February 2007 - American Bonanza Society

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BY DICK PEDERSEN, ABS TECHNICAL CONSULTANTTONY, WISCONSINBroken engine mount boltsI have found several 10-520/550-powered Bonanzas withbroken or missing mounti ng bolts on the left and right rearengine mount fittings, where these fittings bolt to the nose geartunnel sides. Those rear engine mount fitting s are the angledbrackets that are below the engine mount legs that are boltedto the engine, The square rubber Lord mount is installedbetween these two engine mount fittings.On some, the broken bolts were still in place, but the nutside of the bolt was broken off and missing inside the nosegear tunnel. These are AN4-1 OA, -II A or - 12A bolts, dependingon their location on the aft fittings. The top two bolts in thecenter of the aft fittings are usually the ones I find broken.Many times most of the rest of the bolts on the aft fittings areloose, possibly from bolt stretch.I assume the top bolts break from the weight of the enginepushing these fittings outward due to their angled design, especiallyduring turbulence or a hard landing, These bolts probablydon't get checked very often during normalmaintenance.The first time I found one of these brokenbolts in the boltom of the engine compartment,I had to look a long time before discoveringwhere it had come from because the left mufflerand manifold make the top of the fittingsomewhat difficult to see. I usually replacethese bolts at engine change time.The front engine mount fittings don'tseem to have this problem, although I havefound several slightly loose bolts in theselocations, This may be something you willwant your favorite maintenance provider tocheck from time to time.Fuel cell ventsI occasionally find a Bonanza wi th aproblem involving the fuel cell vents on theFuel vent line with small hole (orangearrow) drilled into aft side of linebottom of the wings, back by the flaps next to the fuselage,The two most common problems are the vent line beingplugged by a mud dauber nest, or the vent line is bent aft orbroken completely off.The plugged vent is easy enough to clear out with a pieceof wire or a plastic squirt tube from a WD-40 or LPS aerosolcan, assuming the nest or obstruction isn't too far up the ventline, If the obstruction is beyond the reach of your pokingstick, you will need to disconnect the vent line at a joint orsplice and blow it out with compressed air. Be sure to blow ina direction away from the bladder, as you do not want to blowthe obstruction into the bladder, nor do you want to pressurizethe bladder.A vent line being bent aft instead of in the normal 10° forwardposition is usually caused by someone accidentallybumping it while working under the aircraft or cleaning thebeUy. These vents bend aft very easily, Do be careful when tryingto bend them forward. If not properly done, the aluminumvent line will snap off just below the wing skin and ruin yourwhole day.The reason the vent line snaps off in this location is due toa small anti-icing hole that is drilled, or should be drilled, in theaft side of the vent line, fairly close to the bottom wing skin. Ifthis small hole is not drilled in the vent line or is plugged up withpaint stripper or paint and the vent line gets plugged wi th ice orsome other obstruction, the engine wi ll eventually quit from fuelstarvation as air is not being vented into the bladder to replacethe fuel the engine is drawing out of it.This can also cause the bladder to collapse and comeunsnapped from the top of the tank liner in the wing, If thisgoes unnoticed, you may not be able to put in the amount offuel that the bladder normally holds, as it may not straightenout completely on its own and it most certainly won't resnapitself back to the top skin!There is a way to detect a plugged vent inflight, before your engine quit s, if you knowwhat to watch for. I f one of your fuel gaugesstarts slowly working its way toward the fullmark for no apparent reason, we know forsure your Bonan za is not making gas! As thebladder is sucked up off the bottom of thetank liner as it is collapsing, the fuel gaugesending unit float is also being lifted up,causi ng the gauge to read a higher quantity.If you do nothing at this point, such asswitching to another tank, things could get veryquiet when fuel quits flowing to the engine, Noone has yet figured out how to keep it runningwhen you are that lean of peak IMany owners, mechanics and even FAApersonnel do not realize that these anti-icingholes are there on the aft side of the vent tube,So the ice hole sometimes doesn't get drilledPage 10047 www.bonanza.arg ABS February 2007
into the broken vent replacement tube, or it doesn't getchecked for obstruction after a paint job. Paint stripper caneasily fill this small hole, or masking tape can accidentally getleft on the vent tubes. covering tbe ice hole.While performing an annual inspection, many mechanicscheck to make sure the vent tubes are bent the correct 10° forward,are the proper I 3/4" long, have the 45° beveled openingand check the tube opening for obstructions-but fail to lookat the aft side of the tube to check to see if the small ice holeex ists and is not plugged.A Beech Service Leuer issued May 1957 pertains todrilling a second #40 hole 3/4" above the original hole in a1II0re ice-free area on the earlier Bonanzas. H35 SIN 0-5048and after had this #40 hole installed in the correct location atthe factory.During the S35 production run, starting with 0-7829,recessed fuel vents were installed at the factory to furtherreduce the chance of an iced-over vent. These recessed ventsare adjacent to the regular vent line and are connected to thesame vent line coming from the fuel cell by a Y connection.Even with the recessed vents, the regular vent tube still has thesmall ice hole dri lled into the aft side of the vent tube.If a vent tube on your Bonanza gets bent accidentally, itneeds to be bent forward to the correct 10° forward position toprovide the correct positive air pressure to the fuel cell.Otherwise, if left bent aft, suction will occur in the fuel celland can cause fuel starvation and engine failure.Care must be taken to bend the vent tube below the icehole, while supporting the vent tube in the ice hole area so itdoesn't bend and snap off in that area. If you are repairing abroken vent tube, be sure to drill the ice hole in the repairedtube in the proper location.Richard (Dick) Pedersen has been on ABS technical consultant forwell over a decode. Formerly our primary Service Clinic inspector,Dick now works mainly behind the scenes as a Beech maintenanceexpert and ABS' coordinator with the National Transportation SafetyBoard investigating Beechcroft accidents. When not consulting forABS or answering technical questions at Oshkosh and the ABSConvention, Dick runs a shop in Tony, Wisconsin, working exclusivelyon Beechcroft.If you have some ideas for topics that you would like theABS technical stoff to elaborate on. send your request forarticles to the ABS Magazine. Be sure to include your nome.address. phone. fox and e-mail address so the consultantscan contact you if they have questians. Shoring informationabout your airplane is what keeps the Society and this magazinegrowing. -EditorBeechcraft Service LetterPublished by the Customer Service DivisionIssued May 1957Models: Straight 35 and A35 thru H35FUEL CELL VENT MODIFICATIONIn extremely severe icing conditions, ice may completely block the openings in the main fuelcell vent tubes, resulting in collapse of the fuel cells. A second hole in the aft side of the vent tubenear the wing skin will reduce the possibility of completely blocking the vents; this modification hasbeen made on Bonanzas D-5048 and after.The normal opening in the vent tube is scarfed forward so that in flight ram air wi ll producea slight positive pressure in the cell. However, if the opening is closed by ice or foreign matter, asfuel is withdrawn from the cell a partial vacuum wi ll be produced which is of suffic ient force tocause coll apse of the cell, producing erroneous fuel gauge readings. The purpose of the hole in theaft side of the tube is to relieve the partial vacuum so formed and avoid collapse of the cell. Thelocation of the hole was chosen to be as nearly as possible in an ice-free area.On the aft side of each main fuel cell vent tube, drill a #40 bole 3/8" from the open end ofthe tube. The new hole will be 3/4" above the original hole in the vent tube, whkh may be leftopen.The vent tube openings should be checked occasionally to make sure they are unobstructed,since they are essential to proper fuel system operation.Beech Aircraft Corporation - Wichita, Kansas 67201 USA - Founded in 1932 by Walter H. BeechABS February 2007 www.bonanza.org Page 10048
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February 2007 - American Bonanza Society

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