AVIATOR pOinls - American Bonanza Society

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BY JIM CAVANAGH. KINGSVILLE. MISSOURI Bonanzas are pretty good airplanes. They look good. fly well and are strong as bulls. But there is one downside: If you own one. everybody wants to get into your pocket. J\ nyone active in airplane maintenance knows stories about smart and dumb things that go on. Over the last few years, there has been a tendency to become so conservative at the expense of common sense. The theory is that by being conservative, no matter what the cost, the airplane will be safer or at least less maintenance-prone. Sometimes this is correct, but sometimes it is not. One of the biggest wastes of airplane dollars is spending where you don't have to. and lately there have been stories of owners doing this when their engine cases have developed cracks. Cases can develop different kinds of damage, including, cracking, fretting, disassembly and assembly damage, stud and through-bolt damage, corrosion and catastrophic damage. If a problem is discovered in the field or at overhaul time, an owner must decide whether to have the case repaired, exchanged or replaced with new. The differences in cost are impressive, and the decision needs to be based on an understanding of all the options. An engine case is cast aluminum. It serves the function of containing oil, clamping the drive train together, holding the cylinders on and supporting all the accessories. Altogether Bonanzas have used at least 10 different engine variations out of the factory, with a number of STC'd replacements or upgrades. Some cases will crack and some won 't. Lower-horsepower engines have less power demands and are less prone to damage, while newer engines, from which the manufacturers are demanding more power, seem to suffer more, particularly from cracks. All cases are designed to put the "meat" where it is needed and, in order to save weight, be surprisingly thin where there is little stress. Cases are thick and heavy where there are crankshaft journals, camshaft beds and thrust bearings; slightly thinner where there are idler gear bosses or locations where they are machined for bolts or studs; and quite thin, sometimes down to one-eighth of an inch, where they simply contain oil and vapor. The heavily reinforced areas are the load pathways. While one might think that the thicker and heavier the casting, the less prone to cracking, such is not necessarily the case. With engine manufacturers trying to get as much power as they can out of an engine through the use of stroke and compression, the amount of force trying to blow a cylinder off of a case is tremendous. Coupled with thi s force are the repetition, and the we ll -known fact that, if vibrated enough, metal will harden. The result is resonance, which can transfer to different points within an engine as it is focused by the load paths and harmonics. If there is a weakness in the metallurgy of the case casting, like an impurity, a bubble or a physical imperfection, a crack can occur. Different types of damage as mentioned before, require different forms of attention and at different priorities. Some cracks are considered minor and require mere monitoring. Some are structural and need to be addressed immediately. The only way to know is to confer with a case special ist. If you want to get the real skinny on an engine subject, don't go to the manufacturer; go to the guys who repair them. Technicians have a pretty good idea where a crack is likely to occur on a particular engine model, and when they see a work order, they can pretty much guess where the damage is located. For instance. I've found on the early 10-470s, damage is usually simple wear. with few cracks. 10-5205 will most often have cracks at the upper front through-bolt, and on later 10- 5201550s, the cracks are mostly found at the corner studs. On cases with the front-mounted alternators, cracks are found around the studs. CASE 1'ltASES The first phase was called "Light Cases" and the next ge n eration the "Heavy Case." Different phases of the design theoretically allow for locations where cracks trad itionally showed up as reported by repair stations. The latest phase cases have been performing well with few cracks; but how many owners have the latest cases, or can afford S60,000 for a new engine You can tell a Phase n case from "humps" located on top of the engine over the case bolts. I've heard scuttlebutt that a shop has welded artificial humps on Phase I engines to make them look like Phase 11. If you have the TCM logo on both case halves, then it is a real Phase n engine. I consider Phase III to be the best case. With the exception of a very few of the first production run, it has beefy pads between the cylinder decks. Later on, this is where the seventh stud was located. If the pad is cast into the case, engine rebuilders can add the seventh stud. While an A&P can inspect a crankcase and accessory case in the field visually and with a dye penetrant, it is a good idea to send the case to a specialist for a more thorough inspection. Guys in the field can't get down to the fine measurements or identify fretting as the pros can. If there is a discrepancy, it can be taken care of immediately. IIEI'MII OR REI'LAI:E When a crack is discovered, the owner has the option of repairing or replacing. A replacement can be a used case or a new case. Most used cases wi ll already have been repaired at some point, but should you be comfortable flying behind a case that has been welded My case rebuilder told me a case rarely if ever cracks in the same place it has been repaired. Either it will remain crackfree, or the crack will manifest at a different location because of internal balancing or installation. The decision becomes easier when you consider thaI a Page 11000 www.bononzo.org ABS October 2008
completely overhauled and yellow-tagged case runs just over a grand, a replacement will run a few thousand, and a new case from the factory may cost over $1 OK. THE MOIlAt OF THIS STORY Don't let someone make you feel guilty about opting for the repaired crankcase. While each shop wrires its own manuals and procedures, all are approved by the FAA as Airworthy and able to meet or exceed original standards. What this means to an owner is a considerable amount in savings. The fact remains, though, that some owners and/or their panners, will never feel safe flying behind a repaired case. However mi splaced this perception is, it is real; at least it is to them. The peace of mind that comes from knowing you're flying behi nd a new engine may be what gets a lot of passengers into an airplane. The final decision remains up to the owner. Jim Cavanagh has 30+ yeors flying experience and more than 3,000 hours in nearly 200 airplanes. As on aviation writer, Jim has written thousands of articles and three books. .-- ~~ - - - -- --- _.- - - I ADRIAN EICHHORN & RON TIMMERMANS Continued from page 10997 METAL HOSE CLAMPS VS. NYLON CABLE TIES It's certainly easy and quick for mechanics to secure hoses with nylon cable ties as shown in this example (pink arrows). Metol hose clamps (yellow arrows) recuire more time and effort. Nevertheless, where the hose connection to its fitting may be subjected to heat (as in an engine comportment or on a defroster tube), a metal hose clamp is preferred. Nylon cable ties were developed to secure several wires or cables into a neat installation, they were never intended to be used as hose clamps, although we frequently see them used this way. They may become brittle after exposure to numerous heating cycles and will eventually rupture, allowing the hose to become disconnected fram its fitting. FAA Advisory Circulor AC 43.13-1 B "Acceptable Methods. Techniques & Practices - Aircroft Inspection & Repair" is used by mechanics as guidance. Although nylon cable ties are not specifically prohibited, you should ask yourself what impact you would face if the nylon cable tie broke during a flight and allowed a hose to became disconnected from its fitting. It could be a small investment with a potentially high payoff if your mechanic replaced all nylon cable ties with metal hase clamps in those places where they would be exposed to heat. LTC (Ret) Adrian A. Eichhom of Alexandria. VA. is an A&P with Inspection Authorization and a BPPP Instructor. He owns a 1962 P35 and flfes an A320 Airbus for a major air1ine. Ron Timmermons of Bedford, TX, is a Regional Program Manager for a large Engr IConstr firm in Dallas. TX. He is president of SPPP and hes owned 1wo Bonanzas. Adrian and Ron are both NAFI Moster eFls and Masfer Ground Instructors whom you wlll meet when you attend a SPPP clinic. Vif!oN under the cowling Arrcms show the preferred metal hose clamps VifM under the instrument panel arrow indicates a nylon coble tie whiCh should be replaced with a metal hose clomp ASS October 2008 www.bononzo.org Page 11001
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Page 22 and 23: INTENT VS, INTERPRETATION JOHN ANDR
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Page 42 and 43: 11 - North Eosl Bonanza Group Fly-i

AVIATOR pOinls - American Bonanza Society

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