Brodhead Pietenpol Association

Original Posted By: Isablcorky(at)aol.com
This morning, I dropped by my alma mater, Southern Illinois University, totrack down the wind tunnel that was in the Fluid Dynamics Lab. It has beenover a decade since I took the class and the university has since renovatedthe School of Engineering so I would have been lucky to find it in the sameplace. I had the assistant dean calling several departments to track itdown and it was evidently horse traded to the School of Aviation (where itshould have been in the first place). So I drove out to the airport. I metthe department head and he gave me the grand tour and there it was, rightnext to the supersonic wind tunnel, between several cut-away jet engines,and next to enough airplane stuff to make me want to quit my job and justhang out there every day. He said that they don't use it much, butconsidering that it had the same sample wing section in it as it did 14years ago, I would say they haven't used it at all. He said that if Iwanted to make some wing sections, I could have full access to it. He alsosaid that if I needed some help, they have these things called undergraduatestudents.The only problem is that it only has the instrumentation to do lift anddrag. It would need an additional equipment, such as a third load cell, todetermine center of pressure, which in a university setting is not hard todrum up. Since there has been so much debate regarding the moment generatedby the FC-10 and it other characteristics, I thought a full set of charts onthe airfoil might be nice to have.My questions for the group are: has anyone already produced thisinformation? Is there a computer software package available that analyzeswing sections so building models is not necessary? Not that I wouldn't loveto do this, it's just my time is pretty scare already and I'd hate to wasteit.Robert HainesDu Quoin, Illinois________________________________________________________________________________

Original Posted By: Racing4funn(at)aol.com
Subject: Re: Pietenpol-List: wind tunnelFUCK YOU!!!________________________________________________________________________________

Original Posted By: "Robert Haines"
Subject: Re: Pietenpol-List: wind tunnelRobert, I commend your efforts already! I as a new builder would think that this would be a great asset to all Piet'ers. This would put alot of questions to rest. Greg MenocheDelaware ________________________________________________________________________________

Original Posted By:> "Robert Haines"
Yikes, I hate to think that that's the only response I get from my post!Anyway, last night after sending the following email, I downloaded a fullfeatured demo version of DesignFOIL. The demo only lasts five days, butthat's all I need to get some data on the FC-10. It looks to be an easierand equally valid solution to models in a wind tunnel.Again, if anyone else has generated wing section data for the FC-10, pleaseshare.Robert HainesDu Quoin, Illinois

Original Posted By: BARNSTMR(at)aol.com

Original Posted By: N925WB1(at)aol.com
Robert,Sorry to take a while to get back to you on this topic.I would be very interested in seeing a properly executed wind tunnelanalysis of the Piet airfoil. This has come up a number of times on thisvenue and we never seem to be able to organize well enough to do it.I know Greg Cardinal would like to see it as well as Holcomb and a fewothers.What chord size and width are you contemplating? Would you make the airfoiljust like the real one with ribstitches and everything to have the surfaceas close to actual as possible? I believe the holcomb's Aerodrome websitehas an analysis of the airfoil using one of the canned programs. Does thewind tunnel at SIU work at MSL density or is it pressurized?Chris Bobka________________________________________________________________________________

Original Posted By:> "Christian Bobka"
Chris,The SIU wind tunnel is atmospheric with a test section of 24" in width. Ascale wing I believe would be too small to incorporate detail or an accuratewing section. My inclination is to make a section 6" in cord and the full24" in width. This would be focused toward developing wing sectioninformation as opposed to a three dimensional study.Also, I have been working with DesignFOIL and have been in discussion withKevin Holcomb regarding his results with XFoil. Apparently, there is a lotto be desired with low cost (free) wing section analysis software. I haveresults from DesignFOIL, but they are substantially different from theXFoil. Suffice it to say that there is a difference in location of thecenter of pressure of over 10% cord for a given angle of attack between thetwo programs (imagine designing and building an aircraft and finding thatyou have to move the wing 6", not good).Although I'm an engineer, I don't have any direct experience in wind tunneltests and would appreciate any suggestions to achieve the most accurateresults.Robert HainesDu Quoin, Illinois

Original Posted By: "Robert Haines"
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Original Posted By: "Robert Haines"
Robert,From one Saluki to another, I look forward to results of a wind tunnel teston a Pietenpol airfoil. I am just getting my foot in the door on buildingthe Piet and am looking forward to the thrill of the "First Flight".Alex Sloan----- Original Message -----

Original Posted By: "Alex Sloan"
Yea, a wind tunnel does not provide the results you see in the real world.The only exception I can think of is the full scale wind tunnel at Langleywhere you could actually test a complete airplane. So wind tunnel tests forwing sections or scaled models produce results that provide marginalizedinformation. This usually provides fundamental information to develop aprototype, but the next step is to build the prototype, and then to correctas needed for a production run.The origin of my curiosity for seeking out wind tunnel testing is that itwas mentioned that the FC-10 has some unique characteristics, particularlyit has a large moment (implying that the center of pressure is aft on thewing). But, there was no documented information on the Cl, Cd, or Cm ofthis airfoil to verify and quantify these claims. At the same time, therewere discussions on the appropriate placement of landing gear, discussionsregarding tail volume, discussions regarding trying new wings, anddiscussions on the moving the wing back or increasing the front of theaircraft. All of this really requires knowledge of the relationshipsbetween the CG, center of pressure, and other forces acting on the aircraft.These items seem to be generally known, but nothing (outside of thecollected experience of this group) exists that details them. And althoughsimply determining the properties of the FC-10 wing section will notquantitatively answer all of these questions, it will be fundamentallynecessary and is a pretty good start.You question was not dumb, actually very insightfull. Unfortuately, thereis always error involved when developing information from models (becauseit's not the actual thing) or sample sets (not all things are exactly thesame, but you can't test all things). It then becomes a balance betweenincreasing the detail of testing or moving forward with the currentinformation.Robert "just setting myself up as a target" HainesDu Quoin, IllinoisSubject: Pietenpol-List: Re: wind tunnel==================================Robert and Chris,If I may get in on this discussion, could one of you answer a question thatI have regarding airfoil testing and the real world?The tested airfoil is a reproduction of the profile at the rib and yet inthe real world the fabric sags somewhat between the ribs therefore changingthe profile somewhat. How is this discrepency accounted for in the finalresults? Or must the test section also incorporate these deformitiesbetween the ribs?Just a dumb mechanical engineer trying to get smarter.John==================================________________________________________________________________________________

Original Posted By: Jim Markle
Subject: Re: Pietenpol-List: Re: wind tunnelRobert and friends,Don't over analyze this thing, start making saw dust and build it. You guys are beating this dog to death. If you want to reinvent the wheel go ahead...but in the meantime use the search engine, most of these things have beenaddressed and are archived, if your not too lazy to read old input, which you obviously aren't if you are willing to run all of these tests and calculations.Target acquired, back at ya.In my humble opinion, while you groundlings are still cussing and discussing which is the most efficient design, all the people willing to follow the planswill be flying, albeit a mile or two slower per hour -- but still way over "your" heads !! 75 years, still low and slow...Max, target on his back, DavisArlington, TXDo not achieve________________________________________________________________________________Date: Tue, 17 Feb 2004 12:19:10 -0600 (GMT-06:00)

Original Posted By: "John Dilatush"
John,that was my question to Robert. I would assume that the test section wouldhave to have all the warts of fabric, rib stitches, etc. to make it valid.chris bobka----- Original Message -----

Original Posted By: Gnwac(at)cs.com
Max - starting on my airplane is currently in the queue, it's right behindrestoring my 1866 house (I had it lifted off the foundation and replaced thebasement last winter) and my 1930 Model-A, and this last summer we had oursecond son (yea, my friends and family think I'm nuts). I've got my handsbusy after hours. This wind tunnel thing is something I can sneak in on mylunch hour. More to the point, it's actually part of what I would considermy pre-building "homework" to an aircraft design that I'm sure I willmodify. Until my after-work projects run their course, I'm doing OK flying152's periodically, at least I'm flying.Chris - So if I added little bumps and dips on the 24" scaled wing sectionthe test would then be valid? Otherwise, the information is meaningless?Please reread my previous post regarding error in testing, all testing haserror. At 1/10 scale (I'm considering a wing section with a 6" cord) thesurface irregularities due to rib stitching is too small to matter. Thedeformation of the skin between the ribs is a consideration, but you wouldhave to be a fortune teller to be able to guess what that deformation is toany accuracy since the deformation changes under different speeds and angleof attack. Not to mention there are those who consider adding an aluminumor plywood wrap around the front edge to midigate this and this would thenbe another set of models.Gesh, I'm just trying to do something that would be helpful to the group.Respectfully,Robert HainesDu Quoin, Illinois________________________________________________________________________________

Original Posted By: "bike.mike"
Subject: Re: Pietenpol-List: Re: wind tunnelRobert,Any help and information you can add to the Group would be helpful regarding the FC 10. Please continue. I would like to see what you come up with in theend. Greg MenocheDelaware________________________________________________________________________________

Original Posted By: Robert Haines
Robert, et al:What is it that you expect to learn by performing a wind tunnel test?If you want to enjoy the scientific lab work of building a model, setting upand running a test, and analyzing results, the wind tunnel is a greatexercise that is fun in its own way.If, however, you want to learn how the Piet wing performs, in itsfull-scale, bug-smashed, real-life, application, there are thousands andthousands of hours of actual flight, reported by the thousands of Pietpilots of every possible skill level and scientific background who havebuilt and flown this little beauty in every conceivable configuration andmodification over the last 75 years. A wind tunnel test of any sort, even afull-scale airplane in a large section tunnel at Langley in Virginia or atAmes in California, is only going to give you an approximation of what islearned in actual flight.Enjoy your tunnel testing, but don't expect it to tell you anything usablethat hasn't already been learned.Mike Hardaway(More hours in airplanes than on tunnels, but have enjoyed both for theirown sakes.)----- Original Message -----

Original Posted By: "bike.mike"
Thanks Mike! Well said....----- Original Message -----

Original Posted By: "bike.mike"
Subject: Pietenpol-List: wind tunnel> > Bike.Mike asks-> > >What is it that you expect to learn by performing a wind tunnel test?> > Characteristic curves, man! Graphs of coefficients of lift, and > drag! X > and Y axes, with numbers and things! We nerdy types (I'm an > engineer) live > for graphs and formulae, and when we can reduce "touchy-feely" to > numerical > and graphical quantification, then we can dig in with glee. All > these years > this airfoil has been out there but it was developed by feel and > the > performance results are all empirical. To those of us who live in > the > 'what-if' world, we need graphs and numbers and analyses to slake > our > thirst. To those who are wondering about tweaking the airfoil > (please don't > kick me off the list), a starting point is needed. That starting > point is > the airfoil characteristics, the graphs, the plots, the numbers! > Don't you > see?> > But you knew that, Mike. You wanted to quash technical discussion > out of > respect for a marvelous and time-proven, grand old dame... the > Piet and her > enigmatic airfoil. You wanted to keep people from looking under > her skirts, > from lifting her veil, from seeing her without her makeup on. You > wanted to > protect her from "modernization", from the ugly hands of those who > would > Rutan-ize her and turn her into something other than what she > really needs > to be for all time, for us who see the design in its 75th year of > successful > existence, and for builders and pilots not yet even born. I know > you, Mike! > But cut us engineers a tiny bit of slack and let us play with > the > computers, will ya? It's in our blood...> > Oscar Zuniga> San Antonio, TX> taildrags(at)hotmail.com> website at http://www.flysquirrel.net> > _________________________________________________________________> Stay informed on Election 2004 and the race to Super Tuesday. > > > > > > _-> _-> _-> _-> ======================================================================== > > > > ________________________________________________________________________________

Original Posted By: "bike.mike"
Bike.Mike asks->What is it that you expect to learn by performing a wind tunnel test?Characteristic curves, man! Graphs of coefficients of lift, and drag! X and Y axes, with numbers and things! We nerdy types (I'm an engineer) live for graphs and formulae, and when we can reduce "touchy-feely" to numerical and graphical quantification, then we can dig in with glee. All these years this airfoil has been out there but it was developed by feel and the performance results are all empirical. To those of us who live in the 'what-if' world, we need graphs and numbers and analyses to slake our thirst. To those who are wondering about tweaking the airfoil (please don't kick me off the list), a starting point is needed. That starting point is the airfoil characteristics, the graphs, the plots, the numbers! Don't you see?But you knew that, Mike. You wanted to quash technical discussion out of respect for a marvelous and time-proven, grand old dame... the Piet and her enigmatic airfoil. You wanted to keep people from looking under her skirts, from lifting her veil, from seeing her without her makeup on. You wanted to protect her from "modernization", from the ugly hands of those who would Rutan-ize her and turn her into something other than what she really needs to be for all time, for us who see the design in its 75th year of successful existence, and for builders and pilots not yet even born. I know you, Mike! But cut us engineers a tiny bit of slack and let us play with the computers, will ya? It's in our blood...Oscar ZunigaSan Antonio, TXmailto: taildrags(at)hotmail.comwebsite at http://www.flysquirrel.netStay informed on Election 2004 and the race to Super Tuesday. ________________________________________________________________________________

Original Posted By: Oscar Zuniga
Oscar,I have an engineer's heart, too, and I love numbers as much as anyone. Myconcern is that, considering the understanding that I read between the lineson the list, someone will produce numbers that have no relationship to anyother airfoil numbers. Then I fear that others will use those numbers andassume they're gospel. What good are numbers that can't be relied on?If someone can resurrect Abbot and Von Donhoff and use their techniques andtheir old tunnel at Langley, I'll shut up and groove on those beautifuldrag polars and L/D curves.But if a hobbyist carves a 6" approximation of a Piet wing and claims thathis numbers from a different tunnel can be compared to those of otherairfoils found in NACA Report 824 and give a valid basis for comparison ofthe Piet wing with those other airfoils in flight, he's blowing smoke thickenough to cloud reason.Better numbers can be discerned from the flight testing that has been donefor years on our "grande dame".Mike Hardaway----- Original Message -----

Original Posted By: BARNSTMR(at)aol.com

Original Posted By: "Oscar Zuniga"
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Original Posted By: "bike.mike"
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