page 45 - American Bonanza Society

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www.bonanza.org Turbos and Low Altitude Ops by Bill Compton This article is about comparison of like airframes with various turbo setups and the advantages of turbocharged engines even if operat ing at 10,000 feet and below, both in performance and engine longevity. Close study of the data helps to appreciate the fine points. The 36 Bonanzas were left out of these comparisons to avoid the apples vs. oranges situation; they tend to be about 8 knots slower than the 35 and 33. This will concentrate on the normally aspirated V35 (V35NA) versus its turbocharged (V35TC) and turbonormalized (V35TN) cousins with 520 engines. Bonanzas are flown at night, on instruments, over all kinds of terrain. Operators can, and do, increase capabilities with avionics, anti-icing, radar, SFERICs, standby alternators, turbo-charging, but still hanging it all out on a single engine. Every effort might well be made to minimize the risk of engine failure. Engine monitors, tuned fuel injectors, oil analysis, borescoping, and science-based operating procedures from Advanced Pilot Seminars have been advances in that direction. The newer data does sometimes conflict with POH advice. Test cell research by Tornado Alley Turbo (TAT), a turbo system manufacturer and respected R&D firm, has shown that operators can extend engine life and reliability by avoiding the “Red Box,”, defined as EGTs between 40° lean of peak (LOP) and 180° rich of peak (ROP) at 75% power, and between peak and 100° ROP at 65% power. At 60% and below, there is no “Red Box.” This is controlled with the mixture knob, referencing EGTs and CHTs of all cylinders. Proper mixture control slows the flame front of combustion so that peak internal Photo by Jay Burris combustion pressures (ICPs) are less and occur later in the power stroke, where there is better mechanical advantage and less heat being passed to the cylinder walls. Going from ROP to LOP reduces cylinder head temperatures (CHT) by about 30°F. All this knowledge has changed the way many operate their fuel-injected Bonanza engines, especially the turbocharged models. The V35NA POH prohibits 2300 RPM with MP higher than 24.5", as reduced RPM brings peak ICP closer to Top Dead Center (TDC) of piston travel. However, when operating LOP, the speed of combustion is slowed, so many run the TN conversion at 2300 RPM with full throttle and maximum manifold pressure, knowing that the slower ICP peak is kept further from TDC by LOP operation, and are reassured by normal cylinder head temperatures. Beech produced the V35TC from 1966 through 1969, powered by a turbo - charged IO-520 engine with a reduced compression ratio to improve detonation margin. The airplane earned a rep as fuel hog and cylinder trasher, but in the mid 1990s, operators of the V35TC found they could mostly avoid those problems by operating LOP. It does well with LOP cruise climbs, and will do 200+ KTAS up high. More recently, TAT engineered “turbo normalizing” (TN) for 520 and 550 Bonanzas, using an intercooler rather than a reduced compression ratio to maintain detonation margin. The V35TN performance is superior to the V35TC, as it can maintain power to higher altitudes at lower fuel flows. The V35TN can do 210+ KTAS above 20,000 feet. Illustrated in Table 1 are power choices for IO-520 Bonanzas. Nauti - cal air miles/gallon (Nam/gal) is a refer ence for range performance. 36 AMERICAN BONANZA SOCIETY MAY 2013
Bonanzas are flown at night, on instruments, over all kinds of terrain. Bonanza, Travel Air, Baron SHOULDER HARNESS KITS FAA STC/PMA APPROVED KITS Pwr Mixt GPH KIAS/KTAS Nam/gal Comments At 4,000 feet: V35NA 75% 180° ROP 19 162 / 172 9.0 Less range, dirty engine, yecch 75% peak EGT 15.3 162 / 172 11.2 High CHTs and ICPs, bad news 75% 40° LOP 14.4 162 / 172 11.9 Cooler, clean, fast, poor range 65% 20° LOP 12.4 153 / 163 13.1 Choices of TAS vs range 55% 20° LOP 10.5 143 / 152 14.5 Choices of TAS vs range 45% 20° LOP 8.6 129 / 137 15.9 Choices of TAS vs range • Factory style, 3 point diagonal design • Factory quality, Tso-c114 Amsafe belt systems • Choice of stock colors or special order • Matching rear lap belts available FIXED RESTRAINT INERTIAL REEL EQUIPPED Low Cost Affordable $799.00 Complete $1,099.00 Complete AIRCRAFT JACKS – THAT FIT • Three Leg Design • Rugged Construction • #6000 Capacity Ram • Range 24" - 41" • Locking Safety Collar • No Stamped Parts MODEL 324 $229.00 EA. Online at www.alphaaviation.com Alpha Aviation Inc. 1505 Chateaulin Lane • Burnsville, Minnesota 55337 1-800-653-5112 1-952-856-5158 (fax) At 8,000 feet: V35NA 75% 180° ROP 19 159 / 179 9.4 2700 rpm – forget about it! 65% 20° LOP 12.4 150 / 169 13.6 Choices of TAS vs range 55% 20° LOP 10.5 139 / 157 14.9 Choices of TAS vs range 45% 20° LOP 8.6 124 / 140 16.3 Choices of TAS vs range At 10,000 feet: V35NA 65% ROP 15 149 / 171 11.4 2700 rpm – “best power” 55% 20° LOP 11.5 137 / 159 13.8 Choices of TAS vs range 45% 20° LOP 8.6 122 / 141 16.4 Choices of TAS vs range But at 10,000 feet, the turbo models start looking better: V35TC 75% 40° LOP 15.6 156 / 181 11.6 A 181 knot airplane! 65% 20° LOP 13.3 149 / 171 12.7 Beats NA on range at 171 kt V35TN 75% 40° LOP 14.4 156 / 181 12.5 Outstanding speed + range 65% 20° LOP 12.4 149 / 171 13.8 Beats NA, TC on range at 171 kt Table 1. Standard altitudes. POH numbers. LOP fuel flows based on 14.9 Hp/gal/hr for NA and TN, 13.7 Hp/gal/hr for TC. Engines running LOP require approx 3" more MP to maintain same power as ROP; that MP rapidly becomes unavailable for NA engines with increasing altitude. Note that IAS falls, TAS increases with increasing altitude at same power. Volume 13 • Number 5 AMERICAN BONANZA SOCIETY 37
Page 1 and 2: May 2013 VOLUME 13 • NUMBER 5 BPP
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