March 2003 - American Bonanza Society

LEAN ON FACTS, RICH ON MISCONCEPTIONSBY JACK BYRD. FALLBROOK. CALIFORNIAter~reading Lynn Jenkins' article on lean-of-peak operation(self-inflicted cylinder problems) in the October 2002BS Magazine, I could not let some of what he said gounchallenged. Since he is a respected writer and has the attentionof so many people, he owes it to his readers and the ABSMagazine to provide factual information and be ready to backup what he says with hard relevant data.Lynn's article essentially said that anyone operating aContinental 10-520 turbonormalized engine lean of peak EGTwith a power setting in excess of 65 percent power needs theirhead examined. He said, ".. .I am slllprised that the engille didIlot come apart. It was basically being operatedJlI1I time at sealevel takeoff power ... This engille lVas basically being operatedat 100 percent power all the time."This is simply not true as you can see from actual flightdata I collected using my JPI 700 Graphic Engine Monitor. Anengine can be tuming 2700 rpm at wide-open throttle (WOnand not be at IOO-percent power. When operating lean of peak(LOP). power can be selected by adjusting fuel flow with themixture control. (More fuel , more power; less fuel, less power.)My rebuttal provides real-world experience and actualdata co llected by the JPI 700 installed on my A36 with an 10-520 turbonomlalized engine that is the same configurationLynn refers to in his October article.On most cross-country flight s. I normally fl y betweenFL 150 and FL230 depending on the length of flight and thewinds aloft. 1 use WOT, full-rich mixture until 1 get 10 cruisealtitude and then go 50F 10 70F LOP.At cruise altitude I always use WOT (30.5 inches mp).usually 2450 rpm at 75 to 80 percent power (14.410 15.2 gph).which is primaril y controlled with the mixture control. Thisprovides a true airspeed around 190 to 205 knots. dependingon temperature and altitude.The JPI 700 co llects and records data in near real time toan accuracy of one degree F from sensors located on theengine to obtain EGT and CHT for each cylinder plus TIT, oiltemp and several other parameters. When the workload is lightduring crui se, 1 occasionally jot down pel1inent data on a formthat provides a snapshot of all engine parameters and true airspeed numbers at that instant in time.The above infonnation is intended to describe how I flyand manage engine perfomlance so you can better appreciatethe data that follows.Let's review some actual data that is typical for mostflights. Figure I shows a flight at FL21 0 where 1 was running2500 rpm . 30.5 mp and burning 15.4 gph. This power settingproduced 229 hp or 8 I-perce nt power.Notice that Cyl#I=355F, Cyl#2=33IF. Cyl#3=312F,Cyl#4=342F, Cyl#5=327F and Cyl#6=313F. The TIT = 1564Fand the EGTs ranged from 1415F to 1474F.1 would say these are very cool temperatures, wouldn 'tyou? By the way, my TAS was 208 knots.Figure 2 shows data collected on a night at FLl75. Thisdata comes from a Flight Summary chart produced by JPIFIGURE 1N#: 2019Z MOOEL: A36 ENGtNE: 10-520 COMMENTS: TURBONORMALIZEOAlt (Fl) OAT (C) ROC KIAS MP RPM FF OilT CDMAT KTAS Cyll Cyl2 Cyl3 Cyl 4 Cyl 5 Cyl 6 TIT210 -22 141 30.5 2500 15.4 153 229196 208 CHT 355 331 312 342 327 313EGT 1470 1458 1474 1453 141 6 1415 1564FIGURE 2Aircraft Number: N2019Z Flying Time-hh:mm: 2:19 Flight # 2828 10/12/2El E2 E3 E4 E5 E6 Cl C2 C3 C4 C5 C6 Tl Oil DIF ClD CDT IATMINI 832 972 795 883 742 606 113 116 126 116 110 11 2 606 104 13 -37 87 73AVRG 1372 1375 1386 1374 1341 1342 330 321 315 335 318 304 1451 168 60 -1 180 94MAXI 1481 1489 1498 1501 1494 1572 366 348 363 364 365 339 1572 200 300 0 210 108lIlMITS 1650 1650 1650 1650 1650 1650 450 450 450 450 450 450 1650 230 300 -60AVRG in % 83% 83% 84% 83% 81% 81% 73% 71 % 70% 74% 71% 68%MAXI in % 90% 90% 91 % 91% 91 % 95% 81 % 77% 81 % 81% 81% 75%Page 7716 ABS March 2003