Battson wrote:CamTom12 wrote:
If you did that then you'd encounter detonation at WOT.
Optimized part throttle spark advance is way earlier than optimized WOT spark advance. Fixed timing mags are set to ensure safe maximum performance at WOT and every other power setting suffers inefficiency.
Yes, as I say - accounting for full RPM would be the killer for that assumption.
I think it'd be RPM which varies the necessary timing, rather than throttle setting? Unless you're thinking about a fixed pitch prop.
But my point was more about this - where has the magic "extra power" come from during climb out? Sorry - I'll try to explain myself properly this time.
Assuming you climb out at full power applied, how is the rate of climb supposed to increase with EI vs mags? If anything the EI is often heavier overall in experimentals, as it typically warrants a redundant battery. The efficiency gains from adjusting to the (small) variations in MAP at low level can't be all that significant?
And in terms of the fuel savings, all those numbers quoted above look like ROP numbers? Would you not simply be better to run LOP, I can't image the saving would be so dramatic in that case?
MAP actually has a much larger impact on the flame front speed (which alters the optimum timing advance) than RPM. Especially when you look at the narrow RPM band that the green arc covers.
The extra power at WOT no doubt comes from a hotter spark with longer duration, but the cruise gains (especially LOP) are from that same hot, long spark being adjusted to keep the cylinder pressure peak in the proper location to give the maximum push on the piston surface. Allowing a better BSFC and more efficient performance at lower power settings is the reason I like these systems, though the extra performance at WOT is a nice bonus too.
