Brodhead Pietenpol Association

Original Posted By: "Gary Boothe"
Here's a link to some photos of the Challis Chaffinch that Lowell referred to.http://www.shhas.co.uk/GALLERY_files/ph ... 14.htmlThe aileron push/pull tube can be seen on the right side. Interesting to note thatit is officially not a Pietenpol Air Camper - it is a Challis Chaffinch. Thebuilder 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 thinkthat any builder building their EIGHTH copy of a plane might have a few ideasabout ways they would like to change things.Bill C.Read this topic online here:http://forums.matronics.com/viewtopic.p ... __________

Original Posted By: owner-pietenpol-list-server(at)matronics.com
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 hisdesign with ".some common sense and some homework." I am sure that I'm notthe only one on this list who reveres the designer of this airplane as agenius! And, since you bring up the "sacred Bible", it is a near religiousexperience 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 wearscombat boots! I'm pretty sure Bernard Pietenpol used both common sense andhomework, along with a wealth of experience and education.My second response, after spending 30 minutes attaching the hand-hold at thetail, was the realization that you, nor anyone, can "improve" his design.All you can do is illustrate the genius and flexibility of a fantastic setof plans. Plans that allow you to make many variations to suit yourpersonality (or cover your mistakes!). Have I made changes to that design?ABSOLUTELY! Including push rods similar to, and inspired by, Peter inAustralia. But I am reminded of a friend of mine who lives in the woods ofMontana, who insists on a family prayer every time they cut down a tree. Iam grateful to the Man who designed and built this little plane, and knowthat I cannot improve it.only personalize it! Just a suggestion, as I am sure you are a decent person and obviously askilled woodworker capable of building a show piece and eventuallyhob-nobbing with all the Pieters, a simple, "Thanks, Jack, I'll take thatinto consideration," would have been far more 'politic.'I look forward to the day than you & I can toast a beer (Pale Ale, ofcourse) to this incredible journey made possible by one man.Gary BootheCool, Ca.PietenpolWW Corvair Conversion, mountedTail done, Fuselage on gear(15 ribs down.) _____

Original Posted By: owner-pietenpol-list-server(at)matronics.com
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 aTennessee field goal with 4 seconds left in the game. So Bill Churchbasically said the same thing I was going to say. Here is what I hadstarted to write before the game."Michael, you can certainly put a pushrod control system in. But the designgeometry is much different than the geometry that the Pietenpol has. Forexample, the elevators of a Pietenpol are not connected to each other. Eachelevator has its own pair of cables to deflect it. If you run pushrods, youwill either have to find a way to connect the elevators, or run individualpushrods to each side. More modern airplanes using pushrods are designedwith a single elevator horn internal to the fuselage, requiring a singlepushrod. They also typically have a control system that allows the pushrodwhich connects the front and rear sticks to run under the floorboard so itcan then connect behind the cockpit with the psuhrod which runs aft to theelevators. You can accomplish all this with your Pietenpol, but it will notbe easy, or cheap, or simple. The cable system is light, simple andwell-proven. You are attempting to solve a problem where no problem exists.You are looking to "improve" the design. Where will the improvement be ifit costs more and weighs more and does no better job?"I'm certainly no purist, and in building my Pietenpol I made a number ofchanges to the "pure" Pietenpol design, such as widening the fuselage by 1"(bad idea), widening the centersection by 6" (good idea), changing thedesign of the lift strut fittings to incorporate the steel band that runsunder the belly (good idea), adding a baggage compartment behind thefirewall (good idea), adding a trim system modeled after Mike Cuy's (goodidea), incorporating the heat muffs into construction of the exhaust pipes(bad idea). I'm all for making changes that intend to serve a purpose. Theairplane is yours to do as you please, but there are some changes thatreally need to be well engineered. I'm a licensed professional engineer whoworked many years in the aircraft industry (my first job out of college wasworking on the design team for the F-16), and I wouldn't want to tackleredesigning the control system of the Pietenpol. I just don't see whatpurpose such a change might fulfill, if it will make it heavier, morecomplicated and more expensive (those rod end bearings are not cheap).If you really intend to do this, the way you calculate the area of thepushrod tube is to use the formula : A = p(Doutside2 - Dinside2)/4. Whileyou're at it, calculate the weight of the tube, then compare to the weightof an equivalent length of steel cable. Be sure to add the weight of theend fitting for the tube, and the rod end bearing at each end, plus all thebellcranks that will be required, as well as the brackets and bushings tosupport those bellcranks.As Bill Stout, designer of the Ford trimotor is supposed to have said:"Simplicate and Add Lightness"Jack PhillipsNX899JPRaleigh, NC _____

Original Posted By: "Jack Phillips"
Jack- BTW you did a heck of a job on the Fly-by-wire system on the F-16, but whatwas with that second arm rest!? ;-)Just to add my two cents: building a Pietenpol reminds me of the friends I haverefurbishing 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 exhaustsand 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, itis a tribute to the originator of this design, who through his brilliance andadventurous spirit, created a successful aircraft design and unselfishly authorizedothers to share in it. It's challenge enough crafting a Piet with allthe power tools available today, the Internet, and live samples at Brodhead everyear (thanks guys), so save for the small changes like Jack mentions, I alwayschallenge myself to stick as close as possible to the original, reproductionbeing the highest form of flattery, but thats just me.Read this topic online here:http://forums.matronics.com/viewtopic.p ... __________

Original Posted By: owner-pietenpol-list-server(at)matronics.com
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 sensedforces. Too many pilots had trouble getting used to that so they changed itto have a slight amount of movement, but still it communicated with theFlight Control Computer through 4 load cells at the base of the stick whichsensed the force the pilot was applying to the stick. There was an armrestbehind the stick to support the pilot's arm during high G maneuvers so theg-forces wouldn't make him pull even harder on the stick. There was talkabout providing a second armrest on the left side to support the throttlearm for the same reason, but that was not done before I left.Jack-----Original Message-----

Original Posted By: "Clif Dawson"
You might also note that the airfoil is a 4412., shortened 2 Ft and with an 85HP 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/ph ... ge_14.html> > The aileron push/pull tube can be seen on the right side. Interesting to notethat 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 thefuselage). Undoubtedly there are other changes that are not visible. I would thinkthat any builder building their EIGHTH copy of a plane might have a few ideasabout ways they would like to change things.> > Bill C.Read this topic online here:http://forums.matronics.com/viewtopic.p ... __________

Original Posted By: Robert Ray
As Michael has stated that he wants to thread the tube no oneso 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 stresscalculations. So to get the strength you want you'r egoing tohave to have wall thickness to handle that PLUS the wallthickness to take the threads. Now you've got this fat tubehalf of which is useless weight unless you can lathe thatlong length down. This assumes the threads are on theoutside. 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 thinwall for most of it's length. If I put helium in it it would floataway. 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________________________________________________________________________________Date: Sun, 25 Oct 2009 02:24:29 -0400Subject: Re: Pietenpol-List: Push/pull tubes and rod ends

Original Posted By: Ameet Savant
Subject: Re: Pietenpol-List: Push/pull tubes and rod ends

Original Posted By: Ameet Savant
Perhaps they could be posted on the West Coast Pietenpol site....David Paule

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Lloyd Smith
Subject: Re: Pietenpol-List: Push/pull tubes and rod ends

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Michael Perez
That equation you supplied is ONLY for the shear-out strength of the threads. And that is only one of the things to check for.It does not apply to the net tension strength of the tube, which you'll find is considerably lower than that cable strength.It does not apply to the Euler column strength of the tube, which is dependent upon the length from pin to pin as well as that very low yield strength.However, with that thickness wall, it won't have the D/t crippling I mentioned earlier. There are probably other things to check for, but without an overall design we don't know what those might be.If you are trying to save weight, 6063 heavy wall tube won't get you there. What's more, in general, 6063 is much weaker than most aircraft metals.It's time to draw out the control system to scale, apply the loads that I found for you in FAR Part 23, and work them through to see what the individual loads are in the various parts. Please bear in mind that you need to consider yield and ultimate conditions here.David Paule ----- Original Message -----

Original Posted By: owner-pietenpol-list-server(at)matronics.com
Without doing all the calculations myself I can't tell if your math is goodor not. But one thing to consider with small diameter pushrods is thatunder compression loading they may buckle pretty easily, which could ruinyour whole day. Euler's (pronounced oilers) equation is used to determinethe critical load, beyond which the pushrod will "buckle", displacing themiddle of the pushrod sideways. This equation is:Pe = p2EI l 2 Where Pe is the critical load, beyond which any load will cause buckling, p= 3.1415926., E is the modulus of elasticity (Young's Modulus) for thematerial, I is the moment of inertia (for a circular annulus, I p(do4-di4)/64 ), and l = the length of the pushrod. Once you have your tubechosen, plug its numbers into Euler's equation and see what the bucklingload will be. If you think this is close to the load that the elevators canput on the pushrod, then you may have to go to a larger diameter pushrodtube.If you use pushrods connected directly to the elevators, it would be best toposition the pushrods on top of the elevator, rather than underneath. Thereason for this is that you are more likely to put large loads into pullingthe nose of the airplane up than you will in pushing the nose down. If thepushrods are on the bottom, any up-elevator inputs will be putting thepushrod in compression, so if you prefer to have the pushrods under theelevators, you will probably have to use larger diameter tubing.Good luck,Jack PhillipsNX899JPRaleigh, NC _____

Original Posted By: Michael Perez
Look, I don't mean to be critical at all, but it takes a design concept with dimensions and angles, and then applying forces and finding reactions to them. The techniques are in every basic high school physics books in the chapter on statics. You'll probably need the same sorts of equations as used in the weight and balance calculations, and some general algebra. What you are dealing with here are levers and fulcrums and cables. As a modest suggestion, don't even begin to calculate the strength of the pieces until you have a firm grasp of the loads in the design. David Paule

Original Posted By: Lloyd Smith
Subject: Re: Pietenpol-List: Push/pull tubes and rod ends

Original Posted By: Lloyd Smith
Subject: Re: Pietenpol-List: Push/pull tubes and rod ends

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Michael Perez

Original Posted By: Tim Willis

Original Posted By: Lloyd Smith
Take it from me.... starting with the government's forces at the control stick and working out from there is the easy way to do the job.Make it easy on yourself and install the controls exactly as the plans describe them.David PauleCan anyone supply more info on Mr. Wainfan and his calculations? The process of surface area, speed and deflection to determine load seems to be more relevant in a 80 mph Piet. then doing algebra, trig., calculus, etc. on every nut bolt bracket, rod in the system. (Although, there is nothing wrong with that...and a lot more precise/accurate.)I have gotten some very, very good formulas/equations from the list that are just to complicated and over my head to try and use. If this turns out to be the only way to solve my issues, I will be installing cables. Still, I would think I could at least figure out what tubes would work...even if they turn out to be too large and heavy to consider.Thanks crew...some good stuff is now coming from this thread. ________________________________________________________________________________Date: Sun, 25 Oct 2009 20:13:35 -0400Subject: Re: Pietenpol-List: Push/pull tubes and rod ends

Original Posted By: "Bill Church"
[quote="dpaule(at)frii.com"]Take it from me.... starting with the government'sforces at the control stick and working out from there is the easy way to dothe job. Make it easy on yourself and install the controls exactly as the plans describethem. David Paule [quote] OK, why would I (for instance, and anyone else) take it from you, when the authoritylike Pieti Lowell says on this very thread says the opposite: his personalplane had the push/pull tube AND flew perfectly AND safe for many years? Haveyou got any better argument?Read this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Push/pull tubes and rod ends

Original Posted By: "David Paule"
This will be my last comment on this thread.First off, Michael, if you follow through with a push/pull system, you will notbe the first. It has been done before. Refer to the following link for a photoof a GN-1 with such a system:http://www.westcoastpiet.com/images/Pet ... 28.JPGNote that the control tube for the rudder is not tiny. The control tube for theelevators is likely buried inside the fuselage, and the elevators are most likelybuilt of steel tube, in order to be able to transfer the torque adequately.My thoughts are that if this system was an improvement, we would see more flyingexamples of it. Just because it has been done does not mean it's a goodidea. Secondly, all of the "opinions" that have been expressed regarding the negativeaspects of attempting to use a push/pull system on this aircraft have been basedon sound engineering principles. The reason why nobody has offered data toprove your theory wrong is that your "system" has no data behind it. There areno dimensions to work with. Not even a basic sketch. There are often a thousandways to achieve the same basic goal, with some being better than others, butno one being the "right" way. For instance, as one reply stated, the propersize for the tubes is dependent on the length, in reference to buckling strength.Thirdly, unless someone out there decides that they want to do all the calculationsfor you, you will eventually have to deal with all of that "language andformulas" that, as you put it, are "over your head". As I said before, it's notsimple. Once the routing of the system is determined (including all pivot points),you will need to determine the loads that will be imposed on the system(plus an appropriate factor of safety). From there you will be able to determinethe loads that will be carried by each component, and based on those numbers,you will determine the sizes of each component. (There's a reason why it takesfour years of university to obtain a degree in Engineering).And finally, all of the above is my OPINION. But my opinion is based on more thantwenty years experience working as a Professional Engineer. Take it or leaveit.Bill C.Read this topic online here:http://forums.matronics.com/viewtopic.p ... __________

Original Posted By: "David Paule"
No politics at all here, folks, move along.Just to recap (yet again), I'd previously linked to the FAA's rules for certified aircraft, and particularly to where they specified what the maximum loads at the control stick could be. Then I said to start with those, and figure out the loads as they worked their way to the control surface. This is the easy way to do it, if you want to do it at all.Regardless of how you feel about governmental actions in general, in this instance, here, the specific regulations are sensible and to the point. It's kind of heartening to know that once in a while the government got it right.David Paule -- "Politics is the art of looking for trouble, finding it whether it exists or not, diagnosing it incorrectly, and applying the wrong remedy." --British publisher and writer Ernest Benn (1875-1954)________________________________________________________________________________

Original Posted By: Lloyd Smith
Because the gentleman who wants to learn how to do this basic engineering is finding it difficult to begin the problem, and is getting overwhelmed with the information that's been presented.Obviously a push-pull system can be designed and if done properly, it will work well. That's not the issue. Nor is it an issue whether a redesigned control system should be made; that's a matter of choice. There are pros and cons to any variation to the plans, and the plans design is an excellent "control" to test the goodness of any particular redesign.It can be designed if someone wants to take the effort to do so, although it's not necessary, and they might find it just as enlightening as actually building the aircraft. My motive for writing has been to facilitate his learning and to point out appropriate information which he might find of use. In fact, which anyone who wants to embark on an aircraft design project, might find of use.Here, though, it was becoming apparant that the resources of this List would not extend to providing the requestor with sufficient capability to actually make an engineering judgement of his design, which has been his expressed goal. In light of that, it was proper to advise him to built it stock.David Paule========================>> [quote="dpaule(at)frii.com"]Take it from me.... starting with the > government's forces at the control stick and working out from there is > the easy way to do the job.>> Make it easy on yourself and install the controls exactly as the plans > describe them.>> David Paule> [quote]>> OK, why would I (for instance, and anyone else) take it from you, when the > authority like Pieti Lowell says on this very thread says the opposite: > his personal plane had the push/pull tube AND flew perfectly AND safe for > many years? Have you got any better argument?>>> Read this topic online here:>> http://forums.matronics.com/viewtopic.p ... 402#269402>>> ________________________________________________________________________________Date: Sun, 25 Oct 2009 21:07:46 -0400Subject: Re: Pietenpol-List: Push/pull tubes and rod ends

Original Posted By: Lloyd Smith
dpaule(at)frii.com wrote:> Here, though, it was becoming apparant that the resources of this List would> not extend to providing the requestor with sufficient capability to actually> make an engineering judgement of his design, which has been his expressed > goal. In light of that, it was proper to advise him to built it stock.> > David Paule> He didn't get as far as discussing the tube diameter and wall thickness beforehe was flooded with "don't do it" messages, let alone more complicated meters.Requester had no chance.Read this topic online here:http://forums.matronics.com/viewtopic.p ... ______Date: Sun, 25 Oct 2009 21:19:21 -0400Subject: Re: Pietenpol-List: Push/pull tubes and rod ends