Brodhead Pietenpol Association

Original Posted By: Lou Wither
Subject: Pietenpol-List: Building Video Well, the list is kind of slow, so I present to you a request for somehelp. As most of you know, I'm putting together a Pietenpol Building Video, andI want to make it as complete, and comprehensive as possible. I need somehelp 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 beena 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 fitthe era of the aircraft you are building, and are a part of the whole history ofthe Pietenpol. Quite often, it is concluded that an error exists, but uponfurther study, and some questions asked, the light bulb goes off, and itbecomes crystal clear. Granted there are errors in the plans, but given theenormous amount of information that is included in the plans, the errors are notthatmany. Having said that, builders NEED to know what, and where the errorsare. They also need clarification in some areas. Done correctly, and with goodworkmanship, in the 76 year history of the Pietenpol, there has NEVER been anairframe failure (at least none that has been reported). I can make thatclaim, because a couple years ago, I did an extensive, and exhaustive study=20ofall 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 ofan area of the plans that are confusing, or has an error, to let the listknow. Here are the things I've come up with:1) The scarf splice shown on Dwg 5, shows the scarf to be horizontal. Thescarf 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), andDwg 5 (at the bottom) should NOT be at the angle indicated. The angle should bewhat ever the angle the lift strut is, so as to be in alignment with the liftstrut. This angle is determined by the length of the cabane struts, and ison an individual airplane basis, because the length of the cabane struts arealtered so often.3) The cabane strut fitting that bolts to the spar, on Dwg 4, (lower leftcorner) 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. Ifyou are not all that good of a weldor, then I think this fitting should bebuilt with two U straps, that fit inside each other.4) The belly strap should be included at the front & rear, between the liftstrut / gear lug fittings. On Dwg 3 (lower left corner) it shows the tabshould be bent up 20=BA, but is should read closer to 30=BA, but again, this angleisdetermined by the length of the cabane struts.5) The cross piece at the forward lower fuselage, shown to be a 3/4 X 3/4spruce on Dwg 1(lower right hand portion of the page), is held short of goingall the way to the inside of the longerons, as shown on Dwg 6 (lower edge of thepage), it says "Cut off end of cross strut", to allow the inside engine mountfitting to install on the inboard side of the longeron.6) If you loft the dimension numbers of the rib Dwg 5, it makes a littlecurve down on the top, just past the 50% chord. You should just blend thatlittle curve out.7) I think there must be a dimension on the leading edge of the rudder, thatwhen added up, it causes the rudder to extend about 1/2" below the bottom ofthe fuselage. When laying out the locations of the rudder hinges, you MUSTaccommodate the thickness of the fabric on the top of the fuselage, top andbottom of the horizontal stab, and the fabric on the bottom of the vertical=20stab,BEFORE you locate the bottom rudder hinge.These are some of the things I'm going show in my video. If anyone can thinkof anything else that needs to be addressed in the plans, or anything aboutbuilding the airplane, please make the comment to the list, and lets talk aboutit.Chuck G.NX770CG________________________________________________________________________________Date: Sat, 17 Dec 2005 12:42:01 -0800 (PST)

Original Posted By: Rcaprd(at)aol.com
An additionWhen making fixed gear leg fittings, as per Flying Glider Manual, increase dinmensionsto clear the ash brace on the floor.Dick ----- Original Message -----

Original Posted By: "Philip Miller"
Subject: Re: Pietenpol-List: Building VideoIn a message dated 12/17/2005 1:11:17 PM Central Standard Time, Rcaprd(at)aol.com writes: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 bechanged. Excellent comment....and presented, as you have with a solution to the acknowledged problem. Don Hicks ________________________________________________________________________________

Original Posted By: "Carl Vought"
Chuck,The plans have all the metal parts in gauge thicknesses. Consulting the machinistsequivalents, they seem to fall between the current available thicknessesof 4130. Assuming that one would use 4130 aircraft steel for all those fittings,what is the rule of conversion? Go to the next size up, down, or round tothe nearest? I can think of convincing arguments for any of them.Size up - safer, and 4130 is more brittle than cold rolled steel.Size down - The Pietenpol is an over-engineered plane. BHP said as much in theFlying and Glider Manual.Round to the nearest - stays as close to plans as possible.I'd also like to see about pulleys. The plans call for 2" pulleys for the controls,but AC 43.13 and Tony Bingelis would preach against such small sized pulleys.The loads shown for pulleys don't seem out of line. Sizing up to largerpulleys would mean changing the angles for the brackets, especially the bracketthat holds the pulleys that guide cable to the aileron horns.And about that pesky elevator cable - the one that seems to rub the top LE on everyPiet I've seen; is there a solution that doesn't do that? Can't you extendthe bellcrank so that the cable exits in the fuse are high enough not to causethat rubbing?What about brakes? I've seen hydraulic, mechanical disk, drum, and band brakes.No brakes in the plans, but that would hardly suffice on our modern ramp fullof very expensive airplanes bordering narrow taxiways that you have to S-turnyour way through. And Tailwheels. You can't have a skid. And I've seen alot of very different solutions for tailwheels. The tube LG given on the plans are hardly ever used to my knowledge. Why? Ifyou are going with tube gear, there seem to be much better configurations available.What are the trade-offs?Plank seats. Lotsa folks complain about them. Couldn't one make a frame of woodand sling a sheet of thin kevlar, impregnate it with fast epoxy, encase one'sbutt in a garbage bag smeared with parafin and just sit on it? Not so goodfor the front seat, but it sure makes the pilot's life a lot more comfortable!And what about Wing LE covering. The plans are somewhat non-specific. I've seenAluminum and plywood used. I would imagine you could use some prepreg bendablecomposite too if you wanted light and strong. The bellcrank bearing. The plans don't give enough detail, or if they do, youwouldn't want to use bearings like that now. Really Good bearing are now availableand cheap. What size?I would like to see the plans updated. Not so much to correct errors, but to fulfillomissions, and make compliant to our modern rules and environment. I'dlike to have the LG angles and W&B solutions for more than the Ford Model A.Even the Corvair LG and W&B data on the plans is only good if you are using theblower on top - which nobody does any more - and the LG info is very imprecise.Variances will always occur. What is needed is a best-practices approachto derive such information in a clear manner, set down in one place where thenomenclature, data reference points, and assumptions are consistent and spelledout.Michael Cuy's video mentions the need to extend the tabs.Perhaps I'm just nitpicking, but all of these things leave me scratching my head.Can I build something with this many unknowns? My hats off to all of youwho have. And this list goes a long way to creating a place where the questionscan be answered. Without it, and all of you, I don't think I would attemptit. Phil Miller Altadena, CA________________________________________________________________________________

Original Posted By: "Phillips, Jack"

Original Posted By: Rcaprd(at)aol.com
Subject: Re: Pietenpol-List: Building VideoIn a message dated 12/20/2005 10:29:45 AM Central Standard Time,Jack.Phillips(at)cardinal.com writes:Chuck, the things I remember being flawed were the isometric drawings showingthe compression struts between the spars at the lift strut attach points. The drawings show them in line vertically, but if you mount the lift strutfittings as shown in the plans, the strap fittings interfere with the compressionstruts. 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 inline 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 Idecided to do a little stress analysis to see just how much =E2=80=9Cbetter=E2=80=9DI coulddesign it than Bernard did. To my surprise, I found that the fitting as designedby BHP actually decreased the bending moment in the spars to the extent thatby building the fittings to his design, the wings can withstand almost a full Gmore than they can if the fittings are in line with the struts! The ultimateloading (with a 1050 lb gross weight) goes from 4 G=E2=80=99s to 4.9 G=E2=80=99sJack, You bring up a Very interesting point here. Bernard Harold Pietenpol'sdesign genius is profound, so who am I to question it ?? This includes theBellcrank. However, for 9 years now, I have been wondering why on earth Bernardwould design the lift strut fittings at that angle. It just seems to me thatwith the constant positive / negative loads imposed on those fittings,applying the moment of torque would eventually wallow out the holes in the woodspars, even with the 1" strips of wood on each side of the fittings, and the strapwelded across the top between the two straps. Now, after hearing of yourstress analysis, I ran the scenario through my brain again. Be warned: Thiscould 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,=20andthe wing panel outboard of the lift strut fitting will flex upward. Placing the Lift Strut Spar Fittings at the angle called out in theplans, with the piece welded across the top, (as per plans), and adding G loadcauses the lift strut to be in tension, however, the moment torque applied to thefittings will tend to cause the outboard wing panel to be pulled down. Couldthis 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 thedrawback is that the fittings will eventually loosen up. I doubt it wouldcause an immediate failure, but what would be immediate is a change in the Angleof Incidence, causing a wing heavy condition in flight. Something to keep avery 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 youcould run those numbers again, and / or some of you other engineers out there torun these numbers on the angle of the lift strut fittings, and see if theyagree.Chuck G.NX770CG________________________________________________________________________________

Original Posted By: Tim Willis
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.________________________________________________________________________________Date: Wed, 21 Dec 2005 06:47:37 -0800 (PST)