Quote:
Originally Posted by hecilopter
Why could I not lean slowly as I climbed, maintaining the 1250 EGT and air : fuel ratio the whole way? Very confused....  |
As penguin wrote: "Hey Rusty, John Deakin on AvWeb recommends that you start leaning as early as you like to maintain the take-off EGT."
First, Lyc FI & Carbs are somewhat self leaning in a climb. More about that below but first the problem with Continentals and mixture during climb.
Deakin mostly writes about 350HP 6-cyl Continentals, most of which have mechanical FI, which uses RPM & throttle position
only to control mixture (and of course mixture control). Most Continentals have used this simple RPM controlled FI system till recently. To compensate for this drawback, some Continentals added an altitude compensating fuel pump. As you climb to lower air density, the fuel pump lowered fuel pressure to "trim" the fuel with out pilot input. Bottom line old Continentals YOU almost NEED the pilot to lean in climb. Also those big twins and singles climb slowly compared to a RV which take little time to get to altitude. With the fuel flow difference between one/two BIG 6 bangers and one little 4-banger, fuel saving by leaning during climb is not great for the Lyc. Also the Lyc has the big advantage of a MASS AIRFLOW controlled fuel delivery system.
Your assumption that you are getting richer and richer is true, but you may be over stating how rich. Lycs have MASS AIR FLOW FI. As you climb it senses less air and therefore supplies less fuel. Even the Carbs are mass airflow devices and self leaning as you climb, by design. The less air through the carb (due to air density) the less fuel, automatically. Further some Carb models have an economizer circuit which kicks in when not at WOT.
Typical SOP for a Lyc/CS prop: takeoff full power, goto 25 square about 1000' agl (Carb into econ mode), MAP drops an inch per thousand feet, increase throttle to maintain 25" square as you climb, level off and set cruise power & mixture. DONE and DONE. Leave the mixture alone until you are above 8,000'. A little extra gas in climb helps temps. The extra gas we are talking about is so small for a 8 minute climb to cruise.
Even Lyc allows you to lean for engine smoothness and for high altitude takeoffs, typically at airports of 5,000 feet density altitude or more. So Lyc does understand to get PEAK POWER you may have to lean a little above 75% power.
I would not personally lean at 2,700 RPM and 27" at say 2,000 feet, just after take off. That is pushing it in my opinion. The "target EGT" deal I recall does not hunt for peak EGT, which would be a bad thing to do. It's just leaning with reference to the peak EGT at takeoff. However do you WANT peak takeoff EGT in climb. Don't know, you decide. I like the ideas of letting the EGT's cool a little. However again with 8-channes of EGT/CHT we can watch our engines like we never have in the past. When I learned to fly one of the rental planes had a single cylinder EGT and a LORAN! WOW!
My self going through 5,000 or 6,000 feet I'll take the mixture off the full rich stop to note a slight EGT change. However I don't try to optimize it or watch and trim the mixture all the way from takeoff to level-off. One thing is I'm too lazy, and second I've got better things to do, like watch for traffic.
As long as you are still closer to 100% than 75%, I would NOT touch the mixture myself. Don't look for peak EGT while at high power, even just momentarilly to find peak. If you do the "target EGT thing read those Avweb articles. They are pretty good. Just keep in mind they are mostly referenced for Bonanzas, Barons and C421's, not little Lycs in RV's.
You can cause damage by leaning at higher power than 75%. Pays your monies, takes yo chances. The extra work load and saving is small.
Lyc makes their limits for worse case scenario and just a TACH. We have engine monitors and know our engines and watch them more than the average pilot. Still be aware anytime you lean above 75% you are running at lower detonation margins. You are using some of the margin built into the limit. Detonation can cause very real, expensive, subtle or sometimes catastrophic damage. It's your engine.
PS: ECI's sells a mechanical RPM based FI for the Lycs. It's a throw back (actually a copy) of the old style RPM controlled FI on Continentals. The idea of using RPM only does simplify the FI. It works the same as other FI when you lean, but it's DUMB and does need more pilot input, such as on a long climb to higher altitudes. The Precision, Bendix and AFP FI for Lycs are better in that they are all mass airflow controlled.
Leaning a carbureted engine above 75% power
Linear Mode
