Lean of Peak
Some quotes from blogs about running lean of peak.
Leaning and MP
In terms of what power settings you would want for an IFR approach, I have found that every plane and pilot combination is slightly different from the next. But in my case, I have found that level flight with the gear and 10 degrees of flaps will take about 18 inches of MP. RPM won’t make much of a difference at these power settings. To get a 500 fpm descent and around 100 KIAS with the flaps and gear out will take around 14 to 15 inches of MP. But again every plane and pilot is a bit different.
I also run LOP- usually at 30MP and 2300RPM which yeilds about 160 KTAS on 13.1 GPH,
For the descent. I normally make the first pull back to 25″ then a few minutes later I pull back to 20″ if needed. I do reduce my prop back to 2400 or 2500 if I was running it above that in cruise.
One member cruises at 32 MP, 2400 RPM, 14.6 GPH
AT 12,000′ 28″/2400 using 112 PPH with 1620 TIT, 350-375 Cylinder temps and 175-180 True with cowl flaps closed @ -31C.
Take off full rich, fuel flow above redline. At about 1000ft agl roll rpm back to 2600, adjust fuel flow to about 85pph( roughly 15.5-16gph) and WOT. Climb about 500fpm depending on OAT. Very rarely have to use low boost fuel pump to prevent slow fluctuations in fuel flow-only on very hot days. If CHT’s creep past 380-usually on cyl #5- will lean slightly. Also,in cruise, we found that setting the MP to 34-35 inches makes the engine run cooler, and rpm’s are usually set at 2450-2500rpm.
I never liked messing around slowly leaning from the rich side to find peak. I do it from the lean side. I level off, pull the MP(throttle) to 27″, Prop 2300, big pull to FF 12.5(really feel this loss of power),we are now LOP(%power =13.7xFF for my TSIO520C), we don’t know exactly where but we are LOP, now push the throttle all the way to the fire wall(MP 32″,not going to adjust this any more), adjust the mixture(or now that we’re LOP, power) for the desired power setting you want and let things settle out(i.e. check TIT and CHT’s). Done(but still don’t know how far LOP I am). If I want to know how LOP I am, I’ll set the engine monitor to lean mode, open the cowl flaps, and richen the mixture until the first cyl peaks and note the EGT, then I go back to my cruise FF, note the EGT(of the same cyl that peaked), the difference it how far LOP I am.
Level off at cruise altitude set pwr at 30″ and 2300rpm. If your MP is out of the green just disregard, and let engine stabilize for a few mins with cowl flaps closed. Set your JPI to monitor TIT and lean the mixture SLOWLY untill you determine peak TIT, which should be near/around 1600+/-. Note FF at peak TIT just for reference. Now continue to slowly lean until the TIT is 50* cooler than peak. Also, doublecheck according to the JPI that every cyl egt has decreased, which indicates they are all LOP. Don’t adjust the mixture anymore. Now, here’s where the turbo shines. You’ll note that you have lost some MP, maybe 1-2″ and now just advance the throttle to recapture the lost MP…back to 30″. Now note FF, CHT’s, MP, RPM, and TIT. If your baffeling is tight you should see no CHT above 380, if fact it will probably be far less. Next time you fly use same power settings after level off and make the big pull to the FF you noted gives you 50 LOP should be somewhere around 13-14 GPH or so. JG
Mike Busch from Savvy Aviation has long been a proponent of aggressive leaning.