Brodhead Pietenpol Association

Original Posted By: "walt evans"
I built the long fuselage and then (idiodically) built the horiz. stab for theshort fuse (18" wide instead of 19 3/8") - didn't realize until today when I triedfitting it up. Question: can I glue a wider leading edge to the horizontalstab to make up the difference? Obviously this would add a bit of weightto the tail section.. Or could I just fill in behind the turtle deck to takeup the space? Difference is about 1 3/8". Is the 1 3/8" width going to be missedif I leave it out? Does this cause a problem getting away from the 'airfoilshape'?Another related question: does the horiz. stab get bolted through the longerons?Any help on this would be appreciated.Tom BrantBrooklyn Park, MN________________________________________________________________________________

Original Posted By: Brants
I didn't know they were different. I built the long fuse and the tail was fromthe original prints, so I guess I got the wrong one. but flies great. Whattwo prints show different tails???walt evansNX140DL ----- Original Message -----

Original Posted By: walt evans
Walt,You are concerned with a concept called tail volume. Tail volume is the squareinch area of the horizontal surface (elevator and satbilizer together) timesthe distance in inches from the center of pressure of the horizontal stabilizerto the Center of Gravity, this being the point of rotation about which the aircraftmoves based on input of the controls.As there are three wood fuselages that I know of, namely the version in the F&Gmanual and on the Hoopman drawings at 161 inches, the 1933 "Improved Aircamper"at 163 inches, and the fuselage designed for the Corvair at 172.375 inches,I am not sure which one you mean. I always called the Corvair fuselage the Pavligalong fuselage because, well, it is the longest and it is the fuselage usedon Sky Gypsy.Anyway, if you take the square inch area of each horizontal design times the distancein inches from the loaded CG to the 33% chord point on each stabilizerdesign, you will come up with the tail volume...volume because the units willnow be cubic inches. The hardest thing will be to figure out your loaded CG.If you make the distance between the CG to the CP of the stabilizer longer, youcan get by with a smaller stabilizer area. Shorten up the CG to CP distanceand you need to increase the tail area.My analysis of the different fuselages leads me to believe that using the 172.375fuselage moves the seats back faster than the tail gets longer so it actuallyputs the CG further aft than on the shorter fuselages. This means that theCG to Cp of the stabilizer is actually a shorter distance so a bigger area stabilizeris needed.Unfortunately, the 172.375" fuselage drawing is a stand alone. No landing gearwas ever published for it and neither is there a obviously a stabilizer.I wrote an article on gear placement on the 172.375 inch fuselage that was to bepublished in the Grant MacLaren published BPA NL but it never made it becausethe very issue it was to be published in was never published as he quit thepost. I will dig it out. Only a hard copy exists, and even it is one of thedrafts, so I will have to scan it to OCR software and see if I can post it.I hope this helps. I wish people said what inch fuselage they have when they talkof stuff like this as it really matters (or maybe it doesn't since they allseem to meet each aviator's expectations)Chris Bobka ----- Original Message -----

Original Posted By: Christian Bobka
Chris,I am the one that asked the original question.... You're correct in saying thatthe drawings stand alone, however if I'd been smart I could have figured onmaking a larger stabilizer... According to your comments (if I interpreted correctly) the 172 3/8" fuse (thisis what I have) requires a larger stabilizer (and elevator??)... My previouspost asks this question - can I use the 18" stab (and elevator) now that they'rebuilt, or do I need to modify or rebuild? I would be interested in getting a copy of your article on this.Thanks,Tom BrantBrooklyn Park, MN ----- Original Message -----

Original Posted By: Brants
Tom,I just refined the article and posted it to this list a minute ago. The articleis not about the stabilizer size but it gets you thinking a little bit aboutthe fuselage. I will look around and come up with my opinion on the stabilizer.Wait a little and see what the others say too. It really all depends onwhat loaded CGs others with the same fuselage have. And the CG needs to be givenrelative to a fixed point on the fuselage that is common to your fuselagei.e. the wing leading edge datum (an awful place to use) is not at all usefulunless we know that particular ship's wing leading edge postion relative to thefixed point on the fuselage that is common to your fuselage.ChrisChris ----- Original Message -----

Original Posted By: Brants
Chris,I am building the long fuselage and would appreciate the information you workedup on larger stabs.ThanksAlex Sloanalexms(at)bellsouth.net ----- Original Message -----

Original Posted By: Mike
Subject: Re: Pietenpol-List: horizontal stab dimensionsChris,Please post or send to me too. Have yet to build the tail, but better to research now than later.Greg MenocheDelawareGnwac(at)cs.com________________________________________________________________________________Date: Mon, 19 Jan 2004 20:12:58 -0800

Original Posted By: Brants
Tom,As I see it, there are two stabs. One is rectangular in shape, as in the 1932F and G Manual, and the other sweeps about 80 degrees at the tips, as in the 1933Improved Aircamper. Otherwise, they all have 18" chord. Anybody else in on this? Mike C.?chris bobka ----- Original Message -----

Original Posted By: Clif Dawson

Original Posted By: "Mike"
Mike,As I posted earlier, with the seats moved way aft in the 170+" fuselage, theCG is moving aft faster than the arm is getting longer if the arm getslonger at all, when compared to the shorter fuselages. I would like to seesome numbers from flying ships, with the CG locations given relative to aCOMMON point. The wing LE does not cut it as you move the wing around andthat makes the numbers incomparable from ship to ship. One needs to use afixed location on the fuselage not likely to be tampered with by the builderas is the firewall.I truly believe that the 170+" long fuselage has a tendency to get tailheavy much more easily than the shorter fuselages. I believe that the CG to'Cp of the stab' distance is shortest with the 170+" fuselage, despite howit might look. This would mean the 170+" fuselage would have the smallesttail volume of all the fuselage variants. To compensate, maybe the taildoes need to be made bigger, as Tom Brants suggests. Anyone out there withgood weight and balance data to share, with it converted to use, say, theforward cabane strut to upper longeron fitting bolt on the longeron as thedatum? Need it for both the shorter and longer fuselages.Anyone measure the stabilizer chord on "The Last Original"?Merely my opinion and waiting for facts to roll in. Believe me, I am abuild it stock kind of guy but when you are dealing with the long fuselage,there is not much else given than a fuselage drawing. We are on our own forthe rest.chris bobka----- Original Message -----

Original Posted By: Jim Markle
Jim,Thanks, I really enjoyed that article and pictures. The core of why I built aPietenpol.walt evansNX140DL ----- Original Message -----

Original Posted By: Mike
Hi all Just thought I'd throw this one out there, my pilot/instructor says thatI need control surface stop put in. Just by the way what must thedeflexions be for the control surfaces? I cannot seem to find them anywhere.Regards,Norman StapelbergZS-VJA (115Hrs)South AfricaFASI________________________________________________________________________________Date: Tue, 20 Jan 2004 12:02:12 -0800Subject: Re: Pietenpol-List: horizontal stab dimensions

Original Posted By: Rick Holland
Rick,If you look at the top "plan view" drawing of the 172 3/8" fuse (I'll call it FuselageC), it shows 19 3/8" from the back of the vertical brace (same place asa horizontal brace?) to the tailpost. Then in the layout below which showsthe turtledeck, it shows 18 7/8" from back of turtledeck to the tailpost.. Inailed a 1/8" piece of ply to the back of the brace (19 3/8") to which my turtledeckstringers are mounted. So in theory, the dimension in mine from turtledeckto tailpost is 19 1/4" I don't know how they came up with 18 7/8" unlessI hosed something up, which is entirely possible.Tom B. ----- Original Message -----

Original Posted By: Mike
Re: Pietenpol-List: horizontal stab dimensionsUse a piece of light spruce to fairthe gap. Under the fabric, you won't notice.Chris Bobka ----- Original Message -----

Original Posted By: Jim Vydra
I thought this was posted earlier but don't remember seeing it so.....I'll tryagain.I was invited to cast a critical eye on an almost completed Air Camper while ona house-hunting expedition in N. Florida last week. I was an honored guest ofnoted aviation artist (paintings and models) John Ficklen at his home on St.George Island for a couple of days.His Piet is assembled and rigged and looks like a winner. Lots of little personaltouches that will keep spectators busy looking for an extended time at airshows.It's delightful! Although he does have dihedral and a center-section cutoutYUCK (sorry Mike) he rest of the airplane is to-the-plans and extremely welldone. That's expected from someone who makes historically accurate models formuseums and private collectors, I suppose.Anyway, it is a treat for the eye and, as is always the case, it's a shame to haveto cover it. John's goal is to have it finished for Sun-N-Fun. A two yearbuild time shows what can be done if efforts are directed to the building boardrather than the keyboard .Larry________________________________________________________________________________Date: Wed, 21 Jan 2004 06:51:23 -0800 (PST)