April 1999 - American Bonanza Society

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A good trend:How to mon itoryour airplaneBY GEORGE WILHELMSENFlying and maintaining an airplane is a complicated task,one fi lled with opportunities for both success and failure.What makes the difference in what happens is frequentlyattributed to the owners/operators of the airplane. and how theymanage the airplane. One way aircraft owners can get a grip ontheir airplane's perfonnance- and by doing so. uncover problemsbefore they either cost a lot of money or lead to an inflighl emergency-isby perfonning rouline perfonnance moniloring.Perfonnance moniloring is done for all major pieces of equipmentat large industrial sites, and is used 10 proieci the assets ofthe planl. A good, well-rounded program Iypically will includevibration analysis of mOiors and pumps, lemperalure analysisof any engines and oil analysis-along with a variely of OIherparameters. All of Ihese parameters are Irended to look forchanges that could indicate a degrading situalion.The result of these checks is Ihal predictive maintenancecan be performed on plant equipment based on the Irend. Thismaintenance is typically performed before an expensive andrepair intensive cataslrophic failure can lake place. By taking amore aggressive stance and monitoring their equipment, companiesreap benefits of better equipment performance, less failurerelated downtime and lower maintenance costs.It should come as no surprise thai this approach is used withairplanes, mostly in commercial service. However. il can beEngine Compressions76~~Z=~74~applied to Ihe average aircraft owner's Bonanza or Baron juslas easily. There are lilerally a dozen easy points Ihal the averagepilOi can Irend on a regu lar basis to monitor Ihe performanceof his or her airplane. The amount of rime such trendinatakes is small, bUllhe reward-if a single problem is found-"can be high.What to trend?Whal can be Irended on a Bonanza or Baron? The aircraftengine should be your fi rst trend targel. To start with, cyl indercompressions should be trended at each annual inspection. Thecylinder compressions tell you of the health of your piston ringsand valves. and show a di stinct, downward trend when problemsbegin to emerge in a cylinder or cylinders.As an example, a pilot nOies that the No.2 cylinder of theengine is showing a loss of compression over the past threeyears. The cylinder went from a consistent reading of 72 forseveral years, down to 68, and now 66. With this data in hand,a good look over the engine reveals a worn baffle. Correctionof the barne arrests the compression loss at 66 psi, which allowsthe engine to run several more years until it reaches TBO.While this may sound far-fetched, in reality, it isn't at all.One of the biggest killers of engines is heat, and a bad bafflecan cause a loss of cooling to a cylinder, which in turn cancause damage. Of course. there are dozens of things that couldcause the same problem, and one would hope that the A&Ps wepay to inspect our planes would SpOi a worn baffle and initiaterepairs before it reached the poiI1l of damage. However, thefac t of the matter is that your A&P isn 't trending the parameterof your engine in most cases, and so isn't keyed in to look closelyat the barnes unless instructed to do so.Other points can be trended, too. The key is to focus on thosewith the biggest impact on the operation of the plane, either interms of economy of operation or repair cos I. The top trendtargets obviously revolve around the biggest, most expensivesingle part of an airplane: its engine or engi nes. Keepingan eye on these internal combust ion wonders canhelp keep your repair costs in check. The previouslymentioned cylinder compressions are a good startingpoint, followed by engine CHT and EGT for thoseplanes so equipped to indicate them-and in somecases, record them.All of these trend points indicate general engine conditionand can be used to diagnose problems with the ex72 r-----------------------------------~·~ '" 70 ~----------------------------------------~c.haust system, fuel injectors and even the intake system.68 r-----------------------------------~ For example, suppose your engine has alwayspeaked on cylinder No. I or 2 since you bought your66 r---------------------------------~Insight GEM engi ne monitor. All of a sudden, cylinderNo.6 peaks firsl. Something has changed, and since64 r-----------------------------------~~---------- Cyl 1 _ CyJ 2 CyJ 3 ___----____--1you found it in your trend, you now have somelhing to~ _ ~4 - ~5-~6look for. In Ihis case, you start out with an inspection60 ~--------_.----_+----~----~----~of the cylinder. The barnes look OK, but the intake1981 1982 1983 1984Year1985 1986 1987 hose is scorched and cracked. Tracing the direct ion ofthe burn mark on the hose back to its source finds aPage 5650 ABS April 1999
di me-sized hole in your exhaust manifold. The hot exhaust wasimpinging on the No.6 cylinder intake manifold, making theair entering the cylinder heat up and expand. The air charge asa result was less dense, and the cylinder leaned out early as aresult .The aftermath is a repaired ex haust manifold, and a new intakeboot. after which the cylinders return to nornlal. The costof the repair is around S400,-about one-fourth of what thecost wo uld have been if the problem had progressed unti l theexhaust manifold caused the intake boot or cylinder to fail.Wi th the big hitters out of the picture, another engine trend thatcan tell a story is oil analysis. Spectro, which perfonns such oilanalysis on airplanes, even provides a wrinen report with suggestedpossible causes of these problems.Trend ing these results can find everything from a leaky crankseal to an engine that isn't run frequently enough, and by doingso. can help correct problems before they become major repairs.Long-term trendi ng of oi l analysis results can point out bearingproblems as well. A long term ri se or sudden spike in tinand copper usually indicates degradation of a bearing is takingplace, as these materials are used in the babbit of the bearing.Advance warning of the problem allows you to take action toarrest it. before you throw a rod through the engine in fli ght.Other trend pointsThere are other poi nts that you can trend as we ll to keep aneye on the health of your engine. To trend these points accurately.you need to establish a "state point," or an engine manifold pressure, prop rpm setti ng and al ti lUde where these readingswi ll be taken.Some good things to trend in such conditions are fuel flow,engine oil pressure, engine oi l temperature, vacuum, airspeed,outside air temperature and trim tab position. To make sense ofthese points. we' ll go over some basic facts.[n the case of airspeed, it depends on what instrument youhave installed. Pilots who do not have a true airspeed instrumenton board will need to get out the E6B and-using theoutside air temperature and pressure altitude-
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Page 36 and 37: LEESBURG. VIRGINIA, HAS MANY GREAT
Page 38: C a I e n d a rAMERICAN BONANZA SOC

April 1999 - American Bonanza Society

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