Original Posted By: "colinc"
Clif and Bill ably covered the answer to this question already, so I won't belabor their points. I would ask, well, why? I'm curious what your rationale would be for wanting to make such a modification?Maybe, as Bill mentioned, part of it may be wanting to avoid welding the fitting. To that end I will quote the learned gentleman from Ohio, Mike Cuy:"I'm impressed by the 120 VAC TIG units on the market out there now.- Very reasonable and if you can't TIG you probably can't finger paint. I was amazed by how easy it was to pickup TIG welding (where you feed the filler rod, it is not fed like in MIG) from a mechanic here at work who taught me over a few lunch hours."If you can machine metal, I bet you could finger paint. Maybe you could buy Mike a few lunches? ;)Have a good night,RyanOn Thu, Nov 13, 2008 at 7:07 PM, Michael Perez wrote:Just a hypothetical question here, lets take the flying strut as an example. Instead of making three pieces and welding them together at the top. Then taking it and fitting it over the strut and running bolts through it, how about making the two side pieces only and mill out the strut to the exact size and thickness of the fittings, epoxy in place and run the bolts through. This will give you the two fittings on either side of the spar, both nestled in its own recess, both flush with the spar face,-epoxied and bolted. What say you?________________________________________________________________________________Subject: Pietenpol-List: Re: spar thickness reduction
Pietenpol-List: spar thickness reduction
Pietenpol-List: spar thickness reduction
Original Posted By: "Cuy, Michael D. (GRC-RXD0)[ASRC]"
Re: Pietenpol-List: spar thickness reduction
Original Posted By: Cuy, Michael D. (GRC-RXD0)[ASRC]
Mike: A 1" I-beam has the same strength as a solid 1" spar but less weight. That is why you would pay the money for a 1" spar. I just finished routing my spars (one-piece wing, so 30' long spars) and wish I had weighed them before and after. I can tell you it is a major difference when you pock them up, though! I looked into a built-up spar with a 1/2" web and 1/4" capstrips on either side, but it was more expensive than solid 1" spars.Gene ----- Original Message -----
Mike: A 1" I-beam has the same strength as a solid 1" spar but less weight. That is why you would pay the money for a 1" spar. I just finished routing my spars (one-piece wing, so 30' long spars) and wish I had weighed them before and after. I can tell you it is a major difference when you pock them up, though! I looked into a built-up spar with a 1/2" web and 1/4" capstrips on either side, but it was more expensive than solid 1" spars.Gene ----- Original Message -----
Pietenpol-List: spar thickness reduction
Original Posted By: Michael Perez
Original Posted By: "Gene Rambo"
Consider that the fibres at the top and bottom of the spar are working in tensionand compression and their effectiveness/stress is proportional to the squareof their distance from the neutral axis. You will understand that those forcesreduce as you move toward the axis so that wood is less 'useful' in resistingbending.However the wood in the middle does have to work to keep those highly loaded partsapart and to carry the shear loads in the spar. However it can be routed awayin areas where it does just that job and isn't carrying any loads into thespar/fittings.Narrowing the whole spar will reduce its beam strength proportionate to the reduction,ie. 25% width reduction = 25% capacity reduction. Not a good thing todo.The best way to make the spar more economically is to go for a top/bottom sprucemembers with a ply web. You'll see many pictures of Pietenpols built that wayon the internet. The Jim Will's wing design , the only one approved in the UK,is built like that but also gains considerable strength from using a ply D-boxleading edge which is integral to the spar design. That design has also facilitateda max weight of 1200 lbs in the UK.Hope that helps?ColinRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________
Consider that the fibres at the top and bottom of the spar are working in tensionand compression and their effectiveness/stress is proportional to the squareof their distance from the neutral axis. You will understand that those forcesreduce as you move toward the axis so that wood is less 'useful' in resistingbending.However the wood in the middle does have to work to keep those highly loaded partsapart and to carry the shear loads in the spar. However it can be routed awayin areas where it does just that job and isn't carrying any loads into thespar/fittings.Narrowing the whole spar will reduce its beam strength proportionate to the reduction,ie. 25% width reduction = 25% capacity reduction. Not a good thing todo.The best way to make the spar more economically is to go for a top/bottom sprucemembers with a ply web. You'll see many pictures of Pietenpols built that wayon the internet. The Jim Will's wing design , the only one approved in the UK,is built like that but also gains considerable strength from using a ply D-boxleading edge which is integral to the spar design. That design has also facilitateda max weight of 1200 lbs in the UK.Hope that helps?ColinRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________
Re: Pietenpol-List: Re: Resessed straps
Original Posted By: Michael Perez
Michael:The depth of the routing is not the issue. The routing according to the plans is rounded off at the edges and are not aligned straight across the spar. The routing you describe for the fitting would substantially decrease the strength of the spar in that location as well as add two sharp stress risers that would ensure that the spar would fail at that point. What you suggested is extremely dangerous. What is more, I cannot understand what you want to gain by doing it? The welded piece across the top of the strut fitting is really unnecessary. I know, everyone is going to call it a "safety strap", but if you pull three bolts out of the spar, that little strap over the top is not going to do anything. You note that the cabane fittings do not have the strap. As I said, it really serves no purpose on the strut fitting, but the cabanes carry basically no load at all (more on the 3-piece wing than the one-piece), so even Bernie did not think it was necessary.Do not hesitate to share your ideas. that way, the really bad ones may get headed off, and the good ones will be shared.Gene ----- Original Message -----
Michael:The depth of the routing is not the issue. The routing according to the plans is rounded off at the edges and are not aligned straight across the spar. The routing you describe for the fitting would substantially decrease the strength of the spar in that location as well as add two sharp stress risers that would ensure that the spar would fail at that point. What you suggested is extremely dangerous. What is more, I cannot understand what you want to gain by doing it? The welded piece across the top of the strut fitting is really unnecessary. I know, everyone is going to call it a "safety strap", but if you pull three bolts out of the spar, that little strap over the top is not going to do anything. You note that the cabane fittings do not have the strap. As I said, it really serves no purpose on the strut fitting, but the cabanes carry basically no load at all (more on the 3-piece wing than the one-piece), so even Bernie did not think it was necessary.Do not hesitate to share your ideas. that way, the really bad ones may get headed off, and the good ones will be shared.Gene ----- Original Message -----
Re: Pietenpol-List: build vs. buy?
Original Posted By: hvandervoo(at)aol.com
I used the spar strap design from the Britts built up spar design on my solid 3/4" spruce spars with 1/8" ply under the straps. The Britt's straps are longer than the origional Piet design and align with the struts at 28 degrees. By being aligned with the struts all three bolts carry the load instead of concentrating the load on the lower bolt as in the origional design. speading the bolt holes farther apart seems like it would help the integrity of the spar and they don't require any welding as there is no strap required across the top. Just another option. Ed G.>From: Michael Perez >Reply-To: pietenpol-list(at)matronics.com>To: pietenpol-list(at)matronics.com>Subject: Re: Pietenpol-List: Re: Resessed straps>Date: Fri, 14 Nov 2008 05:29:06 -0800 (PST)>>I am not looking for a reaction, I am looking for some sound advise on >something that people may not have considered.I miss-spoke before. When I >see the way things are done on the prints, I wonder if there is a way to do >it differently. Not that the original design is bad, I just wonder if over >the years anyone has even thought about other ways.>>I understand the need for the strap to be over the strut, but there are the >fittings on the center section that do not go over the strut... the wing >and cabane fittings. They bolt on the strut with some ply wood underneath. >Some people rout out their spars down to 1/2 in the web area. If I were to >go as deep as 1/8" , which is deeper then needed, I would still have the >1/2" web as well as the two metal fittings both epoxied and bolted. I am no >expert, but I don't see the strength loss. Granted, the wing strut fitting >I understand, but what about the center section fittings?>>With permission Bill, I would like to email you directly my ideas in more >detail with pictures rather then tie up the whole list. It seems that maybe >putting my thoughts out to everyone is not that good of an idea. (Space >wise.)>>________________________________________________________________________________Subject: Re: Pietenpol-List: build vs. buy?Date: Fri, 14 Nov 2008 09:39:10 -0500
I used the spar strap design from the Britts built up spar design on my solid 3/4" spruce spars with 1/8" ply under the straps. The Britt's straps are longer than the origional Piet design and align with the struts at 28 degrees. By being aligned with the struts all three bolts carry the load instead of concentrating the load on the lower bolt as in the origional design. speading the bolt holes farther apart seems like it would help the integrity of the spar and they don't require any welding as there is no strap required across the top. Just another option. Ed G.>From: Michael Perez >Reply-To: pietenpol-list(at)matronics.com>To: pietenpol-list(at)matronics.com>Subject: Re: Pietenpol-List: Re: Resessed straps>Date: Fri, 14 Nov 2008 05:29:06 -0800 (PST)>>I am not looking for a reaction, I am looking for some sound advise on >something that people may not have considered.I miss-spoke before. When I >see the way things are done on the prints, I wonder if there is a way to do >it differently. Not that the original design is bad, I just wonder if over >the years anyone has even thought about other ways.>>I understand the need for the strap to be over the strut, but there are the >fittings on the center section that do not go over the strut... the wing >and cabane fittings. They bolt on the strut with some ply wood underneath. >Some people rout out their spars down to 1/2 in the web area. If I were to >go as deep as 1/8" , which is deeper then needed, I would still have the >1/2" web as well as the two metal fittings both epoxied and bolted. I am no >expert, but I don't see the strength loss. Granted, the wing strut fitting >I understand, but what about the center section fittings?>>With permission Bill, I would like to email you directly my ideas in more >detail with pictures rather then tie up the whole list. It seems that maybe >putting my thoughts out to everyone is not that good of an idea. (Space >wise.)>>________________________________________________________________________________Subject: Re: Pietenpol-List: build vs. buy?Date: Fri, 14 Nov 2008 09:39:10 -0500
RE: Pietenpol-List: build vs. buy?
Original Posted By: "Phillips, Jack"
Subject: Re: Pietenpol-List: build vs. buy?I'll throw my 2 cents into this. I'm building a Mustang II from kits. I have three kids, oldest 4, youngest 1. My wife originally was "in". She was all for it, yes dear, I know it will take a lot of time, I want you to be happy all that. 4 yrs later, I'm still building, and get maybe 24 hours of work in per month. I say per month, because I may go two or three weeks with no work being done, then put in a couple 10 or 12 hour days. Nights don't work for mebecause I like to see my kids before bed time, and by the time they are all inbed, and I see the wife for a bit, it's time for me to go to bed. I could stay up till midnight working on the plane, but I have to maintain a full timejob, like everyone else. You can do it, with a family. But, be prepared to spend 5-10 yrs building, as you have to maintain a good balance between family, work, and building.It is very frustrating at times. Maybe the hardest part, and financially most dangerous, is when you drag the project out so long, the chances of it everbeing finished drop dramatically. If I had it to do over, I think I might buy a completed plane. But, I'm in too deep to stop mid project and take a beating on reselling the parts. I do enjoy the work WHEN I can do it. In the meantime, I dream about the day I can fly again! That's my take. You need to figure out how much time you can really put into building.Boyce________________________________________________________________________________Subject: RE: Pietenpol-List: build vs. buy?Date: Fri, 14 Nov 2008 10:06:13 -0500
Subject: Re: Pietenpol-List: build vs. buy?I'll throw my 2 cents into this. I'm building a Mustang II from kits. I have three kids, oldest 4, youngest 1. My wife originally was "in". She was all for it, yes dear, I know it will take a lot of time, I want you to be happy all that. 4 yrs later, I'm still building, and get maybe 24 hours of work in per month. I say per month, because I may go two or three weeks with no work being done, then put in a couple 10 or 12 hour days. Nights don't work for mebecause I like to see my kids before bed time, and by the time they are all inbed, and I see the wife for a bit, it's time for me to go to bed. I could stay up till midnight working on the plane, but I have to maintain a full timejob, like everyone else. You can do it, with a family. But, be prepared to spend 5-10 yrs building, as you have to maintain a good balance between family, work, and building.It is very frustrating at times. Maybe the hardest part, and financially most dangerous, is when you drag the project out so long, the chances of it everbeing finished drop dramatically. If I had it to do over, I think I might buy a completed plane. But, I'm in too deep to stop mid project and take a beating on reselling the parts. I do enjoy the work WHEN I can do it. In the meantime, I dream about the day I can fly again! That's my take. You need to figure out how much time you can really put into building.Boyce________________________________________________________________________________Subject: RE: Pietenpol-List: build vs. buy?Date: Fri, 14 Nov 2008 10:06:13 -0500
Re: Pietenpol-List: build vs. buy?
Original Posted By: Michael Perez
Re: Pietenpol-List: Re: Resessed straps
Original Posted By: Michael Perez
> Re: Pietenpol-List: Re: Resessed straps
Original Posted By: "Bill Church"
No... the British designed spar straps do not use a welded strap over the top of the spar because there is no torque induced by the pull of the struts like there is in the origional design. Because of their increased angle they do need to be moved outboard about and inch to clear the adjacent rib but that's no biggie unless you learn it the hard way like I did. Ed G.>From: Michael Perez >Reply-To: pietenpol-list(at)matronics.com>To: pietenpol-list(at)matronics.com>Subject: Re: Pietenpol-List: Re: Resessed straps>Date: Fri, 14 Nov 2008 07:11:20 -0800 (PST)>>I believe in the supplemental plans, (I don't have them with me now) the >wing strut "strap" is indeed longer then the original strap. This strap is >also at a smaller angle, (more sloped to the spar) then the original. Are >you saying that this configuration does not need the metal welded piece >over the top of the spar?________________________________________________________________________________
No... the British designed spar straps do not use a welded strap over the top of the spar because there is no torque induced by the pull of the struts like there is in the origional design. Because of their increased angle they do need to be moved outboard about and inch to clear the adjacent rib but that's no biggie unless you learn it the hard way like I did. Ed G.>From: Michael Perez >Reply-To: pietenpol-list(at)matronics.com>To: pietenpol-list(at)matronics.com>Subject: Re: Pietenpol-List: Re: Resessed straps>Date: Fri, 14 Nov 2008 07:11:20 -0800 (PST)>>I believe in the supplemental plans, (I don't have them with me now) the >wing strut "strap" is indeed longer then the original strap. This strap is >also at a smaller angle, (more sloped to the spar) then the original. Are >you saying that this configuration does not need the metal welded piece >over the top of the spar?________________________________________________________________________________
RE: Pietenpol-List: Re: Resessed straps
Original Posted By: owner-pietenpol-list-server(at)matronics.com
Okay, just checking. This last question just seemed to be a little "out inleft field". Thought you might be pulling our collective leg.As for the question of whether there are other ways to do things, of coursether are other ways things can be done. There almost always is (in anyfield). Many people, for one reason or another, have decided to "improve" onthe old design. Some ideas work, and others don't. The most important thingto keep in mind is to have a valid reason for changing anything. When youmake one change, it often will have other, possibly unforseen impacts ofseveral other components or functions of those components. And, before goingahead with any change, one must make sure that the new design will notcompromise the integrity of the resulting structure. But it has been saidmany times over that analysis shows that Mr. Pietenpol pretty much didwhatever he did for a reason. The design works very well the way it has beendrawn. The Air Camper is a sturdy design which allows it to be built by aperson with average skills, and with everyday equipment. It is surprisingthat Pietenpol was able to do what he did, given his lack of formal trainingin engineering or aeronautics. Probably the best known example of someonethinking of other ways to build a Pietenpol was Mr. John Grega, whopublished his plans for the GN-1 Aircamper. This design was touted as a"modern" Pietenpol, and incorporated many design changes. Some would arguethat the design changes were not improvements - just changes. The wing fittings (that attach to the lift struts) carry basically the wholeload when in flight.The cabanes carry very little (something like 50 pounds per cabane) when inflight.Thus, the wing fittings need to be much stronger than the cabane fittings.In general, the spars should not be messed with. They are the mainstructural component of the wings, and any cutting into that wood, to acertain extent, compromises the strength of that member. Having said that,we must recognise that a certain amount of cutting is necessary - namely thedrilling of bolt holes for the attachment of necessary fittings. After all,it doesn't matter how strong the wing is, if the wing isn't attached to thefuselage.The spar acts like an I-beam, such as you might see in any steel structure.When a beam is loaded horizontally (like a wing, or a roof) the top part ofthe beam is placed in compression, and the bottom part is placed in tension.The maximum stresses are in the top-most and bottom-most parts of the beam.The very center of the beam is not stressed (neutral). Because of thisloading, scientists (engineers) determined that beams could be made muchlighter, by using the I-beam shape, as opposed to a solid rectangular shape.The resulting I-beam is almost (but not quite) as strong as a solidrectangular beam of the same dimensions. Since the top-most and bottom-mostedges of the spar are under the maximum stresses, they become the mostcritical parts of the beam. Any reduction in their cross-section (notches,holes, etc.) will dramatically reduce the strength of the beam. When a 1"spruce spar is routed, it is essential that the top and bottom parts, whichdo not get routed are left intact, as these will be carrying the higheststresses.As for direct contact with me, offlist - no problem - fire away.Bill C. _____
Okay, just checking. This last question just seemed to be a little "out inleft field". Thought you might be pulling our collective leg.As for the question of whether there are other ways to do things, of coursether are other ways things can be done. There almost always is (in anyfield). Many people, for one reason or another, have decided to "improve" onthe old design. Some ideas work, and others don't. The most important thingto keep in mind is to have a valid reason for changing anything. When youmake one change, it often will have other, possibly unforseen impacts ofseveral other components or functions of those components. And, before goingahead with any change, one must make sure that the new design will notcompromise the integrity of the resulting structure. But it has been saidmany times over that analysis shows that Mr. Pietenpol pretty much didwhatever he did for a reason. The design works very well the way it has beendrawn. The Air Camper is a sturdy design which allows it to be built by aperson with average skills, and with everyday equipment. It is surprisingthat Pietenpol was able to do what he did, given his lack of formal trainingin engineering or aeronautics. Probably the best known example of someonethinking of other ways to build a Pietenpol was Mr. John Grega, whopublished his plans for the GN-1 Aircamper. This design was touted as a"modern" Pietenpol, and incorporated many design changes. Some would arguethat the design changes were not improvements - just changes. The wing fittings (that attach to the lift struts) carry basically the wholeload when in flight.The cabanes carry very little (something like 50 pounds per cabane) when inflight.Thus, the wing fittings need to be much stronger than the cabane fittings.In general, the spars should not be messed with. They are the mainstructural component of the wings, and any cutting into that wood, to acertain extent, compromises the strength of that member. Having said that,we must recognise that a certain amount of cutting is necessary - namely thedrilling of bolt holes for the attachment of necessary fittings. After all,it doesn't matter how strong the wing is, if the wing isn't attached to thefuselage.The spar acts like an I-beam, such as you might see in any steel structure.When a beam is loaded horizontally (like a wing, or a roof) the top part ofthe beam is placed in compression, and the bottom part is placed in tension.The maximum stresses are in the top-most and bottom-most parts of the beam.The very center of the beam is not stressed (neutral). Because of thisloading, scientists (engineers) determined that beams could be made muchlighter, by using the I-beam shape, as opposed to a solid rectangular shape.The resulting I-beam is almost (but not quite) as strong as a solidrectangular beam of the same dimensions. Since the top-most and bottom-mostedges of the spar are under the maximum stresses, they become the mostcritical parts of the beam. Any reduction in their cross-section (notches,holes, etc.) will dramatically reduce the strength of the beam. When a 1"spruce spar is routed, it is essential that the top and bottom parts, whichdo not get routed are left intact, as these will be carrying the higheststresses.As for direct contact with me, offlist - no problem - fire away.Bill C. _____
RE: Pietenpol-List: spar thickness reduction
Original Posted By: owner-pietenpol-list-server(at)matronics.com
Gene,You're close, but not quite accurate. A solid 1" spar has a bit morestrength than a routed 1" spar (not equal).Here's the brief engineering lesson for the day:Every beam, regardless of the material it is made of, has "SectionProperties". These are properties of the shape (provided the section ishomogeneous - all one material throughout) that are used to determine (whencoupled with material properties), the load carrying capacity of that beam.The Section Property in question here is called the Moment of Inertia aboutthe neutral axis (I sub x). The Moment of Inertia is directly related to theload carrying capacity of the section, so a section with a Moment of Inertiavalue of 2 can carry twice the load that a section with a Moment of Inertiavalue of 1, and only half the load that a section with a value of 4 can, andso on. I have calculated the Moments of Inertia for three spar sections(routed 1", solid 1" and solid 3/4"). Using the routed 1" section as thebasis (since this is the section shown in the plans) we see that a solid 1"spar can actually carry 119% as much as a routed 1" spar, and a solid 3/4"spar can carry 89% as much as a routed 1" spar. This relationship holds, nomatter what material the spar is made of. The actual load carrying capacitycomes when we apply the Material Properties (using the appropriate formulas)for the specific material that the spar is made of (Sitka Spruce, DouglasFir, 7075 Aluminum, old cheese etc.).Calculations done by others have indicated that even the routed 1" spar is abit over-designed (let alone a solid 1" spar), and that a solid 3/4" spar issufficient to carry the loads. As we see from above, the solid 3/4" spar cancarry almost 90% the load that the routed 1" spar can, which allows a Pietbuilder to save money and time.I've made up a simple drawing to show these sections and their Moments ofInertia, and attached it to illustrate.There will be a brief written quiz on Monday. This concludes today's lesson.Bill C. _____
Gene,You're close, but not quite accurate. A solid 1" spar has a bit morestrength than a routed 1" spar (not equal).Here's the brief engineering lesson for the day:Every beam, regardless of the material it is made of, has "SectionProperties". These are properties of the shape (provided the section ishomogeneous - all one material throughout) that are used to determine (whencoupled with material properties), the load carrying capacity of that beam.The Section Property in question here is called the Moment of Inertia aboutthe neutral axis (I sub x). The Moment of Inertia is directly related to theload carrying capacity of the section, so a section with a Moment of Inertiavalue of 2 can carry twice the load that a section with a Moment of Inertiavalue of 1, and only half the load that a section with a value of 4 can, andso on. I have calculated the Moments of Inertia for three spar sections(routed 1", solid 1" and solid 3/4"). Using the routed 1" section as thebasis (since this is the section shown in the plans) we see that a solid 1"spar can actually carry 119% as much as a routed 1" spar, and a solid 3/4"spar can carry 89% as much as a routed 1" spar. This relationship holds, nomatter what material the spar is made of. The actual load carrying capacitycomes when we apply the Material Properties (using the appropriate formulas)for the specific material that the spar is made of (Sitka Spruce, DouglasFir, 7075 Aluminum, old cheese etc.).Calculations done by others have indicated that even the routed 1" spar is abit over-designed (let alone a solid 1" spar), and that a solid 3/4" spar issufficient to carry the loads. As we see from above, the solid 3/4" spar cancarry almost 90% the load that the routed 1" spar can, which allows a Pietbuilder to save money and time.I've made up a simple drawing to show these sections and their Moments ofInertia, and attached it to illustrate.There will be a brief written quiz on Monday. This concludes today's lesson.Bill C. _____
Re: Pietenpol-List: spar thickness reduction
Original Posted By: owner-pietenpol-list-server(at)matronics.com
Subject: Re: Pietenpol-List: spar thickness reductionWell Done and thanks BillJohnIn a message dated 11/14/2008 3:28:55 P.M. Eastern Standard Time, eng(at)canadianrogers.com writes:Gene,You're close, but not quite accurate. A solid 1" spar has a bit more strength than a routed 1" spar (not equal).Here's the brief engineering lesson for the day:Every beam, regardless of the material it is made of, has "Section Properties". These are properties of the shape (provided the section is homogeneous- all one material throughout) that are used to determine (when coupled with material properties), the load carrying capacity of that beam. The Section Property in question here is called the Moment of Inertia about the neutral axis(I sub x). The Moment of Inertia is directly related to the load carrying capacity of the section, so a section with a Moment of Inertia value of 2 cancarry twice the load that a section with a Moment of Inertia value of 1, and only half the load that a section with a value of 4 can, and so on. I have calculated the Moments of Inertia for three spar sections (routed 1", solid 1"and solid 3/4"). Using the routed 1" section as the basis (since this is the section shown in the plans) we see that a solid 1" spar can actually carry 119%as much as a routed 1" spar, and a solid 3/4" spar can carry 89% as much as a routed 1" spar. This relationship holds, no matter what material the spar is made of. The actual load carrying capacity comes when we apply the MaterialProperties (using the appropriate formulas) for the specific material that the spar is made of (Sitka Spruce, Douglas Fir, 7075 Aluminum, old cheese etc.).Calculations done by others have indicated that even the routed 1" spar is a bit over-designed (let alone a solid 1" spar), and that a solid 3/4" spar is sufficient to carry the loads. As we see from above, the solid 3/4" spar can carry almost 90% the load that the routed 1" spar can, which allows a Piet builder to save money and time.I've made up a simple drawing to show these sections and their Moments of Inertia, and attached it to illustrate.There will be a brief written quiz on Monday. This concludes today's lesson.Bill C.____________________________________
Subject: Re: Pietenpol-List: spar thickness reductionWell Done and thanks BillJohnIn a message dated 11/14/2008 3:28:55 P.M. Eastern Standard Time, eng(at)canadianrogers.com writes:Gene,You're close, but not quite accurate. A solid 1" spar has a bit more strength than a routed 1" spar (not equal).Here's the brief engineering lesson for the day:Every beam, regardless of the material it is made of, has "Section Properties". These are properties of the shape (provided the section is homogeneous- all one material throughout) that are used to determine (when coupled with material properties), the load carrying capacity of that beam. The Section Property in question here is called the Moment of Inertia about the neutral axis(I sub x). The Moment of Inertia is directly related to the load carrying capacity of the section, so a section with a Moment of Inertia value of 2 cancarry twice the load that a section with a Moment of Inertia value of 1, and only half the load that a section with a value of 4 can, and so on. I have calculated the Moments of Inertia for three spar sections (routed 1", solid 1"and solid 3/4"). Using the routed 1" section as the basis (since this is the section shown in the plans) we see that a solid 1" spar can actually carry 119%as much as a routed 1" spar, and a solid 3/4" spar can carry 89% as much as a routed 1" spar. This relationship holds, no matter what material the spar is made of. The actual load carrying capacity comes when we apply the MaterialProperties (using the appropriate formulas) for the specific material that the spar is made of (Sitka Spruce, Douglas Fir, 7075 Aluminum, old cheese etc.).Calculations done by others have indicated that even the routed 1" spar is a bit over-designed (let alone a solid 1" spar), and that a solid 3/4" spar is sufficient to carry the loads. As we see from above, the solid 3/4" spar can carry almost 90% the load that the routed 1" spar can, which allows a Piet builder to save money and time.I've made up a simple drawing to show these sections and their Moments of Inertia, and attached it to illustrate.There will be a brief written quiz on Monday. This concludes today's lesson.Bill C.____________________________________
Re: Pietenpol-List: spar thickness reduction
Original Posted By: "walt"
Re: Pietenpol-List: spar thickness reduction
Original Posted By: ALAN LYSCARS
Thanks for the "lesson", but I completely disagree. I won't argue engineering on here though.Gene ----- Original Message -----
Thanks for the "lesson", but I completely disagree. I won't argue engineering on here though.Gene ----- Original Message -----
RE: Pietenpol-List: spar thickness reduction
Original Posted By: "Gene & Tammy"
Gene,What part do you "completely disagree" with?I think this List is a better venue to discuss engineering than it is todiscuss the merits of Chinese imports, so if you take issue with anything Iwrote, please share your thoughts. Maybe I've overlooked something. Unlesssomeone can point out any errors in what I've written, I stand by what Iwrote. By the way, the "lesson" was directed at the list members in general, not anany one person. But more specifically, it was directed to those on the listthat are not familiar with strengths of materials, and who might appreciatea basic explanation of some things that get brought up from time to time,such as spar design.Bill C. ________________________________________________________________________________
Gene,What part do you "completely disagree" with?I think this List is a better venue to discuss engineering than it is todiscuss the merits of Chinese imports, so if you take issue with anything Iwrote, please share your thoughts. Maybe I've overlooked something. Unlesssomeone can point out any errors in what I've written, I stand by what Iwrote. By the way, the "lesson" was directed at the list members in general, not anany one person. But more specifically, it was directed to those on the listthat are not familiar with strengths of materials, and who might appreciatea basic explanation of some things that get brought up from time to time,such as spar design.Bill C. ________________________________________________________________________________
Re: Pietenpol-List: build vs. buy?
Original Posted By: "Jim Ash"
Jim.As I understand it, it is basically the same, except the conditional can be signed off by an A&P and the Annual needs to be signed off by an A&P with an inspection authorization. See FAR 91.409 (c). There may be more to it than that and I'm sure someone here knows ....the rest of the story.Gene in rainy, foggy Tennessee----- Original Message -----
Jim.As I understand it, it is basically the same, except the conditional can be signed off by an A&P and the Annual needs to be signed off by an A&P with an inspection authorization. See FAR 91.409 (c). There may be more to it than that and I'm sure someone here knows ....the rest of the story.Gene in rainy, foggy Tennessee----- Original Message -----
>>>> Pietenpol-List: build vs. buy?
Original Posted By: Michael Perez