Brodhead Pietenpol Association

Original Posted By: "jimd"
Hi,Just had an A&I leave my house after looking over my biplane GN-1 project. He hada concern about the landing gear placement of my plane, based on the weight/placementof the engine.To correctly determine where the gear should be he said I needed to find out wherethe CG of the plane is, but with it being a biplane configuration, he saidthat I needed to have the mean center of lift information for both the upperand lower wings, as well as a number of measurements from the assembled plane,like information about the spacing horizontally between the wings. Then oncethe weights, and measurements are known, the acceptable range of locations forthe axle of the landing gear can be determined from some engineering formulas.Did some searching, found two engineering articles on finding the CG/center oflift on biplanes, and they require information about the airfoil.I was able to find information on the Pietenpol FC-10 airfoil, which I believeis what my lower wing has, as the Aerial biplane conversion plans say the airfoilis the same. http://www.airminded.net/piet/piet.html has piet airfoil info with Cl,Cm,Cd, type info.However presuming my plane has the Gregga airfoil, which the plans say have a rounderleading edge.. and which appear to be thicker.. I would think it is a differentairfoil, with different values. Have not seen it listed in the commonairfoils databases.Anyone have information on the GN-1 airfoil? I have the plans, have a jig, andwings, but only can guestimate it as being like the piet. We are thinking I may have to rework the landing gear to get it right, but no oneknows how much if any it must be changed.So any GN-1 ordinates, or the Cl,Cm,Cd type info, or naca airfoil numbers... anythinglike that would be helpful.You can see my gear/plane on the westcoastpiet site, its under Jim D.Thanks,JimRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: GN-1 airfoil information needed

Original Posted By: Thomas Bernie
Ok,How about the MAC for the pietenpol wing? If I can get that value I can get a ballparkidea of the biplane MAC values, and use it to have a better idea of wherethe landing gear should be placed.JimRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________

Original Posted By: Thomas Bernie
Hi Jim,My GN-1 was built according to the CAD plans -- the plans are loaded with errors and the weight and balance example is bogus. That being said, the aerodynamic is supposed to be 14 inches, but the example aircraft uses J-3 wings. I'm in the process of determining the real crew and fuel moments, since the plans can't be trusted.Regards,Tom BernieGloucester, MassOn May 10, 2008, at 5:47 PM, jimd wrote:>> Hi,>> Just had an A&I leave my house after looking over my biplane GN-1 > project. He had a concern about the landing gear placement of my > plane, based on the weight/placement of the engine.>> To correctly determine where the gear should be he said I needed to > find out where the CG of the plane is, but with it being a biplane > configuration, he said that I needed to have the mean center of lift > information for both the upper and lower wings, as well as a number > of measurements from the assembled plane, like information about the > spacing horizontally between the wings. Then once the weights, and > measurements are known, the acceptable range of locations for the > axle of the landing gear can be determined from some engineering > formulas.>> Did some searching, found two engineering articles on finding the CG/ > center of lift on biplanes, and they require information about the > airfoil.>> I was able to find information on the Pietenpol FC-10 airfoil, which > I believe is what my lower wing has, as the Aerial biplane > conversion plans say the airfoil is the same.>> http://www.airminded.net/piet/piet.html has piet airfoil info with > Cl,Cm,Cd, type info.>> However presuming my plane has the Gregga airfoil, which the plans > say have a rounder leading edge.. and which appear to be thicker.. I > would think it is a different airfoil, with different values. Have > not seen it listed in the common airfoils databases.>> Anyone have information on the GN-1 airfoil? I have the plans, have > a jig, and wings, but only can guestimate it as being like the piet.>> We are thinking I may have to rework the landing gear to get it > right, but no one knows how much if any it must be changed.>> So any GN-1 ordinates, or the Cl,Cm,Cd type info, or naca airfoil > numbers... anything like that would be helpful.>> You can see my gear/plane on the westcoastpiet site, its under Jim D.>> Thanks,>> Jim>>> Read this topic online here:>> http://forums.matronics.com/viewtopic.p ... 01>>Thomas Bernietsbe________________________________________________________________________________

Original Posted By: "jimd"
"aerodynamic" should read "aerodynamic center of the wing"tbOn May 11, 2008, at 3:53 PM, Thomas Bernie wrote:> >>> Hi Jim,>> My GN-1 was built according to the CAD plans -- the plans are > loaded with errors and the weight and balance example is bogus. > That being said, the aerodynamic is supposed to be 14 inches, but > the example aircraft uses J-3 wings. I'm in the process of > determining the real crew and fuel moments, since the plans can't be > trusted.>> Regards,> Tom Bernie> Gloucester, Mass>>> On May 10, 2008, at 5:47 PM, jimd wrote:>>>>> Hi,>>>> Just had an A&I leave my house after looking over my biplane GN-1 >> project. He had a concern about the landing gear placement of my >> plane, based on the weight/placement of the engine.>>>> To correctly determine where the gear should be he said I needed to >> find out where the CG of the plane is, but with it being a biplane >> configuration, he said that I needed to have the mean center of >> lift information for both the upper and lower wings, as well as a >> number of measurements from the assembled plane, like information >> about the spacing horizontally between the wings. Then once the >> weights, and measurements are known, the acceptable range of >> locations for the axle of the landing gear can be determined from >> some engineering formulas.>>>> Did some searching, found two engineering articles on finding the >> CG/center of lift on biplanes, and they require information about >> the airfoil.>>>> I was able to find information on the Pietenpol FC-10 airfoil, >> which I believe is what my lower wing has, as the Aerial biplane >> conversion plans say the airfoil is the same.>>>> http://www.airminded.net/piet/piet.html has piet airfoil info with >> Cl,Cm,Cd, type info.>>>> However presuming my plane has the Gregga airfoil, which the plans >> say have a rounder leading edge.. and which appear to be thicker.. >> I would think it is a different airfoil, with different values. >> Have not seen it listed in the common airfoils databases.>>>> Anyone have information on the GN-1 airfoil? I have the plans, have >> a jig, and wings, but only can guestimate it as being like the piet.>>>> We are thinking I may have to rework the landing gear to get it >> right, but no one knows how much if any it must be changed.>>>> So any GN-1 ordinates, or the Cl,Cm,Cd type info, or naca airfoil >> numbers... anything like that would be helpful.>>>> You can see my gear/plane on the westcoastpiet site, its under Jim D.>>>> Thanks,>>>> Jim>>>>>>>>>> Read this topic online here:>>>> http://forums.matronics.com/viewtopic.p ... 401#182401>>>>>>>>>>>>>>>>>>>>>> Thomas Bernie> tsbe>>Thomas Bernietsbe________________________________________________________________________________Subject: Pietenpol-List: Re: GN-1 airfoil information

Original Posted By: Oscar Zuniga
Sounds like you could use same kind of info. Saw Xfoil could figure some of theinfo if I figure out the coordinates, but it didn't look like it would give theMAC value. There is pricey software that will give it, but I don't plan onusing this kind of thing much. There is an EAA spreadsheet to calculate the equivelentbiplane MAC, once I get the rest the values, then I can find out whatthe acceptable range is for locating the landing gear axle.. which is reallyimportant.Have little doubt someone has these numbers and did this same exercise.JimRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________

Original Posted By: "jimd"
Jim wrote;> Just had an A&I leave my house after looking over my biplane GN-1 project.Jim, that's always a good thing but remember that these are experimental aircraftand most A&Ps/A&Is are from the certified world and are usually on unfamiliarground. Not only that, they tend to forget that we aren't shooting for certificationand are essentially test pilots, so if we don't get things bang-onwhen we begin testing the aircraft, we can make adjustments and it doesn't affectall of the engineering paperwork that we (didn't) send in to Oklahoma Citywhen we registered the aircraft. That said, my next statement is that I'm NOTan aeronautical engineer and I'm shooting from the hip with what follows, buthere goes.> To correctly determine where the gear should be he said I needed to find outwhere> the CG of the plane isCorrect, but some of that info should have come with the St. Croix "Aerial" biplaneplans that you got from Chad Wille. If not, I guess then you are truly onyour own here.>but with it being a biplane configuration, he said> that I needed to have the mean center of lift information for both the upper> and lower wingsProbably correct if the wings are staggered, which I don't know since I've neverseen the plans for the Aerial, but if there is no stagger then it's just a geometryproblem. If there is no stagger, then in the level configuration (whereW&B is done) the CG range will be the same as for most airplanes in our sizeand class... 22 to 34% of the wing chord, or 13.2 to 20.4" aft of the wing leadingedge.> as well as a number of measurements from the assembled plane,> like information about the spacing horizontally between the wings. Then once> the weights, and measurements are known, the acceptable range of locations for> the axle of the landing gear can be determined from some engineering formulas.There are good, useful rules of thumb for these things and you're on the righttrack with your thinking. Many of the early airplanes, homebuilt and otherwise,were biplanes so a lot of thought has gone into their design and setup. Iwill look through what I have in the way of "armchair engineering" books on thesubject, such as Evans' "Lightplane Designer" and see what I can find.> However presuming my plane has the Grega airfoil, which the plans say have arounder> leading edge.. and which appear to be thicker.. I would think it is a different> airfoil, with different values. Have not seen it listed in the common> airfoils databases.I don't think much changed between the Pietenpol and the Grega until it comes tothe sharpness of the stall (thus the rounder leading edge), and I would thinkthat for purposes of setting up your landing gear it wouldn't matter too much(even though you're essentially in the stall configuration in a 3-point landing).You have to start somewhere unless you are determined to make it an engineeringand aerodynamic analysis, in which case I can't help.As to the earlier mention of the mean aerodynamic chord (MAC), that is for taperedand swept wings, and your wings should both be constant-chord with no sweepso the MAC is simply the chord, which should be 60" for both wings.Oscar ZunigaAir Camper NX41CCSan Antonio, TXmailto: taildrags(at)hotmail.comwebsite at http://www.flysquirrel.net________________________________________________________________________________Subject: Pietenpol-List: Re: GN-1 airfoil information