My hats off to Jack, for taking the time to satisfy his curiosity and my concern regarding his bent push rod, what makes this group such a success is the willingness of guys like Jack to the time to share?
In the Certified aircraft world flight controls are designed with a system jam in mind, (Lost wrenches or anything else that can find a way to block the movement) whether it's a fully manual flight control system to the control surface or a hydraulic assisted flight control the pilot input force in a jammed condition is generally the basis for ultimate loads. i.e. input force from the pilot times lever arms. So laughing about flight controls is not high on my list of pass time activities, It's serious and should be treated as such, In terms of the effect of vibration has on joint strength the real issue that is induced vibrations can cause a harmonic a response that resonates with the natural frequency of a push rod or any structure for that matter. For GA The most severe of these can come from things like in balanced propeller, crankshafts etc, In turbine engine aircraft the survival frequencies required come from the rotation speed of compressor blades when one or more disintegrate, and eventually stop the rotation of the engine. Our problems are not that severe, but its certainly good practice to inspect for wear and looseness of the control system during your annuals. Turbulence can effectively induce bending on a long push rod by the weight of the rod its self times a force of gravity factor, as an example: My longest push rod to the elevator will be around 80 inches made from 1.25 OD X .049 2024 T42 aluminum tube for the elevator and will take a compression load of 530 Lbs, its natural freq is 19 Hz, so it will react to that number, The lateral strength comes out to about 166 pounds, (applied side load in the middle of the rod) its mass will be 1.6 pounds with end fittings, so the effect of turbulence, would need to be around 10Gs before it bends the tube. Over designed? I suppose but 1.00 X .049 only save me .30 pounds and I have the 1.25 laying around. So the likelihood of the need to design for vibrations are pretty low, to each his/her own, its experimental and your results may vary. Dead horse or not, having the dialog may help expand the knowledge of everyone, or maybe only one builder, my thanks to Jack for the test and the feed back on the subject Jim Mullen KR2S boat, rigging controls is next From: Jeff Scott [mailto:jscott.pi...@juno.com] Sent: Wednesday, September 28, 2005 5:27 AM To: kr...@mylist.net Subject: Re: KR> Control tube test Somehow I doubt that Jack feels the need to destroy his control system to satisfy the curiosity. If you ever need anywhere close to 50# of force on the stick of a KR, you're already toast. FWIW, my KR has a much lighter control rod assembly than Jacks and has 525 hours of vibration testing, moderate to heavy turbulence, hot passes, and bad landings. In the last month I have had every single piece of the control system out on the bench for adjustments and a close inspection. I can tell you that you are beating a dead horse here. Jeff Scott N1213W -- Scott William <scot...@yahoo.com> wrote: Ok, here's just a dumb thought, so don't laugh at me too hard, ok? :-) Applying a force at the stick to measure how much bend you get is ok, but I would think you would want to measure how much force it took for catastrophic failure, where ever that point may be. Also, what about vibration and it's long term affect on a tube as opposed to a cable? Also, what about the integrity of the connection on the elevator end should you experience sudden pressure from turbulence? Ok, laugh now.....but when it comes to safety, I like to question everything, including whether or not you should wear boxers of briefs while flying. Scott --- Jack Cooper <kr2coo...@earthlink.net> wrote: > Jim Mullen and others have questioned my elevator > control tube system especially the bent tube from > the stick to the bell crank just behind the aft > spar. To satisfy my and others curiosity I conducted > a test of the system tonight. see my test at > http://jackandsandycooper.com/controltest.html . > Your comments are welcomed. > > > Jack Cooper > kr2coo...@earthlink.net > _______________________________________ > Search the KRnet Archives at > http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to > krnet-le...@mylist.net > please see other KRnet info at > http://www.krnet.org/info.html > __________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005 http://mail.yahoo.com _______________________________________ Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net please see other KRnet info at http://www.krnet.org/info.html _______________________________________ Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net please see other KRnet info at http://www.krnet.org/info.html
