Bravo Magnetos

[FlyDave]

A friend with a T210 told me that he can replace his pressurized slick mags with Bendix that are not pressurized. He said that Bendix point gap (not sure that's the correct term) is much smaller so it doesn't require pressurization.

Does this seem plausible? Anyone have Bendix mags on a Bravo?

[chrisk]

My understanding is that you will get more arcing with a smaller gap, especially at lower atmospheric pressure.  I don't know enough about Slick or Bendix mags to know if other design considerations (different capacitor, better insulators) might make the difference.

[jlunseth]

If you have ever experienced high altitude miss, you won't ever want to again.  First, I doubt that the substitution will work at altitude.  It would be a gamble.  Second, it probably renders your aircraft unairworthy.  I say "probably" only because I have not parsed through the Bravo type certificate to check, but I am quite positive the type certificate specifies the mags, and you cannot use a different mag without an STC or 337 approval.  The exact mags would be in one of the footnotes in the TC.

[FlyDave]

I haven't experienced a high altitude miss - and don't care to. I don't know all the ins and outs of magneto's and the effects of different atmospheric conditions on their operation. My friend mentioned this to me and I was wondering if anyone has any input on it. I do understand the type certificate issue and STC or 337 requirements and was just wondering if anyone knew anything about putting Bendix mags (pressurized or non-pressurized) on a Bravo.

I'm at 420/440 hours on my mags and with the issues I experienced getting the Slick mags on my J rebuilt along with what I've read about the quality of Slick mags, I'm exploring any alternatives.

So are Slick 6360/6361 are the only options?

[jetdriven]

From the TIO-540 TCDS, yes, it appears that the Slick mags are the only option. Some models of Lycoming engines still allow Bendix mags on (ours does) and I took that option. We've noticed an epidemic of Slick mags failing, mostly the points, condensers, and coils. The latest is the customer's Aeronca Champ that had a bad left mag. The bearings in is went bad and the rotor chewed up the cap.  A new Slick mag was 1150$, plus 3 hours labor to troubleshoot the mag it was popping at idle and would shut off when L was selected.

The new mag comes in, and it doesnt work.    Right. out. of. the. box.    Send it back, wait, and 3 weeks and 2 grand later the Champ is flying again.  thats 10% of his hull value.  Tel me this is OK.

 

Excellent quality control. Champion Slick are you listening?

 

[jetdriven]

Update the 2200$ in Slick mags to replace the faulty new one and the RH one, both do not work. That's three mags from slick in a row that are defective.

[FlyDave]

Geeze - your issues with slick mags are giving me the willies!

I wish I had an alternative.

[jlunseth]

I am sorry I did not take time to explain.  I assumed you understood the "pressurized mag" issue.  The reason mags are pressurized for flight at high altitude, is that air serves as resistance to tracking across the mag cap.  Insufficient air, as in a nonpressurized mag at high altitude, and you will get tracking.  And the problem with tracking is that it means that the mag is causing the wrong cylinder to fire at the wrong time, the spark having tracked across the cap to a different cylinder than the one intended.  This causes high altitude miss, in which one or more cylinders fire at the wrong moment in their cycle.  It can be fairly violent, and can harm the engine.  Typically, it is caused by an air leak somewhere that allows the mag to run unpressurized.

 

My thought on the "small gap" theory, is that a smaller gap may cause less resistance, and since current follows the path of least resistance, the current will not want to run across the cap even though there is insufficient air present.  To me, that is a gamble, and the effect would vary with altitude, there being less pressure as you ascend and therefore less resistance to tracking.  Sooner or later you will get high enough and even if the smaller gap is having an effect, the lack of air resistance will win and you will get tracking - and high altitude miss.