Mags at high altitudes

[emteeoh]

From another thread

( I would say you really need EI to go high, unpressurized Mags start missfiring as you increase altitude. I have had mags (bendix) do OK at FL180, but the current mag I hav starts missfiring at FL150 and is completely dead by the time I get to FL180)

 

I don't get that. Magnetos are basically a magnet, a turning coil, and a cam-operated switch. How would altitude and atmospheric pressure figure into their operation?

[ZUCZZ]

Not so ...

 

if that were the case planes fitted with these would not fly public, would not be cleared for IF etc.

 

There would also be a warning on the installation papers etc.

 

I have taken mine to 19500 and no evidence.

[Waiter]

Please google

 

"Pressurized Magneto"

 

I've had standard unpresurized Bendix mags work OK up to FL210, I've also had standard unpresurized Bendix mags start misfiring at FL150 and become totallly inoperative by the time I'm up to FL180.

 

Waiter

[argoldman]

From another thread

 

 

I don't get that. Magnetos are basically a magnet, a turning coil, and a cam-operated switch. How would altitude and atmospheric pressure figure into their operation?

 

Air is an insulator. It keeps the sparks from flippping to the wrong plugs as the distributor thingy rotates around hoping to spark the right Champion. As the air gets rarer with altitude the sparks can take an errant path.

 

Note that when plugs are tested in a plug tester, this is done at high pressure, not specifically to simulate the conditions in the cylinder at compression but to make the insulator between the electrodes (pressurized air) as great as possible to determine if the plug is misdirecting its energy to another place.

[Kent Ashton]

Pretty good article discussing high altitude misfire here

http://www.avweb.com/news/maint/182843-1.html

[ZUCZZ]

So it appears I stand corrected ...

[Waiter]

So it appears I stand corrected ...

I would say "better informed"

 

If your engine starts running a little rough at altitude, but seems to clear up when you descend, this is probably the culpret

 

Waiter

[ZUCZZ]

So I'll be looking out for that during my climb tests

 

Thanks for the advice!

[Wayne Hicks]

Lancair IV-P's run pressurized mags for this very reason.