---------------------------------------------------------- Pietenpol-List Digest Archive --- Total Messages Posted Tue 12/20/05: 11 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:19 AM - Re: building video (Rick Holland) 2. 08:27 AM - Re: Building Video (Phillips, Jack) 3. 10:33 AM - pesky elevator cable (Oscar Zuniga) 4. 12:16 PM - teflon, anyone ? (Michael D Cuy) 5. 12:20 PM - cable going thru the stabilizer (Michael D Cuy) 6. 03:23 PM - Re: pesky elevator cable: (John and Phyllis Smoyer) 7. 03:56 PM - Re: pesky elevator cable: (Rcaprd@aol.com) 8. 06:24 PM - Re: building video () 9. 07:48 PM - Re: pesky elevator cable: (Graham Hansen) 10. 08:54 PM - Re: Building Video (Rcaprd@aol.com) 11. 09:08 PM - Re: pesky elevator cable: (Rcaprd@aol.com) ________________________________ Message 1 _____________________________________ Time: 06:19:20 AM PST US From: Rick Holland Subject: Re: Pietenpol-List: building video Is that one inch from the 7" position or from the 9" position Greg? Rick H On 12/19/05, gcardinal@mn.rr.com wrote: > > From experience I can tell you that raising the bellcrank 1 inch is NOT > enough > to allow the cables to clear the stabilizer. > > Greg Cardinal > > ----- Original Message ----- > *From:* Rick Holland > > Never noticed the 2" difference until you mentioned it Oscar. I guess I > was looking at drawing #4 the day I installed my bellcrank (fortunately). > How high do you place it to eliminate the cable problem? > > Rick H. > > -- Rick Holland ________________________________ Message 2 _____________________________________ Time: 08:27:27 AM PST US Subject: RE: Pietenpol-List: Building Video From: "Phillips, Jack" Chuck, the things I remember being flawed were the isometric drawings showing the compression struts between the spars at the lift strut attach points. The drawings show them in line vertically, but if you mount the lift strut fittings as shown in the plans, the strap fittings interfere with the compression struts. I made my lift strut fittings per the plans (I'l explain why below) and had to offset the compression struts to clear them. On your item #2, I was planning to do as you did (and most people would do, since most modern airplanes do so) and make the lift strut fitting strap in line with the strut, so the strut would not impose a moment (torque) on the spar. I assumed that BHP designed it the way he did out of ignorance. Then I decided to do a little stress analysis to see just how much "better" I could design it than Bernard did. To my surprise, I found that the fitting as designed by BHP actually decreased the bending moment in the spars to the extent that by building the fittings to his design, the wings can withstand almost a full G more than they can if the fittings are in line with the struts! The ultimate loading (with a 1050 lb gross weight) goes from 4 G's to 4.9 G's You might want to include some of the alternate methods of assembly that various people have done. I made quite a few changes on mine, most of which I'm pleased with. For example: a. I made little plywood sockets for the spruce compression struts to nest in, which allowed them to sit in place until I got the tension on the drag and anti-drag wires. This allowed me to avoid toe-nailing the struts. b. I made brackets to hold an extra pulley for the elevator cables, as well as pulleys for the rudder cables so the fairleads don't have to constrain a large angle change in the cable. All my pulleys are ball-bearing and the controls are very smooth. c. For my tail hinges, I used AN42 eyebolts, inset into the beams to minimize the gap between the stabilizers and control surfaces. I ground a flat on the flange of each eyebolt and set them in epoxy before attaching with a locknut, so they can't rotate and cause binding. d. I used piano hinges for my aileron hinges, to provide a strong, lightweight hinge and seal the gaps e. I laminated my wingtips in a form that held them to the proper curve, and made them much stronger than a single piece would be. They withstood dragging on the ground in a groundloop after my forced landing. f. I also laminated several other structural pieces, including the curved centersection cutout, all the circular bows which support the aluminum around the cockpits, and the landing gear struts. Laminating thin strips of spruce with resorcinol glue makes an incredibly stiff and lightweight structure. Jack Phillips, PE Sr. Manager, Disposables Product Development Clinical Technologies and Services Cardinal Health Creedmoor, NC (919) 528-5212 -----Original Message----- From: owner-pietenpol-list-server@matronics.com [mailto:owner-pietenpol-list-server@matronics.com] On Behalf Of Rcaprd@aol.com Subject: Pietenpol-List: Building Video Well, the list is kind of slow, so I present to you a request for some help. As most of you know, I'm putting together a Pietenpol Building Video, and I want to make it as complete, and comprehensive as possible. I need some help to hear what everyone thinks should be included in the video. I'm going to include a detailed look at the plans. There has NEVER been a set of plans, for ANY type of airplane, that does not have errors in them, and in my humble opinion, I think the plans should NOT be changed. They fit the era of the aircraft you are building, and are a part of the whole history of the Pietenpol. Quite often, it is concluded that an error exists, but upon further study, and some questions asked, the light bulb goes off, and it becomes crystal clear. Granted there are errors in the plans, but given the enormous amount of information that is included in the plans, the errors are not that many. Having said that, builders NEED to know what, and where the errors are. They also need clarification in some areas. Done correctly, and with good workmanship, in the 76 year history of the Pietenpol, there has NEVER been an airframe failure (at least none that has been reported). I can make that claim, because a couple years ago, I did an extensive, and exhaustive study of all the NTSB accident reports, back as far as they go, found about 80 reports, and NO airframe failures, if it was built to the plans. Hence, the reason for this e-mail. I'd like to ask everyone who knows of an area of the plans that are confusing, or has an error, to let the list know. Here are the things I've come up with: 1) The scarf splice shown on Dwg 5, shows the scarf to be horizontal. The scarf should be a 12 to 1, as a reference to AC 43.13 publication. 2) The angle of the lift strut fitting, on Dwg 4 (lower left corner), and Dwg 5 (at the bottom) should NOT be at the angle indicated. The angle should be what ever the angle the lift strut is, so as to be in alignment with the lift strut. This angle is determined by the length of the cabane struts, and is on an individual airplane basis, because the length of the cabane struts are altered so often. 3) The cabane strut fitting that bolts to the spar, on Dwg 4, (lower left corner) is open to interpolation. It shows the a U strap around under the spar, with a tab welded on each side, which is 3 pieces total for each fitting. If you are not all that good of a weldor, then I think this fitting should be built with two U straps, that fit inside each other. 4) The belly strap should be included at the front & rear, between the lift strut / gear lug fittings. On Dwg 3 (lower left corner) it shows the tab should be bent up 20=BA, but is should read closer to 30=BA, but again, this angle is determined by the length of the cabane struts. 5) The cross piece at the forward lower fuselage, shown to be a 3/4 X 3/4 spruce on Dwg 1(lower right hand portion of the page), is held short of going all the way to the inside of the longerons, as shown on Dwg 6 (lower edge of the page), it says "Cut off end of cross strut", to allow the inside engine mount fitting to install on the inboard side of the longeron. 6) If you loft the dimension numbers of the rib Dwg 5, it makes a little curve down on the top, just past the 50% chord. You should just blend that little curve out. 7) I think there must be a dimension on the leading edge of the rudder, that when added up, it causes the rudder to extend about 1/2" below the bottom of the fuselage. When laying out the locations of the rudder hinges, you MUST accommodate the thickness of the fabric on the top of the fuselage, top and bottom of the horizontal stab, and the fabric on the bottom of the vertical stab, BEFORE you locate the bottom rudder hinge. These are some of the things I'm going show in my video. If anyone can think of anything else that needs to be addressed in the plans, or anything about building the airplane, please make the comment to the list, and lets talk about it. Chuck G. NX770CG ________________________________ Message 3 _____________________________________ Time: 10:33:12 AM PST US From: "Oscar Zuniga" Subject: Pietenpol-List: pesky elevator cable --> Pietenpol-List message posted by: "Oscar Zuniga" Rick asks- >How high do you place it to eliminate the cable problem? To which I would respond, drawing it up with the 9" dimension reveals that the cable should clear. And Greg adds- >I can tell you that raising the bellcrank 1 inch is NOT enough to allow the >cables to clear the stabilizer. OK, so 8" won't do it, but 9" should. But Chuck adds- >I built my bellcrank to the '34 plans location, Dwg. #4 (dated 2-26-34) >with the 9" call out, and used a piece of thick leather on the L.E. of the >horizontal stab as the anti-chafe. Which leaves me puzzled, because graphically (AutoCAD and my Piet drawings), using the 9" dimension should have the upper elevator cable clear the LE of the HS. Go figure... or just plan on "using protective measures" since it's not a big deal anyway. Oscar Zuniga San Antonio, TX mailto: taildrags@hotmail.com website at http://www.flysquirrel.net ________________________________ Message 4 _____________________________________ Time: 12:16:14 PM PST US From: Michael D Cuy Subject: Pietenpol-List: teflon, anyone ? --> Pietenpol-List message posted by: Michael D Cuy I put a small pieces of teflon sheet screwed to the LE of my stab.on either side and been flying happily ever since. Mike C. ________________________________ Message 5 _____________________________________ Time: 12:20:55 PM PST US From: Michael D Cuy Subject: Pietenpol-List: cable going thru the stabilizer I even saw one Piet that allowed the upper elevator cables to go thru the fabric on the stabilizer. Neat solution, but in that case you might have to actually lower the bellcrank ! Mike C. ________________________________ Message 6 _____________________________________ Time: 03:23:23 PM PST US From: "John and Phyllis Smoyer" Subject: Re: Pietenpol-List: pesky elevator cable: --> Pietenpol-List message posted by: "John and Phyllis Smoyer" One factor that influences the elevator cable's clearance over the stabilizer leading edge is the amount of the elevator's downward deflection. How much down deflection is enough? Maybe the cable doesn't rub the LE at that angle. Also, in the Piet's I've seen, it doesn't appear that any amount of "up" elevator deflection will cause an interference on the stabilizer?.Any comments on that observation? This has been a very interesting and illuminating discussion, and I really appreciate the insights and efforts made by all the contributors. Thanks to all of you. -- ________________________________ Message 7 _____________________________________ Time: 03:56:20 PM PST US From: Rcaprd@aol.com Subject: Re: Pietenpol-List: pesky elevator cable: In a message dated 12/20/2005 5:24:56 PM Central Standard Time, jpsmoyer@verizon.net writes: One factor that influences the elevator cable's clearance over the stabilizer leading edge is the amount of the elevator's downward deflection. How much down deflection is enough? Maybe the cable doesn't rub the LE at that angle. Also, in the Piet's I've seen, it doesn't appear that any amount of "up" elevator deflection will cause an interference on the stabilizer?.Any comments on that observation? John, The fouling of the flipper cables on the L.E. of the stab, is just one part of the observation. You see, in addition to that, there is a difference in symmetry in the bellcrank, and the flipper horns, such that when they are in the neutral position, the bottom cable is slack. When the flippers are in the up, or down position, both the top and bottom cables have no slack in them, but they SHOULD NOT be tight. I always refer to them as 'Flippers', as opposed to 'Elevators'...even at work, dealing with jet planes. The name Elevator is a poor description of what those control surfaces actually do. They are NOT what make the plane go up & down - POWER controls altitude, and PITCH controls airspeed. Chuck G. NX770CG ________________________________ Message 8 _____________________________________ Time: 06:24:42 PM PST US From: Subject: Re: Pietenpol-List: building video 1" from the 9" position. Long fuselage. Anti chafe patch was glued to the LE of the stabilizer. Elevator horns and walking beam were drilled carefully to maintain a parallelogram in the cable system. No cable slack issues except at very extreme limits and even then it is minimal. Greg Cardinal Minneapolis ----- Original Message ----- From: Rick Holland To: pietenpol-list@matronics.com Sent: Tuesday, December 20, 2005 8:18 AM Subject: Re: Pietenpol-List: building video Is that one inch from the 7" position or from the 9" position Greg? Rick H On 12/19/05, gcardinal@mn.rr.com wrote: From experience I can tell you that raising the bellcrank 1 inch is NOT enough to allow the cables to clear the stabilizer. Greg Cardinal ----- Original Message ----- From: Rick Holland Never noticed the 2" difference until you mentioned it Oscar. I guess I was looking at drawing #4 the day I installed my bellcrank (fortunately). How high do you place it to eliminate the cable problem? Rick H. -- Rick Holland ________________________________ Message 9 _____________________________________ Time: 07:48:33 PM PST US From: "Graham Hansen" Subject: Re: Pietenpol-List: pesky elevator cable: --> Pietenpol-List message posted by: "Graham Hansen" Group, The interference between the elevator/"flipper" cable and the leading edge of the horizontal stabilizer is not restricted to the Pietenpol. Other early designs, notably the DeHavilland Moths, share this characteristic. Essentially, it isn't a big problem and, in the case of the Pietenpol, can be solved by placing rub strips on the L.E. of the stab. Like Michael Cuy, I use teflon pieces about 1/8"x3/4"x3" screwed to the upper surface of the L.E. The interference noted above, together with cable slackening, was dramatically reduced by restricting the elevator travel. Adjustable stops were welded to the torque tube (in front of and behind the stick) after the first 90 hours of operation, allowing 32 degrees up and 25 degrees down elevator travel. My Piet now has 750 hours on it and this modification has proved to be satisfactory. Generally, when the elevators are at, or near, the neutral position, the upper cable is not in heavy contact with the stabilizer L.E.--at least this is the case with the four different Pietenpols I have flown. Drastically changing the geometry of the elevator (oops, "flipper") circuit, in my humble opinion, really isn't worthwhile. It is a good idea to inspect the forward elevator cables for wear at the torque tube pulleys. The plans call for 2 inch pulleys which are pretty small. Early on, I made the mistake of using aluminum pulleys (I got them "for free") and the cables wore out very quickly. Buying some fibre pulleys solved the problem. Nevertheless, I frequently check the cables at this location. So far, so good! Graham Hansen Pietenpol CF-AUN ________________________________ Message 10 ____________________________________ Time: 08:54:41 PM PST US From: Rcaprd@aol.com Subject: Re: Pietenpol-List: Building Video In a message dated 12/20/2005 10:29:45 AM Central Standard Time, Jack.Phillips@cardinal.com writes: Chuck, the things I remember being flawed were the isometric drawings showing the compression struts between the spars at the lift strut attach points. The drawings show them in line vertically, but if you mount the lift strut fittings as shown in the plans, the strap fittings interfere with the compression struts. I made my lift strut fittings per the plans (I=E2=80=99l explain why below) and had to offset the compression struts to clear them. On your item #2, I was planning to do as you did (and most people would do, since most modern airplanes do so) and make the lift strut fitting strap in line with the strut, so the strut would not impose a moment (torque) on the=20spar. I assumed that BHP designed it the way he did out of ignorance. Then I decided to do a little stress analysis to see just how much =E2=80=9Cbetter=E2=80=9D I could design it than Bernard did. To my surprise, I found that the fitting as designed by BHP actually decreased the bending moment in the spars to the extent that by building the fittings to his design, the wings can withstand almost a full G more than they can if the fittings are in line with the struts! The ultimate loading (with a 1050 lb gross weight) goes from 4 G=E2=80=99s to 4.9 G=E2=80=99s Jack, You bring up a Very interesting point here. Bernard Harold Pietenpol's design genius is profound, so who am I to question it ?? This includes the Bellcrank. However, for 9 years now, I have been wondering why on earth Bernard would design the lift strut fittings at that angle. It just seems to me that with the constant positive / negative loads imposed on those fittings, applying the moment of torque would eventually wallow out the holes in the wood spars, even with the 1" strips of wood on each side of the fittings, and the strap welded across the top between the two straps. Now, after hearing of your stress analysis, I ran the scenario through my brain again. Be warned: This could be the Irish Beer talking... Here is what my brain came up with: Placing the Lift Strut Spar Fittings in alignment with the Lift struts (not per plans), and adding G load causes the lift struts to be in tension,=20and the wing panel outboard of the lift strut fitting will flex upward. Placing the Lift Strut Spar Fittings at the angle called out in the plans, with the piece welded across the top, (as per plans), and adding G load causes the lift strut to be in tension, however, the moment torque applied to the fittings will tend to cause the outboard wing panel to be pulled down. Could this be the reason it can withstand almost 1 G more load before failure ??? Maybe the ultimate load is higher with the B.H.P. design angle, but the drawback is that the fittings will eventually loosen up. I doubt it would cause an immediate failure, but what would be immediate is a change in the Angle of Incidence, causing a wing heavy condition in flight. Something to keep a very close eye on. Jack: In your stress analysis, specifically, what was it that failed ?? Forgive my skepticism, Jack, but I think it would be Very helpful if you could run those numbers again, and / or some of you other engineers out there to run these numbers on the angle of the lift strut fittings, and see if they agree. Chuck G. NX770CG ________________________________ Message 11 ____________________________________ Time: 09:08:08 PM PST US From: Rcaprd@aol.com Subject: Re: Pietenpol-List: pesky elevator cable: In a message dated 12/20/2005 9:50:02 PM Central Standard Time, grhans@cable-lynx.net writes: The interference noted above, together with cable slackening, was dramatically reduced by restricting the elevator travel. Adjustable stops were welded to the torque tube (in front of and behind the stick) after the first 90 hours of operation, allowing 32 degrees up and 25 degrees down elevator travel. My Piet now has 750 hours on it and this modification has proved to be satisfactory. Graham, I can certainly see how installing stops on the torque tube would dramatically reduce the cable slack, at the neutral position of the flipper travel. I now have another item on my List of To Do's, for this winter. Chuck G.