Original Posted By: "Cuy, Michael D. (GRC-RXD0)[ASRC AEROSPACE CORP]"
I am seeking information on jury strut material and attachment to spar methods. I understand the off center rational. Is there any advantage to above versus below center on the strut? Are there any photos or drawings showing the bracket on the spar? I assume a bolt through the center of the spar is the least harmful. Where should the second bolt be located? Is there a rule of thumb for distance from the edge of a spar to make a bolt penetration? Is a U shaped bracket with a tab welded on for attachment or two flat strips bolted on better or easier? I have observed various methods of attaching brackets on the struts at the Brodhead meets but have never found a spar bracket to observe.Thank you.Ralph in SD________________________________________________________________________________
Pietenpol-List: jury struts
Pietenpol-List: Re: jury strut to spar idea--attach points
Original Posted By: "tools"
Subject: Pietenpol-List: jury strut to spar idea--attach pointsRalph,I hope this sketch helps you out.Mike C.________________________________________________________________________________Subject: Pietenpol-List: Re: jury strut to spar idea--attach points
Subject: Pietenpol-List: jury strut to spar idea--attach pointsRalph,I hope this sketch helps you out.Mike C.________________________________________________________________________________Subject: Pietenpol-List: Re: jury strut to spar idea--attach points
Original Posted By: Michael Perez
Mike,Based on the spar design and your previous post... I'm guessing this is an archivalsketch as well. Is there a central repository of these available?This sketch answers my previous question about forming the full thickness sectionsas well using 1/2" material as a spar base.Thanks,ToolsRead this topic online here:http://forums.matronics.com/viewtopic.p ... ______Date: Tue, 10 Jan 2012 10:06:53 -0800 (PST)
Mike,Based on the spar design and your previous post... I'm guessing this is an archivalsketch as well. Is there a central repository of these available?This sketch answers my previous question about forming the full thickness sectionsas well using 1/2" material as a spar base.Thanks,ToolsRead this topic online here:http://forums.matronics.com/viewtopic.p ... ______Date: Tue, 10 Jan 2012 10:06:53 -0800 (PST)
RE: Pietenpol-List: jury struts
Original Posted By: owner-pietenpol-list-server(at)matronics.com
Ralph, everyone seems anxious to show how they made their jury strutbrackets without actually answering your questions. Your first question was"is there any advantage to above versus below center on the strut?" Yes,there is an advantage to positioning the jury struts toward the outboardside of the lift strut. What is the advantage? This location requires ashorter jury strut.Your second question was where to drill the holes in the spar to mount thejury strut bracket. Ideally, all holes in the spar should be along theneutral axis, which is the center of the spar. However, as long as theholes are small and are within the central third of the spar.Since everyone else is showing their brackets, I'll show mine:I made them from aluminum angle from Home Depot, bolted to the spar with AN3bolts in that central third of the spar mentioned above. On the rear spars,which are routed, I added a spruce doubler under the bracket. The jurystruts attach to the lift struts with an AN42 eyebolt welded into a holedrilled through the lift struts as described by Mike Cuy.Hope this answers your questions,Jack PhillipsNX899JPSmith Mouuntain Lake, Virginia _____
Ralph, everyone seems anxious to show how they made their jury strutbrackets without actually answering your questions. Your first question was"is there any advantage to above versus below center on the strut?" Yes,there is an advantage to positioning the jury struts toward the outboardside of the lift strut. What is the advantage? This location requires ashorter jury strut.Your second question was where to drill the holes in the spar to mount thejury strut bracket. Ideally, all holes in the spar should be along theneutral axis, which is the center of the spar. However, as long as theholes are small and are within the central third of the spar.Since everyone else is showing their brackets, I'll show mine:I made them from aluminum angle from Home Depot, bolted to the spar with AN3bolts in that central third of the spar mentioned above. On the rear spars,which are routed, I added a spruce doubler under the bracket. The jurystruts attach to the lift struts with an AN42 eyebolt welded into a holedrilled through the lift struts as described by Mike Cuy.Hope this answers your questions,Jack PhillipsNX899JPSmith Mouuntain Lake, Virginia _____
Pietenpol-List: jury struts
Original Posted By: Rick Schreiber
I only get the list every morning, so the "jury strut" answer has alreadybeen put out here, but I feel so strongly about it I want to chime in too.As mentioned.1. This is all discussed in the archives2. The jury strut supports the strut, not the wing3. The jury strut supports the strut in negative G's only4. The wing experiences surprisingly strong G's ALL THE TIME in evenmoderate turbulence (afternoon flights) and landings5. In such a cluttered airframe as a Piet, the "drag" of four jurystruts is probably un-measurable6. The old strut tubing Bernhard used DID have internal webbing, oursdoes NOT.7. There is a substantiated old case of a guy trying to loop a Piet,(idiot) he let some negative G's creep in and the wings folded up.8. Jury struts should not be placed in the center of the strut, butoffset towards the wingtip.In conclusion. DON'T EVEN THINK ABOUT NOT PUTTING JURY STRUTS ON.Douwe________________________________________________________________________________Date: Fri, 24 May 2013 08:57:59 -0500
I only get the list every morning, so the "jury strut" answer has alreadybeen put out here, but I feel so strongly about it I want to chime in too.As mentioned.1. This is all discussed in the archives2. The jury strut supports the strut, not the wing3. The jury strut supports the strut in negative G's only4. The wing experiences surprisingly strong G's ALL THE TIME in evenmoderate turbulence (afternoon flights) and landings5. In such a cluttered airframe as a Piet, the "drag" of four jurystruts is probably un-measurable6. The old strut tubing Bernhard used DID have internal webbing, oursdoes NOT.7. There is a substantiated old case of a guy trying to loop a Piet,(idiot) he let some negative G's creep in and the wings folded up.8. Jury struts should not be placed in the center of the strut, butoffset towards the wingtip.In conclusion. DON'T EVEN THINK ABOUT NOT PUTTING JURY STRUTS ON.Douwe________________________________________________________________________________Date: Fri, 24 May 2013 08:57:59 -0500
Pietenpol-List: Re: jury struts
Original Posted By: "BYD"
Rick,Look at what 20 degrees looks like when you get it set, and I think that you willagree that you are unlikely to pitch the nose up that high on a regular basis,so 20 should work just fine.people don't realize that 25-30 degrees looks like about 45 degrees when simplylooking outside. It is just not a pitch attitude you will see much of.--------Semper Fi,Terry HandAthens, GARead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: jury struts
Rick,Look at what 20 degrees looks like when you get it set, and I think that you willagree that you are unlikely to pitch the nose up that high on a regular basis,so 20 should work just fine.people don't realize that 25-30 degrees looks like about 45 degrees when simplylooking outside. It is just not a pitch attitude you will see much of.--------Semper Fi,Terry HandAthens, GARead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: jury struts
Original Posted By: Mario Giacummo
> Jury struts, Yes or no? YESI made straps that wrap around the lift struts and grab the jury struts out of.025-inch aluminum 1-inch wide quick and easy, but not adequate. While breakingin the Model-A, the brackets on both front lift struts broke. I replacedall brackets with a little thicker stainless-steel brackets and all seems finebut I can tell you those forward struts see a lot of pulsing (vibration) fromthe prop blast even while just sitting on the ground.Find a Piet with jury struts and try to move the struts up and down, then unboltone end of the strut and try again youll quickly see why they are there.Read this topic online here:http://forums.matronics.com/viewtopic.p ... __________
> Jury struts, Yes or no? YESI made straps that wrap around the lift struts and grab the jury struts out of.025-inch aluminum 1-inch wide quick and easy, but not adequate. While breakingin the Model-A, the brackets on both front lift struts broke. I replacedall brackets with a little thicker stainless-steel brackets and all seems finebut I can tell you those forward struts see a lot of pulsing (vibration) fromthe prop blast even while just sitting on the ground.Find a Piet with jury struts and try to move the struts up and down, then unboltone end of the strut and try again youll quickly see why they are there.Read this topic online here:http://forums.matronics.com/viewtopic.p ... __________
Re: Pietenpol-List: jury struts
Original Posted By: Bill Roach
Subject: Re: Pietenpol-List: jury strutsI though jury struts where to kill/eliminate/prevent resonance on strus,that's why they are not in the midle/center of them and are so thin.Mario Giacummo2013/5/24 Douwe Blumberg > I only get the list every morning, so the =93jury strut=94 answer has> already been put out here, but I feel so strongly about it I want to chime> in too.****>> ** **>> As mentioned=85****>> ** **>> 1. This is all discussed in the archives****> 2. The jury strut supports the strut, not the wing****> 3. The jury strut supports the strut in negative G=92s only****> 4. The wing experiences surprisingly strong G=92s ALL THE TIME in even> moderate turbulence (afternoon flights) and landings****> 5. In such a cluttered airframe as a Piet, the =93drag=94 of four jury> struts is probably un-measurable****> 6. The old strut tubing Bernhard used DID have internal webbing, ours> does NOT.****> 7. There is a substantiated old case of a guy trying to loop a Piet,> (idiot) he let some negative G=92s creep in and the wings folded up.****> 8. Jury struts should not be placed in the center of the strut, but> offset towards the wingtip.****>> ** **>> In conclusion. DON=92T EVEN THINK ABOUT NOT PUTTING JURY STRUTS ON.****>> ** **>> Douwe****>> *>============================================> *>>________________________________________________________________________________Date: Fri, 24 May 2013 08:31:34 -0700 (PDT)
Subject: Re: Pietenpol-List: jury strutsI though jury struts where to kill/eliminate/prevent resonance on strus,that's why they are not in the midle/center of them and are so thin.Mario Giacummo2013/5/24 Douwe Blumberg > I only get the list every morning, so the =93jury strut=94 answer has> already been put out here, but I feel so strongly about it I want to chime> in too.****>> ** **>> As mentioned=85****>> ** **>> 1. This is all discussed in the archives****> 2. The jury strut supports the strut, not the wing****> 3. The jury strut supports the strut in negative G=92s only****> 4. The wing experiences surprisingly strong G=92s ALL THE TIME in even> moderate turbulence (afternoon flights) and landings****> 5. In such a cluttered airframe as a Piet, the =93drag=94 of four jury> struts is probably un-measurable****> 6. The old strut tubing Bernhard used DID have internal webbing, ours> does NOT.****> 7. There is a substantiated old case of a guy trying to loop a Piet,> (idiot) he let some negative G=92s creep in and the wings folded up.****> 8. Jury struts should not be placed in the center of the strut, but> offset towards the wingtip.****>> ** **>> In conclusion. DON=92T EVEN THINK ABOUT NOT PUTTING JURY STRUTS ON.****>> ** **>> Douwe****>> *>============================================> *>>________________________________________________________________________________Date: Fri, 24 May 2013 08:31:34 -0700 (PDT)
Re: Pietenpol-List: jury struts
Original Posted By: Jack
Nope. The resonance problem is a result not a cause.By putting the connection in the exact center you arecreating a "node" such that when a sideways motionoccurs on one side an equal but opposite motionis induced in the other side. In essence a wavesimiliar to an electronic sine wave occurs. the rapidbending back and forth will eventualy rip the strutapart in the same manner as you snapping a paperclip by bending it back and forth.By moving the connecting point a short ways fromcenter you destroy the possibilty of resonance.You don't want to make the difference in lengthtoo large however, as you could arrive at a secondarynode. If you know anything about music, you'llunderstand this as harmonics.Clif I though jury struts where to kill/eliminate/prevent resonance on strus, that's why they are not in the midle/center of them and are so thin. Mario Giacummo________________________________________________________________________________Subject: Re: Pietenpol-List: jury struts
Nope. The resonance problem is a result not a cause.By putting the connection in the exact center you arecreating a "node" such that when a sideways motionoccurs on one side an equal but opposite motionis induced in the other side. In essence a wavesimiliar to an electronic sine wave occurs. the rapidbending back and forth will eventualy rip the strutapart in the same manner as you snapping a paperclip by bending it back and forth.By moving the connecting point a short ways fromcenter you destroy the possibilty of resonance.You don't want to make the difference in lengthtoo large however, as you could arrive at a secondarynode. If you know anything about music, you'llunderstand this as harmonics.Clif I though jury struts where to kill/eliminate/prevent resonance on strus, that's why they are not in the midle/center of them and are so thin. Mario Giacummo________________________________________________________________________________Subject: Re: Pietenpol-List: jury struts
Original Posted By: "C N Campbell"
Cliff, to clarify, you mean offset from the center of the strut, correct? Also could you specify how far, an inch, foot? Is it best to offset up or down the strut?Thanks!Sent from my iPadJack TextorOn May 25, 2013, at 2:12 AM, "Clif Dawson" wrote:> Nope. The resonance problem is a result not a cause.> By putting the connection in the exact center you are> creating a "node" such that when a sideways motion> occurs on one side an equal but opposite motion> is induced in the other side. In essence a wave> similiar to an electronic sine wave occurs. the rapid> bending back and forth will eventualy rip the strut> apart in the same manner as you snapping a paper> clip by bending it back and forth.> By moving the connecting point a short ways from> center you destroy the possibilty of resonance.> You don't want to make the difference in length> too large however, as you could arrive at a secondary> node. If you know anything about music, you'll> understand this as harmonics.> > Clif> > > > > > I though jury struts where to kill/eliminate/prevent resonance on strus, that's why they are not in the midle/center of them and are so thin.> Mario Giacummo> > > > > ============================================================================================================================================> ________________________________________________________________________________
Cliff, to clarify, you mean offset from the center of the strut, correct? Also could you specify how far, an inch, foot? Is it best to offset up or down the strut?Thanks!Sent from my iPadJack TextorOn May 25, 2013, at 2:12 AM, "Clif Dawson" wrote:> Nope. The resonance problem is a result not a cause.> By putting the connection in the exact center you are> creating a "node" such that when a sideways motion> occurs on one side an equal but opposite motion> is induced in the other side. In essence a wave> similiar to an electronic sine wave occurs. the rapid> bending back and forth will eventualy rip the strut> apart in the same manner as you snapping a paper> clip by bending it back and forth.> By moving the connecting point a short ways from> center you destroy the possibilty of resonance.> You don't want to make the difference in length> too large however, as you could arrive at a secondary> node. If you know anything about music, you'll> understand this as harmonics.> > Clif> > > > > > I though jury struts where to kill/eliminate/prevent resonance on strus, that's why they are not in the midle/center of them and are so thin.> Mario Giacummo> > > > > ============================================================================================================================================> ________________________________________________________________________________
Re: Pietenpol-List: jury struts
Original Posted By: Jack
Jack, I asked a similar question to Douwe yesterday and he sent me a front view picture of his Piet. By measuring the photo (I copied the picture to a piece of paper first) we determined that the jury struts were moved up the strut (toward the wing) about 6 inches. That's not necessarily the only dimension that will work but at least we know his jury struts do the job they are meant to do. The struts are not moved down the main struts because the added length of the vertical members of the jury struts would just add weight. Chuck ----- Original Message -----
Jack, I asked a similar question to Douwe yesterday and he sent me a front view picture of his Piet. By measuring the photo (I copied the picture to a piece of paper first) we determined that the jury struts were moved up the strut (toward the wing) about 6 inches. That's not necessarily the only dimension that will work but at least we know his jury struts do the job they are meant to do. The struts are not moved down the main struts because the added length of the vertical members of the jury struts would just add weight. Chuck ----- Original Message -----
Re: Pietenpol-List: jury struts
Original Posted By: "Douwe Blumberg"
Yes, from the center. As per chuck's message relating to Douwe's 6"offset. This is obviously good. It certainly hasn't fallenapart.
I think a foot is a bit much but there aresuccessful Piets with what appear to be that much.You could offset either up or down for effect but up will make for shorter vertical arms, saving a fewounces. . I think it looks better too.Clif Cliff, to clarify, you mean offset from the center of the strut, correct? Also could you specify how far, an inch, foot? Is it best to offset up or down the strut? Thanks! Sent from my iPad Jack Textor________________________________________________________________________________
Yes, from the center. As per chuck's message relating to Douwe's 6"offset. This is obviously good. It certainly hasn't fallenapart.
I think a foot is a bit much but there aresuccessful Piets with what appear to be that much.You could offset either up or down for effect but up will make for shorter vertical arms, saving a fewounces. . I think it looks better too.Clif Cliff, to clarify, you mean offset from the center of the strut, correct? Also could you specify how far, an inch, foot? Is it best to offset up or down the strut? Thanks! Sent from my iPad Jack Textor________________________________________________________________________________Pietenpol-List: Re: insurance when hopping rides
Original Posted By: "tools"
Hey all,How does liability work when "hopping" rides, like at Brodhead? What type of insurance covers this, or does it?Douwe________________________________________________________________________________Subject: Pietenpol-List: Re: insurance when hopping rides
Hey all,How does liability work when "hopping" rides, like at Brodhead? What type of insurance covers this, or does it?Douwe________________________________________________________________________________Subject: Pietenpol-List: Re: insurance when hopping rides
Original Posted By: "G Hansen"
Do you mean if you're flying someone else's plane? In the case of what I HAD (justgot a note saying they're not covering planes any more so I'll have to changecompanies...), there was a clause that anyone else could fly my plane andbe covered if they had a tail wheel endorsement, 300 hrs total, I felt they werequalified and some 10 hours in a Piet. If you just mean giving rides, as along as it's "not for hire", or "giving instruction",it was no big deal. ToolsRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________
Do you mean if you're flying someone else's plane? In the case of what I HAD (justgot a note saying they're not covering planes any more so I'll have to changecompanies...), there was a clause that anyone else could fly my plane andbe covered if they had a tail wheel endorsement, 300 hrs total, I felt they werequalified and some 10 hours in a Piet. If you just mean giving rides, as along as it's "not for hire", or "giving instruction",it was no big deal. ToolsRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________
Pietenpol-List: Re: insurance when hopping rides
Original Posted By: "Don Emch"
When I built my Piet many years back I used Aeronca Champion front strut material for the front struts. The welded-in small bushing for the jury strut attachment wound up a few inches outboard of center as a matter of course, and this was not considered a problem. Salvaged rear Taylorcraft struts became my rear struts and small bushings were welded in to match those on the front struts. I had always intended to use jury struts because I had flown a friend=99s Piet that didn=99t have them. His struts seemed to have a definite harmonic vibration related to engine rpm (the propeller was not out of balance or track) and, from an engineering standpoint, jury struts dramatically increase the resistance to buckling in compression. The positioning of my jury struts off center was a happy coincidence in that it established different harmonic modes over the strut length. This was not realised at the time, but sometimes good things just happen.Regardless of what some may say, it is prudent to use jury struts on a high wing airplane, unless the lift struts are of relatively =9Cfat=9D cross section (i.e. Luscombe (metal wing), Cessnas, etc.). Most high wing light planes over the years have them because the lift struts are relatively slim thin-wall streamline tubing, susceptible to buckling under compression loads (negative g in flight or heavy snow loads, etc.).Cheers,Graham Hansen (Pietenpol CF-AUN in Alberta, Canada)________________________________________________________________________________Subject: Pietenpol-List: Re: insurance when hopping rides
When I built my Piet many years back I used Aeronca Champion front strut material for the front struts. The welded-in small bushing for the jury strut attachment wound up a few inches outboard of center as a matter of course, and this was not considered a problem. Salvaged rear Taylorcraft struts became my rear struts and small bushings were welded in to match those on the front struts. I had always intended to use jury struts because I had flown a friend=99s Piet that didn=99t have them. His struts seemed to have a definite harmonic vibration related to engine rpm (the propeller was not out of balance or track) and, from an engineering standpoint, jury struts dramatically increase the resistance to buckling in compression. The positioning of my jury struts off center was a happy coincidence in that it established different harmonic modes over the strut length. This was not realised at the time, but sometimes good things just happen.Regardless of what some may say, it is prudent to use jury struts on a high wing airplane, unless the lift struts are of relatively =9Cfat=9D cross section (i.e. Luscombe (metal wing), Cessnas, etc.). Most high wing light planes over the years have them because the lift struts are relatively slim thin-wall streamline tubing, susceptible to buckling under compression loads (negative g in flight or heavy snow loads, etc.).Cheers,Graham Hansen (Pietenpol CF-AUN in Alberta, Canada)________________________________________________________________________________Subject: Pietenpol-List: Re: insurance when hopping rides
Pietenpol-List: Re: Wing Strut Fittings on Spars
Original Posted By: "Mild Bill"
Subject: Re: Pietenpol-List: jury struts UNCLASSIFIEDGee, it seems that slightly more than half of the Pieters think the strut is agood Idea ;-} (OK so far everyone). Guess, I will keep them.Thanks all for the great input. And thanks Douwe for summarizing it. Blue Skies,Steve D On 05/24/13, Douwe Blumberg wrote:> > > > > I only get the list every morning, so the “jury strut” answer hasalready been put out here, but I feel so strongly about it I want to chime intoo.> > > > As mentioned…> > > > This is all discussed in the archives> The jury strut supports the strut, not the wing> The jury strut supports the strut in negative G’s only> The wing experiences surprisingly strong G’s ALL THE TIME in even moderateturbulence (afternoon flights) and landings> In such a cluttered airframe as a Piet, the “drag” of four jury strutsis probably un-measurable> The old strut tubing Bernhard used DID have internal webbing, ours does NOT.> There is a substantiated old case of a guy trying to loop a Piet, (idiot) helet some negative G’s creep in and the wings folded up.> Jury struts should not be placed in the center of the strut, but offset towardsthe wingtip.> > > > > In conclusion. DON’T EVEN THINK ABOUT NOT PUTTING JURY STRUTS ON.> > > > Douwe> > UNCLASSIFIED________________________________________________________________________________Subject: Pietenpol-List: Re: Wing Strut Fittings on Spars
Subject: Re: Pietenpol-List: jury struts UNCLASSIFIEDGee, it seems that slightly more than half of the Pieters think the strut is agood Idea ;-} (OK so far everyone). Guess, I will keep them.Thanks all for the great input. And thanks Douwe for summarizing it. Blue Skies,Steve D On 05/24/13, Douwe Blumberg wrote:> > > > > I only get the list every morning, so the “jury strut” answer hasalready been put out here, but I feel so strongly about it I want to chime intoo.> > > > As mentioned…> > > > This is all discussed in the archives> The jury strut supports the strut, not the wing> The jury strut supports the strut in negative G’s only> The wing experiences surprisingly strong G’s ALL THE TIME in even moderateturbulence (afternoon flights) and landings> In such a cluttered airframe as a Piet, the “drag” of four jury strutsis probably un-measurable> The old strut tubing Bernhard used DID have internal webbing, ours does NOT.> There is a substantiated old case of a guy trying to loop a Piet, (idiot) helet some negative G’s creep in and the wings folded up.> Jury struts should not be placed in the center of the strut, but offset towardsthe wingtip.> > > > > In conclusion. DON’T EVEN THINK ABOUT NOT PUTTING JURY STRUTS ON.> > > > Douwe> > UNCLASSIFIED________________________________________________________________________________Subject: Pietenpol-List: Re: Wing Strut Fittings on Spars
Pietenpol-List: Re: Jury struts...
Original Posted By: "Mild Bill"
OK. I thought you might be thinking about other places such as the tail. :DLengthening the strut attachment fittings to gain a little clearance for wrenches and washers shouldn't be a problem, assuming the fittings are at least the same thickness as specified on the early plans which had the fittings at an angle only about 25 deg from vertical. That angle would put an eccentric load on the fittings, and if they had enough beef to handle that (and as far as I know there were no failures of eccentrically loaded fittings), then they would have enough beef to handle a little extra length when dealing with a smaller eccentric load (i.e. when the strap fitting is oriented more in line with the strut axis.)Something I would be more concerned about is the cross sectional area between the bottom of the lowest bolt hole going through the spar and the bottom of the spar. In one of the earlier pictures in this thread the depth of this area on a proposed drilling pattern looks to be only a little more than 1/4". The problem is that all of the lift generated outboard of the strut attachment creates a bending moment around the point of attachment, which moment must be resisted by compression along the top of the spar and tension along the bottom. The wood above the neutral axis (essentially the centerline on a spar of this type) only handles compression. The wood between the neutral axis and the top of the lowest bolt hole doesn't handle much tension at all. There isn't any wood or other material to absorb tension loads through the area of the bolt hole. (Well, the bolt is there, but who's got glue strong enough to transmit the tension between the wood and the metal?). So it's basically up to the area between the hole and the bottom of the spar to keep the wing together.A little more than 1/4" depth seems a bit skimpy. What do the plans specify for the distance between the bottom of the spar and the bottom of the lowest hole through the spar?--------Bill FrankRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Jury struts...
OK. I thought you might be thinking about other places such as the tail. :DLengthening the strut attachment fittings to gain a little clearance for wrenches and washers shouldn't be a problem, assuming the fittings are at least the same thickness as specified on the early plans which had the fittings at an angle only about 25 deg from vertical. That angle would put an eccentric load on the fittings, and if they had enough beef to handle that (and as far as I know there were no failures of eccentrically loaded fittings), then they would have enough beef to handle a little extra length when dealing with a smaller eccentric load (i.e. when the strap fitting is oriented more in line with the strut axis.)Something I would be more concerned about is the cross sectional area between the bottom of the lowest bolt hole going through the spar and the bottom of the spar. In one of the earlier pictures in this thread the depth of this area on a proposed drilling pattern looks to be only a little more than 1/4". The problem is that all of the lift generated outboard of the strut attachment creates a bending moment around the point of attachment, which moment must be resisted by compression along the top of the spar and tension along the bottom. The wood above the neutral axis (essentially the centerline on a spar of this type) only handles compression. The wood between the neutral axis and the top of the lowest bolt hole doesn't handle much tension at all. There isn't any wood or other material to absorb tension loads through the area of the bolt hole. (Well, the bolt is there, but who's got glue strong enough to transmit the tension between the wood and the metal?). So it's basically up to the area between the hole and the bottom of the spar to keep the wing together.A little more than 1/4" depth seems a bit skimpy. What do the plans specify for the distance between the bottom of the spar and the bottom of the lowest hole through the spar?--------Bill FrankRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Jury struts...
Original Posted By: "Jack Phillips"
Yep, that's what my father did on his Tailwind. The struts were fabricated fromstreamline steel tubing originally manufactured for use as antenna masts forsome WW II fighter or trainer. A snug fitting dowel was shoved into the centerto prevent buckling if the strut bowed a little bit from negative g's.Somebody else was testing a different Tailwind at full gross load when a sandbagon the passenger side of the seat worked loose and fell into the gap betweenthe seat and the control stick, forcing the stick full forward during high speedflight. The negative g loads were enough to bend the tubing in the fuselagea bit, but the struts never buckled.--------Bill FrankRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________
Yep, that's what my father did on his Tailwind. The struts were fabricated fromstreamline steel tubing originally manufactured for use as antenna masts forsome WW II fighter or trainer. A snug fitting dowel was shoved into the centerto prevent buckling if the strut bowed a little bit from negative g's.Somebody else was testing a different Tailwind at full gross load when a sandbagon the passenger side of the seat worked loose and fell into the gap betweenthe seat and the control stick, forcing the stick full forward during high speedflight. The negative g loads were enough to bend the tubing in the fuselagea bit, but the struts never buckled.--------Bill FrankRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________
RE: Pietenpol-List: Re: Jury struts...
Original Posted By: owner-pietenpol-list-server(at)matronics.com
So what I can gather from this is, if you want to have a plane with no jurystruts, you should build a Tailwind (or buy a later model Cessna).Comparing two different airplanes and saying "gee, this one doesn't havejury struts, so that one obviously doesn't need them" is illogical.Bernard Pietenpol was a practical man. When he designed the Pietenpol, heused strut material that didn't require jury struts to achieve sufficientstiffness, so his plans didn't show jury struts (but did specify the strutmaterial). Once that strut material was no longer available, he added jurystruts to his planes. Note the jury struts in place on the last Air Camperhe built.Buckling under compressive loading is a real phenomenon, which occursanytime the length to thickness ratio of a column (strut) exceeds a criticalvalue, and the compressive loading exceeds a critical load (which issurprisingly small). That ratio can be improved by either making the strutthicker (Cessna's solution) or making it shorter (which is really whataTailwind does - their struts are pretty short). Pietenpols, particularlythose with longer wings or centersections, or those with wings raised higherabove the fuselage (both conditions require longer lift struts) are in therange with a length to thickness ratio that is well into the critical range.Jury struts are easy to make, add little weight and little drag, and addsubstantial safety. Not putting them on is an effective way of declaring tothe world that the builder of the airplane doesn't understand engineering.Jack PhillipsNX899JPSmith Mountain Lake, Virginia-----Original Message-----
So what I can gather from this is, if you want to have a plane with no jurystruts, you should build a Tailwind (or buy a later model Cessna).Comparing two different airplanes and saying "gee, this one doesn't havejury struts, so that one obviously doesn't need them" is illogical.Bernard Pietenpol was a practical man. When he designed the Pietenpol, heused strut material that didn't require jury struts to achieve sufficientstiffness, so his plans didn't show jury struts (but did specify the strutmaterial). Once that strut material was no longer available, he added jurystruts to his planes. Note the jury struts in place on the last Air Camperhe built.Buckling under compressive loading is a real phenomenon, which occursanytime the length to thickness ratio of a column (strut) exceeds a criticalvalue, and the compressive loading exceeds a critical load (which issurprisingly small). That ratio can be improved by either making the strutthicker (Cessna's solution) or making it shorter (which is really whataTailwind does - their struts are pretty short). Pietenpols, particularlythose with longer wings or centersections, or those with wings raised higherabove the fuselage (both conditions require longer lift struts) are in therange with a length to thickness ratio that is well into the critical range.Jury struts are easy to make, add little weight and little drag, and addsubstantial safety. Not putting them on is an effective way of declaring tothe world that the builder of the airplane doesn't understand engineering.Jack PhillipsNX899JPSmith Mountain Lake, Virginia-----Original Message-----