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Old Jan 05, 2012, 07:28 PM
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Knoll53's Avatar
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Ortrographic Views

Should have mentioned, previous views were perspective.
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Old Jan 06, 2012, 03:37 AM
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Originally Posted by Knoll53 View Post
Let me ask about "copyleft" agreement. I plan on publishing my drawings derived from your work here in this forum as part of the build log. I trust that that is an acceptable use. Let me know if there are any restrictions. As standard practice in my drawings, I will list you as the designer and copyright owner.
Kent, you can publish the plans anywhere you want. The only condition is that you cannot change the licence type, i.e. once open source always open source. By the way, one is not obliged to publish So, if you should want to publish, you can do it here. If you agree, I would like to put also a copy into the Horten-Manatee repository at SourceForge to get a nice and round open design package.

The Rhino pictures look great!

Regards,
Andrés
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Old Jan 06, 2012, 05:08 AM
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Version 0.1 available

Hi,

I used the morning to calculate the load distributions. I included a graph into the project of the
  • bending moment
  • shearing force
  • torsional moment
  • mass distribution

I assumed a load factor of n=20, which is quiet a lot: full pull-up at 40 m/s. Use it, therefore, only as a reference and decide yourself what you want it to withstand. The load distributions were determined along the main spar shown in yellow in the DXF file. The distribution is shown against the spanwise coordinate. Do not get confused, the loads are still along the spar!

Best ragrds,

Andrés
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Old Jan 06, 2012, 07:54 AM
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Knoll53's Avatar
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Originally Posted by andrecillo76 View Post
If you agree, I would like to put also a copy into the Horten-Manatee repository at SourceForge to get a nice and round open design package.
Regards,
Andrés
OK, got it. Once open source, always open source. No requirement to publish. I will publish the current Rhino 3D file in native format and .DXF. The Rhino 3D file is too large to post here. Please feel free to download such files and add them to your SourceForge project. May be I do not fully understand the idea behind SourceForge. Shall I upload the files to SourceForge myself as a contributing member ???

A free viewer of Rhino 3D files is available here by simply downloading the demo version of Rhino 3D. That demo is a full working version.

As a techinical note, I have created the existing NURBS model from your profiles with no modification whatsoever. That model uses the power of NURBS to blend the airfoils you have provided per the planform.

From this point, I will extend and modify that surface for the tip, which will be largely hand shaped. Also, the structural elements may be arranged differently to suit other requirements.

Regards,
Kent
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Old Jan 06, 2012, 08:28 AM
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Hi,
I used the morning to calculate the load distributions.
Do not get confused, the loads are still along the spar!
Andrés
Wow, nice work. 40 m/s = 90 mph! That should cover most flying conditions. Maybe not a terminal dive, but who gives full up after a terminal dive? I do not plan to Dynamic Soar this glider.

Surprised to see the torsional moment is 1/4 of the bending moment. I was assuming less.

I'm familiar with the graphs and the engineering principles. At the risk of starting a full blown structural design class, I do have a few questions, if you please.

Does load factor of n=20 mean 20 times the dead weight of the plane? (20 G's)
4.5 kg plane x 20 = 90 kg?

Is the cross spar is ignored in these graphs? The bending moment graph appears to ignore the cross spar but the shear graph appears to consider it. Maybe this is just a function of the load distribution.

Thanks,
Kent
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Old Jan 06, 2012, 09:50 AM
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Nm - newton metres ie a torque of 1Nm is 1 Newton at a distance of 1 metre or 0.5N at 2m etc etc
9.81N = 1kg (under conditions of standard gravity).
1metre = 39.37inches

Stand by for imperial - metric fun!!! ;-)
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Old Jan 06, 2012, 10:18 AM
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Nm - newton metres ie a torque of 1Nm is 1 Newton at a distance of 1 metre or 0.5N at 2m etc etc
9.81N = 1kg (under conditions of standard gravity).
1metre = 39.37inches
Stand by for imperial - metric fun!!! ;-)
Ah yes, the Newton. I'll have to use that one at work. I'm sure the steel fabricators will be amused.

For me: 1 Newton/meter = 0.7376 lb./ft

Thanks,
Kent
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Old Jan 06, 2012, 11:14 AM
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Hi Kent,

SourceForge is a hoster for open source projects. Just a sort of dowload host service. If you create an account, I could include you as a developer and you could upload your things directly using git.

Yes, a load factor n=20 means 20 G and, hence, 90 kg! That is what you get when you fly 40 m/s und make a full pull. You could fly faster, but you should not make a full pull then One kg is subjected to a force of 1 kg * G = 9.81 Newton (N) or 1 N ≈ 0,225 lbf. For the torque/moment we have 1 Nm = 0,7375621 ft lb. I hope that helps I attached graphs in US customary units.

The high torsional moment is the price one pays for stability: outer sections have to pull up the inner lift producing ones. In a tailed airplane this is done by the long tail. A good property of an allwing is that the bending moment is smaller than in a tailed airplane, because mass is better distributed and is not virtually a pointwise load as in tailed airplanes. The high torsional moment compared to the bending moment comes from this two reasons: price of stability and good mass/lift balance.


The cross spar is included in the calculation. You see it best in the bending moment Mz around z-axis (last image). The values of the cutting loads are determined in a local coordinate system along the spar. The x-axis points along the spar, the y-axis aftwards and the z-axis to the top. The convention used is as follows. The forces and moments are shown, which arising inside the structure and counteract the external forces. Take for example the bending moment My. It is positive telling us that the external forces produce a negative moment. Hence, the mass in the center forces the tips of the wing to point upwards, as one expects if a full pull at 40 m/s is made.

Regards,

Andrés
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Old Jan 06, 2012, 12:59 PM
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Originally Posted by andrecillo76 View Post
I attached graphs in US customary units.
Thanks for the new graphs and explanation. It all is clear. Any units are fine with me..... even Newtons.

The upward bending moment graph for the spar "My" is a wild one. Lucky thing the wing is so thick at the center. It's like this plane is designing itself.

Take a look at my last image. Did I show the max. moment, "My" direction, at the right location? I was thinking that the cross spar might cause a spike at it's connection to the main spar.

Thanks,
Kent
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Old Jan 06, 2012, 01:54 PM
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Isn't the cross member of the "A" the main bending element? And the lateral members "/ \" are also pinned at the center much like the compression spar (AKA false spar) of an unswept wing?
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Old Jan 06, 2012, 02:00 PM
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Kent,

your pictures look fine. The direction correspond to the definitions I used. The discontinuities appear at the other moment and forces. I use a discretized beam approach: small beams between the ribs have an own coordinate system. The beams touch at a joining surface and exchange stresses. At the surface the moments and forces, which are vectors and do not care about coordinate systems, are transformed into the new cantilever local coordinate system and are used as a boundary condition. I calculate for this small cantilever the forces and moment and plot them against the spanwise coordinate at which the cantilever center is located.

A finite element method would actually be needed to calculate the stresses correctly at a joint like the one between the spars...

Greetings,

Andrés
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Old Jan 06, 2012, 05:16 PM
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Thanks Andres,

I agree that FEA would be needed to fully analyze this framing. With the variety of ever changing loads coupled with the angled framing layout, it does not lend itself to a simplified analysis.

I can imagine the cross spar floating up with load and not contributing to bending resistance of the main spar. This would not consider the connection between the main and cross spar as provided by the ribs and plywood skins. Of course the entire structure works as one structural element. I am happy to take my best guess and test fly. If it does not flutter at 90 mph, I'll call that success.

Although I will attempt to make moment connections at the cross spar to the main spar, I'm sure that it will act as a pinned connection.

I will use your maximum bending moment and carry it out past the cross beam connection. The spar cap will be carbon tow, the spar will be deep, so it will be cheap and easy and stiff.

My wing joiner is past the cross spar connection and the bending moment looks quite light out there.

Thanks again for your analysis,
Kent
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Old Jan 07, 2012, 04:08 AM
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Kent,

Norman's comment helped me to understand why you are confused (thanks Norm!). The analysis considers only one spar, which can be kinked. So either I decide for the "/\" as the main spar, or for "/--\" but the analysis does not cover the full "A". The analysis was made for the "/--\" case, considering that "--" acts as the main spar at the center. I made the same calculation for the "/\" as the main spar. See attached figures.

The torsional moment is substantially smaller now, because the complete spar is located very near to the local AC. For the "/--\" case, the torsional moment at the cross spar increased due to the lifting force acting far away from it and creating an additional torque.

Regards,

Andrés
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Old Jan 07, 2012, 01:12 PM
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Kent,
The analysis considers only one spar, which can be kinked. So either I decide for the "/\" as the main spar, or for "/--\" but the analysis does not cover the full "A".
OK, understood. The analysis is helpful, but I will not generate calculations for the spar, inasmuch as it is so deep and I plan on using carbon tow for the caps and full width vertical grain shear webs, then wrapping the spar. Spar is 3/8" wide. I predict that it will be very very stiff. This method is easy to build with all parts laser cut from the model. It's like cheating...

After sketching out some details and looking at the construction sequence, I've decided to build the center section ( 40" wing span ) as one piece which will allow the carbon tow to be install as continuous curved spar caps. This removes the kink at the center. The main spar is of course tied to the plywood D-tube. I'm happy with this.

The main spar appears to more closely match the center of lift line at the root area better with the curved spar.

Thanks,
Kent
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Old Jan 07, 2012, 02:13 PM
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Kent,

good idea! We've made very good experiences with main curved spars. The small and large Schapel have this type of spars and both have been subjected to very large stresses . We used also the cross spar, though. I'm sure that the structure will be stiff. The thickness of the foil will do the trick and 3/8" would also be my choice for this wing.

Regards,

Andrés
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