Original Posted By: "David B. Schober"
If there is no front plate (or is to thin) the bolt will shear, no matter ifthey are grade 5, AN, Titanium or any space age material. The force of thebolts have to be AGAINST the WOOD BOTH SIDES, so you dont need to muchtorque to fasten them, is the "area of wood" in contact to the flange whatis doing most of the work. Keep them torqued in specifications and theywill do they work perfectly. let them loose and they will shear AN or not.SaludosGary Gower >I wonder about the front plate on the prop that was lost. Wood is a soft>material 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 fastener>and no amount of retightening could keep it fronm working loose. Most>factory prop hubs I have seen for wood props have the front plate splined to>the 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 are>compressing the wood prop hub. The torque is tranfered to the prop by the>STATIC friction between the hub and flanges. Any evidence of burning infers>that there has been considerable motion between the two parts.>> If the plate under the bolt heads deforms, the bolts would try to>stretch as they are now the hypotenuse of a right triangle (a longer>distance) as the prop moves on the hub. This stretch and relax cycle would>happen twice per revolution on a 4 cylinder four stroke. That makes it about>5000 cycles per minute ! The bolts, even "proper prop" hardware would never>stand this for long. Properly done the bolts that hold the prop to a Ford>Crank could be Grade 5 but they must be torqued using a thrust plate between>the head of the bolt and the prop. The tension on the bolt's shaft must be>higher 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 they>are 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 most>likely use an adapter to Continetal or Lycoming bolt pattern just so that if>I ever needed a different prop in a hurry it would be much easier to find>one.> John McNarry>-----Original Message----->From: Earl Myers >To: Pietenpol Discussion >Date: Saturday, October 02, 1999 10:17 PM>Subject: Re: Burnt props and grade 5 bolts.>>>>LAUREN;>> The threads in the Ford crank flange are COARSE thread, hence the use of>>the commercial bolts. The two engine mfgr's , Lycoming and Continental>both>>use commercial bolts on their engines as do many component mfgrs.>>(alternators, pumps & so on). These two Piets otherwise are reported to be>>VERY nice!>> You said the VW guys have had this problem for years while using the>>direct drive I assume?>>This friction is from the bolts not being torked enough.......I will pass>>that on to see what reaction I get. Guys, this is the kind of info I need,>>keep it coming!>>Earl Myers>>-----Original Message----->>From: Lauren Williams >>To: Pietenpol Discussion >>Date: Saturday, October 02, 1999 10:50 PM>>Subject: Burnt props and grade 5 bolts.>>>>>>>>Haven't we seen this before?>>>>The Volkswagen engined guys have had this problem for years. They have>>lost a few props too. If they don't keep their prop bolts tight, the>>surface against the driving flange will char because of the friction>>caused by movement between the prop and flange..>>>>Grade 5 bolts!!!! That's common, autoparts store stuff. I thought that>>the word had gotten to everyone about using aircraft (AN) hardware in>>all structural applications in homebuilts, regardless of what the 1930s>>plans say. Certainly the prop bolts are the most structural fastener in>>the whole plane. There are wonderful aircraft propeller bolts availiable>>for all dimensions with fine threads, drilled heads for safety wire and>>huge strength.>>>>I am afraid that I would want to look over the rest of the plane and see>>if 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't>>look at the type of fasteners being used. A first time builder, who>>hasn't been following the literature for 20 years can be forgiven a>>mistake like this. What is the inspector's excuse?>>>>I am building a Pietenpol so that I can experience and share the>>adventures of the early day aviators. I really have no intrest in>>reexperiancing their "misadventures".>>>>I guess this got me excited!>>>>Lauren>>>>>>>>>>________________________________________________________________________________