Maintenance Forum Friday, October 1, 2004
Bill Milton The West Texas rains didn't dampen the interchange of information at this year's Cessna 195 Fly-in in Midland! Over the past few fly-ins, the Maintenance Forum has become a central focus for an increasing number of members. It's good to see that the health and well-being of our airplanes is getting added attention from the owners. Experts like "The 195 Factory" (http://www.the195factory.net), Radial Engines, Ltd. (http://www.radialengines.com), Barron Aviation (http://barronaviation.com), Butterfly Aviation and experienced owners shared their experiences in maintaining our airplanes and described improvements that they have developed. It's more than a little amazing (and confidence-inspiring) to be reminded of how extensive the support for our 190/195s remains, some 50+ years following the cessation of production! With such great resources, it's assured that we will be able to continue the practical use of these airplanes for many years to come. This year's Forum, hosted by "The 195 Factory's" Bill Milton was especially well attended and featured such notables as John Collett of Butterfly Aviation, John and Mike Barron of Barron Aviation, Caleb Curry of Radial Engines, Ltd., Richard Pulley of Anchorage, AK, and Ray Allen of Bakersfield, CA. It ran for the allocated three hours and many one-on-one conversations continued well into the afternoon. A great success! A very special thanks to goes out to Bill for arranging the speakers and topics. Radial Engines provided door prizes for lucky attendees. Member Richard Hawley was the happy recipient of a full set of rocker box gaskets, Mark Holmes was awarded an original Jacobs cylinder base wrench and Ron Karwacky received a full set of Jacobs maintenance, repair and operator manuals. Thanks, Caleb!
Let's delve into some of the details from the sessions:
John Collett Doorposts One area worthy of inspection is the so-called doorpost bulkhead. This bulkhead is a key structural member that effectively distributes the load of the aircraft between the main wingspar and the landing gearbox. John Collett and the Barrons both emphasized the importance of checking the doorpost bulkhead for cracks at annual inspections and cited some isolated cases of significant corrosion being found. There was concurrence that the right hand doorpost seems to be most affected, although a few cracks have been seen in airplanes that have the left-hand emergency door. In the past there was a theory that only high-time airframes were subject, but that is changing with some relatively low time airplanes developing cracks. Mike Barron said that every bulkhead that had the crack had a history of wing contact with the ground or other obstruction, which would transfer an unusual load to this member. If corrosion is bad, the bulkhead must be replaced. If a small crack is found, it often can be repaired by installing a 0.040" stainless steel doubler (available from Butterfly at about $60). Since the wing must be removed, about three days of labor is required. Doublers are available for both right-hand and left-hand doorposts. Butterfly holds a multiple field approval for the doorposts. Fuselage Jigs The 195 Factory, Butterfly Aviation and Barron Aviation have fuselage jigs in the event major rebuilds are required. Brake Master Cylinders There was discussion of the original brake master cylinders that have serrated piston stems, and the tendency for them to fail due to breakage at one of the serrations. It's a good idea to replace them if your aircraft is so equipped. They were primarily on earlier airframes. One good alternative is the Cessna 421 master cylinders, which John Collett reports is now STC'd for the 195s. An added benefit is that the larger diameter of its piston takes some of the sensitivity out of the braking system for those of us who have installed the very powerful Cleveland brakes. Skylane cylinders through the 1980 model year are useable as are new production Cleveland master cylinders. Gascolators The gascolator body that is located at the bottom center of the firewall often has corroded threads due to internal water retention. Butterfly is rebuilding them by cutting out the damaged area and welding in a new fitting. He's also installing a #00 mesh screen (in place of the original #80 mesh) which is compatible with the fuel injection STC at the same time. Cost is $300, exchange. Fuel Control Valve The original Thompson Fuel Control Valve (in the cockpit) is available new from Cessna for $1,600. Some of the newer valves can be re-O-ringed if they become leaky. As an alternative, Butterfly has been rebuilding used, serviceable 180-182 valves and selling them for $800 outright under a field approval.
John Barron Aileron Inboard Hinge Brackets Mike Barron had examples of unairworthy parts. Often the urethane paint used hides corrosion and cracks since the magnesium's corrosion salts don't "swell up" as much as aluminum. An effective inspection requires that the original parts be removed and the paint be removed and the part bead-blasted. The upcoming AD notice will be satisfied by a recurring inspection of the original hinge brackets or by installation of new aluminum hinges available from Cessna or from Barron Aviation. Cessna's brackets are about $1,265 each; Barron's are $1,250 for the pair. Barron's are STC'd and PMA'd. Their installation requires only the filing of a Form 337 to show conformance with the STC, no field approval is needed. Corrosion Protection Barron Aviation has begun some comparative tests between ACF-50 and Boeshield T-9 (from Boeing) corrosion protection treatments. The preliminary findings indicate that either treatment is good as a preventative, but the ACF-50 seems to "eat the salts" better if the part is already corroded. The Boeshield is a little cleaner in application if corrosion has not already progressed. Airframe Parts and Skins, General A very comprehensive listing of airframe parts available from The 195 Factory, you can visit their site for details. Barron Aviation has added wheel pants, lower cowling skins and the cowling air intake skins to their repertoire of airframe parts.
Bill Milton Cowling Maintenance Bill Milton reported that maintenance of the cowling is inadequate.. At annual time it's the first part to be removed and the last part to be reinstalled, so it's often ignored. The rub strips of micarta inside the steel cowling ring are very important since they take the full air load of the cowling. If they're worn or missing, the metal-on-metal contact between the cylinder head lugs and the cowling ring will quickly wear the parts beyond serviceability. Field expedients such as rubber hose around the lugs are only a temporary fix; the micarta rub strips are the only real solution. A full set of strips is available from The 195 Factory for about $40, including rivets. Bill's experience is that an effective inspection will result in at least one or two rub strips needing replacement at each annual, so it would be good to have these parts on hand. If someone neglected the strips and your cowling rings are worn, The 195 Factory has replacements for the lower cowling's ring (the two upper cowling rings are not currently available). Butterfly Aviation has successfully repaired some worn rings by TIG welding them. The vinyl tubing sleeves for the cylinder head lugs is available from The 195 Factory. Replacement intercylinder baffles are also available from The 195 Factory. Goodyear Crosswind Landing Gear Ray Allen has devised a tool to aid in disassembling the landing gear. Also, he is manufacturing replacement brake friction pads. His contact information is available in the Members' Section of the website. Elevator Trim Tabs Christy Barden discussed elevator trim tab mechanism wear. He feels that this is responsible for sloppiness in maintaining a trim airspeed. No play = no porpoising. Looseness in the mechanism is often the result of a worn hinge pin. If it's the actuator itself, it must be replaced as individual components are not available. Christy's contact information is available in the Members' Section. Landing Lights The original GE 4561 bulbs are no longer available. Barron Aviation has a replacement for $96.
If the landing lamp motor fails, there are no known sources for new ones, but some members said that Jeff Pearson (see Members' Section for contact info) can often repair them.
Caleb Curry Fuel Injection Certainly one of the hottest topics was an update from Caleb Curry of Radial Engines regarding the fuel injection STC for the Jacobs. The engine STC was granted the week prior to Oshkosh. The separate airframe STC required additional testing (Aubie Pearman's airplane was the test bed) which has been successfully completed. That paperwork is in process by the FAA and is imminent. Here are the highlights:
In general, Caleb described increased smoothness and power and reduced fuel burn for the engine. Roger McDowell's new engine is being modified at Radial Engines and will be installed by Bill Milton soon. Ignition Butterfly Aviation can supply an STC'd Echlin coil and condenser to replace the no-longer-available Bendix coil for the battery ignition system. The kit price is $300 and includes the coil with the same form factor as the original, a condenser of the proper value, a special tool to facilitate installation and instructions. Many owners have reported that ignition noise degrades the performance of their radios. Some felt that Garmin NavComms were worse affected than some others. In some cases, resetting of the internal squelch on the Garmins is necessary to quiet the noise (but setting the squelch to a tighter setting also reduces the radio's sensitivity to transmissions, too). Caleb says that ignition noise isn't limited to C-195s; Wacos have the same issues and Garmins seem to be more affected. The reduction of electrical noise is well described as an "archeological expedition" where a cause is identified and corrected, then the next source is identified and so on. Here are excerpts from the discussion: Begin by disconnecting the antenna from the affected receiver. If the noise persists, it's being picked up by the electrical wiring. If it's reduced or eliminated, it's being picked up by the antenna If it's being picked up by the electrical wiring:
Make an "antenna on a stick" from a short length of coaxial cable (RG-58 or RG-142 is available from Radio Shack). Terminate one end in a connector compatible with your handheld comm. (BNC is common). Simply leave the other end cut off flush. Using heat shrinkable tubing, affix the open end to an 18" wooden dowel. With this tool and your handheld comm, you can probe for noise sources. With the engine running and the cowling removed, you can put the open end of the antenna in the vicinity of the generator, magneto and battery timer listening for noise through headphones. The aperture of the open end is small, so you can isolate a source. Be careful to not press the transmit button on the handheld or you might damage the transmitter. If the handheld has an adjustment for high or low power, select "low" for more protection in case the button is accidentally pressed. It will likely take a fair amount of iterative tests to quiet the noise to its minimum. The Barrons described one airplane that consumed about 150 manhours and still had some residual noise. Torquing of Cylinder Bases Radial Engines recommends retorquing of the cylinder base nuts after the first 25 hours or operation, and at 100 hour intervals thereafter. Since the cylinder bases are at the junction of three different metals (magnesium, steel and aluminum) each with different temperature expansion rates, the hold downs have a tendency to loosen after many temperature cycles. Caleb said that many engines they see have the easily accessible front nuts overtorqued apparently in hopes of compensation for skipping the harder to get to rear nuts. This is probably worse than not retorquing at all, since it places lots of stress on the overtorqued nuts. Doing it right is a time-consuming job. It requires removing or at least loosening and repostitioning most of the inter-cylinder baffling and some exhaust segments. Figure on a day or so of labor. In the field, examples of inter-cylinder baffling whose bottoms have been shortened about ¾" and fitted with rubber baffle material to close the gaps have been seen. This significantly shortens the time to retorque since the baffling no longer has to be removed. The source of this modification is unknown. Hydraulic Lock There have been instances of engines bending or breaking their aluminum link rods due to hydraulic lock. Sometimes a bent link rod will fail immediately; sometimes it will go to TBO. Hydraulic lock is caused when the amount of oil "above" the piston exceeds the roughly ½ pint of available space. Only cylinders #4 and #5 (the lower ones) are subject. The oil either collects directly in the cylinder's combustion chamber or can accumulate in one of the intake tubes and be drawn into the cylinder after startup. John Barron cautions against starting the engine if you hear s "slurping" sound on the intake stroke of #4 or #5 on pull though; that sound indicates a constricted (by oil) intake tube for that cylinder. A clean kit helps. So does regular flying of the airplane (oil seeps past the check valves in the oil system during long periods of disuse). Barron Aviation has STC'd and PMA'd a kit that provides drains for intake tubes for #4 and #5. No user action is required; any oil accumulation is automatically drained from short tubes through vacuum-actuated valves. The kit costs $250, exchange, and any IA can install and file the Form 337. John estimates that three or four hours of labor are required. For those of us who like to "park" the prop in a certain position, Richard Pulley provided an useful discussion and demonstration with a schematic showing piston locations and valve positions for various propeller rotations. There was considerable discussion and debate over the "best" place to park the prop, but the majority opinion was that #1 blade should be just barely past TDC on the compression stroke of #7 cylinder. Oil Filters An increasing number of owners are installing engine oil filters. The current wisdom is that utilizing an oil filter won't extend the TBO of the engine, but many parts (like the crankpin) fare better with filtered oil, thus making overhaul at TBO less expensive. Universally, the experts felt that adding an oil filter does not extend the period for regular oil changes since the filter captures particulate material but it cannot remove the chemical contaminants (acids) from combustion. There are three popular choices: the Air Wolf filter, the ADC filter and the so-called Moen STC which is held by the Eastern Cessna 195 Organization and is available to its members for a nominal fee. As an overview, the discriminating features are that the Air Wolf and ADC filters are full flow (meaning 100% of the engine oil flows through them) while the Moen STC is partial flow (although Moen argues that all the oil circulates through the filter multiple times per hour due to the volume of the pump). The Air Wolf filters the scavenge output of the engine back to the oil tank, the ADC filters the oil before it gets to the engine. The Moen filter is tertiary to the system, inline with the inlet to the propeller governor. There have been cases where the Air Wolf filter caused excessive oil pressure or fluctuation and high oil temperatures ostensibly due to backpressure on the scavenge side. In at least one case, the problem was unsolvable, even with assistance from Air Wolf. The solution was to remove the filter system. No such issues were reported for either the ADC or the Moen systems. The ADC has an added advantage of a chip detector light and a bypass light. The Moen has the advantage of lower cost (probably less than $100 in parts procured locally compared with over $500 for the ADC). Also mentioned was the Winslow oil filter system, which had good field experience, but filter elements are no longer available for it. Contributed by Coyle Schwab |
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