Pietenpol-List: Caution - Rudder Bar Failure
Posted: Mon May 04, 2015 7:23 pm
Original Posted By: "Jack Philips"
This email is primarily being sent to advise all Pietenpol builders of apotential problem. Hopefully I=92m the only one that this has or will happento, but I thought the Pietenpol community at large should be aware of it.Saturday, my wife and I flew from our home at Smith Mountain Lake, Virginiato Roxboro, NC to attend the annual Antique Fly-In of VAA Chapter 3, theCarolinas Virginia Antique Airplane Foundation. As I turned final forrunway 06, with a slight crosswind from the left (wind was 010=B0 at 5 knots),I noticed the rudder suddenly felt =93loose=94, although when I tried rudderinputs, it still worked. Karen commented on the intercom that she heard a=93clunk=94. I landed the airplane (made a good landing, for once), and then aswe slowed below rudder effectiveness speed, all Hell broke loose. A slightgust of wind hit from the left and the plane immediately turned left andheaded for the weeds. Tailwheel steering was completely gone. I got on thebrakes and got it straightened out, but it was the closest I=92ve come toground-looping in a long time. As we taxied to the flight line I lookedback over my shoulder and verified the rudder moved correctly with inputfrom my feet, although it felt funny. Tailwheel steering still didn=92t workat all, so I continued to steer with brakes and we got it to our place onthe flight line and shut it down.Once parked, I looked back at the rudder and the cables were slack ' notension at all. The rudder was banging back and forth in the breeze. Assoon as Karen got out of the front cockpit I removed the front seat to seewhat was going on. What I found was that the rudder bar pivot, the boltwith its head welded to the underside of the rudder bar mounting bracket,had broken completely off. The only thing holding the rudder bar atanything like the correct position was the single diagonal brace. No wonderthe rudder felt a bit strange!Assessing my options, I finally decided the only way to fix it and get backhome was to remove the bracket, drill out the welded bolt head and insert anew bolt. I built this system exactly according to the plans, except forthe use of 4130 chrome moly steel and I welded the bolt head to the bracketinstead of brazing it as the plans show (I had read that brazing 4130 wasnot recommended). The bolt broke right at the point where the shank met thehead and the crack was completely within the bracket so it was undetectable.I had just completed the annual condition inspection on the airplane twoweeks ago and as part of the inspection I had inspected and assured thesecurity of the rudder bar (as well as I could). This failure wascompletely hidden, and I don=92t know how it could have been detected, otherthan X-Ray inspection.To remove the bracket I had to cut a couple of holes in the fabric on thebelly of the airplane, because when I built it I was not smart enough toinstall nutplates for all the bolts that penetrate the floorboard. Evenworse, I had used castellated nuts with cotter pins, which made itespecially difficult to remove the nuts so I could repair the bracket. Once the bracket was free we examined the failure. Apparently the heat fromthe welding caused a small crack to form in the shank of the bolt adjacentto the head. Over the last 10 years and 317 hours of flying, the forces onthe rudder bar were sufficient to cause that crack to grow, to the pointthat it ruptured completely Saturday. The fractured bolt is shown below:Note the smooth almost polished appearance of the fracture.Here is an excerpt from the plans, showing the area in question:Of course, if you have to have a problem with your Pietenpol while away fromhome, it sure is nice to be at a fly-in like Brodhead or Oshkosh, or aVintage Airplane fly-in. People were very helpful, particularly Jimmy Deanand Jim Wilson, and a young man whom I only know as =93Dusty=94. As soon as Igot the bracket off, Dusty took it to his workshop and carefully drilled,then reamed a hole through the welded in bolt head and pressed a new 5/16=94AN5 bolt in it. Jimmy Dean and I reinstalled the bracket and mounted therudder bar. I patched the holes in the belly with Duct Tape and we wereback in business.So what can I learn from this and pass on to my friends in the Pietenpolcommunity? First, understand that there are some parts of these airplanesthat are very hard to inspect in a meaningful way. I had literallyinspected this part exactly two weeks before as part of the annual conditioninspection, and detected nothing wrong with a part that was obviously readyto fail catastrophically. I did inspect the security of the cotter pin inthe nut that secures the rudder bar to this bolt. I grabbed the rudder barand wiggled it to see if everything was tight, and the diagonal braceprevented any movement from alerting me to the failure. What more can bedone in an inspection? I don=92t know and am open to suggestions.What am I going to do with it now? I=92m going to make a new rudder barbracket, for one thing. I=92m not sure that brazing the bolt is the answer,so I think I=92m going to weld an extra thickness of 1/8=94 4130 in the middleof the bracket, then drill and ream an under sized hole and press fit thebolt in place. I=92m also going to add a second diagonal brace to withstandrudder bar forces better. Jimmy Dean said that the early Wacos had thistype of design and ended up adding a second brace to prevent failures. I=92malso going to install nutplates under the floorboard so it will be easier toremove and install the rudder bar bracket in the future. Then of courseI=92ve got to repair the holes I cut in the fabric.If you are building a Pietenpol and have not yet made these parts, study theplans carefully and determine how you want to do it. As I said, other thanusing 4130 for the bracket and welding the bolt head rather than brazing it,I made it exactly to the plans. I certainly would NOT weld the bolt head.If you can braze, then braze it. As far as I know there has not been afailure of a brazen bolt head, but then I haven=92t heard of any failures ofwelded ones until now. I do think two diagonal braces is better than oneand should provide much better bracing.Be careful up there,Jack PhillipsNX899JPSmith Mountain Lake, Virginia________________________________________________________________________________
This email is primarily being sent to advise all Pietenpol builders of apotential problem. Hopefully I=92m the only one that this has or will happento, but I thought the Pietenpol community at large should be aware of it.Saturday, my wife and I flew from our home at Smith Mountain Lake, Virginiato Roxboro, NC to attend the annual Antique Fly-In of VAA Chapter 3, theCarolinas Virginia Antique Airplane Foundation. As I turned final forrunway 06, with a slight crosswind from the left (wind was 010=B0 at 5 knots),I noticed the rudder suddenly felt =93loose=94, although when I tried rudderinputs, it still worked. Karen commented on the intercom that she heard a=93clunk=94. I landed the airplane (made a good landing, for once), and then aswe slowed below rudder effectiveness speed, all Hell broke loose. A slightgust of wind hit from the left and the plane immediately turned left andheaded for the weeds. Tailwheel steering was completely gone. I got on thebrakes and got it straightened out, but it was the closest I=92ve come toground-looping in a long time. As we taxied to the flight line I lookedback over my shoulder and verified the rudder moved correctly with inputfrom my feet, although it felt funny. Tailwheel steering still didn=92t workat all, so I continued to steer with brakes and we got it to our place onthe flight line and shut it down.Once parked, I looked back at the rudder and the cables were slack ' notension at all. The rudder was banging back and forth in the breeze. Assoon as Karen got out of the front cockpit I removed the front seat to seewhat was going on. What I found was that the rudder bar pivot, the boltwith its head welded to the underside of the rudder bar mounting bracket,had broken completely off. The only thing holding the rudder bar atanything like the correct position was the single diagonal brace. No wonderthe rudder felt a bit strange!Assessing my options, I finally decided the only way to fix it and get backhome was to remove the bracket, drill out the welded bolt head and insert anew bolt. I built this system exactly according to the plans, except forthe use of 4130 chrome moly steel and I welded the bolt head to the bracketinstead of brazing it as the plans show (I had read that brazing 4130 wasnot recommended). The bolt broke right at the point where the shank met thehead and the crack was completely within the bracket so it was undetectable.I had just completed the annual condition inspection on the airplane twoweeks ago and as part of the inspection I had inspected and assured thesecurity of the rudder bar (as well as I could). This failure wascompletely hidden, and I don=92t know how it could have been detected, otherthan X-Ray inspection.To remove the bracket I had to cut a couple of holes in the fabric on thebelly of the airplane, because when I built it I was not smart enough toinstall nutplates for all the bolts that penetrate the floorboard. Evenworse, I had used castellated nuts with cotter pins, which made itespecially difficult to remove the nuts so I could repair the bracket. Once the bracket was free we examined the failure. Apparently the heat fromthe welding caused a small crack to form in the shank of the bolt adjacentto the head. Over the last 10 years and 317 hours of flying, the forces onthe rudder bar were sufficient to cause that crack to grow, to the pointthat it ruptured completely Saturday. The fractured bolt is shown below:Note the smooth almost polished appearance of the fracture.Here is an excerpt from the plans, showing the area in question:Of course, if you have to have a problem with your Pietenpol while away fromhome, it sure is nice to be at a fly-in like Brodhead or Oshkosh, or aVintage Airplane fly-in. People were very helpful, particularly Jimmy Deanand Jim Wilson, and a young man whom I only know as =93Dusty=94. As soon as Igot the bracket off, Dusty took it to his workshop and carefully drilled,then reamed a hole through the welded in bolt head and pressed a new 5/16=94AN5 bolt in it. Jimmy Dean and I reinstalled the bracket and mounted therudder bar. I patched the holes in the belly with Duct Tape and we wereback in business.So what can I learn from this and pass on to my friends in the Pietenpolcommunity? First, understand that there are some parts of these airplanesthat are very hard to inspect in a meaningful way. I had literallyinspected this part exactly two weeks before as part of the annual conditioninspection, and detected nothing wrong with a part that was obviously readyto fail catastrophically. I did inspect the security of the cotter pin inthe nut that secures the rudder bar to this bolt. I grabbed the rudder barand wiggled it to see if everything was tight, and the diagonal braceprevented any movement from alerting me to the failure. What more can bedone in an inspection? I don=92t know and am open to suggestions.What am I going to do with it now? I=92m going to make a new rudder barbracket, for one thing. I=92m not sure that brazing the bolt is the answer,so I think I=92m going to weld an extra thickness of 1/8=94 4130 in the middleof the bracket, then drill and ream an under sized hole and press fit thebolt in place. I=92m also going to add a second diagonal brace to withstandrudder bar forces better. Jimmy Dean said that the early Wacos had thistype of design and ended up adding a second brace to prevent failures. I=92malso going to install nutplates under the floorboard so it will be easier toremove and install the rudder bar bracket in the future. Then of courseI=92ve got to repair the holes I cut in the fabric.If you are building a Pietenpol and have not yet made these parts, study theplans carefully and determine how you want to do it. As I said, other thanusing 4130 for the bracket and welding the bolt head rather than brazing it,I made it exactly to the plans. I certainly would NOT weld the bolt head.If you can braze, then braze it. As far as I know there has not been afailure of a brazen bolt head, but then I haven=92t heard of any failures ofwelded ones until now. I do think two diagonal braces is better than oneand should provide much better bracing.Be careful up there,Jack PhillipsNX899JPSmith Mountain Lake, Virginia________________________________________________________________________________