than the non dependence on the vehicle's electrical system, the reason they are considered reliable on aircraft is because two of them are used, each firing a separate set of spark plugs (two plugs per cylinder). I've got less than 100 hours in my logbook and I have still had a mag failure on an airplane I was flying. Then on the next (and last) time I flew it, it had an alternator failure, but at least due to the magneto ignition that just meant the radio got quiet.

---------------------------------------------------- Del Rawlins- del@_kills_spammers_rawlinsbrothers.org Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website:

A magneto doesn't replace an alternator, it replaces the distributor. Even with a magneto ignition, you'll still need your charging system. Magnetos use points. they are not as reliable as an electronic ignition. Also, most of them don't have a mechanical advance, and none I know of has a vacuum advance. This means your timing will not be optimized for light load conditions with the vacuum advance. You can use a magneto on anything they make magnetos for.

Chris

A magneto is useful for shocking worms out of the ground, but on my Jeepster, i prefer the HEI.

On 29 Nov 2003 07:17 PM, c posted the following:

From the standpoint of ignition, the magneto does replace the alternator and battery, since the mag generates its own power. You will undoubtedly still want the alternator and battery to get the thing started and to run electrical accessories. As for reliability, the magneto doesn't have to be more reliable than the electronic ignition, it only has to be more reliable than the battery and its charging system. Other than lack of self-generating ability, the electronic ignition is better in every way.

This is true.

---------------------------------------------------- Del Rawlins- del@_kills_spammers_rawlinsbrothers.org Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website:

I knew they were used on aircraft, and this is what led me to believe they must be more reliable.

Thanks

Your planes specs are close to that of a Maule.

On 30 Nov 2003 05:01 PM, Kevin posted the following:

When he designed the Bearhawk, Bob Barrows incorporated design elements from a lot of different airplanes. The landing gear and cargo door are the same style as the Maule uses, while the fuselage and controls are real similar to the maule and also the piper pacer, which the maule is a rip-off of. The wings rely heavily on Van's RV and Midget Mustang construction methods, and the tailfeathers use skybolt type hinges (I'm using standard pin-type hinges). The wing struts are off of a Cessna

The overall result is a visually attractive airplane which performs extremely well, while carrying 4 people and a good amount of stuff. One builder who got time in a Maule prior to his first test flight, says that the Bearhawk is about 10 times easier to handle, although they both perform much the same mission.

---------------------------------------------------- Del Rawlins- del@_kills_spammers_rawlinsbrothers.org Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website:

I think that if a magneto ignition was suitable for use on an automobile, then we would still be using them today instead of having devised a means of getting rid of them 70-some-odd years ago.

My lawn mower has a magneto and has no battery or alternator. The magneto replaces the ignition system, not the charging system. It also is a magnetic device not a points-based device as another poster suggested -- perhaps the powerful magnet is the basis for the name, magneto. The large magnet whirling around the pick up is what creates the electrical pulse needed for the ignition, not opening and closing points.

I have never seen a magneto system that uses any sort of advance. but this could be acheived relatively easily. All that is needed is to mount the pick up on a plate that rotates around the crank shaft. Then, all that would be required is a means of moving this plate a few degrees when it was desired. Like I said, I have not seen this sort of thing, but it shouldn't be impossible to acheive. I think the largest problem to solve in the magneto system is the length of time it takes to build enough charge to give a powerful spark. I am not positive, but I think part of the reason that airplanes have two magnetos is that they are on half cycle duty cycle. That is, they fire alternately so that they get a rest between firings. Admittedly, that is a SWAG, but I thought I would throw it out anyway. Airplanes could use two just so that there is a back up system in case the primary ignitin system fails. A plane, after all, has considerable safety problems when the motor quits running, all that happens to a car is that it rolls to the side of the road.

An automobile has space constraints that would prohibit the application of a magneto, and one would still need the alternator to power the other electrical systems on board. It makes more sense from a design perspective to use the charging system to set up the electrical pulse needed to get the spark, then use a timing system to provide the spark at the correct instant.

Approximately 12/1/03 13:44, CRWLR uttered for posterity:

Judson magnetos were still popular as a more reliable and higher performance replacement for the stock ignition in British sports cars a mere 35-40 years ago. Whether this is evidence of merit for the magneto or a comment on British electrics may be a matter of personal opinion.

They were still popular as working better than the first coupla generations of transistor ignition systems. Then somebody from the radar engineer folks married a pulse transformer to a magnetron type supply with solid state controls and pretty much kept all of the benefits of the magneto [better high rpm performance due to dI/dT] and the transistor [better low rpm performance] by using multiple pulses at low rpm, tailing off the number of such as rpm rose. Some of these used the standard points, some used optical pickups, some used the emerging hall effect sensors.

As soon as good high energy ignition systems from the manufacturers hit the streets, magnetos pretty much disappeared, only to be remembered by aging pilots and old farts.

I can still buy a BSA motorcycle timing cover made to run carry a mag for racing, but modern electronics have made that more of a nostalgia piece. I used to work for the guy who got all of the mags from the Harrah's Collection auction. The magnets would go bad unless stored in the correct position, and they all had points. Some had mechanical advances connected to a lever in the sterring wheel. We used to zap unsuspecting visitors often.

On 01 Dec 2003 12:44 PM, CRWLR posted the following:

If automobiles had certification requirements similar to those found in the aviation world, we would still be using mags in our cars. Electronic ignition is only now just beginning to be used in piston aircraft, and has a long way to go before it can be considered common.

---------------------------------------------------- Del Rawlins- del@_kills_spammers_rawlinsbrothers.org Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website:

On 01 Dec 2003 01:02 PM, CRWLR posted the following:

That's the point. If your lawnmower had an automotive type ignition system, it would need a battery and alternator or generator to run. The magneto doesn't replace the battery or alternator for engine starting or running accessories, but it does eliminate the need for a charging system with regard to the ignition. An airplane can suffer a total electrical system failure (as I did one day) and the engine keeps firing just fine.

The magneto does use points and the timing of the points is critical to the operation of the mag. All the magnet does is generate electrical current, and the pulse is generated by the opening of the points which interrupts current in the primary windings of the coil. This causes the magnetic field which was induced in the primary windings to collapse, which in turn induces a high voltage current in the secondary windings. It is the current induced in the secondary windings of the coil which are sent to the plugs via the distributor. A magneto is really just a self-contained system which includes the generator, points, coil, and distributor all in one handy package. I can post a schematic if you'd like, since I took a test on aircraft ignition systems a few weeks ago and still have textbooks and stuff laying around (I'm about 6 months away from having my A&P mechanic's certificate).

It isn't done simply because mags are mostly used in aircraft these days, which run for hours on end in the same narrow range of RPM and power output (the same could be said for your mower). The timing can be fixed at the optimal setting for these conditions, so there isn't much to be gained by a variable advance mechanism and it would be just one more thing to fail.

That is incorrect. Both mags fire each cylinder simultaneously (two plugs per cylinder).

The most often quoted reason for two mags is reliability as you mention, but that is followed with "oh by the way" the engine won't run right or make anywhere near full power on just one mag. This is because aircraft engines typically have huge pistons and the flame front won't propogate correctly without both spark plugs firing. In most cases the loss of a mag should allow you to limp home but if you are heavy or at a high density altitude that is by no means certain. It may mean that you just have more time to choose the crash site.

You should try working on an airplane sometime. 8^P

I am in total agreement. The only reason that mags are any good at all on an aircraft is because we use two of them. Work is underway to switch to more modern equipment, but the aviation world is extremely resistant to change for a number of reasons. About the only place modern ignition is seen in any significant numbers (significant being a relative term) is in the experimental/homebuilt world. And a lot of those guys retain one of their mags just for redundancy.

We now return you to your regularly scheduled Jeep newsgroup. 8^)

---------------------------------------------------- Del Rawlins- del@_kills_spammers_rawlinsbrothers.org Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website:

On 01 Dec 2003 02:19 PM, Lon Stowell posted the following:

As the owner of a 1959 MGA, I am inclined to believe the latter. When I finally get around to restoring my car, the Lucas distributor will be fitted with one of the available drop-in electronic ignition modules. That way, it will look stock and run better.

Some of us are young farts, although a look in the mirror is starting to show less hair than is supposed to be there. I think my '73 chev was one of the last pickups that GM made that still used points. I converted it to HEI about 3 years ago and it now runs better than it has in at least 15 years, and it actually passed its first ever emmissions inspection this past summer (that shocked the hell out of me). The gas mileage still sucks though.

---------------------------------------------------- Del Rawlins- del@_kills_spammers_rawlinsbrothers.org Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website:

A/C require a dual ignition system per the FAA. They run independantly and one at a time - part of the pre=flight is to switch mags and watch for an RPM drop. I was damned glad to have mag ingintion a couple of times when the rest of the electrical system went AWOL on me .

Best use I ever saw for a suplus C-47 magneto was the > My lawn mower has a magneto and has no battery or alternator. The magneto

I can go along with that. The magneto is the charging system (battery and alternator) and ignition system, all rolled into one. It that respect, it replaces the battery and alternator.

The magneto systems that I have played with were very rudementry, and they were simply an induction coil thingie that was set off by the large magnet flying by that was embedded into a huge chunk of metal. I can see where an aircraft might use a considerably more sophisticated system that actually employed points and other hardware.

Do you have a manual control on the magneto that you can trim the timing for optimal performance? For instance, we once had a manual choke on our carburators that Grandpa had to play with to get the motor to even run. I seem to remember that Grandpa's first car might have had a magneto to adjust too. It would have been a similar sort of mechanical thingie as the choke, but maybe it was mounted in the center of the steering wheel.

I would think that a similar sort of thing might be useful to trim the mags for different kinds of engine operation. I understand that the plane engine will run for hours on end at a fixed speed, but I was thinking that taxiing at 2500 rpm might demand a different mag setting than sustained flight at

Doesn't the magneto add a s*it load of weight to the crankshaft? I always thought that my lawnmower took so long to shut down was because the flywheel (where the magneto's magnets are located) was so damn heavy. Of course, the single jug will take a long time to stop the motor too, where a multi-jug motor will have more opportunities to arrest the speeding flywheel with additional compression strokes ...