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Help with Spar Decision

 
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Ozzietx



Joined: 06 Jul 2017
Posts: 2
Location: San Antonio, Texas

PostPosted: Sun Sep 17, 2017 7:51 am    Post subject: Help with Spar Decision Reply with quote

I am in the process of building my rib jig, and need to make a decision
on what size spar slot to incorporate.
My priorities are Safety, Weight and cost in that order.
I weigh a little over 200 lbs, and will likely have passengers in that range.
I am attempting to keep my weight down as low as possible. Yes, I know if I were to lose some weight, that would also help me.
I had initially decided on a 1" routed spar.
My concerns with that are weight, and my ability to rout an expensive blank
without screwing it up. I also hate to waste the wood that will be routed out.
Ultimately, I'm sure I can eventually determine how to rout it out.
I have seen mention, and some drawings of the "UK box spar"
I have spent hours using the search function, but have not seen a solid
opinion, and explanation of this design.
From what I understand, this is a required method in the UK for Piet builders. Apparently it is quite light, and strong. From my model airplane
experience, it seems like a great option, that includes a strong D box.
From what I have read, this is a modification that has actually been properly stress analyzed.
I have read many times, just build it as Bernard designed it. I get that, and may very well do exactly that.
I am seeking qualified opinions on the UK box spar idea. In my mind (sometimes a dangerous place) this seems stronger, lighter, and less expensive option.
I do have a complete woodworking shop to fabricate any type of spar.
I would appreciate any input form people that truly understand the box spar design.
Here are a couple of links in which it was discussed:

http://forums.matronics.com/viewtopic.php?t=65138&postdays=0&postorder=asc&start=0&sid=c79b4120a295a0875655e3c1870c5f8a

http://pietenpol.cpc-world.com/?page_id=4376


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jack(at)textors.com
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PostPosted: Sun Sep 17, 2017 8:37 am    Post subject: Help with Spar Decision Reply with quote

This what I did, not flying. Design was checked by engineer.
http://textors.com/SparSketch2.jpg
Other pictures herehttp://textors.com/PietProject.html

Jack Textor
Sent from my iPad
On Sep 17, 2017, at 10:51 AM, Ozzietx <ozzietx(at)gmail.com (ozzietx(at)gmail.com)> wrote:
Quote:
--> Pietenpol-List message posted by: "Ozzietx" <ozzietx(at)gmail.com (ozzietx(at)gmail.com)>

I am in the process of building my rib jig, and need to make a decision
on what size spar slot to incorporate.
My priorities are Safety, Weight and cost in that order.
I weigh a little over 200 lbs, and will likely have passengers in that range.
I am attempting to keep my weight down as low as possible. Yes, I know if I were to lose some weight, that would also help me.
I had initially decided on a 1" routed spar.
My concerns with that are weight, and my ability to rout an expensive blank
without screwing it up. I also hate to waste the wood that will be routed out.
Ultimately, I'm sure I can eventually determine how to rout it out.
I have seen mention, and some drawings of the "UK box spar"
I have spent hours using the search function, but have not seen a solid
opinion, and explanation of this design.
Quote:
From what I understand, this is a required method in the UK for Piet builders. Apparently it is quite light, and strong. From my model airplane
experience, it seems like a great option, that includes a strong D box.
Quote:
From what I have read, this is a modification that has actually been properly stress analyzed.
I have read many times, just build it as Bernard designed it. I get that, and may very well do exactly that.
I am seeking qualified opinions on the UK box spar idea. In my mind (sometimes a dangerous place) this seems stronger, lighter, and less expensive option.
I do have a complete woodworking shop to fabricate any type of spar.
I would appreciate any input form people that truly understand the box spar design.
Here are a couple of links in which it was discussed:

http://forums.matronics.com/viewtopic.php?t=65138&postdays=0&postorder=asc&start=0&sid=c79b4120a295a0875655e3c1870c5f8a

http://pietenpol.cpc-world.com/?page_id=4376


Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=472946#472946

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braywood



Joined: 29 Sep 2012
Posts: 5
Location: Northern Ireland

PostPosted: Sun Sep 17, 2017 12:35 pm    Post subject: Re: Help with Spar Decision Reply with quote

Here is a part of the UK spar drawing - gives you an idea of how it is built - similar to Jack's, but the web is on the front side of the spar. Several areas are blocked in with additional spruce between the caps and some sections of 1/8" ply on the backside as well.
I have not built mine yet, but will use this design, as it requires much smaller pieces of wood! I am told it has been analysed, but have not been able to get any of that info. It is supposed to be good to 1200lb.
Mark


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Greg Cardinal



Joined: 12 Sep 2013
Posts: 47

PostPosted: Sun Sep 17, 2017 1:11 pm    Post subject: Help with Spar Decision Reply with quote

Not UK box spar but worth investigating...

http://www.westcoastpiet.com/images/Construction/I%20Beam%20Analysis.pdf
Greg Cardinal
Minneapolis

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PostPosted: Sun Sep 17, 2017 8:52 pm    Post subject: Help with Spar Decision Reply with quote

Just a word of caution. If you decide to build the Jim Will's "UK Box Spar" then be aware that the wing design has changed from the original.

The Jim Will's design has a different strut attachment point on the wing and four bay's per wing panel rather than three.I'm sure the strut attachment location is significant in the Will's spar design.

Whether the four bay has any significance to the final design strength, I'm not sure.
I am building my wing using Jim will's design as I can't afford to purchase solid spruce spars here in Australia.
JohnW


On 17 September 2017 at 23:51, Ozzietx <ozzietx(at)gmail.com (ozzietx(at)gmail.com)> wrote:
Quote:
--> Pietenpol-List message posted by: "Ozzietx" <ozzietx(at)gmail.com (ozzietx(at)gmail.com)>

I am in the process of building my rib jig, and need to make a decision
on what size spar slot to incorporate.
My priorities are Safety, Weight and cost in that order.
I weigh a little over 200 lbs, and will likely have passengers in that range.
I am attempting to keep my weight down as low as possible. Yes, I know if I were to lose some weight, that would also help me.
I had initially decided on a  1" routed spar.
My concerns with that are weight, and my ability to rout an expensive blank
without screwing it up. I also hate to waste the wood that will be routed out.
Ultimately, I'm sure I can eventually determine how to rout it out.
I have seen mention, and some drawings of the "UK box spar"
I have spent hours using the search function, but have not seen a solid
opinion, and explanation of this design.
>From what I understand, this is a required method in the UK for Piet builders. Apparently it is quite light, and strong. From my model airplane
experience, it seems like a great option, that includes a strong D box.
>From what I have read, this is a modification that has actually been properly stress analyzed.
I have read many times, just build it as Bernard designed it. I get that, and may very well do exactly that.
I am seeking qualified opinions on the UK box spar idea. In my mind (sometimes a dangerous place) this seems stronger, lighter, and less expensive option.
I do have a complete woodworking shop to fabricate any type of spar.
I would appreciate any input form people that truly understand the box spar design.
Here are a couple of links in which it was discussed:

http://forums.matronics.com/viewtopic.php?t=65138&postdays=0&postorder=asc&start=0&sid=c79b4120a295a0875655e3c1870c5f8a

http://pietenpol.cpc-world.com/?page_id=4376




Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=472946#472946






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jarheadpilot82



Joined: 21 Mar 2011
Posts: 673
Location: Athens, GA

PostPosted: Mon Sep 18, 2017 1:33 am    Post subject: Re: Help with Spar Decision Reply with quote

"The Jim Will's design has a different strut attachment point on the wing and four bay's per wing panel rather than three."

John,

I am looking at my Pietenpol plans, specifically, Drawing #5 dated 3/3/34 and drawn by Orrin Hoopman. I see two bays per wing with the lift strut attach point at the compression struts and the point where the two bays converge. What plans show three bays? What plans show four?

Am I missing something?


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PostPosted: Mon Sep 18, 2017 7:11 am    Post subject: Help with Spar Decision Reply with quote

Sorry, my mistake. You're correct. I should have written two bays on the original and three bays on the Will's. My bad. Thanks for the correction Terry.

On 18 Sep. 2017 17:35, "jarheadpilot82" <jarheadpilot82(at)hotmail.com (jarheadpilot82(at)hotmail.com)> wrote:
Quote:
--> Pietenpol-List message posted by: "jarheadpilot82" <jarheadpilot82(at)hotmail.com (jarheadpilot82(at)hotmail.com)>

"The Jim Will's design has a different strut attachment point on the wing and four bay's per wing panel rather than three."

John,

I am looking at my Pietenpol plans, specifically, Drawing #5 dated  3/3/34 and drawn by Orrin Hoopman. I see two bays per wing with the lift strut attach point at the compression struts and the point where the two bays converge. What plans show three bays? What plans show four?

Am I missing something?

--------
Semper Fi,

Terry Hand
Athens, GA




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PostPosted: Mon Sep 18, 2017 7:18 am    Post subject: Help with Spar Decision Reply with quote

I should emphasize though that the different strut attachment point in the Will's design still stands and should be taken into consideration if using his soar design. It would be wise NOT to use his spar design unless you are building from his wing design.

JohnW
On 18 Sep. 2017 23:09, "John Woods" <jawesma(at)gmail.com (jawesma(at)gmail.com)> wrote:
Quote:
Sorry, my mistake. You're correct. I should have written two bays on the original and three bays on the Will's. My bad. Thanks for the correction Terry.

On 18 Sep. 2017 17:35, "jarheadpilot82" <jarheadpilot82(at)hotmail.com (jarheadpilot82(at)hotmail.com)> wrote:
Quote:
--> Pietenpol-List message posted by: "jarheadpilot82" <jarheadpilot82(at)hotmail.com (jarheadpilot82(at)hotmail.com)>

"The Jim Will's design has a different strut attachment point on the wing and four bay's per wing panel rather than three."

John,

I am looking at my Pietenpol plans, specifically, Drawing #5 dated  3/3/34 and drawn by Orrin Hoopman. I see two bays per wing with the lift strut attach point at the compression struts and the point where the two bays converge. What plans show three bays? What plans show four?

Am I missing something?

--------
Semper Fi,

Terry Hand
Athens, GA




Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=472973#472973






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jarheadpilot82



Joined: 21 Mar 2011
Posts: 673
Location: Athens, GA

PostPosted: Mon Sep 18, 2017 8:35 am    Post subject: Re: Help with Spar Decision Reply with quote

John,

No worries. I just wanted to make sure that I was reading the correct set of plans.

I agree with you that is not a good idea to combine different plans and methods for such critical items a spars and wing design. Without having the ability or the funds to pay someone with the ability to analyze the proposed combination, I would caution someone before doing so.


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johnnysdrop



Joined: 30 Jun 2011
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Location: England

PostPosted: Mon Sep 18, 2017 1:17 pm    Post subject: Re: Help with Spar Decision Reply with quote

Ozzietx
I am using the Jim Wills design wing and have built the spars, it is straightforward.
Of note this design is not a box spar, it has a full ply backing on 1 face only and the
other face has ply where there is blocking.
Also of note this is a 3 piece wing and must use a front jury strut.
Please note this design is used in conjunction with the Hoopman drawings for the remainder of the aeroplane.
Regards
English Johnny


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Bill Church



Joined: 21 Feb 2008
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PostPosted: Mon Sep 18, 2017 1:39 pm    Post subject: Re: Help with Spar Decision Reply with quote

One other point to keep in mind, regarding the UK spar design is that it is to be used in conjunction with the leading edge 1/16" plywood wrapping from the top of the front spar all the way around the leading edge, to the bottom of the front spar (practically creating D-cell), as opposed to the original Pietenpol plans which only have the plywood skin on the top side. This added leading edge ply likely is a significant contributor to the claims of being "stronger".
The overall weight of the built-up spar, plus the extra leading edge ply is not significantly lighter than the original routed Spruce spars with original leading edge ply. Cost-wise, there also isn't much savings to be had, in North America, at least. Likely a different story in other parts of the world.


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Ozzietx



Joined: 06 Jul 2017
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Location: San Antonio, Texas

PostPosted: Mon Sep 18, 2017 3:44 pm    Post subject: Re: Help with Spar Decision Reply with quote

I want to thank everyone for their responses.
Since I can get S2 spar spruce in Houston for around $11 Bd Ft,
and I have the ability to rip, and plane that stock,
I think I'll just go with routed 1" spars.

I really appreciate all of the input though, it has been educational.

I did not realize that the Jim Wills spar was part of a structural re-design of the original wing.

While I like the design, I will just keep doing what I hear.

Just build it like Bernard designed it.


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glen



Joined: 17 Sep 2013
Posts: 143
Location: Oregon Coast

PostPosted: Mon Sep 18, 2017 5:44 pm    Post subject: Help with Spar Decision Reply with quote

That's The smartest thing I've heard yet in this discussion. I'm fortunate in that I build Stearman biplanes for a living do you realize that the main spar in a stearman wing has the same dimensions as what Mr Pietenpol calls for in his wing?
The story is that WWII instructors would try to break them by overstressing in a dive. It couldn't be done. Stearman spars aren't routed like what you're talking about but that was more of a manufacturing process issue than caring about saving a little weight
One other curiosity as a testament to just how robust the pietenpol really is. Stearman cap strips:7/32 square 1/16 gussets. Pietenpol capstrips:1/2 X1/4. Centers about the same. Same warren truss beefier nose rib gussets aluminum sheeted l.e.for Stearman

Quote:
On Sep 18, 2017, at 4:44 PM, Ozzietx <ozzietx(at)gmail.com> wrote:



I want to thank everyone for their responses.
Since I can get S2 spar spruce in Houston for around $11 Bd Ft,
and I have the ability to rip, and plane that stock,
I think I'll just go with routed 1" spars.

I really appreciate all of the input though, it has been educational.

I did not realize that the Jim Wills spar was part of a structural re-design of the original wing.

While I like the design, I will just keep doing what I hear.

Just build it like Bernard designed it.




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