Typical "high altitude" XC alts for IO-550 ES Owners?


Hi all,

I am polling the crowd to see what y'all are flying for high altitude XC profiles in NA IO-550 birds. I typically fly 1-4 hr XC lengths and base most of my alt decisions on maximizing TAS and reducing enroute time based off the winds. 

That typically puts me in the 7,500-12,500 range VFR. I have portable O2 available, but it seems unless there is a really killer tailwind, my TAS drops off above 10k. Are any of you routinely flying higher? If so, what's in your decision calculus and what's your speed penalty? 

As a side note, I hear the PMags or other electronic ignition really helps max power available at high alt. What is that altitude where y'all see the gains?



Mmspeare's picture

Good morning Ryan:

Good morning Ryan:

I see the TAS drop above 10k as well (IO-550-N engine) and cruise in the same altitudes you do as well.  Peak TAS for me is typically in the 8-9k range at 187-190 KTAS.  I do not have EMags on my ES.

I had EMags on my Lancair 360 and may have extended power a bit longer to 12.5k, but not much help above that.


Legacyl2k's picture

When I lived in AZ with all

When I lived in AZ with all of it high terrain.  I would regularly cruise at 13,500~17,500.  Running an IO-550N ported & polished at 10-1 compression with Dual Light Speed Engineering ignition in my Legacy.  This would yield 230kts TAS @ 12.7gph lop @ 13,500.  225kts TAS @ 11.7gph lop @ 15,500 220kts TAS @ 10.8gph lop @ 17,500.

My most common flight now is NC to FL

230kts TAS @ 13.2gph lop @ 11,500


Mike, those are some serious

Mike, those are some serious speeds in your Legacy! I got to fly one years ago and it was a blast to fly. How do you like the Light Speed ignition?

Legacyl2k's picture

I only have Emag and magnetos

I only have Emag and magnetos to compare against.  Over the course of 16 years and 1100+ hrs I have replaced spark plugs, wires, and two coils.  The older style plugs change rate was every 100 hrs @ $3.00 a plug. I upgraded at 600 hrs to Iridium plugs.  Yielding better life and lower maintenance @ $20.00 a plug and 250hr change rate. The performance was negligible. The wires were replaced due to vibration erosion over time (the LSE wires are not steal bradded like magnetos. @$250.00.  Two coils failed over the past 16 years at a cost of $85.00 each.  When we built up the system we installed the coils on top of the engine where the old magnetos lived.  This area can overheat the coils when taxing downwind.  At engine rebuild I will be relocating them.  So for the most part and by comparison the LSE had been maintenance free.  The advantages are huge.  I have flown other Legacy's with different systems and so far I think the LSE is the best system I have used.  One story I tell is being in Aspen on a -4 deg F morning.  With LSE and Exxon Elite oil.  And we wanted to document a cold start at this temp.  We checked the viscosity of the old for flow and then tried a start.  Fired on the first blade and made proper pressure.  Other notables: significantly better fuel specifics than mags, ability to run LOP easily, and cold weather starting.  The only negative if you wanna call it a negative is the location requirements of the ignition box and the need for two power sources.  The ign box is not hardened.  So I should be located out of the elements.  I know a few that have mounted them under the cowling and are that way to this day.  Most of them have had contamination issues over the years requiring repairs.  Secondly the power requirements.  The LSE uses very little power (aprox 1~2 amp/hr).  The simplest system Is to build a system with two batteries (one large one small) using a high current diode block decated to one ign system and you will have more power then fuel.  I run a dual/dual system, dual battery, dual alternator split system due to an all electric 5 screen EFIS package which needed redundancy.

I conclusion I find the LSE to be easy to use and virtually maintenance free out side of normal wear items.  Cost over time is much less than mags and emags.  

Side note, Emags were not available in 2006 in 6 cylinder version until only a few years ago(est 2018). Emags work great.  They also require supplementary power for starting and low idle.  Emags are mechanical devices and have where parts that require maintenance and overhaul.  Other than that they IMO are on par with LSE.



Lancairmikees's picture

I have a IO-550N ES with dual

I have a IO-550N ES with dual EMags. Typically flight plan for 175 kts, 50 deg LOP, 65% power, 12.3 GPH. I adjust RPM to get to 65% at whatever altitude, with 2500 being about the max. As you state, TAS drops above 12,000. . 8-10,000 is the sweet spot but fly up to 14K if going out west. The Emags give a bit better performance up high but not dramatic. Their value to me is starting, smoothness, LOP operation, and being able to use auto plugs. To be fair, I did not do an extensive analysis when switching to the Emags from the Bendix mags, but I did not see TAS jump by 10 or GPH drop by 1. Mike

Legacyl2k's picture

One other item of note using

One other item of note using regular magnetos.  Most single airplane wo/turbo charges never get above 12,000ft.  Lancair's go high all the time wo/turbos.  On turbo powered airplanes they use pressurized magnetos.  The reason is as the pressure falls the spark will expand it propagation and become more erratic.  This causes carbon tracing and will eventually lead to miss-firing and possable engine failure.  This only starts to become an issue for altitudes above 12,000~15,000ft/da.  And above.  Just something to think about.  

One last issue I see in the field.  One mag and one electronic ign.  Sounds great but just know that the timing on electronic igns. are on there own timing schedule and don't match the mag.  So in effect you are only using one system at a time for combustion thus reducing efficiency.  At high alt cruse the LSE can have a timing advance as high as 30deg btc while the mag is still at 20deg tdc.  Food for thought.