I subscribed to this list because a couple of the members asked me to
come here and try to enlighten some of the misunderstandings that
seemed to exist concerning engine management.   It's all yours.  I have
other things to do.  If anyone has any questions, you all know how to
contact me.

Walter,

 

I'm sorry to see that you would let me influence your interest in posting.  By "carping" I meant that you will always comment that in some way anything other than mags leads to engine problems. And, it is always general so that the reader could only conclude not to try existing experimental products for fear of something bad happening to their experimental airplane and experimental engine.  If the lurkers you later mention are in a STC'd airplane, like a Bonanza, they are stuck with using only those certified, well tested, proven thru the ages devices anyway.

 

Given the coarse hand controls we fly by - throttle, prop and mixture - It would be nice to hear practical information on how we could use "data" from the crummy engine monitors we have (no pressure monitor) - GPH, CHT and EGT - to determine the quality of the engine operation.  Those of us leaping into a pit of lions by installing advanced ignition systems generally see positive results - higher horsepower felt in the seat-of-pants dyno, fuel savings at lower power settings, easier starts and higher speeds.  We also see lower EGTs and higher CHTs, all explained in the product sales brochure. 

 

Sometimes the results are not as great as advertised.  In my interestingly tweaked IO320, the LASAR system did not perform better than magnetos at low power (<24" MAP) - Why?  Could it be that Unison developed the timing curve in a low compression ratio O320 running in a C172?  I don't know and they won't provide timing information.  In every other aspect, their EI worked fine.

 

Anyway, you said:

<<<

There are some very interesting harmonics which have been measured on
crankshafts on engines with EIs.   What do you know and what can you
tell us about crankshaft harmonic effects as a result of electronic
ignitions... and why they are being observed when they are not observed
in engines with less efficient and antiquated magnetos?  Please tell
us.>>>

 

Well, a Google search using:

 

crankshaft harmonics electronic ignition aircraft engine 

 

did not turn up anything.  Perhaps you could point me to a report somewhere.  Of course,

is always interesting as the discussion is about torsional loads on the crankshaft.

 

<<<<

As I have stated before, at high
power settings even small advances in timing can result in large
changes in stress in the cylinder while those changes have little
effect on HP.  At lower power settings this is not the case.  If an
electronic system has a hotter spark (which is fairly well appreciated)
it has the result of advancing the effective timing and the thetaPP. 
It could well be that setting the same timing for takeoff as a mag
using an electronic system is not the optimum thing to do.  Retarding
the timing of that system would result in lower stress and higher HP. 
I am sorry if those facts upset you.
>>>>>

 

The facts don't upset me at all.  Indeed, some electronic ignitions do provide for a retarded spark at high power settings.  Usually, us experimenters make the comment "Gee, takeoff works better with a retarded base timing." This seems to be the case on a NA engine with CRs greater than 8.5.  If only we could measure this - even indirectly with the current engine monitors.

 

Again, still waiting for the reference on why the reduced combustion mixture pressure achieved at higher altitudes where WOT yields MAPs below 21" would require greater voltage to arc the plug than that required at sea level where the MAP might be 30" (same compression ratio).

 

Maybe the problem is that you have seen too many different engines (pistons hanging out, crankshafts twisted, etc.) floating in your mind whilst I now only have the current one, a mere IO320, that I keep beating with a hammer to make it appear bigger.

 

Without our apparent tension, how could anyone be interested in all this stuff?  Well, maybe it gets them to follow the directions "some assembly required" when trying something different.