Original Posted By: "Christian Bobka"
I have completed my examination of the Pietenpol Airfoil. I started withthe coordinates in the 1932 Flying and Glider Manual with the exception thatI used two mid chord upper surface coordinates from the 1933 manual (skyscout) as they provided a much smoother curve. Using an engineers scaleand a pair of dividers I took my best guess on the leading edge based on thecurve shown in the 1932 manual. Then I keyed the points into the computerand used several lofting features in unigraphics to get a best fit throughthe points. By allowing the software to move the points around by up to1/32 I was able to get a much smoother curve. As the dimensions shown wereonly to the nearest 1/32 some smoothing was required. From there Inormalized the airfoil (divided the x and y by the chord length) and createda number of additional points on the curve to provide better definition forXFOIL (the airfoil analysis package that I used.) XFOIL is interactiveprogram for the development/analysis of airfoils developed by Mark Drela atMIT (thanks Mark). Best of all it is freeware(http://raphael.mit.edu/xfoil/). XFOIL can provide both viscous andinviscid solutions.Based on this analysis I can say that the Pietenpol airfoil isnt bad, butits not great either. It has good lift characteristics, however it is ahigh drag airfoil. Here is a sumary of my results:At Reynolds number 1,600,000 (35 mph, Sea Level, 60 inch chord):2 deg angle of attack: Cl=.8087, Cm=-.0929, Cd=.00691, L/D=116.964 deg angle of attack: Cl=1.0248, Cm=-.0939, Cd=.00881, L/D=116.3510 deg angle of attack: Cl=1.4898, Cm=-.0702, Cd=.02173, L/D=68.5612 deg angle of attack: Cl=1.5361, Cm=-.0578, Cd=.03447, L/D=44.56At Reynolds number 3,500,000 (75 mph, Sea Level, 60 inch chord)2 deg angle of attack: Cl=.8177, Cm=-.0949, Cd=.00790, L/D=103.544 deg angle of attack: Cl=1.0357, Cm=-.0960, Cd=.00753, L/D=137.5710 deg angle of attack: Cl=1.5665, Cm=-.0813, Cd=.01685, L/D=92.9512 deg angle of attack: Cl=1.6723, Cm=-.0697, Cd=.02303, L/D=72.62For comparison I ran a few modern airfoils also using XFOIL and divided thepietenpol numbers by the modern airfoil numbers. Here is a summary of thoseresults:Piet/NACA4412 at Re=1,600,000, angle of attack=12 deg (i.e. take off /landing performace) : Cl= 97% (higher than 100% means pietenpol airfoilprovides more lift), Cm=84% (higher than 100% means pietenpol airfoil has ahigher pitching moment which is generally considered bad), Cd=170% (higherthan 100% means the pietenpol airfoil is higher drag, high is bad.)NACA 4412, Re=3,500,000, angle of attack=2 deg (cruise performance):Cl=116%, Cm=90%, Cd=144%.NACA 2412, Re=1,600,000, angle of attack = 12 deg: Cl=106%, Cm=177%,Cd=196%.NACA 2412, Re=3,500,000, angle of attack = 2 deg: Cl=175%, Cm=179%, Cd=156%NACA 23012, Re=1,600,000, angle of attack = 12 deg: Cl=108%, Cm=932%,Cd=243%.NACA 23012, Re=3,500,000, angle of attack = 2 deg, Cl=234%, Cm=999%,Cd=141%.Bottom line is that it is easy to see why this airfoil is not in use oncurrent production airplanes. That said, it does in general provide aboveaverage lift. The Cm is high, but is within that of the NACA 4412 which isa well accepted low speed airfoil. Cd is very high; however, if speed iswhat you desire, you probably are not building a Pietenpol. For furtherstudy I would like to repeat the process with the Clark Y and the Eiffel 36to better understand how this airfoil compares with other contemporaryairfoils.Just for grins I used the Clmax computed by XFOIL to predict stall speed andcame up with 43 mph at 1010 lbs and just barely under 45 mph at 1080 lbs.Actual numbers may be slightly worse than these as they are based on 2dimensional airfoils. These numbers are just within the 45 mph limit in theSport Pilot NPRM. These numbers are probably good enough for rough order ofmagnitude calculations, however beyond that they should not be taken asanything more than an educated guess. Also, as with everything else, yourmilage will vary.Kevin Holcombhttp://www.angelfire.com/va2/aerodrome/----- Original Message -----
Pietenpol-List: Pietenpol airfoil properties
Re: Pietenpol-List: Pietenpol airfoil properties
Original Posted By: "Michael Brusilow"
Kevin,Are you suggesting alternatives to the traditional Piet airfoil(s)?Robert HainesDu Quoin, Illinois________________________________________________________________________________
Kevin,Are you suggesting alternatives to the traditional Piet airfoil(s)?Robert HainesDu Quoin, Illinois________________________________________________________________________________
Re: Pietenpol-List: Pietenpol airfoil properties
Original Posted By: "Robert Haines"
Nope. I can't imagine building a Pietenpol with anyone elses airfoil. Thatsaid, it does suggest that there is room for a new plane along the samelines as a Pietenpol. Perhaps a future project; I seem to have no troublefinding intersting projects for the future. For now I have a large enoughproject just deciding between the various options in the existing plans.Long fuselage or short? Steel tube or wood? Change the wing ribs to 1/4 x1/4 instead of the 1/2 x 1/4? Fir or Spruce? Tail wheel or skid? Darn, ifI add a steerable tailwheel I need brakes, and the rudder horn probablyneeds to be moved to the bottom. Speaking of brakes, should they be toe,heel or actuated by a lever on the stick? Jury struts or heavier struts?Should I add a door to the forward cockpit? At the Pietenpol flyin lastSunday (Arthur Dunn Airpark), my old lady saw that other builders put themin and is being most persistant in her demands for a door (that is one thingit would have been better if she hadn't seen.) Should I raise the turtledeck to allow for the shoulder harness ancors to be above my shoulders? Andmost of all, model A or A-65. Worst of all is if I went with a model A Iwould probably want to relocate the radiator (howabout beneath the fuselagelike on several OX-5 airplanes with a header tank in the wing leading edge)as it is darn hot most of the year here in Florida. Anyway, those questionsright now are my own personal hell. I settled on the Piet because it has 2seats, is a reasonable first project and has the look and feel of anantique. That said, I want to make it as close to prints as possible, butwhich prints? The tail wheel is very tempting as there are so few grassstrip destinations but the cascading design changes are enough to drive meto drink.I ran the numbers for my own understanding. What is interesting is it doesexplain how the Pietenpol gets away with a fairly small wing (140 sq ft) fora two seater. The drag numbers are not quite as bad if you compare the Pietat 0 deg (Cl=.6) to the other airfoils at the same Cl value (the 23012 wouldneed to be at a bit over 4 deg angle of attack). However, the Piet is stilla high drag airplane even if you look at it from that point of view. Atbest it has 25% more drag than you would expect from a modern airfoil. Asdrag is a product of velocity squared and the Pietenpol has so littlevelocity, I am not sure it matters. I'll keep it close to the plans and beprepared to descend rapidly when the engine fails. Although the high dragwill preclude much of a glide, the high lift will allow you to use smallerfields should you have to. I cant imagine trying to use the airplane forserious transportation (serious recreation is more my speed.) I suppose youcould clean it up, replace the cables with streamline wires, use internalpushrods instead of external wires, change the airfoil, fair everything insight and pick up a bit of speed. Thats more of a project than I want, andI cant help but wonder 'why bother'? If thats what I wanted I suppose Iwould build a Bakeing Duce.Best Regards,Kevin Holcomb----- Original Message -----
Nope. I can't imagine building a Pietenpol with anyone elses airfoil. Thatsaid, it does suggest that there is room for a new plane along the samelines as a Pietenpol. Perhaps a future project; I seem to have no troublefinding intersting projects for the future. For now I have a large enoughproject just deciding between the various options in the existing plans.Long fuselage or short? Steel tube or wood? Change the wing ribs to 1/4 x1/4 instead of the 1/2 x 1/4? Fir or Spruce? Tail wheel or skid? Darn, ifI add a steerable tailwheel I need brakes, and the rudder horn probablyneeds to be moved to the bottom. Speaking of brakes, should they be toe,heel or actuated by a lever on the stick? Jury struts or heavier struts?Should I add a door to the forward cockpit? At the Pietenpol flyin lastSunday (Arthur Dunn Airpark), my old lady saw that other builders put themin and is being most persistant in her demands for a door (that is one thingit would have been better if she hadn't seen.) Should I raise the turtledeck to allow for the shoulder harness ancors to be above my shoulders? Andmost of all, model A or A-65. Worst of all is if I went with a model A Iwould probably want to relocate the radiator (howabout beneath the fuselagelike on several OX-5 airplanes with a header tank in the wing leading edge)as it is darn hot most of the year here in Florida. Anyway, those questionsright now are my own personal hell. I settled on the Piet because it has 2seats, is a reasonable first project and has the look and feel of anantique. That said, I want to make it as close to prints as possible, butwhich prints? The tail wheel is very tempting as there are so few grassstrip destinations but the cascading design changes are enough to drive meto drink.I ran the numbers for my own understanding. What is interesting is it doesexplain how the Pietenpol gets away with a fairly small wing (140 sq ft) fora two seater. The drag numbers are not quite as bad if you compare the Pietat 0 deg (Cl=.6) to the other airfoils at the same Cl value (the 23012 wouldneed to be at a bit over 4 deg angle of attack). However, the Piet is stilla high drag airplane even if you look at it from that point of view. Atbest it has 25% more drag than you would expect from a modern airfoil. Asdrag is a product of velocity squared and the Pietenpol has so littlevelocity, I am not sure it matters. I'll keep it close to the plans and beprepared to descend rapidly when the engine fails. Although the high dragwill preclude much of a glide, the high lift will allow you to use smallerfields should you have to. I cant imagine trying to use the airplane forserious transportation (serious recreation is more my speed.) I suppose youcould clean it up, replace the cables with streamline wires, use internalpushrods instead of external wires, change the airfoil, fair everything insight and pick up a bit of speed. Thats more of a project than I want, andI cant help but wonder 'why bother'? If thats what I wanted I suppose Iwould build a Bakeing Duce.Best Regards,Kevin Holcomb----- Original Message -----
Re: Pietenpol-List: Pietenpol airfoil properties
Original Posted By: Kip & Beth Gardner
Re: Pietenpol-List: Pietenpol airfoil properties
Original Posted By: "Christian Bobka"
Kip Gardner pointed out:> I have an old copy of KitPlanes that has a picture of a Piet with the> radiator up front, like on a Model A (the car). The prop shaft goesthrough> the radiator.There have been Piets as well in which the radiator was mounted under theengine, tilted to minimize the vertical size, with air ducted through it andexiting the bottom of the cowl. The radiator itself was half as high asusualand with two layers. Can't remember whether the water ran through themin parallel or in series. I believe The Master himself built one such, butyou've already seen what my memory is like. No idea whether it workedwell enough, or whether the improved visibility was useful enough, tojustify going to all the work.Owen Davies________________________________________________________________________________
Kip Gardner pointed out:> I have an old copy of KitPlanes that has a picture of a Piet with the> radiator up front, like on a Model A (the car). The prop shaft goesthrough> the radiator.There have been Piets as well in which the radiator was mounted under theengine, tilted to minimize the vertical size, with air ducted through it andexiting the bottom of the cowl. The radiator itself was half as high asusualand with two layers. Can't remember whether the water ran through themin parallel or in series. I believe The Master himself built one such, butyou've already seen what my memory is like. No idea whether it workedwell enough, or whether the improved visibility was useful enough, tojustify going to all the work.Owen Davies________________________________________________________________________________
RE: Pietenpol-List: Pietenpol airfoil properties
Original Posted By: owner-pietenpol-list-server(at)matronics.com
Kevin,Excellent analysis. I need to reread.Did you mean knots at the end when referencing sport pilot?Chris-----Original Message-----
Kevin,Excellent analysis. I need to reread.Did you mean knots at the end when referencing sport pilot?Chris-----Original Message-----
Re: Pietenpol-List: Pietenpol airfoil properties
Original Posted By: "Christian Bobka"
Thanks, I did it for myself, however I am glad that others are interested.Please let me know if you find any errors as there is much that I can learn.I meant 39 knots/45 mph. I believe that is the requirement for stall speedin the landing configuration. Folks with flaps also have to worry about 45knots/52 mph which applies to the cruise configuration, but thats not aPietenpol problem. Are these numbers incorrect? I must admit I didnt go tothe source (the actuall NPRM) when I grabbed those numbers, I pulled themout of an EAA publication.Kevin----- Original Message -----
Thanks, I did it for myself, however I am glad that others are interested.Please let me know if you find any errors as there is much that I can learn.I meant 39 knots/45 mph. I believe that is the requirement for stall speedin the landing configuration. Folks with flaps also have to worry about 45knots/52 mph which applies to the cruise configuration, but thats not aPietenpol problem. Are these numbers incorrect? I must admit I didnt go tothe source (the actuall NPRM) when I grabbed those numbers, I pulled themout of an EAA publication.Kevin----- Original Message -----
RE: Pietenpol-List: Pietenpol airfoil properties
Original Posted By: owner-pietenpol-list-server(at)matronics.com
We have been waiting for someone to do this a long time. can you compare itto a Munk M-6 in addition to the clark Y? Also maybe the USA 35B used onthe J-3 cub?-----Original Message-----
We have been waiting for someone to do this a long time. can you compare itto a Munk M-6 in addition to the clark Y? Also maybe the USA 35B used onthe J-3 cub?-----Original Message-----
Re: Pietenpol-List: Pietenpol airfoil properties
Original Posted By: John_Duprey(at)vmed.org
While I have no hard data on the stalling speed of the Pietenpol,it seems that each of the four different Pietenpols I have flownstalled at considerably less than 45 mph. Over the years, I havehad many opportunities to test my Pietenpol's landing speed against that of other lightplanes.Back in the 1970's, I was able to compare its touchdown speedto that of my 65 hp.Taylorcraft BC12D and this was noticeablyless than that of the T'Craft under the same conditons. How much, I cannot say, but it was less than the 38 - 40 mph stalling/landingspeed of the T'Craft. I didn't compare ASI readings at the stall be-cause they were unreliable (position error, etc.). Only three-point,engine at idle, landings were made.Later on I owned a Luscombe 8E with a stated power-off stalling speed of 48 mph. Its touchdown speed was dramatically higherthan that of my Pietenpol. My son had a rag wing Luscombe 8A,but it too landed somewhat faster than my Piet.At present I have a 65hp. Wag-A-Bond reproduction of a PiperPA 17 Vagabond which is pretty much stock. The advertised stalling speed of the PA 17 is 45 mph. Again, its touchdown speed is dramatically higher than that of my Piet under the sameconditions of loading, etc.So my conclusion is that a Pietenpol should easily meet the 45mph stalling speed requirement. Of course, if a Piet is too heavyits stalling speed could crowd that 45 mph figure.This analysis is great and finally we know how it compares withother airfoil types. BHP was looking for a section with good lift-ing capability and it seems he found it. He needed lots of lift onlow power and speed wasn't a priority. Locally we have a saying that Pietenpols have a "hull speed", like that of a boat, and they cannot be forced to go much faster. Besides the obvious parasitedrag, the airfoil analysis shows why this is so.Graham Hansen (Pietenpol CF-AUN)________________________________________________________________________________
While I have no hard data on the stalling speed of the Pietenpol,it seems that each of the four different Pietenpols I have flownstalled at considerably less than 45 mph. Over the years, I havehad many opportunities to test my Pietenpol's landing speed against that of other lightplanes.Back in the 1970's, I was able to compare its touchdown speedto that of my 65 hp.Taylorcraft BC12D and this was noticeablyless than that of the T'Craft under the same conditons. How much, I cannot say, but it was less than the 38 - 40 mph stalling/landingspeed of the T'Craft. I didn't compare ASI readings at the stall be-cause they were unreliable (position error, etc.). Only three-point,engine at idle, landings were made.Later on I owned a Luscombe 8E with a stated power-off stalling speed of 48 mph. Its touchdown speed was dramatically higherthan that of my Pietenpol. My son had a rag wing Luscombe 8A,but it too landed somewhat faster than my Piet.At present I have a 65hp. Wag-A-Bond reproduction of a PiperPA 17 Vagabond which is pretty much stock. The advertised stalling speed of the PA 17 is 45 mph. Again, its touchdown speed is dramatically higher than that of my Piet under the sameconditions of loading, etc.So my conclusion is that a Pietenpol should easily meet the 45mph stalling speed requirement. Of course, if a Piet is too heavyits stalling speed could crowd that 45 mph figure.This analysis is great and finally we know how it compares withother airfoil types. BHP was looking for a section with good lift-ing capability and it seems he found it. He needed lots of lift onlow power and speed wasn't a priority. Locally we have a saying that Pietenpols have a "hull speed", like that of a boat, and they cannot be forced to go much faster. Besides the obvious parasitedrag, the airfoil analysis shows why this is so.Graham Hansen (Pietenpol CF-AUN)________________________________________________________________________________
Pietenpol-List: rudder pedals
Original Posted By: "Mike Bell"
05/21/2002 07:51:56 AMHi Javier: Please send me photos of this at: John_Duprey(at)vmed.orgThanksJohnjavier cruz (at)matronics.com on 05/21/2002 12:55:50 AMPlease respond to pietenpol-list(at)matronics.comSent by: owner-pietenpol-list-server(at)matronics.comcc:Subject: Pietenpol-List: rudder pedalsHi groupAfter to take a training on St. Louis MO, i had timeto visit Creeve airport , there was friendly man thatis building a Piet and have too a beautifull biplane,so a good museum with about 45 old planes, greatvisit.About the Piet, i change the rudder bar with twosmallest bars joined by an "T" arm with pedals whitthree pivot points so the arm for the peddals ever is90 degrees with the longitudinal axe, i use standardaluminium pedal and brakes, about the weight is 700grs. This bars not send pressure to the rudder , thisis just experimental, but this fill god. Let my trya little draw of this.. ***** pedals pivot point || |||||| | T arm || small bars T arm ||=============|| ||||||| | | ||||||| ***** ||=============|| *****If you put the pedals directly on the rudder bar, thepedal turn and maybe you have a toe pain, other youcan't use cylinders brakes on the rear side so pedalswith "I" support for the front side, joined with 3/84130 tubbing, i have all for brakes on the front, butbecause the planes like a Piet (with tail wheel)arebrake sensitive , i let the front side whitout brakes,i know, whit my poor english this is hard tounderstand, if someone is interesting on the pedals ican e-mail directly some pictures of this so some caddrawings ..SaludosJavier Cruzhttp://launch.yahoo.com________________________________________________________________________________
05/21/2002 07:51:56 AMHi Javier: Please send me photos of this at: John_Duprey(at)vmed.orgThanksJohnjavier cruz (at)matronics.com on 05/21/2002 12:55:50 AMPlease respond to pietenpol-list(at)matronics.comSent by: owner-pietenpol-list-server(at)matronics.comcc:Subject: Pietenpol-List: rudder pedalsHi groupAfter to take a training on St. Louis MO, i had timeto visit Creeve airport , there was friendly man thatis building a Piet and have too a beautifull biplane,so a good museum with about 45 old planes, greatvisit.About the Piet, i change the rudder bar with twosmallest bars joined by an "T" arm with pedals whitthree pivot points so the arm for the peddals ever is90 degrees with the longitudinal axe, i use standardaluminium pedal and brakes, about the weight is 700grs. This bars not send pressure to the rudder , thisis just experimental, but this fill god. Let my trya little draw of this.. ***** pedals pivot point || |||||| | T arm || small bars T arm ||=============|| ||||||| | | ||||||| ***** ||=============|| *****If you put the pedals directly on the rudder bar, thepedal turn and maybe you have a toe pain, other youcan't use cylinders brakes on the rear side so pedalswith "I" support for the front side, joined with 3/84130 tubbing, i have all for brakes on the front, butbecause the planes like a Piet (with tail wheel)arebrake sensitive , i let the front side whitout brakes,i know, whit my poor english this is hard tounderstand, if someone is interesting on the pedals ican e-mail directly some pictures of this so some caddrawings ..SaludosJavier Cruzhttp://launch.yahoo.com________________________________________________________________________________