Wow, amazed that you don't have more views and comments after nearly a month. Great project! I'm sure you've gone through all the engineering multiple times, so I'm likely not adding anything, but here goes.... My experience with blue and pink insulating foam has shown me that it has very little peal strength, even when the surface has been abraded and/or perforated to provide more adhesive surface area. I was astonished in all of my coupon tests with this type of foam that these foams failed severely in both mild crush (compression) and in skin tension forces. The skins (two layers of 45 deg cross uni S-glass with/without a veil layer against the core) pealed from the core much too easily. After these coupon tests, I tried Divinicell (slightly heavier per cubic unit) and found I could reduce the thickness of the part while being much stronger in all dimensions compared to the blue foam alternatives at comparable calculated assembled weights. There was no skin delamination with the Divinicell under far-excessive design loadings. I would never trust the insulation foams on a structural member. Perhaps they can be ok on ribs, but even then I'd have serious reservations. Loads can increase to higher levels than what are imagined under some circumstances, in some applications. Also, your spar attachment points appear to have inadequate surface area for secondary bonding, even though you are planning on wrapping the pultruded CF strips around them. You've likely tested similar constructed structures to destruction so hopefully I am all wet. Great project and design!
Hi: Thanks for taking the time to write! I agree with you, I should have tons more views. I hope you will help spread the news so we can increase the discussions and we will all learn more, I'm sure. Now, your comments on core material are VERY interesting and an important topic for all ultralight aircraft designers. That said, you now have become only the second person to ask questions that I think warrant a follow-up video. So, next in line I will be providing my thoughts and experience on the various core materials and their pluses and minuses. Look for it soon and keep watching - Rol
@SagaSeaCraft I agree with what you are saying but yet most of Burt Rutan's designs used insulating foam in structural members. In this instance the foam is encased on all sides by composite material, so the foam core probably doesn't need to provide much strength. Would it be stronger if it did ? Yes. I can't wait to see this load tested.
I used the same foam on my first wing for the shear web. I think I discuss that in the first video of the Materials and Structural Trade Study series. Unfortunately, I didn't have video way back then, but buried in some box are stills of the test loading of that spar. All went well, that that spar had a face sheet on only one side of the foam and some local reinforcements on the the other side - very unconventional, but it worked! When you pushing the limits on weight (trying to go way low) you are often forced to try something unconventional.
Rol - Thank you so much for your excellent videos - they give me a lot of ideas and a lot to think about! May I ask, where are you buying your continuous length 1 x 10mm pultruded carbon strip from? I have not been able to find a source of continuous length pultruded carbon strip/rod wider than about 5mm. I am in the early stages of planning my next project and would like to use wide carbon strip like the stuff you are using. Thanks, and keep the videos coming!
Hi Phil: Thanks for the kind words. I have watched your videos also so we both know how much work is required to both build an aircraft and document the process on video along the way. It adds lots of work. I'm sure you know the many, many hours it takes to hunt down all the material sources. I normally make mine available to my Patrons on Patreon at: www.patreon.com/klingbergwing The Welcome Packages comes with many goodies like: Source List Weight Breakdown Material properties and costs Plans for the R/C version, and there is even a set of data files for a simulator one can fly on XPlane! Because of all you have done to share your work with the aviation community, my wonderful Welcome Package is yours for FREE! It will contain the supplier info you need. Just email me at rolkling@gmail.com and you'll get your goodies via return email. Fly Safe, Rol
It seems to me, that by putting the pultruded carbon fiber strips on the flanges of the spar, they would've had to carry smaller loads by achieving the greatest possible Area Moment of Inertia for the same weight. You chose instead to put the carbon fiber strips on the edges of the shear web. May I ask why? Thank you
Yes, but also a "No". The gain by moving them out a little is only about 5% and then attaching them to the root fittings becomes a big problem because they will be above and below where the root fittings need to be. This would require added structure to transfer the loads from the spar caps to the root fittings. And, no the root fittings can't be moved with the spar caps because they need to form a clevis arrangement with the receiving side. There are of course hundreds of different designs that would work, but it is not clear they would actually be lighter. Plus, I did the design this way to make it easy for a home builder to achieve a sound structure without needing special tools or jigs. What we learn in the process is that a detailed aircraft design is a balance of dozens and dozens of factors that go way beyond what the optimum configuration is for one component. This is why it takes years and years of work and analysis to create a new design - and a strong understanding of systems engineering and trade studies - the final answers are usually quite complex.
Great video! Thank you. You taught me more stuff! This is becoming a habit! One quick question - did you weigh out the resin based on the cloth weight or wet out to excess and squeegee the excess off/
Excellent question as this is an area of "hot" debate. The key to answering is in understanding the differences of the core material. PVC and similar foams (Airex, Divinycell, etc) have a fairly open cell structure. Styrene foam (Dow) has a very small closed cell structure. For "open" cell foams it is best to measure the epoxy first (about 1.5 times the cloth weight; allows for wastage) and apply it to the cloth on a clean working surface and then transfer the cloth to the foam and vacuum bag to ensure good contact. A bleeder layer will take care of any excess epoxy in this case. For the closed cell foams one can apply the epoxy directly to the cloth on the foam because the foam will not "soak" up extra epoxy. A good squeegee job removes any excess epoxy. A layer of bleeder cloth also helps keep the weight down. In some cases vacuum bagging can be avoided. Finally, all of these comments pertain to structures that are using only a single layer of cloth. If multiple layers are involved, the answers are different.
Brilliantly educative. Thank you so much
Glad it was helpful! That's what I'm aiming for - Rol
thanks for this video, helps a lot to figure out of how to build a wing spar ... waiting for your D-tube video ;-) .... keep going and have fun :-)
Wow, amazed that you don't have more views and comments after nearly a month. Great project!
I'm sure you've gone through all the engineering multiple times, so I'm likely not adding anything, but here goes....
My experience with blue and pink insulating foam has shown me that it has very little peal strength, even when the surface has been abraded and/or perforated to provide more adhesive surface area. I was astonished in all of my coupon tests with this type of foam that these foams failed severely in both mild crush (compression) and in skin tension forces. The skins (two layers of 45 deg cross uni S-glass with/without a veil layer against the core) pealed from the core much too easily.
After these coupon tests, I tried Divinicell (slightly heavier per cubic unit) and found I could reduce the thickness of the part while being much stronger in all dimensions compared to the blue foam alternatives at comparable calculated assembled weights. There was no skin delamination with the Divinicell under far-excessive design loadings.
I would never trust the insulation foams on a structural member. Perhaps they can be ok on ribs, but even then I'd have serious reservations. Loads can increase to higher levels than what are imagined under some circumstances, in some applications.
Also, your spar attachment points appear to have inadequate surface area for secondary bonding, even though you are planning on wrapping the pultruded CF strips around them. You've likely tested similar constructed structures to destruction so hopefully I am all wet.
Great project and design!
Hi: Thanks for taking the time to write! I agree with you, I should have tons more views. I hope you will help spread the news so we can increase the discussions and we will all learn more, I'm sure. Now, your comments on core material are VERY interesting and an important topic for all ultralight aircraft designers. That said, you now have become only the second person to ask questions that I think warrant a follow-up video. So, next in line I will be providing my thoughts and experience on the various core materials and their pluses and minuses. Look for it soon and keep watching - Rol
@SagaSeaCraft I agree with what you are saying but yet most of Burt Rutan's designs used insulating foam in structural members.
In this instance the foam is encased on all sides by composite material, so the foam core probably doesn't need to provide much strength. Would it be stronger if it did ? Yes.
I can't wait to see this load tested.
I used the same foam on my first wing for the shear web. I think I discuss that in the first video of the Materials and Structural Trade Study series. Unfortunately, I didn't have video way back then, but buried in some box are stills of the test loading of that spar. All went well, that that spar had a face sheet on only one side of the foam and some local reinforcements on the the other side - very unconventional, but it worked! When you pushing the limits on weight (trying to go way low) you are often forced to try something unconventional.
Rol - Thank you so much for your excellent videos - they give me a lot of ideas and a lot to think about! May I ask, where are you buying your continuous length 1 x 10mm pultruded carbon strip from? I have not been able to find a source of continuous length pultruded carbon strip/rod wider than about 5mm. I am in the early stages of planning my next project and would like to use wide carbon strip like the stuff you are using. Thanks, and keep the videos coming!
Hi Phil: Thanks for the kind words. I have watched your videos also so we both know how much work is required to both build an aircraft and document the process on video along the way. It adds lots of work. I'm sure you know the many, many hours it takes to hunt down all the material sources. I normally make mine available to my Patrons on Patreon at: www.patreon.com/klingbergwing
The Welcome Packages comes with many goodies like:
Source List
Weight Breakdown
Material properties and costs
Plans for the R/C version, and
there is even a set of data files for a simulator one can fly on XPlane!
Because of all you have done to share your work with the aviation community, my wonderful Welcome Package is yours for FREE! It will contain the supplier info you need. Just email me at rolkling@gmail.com and you'll get your goodies via return email. Fly Safe, Rol
It seems to me, that by putting the pultruded carbon fiber strips on the flanges of the spar, they would've had to carry smaller loads by achieving the greatest possible Area Moment of Inertia for the same weight. You chose instead to put the carbon fiber strips on the edges of the shear web. May I ask why? Thank you
Yes, but also a "No". The gain by moving them out a little is only about 5% and then attaching them to the root fittings becomes a big problem because they will be above and below where the root fittings need to be. This would require added structure to transfer the loads from the spar caps to the root fittings. And, no the root fittings can't be moved with the spar caps because they need to form a clevis arrangement with the receiving side. There are of course hundreds of different designs that would work, but it is not clear they would actually be lighter. Plus, I did the design this way to make it easy for a home builder to achieve a sound structure without needing special tools or jigs. What we learn in the process is that a detailed aircraft design is a balance of dozens and dozens of factors that go way beyond what the optimum configuration is for one component. This is why it takes years and years of work and analysis to create a new design - and a strong understanding of systems engineering and trade studies - the final answers are usually quite complex.
@@KlingbergWingMkII Thank you Sir!
My (admittedly amateurish) analysis also showed only small gains from moving the strips to the flanges.
For which aircraft did you build this spar please?
Can you give me the name of the airplane?
Klingberg Wing MkII
Great video! Thank you. You taught me more stuff! This is becoming a habit! One quick question - did you weigh out the resin based on the cloth weight or wet out to excess and squeegee the excess off/
Excellent question as this is an area of "hot" debate. The key to answering is in understanding the differences of the core material. PVC and similar foams (Airex, Divinycell, etc) have a fairly open cell structure. Styrene foam (Dow) has a very small closed cell structure. For "open" cell foams it is best to measure the epoxy first (about 1.5 times the cloth weight; allows for wastage) and apply it to the cloth on a clean working surface and then transfer the cloth to the foam and vacuum bag to ensure good contact. A bleeder layer will take care of any excess epoxy in this case. For the closed cell foams one can apply the epoxy directly to the cloth on the foam because the foam will not "soak" up extra epoxy. A good squeegee job removes any excess epoxy. A layer of bleeder cloth also helps keep the weight down. In some cases vacuum bagging can be avoided. Finally, all of these comments pertain to structures that are using only a single layer of cloth. If multiple layers are involved, the answers are different.
Klingberg Wing MkII Got it! Thank you!