Help me understand, please

[Toobuilder]

Just re read the OP and I think what you are asking is: If a magneto fires at 25 degrees BTDC, and a given EI fires at 25 degrees BTDC, then why does the prop care?

If thats the question, I'm right there with you.

[Bill Boyd]

I have no expertise in this area so my contribution this morning is one of pure, under-caffeinated speculation - and offered up for my personal entertainment only.

I suspect the answer we're going to get from Hartzell is that even with fixed timing at the same degree of advance, there may exist a difference in spark energy, voltage rise times or whatever between magneto and EI ignition systems that Hartzell's legal team, if not their engineers, are concerned about. Kind of like what one poster said: "more is going on at a deeper level and precision instruments see more variability."

"...you are applying logic to a decision driven by liability attorneys." Yeah, we need to stop doing that. As in right now - stop.

Perhaps what aviation needs is what I saw in Ross' comment: "...zero out all the... retard values."

As long as there are litigators, ^^ this will never happen.
__________________

[TParker]

The timing value sets when the ignition system triggers. There are a myriad of things that follow that trigger event, but, fundamentally, they contribute to the phase/load/frequency relationship that is eventually transmitted to the propeller. Due to the functional differences between magneto ignitions and electronic ignitions, an electronic ignition can alter that phase/load/frequency relationship in a meaningful way, by potentially altering how quickly and completely the mixture is ignited and combusted, even if the trigger angle is identical to that of the magneto.

This is not a purely theoretical consideration. Test data supports that this can make a difference to propeller loads and that the resulting differences in loads, and whether that difference is of concern, can be specific to the propeller, engine, ignition system combination. Unfortunately, the test data available at this point in time does not support making any more definitive of a statement as applied to EI systems in general; it would not be sufficient to publish a range of timing settings independent of the ignition system specifics. Specific propeller, engine, and electronic ignition system combinations that have completed sufficient testing to be determined to be compatible are listed in the tables in Manual 193, Volume 1. Testing of additional configurations is ongoing, but takes time.

Propellers are subject to vibratory loads created by the engine and are therefore subject to fatigue. These vibratory frequency orders are often high, leading to a large number of accumulated cycles that must be sustained (or avoided with an operating restriction or life limit). The relationship between stress amplitude and frequency (S-N) means that small increases in stress at high frequencies can lead to reductions in component life. It is for this reason that we must be so specific and careful about changes to the system. As engineers, when we say a system is compatible it means that we have determined that the design life is not compromised, that the system (as specified) is safe; we must therefore restrict ourselves to the conclusions for which we have sufficient data. An untested combination may be safe, it may be unsafe, it may be safe if used with an operating restriction, but without the data we don’t know and cannot make a statement of compatibility.

Our compatibility determinations are made with the ignition set up per the manufacturer's recommendations. This means that for magneto ignitions, the timing is set per the type certificate (data plate) for the subject engine; usage of timing settings other than those are, just like other modifications, not determined to be compatible. For electronic ignitions, the EI is set up and operated per the EI manufacturer instructions and predetermined timing profiles. Customized user variations to base timing and/or timing advance profiles are unlikely to be supported due to the significant variation possible, but this is still TBD as we continue testing.

Manual 193 was born in the engineering department and is the result of us here at Hartzell, some of whom are homebuilders ourselves, wanting to communicate helpful information for the experimental community and to promote safety by providing a documented resource of compatible combinations and the factors that alter compatibility. Manual 193, Volume 2, which should be published soon, will attempt to explain a little more of the "why" behind some of these factors, though much of it is paraphrased here as it relates to EI. We intend to revise and add to this manual as we complete more testing. We always welcome feedback on the effectiveness of our communication.

[rv8ch]

Originally Posted by TParker

The timing value sets when the ignition system triggers. There are a myriad of things that follow that trigger event, but, fundamentally, they contribute to the phase/load/frequency relationship that is eventually transmitted to the propeller. Due to the functional differences between magneto ignitions and electronic ignitions, an electronic ignition can alter that phase/load/frequency relationship in a meaningful way, by potentially altering how quickly and completely the mixture is ignited and combusted, even if the trigger angle is identical to that of the magneto.

This is not a purely theoretical consideration. Test data supports that this can make a difference to propeller loads and that the resulting differences in loads, and whether that difference is of concern, can be specific to the propeller, engine, ignition system combination. Unfortunately, the test data available at this point in time does not support making any more definitive of a statement as applied to EI systems in general; it would not be sufficient to publish a range of timing settings independent of the ignition system specifics. Specific propeller, engine, and electronic ignition system combinations that have completed sufficient testing to be determined to be compatible are listed in the tables in Manual 193, Volume 1. Testing of additional configurations is ongoing, but takes time.

Propellers are subject to vibratory loads created by the engine and are therefore subject to fatigue. These vibratory frequency orders are often high, leading to a large number of accumulated cycles that must be sustained (or avoided with an operating restriction or life limit). The relationship between stress amplitude and frequency (S-N) means that small increases in stress at high frequencies can lead to reductions in component life. It is for this reason that we must be so specific and careful about changes to the system. As engineers, when we say a system is compatible it means that we have determined that the design life is not compromised, that the system (as specified) is safe; we must therefore restrict ourselves to the conclusions for which we have sufficient data. An untested combination may be safe, it may be unsafe, it may be safe if used with an operating restriction, but without the data we don’t know and cannot make a statement of compatibility.

Our compatibility determinations are made with the ignition set up per the manufacturer's recommendations. This means that for magneto ignitions, the timing is set per the type certificate (data plate) for the subject engine; usage of timing settings other than those are, just like other modifications, not determined to be compatible. For electronic ignitions, the EI is set up and operated per the EI manufacturer instructions and predetermined timing profiles. Customized user variations to base timing and/or timing advance profiles are unlikely to be supported due to the significant variation possible, but this is still TBD as we continue testing.

Manual 193 was born in the engineering department and is the result of us here at Hartzell, some of whom are homebuilders ourselves, wanting to communicate helpful information for the experimental community and to promote safety by providing a documented resource of compatible combinations and the factors that alter compatibility. Manual 193, Volume 2, which should be published soon, will attempt to explain a little more of the "why" behind some of these factors, though much of it is paraphrased here as it relates to EI. We intend to revise and add to this manual as we complete more testing. We always welcome feedback on the effectiveness of our communication.

Trevor, I'm very happy to keep getting these updates. Thanks for sharing your views and plans. As mentioned in the other thread, there are lots of us running your props with EI, and we want to do it in as safe a way as possible. If that means avoiding RPM ranges, or specific timing, so be it.

There are so many variables to the stresses on the prop, I am amazed that you guys can get even one combination approved.

[DanH]

Yes indeed, Trevor, thank you for posting.

Due to the functional differences between magneto ignitions and electronic ignitions, an electronic ignition can alter that phase/load/frequency relationship in a meaningful way, by potentially altering how quickly and completely the mixture is ignited and combusted, even if the trigger angle is identical to that of the magneto.

I've been poking around on my bookshelves, reviewing ignition fundamentals. I don't have anything specific regarding differences between aircraft magneto and inductive EI in the breakdown, arc, and glow phases...and we can't forget CDI, like Lightspeed. I realize you may not be able to share Hartzell data, but can you recommend reading material specific to the subject?

[Freemasm]

@TParker. Was gonna post a long, comment specific reply but don't feel like getting into anything today. We understand the potential relationship between the combustion events and prop responses. If a higher energy spark significantly erodes design margin, it does not breed confidence. With the other plethora of potential combustion variables (nominal and slightly off nominal), creates more questions. That said, while initial testing may have not covered it, operating hours has established validation for the mature products. BTW, I owned/flew behind an HC Hartzell for a few decades; plus a few other H props.

All of that said, I still personally don't think the document provides a lot of help to the EAB community versus attempting to shield Hartzell. Others may/probably see it differently. This is understandable but an interesting case-in-point (to me at least); the Hartzell rep's prop recommendation to me at SnF is in contradiction to the subject release.

The effort is appreciated. At the very least, I'd take some points from the associated responses back to my employer for possible incorporation into future releases and/or revisions. Some are very valid and identify points where the information is unclear, contradictory, leaves Hartzell open to exposure, etc. (e.g. timing deviation from data plate is only mentioned in the EI compatibility that I saw).

Is it 1700 yet?

[TParker]

Dan: Unfortunately I don't have any reading material to offer, sorry. To be clear, I'm not claiming to be an expert on ignition systems.

[Bcone1381]

The following is theory with no science....

Resonant harmonics is the concern. I've wondered if a Mag has a slight randomness to its spark that helps avoid or interrupt and dampen the harmonics of the spark/ignition event. Now we put on EI with super precise spark events giving the harmonics a better chance to resonate and magnify our spinning tuning forks.

I also wonder if dual EI might have a slightly softer ignition event if we time the L and Right sides one or two degrees apart.

If so then could not the future Ei be produced to randomize the spark just enough to protect against harmonics? Maybe Hartzel will manufacture there own ignition some day