Brodhead Pietenpol Association

Original Posted By: nle97(at)juno.com
Subject: Pietenpol-List: Burnt props and grade 5 bolts.Haven't we seen this before?The Volkswagen engined guys have had this problem for years. They havelost a few props too. If they don't keep their prop bolts tight, thesurface against the driving flange will char because of the frictioncaused by movement between the prop and flange..Grade 5 bolts!!!! That's common, autoparts store stuff. I thought thatthe word had gotten to everyone about using aircraft (AN) hardware inall structural applications in homebuilts, regardless of what the 1930splans say. Certainly the prop bolts are the most structural fastener inthe whole plane. There are wonderful aircraft propeller bolts availiablefor all dimensions with fine threads, drilled heads for safety wire andhuge strength.I am afraid that I would want to look over the rest of the plane and seeif the lift and cabane strut attach fittings, the wire attach fittings,etc. had correct AN fasteners.I wonder what the FAA inspector looked at on this aircraft if he didn'tlook at the type of fasteners being used. A first time builder, whohasn't been following the literature for 20 years can be forgiven amistake like this. What is the inspector's excuse?I am building a Pietenpol so that I can experience and share theadventures of the early day aviators. I really have no intrest inreexperiancing their "misadventures".I guess this got me excited!Lauren________________________________________________________________________________

Original Posted By: Gary Leopold
Haven't we seen this before?The Volkswagen engined guys have had this problem for years. They havelost a few props too. If they don't keep their prop bolts tight, thesurface against the driving flange will char because of the frictioncaused by movement between the prop and flange..Grade 5 bolts!!!! That's common, autoparts store stuff. I thought thatthe word had gotten to everyone about using aircraft (AN) hardware inall structural applications in homebuilts, regardless of what the 1930splans say. Certainly the prop bolts are the most structural fastener inthe whole plane. There are wonderful aircraft propeller bolts availiablefor all dimensions with fine threads, drilled heads for safety wire andhuge strength.I am afraid that I would want to look over the rest of the plane and seeif the lift and cabane strut attach fittings, the wire attach fittings,etc. had correct AN fasteners.I wonder what the FAA inspector looked at on this aircraft if he didn'tlook at the type of fasteners being used. A first time builder, whohasn't been following the literature for 20 years can be forgiven amistake like this. What is the inspector's excuse?I am building a Pietenpol so that I can experience and share theadventures of the early day aviators. I really have no intrest inreexperiancing their "misadventures". I guess this got me excited!Lauren________________________________________________________________________________

Original Posted By: Lauren Williams
LAUREN; The threads in the Ford crank flange are COARSE thread, hence the use ofthe commercial bolts. The two engine mfgr's , Lycoming and Continental bothuse commercial bolts on their engines as do many component mfgrs.(alternators, pumps & so on). These two Piets otherwise are reported to beVERY nice! You said the VW guys have had this problem for years while using thedirect drive I assume?This friction is from the bolts not being torked enough.......I will passthat on to see what reaction I get. Guys, this is the kind of info I need,keep it coming!Earl Myers-----Original Message-----

Original Posted By: Earl Myers
I wonder about the front plate on the prop that was lost. Wood is a softmaterial and needs to have the clamping load spread out over a large area.If the front plate was to thin, or soft, it would deform at the fastenerand no amount of retightening could keep it fronm working loose. Mostfactory prop hubs I have seen for wood props have the front plate splined tothe hub to eliminate the twisting action as the crank tranfers to the prop.The bolts then are only in tension between the plates and the plates arecompressing the wood prop hub. The torque is tranfered to the prop by theSTATIC friction between the hub and flanges. Any evidence of burning infersthat there has been considerable motion between the two parts. If the plate under the bolt heads deforms, the bolts would try tostretch as they are now the hypotenuse of a right triangle (a longerdistance) as the prop moves on the hub. This stretch and relax cycle wouldhappen twice per revolution on a 4 cylinder four stroke. That makes it about5000 cycles per minute ! The bolts, even "proper prop" hardware would neverstand this for long. Properly done the bolts that hold the prop to a FordCrank could be Grade 5 but they must be torqued using a thrust plate betweenthe head of the bolt and the prop. The tension on the bolt's shaft must behigher at installation than it will ever be subjected to as the engine runs. I have never heard of a flywheel coming off of a Model A but then theyare dowelled as well as bolted to ensure the bolts only act in tension.I still have a Ford B engine that I could use in my aircraft but I will mostlikely use an adapter to Continetal or Lycoming bolt pattern just so that ifI ever needed a different prop in a hurry it would be much easier to findone. John McNarry-----Original Message-----