Pietenpol-List: Fuselage length, wing placement and wheel axle placement
Posted: Fri Aug 11, 2006 5:59 pm
Original Posted By: Gary Gower
Subject: Pietenpol-List: Fuselage length, wing placement and wheel axle placement(long)Hello to everybody!First of all, a big THANK YOU to the list for the response to the firstbunch of questions! I collected and stored all the photos and documentsyou guys provided, and I especially thank Chris Tracy who provided thelink to his website and to Chris Bobka's document about wheel axlesplacement. Again, thanks!Well, I decided to fire up the CAD and try to assemble a virtual Pietwith all the modifications/clarifications available so far. Not toredesign the Piet itself but just to be a quick and clean method tocheck dimensions and placements. And here is, obviously, whereconfusion begins. :-(Before getting into the hang of it, I want to explain a couple ofpoints which form the base for the whole discussion:1) Our Piet is not going to enjoy any of the three de-facto "standard"powerplants (Ford Model A, Corvair or Continental A65-8) simply becausenone is available to us in Europe (even A65-8 are rarer than hen'steeth these days, in spite of their past wide availability here).Therefore, the powerplant will have to be something quite different,probabily derived from a modern gas/diesel auto engine or somethinglike that. When time comes, appropriate calculations will be made forengine placement, in order to obtain the correct Center of Gravityrange. I'm familiar with this procedure as I've already done it in thepast for two other airplanes, and they then checked correctly on thescales.2) Because of the aforementioned point, I decided to reference all mywork to the original 1933 Improved Plans i.e. considering the Piet ashaving the wing position determined by the cabane struts at rightangles with the upper longeron. That is, with the important change ofthe 172 3/8" long fuselage (because we believe we need the increasedtail arm as we assume a longer nose). As already said, that's where confusion begins, because after lookingat all the photos I could see, reading Chris Bobka's comments, and evenchecking the Weight and Balance sheet provided by Don Pietenpol, I sawthat the wing position can be quite different from the original one,and not always the same. This is not very good from an engineeringstandpoint, because every kind of W&B calculation assumes a CG rangewith respect to the airplane Center of Lift, and not the other wayaround. Not to mention the fact that, as wing placement change, so doesthe tail arm length, which should be something to be taken veryseriously and not changed all too easily.Chris Bobka's document is fine in that it works out a well-weighedlogical conclusion from a huge amount of data, but it does NOT mentionthe WING anywhere. However, let's start working on BOTH fuselages(standard and long) using some known data:1) Standard fuselage: Bobka's axle distance from firewall: 17"2) Long fuselage: Bobka's axle distance from firewall: 21"3) Distance between firewall and wing leading edge, std fuselage: 6.8"4) Distance between firewall and wing leading edge, long fuselage: 8.8"5) Most rearward CG position (Don Pietenpol): 33% or 20" from LEOkay, working out the math makes for TWO DIFFERENT distances betweenwheel axle and most rearward C of G position for the two fuselages:7.8" for the LONG fuselage, and 9.8" for the STANDARD fuselage.Logic says that the distance should be the same for both fuselages, soobviously one of them is not correct.My own understanding says 7.8" is way too little. When the Piet issitting without pilots and with empty wing tank, the CG ought to bevery close to its most FORWARD position, which is probabily AHEAD ofthe wheel axle in level flight, meaning the fuselage will barely standon the tailwheel (if it has not already tipped over). 9.8" does notlook really good either, but it's the closest (by 1/2" if I'm notmistaken) to the measurements on the Improved 1933 Plans.Again, I state that the wing is going to be exactly where shown on theplans, and the correct placement of the powerplant will bring the CGrange within the correct limits. And none of the measurements forplacing Ford/Corvair/Continental engines will apply, as the powerplantwill NOT be either one of these.So, where should I place my wheel axles?All the Pieters out there, where is YOUR wheel axle and YOUR wingleading edge with respect to the firewall, and HOW does your Pietbehave during landing and on the ground?Thanks in advance for the answers.SeeYa!Andrea VavassoriVolksplane VP-1 I-BYRAEAA #348037FCAP I-146Homepage: http://andrea.modelberg.it________________________________________________________________________________Date: Sat, 12 Aug 2006 01:05:32 -0700 (PDT)
Subject: Pietenpol-List: Fuselage length, wing placement and wheel axle placement(long)Hello to everybody!First of all, a big THANK YOU to the list for the response to the firstbunch of questions! I collected and stored all the photos and documentsyou guys provided, and I especially thank Chris Tracy who provided thelink to his website and to Chris Bobka's document about wheel axlesplacement. Again, thanks!Well, I decided to fire up the CAD and try to assemble a virtual Pietwith all the modifications/clarifications available so far. Not toredesign the Piet itself but just to be a quick and clean method tocheck dimensions and placements. And here is, obviously, whereconfusion begins. :-(Before getting into the hang of it, I want to explain a couple ofpoints which form the base for the whole discussion:1) Our Piet is not going to enjoy any of the three de-facto "standard"powerplants (Ford Model A, Corvair or Continental A65-8) simply becausenone is available to us in Europe (even A65-8 are rarer than hen'steeth these days, in spite of their past wide availability here).Therefore, the powerplant will have to be something quite different,probabily derived from a modern gas/diesel auto engine or somethinglike that. When time comes, appropriate calculations will be made forengine placement, in order to obtain the correct Center of Gravityrange. I'm familiar with this procedure as I've already done it in thepast for two other airplanes, and they then checked correctly on thescales.2) Because of the aforementioned point, I decided to reference all mywork to the original 1933 Improved Plans i.e. considering the Piet ashaving the wing position determined by the cabane struts at rightangles with the upper longeron. That is, with the important change ofthe 172 3/8" long fuselage (because we believe we need the increasedtail arm as we assume a longer nose). As already said, that's where confusion begins, because after lookingat all the photos I could see, reading Chris Bobka's comments, and evenchecking the Weight and Balance sheet provided by Don Pietenpol, I sawthat the wing position can be quite different from the original one,and not always the same. This is not very good from an engineeringstandpoint, because every kind of W&B calculation assumes a CG rangewith respect to the airplane Center of Lift, and not the other wayaround. Not to mention the fact that, as wing placement change, so doesthe tail arm length, which should be something to be taken veryseriously and not changed all too easily.Chris Bobka's document is fine in that it works out a well-weighedlogical conclusion from a huge amount of data, but it does NOT mentionthe WING anywhere. However, let's start working on BOTH fuselages(standard and long) using some known data:1) Standard fuselage: Bobka's axle distance from firewall: 17"2) Long fuselage: Bobka's axle distance from firewall: 21"3) Distance between firewall and wing leading edge, std fuselage: 6.8"4) Distance between firewall and wing leading edge, long fuselage: 8.8"5) Most rearward CG position (Don Pietenpol): 33% or 20" from LEOkay, working out the math makes for TWO DIFFERENT distances betweenwheel axle and most rearward C of G position for the two fuselages:7.8" for the LONG fuselage, and 9.8" for the STANDARD fuselage.Logic says that the distance should be the same for both fuselages, soobviously one of them is not correct.My own understanding says 7.8" is way too little. When the Piet issitting without pilots and with empty wing tank, the CG ought to bevery close to its most FORWARD position, which is probabily AHEAD ofthe wheel axle in level flight, meaning the fuselage will barely standon the tailwheel (if it has not already tipped over). 9.8" does notlook really good either, but it's the closest (by 1/2" if I'm notmistaken) to the measurements on the Improved 1933 Plans.Again, I state that the wing is going to be exactly where shown on theplans, and the correct placement of the powerplant will bring the CGrange within the correct limits. And none of the measurements forplacing Ford/Corvair/Continental engines will apply, as the powerplantwill NOT be either one of these.So, where should I place my wheel axles?All the Pieters out there, where is YOUR wheel axle and YOUR wingleading edge with respect to the firewall, and HOW does your Pietbehave during landing and on the ground?Thanks in advance for the answers.SeeYa!Andrea VavassoriVolksplane VP-1 I-BYRAEAA #348037FCAP I-146Homepage: http://andrea.modelberg.it________________________________________________________________________________Date: Sat, 12 Aug 2006 01:05:32 -0700 (PDT)