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In case my previous post pops up, be aware that this is my second attempt to share this information with the Bearhawk Family. This time, I will say that I have NOT purchased any plans yet; I will be building a "B" model BH (QB); and that I find the fellowship and camaraderie living here most encouraging - especially when I consider how large and diverse this family is!
I am a retired A&P with a rather diverse set of careers ranging from working on the Space Shuttle (landing gear tech rep) to line maintenance on DC-6B's with P&W R2800's at an all-cargo airline in Detroit/Chicago before many of you were born. I studied AE in college, but my degree is in Secondary Ed (thanks in no small part to the VN War!!). I worked 5 years as a Blast Furnace Foreman in Ford Steel Division and spent 3 years as a Goodrich Landing Gear Tech Rep working here and overseas in certification flight test. And yes, I did teach school - for a short time anyway (LOL).
So, among my several pet peeves is disappointment over the antiquated ignition systems we live with in piston aviation. Magneto ignition reliability (more talk than reality IMHO) seems to override the vast advantages cars have seen with electronic ignition systems for years. My mantra is "Detonation is Deadly!". Let's talk about detonation in spark ignition internal combustion engines and then I will make my point. BTW, I am intentionally not talking about preignition which can lead to detonation, but is not the same thing.
First, please know that I am very impressed with the various levels of experience, knowledge, and competence evident in this Forum amongst you Builders. Much of what I offer, you already know. Some of it you may disagree with, and if so, please challenge me - that's how I learn!
For starters, we all have at one time or another heard "pinging" in our automotive engines as we try to accelerate going up a hill on a warm summer day (perhaps). This pinging is detonation. You will not hear it in your airplane - any airplane - because of prop and exhaust noise. But it can and does happen and it destroys engines. Usually, the damage is gradual and cumulative, but it can be instantaneous and catastrophic. We all know about fuel octane ratings and most are aware that avgas contains lead, giving it a higher octane rating. Why is this not enough? Let's look at the lead in avgas and what it does. If we just mixed the element, lead (Pb), into gasoline, it would rapidly settle out of solution and collect in the bottom of the tank. So, the chemists came up with a version of the Ethyl molecule, called Tetraethylene (TEL), to support the lead in gasoline. This additive lead serves to shield the "end gases" from flame front infrared energy. It blocks some of the heat transfer (by radiation) to the "end gases". But most importantly, it does nothing to affect pressure in the combustion chamber. Let's look at these "end gases".
As the piston begins to travel up in the cylinder on the compression stroke (let's stick with 4 cycle for now), the trapped mixture of gases inside the cylinder become compressed. As any gas compresses, it generates heat and becomes hot. At some point before TDC, a spark event ignites this mixture, initiating a subsonic flame front that advances across the combustion chamber from the spark loci (usually 2 separate positions in aircraft and some cars). The unburned portion of the mixture - often referred to as "end gases" - is subjected to two sources of ignition: 1) radically increasing pressure from the advancing flame front, and 2) infared energy from the already burning mixture. It is these "end gases" that initiate the phenomenon we call "detonation". If they "explode" (a super-sonic event as opposed to subsonic flame front burning), we have detonation. If they burn (and remember, at this point the oxygen/hydrocarbon ratio has become rather unfavorable for combustion), we have the beginning of a normal power stroke. The piston approaching and passing through TDC is moving at its slowest velocity (remember crankshaft angle converts to linear motion), so it contributes very little to the combustion chamber gas pressure increases. The real pressure driver here is the flame front.
By controlling the initiation of the flame front timing relative to piston travel (crankshaft rotation), we can partially modulate this combustion chamber dynamic pressure. But that amounts to retarding the ignition timing and we know that robs power. So, we are faced with a dilemma: advance the timing to get good acceleration and more power, or retard the timing to increase our detonation margin. Electronic ignition systems with "knock sensors" exist in car engines, but none of our aircraft electronic ignition systems have them, and for good reason: they are very unreliable and not full authority. But what about an ignition system that monitors the combustion chamber dynamic pressure and alters the timing slightly - within what in fact is a "sweet-spot" - in response to that pressure. Such a system exists - its called PRISM (Pressure Reactive Intelligent Spark management) and was developed years ago by GAMI (remember GAMIJECTORS?) in Ada, OK. But they have not offered it for sale...yet. I suspect the principle reason lies in the fact that PRISM allows alcohol-free mogas to burn in aircraft engines and that would cut into GAMI's all-time big project: G100UL unleaded avgas.
But in a recent phone conversation with Tim Roehl (pronounced "rail") at GAMI, I detected a change and I think if enough people (ie- OSH attendees) ask about it and ask questions, it might be offered to EAB people like us as early as this Fall. Their installation configuration has changed from what you will see on their website, but the principle remains the same: prevent detonation by scheduling the spark event according to combustion chamber dynamic pressure. Its an electronic ignition system like all the rest, but it has this one great advantage: it prevents detonation.
I am an EAB builder (trying to get rid of my partially finished GP-4 now) just like you. I am not affiliated with GAMI; I do not receive anything from GAMI; and, frankly, they would probably wish I would dry-up and blow away rather than keep pestering them. I have no idea about price, but as expensive as my engine is, it would have to be way up there for me to walk away from this system.
I am a retired A&P with a rather diverse set of careers ranging from working on the Space Shuttle (landing gear tech rep) to line maintenance on DC-6B's with P&W R2800's at an all-cargo airline in Detroit/Chicago before many of you were born. I studied AE in college, but my degree is in Secondary Ed (thanks in no small part to the VN War!!). I worked 5 years as a Blast Furnace Foreman in Ford Steel Division and spent 3 years as a Goodrich Landing Gear Tech Rep working here and overseas in certification flight test. And yes, I did teach school - for a short time anyway (LOL).
So, among my several pet peeves is disappointment over the antiquated ignition systems we live with in piston aviation. Magneto ignition reliability (more talk than reality IMHO) seems to override the vast advantages cars have seen with electronic ignition systems for years. My mantra is "Detonation is Deadly!". Let's talk about detonation in spark ignition internal combustion engines and then I will make my point. BTW, I am intentionally not talking about preignition which can lead to detonation, but is not the same thing.
First, please know that I am very impressed with the various levels of experience, knowledge, and competence evident in this Forum amongst you Builders. Much of what I offer, you already know. Some of it you may disagree with, and if so, please challenge me - that's how I learn!
For starters, we all have at one time or another heard "pinging" in our automotive engines as we try to accelerate going up a hill on a warm summer day (perhaps). This pinging is detonation. You will not hear it in your airplane - any airplane - because of prop and exhaust noise. But it can and does happen and it destroys engines. Usually, the damage is gradual and cumulative, but it can be instantaneous and catastrophic. We all know about fuel octane ratings and most are aware that avgas contains lead, giving it a higher octane rating. Why is this not enough? Let's look at the lead in avgas and what it does. If we just mixed the element, lead (Pb), into gasoline, it would rapidly settle out of solution and collect in the bottom of the tank. So, the chemists came up with a version of the Ethyl molecule, called Tetraethylene (TEL), to support the lead in gasoline. This additive lead serves to shield the "end gases" from flame front infrared energy. It blocks some of the heat transfer (by radiation) to the "end gases". But most importantly, it does nothing to affect pressure in the combustion chamber. Let's look at these "end gases".
As the piston begins to travel up in the cylinder on the compression stroke (let's stick with 4 cycle for now), the trapped mixture of gases inside the cylinder become compressed. As any gas compresses, it generates heat and becomes hot. At some point before TDC, a spark event ignites this mixture, initiating a subsonic flame front that advances across the combustion chamber from the spark loci (usually 2 separate positions in aircraft and some cars). The unburned portion of the mixture - often referred to as "end gases" - is subjected to two sources of ignition: 1) radically increasing pressure from the advancing flame front, and 2) infared energy from the already burning mixture. It is these "end gases" that initiate the phenomenon we call "detonation". If they "explode" (a super-sonic event as opposed to subsonic flame front burning), we have detonation. If they burn (and remember, at this point the oxygen/hydrocarbon ratio has become rather unfavorable for combustion), we have the beginning of a normal power stroke. The piston approaching and passing through TDC is moving at its slowest velocity (remember crankshaft angle converts to linear motion), so it contributes very little to the combustion chamber gas pressure increases. The real pressure driver here is the flame front.
By controlling the initiation of the flame front timing relative to piston travel (crankshaft rotation), we can partially modulate this combustion chamber dynamic pressure. But that amounts to retarding the ignition timing and we know that robs power. So, we are faced with a dilemma: advance the timing to get good acceleration and more power, or retard the timing to increase our detonation margin. Electronic ignition systems with "knock sensors" exist in car engines, but none of our aircraft electronic ignition systems have them, and for good reason: they are very unreliable and not full authority. But what about an ignition system that monitors the combustion chamber dynamic pressure and alters the timing slightly - within what in fact is a "sweet-spot" - in response to that pressure. Such a system exists - its called PRISM (Pressure Reactive Intelligent Spark management) and was developed years ago by GAMI (remember GAMIJECTORS?) in Ada, OK. But they have not offered it for sale...yet. I suspect the principle reason lies in the fact that PRISM allows alcohol-free mogas to burn in aircraft engines and that would cut into GAMI's all-time big project: G100UL unleaded avgas.
But in a recent phone conversation with Tim Roehl (pronounced "rail") at GAMI, I detected a change and I think if enough people (ie- OSH attendees) ask about it and ask questions, it might be offered to EAB people like us as early as this Fall. Their installation configuration has changed from what you will see on their website, but the principle remains the same: prevent detonation by scheduling the spark event according to combustion chamber dynamic pressure. Its an electronic ignition system like all the rest, but it has this one great advantage: it prevents detonation.
I am an EAB builder (trying to get rid of my partially finished GP-4 now) just like you. I am not affiliated with GAMI; I do not receive anything from GAMI; and, frankly, they would probably wish I would dry-up and blow away rather than keep pestering them. I have no idea about price, but as expensive as my engine is, it would have to be way up there for me to walk away from this system.
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