Brodhead Pietenpol Association

Original Posted By: "Billy McCaskill"
Subject: Re: Fwd: Propeller Pictures > G'day Steve,> > Leave the scallops. The experimental evidence (?) suggests that the propeller> is more efficient with the scallops. The likely reason is that the scallops> transition the boundary layer from laminar to turbulent. The turbulent boundary> layer then stays attached longer which results in more lift (thrust).> > A propeller is nothing more than a wing spinning in a circle. I suspect that> the Reynolds number is quite low, hence the turbulent boundary layer is better.> > There is a direct analogy with some towing tank studies done on a small sailboat> rudder. The drag on the rudder was actually lower with a slightly rough finish,than with> an ultra smooth finish for the same reason.> > On the other hand, if you don't like the results you can always strip it, sandit> and refinish it. It is harder to do the reverse .> > Dave Rogers> > On 8/22/2013 6:42 PM, Dortch, Steven D MAJ MIL USA NGB wrote:> >UNCLASSIFIED Dr. Dave, As you know I am finishing the restoration on a PietenpolAir camper.> >A gentleman on the Pietenpol list posted this with the attached photos. Thequestion is "Do> >the scallops help or hurt the prop efficiency? " I told him I would ask youas a recognized> >aerodynamics expert.> >> >"I received my CloudCars propeller yesterday. It is a 76 X 38 all maple scimitarthat I> >ordered not finished...which saved me some money and allows me to finish, stain,paint,> >varnish as I want. As shipped, it weighs 10#. With it was a note from Jay Andersonto call> >him for some finishing tips. During our conversation, he told me that they seemto get better> >performance from the props. that are left with the "scallops" intact as opposedto the> >propellers that are sanded smooth. He also recommended that the "fields", (fiberglasscovered> >tips) stay intact. Sounded like most people don't like the rough, patch-worklook of them and> >try to fill/sand smooth. These fields form a nice, hard edge around the woodthat should also> >be left intact. My plan was to sand the propeller smooth and make it as slickas I could.> >After our 40 min. conversation, I am now going to leave the prop. as shipped.Jay said some> >MILD sanding is fine to prep. it for it's first coat of protection, (paint,! varnish,> >stain...) but nothing more than that is needed. MILD sanding between coats isalso OK, but> >keep it to a minimum."> >> >In other words "is it better to leave the "scallops" or is that an Old PilotsTale?> >> >Blue Skies, Steve D. UNCLASSIFIED> > -- > David F. Rogers, PhD, ATP> Professor of Aerospace Engineering (Emeritus)> Annapolis, MD> > Rogers Aerospace Engineering & Consulting> Annapolis, MD> Over 50 years of experience> www.nar-associates.com> 410 271 1968 (c)UNCLASSIFIED________________________________________________________________________________Subject: Pietenpol-List: Re: NX626E

Original Posted By: "Billy McCaskill"
Subject: Re: Fwd: Propeller Pictures > G'day Steve,> > Leave the scallops. The experimental evidence (?) suggests that the propeller> is more efficient with the scallops. The likely reason is that the scallops> transition the boundary layer from laminar to turbulent. The turbulent boundary> layer then stays attached longer which results in more lift (thrust).> > A propeller is nothing more than a wing spinning in a circle. I suspect that> the Reynolds number is quite low, hence the turbulent boundary layer is better.> > There is a direct analogy with some towing tank studies done on a small sailboat> rudder. The drag on the rudder was actually lower with a slightly rough finish,than with> an ultra smooth finish for the same reason.> > On the other hand, if you don't like the results you can always strip it, sandit> and refinish it. It is harder to do the reverse .> > Dave Rogers> > On 8/22/2013 6:42 PM, Dortch, Steven D MAJ MIL USA NGB wrote:> >UNCLASSIFIED Dr. Dave, As you know I am finishing the restoration on a PietenpolAir camper.> >A gentleman on the Pietenpol list posted this with the attached photos. Thequestion is "Do> >the scallops help or hurt the prop efficiency? " I told him I would ask youas a recognized> >aerodynamics expert.> >> >"I received my CloudCars propeller yesterday. It is a 76 X 38 all maple scimitarthat I> >ordered not finished...which saved me some money and allows me to finish, stain,paint,> >varnish as I want. As shipped, it weighs 10#. With it was a note from Jay Andersonto call> >him for some finishing tips. During our conversation, he told me that they seemto get better> >performance from the props. that are left with the "scallops" intact as opposedto the> >propellers that are sanded smooth. He also recommended that the "fields", (fiberglasscovered> >tips) stay intact. Sounded like most people don't like the rough, patch-worklook of them and> >try to fill/sand smooth. These fields form a nice, hard edge around the woodthat should also> >be left intact. My plan was to sand the propeller smooth and make it as slickas I could.> >After our 40 min. conversation, I am now going to leave the prop. as shipped.Jay said some> >MILD sanding is fine to prep. it for it's first coat of protection, (paint,! varnish,> >stain...) but nothing more than that is needed. MILD sanding between coats isalso OK, but> >keep it to a minimum."> >> >In other words "is it better to leave the "scallops" or is that an Old PilotsTale?> >> >Blue Skies, Steve D. UNCLASSIFIED> > -- > David F. Rogers, PhD, ATP> Professor of Aerospace Engineering (Emeritus)> Annapolis, MD> > Rogers Aerospace Engineering & Consulting> Annapolis, MD> Over 50 years of experience> www.nar-associates.com> 410 271 1968 (c)UNCLASSIFIED________________________________________________________________________________Subject: Pietenpol-List: Fwd: Re: Fwd: Propeller Pictures

Original Posted By: dfr
Subject: Pietenpol-List: Fwd: Re: Fwd: Propeller Pictures UNCLASSIFIED Michael Perez and other Pietenfolk, Below is the answer on why you should leavescallops in your prop. The expert is Dave Rogers. He is a professor of aerodynamicsat a little boating school in Annapolis, Maryland. He owns and fliesBonanzas and loves most everything that flies.Blue Skies,Steve D-------- Original Message --------

Original Posted By: "Billy McCaskill"
Outstanding! Very good looking airplane!--------Billy McCaskillBaker, LAtail section almost done, starting on ribs soonRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Fwd: Re: Fwd: Propeller Pictures

Original Posted By: dfr
Subject: Re: Pietenpol-List: Fwd: Re: Fwd: Propeller Pictures UNCLASSIFIEDBilly, Did it come through below? Michael Perez and other Pietenfolk, Below is the answer on why you should leavescallops in your prop. The expert is Dave Rogers. He is a professor of aerodynamicsat a little boating school in Annapolis, Maryland. He owns and fliesBonanzas and loves most everything that flies.Blue Skies,Steve D-------- Original Message --------

Original Posted By: Michael Perez
Still nothing, Steve.--------Billy McCaskillBaker, LAtail section almost done, starting on ribs soonRead this topic online here:http://forums.matronics.com/viewtopic.p ... ______Date: Fri, 23 Aug 2013 03:54:32 -0700 (PDT)

Original Posted By: "Jack Phillips"
Subject: Re: Pietenpol-List: Fwd: Re: Fwd: Propeller Pictures UNCLASSIFIEDDid anyone else get it? It comes back to me complete.On 08/23/13, Billy McCaskill wrote:> > Still nothing, Steve.> > --------> Billy McCaskill> Baker, LA> tail section almost done, starting on ribs soon> > > > > Read this topic online here:> > http://forums.matronics.com/viewtopic.p ... 311#407311> > > > > > > UNCLASSIFIED________________________________________________________________________________

Original Posted By: owner-pietenpol-list-server(at)matronics.com
I got it, and it made perfect sense. It's the same principle as puttingdimples on golf balls to make the boundary layer transition from Laminar toTurbulent flow. It used to be that all golf balls were smooth, but somegolfers discovered that an old, cut up ball with dings and gouges wouldtravel further than a new smooth ball. Wind tunnel testing confirmed it andthe manufacturers starting putting dimples on golf balls. Check out:http://entertainment.howstuffworks.com/ ... 37.htmJack PhillipsNX899JPSmith Mountain Lake, Virginia-----Original Message-----

Original Posted By: Michael Perez
Subject: Re: Pietenpol-List: Fwd: Re: Fwd: Propeller Pictures UNCLASSIFIEDMicheal, sounds like your plane will be a speed demon. Are ready to compete inthe low and really slow experimental division at Reno? Perhaps you should stepup to unlimited! ;+}Blue Skies,Steve DOn 08/23/13, Michael Perez wrote:> > > > Steve, thank you and Dave for the intell. below. I always like to get multipleinputs on matters that I am not sure of one way or another. (The mixing of coveringproducts/techniques is another good thread...) I know here at work we,(not myself personally) have done some work with boundary layers and their advantageto flying surfaces, so what I am hearing seems to ring true.> > I am finished with my propeller, I applied the last coat of varnish yesterday.I did, in fact, leave it as shipped. As Dave mentioned, I figured worst case,I could sand it all down smooth as glass later if needed...sounds like I won't.> > As some of you may know, I also was not concerned with the "glass" like finishon the entire AC; the whole thing is painted by brush. Perhaps that slightly"textured" surface will actually help performance on some small scale...> > Next up is the dimple tape all around all of the exposed round tube and maybethe LE of the streamline tube. (I kid...)> > Thanks again.> > > > Michael Perez> Pietenpol HINT Videos> Karetaker Aero> www.karetakeraero.com> > > > > > > > > G'day Steve,> > > > > > Leave the scallops. The experimental evidence (?) suggests that the propeller> > > is more efficient with the scallops. The likely reason is that the scallops> > > transition the boundary layer from laminar to turbulent. The turbulent boundary> > > layer then stays attached longer which results in more lift (thrust).> > > > > > A propeller is nothing more than a wing spinning in a circle. I suspect that> > > the Reynolds number is quite low, hence the turbulent boundary layer is better.> > > > > > There is a direct analogy with some towing tank studies done on a small sailboat> > > rudder. The drag on the rudder was actually lower with a slightly rough finish,than with> > > an ultra smooth finish for the same reason.> > > > > > On the other hand, if you don't like the results you can always strip it,sand it> > > and refinish it. It is harder to do the reverse .> > > > > > Dave Rogers> > > > > > On 8/22/2013 6:42 PM, Dortch, Steven D MAJ MIL USA NGB wrote:> > > >UNCLASSIFIED Dr. Dave, As you know I am finishing the restoration on a PietenpolAir camper.> > > >A gentleman on the Pietenpol list posted this with the attached photos.The question is "Do> > > >the scallops help or hurt the prop efficiency? " I told him I would askyou as a recognized> > > >aerodynamics expert.> > > > > > > > > > > > > UNCLASSIFIED________________________________________________________________________________Date: Fri, 23 Aug 2013 05:00:38 -0700 (PDT)

Original Posted By: Michael Perez
Subject: Re: Pietenpol-List: Re: NX626EMuy bueeeno!!! Felicitaciones!!!Mario Giacummo2013/8/22 BYD >> Just to prove I=92m not a four flusher ' here=92s the photographic proof I> said would be coming....>> http://youtu.be/0y4PnKwikvM>>> Read this topic online here:>> http://forums.matronics.com/viewtopic.p ... ______Date: Fri, 23 Aug 2013 05:35:53 -0700 (PDT)

Original Posted By: "Billy McCaskill"
Thanks Bill. I'll give it a try this weekend. Hope it doesn't throw off my W&B.--------Scott LiefeldFlying N11MS since March 1972Steel TubeC-85-12Wire WheelsBrodhead in 1996Read this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Fwd: Re: Fwd: Propeller Pictures

Original Posted By: "BYD"
The explanation showed up in the email digest this morning, but wasn't showingup on the forum. Odd.--------Billy McCaskillBaker, LAtail section almost done, starting on ribs soonRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: NX626E

Original Posted By: Claude Corbett
> "speedbrake(at)sbcglobal.n"]> Congratulations Bill! Very nice plane and video. Go Pro I am guessing?> > Michael PerezDrift Innovation HD720Has built in screen (for aiming/setting up) and rotatable lens so if the camerais at an angle you can still get a level shot. Well under $100 new in box atAmazon.Read this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Re: Pietenpol-List: Re: NX626E

Original Posted By: "taildrags"
Sent from my iPadOn Aug 23, 2013, at 12:58 PM, "BYD" wrote:> > > ________________________________________________________________________________Subject: Pietenpol-List: Re: NX626E

Original Posted By: "BYD"
I just had a chance to view the video. Now I see what the patented parking brakelooks like! Super nice flight Bill, and the landing could not have been better.I must say, the prop sure does stop suddenly when you shutdown the engine.Must be that 12:1 compression ;o)I don't think I've ever seen a setup where the cabanes are braced with the X-wireson one side and a brace tube on the other. Makes perfect sense since thepassenger always boards from the port side, but still a little unusual.Congratulations again!--------Oscar ZunigaMedford, ORAir Camper NX41CC "Scout"A75 powerRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: NX626E

Original Posted By: "taildrags"
Hi Oscar, The patented parking brake came to me when I was wondering how to securethe ship at a location that didnt offer someplace to tie the tail. It occurredto me that Id have ropes to tie the plane down and I could use them fordouble-duty like you see in the video.You have seen the cabane support system I used before go back and look at N2431that I used to own and youll recognize it. After a discussion with Vi Kaplerwhere he mentioned that just the cross-wires alone made for a flexing wing,I decided to replicate that feature.And although I am running a high-compression head (for a Model-A), I think thesudden stop is more a factor of a newly broken-in engine. I imagine both factorin.Thanks for the compliments, and now that youre on the west coast again, maybe wellmeet at a function in between our locations!BillRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: NX626E