Sine wave spar

[Konrad]

Ok, what you show in the retaining wall is an elegant way to add a buttress to a wall. It is not a web dealing with shear loads. Its only application here is that it might help in the wet assembly of the wing, as sine wave web would stand proud a lot easier than a straight web.

Tubes work well to transfer torque. The issue with them is how to introduce the torque into the tube. Often this is done with splines.

Not sure I follow your questioning of putting webs inside a tube. You might want to look into the tubes used in heat exchangers (boiler). Often times these have internal walls (fins).

As a load beam the tube is horrible as a function of mass. This is because most of the mass is not orientated properly. If one remembers that a beam responds as a function of distance in its load bearing members, most of the mass in a tube is not at the top and bottom. This is why webs in the load beams are a lot thinner than the caps. (The only reason we see tubes in some ARF gliders is convenience. Most need at least two beams for any hope of working, or are very thick walled).

Top Model Grafas Maxi

Top Model, Grafas Maxi, 3.5 meters of electric fun!

alofthobbies.com

As to the failure mode of the sine wave spar it will be in the "I" beam BB section if the beam is subjected to torsional over load. It will be in the at the "C" beam (AA-CC section) in bending moment. Rarely are the loads purely one type or the other. The sine wave beam can address both and as a result is a stronger structure for any given mass. You are correct that each section of the beam will respond differently to different loads.

If one is constrained by needing to use a single load bearing element to address both bending and torsional loads there is little to can out perform the sine wave beam.

This sine wave beam has a huge cost as it is difficult for a mill to produce such a structure. The "I" beam is used mainly because it is easy to make and can handle bending loads. But when needing to address dynamic load that have a rotational component they as horrible. (I like looking at structures that have failed in hurricanes. I often think how these might have survived had they used a sine wave beam rather than a "I" beam.

In the composite sine wave beam the weak point is as Doc. mentions the spar cap adhesion. The Boeing patent is trying to address this limitation. With the stability that the green section of web provides, this bonded weak point is greatly enhanced. This is why the Aeroic HSWS still offer a substantial improvement over the classic I beam and box spar wings, used by other glider builders, even when both OEMs are using the same dry modular construction methods.

All the best,
Konrad

P.S.
Not sure I made it clear, tubes are horrable as load beams, for any given mass.

 

[Old_Salt]

Konrad, I did not suggest webs inside a circular tube. I do not understand why you might think that was the case. Cooling fins is a tangent I did not suggest as part of this discussion. Boilers are a completely different subject. Adding boilers to the discussion is yours.

I am pondering the comment about the basic weakness (adhesive performance) in I beams and sine beams. In both cases I would expect that the web, whether straight or convoluted/sine, would be compressed by bending loads. My understanding is the web functions to keep the spar caps separated when the beam is loaded in both sine and I beams. If that is the case why is the adhesive junction the weak link? When I have looked at broken wing spars (i beam) the failures suggest that the shear webs have been crushed and the cap strips have broken top and bottom. Why would a adhesive joint under compression be a weak point? Is the weak point with a sine beam adhesive a torque issue? There I would expect the sine wave web to see compression at one amplitude peak of the sine wave and a tension load on the peak +/- pi radians away? Is that tension load the adhesive weakness cited? Is there something else?

My thought about a circular beam is not that it is great in carrying a bending load but that it might be able to both handle bending and torque loads adequately. Tubes and rods find numerous applications in dealing with torque loads. I would agree that splines are one way to connect tubes and torque loads. I am not sure how that is necessarily applicable to a wing. Tubes are certainly easy to insert into a structure. Sine wave spars are certainly complicated. Or is it that a tube is simply deficient when it comes to bending loads? The comments above suggest that is the case. I have seen the problems that can occur when one attempts to bend tubes. The failure is often seen as flattening of the tube and a kink with no further resistance to additional bending loads. Successfully bending tubes needs mandrils and often temporary internal support to keep the tube from collapsing. Tube walls on the outside of the bend are generally thinned and wrinkling on the inside of the bend is another issue.

My comments and questions are because I would like to understand the limits and strengths of the various beams being discussed. I intuitively understand that a sine beam will handle torque loads more easily than an I beam. I suspect that in a sine beam there is a weakening of the bending capacity and increase in weight with increasing torque capacity. It is not clear to me where i beam, sine beam, box, and circular cross sections fall in comparison both for bending and torque loads and weight.

Doc made an observation about the frequency of the sine wave. Was that suggesting is higher frequency sines are more resistant to torque loads than lower frequency sine webs? I suspect that the opposite is the case when bending loads are considered. Or could the frequency comment be related to the resonant behavior of a spar in general not related to the frequency of the sine spar? The earlier sketches suggest a variation in the period of the sine spar. Is that the intent? Lots of parameters are in play.

I suspect that square, circular, and sine beam structures are good at handling both (or some) bending and torque loads simultaneously. I would expect that the magnitudes of the torques and bending loads compared to each other would play into which structure is preferred. Is it appropriate to think of an i beam as a good choice for bending (only) and a tube as good for torsion (only)?

It is certainly easy to make something complicated. The goal is to make a structure simple and still satisfy a multitude of constraints.

What is the point of the reference to the Grafas Maxi?

Are there other beam structures that exhibit both torque and bending resistance to shed additional light on the discussion? I would not be surprised to find that a tetrahedron based structure to have equally interesting features and also approach a nightmare to build. I suspect that sine based beams are not often seen because of the fabrication complexity and possibly the need for high performance adhesives. In practice is a sine spar worth the performance improvement or is it only useful in the context of DS like wing loading? They do look good in person.

Can you recommend any particularly useful references for beams that relate to these issues?

 

[Konrad]

I mention the tube configuration that are often found in boiler. Not boilers themselves. The internal fins in boiler tubes can act as a T to resist bending. A tube by itself is a horrible shape for that. BTW; tubes fail at 45° to the axis in rotation. If you want to use tubes as a wing beam (spar), I strongly recommend against it.

Not only does the web in the I beam keep the spar caps apart it also so keeps them together. That is the basis for the fiber in the Boeing patent, adding some fiber across the bond line. Most wings that are over loaded fail with the compression member buckling. If you are seeing the web crushed it is an indication that the web was too thin or the beams where too thick. Again nowhere near being optimized for weight. If you get a chance look a the structure of failed wings used in the certification of transport aircraft. (I think these can be found on You Tube, maybe not as the public might panic that the wings are only designed to meet 150% of maximun anticipated load before failure)

Yes. the geometry of the beam is critical to its intended application. Also cost of manufacture can't be over emphasized.

I tried to direct folks to the Boeing patent as a reference for composite (fiber) manufacture of the sine wave beam.

You asked, how does a tubular or conical spar compare to the sine spar? Very poorly when measured a a function of strength to weight. Rods are the worse, well short of a wet noodle!

The torsional loads of a structure under flutter are often grossly under estimated. Here is a classic example of such a failure in our toys

TopModel Samsara 3.2 meter glider, build thread on Aloft's Forum.

If by hi res you mean 1080, it’s there. You just have to select it for playback. Youtube seem to be doing everything it can to drive users to its premium service. Like defaulting all playback to the lowest res version of the video.

forum.alofthobbies.com

Now if you want to go beyond the discussion of the merits of the sine wave beam give MacCready a read. He used a tubular spar in the Gossamer Condor. Then start a thread about that and we can go into a detailed discussion about its use in that application.

MacCready Gossamer Condor - Wikipedia

en.wikipedia.org

 

[Doc James Hammond]

Hi Salt - as the perpetrator of the HSWS - at least as far as model sailplanes are concerned - some moments from me below.

Konrad, I did not suggest webs inside a circular tube. I do not understand why you might think that was the case. Cooling fins is a tangent I did not suggest as part of this discussion. Boilers are a completely different subject. Adding boilers to the discussion is yours.

I am pondering the comment about the basic weakness in I beams and sine beams. In both cases I would expect that the web, whether straight or convoluted/sine, would be compressed by bending loads.

Actually both compressed, and under tension at the same time. If the wing is being stressed upwards, the bottom of the spar is in tension while the top is in compression. And vice-versa.

My understanding is the web functions to keep the spar caps separated when the beam is loaded.

Not correct, its part of the integral structure. This in the same way as the top horizontal, middle vertical and bottom horizontal webs of an I-Beam are integral.

If that is the case why is the adhesive junction the weak link?

Because the parts (Spar caps and spar) need to be made separately, which unless they are joined wet or at least green, will always give the possibility of variable adhesion in the junction. Obviously the larger the area actually joined, then less the chances of failure are.

When I have looked at broken wing spars (i beam) the failures suggest that the shear webs have been crushed and the cap strips have broken top and bottom.

That would depend entirely on the crash. Was it cause by spar failure? If not, then the spars and their caps could display any number of breakage and failure types.

Why would a adhesive joint under compression be a weak point? Is the weak point with a sine beam adhesive a torque issue? There I would expect the sine wave to see compression at one amplitude peak of the sine wave and a tension load on the peak +/- 180 degrees away? Is that tension load the adhesive weakness cited? Is there something else?

Any monolithic structure (spar) that is joined by adhesive to other monolithic structures (caps) will always have a weak point where the two joined members are not made as a single entity. This is the adhesive.

My thought about a circular beam is not that it is great in carrying a bending load but that it might be able to both handle bending and torque loads.

A circular beam might be able to carry the loads, but possibly not so well, with a lot of practical limitations, and would be extremely difficult to make.

Why?

1. The spar alignment would have to be straight down the wing and not following the thickest point.
2. It would be hard to join to the wing joiner box.
3. With an elliptical wing, the shape of the tubular spar would also have to be elliptical along its length.
4. The elliptically tapered tubular spar that would be needed, would then have only a tiny surface area to join it to the spar caps.
5. Frankly it would be a true nightmare to accurately make as a compound taper, and each model would have to have a special version.

Tubes and rods find numerous applications in dealing with torque loads. I would agree that splines are one way to connect tubes and torque loads. I am not sure how that is necessarily applicable to a wing.
Tubes are certainly easy to insert into a structure.
No they are not - see above. The spar would have to elliptically tapered.

Sine wave spars are certainly complicated.
Again incorrect, one mould that makes one sheet of HSWS will cover anything from a 60" to a 160" model and yields multiple spars. They don't have to be made one by one like beam spars.
We make all these various sized models and we ONLY HAVE ONE MOULD.

My comments and questions are because I would like to understand the limits and strengths of the various beams being discussed. I intuitively understand that a sine beam will handle torque loads more easily than an I beam.

I suspect that in a sine beam there is a weakening of the bending capacity and increase in weight with increasing torque capacity.
That would be hard to do actually. Typically the HSWS is about 25% of the weight of a "conventional" Beam spar. Weight, therefore, is not a primary consideration.

It is not clear to me where i beam, sine beam, box, and circular cross sections fall in comparison both for bending and torque loads and weight.
At least that's easy. Buy a Machinery's handbook.

Doc made an observation about the frequency of the sine wave. Was that suggesting is higher frequency sines are more resistant to torque loads than lower frequency sine webs? I suspect that the opposite is the case when bending loads are considered. Or could it be related to the resonant behavior of a spar in general not related to the frequency of the sine spar? The earlier sketches suggest a variation in the period of the sine spar. Is that the intent? Lots of parameters are in play.
No, it was suggesting that for perfect balance of strength between torque and tension/compression the frequency reduces with the wing Chord

I suspect that square, circular, and sine beam structures are good at handling both (or some) bending and torque loads simultaneously. I would expect that the magnitudes of the torques and bending loads compared to each other would play into which structure is preferred. Is it appropriate to think of an i beam as a good choice for bending (only?) and a tube as good for torsion (only?)?
NO it is not, and that was never the intention.

It is certainly easy to make something complicated. The goal is to make a structure simple and still satisfy a multitude of constraints.
There ya go! I'm off to Lowes to buy me a sheet of corrugated plastic...

Can you recommend any particularly useful references for beams that relate to these issues?

1. Machinery's handbook.
2. Any paper on Hooke's law.
3. Any paper on Young's modulus of elasticity for UHM Carbon fibre.

Cheers,

Doc.

 

[Konrad]

Machinery's Handbook!! I need to go back to my machinist roots, there is a lot of real world engineering in that handbook.

 

[Old_Salt]

I happen to have a copy, My recollection is that it is the 38th edition. It is one of the places I was going to look as a starting point. It still has sine and log tables in the back.

Is it correct to think of the caps in an i beam as seeing tension loads on the bottom cap and compression loads on the top for upward bending loads? Is that reversed when the bending is in the opposite direction. In either case does the web see compression from the caps? Now for the web, does it see loads from the caps as they bend and additional bending loads that might mirror a thin rectangular beam being bent in the wide dimension plane?

If this is not an appropriate way to think of an i beam, will you offer an alternate description?

The particular wing failure I mentioned was caused not by a crash but was due to a tight loop and one wing folded in flight about a third of the way out from the center. The wing was constructed with spruce caps and end grain balsa webs between the ribs and spars. I tried for a tight fit for the webs ( grain perpendicular to the spars and the spars had straight grain). Of course there was a crash but only after the wing folded.

You mention that a HSWS spar can be 25% of the weight of a conventional spar. Are the caps and web of the conventional spar significantly different compared to the HSWS cross section? The sine web has greater line length than a i beam web. If both are built using the same materials I am astounded to hear that the sine spar is so much lighter. What is going on there? Does the question make sense to you or do I need to refine it further? I expected that the HSWS would be slightly heavy because of the convoluted web path.

I will go spend some time with the Handbook.

 

[Doc James Hammond]

Machinery's Handbook!! I need to go back to my machinist roots, there is a lot of real world engineering in that handbook.

Yowser!

More Below, Salt.

Doc.

I happen to have a copy, My recollection is that it is the 38th edition. It is one of the places I was going to look as a starting point. It still has sine and log tables in the back.
There ya go.

Is it correct to think of the caps in an i beam as seeing tension loads on the bottom cap and compression loads on the top for upward bending loads? Is that reversed when the bending is in the opposite direction. In either case does the web see compression from the caps? Now for the web, does it see loads from the caps as they bend and additional bending loads that might mirror a thin rectangular beam being bent in the wide dimension plane?
Yes correct.

If this is not an appropriate way to think of an i beam, will you offer an alternate description?

The particular wing failure I mentioned was caused not by a crash but was due to a tight loop and one wing folded in flight about a third of the way out from the center. The wing was constructed with spruce caps and end grain balsa webs between the ribs and spars. I tried for a tight fit for the webs ( grain perpendicular to the spars and the spars had straight grain). Of course there was a crash but only after the wing folded.
Sounds like more load than you allowed for - simple catastrophic failure of an I-Beam structure that was not a suitable design in the first place.

You mention that a HSWS spar can be 25% of the weight of a conventional spar.
Yes in my case, correct. I don't know of any other examples so I cannot use this as a general rule. Basically the more we played with it, the less carbon it needed to do the job - so the lighter it got.

Are the caps and web of the conventional spar significantly different compared to the HSWS cross section?
No, the same.

The sine web has greater line length than a i beam web. If both are built using the same materials I am astounded to hear that the sine spar is so much lighter.
You miss the point. We have been though this.
The I-Beam section cannot be used as a spar in a conventional wing as its only one vertical web so the torque will kill it straight away. It has to be two vertical webs. ie a box spar.

What is going on there? Does the question make sense to you or do I need to refine it further?
As mentioned, you miss the point.

I expected that the HSWS would be slightly heavy because of the convoluted web path.
If it were or needed to be a double vertical web spar then that would indeed be the case.
The point is that its replacing a DOUBLE vertical web BOX spar which is the norm in almost all moulded model gliders.

I will go spend some time with the Handbook.

 

[Konrad]

We are talking about one part of a wing, the spar. When looking at this spar one need to normalize the mass. That is for any given amount of weight the Sine Wave Spar is much stronger that the I beam as a spar (a structure that needs to deal with both bending and rotational loads). The I beam alone is totally unacceptable at this. As a result wing designers are forced to use other parts of the wing to address this. A classic case is the leading edge "D" tube. (The I beam is the back side of the D tube) This added mass is often tolerated as it allows for the smooth surface of the leading edge to improve airflow. So the designer gets two benefits from the added mass from the front fairing of with the "D" tube, better airflow and improved resistance to flutter. Now would the D tube perform better with a SWS? You bet it would!

 

[Old_Salt]

Interesting features are being discussed.

I beams are rejected as having minimal resistance to torque loads. They are also prone to adhesive failures, particularly when subjected to twisting. Tubular spars are rejected because they are marginally able to reset bending while capable of withstanding torque loads. Flutter loads are particularly difficult to resist and are also particularly damaging.

What I am hearing is that tubular ( two web, D-section, box, etc.) structures offer one solution with a spar that is capable of withstanding both torque and bending loads. The sine spar, HSWS, is another. One assumption is that the sine spar is constructed from two caps and the sine web. Hence, the discussion of adhesive and subsequent/potential failures should bonding be insufficient. I wonder how the sine spar would perform if it were constructed using a CNC mill and a base rectangular (or curved) beam. The need for secondary adhesives could be eliminated, particularly as they are described as weak links. Material could be removed with a mill to leave the convoluted sine web still separating two cap strips without secondary adhesive joints. I do not have a CNC mill in my garage.

I note the suggested sine spar dimensions following common corrugated roofing material as a starting point. It was also mentioned that variable period sine webs were not particularly productive.

The cap sections in a sine spar will see alternating compression and tension loading as the sign of the bending load reverses. The web would be compressed during bending and both tension and compression forces along the length when subjected to torque loading.

I was perplexed about the weight reduction to 25% for the sine spar until it was explained that the weight reduction reference was from an initial conventional spar configuration that I imagine was some sort of square tube with much thicker dimensions. Reduced wall thickness would certainly reduce weight. Replacing two webs with a single sine web would reduce weight further.

 

[Old_Salt]

My Machinery's Handbook is the 14th edition and the tables are in the front and not the back as I had recalled earlier.

 

[Doc James Hammond]

Interesting features are being discussed.

I beams are rejected as having minimal resistance to torque loads. They are also prone to adhesive failures, particularly when subjected to twisting. Tubular spars are rejected because they are marginally able to reset bending while capable of withstanding torque loads. Flutter loads are particularly difficult to resist and are also particularly damaging.

What I am hearing is that tubular ( two web, D-section, box, etc.) structures offer one solution with a spar that is capable of withstanding both torque and bending loads. The sine spar, HSWS, is another. One assumption is that the sine spar is constructed from two caps and the sine web. Hence, the discussion of adhesive and subsequent/potential failures should bonding be insufficient. I wonder how the sine spar would perform if it were constructed using a CNC mill and a base rectangular (or curved) beam. The need for secondary adhesives could be eliminated, particularly as they are described as weak links. Material could be removed with a mill to leave the convoluted sine web still separating two cap strips without secondary adhesive joints. I do not have a CNC mill in my garage.

I note the suggested sine spar dimensions following common corrugated roofing material as a starting point. It was also mentioned that variable period sine webs were not particularly productive.

The cap sections in a sine spar will see alternating compression and tension loading as the sign of the bending load reverses. The web would be compressed during bending and both tension and compression forces along the length when subjected to torque loading.

I was perplexed about the weight reduction to 25% for the sine spar until it was explained that the weight reduction reference was from an initial conventional spar configuration that I imagine was some sort of square tube with much thicker dimensions. Reduced wall thickness would certainly reduce weight. Replacing two webs with a single sine web would reduce weight further.

You are getting it Salty, but you are going over ground that was covered, and deductions made many moons ago.

All on the same road I think, but you are about two lights behind.

Doc.

 

[Old_Salt]

No comment about the milled sine spar?

 

[Doc James Hammond]

No comment about the milled sine spar?

Theory is great - I'm full of them - stuffed to the gills in fact - but anyway, to answer your question: NO a milled spar would be worse, in fact significantly worse, to the point of being a complete and utter waste of time.

Why?

On a milled spar it would be impossible to control and calibrate the the direction of fibre orientation(s) and therefore affect stress management. With a moulded composite HSWS, its really easy and effective.

To make it simple and talk about stress resistance only: In milling you are removing parts of a pre orientated crystalline structure (lets say a bar of metal) to re-form it into an entirely new shape (A sine wave spar) Unless its a single crystal, the structure is usually made up of crystalline grains - Who knows which crystals point where?

Of course if it were of aluminium or titanium or another metallic pre-forged structure, this may not be so bad - but only NOT SO BAD - it would still be really dreadful.

Light's gone red again.

Doc.

 

[Konrad]

No comment about the milled sine spar?

I covered this in the first post about monolithic structure. This was done the eliminate any material variation in the test coupons.
I mentioned that the sine wave beam would be a bit more difficult for a mill to manufacture (hence cost more). As a result we don't see it much in the construction industry.
I'm at a total loss about CNC milling. No need for a CNC. Heck many aluminum wing structures are chemically etched!

Salt, what are you trying to get at? In the real and theoretical world the SWS is a superior beam to most other structures if both structures have the same manufacturing limitation. This is why Boeing and most aerospace firms use it.

There is nothing new about the SWS structure.

The weight reduction comes from the stability the webs (green) added to the transition from the web to the caps. This is even more acute when looking at cycle fatigue. The limitation from the grain structure whether the material is as cast, forged, directional solidification, single crystal or heck even composite, is again way out of the scope of this thread.

What I was trying to show were the features that allowed the HSWS to perform so much better than the I beam and even the box spar for any given mass. If you want to get into a PHD thesis about the beam, I fear there is going to be a lot of ground work needed just in covering some of the basics of structures. Again not the aim of this thread.

 

[Konrad]

...
What I am hearing is that tubular ( two web, D-section, box, etc.) structures offer one solution with a spar that is capable of withstanding both torque and bending loads. The sine spar, HSWS, is another. One assumption is that the sine spar is constructed from two caps and the sine web. Hence, the discussion of adhesive and subsequent/potential failures should bonding be insufficient. I wonder how the sine spar would perform if it were constructed using a CNC mill and a base rectangular (or curved) beam. The need for secondary adhesives could be eliminated, particularly as they are described as weak links. Material could be removed with a mill to leave the convoluted sine web still separating two cap strips without secondary adhesive joints. I do not have a CNC mill in my garage.
...

I'm not saying this at all. Heck, the classic forged I beam still has 2 caps and a center web feature as they come straight from the mill

 

[Old_Salt]

I was thinking of a milling machine to remove material not a rolling mill where forging is performed.

What is the preferred fiber orientation in a sine spar? Are fillets included? What features, if any, are to accommodate adhesive bonding?

 

[Konrad]

I knew what you were thinking with the term "mill". As a former manufacturing engineer my point was that the SWS does not need a CNC cutting center* to be used in its manufacture. Heck, the old tracer machines could easily handle the geometries of the SWS.

Salt, I think you are getting lost in the weeds. Many of your questions are basic to any beam construction. What this thread's aim was to show what features made the sine wave preferable to the classic I and box beams seen in most wings. And that was the sine wave web has material that directly resists torsional loads (the green part of the web in the cartoons I provided).

The "fillet" question leads me to think you are not aware of the concept of force concentrator (stress risers) particularly as it applies to cycle fatigue.

As to material orientation wether it be grain structure in metals or fibers in composite these can be manipulated at the time of manufacture.
As you specifically mention fiber I assume you have little back ground in composite construction. One of the neat things about composites is that the lay up can be tuned to the specific needs of the application. I think the Boeing patent goes into great detail about that.

* The term CNC is thrown around far too easily by the marketing guys. The true power of a CNC is that it frees the design engineer from the constraint of circle and straight lines that conventional machining practices place on the design. Most of the other attributes assigned to CNC machining center really should be attributed to the advances in the cutter materials and subsequent cutter geometries.

 

[Doc James Hammond]

I knew what you were thinking with the term "mill". As a former manufacturing engineer my point was that the SWS does not need a CNC cutting center* to be used in its manufacture. Heck, the old tracer machines could easily handle the geometries of the SWS.

Salt, I think you are getting lost in the weeds. Many of your questions are basic to any beam construction. What this thread's aim was to show what features made the sine wave preferable to the classic I and box beams seen in most wings. And that was the the sine wave web has material that directly resists torsional loads (the green part of the web in the cartoons I provided).

The "fillet" question leads me to think you are not aware of the concept of force concentrator (stress risers) particularly as it applies to cycle fatigue.

As to material orientation wether it be grain structure in metals or fibers in composite these can be manipulated at the time of manufacture.
As you specifically mention fiber I assume you have little back ground in composite construction. One of the neat things about composites is that the lay up can be tuned to the specific needs of the application. I think the Boeing patent goes into great detail about that.

* The term CNC is thrown around far too easily by the marketing guys. The true power of a CNC is that it frees the design engineer from the constraint of circle and straight lines that conventional machining practices place on the design. Most of the other attributes assigned to CNC machining center really should be attributed to the advances in the cutter materials and subsequent cutter geometries.

All of the above,

Doc.

 

[Old_Salt]

My thought with the CNC mill is that a sine shaped web could be easily produced. A machinist would not have to be really good at turning handles on a manual mill to get that particular shape. A program could be produced to cut a particular profile, sine or something similar. I have no doubt that there are various machines capable of cutting the profile.

It was not apparent to me that the spirit here was to contrast a dual beam spar with a sine spar when I started reviewing the thread. It took a number of questions before that became more clear. I beams and various structures and sleeves were discussed as well making it difficult to recognize the central theme.

The discussion now assumes a carbon fiber based material and some sort of resin matrix to keep the fiber in line (appropriately arranged). The direction of the fiber can be thought of as analogous to wood grain with various weave and tow patterns possible. The comment was made that controlling the fiber configuration was one of the drivers for the use of adhesive in the construction. My question is what would that ideal configuration look like?

My experience is that corners in structures can lead to unexpected failures and hence the mention of fillets. It was also mentioned that increased surface area could enhance adhesive performance. I mentioned fillets for both reasons.

I would agree, my questions are also about the basic performance of beams.

 

[Doc James Hammond]

OK lets straighten this out:

My thought with the CNC mill is that a sine shaped web could be easily produced. A machinist would not have to be really good at turning handles on a manual mill to get that particular shape. A program could be produced to cut a particular profile, sine or something similar. I have no doubt that there are various machines capable of cutting the profile.

NO, NO, NO we are talking about a sine wave spar suitable for use on model gliders.

It was not apparent to me that the spirit here was to contrast a dual beam spar with a sine spar when I started reviewing the thread. It took a number of questions before that became more clear. I beams and various structures and sleeves were discussed as well making it difficult to recognize the central theme.

The spirit/central theme here is HSWS compared to NORMAL MODEL GLIDER SPAR TYPES, THIER MANUFACTURING, AND THEIR PERFORMANCE

The discussion now assumes a carbon fiber based material and some sort of resin matrix to keep the fiber in line (appropriately arranged). The direction of the fiber can be thought of as analogous to wood grain with various weave and tow patterns possible.

YES, YES, YES, we are talking about a sine wave spar suitable for use on model gliders. NOT WOOD, NOT METAL, but COMPOSITES

The comment was made that controlling the fiber configuration was one of the drivers for the use of adhesive in the construction. My question is what would that ideal configuration look like?

It was worked out long long ago, and he's been in good use for over 3 years, Salt - you are now miles behind down the road.

My experience is that corners in structures can lead to unexpected failures and hence the mention of fillets. It was also mentioned that increased surface area could enhance adhesive performance. I mentioned fillets for both reasons.

Wow...that sounds like a good idea.

I would agree, my questions are also about the basic performance of beams.

Great then let's start another thread about beam performance and NOT COMPOSITE MODEL AIRCRAFT SPARS.

How about a nice one on "Inter-metallic growth due to the non stoichiometric nature of welded alloy spars?"
Or a nice juicy "Grain boundary separation leading to catastrophic failure on the monolithic machines structures under stress?"
Or "Non- covalent alloys"? etc etc

Or maybe we could go for a model aircraft application?

Please?

James D. Hammond, PhD (Cantab), DBA, MSc (Cantab), Ba Hons. MInstMechE, FInstDiagE.