---------------------------------------------------------- Pietenpol-List Digest Archive --- Total Messages Posted Sat 10/24/09: 20 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:41 AM - 106 years ago today-prelude to flight (helspersew@aol.com) 2. 06:23 AM - Re: 106 years ago today-prelude to flight (Wayne Bressler) 3. 07:52 AM - Push/pull tubes and rod ends (Michael Perez) 4. 09:22 AM - Re: Push/pull tubes and rod ends (Jack Phillips) 5. 12:06 PM - Re: Push/pull tubes and rod ends (Michael Perez) 6. 01:04 PM - Re: Push/pull tubes and rod ends (Michael Perez) 7. 01:12 PM - Re: Push/pull tubes and rod ends (helspersew@aol.com) 8. 01:55 PM - Re: Push/pull tubes and rod ends (Bill Church) 9. 01:57 PM - Re: Push/pull tubes and rod ends (Pieti Lowell) 10. 02:05 PM - Re: Push/pull tubes and rod ends (David Paule) 11. 02:09 PM - Re: Push/pull tubes and rod ends (Ryan Mueller) 12. 02:36 PM - Re: Push/pull tubes and rod ends (Bill Church) 13. 02:43 PM - Re: Push/pull tubes and rod ends (Gary Boothe) 14. 03:00 PM - Re: Re: Push/pull tubes and rod ends (David Paule) 15. 04:48 PM - Re: Push/pull tubes and rod ends (Jack Phillips) 16. 05:26 PM - Re: Push/pull tubes and rod ends (chase143) 17. 07:04 PM - Re: Re: Push/pull tubes and rod ends (Jack Phillips) 18. 07:39 PM - Re: Push/pull tubes and rod ends (Pieti Lowell) 19. 08:13 PM - Re: Push/pull tubes and rod ends (Clif Dawson) 20. 11:27 PM - Re: Push/pull tubes and rod ends (Robert Ray) ________________________________ Message 1 _____________________________________ Time: 04:41:33 AM PST US Subject: Pietenpol-List: 106 years ago today-prelude to flight From: helspersew@aol.com >From the diary of Orville Wright. Saturday, Oct. 24,1903 Kitty Hawk, N.C. Had strong wind from northeast during night, with some rain, which continu ed during day at velocities of 25 to 40 miles. We put in the uprights betw een surfaces and trussed the center section. Had much trouble with wires made up at home, which for some reason unexplainable failed to fit. Wind at 7 o'clock this evening blowing 45 miles. Air very damp and cold. do not archive ________________________________ Message 2 _____________________________________ Time: 06:23:46 AM PST US From: Wayne Bressler Subject: Re: Pietenpol-List: 106 years ago today-prelude to flight I could read these every day. Please don't stop! This is great stuff! Thank you for sharing. Do not archive Wayne Bressler Jr. Taildraggers, Inc. taildraggersinc.com Sent from the phone that made the Blackberry obsolete. On Oct 24, 2009, at 7:40 AM, helspersew@aol.com wrote: > From the diary of Orville Wright. > > Saturday, Oct. 24,1903 > Kitty Hawk, N.C. > > Had strong wind from northeast during night, with some rain, which > continued during day at velocities of 25 to 40 miles. We put in the > uprights between surfaces and trussed the center section. Had much > trouble with wires made up at home, which for some reason > unexplainable failed to fit. Wind at 7 o'clock this evening blowing > 45 miles. Air very damp and cold. > > do not archive > > ________________________________ Message 3 _____________________________________ Time: 07:52:18 AM PST US From: Michael Perez Subject: Pietenpol-List: Push/pull tubes and rod ends I am trying to figure out what size and material tube to use to go from the control stick to the elevator bell crank.- I see in the Bingelis books, he talks about heavy wall aluminum threaded tubing.- Since I am all about saving weight on my plane, I would prefer aluminum. The plans call for 1/8 " cable, which-is rated between 1760 and 2100 lbs. I would hope that a tu be/rod end combination that rated at these numbers would work.- So, I am trying to figure out what size tube and threaded rod end will give me the 1 760-2100 lb. rating.-- If someone can prvide a usable formula, I may be able to figure it out myself. - Thanks group. ________________________________ Message 4 _____________________________________ Time: 09:22:40 AM PST US From: "Jack Phillips" Subject: RE: Pietenpol-List: Push/pull tubes and rod ends Are you planning on re-designing the entire elevator control system with pushrods, requiring a pushrod attached to each elevator, a pushrod from the bellcrank to the rear stick and a pushrod between sticks? It probably will require an additional pushrod and bellcrank to enable you to pass underneath the rear seat (where the cable from the stick to the bellcrank makes a bend, with the plans showing it just passing through a hole drilled in the wood - I added a pulley here). If so, figure out the yield strength of whatever alloy of aluminum you intend to use, then determine what area will be required to withstand the load (1760 lbs, if you want to equal the cable strength) without exceeding that stress level. Use the formula Stress = Load divided by Area (s = P/A), and solve for area (A) since you know the load (P = 1760) and you know the stress (s = yield strength of your alloy times whatever safety factor you feel like throwing in). Once you know the area, then determine what wall thickness and tube diameter will produce the required area. Of course, there will be machined fittings required on each end of the pushrods, and rod end bearings to reduce the amount of slop. As an engineer, I have to wonder why are you doing this? The cables work well. Any arrangement with pushrods is going to be much more complicated, due to the geometry of the airplane. Pushrods will end up being far more expensive and heavier. I don't understand what advantage you are trying to achieve here, other than to be "different". You could accomplish that by painting it Pink. Jack Phillips NX899JP Raleigh, NC Enjoying a rainy day by building the wings of my RV-10 in the basement _____ From: owner-pietenpol-list-server@matronics.com [mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of Michael Perez Sent: Saturday, October 24, 2009 10:52 AM Subject: Pietenpol-List: Push/pull tubes and rod ends I am trying to figure out what size and material tube to use to go from the control stick to the elevator bell crank. I see in the Bingelis books, he talks about heavy wall aluminum threaded tubing. Since I am all about saving weight on my plane, I would prefer aluminum. The plans call for 1/8" cable, which is rated between 1760 and 2100 lbs. I would hope that a tube/rod end combination that rated at these numbers would work. So, I am trying to figure out what size tube and threaded rod end will give me the 1760-2100 lb. rating. If someone can prvide a usable formula, I may be able to figure it out myself. Thanks group. ________________________________ Message 5 _____________________________________ Time: 12:06:36 PM PST US From: Michael Perez Subject: Re: Pietenpol-List: Push/pull tubes and rod ends Push/pull tubes are used in all kinds of aircraft safely. All of which have more aggressive performance then a slow, draggy, 80+ year old designed Pie t. Yet most seem to think to make the switch to push/pull is a bad idea...w hy? I know most just get upset because I stray from the sacred bible of bui lding the Pietenpol...the prints. Yet non have legitimate reasons for not d oing it...at least not any they share.- If you guys have facts for NOT us ing them, please, do tell. To make a statement and not back it up is useles s. - The Bingelis books talks about aluminum tubes-for push/pull...-you know , the books everyone raves over. He also talks about how these systems-MA Y weigh less then a cable system with the cables, pulleys, brackets, shackl es, bearings, nicopress fittings, etc.- - If you could run a tube from the firewall to the rudder and support the len gth along the way-with, say bushings,-there would be no flexing/bending , yes? - I don't have the answers...yet, that is why I am here. I am looking for ANS WERS, not opinion, guesses, or dialog on how this 80 year old plane built b y a guy in his garage can't be improved upon with some common sense and som e homework. - Here is what one engineer sent me:- - Pull out load = (1/3)(dia rod)(pi)(shear load)(length of engagement) - For some generic heavy wall tube from McMaster Carr and a 1/4-28 male threa d rod end, I get:- 1962 lbs. worse case with .500" thread engagement, 294 4 lbs. with .75" engagement. - The 7X19 SS cable is rated at 1760 lbs.- Using the controls in the Pieten pol, can a person ever pull 1760 lbs. on the cable?- If they could, would n't a wood structure fail first...I don't know...like the elevator itself? - Since no one here seems to have heard of a control cable failure, that must mean no Pietenpol has seen 1760 lbs. of force on a 1/8" control cable, so what are the REAL loads on this plane and it's controls?- I think peo ple get a little too extreme and have a plane built for mach 2 when it real ly only flies at 70 MPH. - HOWEVER, my disclaimer...I have been wrong before and have abandoned other "great" ideas that I have had, this may yet be another. But that decision w on't be made until I have some facts, and some REAL numbers. - Anyone have another formula for pull out stress or bolt sheer? - ________________________________ Message 6 _____________________________________ Time: 01:04:12 PM PST US From: Michael Perez Subject: RE: Pietenpol-List: Push/pull tubes and rod ends Jack, I got as far as finding the area using the formula you gave me. That number is .11733.- I am not clear how to figure tube dia. and wall thickn ess to this number. ________________________________ Message 7 _____________________________________ Time: 01:12:55 PM PST US Subject: Re: Pietenpol-List: Push/pull tubes and rod ends From: helspersew@aol.com Sounds to me like this push-pull tube idea is opening the preverbial Pando ra's Box of "if I change this, then I must change that,.......... and that , and that................ -----Original Message----- From: Michael Perez Sent: Sat, Oct 24, 2009 3:03 pm Subject: RE: Pietenpol-List: Push/pull tubes and rod ends Jack, I got as far as finding the area using the formula you gave me. That number is .11733. I am not clear how to figure tube dia. and wall thickn ess to this number. ======================== =========== -= - The Pietenpol-List Email Forum - -= Use the Matronics List Features Navigator to browse -= the many List utilities such as List Un/Subscription, -= Archive Search & Download, 7-Day Browse, Chat, FAQ, -= Photoshare, and much much more: - -= --> http://www.matronics.com/Navigator?Pietenpol-List - -======================== ======================== =========== -= - MATRONICS WEB FORUMS - -= Same great content also available via the Web Forums! - -= --> http://forums.matronics.com - -======================== ======================== =========== -= - List Contribution Web Site - -= Thank you for your generous support! -= -Matt Dralle, List Admin. -= --> http://www.matronics.com/contribution -======================== ======================== =========== ________________________________ Message 8 _____________________________________ Time: 01:55:47 PM PST US Subject: Pietenpol-List: Re: Push/pull tubes and rod ends From: "Bill Church" Whoa - what comments are you responding to Mike? The only reply to your post that I saw was from Jack, and all I saw in his reply were sound reasons explaining why the cables are a better system FOR THIS AIRPLANE. As he stated, the geometry of the Air Camper will result in a heavier and more expensive linkage as compared to the cables. Tony Bingelis says that push/pull tubes MAY weigh less than a cable system. That will depend on the layout of the airplane, and in this case, the control system has to go under the seat, and then get back up into alignment with the elevators and rudder. Cables can change direction with the addition of a simple pulley, where push/pull tubes will require bellcranks - which one do you think is heavier? It is not possible to run a tube straight from the firewall to the rudder in this airplane, unless you have a properly sized and located hole in your torso for the tube to pass through. Also, in THIS airplane, the elevators are separate entities, so you would either have to redesign them so that they are tied together, or run two push/pull tubes for the elevators. To quote your original post "I'm all about saving weight on my plane". Jack's reply explained that the push/pull system will end up being heavier than the cable system. So what IS the motivation to change to the push/pull system? Regarding your request for a formula, the thing to keep in mind is that in designing a mechanism like a push/pull system, you need to analyze each component and each connection in the system, and the loads that could be imposed on each component. Those loads are used to determine the size and shape that each component will assume. There are the different tubes that need material, diameter and wall thickness to be determined, and the size of all the threaded connections, and the design and positioning and fastening of the bellcranks, etc. It's not simple. Not something that I would feel like spending a couple of days working on - especially since there doesn't appear to be any benefit to changing the system. Or do you know of a REAL benefit? (not just an opinion or guess) Bill C. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=269255#269255 ________________________________ Message 9 _____________________________________ Time: 01:57:07 PM PST US Subject: Pietenpol-List: Re: Push/pull tubes and rod ends From: "Pieti Lowell" Hosey Challis built his 8Th Piet, Challis Chafinch with a push-pull tube that operated from the stick up to the wing centersection it eliminated the cross control wires. This is the Piet that I flew for many years, all worked perfect, is in a Museum now in England Pieti Lowell Read this topic online here: http://forums.matronics.com/viewtopic.php?p=269256#269256 ________________________________ Message 10 ____________________________________ Time: 02:05:59 PM PST US From: "David Paule" Subject: Re: Pietenpol-List: Push/pull tubes and rod ends The equation you introduced is effective for the pull-out strength of the threads in a hole. The "(shear load)" you mentioned is the shear stress that the material can take, not the applied load. A good (in fact, one of the best) sources for structural analysis is free: http://euler9.tripod.com/analysis/asm.html It's not really for beginners, though, so be careful if this is new to you. This is reasonably comprehensive. While the Piet isn't an FAA certified airplane, it often makes sense to use the certification requirements for determining the loads. Federal Air Regulations, Part 23, covers this: http://www.flightsimaviation.com/data/FARS/part_23.html Control system loads are covered in 23.395 and more to the point in 23.397: http://www.flightsimaviation.com/data/FARS/part_23-397.html As you see, the control system doesn't need to be stronger than these forces applied to the control stick. It's a simple matter to go from there to the loads in any single part of the system. Without looking at the system you are designing, but thinking only of push-pull tubes, it strikes me that the major things to look at are: a) the end fittings, which can get complicated. Look at the holes, the pins, the clevis (if any) and the connection to the tube, including any welds or fasteners, and their holes if there are any. b) the tension strength of the tube, that is, accounting for any holes or threads, c) the compression strength, d) the Euler buckling strength, e) and finally the local crippling, sometimes referred to as D/t crippling. f) It's also important to make sure that the new system is no more flexible than the old one. You'll need to know the effective modulus of elasticity of the cabling, and that often seems to be around 11 x10^6 psi, based upon the nominal area. You can get better data from MIL-HDBK-5, I think. There might not be much, though, I simply don't remember. But the 11 msi value is ball-park. I'm sorry that I don't have a handy link to MIL-HDBK-5H, the best source for metal data, but after you download a copy, which should be free, look at the end of Chapter 2 for steel or 3 for aluminum; chapter 2.8 or 3.11. There are handy graphs of element properties for tubes, which include both forms of buckling. Incidentally, H is the best version. The newer letters miss some of the data more applicable to general aviation and are harder to use. David Paule ----- Original Message ----- From: Michael Perez To: pietenpol-list@matronics.com Sent: Saturday, October 24, 2009 1:05 PM Subject: Re: Pietenpol-List: Push/pull tubes and rod ends Push/pull tubes are used in all kinds of aircraft safely. All of which have more aggressive performance then a slow, draggy, 80+ year old designed Piet. Yet most seem to think to make the switch to push/pull is a bad idea...why? I know most just get upset because I stray from the sacred bible of building the Pietenpol...the prints. Yet non have legitimate reasons for not doing it...at least not any they share. If you guys have facts for NOT using them, please, do tell. To make a statement and not back it up is useless. The Bingelis books talks about aluminum tubes for push/pull... you know, the books everyone raves over. He also talks about how these systems MAY weigh less then a cable system with the cables, pulleys, brackets, shackles, bearings, nicopress fittings, etc. If you could run a tube from the firewall to the rudder and support the length along the way with, say bushings, there would be no flexing/bending, yes? I don't have the answers...yet, that is why I am here. I am looking for ANSWERS, not opinion, guesses, or dialog on how this 80 year old plane built by a guy in his garage can't be improved upon with some common sense and some homework. Here is what one engineer sent me: Pull out load = (1/3)(dia rod)(pi)(shear load)(length of engagement) For some generic heavy wall tube from McMaster Carr and a 1/4-28 male thread rod end, I get: 1962 lbs. worse case with .500" thread engagement, 2944 lbs. with .75" engagement. The 7X19 SS cable is rated at 1760 lbs. Using the controls in the Pietenpol, can a person ever pull 1760 lbs. on the cable? If they could, wouldn't a wood structure fail first...I don't know...like the elevator itself? Since no one here seems to have heard of a control cable failure, that must mean no Pietenpol has seen 1760 lbs. of force on a 1/8" control cable, so what are the REAL loads on this plane and it's controls? I think people get a little too extreme and have a plane built for mach 2 when it really only flies at 70 MPH. HOWEVER, my disclaimer...I have been wrong before and have abandoned other "great" ideas that I have had, this may yet be another. But that decision won't be made until I have some facts, and some REAL numbers. Anyone have another formula for pull out stress or bolt sheer? ________________________________ Message 11 ____________________________________ Time: 02:09:25 PM PST US Subject: Re: Pietenpol-List: Push/pull tubes and rod ends From: Ryan Mueller Mike, I believe the statement you are referring to regarding weight is as follows: "It is well to reflect on the fact that although individual cables are lighter then push-pull tubes, the cable systems in high wing aircraft do require the fabrication and installation of many pulleys, brackets and guards. As a consequence the cable installation tends to become heavier and more complex than *you would expect*." No direct comparison is made to one being heavier than the other. A nitpicking point I know.... Anywho...if you want a Tony B. statement in support of control cables you can find it on page 120 of 'The Sportplane Builder' (the blue book): "I marvel at the genius of the old time aircraft builder. His basic concepts have hardly been changed or improved. Whatever improvements there have been, it seems, are mostly in the development of improved designs and sophisticated materials. The cable-operated control system is a good example. It's as popular and as useful today as it ever was, and you can find it in use on the most up-to-date aircraft as well as the oldest antique. It's quite reasonable to say that using aircraft cables to activate your controls surfaces gives you the lightest, simplest, safest, most economical, and most effective way of doing the job ever conceived." He then talks about cable specs for a paragraph or two. A bit farther down the page he states: "The advantages of cables are many. They are light, strong, and flexible. They do not require line-of-sight routing, and slight deviations to bypass structural obstacles present no problem. The cables can be deflected by simple fairleads and even routed around pulleys to change direction. Try that with a push-pull tube! Since the cable is light in weight, it can be installed over considerable lengths without intermediate support. Cable-operated surfaces respond instantly and precisely to cockpit control movements because they are used in pairs and are stretched to the proper tension by turnbuckles. This effectively eliminates all play in the control system." Etc, etc. Tony B thinks cables work pretty darn good. So did Bernard Pietenpol, as he designed his airplane with a cable operated control system, and in all the years and all the other aircraft he built he apparently didn't see the benefit to designing a push-pull tube control system for it. I'm not a betting man, but I would feel confident in wagering that an overwhelming majority of all of those that successfully built and flew Piets in the past 80 years used a cable control system as well. I don't think the resistance to your proposed changes is because of some "stick to the plans, just because" snobbery. I think it is because if you build to the plans, the airplane will work (and work well). 80 years of Pietenpol building has shown that to be the case. Are there certain deficiencies here and there, or areas that can be changed to improve certain things here and there? Sure, it's not a 100% perfect design. You can emulate what other builder's have done, or come up with your own solutions. A wider center section for more fuel in the wing, tilt the seat back for comfort, so on and so forth. However in this case I don't see the need to "improve" this area of the design. I can't recall having heard anyone with a properly constructed flying Pietenpol say that the cable operated control is deficient in practical application. You don't have a flying Pietenpol (and neither do I), so we can't speak from firsthand experience. We can compare it to other types of control systems, and run the numbers, which is all well and good. But I would look at what those that have well built and nice flying Pietenpols have to say about it. What they have built and are successfully and happily flying (a cable actuated control system) would indicate that it works well. Therefore, I would also say that I fail to see how you can improve here; it just seems to be a change for the sake of change. And if that is what you want to do, go right ahead. It is your airplane, you can do what you would like with it. Have a good day, Ryan On Sat, Oct 24, 2009 at 2:05 PM, Michael Perez wrote: > Push/pull tubes are used in all kinds of aircraft safely. All of which have > more aggressive performance then a slow, draggy, 80+ year old designed Piet. > Yet most seem to think to make the switch to push/pull is a bad idea...why? > I know most just get upset because I stray from the sacred bible of building > the Pietenpol...the prints. Yet non have legitimate reasons for not doing > it...at least not any they share. If you guys have facts for NOT using > them, please, do tell. To make a statement and not back it up is useless. > > The Bingelis books talks about aluminum tubes for push/pull... you know, > the books everyone raves over. He also talks about how these systems MAY > weigh less then a cable system with the cables, pulleys, brackets, shackles, > bearings, nicopress fittings, etc. > > If you could run a tube from the firewall to the rudder and support the > length along the way with, say bushings, there would be no flexing/bending, > yes? > > I don't have the answers...yet, that is why I am here. I am looking for > ANSWERS, not opinion, guesses, or dialog on how this 80 year old plane built > by a guy in his garage can't be improved upon with some common sense and > some homework. > > Here is what one engineer sent me: > > > Pull out load = (1/3)(dia rod)(pi)(shear load)(length of engagement) > > > For some generic heavy wall tube from McMaster Carr and a 1/4-28 male > thread rod end, I get: 1962 lbs. worse case with .500" thread engagement, > 2944 lbs. with .75" engagement. > > > The 7X19 SS cable is rated at 1760 lbs. Using the controls in the > Pietenpol, can a person ever pull 1760 lbs. on the cable? If they could, > wouldn't a wood structure fail first...I don't know...like the elevator > itself? Since no one here seems to have heard of a control cable failure, > that must mean no Pietenpol has seen 1760 lbs. of force on a 1/8" control > cable, so what are the REAL loads on this plane and it's controls? I think > people get a little too extreme and have a plane built for mach 2 when it > really only flies at 70 MPH. > > > HOWEVER, my disclaimer...I have been wrong before and have abandoned other > "great" ideas that I have had, this may yet be another. But that decision > won't be made until I have some facts, and some REAL numbers. > > > Anyone have another formula for pull out stress or bolt sheer? > > > * > > * > > ________________________________ Message 12 ____________________________________ Time: 02:36:51 PM PST US Subject: Pietenpol-List: Re: Push/pull tubes and rod ends From: "Bill Church" Here's a link to some photos of the Challis Chaffinch that Lowell referred to. http://www.shhas.co.uk/GALLERY_files/photos/Challis%20Chaffinch%20Test%20Flight/image_14.html The aileron push/pull tube can be seen on the right side. Interesting to note that it is officially not a Pietenpol Air Camper - it is a Challis Chaffinch. The builder made a number of visible changes - including the shape of the empennage, a widened center-section (although the fuel tank appears to be in the fuselage). Undoubtedly there are other changes that are not visible. I would think that any builder building their EIGHTH copy of a plane might have a few ideas about ways they would like to change things. Bill C. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=269260#269260 ________________________________ Message 13 ____________________________________ Time: 02:43:36 PM PST US From: "Gary Boothe" Subject: RE: Pietenpol-List: Push/pull tubes and rod ends Michael, I'm not an engineer.not even college educated, so I cannot answer, directly, the question you raise about engineering push tubes. So what bothers me about this post? First is an emotional response - that to someone who feels that Mr. Pientenpol was, ".a guy in his garage." and that you can improve upon his design with ".some common sense and some homework." I am sure that I'm not the only one on this list who reveres the designer of this airplane as a genius! And, since you bring up the "sacred Bible", it is a near religious experience for me, as I have wanted to build a Pietenpol for over 35 years! You may as well be saying that Jesus was a fraud, or that my mother wears combat boots! I'm pretty sure Bernard Pietenpol used both common sense and homework, along with a wealth of experience and education. My second response, after spending 30 minutes attaching the hand-hold at the tail, was the realization that you, nor anyone, can "improve" his design. All you can do is illustrate the genius and flexibility of a fantastic set of plans. Plans that allow you to make many variations to suit your personality (or cover your mistakes!). Have I made changes to that design? ABSOLUTELY! Including push rods similar to, and inspired by, Peter in Australia. But I am reminded of a friend of mine who lives in the woods of Montana, who insists on a family prayer every time they cut down a tree. I am grateful to the Man who designed and built this little plane, and know that I cannot improve it.only personalize it! Just a suggestion, as I am sure you are a decent person and obviously a skilled woodworker capable of building a show piece and eventually hob-nobbing with all the Pieters, a simple, "Thanks, Jack, I'll take that into consideration," would have been far more 'politic.' I look forward to the day than you & I can toast a beer (Pale Ale, of course) to this incredible journey made possible by one man. Gary Boothe Cool, Ca. Pietenpol WW Corvair Conversion, mounted Tail done, Fuselage on gear (15 ribs down.) _____ From: owner-pietenpol-list-server@matronics.com [mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of Michael Perez Sent: Saturday, October 24, 2009 12:06 PM Subject: Re: Pietenpol-List: Push/pull tubes and rod ends Push/pull tubes are used in all kinds of aircraft safely. All of which have more aggressive performance then a slow, draggy, 80+ year old designed Piet. Yet most seem to think to make the switch to push/pull is a bad idea...why? I know most just get upset because I stray from the sacred bible of building the Pietenpol...the prints. Yet non have legitimate reasons for not doing it...at least not any they share. If you guys have facts for NOT using them, please, do tell. To make a statement and not back it up is useless. The Bingelis books talks about aluminum tubes for push/pull... you know, the books everyone raves over. He also talks about how these systems MAY weigh less then a cable system with the cables, pulleys, brackets, shackles, bearings, nicopress fittings, etc. If you could run a tube from the firewall to the rudder and support the length along the way with, say bushings, there would be no flexing/bending, yes? I don't have the answers...yet, that is why I am here. I am looking for ANSWERS, not opinion, guesses, or dialog on how this 80 year old plane built by a guy in his garage can't be improved upon with some common sense and some homework. Here is what one engineer sent me: Pull out load = (1/3)(dia rod)(pi)(shear load)(length of engagement) For some generic heavy wall tube from McMaster Carr and a 1/4-28 male thread rod end, I get: 1962 lbs. worse case with .500" thread engagement, 2944 lbs. with .75" engagement. The 7X19 SS cable is rated at 1760 lbs. Using the controls in the Pietenpol, can a person ever pull 1760 lbs. on the cable? If they could, wouldn't a wood structure fail first...I don't know...like the elevator itself? Since no one here seems to have heard of a control cable failure, that must mean no Pietenpol has seen 1760 lbs. of force on a 1/8" control cable, so what are the REAL loads on this plane and it's controls? I think people get a little too extreme and have a plane built for mach 2 when it really only flies at 70 MPH. HOWEVER, my disclaimer...I have been wrong before and have abandoned other "great" ideas that I have had, this may yet be another. But that decision won't be made until I have some facts, and some REAL numbers. Anyone have another formula for pull out stress or bolt sheer? ________________________________ Message 14 ____________________________________ Time: 03:00:41 PM PST US From: "David Paule" Subject: Re: Pietenpol-List: Re: Push/pull tubes and rod ends Historically, the major benefit to a push rod control system compared to a cable control system is that the push rod system has lower friction since there's no need for the cable tension in the cable system. No preload tension, and you've eliminated a major part of the friction. Also, typically, they have rod-end or other bearings for the joints, again with lower friction. Another benefit is that they can be stiffer, but that's generally only beneficial for larger, faster aircraft. Push-rod systems are almost always heavier. There's an often unanticipated benefit of building per the plans: it reduces the chances of inadvertently designing in some unanticipated failure mode. So if weight or simplicity or safety matters, follow the plans. David Paule ----- Original Message ----- From: "Bill Church" Sent: Saturday, October 24, 2009 2:55 PM Subject: Pietenpol-List: Re: Push/pull tubes and rod ends > > > Whoa - what comments are you responding to Mike? > The only reply to your post that I saw was from Jack, and all I saw in his > reply were sound reasons explaining why the cables are a better system FOR > THIS AIRPLANE. As he stated, the geometry of the Air Camper will result in > a heavier and more expensive linkage as compared to the cables. Tony > Bingelis says that push/pull tubes MAY weigh less than a cable system. > That will depend on the layout of the airplane, and in this case, the > control system has to go under the seat, and then get back up into > alignment with the elevators and rudder. Cables can change direction with > the addition of a simple pulley, where push/pull tubes will require > bellcranks - which one do you think is heavier? It is not possible to run > a tube straight from the firewall to the rudder in this airplane, unless > you have a properly sized and located hole in your torso for the tube to > pass through. Also, in THIS airplane, the elevators are separate entities, > so you would either have to redesign them so that ! > they are tied together, or run two push/pull tubes for the elevators. > To quote your original post "I'm all about saving weight on my plane". > Jack's reply explained that the push/pull system will end up being heavier > than the cable system. So what IS the motivation to change to the > push/pull system? > > Regarding your request for a formula, the thing to keep in mind is that in > designing a mechanism like a push/pull system, you need to analyze each > component and each connection in the system, and the loads that could be > imposed on each component. Those loads are used to determine the size and > shape that each component will assume. There are the different tubes that > need material, diameter and wall thickness to be determined, and the size > of all the threaded connections, and the design and positioning and > fastening of the bellcranks, etc. It's not simple. Not something that I > would feel like spending a couple of days working on - especially since > there doesn't appear to be any benefit to changing the system. Or do you > know of a REAL benefit? (not just an opinion or guess) > > Bill C. > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=269255#269255 > > > ________________________________ Message 15 ____________________________________ Time: 04:48:14 PM PST US From: "Jack Phillips" Subject: RE: Pietenpol-List: Push/pull tubes and rod ends Michael, I got behind in answering emails because I had to watch my alma mater (Tennessee) almost beat the #1 team in the nation (Alabama). Final score, Alabama 12, Tennessee 10 but it wasn't decided until Bama blocked a Tennessee field goal with 4 seconds left in the game. So Bill Church basically said the same thing I was going to say. Here is what I had started to write before the game. "Michael, you can certainly put a pushrod control system in. But the design geometry is much different than the geometry that the Pietenpol has. For example, the elevators of a Pietenpol are not connected to each other. Each elevator has its own pair of cables to deflect it. If you run pushrods, you will either have to find a way to connect the elevators, or run individual pushrods to each side. More modern airplanes using pushrods are designed with a single elevator horn internal to the fuselage, requiring a single pushrod. They also typically have a control system that allows the pushrod which connects the front and rear sticks to run under the floorboard so it can then connect behind the cockpit with the psuhrod which runs aft to the elevators. You can accomplish all this with your Pietenpol, but it will not be easy, or cheap, or simple. The cable system is light, simple and well-proven. You are attempting to solve a problem where no problem exists. You are looking to "improve" the design. Where will the improvement be if it costs more and weighs more and does no better job?" I'm certainly no purist, and in building my Pietenpol I made a number of changes to the "pure" Pietenpol design, such as widening the fuselage by 1" (bad idea), widening the centersection by 6" (good idea), changing the design of the lift strut fittings to incorporate the steel band that runs under the belly (good idea), adding a baggage compartment behind the firewall (good idea), adding a trim system modeled after Mike Cuy's (good idea), incorporating the heat muffs into construction of the exhaust pipes (bad idea). I'm all for making changes that intend to serve a purpose. The airplane is yours to do as you please, but there are some changes that really need to be well engineered. I'm a licensed professional engineer who worked many years in the aircraft industry (my first job out of college was working on the design team for the F-16), and I wouldn't want to tackle redesigning the control system of the Pietenpol. I just don't see what purpose such a change might fulfill, if it will make it heavier, more complicated and more expensive (those rod end bearings are not cheap). If you really intend to do this, the way you calculate the area of the pushrod tube is to use the formula : A = p(Doutside2 - Dinside2)/4. While you're at it, calculate the weight of the tube, then compare to the weight of an equivalent length of steel cable. Be sure to add the weight of the end fitting for the tube, and the rod end bearing at each end, plus all the bellcranks that will be required, as well as the brackets and bushings to support those bellcranks. As Bill Stout, designer of the Ford trimotor is supposed to have said: "Simplicate and Add Lightness" Jack Phillips NX899JP Raleigh, NC _____ From: owner-pietenpol-list-server@matronics.com [mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of Michael Perez Sent: Saturday, October 24, 2009 3:06 PM Subject: Re: Pietenpol-List: Push/pull tubes and rod ends Push/pull tubes are used in all kinds of aircraft safely. All of which have more aggressive performance then a slow, draggy, 80+ year old designed Piet. Yet most seem to think to make the switch to push/pull is a bad idea...why? I know most just get upset because I stray from the sacred bible of building the Pietenpol...the prints. Yet non have legitimate reasons for not doing it...at least not any they share. If you guys have facts for NOT using them, please, do tell. To make a statement and not back it up is useless. The Bingelis books talks about aluminum tubes for push/pull... you know, the books everyone raves over. He also talks about how these systems MAY weigh less then a cable system with the cables, pulleys, brackets, shackles, bearings, nicopress fittings, etc. If you could run a tube from the firewall to the rudder and support the length along the way with, say bushings, there would be no flexing/bending, yes? I don't have the answers...yet, that is why I am here. I am looking for ANSWERS, not opinion, guesses, or dialog on how this 80 year old plane built by a guy in his garage can't be improved upon with some common sense and some homework. Here is what one engineer sent me: Pull out load = (1/3)(dia rod)(pi)(shear load)(length of engagement) For some generic heavy wall tube from McMaster Carr and a 1/4-28 male thread rod end, I get: 1962 lbs. worse case with .500" thread engagement, 2944 lbs. with .75" engagement. The 7X19 SS cable is rated at 1760 lbs. Using the controls in the Pietenpol, can a person ever pull 1760 lbs. on the cable? If they could, wouldn't a wood structure fail first...I don't know...like the elevator itself? Since no one here seems to have heard of a control cable failure, that must mean no Pietenpol has seen 1760 lbs. of force on a 1/8" control cable, so what are the REAL loads on this plane and it's controls? I think people get a little too extreme and have a plane built for mach 2 when it really only flies at 70 MPH. HOWEVER, my disclaimer...I have been wrong before and have abandoned other "great" ideas that I have had, this may yet be another. But that decision won't be made until I have some facts, and some REAL numbers. Anyone have another formula for pull out stress or bolt sheer? ________________________________ Message 16 ____________________________________ Time: 05:26:52 PM PST US Subject: Pietenpol-List: Re: Push/pull tubes and rod ends From: "chase143" Jack- BTW you did a heck of a job on the Fly-by-wire system on the F-16, but what was with that second arm rest!? ;-) Just to add my two cents: building a Pietenpol reminds me of the friends I have refurbishing cars. Some refurbish to classic original condition (my favorite), and some take a beautiful vintage automobile and refurbish it into a streetrod. Sure, a Model-T ford or a 57' chevy with a 400hp V-8, glass pack exhausts and racing wheels has a lot more power, but to me losses something in translation. I don't think the term purist need have a negative connotation. Rather, it is a tribute to the originator of this design, who through his brilliance and adventurous spirit, created a successful aircraft design and unselfishly authorized others to share in it. It's challenge enough crafting a Piet with all the power tools available today, the Internet, and live samples at Brodhead ever year (thanks guys), so save for the small changes like Jack mentions, I always challenge myself to stick as close as possible to the original, reproduction being the highest form of flattery, but thats just me. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=269277#269277 ________________________________ Message 17 ____________________________________ Time: 07:04:13 PM PST US From: "Jack Phillips" Subject: RE: Pietenpol-List: Re: Push/pull tubes and rod ends Second arm rest? Which side? Right or left? The original versions (F-16A's) had a fixed side stick that didn't move at all - just sensed forces. Too many pilots had trouble getting used to that so they changed it to have a slight amount of movement, but still it communicated with the Flight Control Computer through 4 load cells at the base of the stick which sensed the force the pilot was applying to the stick. There was an armrest behind the stick to support the pilot's arm during high G maneuvers so the g-forces wouldn't make him pull even harder on the stick. There was talk about providing a second armrest on the left side to support the throttle arm for the same reason, but that was not done before I left. Jack -----Original Message----- From: owner-pietenpol-list-server@matronics.com [mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of chase143 Sent: Saturday, October 24, 2009 8:26 PM Subject: Pietenpol-List: Re: Push/pull tubes and rod ends Jack- BTW you did a heck of a job on the Fly-by-wire system on the F-16, but what was with that second arm rest!? ;-) Just to add my two cents: building a Pietenpol reminds me of the friends I have refurbishing cars. Some refurbish to classic original condition (my favorite), and some take a beautiful vintage automobile and refurbish it into a streetrod. Sure, a Model-T ford or a 57' chevy with a 400hp V-8, glass pack exhausts and racing wheels has a lot more power, but to me losses something in translation. I don't think the term purist need have a negative connotation. Rather, it is a tribute to the originator of this design, who through his brilliance and adventurous spirit, created a successful aircraft design and unselfishly authorized others to share in it. It's challenge enough crafting a Piet with all the power tools available today, the Internet, and live samples at Brodhead ever year (thanks guys), so save for the small changes like Jack mentions, I always challenge myself to stick as close as possible to the original, reproduction being the highest form of flattery, but thats jus! t me. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=269277#269277 ________________________________ Message 18 ____________________________________ Time: 07:39:36 PM PST US Subject: Pietenpol-List: Re: Push/pull tubes and rod ends From: "Pieti Lowell" You might also note that the airfoil is a 4412., shortened 2 Ft and with an 85 HP Cont it could cruse 105 plus. The center- section is 3 Ft. wide. Pieti Lowell Bill Church wrote: > Here's a link to some photos of the Challis Chaffinch that Lowell referred to. > > http://www.shhas.co.uk/GALLERY_files/photos/Challis%20Chaffinch%20Test%20Flight/image_14.html > > The aileron push/pull tube can be seen on the right side. Interesting to note that it is officially not a Pietenpol Air Camper - it is a Challis Chaffinch. The builder made a number of visible changes - including the shape of the empennage, a widened center-section (although the fuel tank appears to be in the fuselage). Undoubtedly there are other changes that are not visible. I would think that any builder building their EIGHTH copy of a plane might have a few ideas about ways they would like to change things. > > Bill C. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=269291#269291 ________________________________ Message 19 ____________________________________ Time: 08:13:25 PM PST US From: "Clif Dawson" Subject: Re: Pietenpol-List: Push/pull tubes and rod ends As Michael has stated that he wants to thread the tube no one so far has considered what that means. The depth of those threads eliminates that much of the wall thickness from the overall thickness of the tube for stress calculations. So to get the strength you want you'r egoing to have to have wall thickness to handle that PLUS the wall thickness to take the threads. Now you've got this fat tube half of which is useless weight unless you can lathe that long length down. This assumes the threads are on the outside. However, if they happen to be on the inside........ I have a tube joining my throttles that's off some I-know-not- what, expensive military hardware. It's 1" dia and VERY thin wall for most of it's length. If I put helium in it it would float away. Then it narrows down to take a 1/4" threaded ball end which is inside a 3/8" dia. weldment at the end. So tubes can be made light but then KISS disappears from the equation. :-) Clif "Creativity is allowing yourself to make mistakes. Art is knowing which ones to keep." (Scott Adams) Michael, If you really intend to do this, the way you calculate the area of the pushrod tube is to use the formula : A = p(Doutside2 - Dinside2)/4. While you're at it, calculate the weight of the tube, then compare to the weight of an equivalent length of steel cable. Be sure to add the weight of the end fitting for the tube, and the rod end bearing at each end, plus all the bellcranks that will be required, as well as the brackets and bushings to support those bellcranks. As Bill Stout, designer of the Ford trimotor is supposed to have said: "Simplicate and Add Lightness" Jack Phillips ________________________________ Message 20 ____________________________________ Time: 11:27:48 PM PST US Subject: Re: Pietenpol-List: Push/pull tubes and rod ends From: Robert Ray Ask a Grega builder, I think it uses a tube. Russell On Sat, Oct 24, 2009 at 12:18 PM, Jack Phillips wro te: > Are you planning on re-designing the entire elevator control system with > pushrods, requiring a pushrod attached to each elevator, a pushrod from t he > bellcrank to the rear stick and a pushrod between sticks? It probably wi ll > require an additional pushrod and bellcrank to enable you to pass underne ath > the rear seat (where the cable from the stick to the bellcrank makes a be nd, > with the plans showing it just passing through a hole drilled in the wood ' > I added a pulley here). > > > If so, figure out the yield strength of whatever alloy of aluminum you > intend to use, then determine what area will be required to withstand the > load (1760 lbs, if you want to equal the cable strength) without exceedin g > that stress level. Use the formula Stress = Load divided by Area (s > P/A), and solve for area (A) since you know the load (P = 1760) and yo u > know the stress (s = yield strength of your alloy times whatever safety > factor you feel like throwing in). Once you know the area, then determin e > what wall thickness and tube diameter will produce the required area. Of > course, there will be machined fittings required on each end of the > pushrods, and rod end bearings to reduce the amount of slop. > > > As an engineer, I have to wonder why are you doing this? The cables work > well. Any arrangement with pushrods is going to be much more complicated , > due to the geometry of the airplane. Pushrods will end up being far more > expensive and heavier. I don=92t understand what advantage you are tryin g to > achieve here, other than to be =93different=94. You could accomplish tha t by > painting it Pink. > > > Jack Phillips > > NX899JP > > Raleigh, NC > > Enjoying a rainy day by building the wings of my RV-10 in the basement > > > ------------------------------ > > *From:* owner-pietenpol-list-server@matronics.com [mailto: > owner-pietenpol-list-server@matronics.com] *On Behalf Of *Michael Perez > *Sent:* Saturday, October 24, 2009 10:52 AM > *To:* pietenpol-list@matronics.com > *Subject:* Pietenpol-List: Push/pull tubes and rod ends > > > I am trying to figure out what size and material tube to use to go from t he > control stick to the elevator bell crank. I see in the Bingelis books, h e > talks about heavy wall aluminum threaded tubing. Since I am all about > saving weight on my plane, I would prefer aluminum. The plans call for 1/ 8" > cable, which is rated between 1760 and 2100 lbs. I would hope that a > tube/rod end combination that rated at these numbers would work. So, I a m > trying to figure out what size tube and threaded rod end will give me the > 1760-2100 lb. rating. If someone can prvide a usable formula, I may be > able to figure it out myself. > > > Thanks group. > > * * > > * * > > ** > > ** > > ** > > *http://www.matronics.com/Navigator?Pietenpol-List* > > ** > > ** > > *http://forums.matronics.com* > > ** > > ** > > *http://www.matronics.com/contribution* > > * * > > * > =========== =========== =========== =========== > * > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message pietenpol-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Pietenpol-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/pietenpol-list Browse Digests http://www.matronics.com/digest/pietenpol-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.