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Harmonic vibrations due electronic ignition??

JPalese

JPalese

Well Known Member
A buddy told me that he believes when a single or dual electronic ignition module is used it changes the frequency that the engine operates at vice magnetos only.

This change in frequency, according to my friend, is bad juju for metal props and the engine itself.

Anyone heard of this?
 
It's possible, yes. But the main reason you see Hartzel placing a warning in their manuals is because they have not tested that configuration before. In other words, unless they have done a vibration survey and its shown good, it is NOT good. Like many things involving aviation, it's a conservative, default position.
 
Toobuilder said:
It's possible, yes. But the main reason you see Hartzel placing a warning in their manuals is because they have not tested that configuration before. In other words, unless they have done a vibration survey and its shown good, it is NOT good. Like many things involving aviation, it's a conservative, default position.
Click to expand...

I'm pretty sure they have tested otherwise identical mag and EI setups.
 
Perhaps, but when I most recently read the reason from Hartzel, they said it was because they have not tested the aftermarket EI systems. I can only take them at their word.

Edit:

They have tested ONE engine (O-360-A1A) with a Plazma II and the 7666A-2 blades. As for the rest, the HC-SL-61-61Y (Rev.3 Nov 13/09) says this:

"The engine models listed are the configurations tested. Modification to the engine
that alters the power of the engine models listed in Table 2 during any phase of
operation have the potential to increase propeller stresses and are not approved by
this list. Such modifications include, but are not limited to, the addition of a turbo
charger or turbonormalizer, increased boost pressure, increased compression ratio,
increased RPM, altered ignition timing, electronic ignition, full authority digital engine
controls (FADEC), or tuned induction or exhaust. Also, any change to the mass or
stiffness of the crankshaft/counterweight assembly is not approved by this list."
 
Last edited:
I have email confirmation that they also tested the Electroair EI on the same engine/prop combination.

BTW, the EI does not change the frequencies,just the amplitude of the excitation of the prop. The EI systems tend to have a higher amplitude of input to the prop, thereby increasing vibrator loads. Frequency remains unchanged.
 
If you're really concerned about the change in vibration from an electronic ignition, also consider the changes that occur when using the black knob and the red knob. We all get excited about potential changes due to ignition timing, but forget that changing the mixture, in particular running at peak and lean of peak, changes how the mixture burns and therefore has a significant impact of what the prop experiences. The characteristics of the airframe must also have an impact.

Hartzell is a responsible company that can only draw conclusions from data, and not supposition, so it is not reasonable to expect them to approve (or otherwise condone) what they have not tested. Prop testing is expensive so most ignition manufacturers cannot afford it. So I don't see much prospect of any un-certified ignition ever getting a prop manufacturer's blessing. However, how many Hartzell (and Sensenich) props are turned by engines with EIs, and how many props have had problems? Many and very, very few, I would suggest. Because of the severity of any prop problems I suspect we would hear of the quickly. I can't remember the last time a report of serious trouble with a Hartzell prop surfaced.

My own conclusion is that the magnitude of the changes in vibration from fitting an EI are not sufficient to cause an issue with the reliability of Hartzell or Sensenich props.

Pete
 
As a previous poster stated, Hartzell has documented compatibility with Lightspeed Plasma II EI on an O-360 in Service Letter SL061-61Y. I contacted them by Email and confirmed that they tested the Electroair EI and it was found to be compatible with my prop on the O-360 also.
 
We've tested some EI systems

This is a very complex question. It's not complex from a technical standpoint, it's complex due to the "web" of possible configurations and the reality that we cannot test them all. What engine? 340, 360, 370, 375, 400, 409? The statement posted above is our disclaimer and true that anything that changes the torsional vibration signature can affect our endorsement. If we start with the crankshaft configuration alone, there are at least four distinct configurations; the 180 Hp variety and the 200 Hp variety and either one could have torsional dampers. Now there is another one on the XP-400. There are probably a few more that I'm missing like the -340... Moving on to pistons, there is 8.5, 8.7, 9, 10 and even higher out there. I forgot about 8.9 on the IO-390. Then there is the induction system. Is it carbureted, injected, throttle body, horizontal, vertical, tuned? Exhaust? We've seen a noticeable difference with the PowerFlow so it does have an effect. What about cylinders? Ported & polished, special valves or lifters? All that before we even get to the ignition systems that are available. We've tested a few. Lightspeed, LASAR, and some others that I can't remember right now. All of these had slightly different timing curves. Then there is operation... Should we only approve propellers if tested to the most aggressive aerobatic manuevers that some may fly?

The best possible scenario is you are using an engine configuration that we've tested and can officially approve for use with our propeller models. If not, maybe we can look at our tested configurations and at lest give you some idea whether it's close and provide some guidance. It is not our intent to deter inovation or personal taste and pigeon-hole everybody, we just can't stay ahead of all the possible configurations. We would like to sell to anyone that wants a Hartzell but we would rather you operate a safe configuration. And that viewpoint doesn't even broach the subjects of durability and reliability. You may be safe but who wants to deal with service difficulties every few hundred hours? Propellers fall into the same category as wing spars in my book and I don't think anybody wants to slightly overload their wing spar at up to 450 times a second... The spar will eventually fail and only testing can predict when that will happen.

If you aren't sure, just call us and ask about your configuration. Be ready with the specifics of your configuration. We may say "yes," "no," or "we haven't tested that, but.." You are all EABs and you have the freedom to do whatever you want so please don't get frustrated for sticking to our standards and wanting to keep you safe if you don't like our answer. I recommend you at least get some information and make an informed decision on whether you want to operate with one of our props.

I'm sorry for this long explanation, hopefully it helps answer some questions. I will try to update the table that Doug has posted on this site with the latest information we have. That may help answer more of your detailed questions.

Be safe!

Les Doud
Hartzell Propeller
 
I forgot to answer the first question!

Yes, the resonant torsional frequencies are normally dictated by the basic crankshaft configuration. The most common modes on these engines are at frequencies of 6X, 8X, and 10X RPM. All the other "goodies" normally affect the amplitudes. If torsional amplitudes are high enough, sometimes the crankshaft might fail before the propeller, like has happened recently on hopped-up aerobatic ships.

Les
 
lesdoud said:
This is a very complex question. It's not complex from a technical standpoint, it's complex due to the "web" of possible configurations and the reality that we cannot test them all. What engine? 340, 360, 370, 375, 400, 409? The statement posted above is our disclaimer and true that anything that changes the torsional vibration signature can affect our endorsement. If we start with the crankshaft configuration alone, there are at least four distinct configurations; the 180 Hp variety and the 200 Hp variety and either one could have torsional dampers. Now there is another one on the XP-400. There are probably a few more that I'm missing like the -340... Moving on to pistons, there is 8.5, 8.7, 9, 10 and even higher out there. I forgot about 8.9 on the IO-390. Then there is the induction system. Is it carbureted, injected, throttle body, horizontal, vertical, tuned? Exhaust? We've seen a noticeable difference with the PowerFlow so it does have an effect. What about cylinders? Ported & polished, special valves or lifters? All that before we even get to the ignition systems that are available. We've tested a few. Lightspeed, LASAR, and some others that I can't remember right now. All of these had slightly different timing curves. Then there is operation... Should we only approve propellers if tested to the most aggressive aerobatic manuevers that some may fly?

The best possible scenario is you are using an engine configuration that we've tested and can officially approve for use with our propeller models. If not, maybe we can look at our tested configurations and at lest give you some idea whether it's close and provide some guidance. It is not our intent to deter inovation or personal taste and pigeon-hole everybody, we just can't stay ahead of all the possible configurations. We would like to sell to anyone that wants a Hartzell but we would rather you operate a safe configuration. And that viewpoint doesn't even broach the subjects of durability and reliability. You may be safe but who wants to deal with service difficulties every few hundred hours? Propellers fall into the same category as wing spars in my book and I don't think anybody wants to slightly overload their wing spar at up to 450 times a second... The spar will eventually fail and only testing can predict when that will happen.

If you aren't sure, just call us and ask about your configuration. Be ready with the specifics of your configuration. We may say "yes," "no," or "we haven't tested that, but.." You are all EABs and you have the freedom to do whatever you want so please don't get frustrated for sticking to our standards and wanting to keep you safe if you don't like our answer. I recommend you at least get some information and make an informed decision on whether you want to operate with one of our props.

I'm sorry for this long explanation, hopefully it helps answer some questions. I will try to update the table that Doug has posted on this site with the latest information we have. That may help answer more of your detailed questions.

Be safe!

Les Doud
Hartzell Propeller
Click to expand...

lesdoud said:
Yes, the resonant torsional frequencies are normally dictated by the basic crankshaft configuration. The most common modes on these engines are at frequencies of 6X, 8X, and 10X RPM. All the other "goodies" normally affect the amplitudes. If torsional amplitudes are high enough, sometimes the crankshaft might fail before the propeller, like has happened recently on hopped-up aerobatic ships.

Les
Click to expand...


What a well stated and reasoned response. Thank you.

Guy
 
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