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Very impressive lecture. When you performed the load testing of the complete wing, even though the wing withstood the load, how do you know if internal damage has occurred ? Do you have inspection hatches/ holes to enable say fibre optic visual inspection, or are there other NDT testing methods available….strain gauges, ultrasound etc… Inevitably the wing will experience stress/strain reversal which in an Al structure will lead to fatigue, do these composite structures delaminate ? How do you plan to verify the structural integrity while in service ?
I really, really, really like that you guys are product-focused and engineering-centric. That takes care of marketing by itself, as opposed to others "sell impossible performance first, figure out how to make it close-ish enough that you are not sued later" like the Raptor fiasco.
I really like your project and your videos. As a mechanical engineer myself I like your factual, no marketing bullshit approach to your videos and also to your product itself. A breath of fresh air in the "sell pie in the sky" startup world.
Chances are low that i will build my own airplane (except a small one out of paper) , but i really enjoy your vids. Very informative and a joy to watch. Well done!
This is really sick stuff, innovative, different. Interesting thing I noted about y’alls hollow core concept is that something similar is has been used in some 3D printing RC airplane designs too, going as far as to place stingers at angles to the width span of the wings. Its all fascinating
A similar design is used in fighter jet wings also. One that comes to mind, is the F-104. Where compressed bleed air from the engine was sent outboard through the wing, and emerged from ports precisely located to blow air over the flaps when deployed. "Blown flaps" as they were called, reduced approach speeds significantly as long as the engine was kept spooled up and compressing plenty of bleed air. Losing the engine in this configuration, when landing, was unrecoverable. Such were the 1950s.
G,day Riley, River and Keagan from Sydney Australia. I was wondering how you design structures (aerospace). I knew the components; ribs, spars, struts etc. I now have a idea of testing to resist G force loading. So... one could purchase plans with specified materials or "build and carry out testing to "with a coupon calculations measurement system recognised by the FAA" On the other hand; completely experimental categories. Then there's materials; * Wood, fabric, aluminium, composite material such as fibreglass, carbon fibre in moulds etc. "Speed, just a matter of money, how fast do you want to go?" That was was a great lecture sir, you got my brain to spark on two cylinders. 🍏🇭🇲
so, you used a type of Wing Box instead of a traditional wing spar. the construction method is brilliant though, as you say makes design changes much easier.
You have very satisfying engineering and manufacture discipline. Where you might have opportunities is in simplicity. Have you considered a completely hollow closed shell wing? I believe Elixir does this. Because carbon fiber is stiff, it might hold its shape well enough with little weight penalty if any. And the shear forces transferred diagonally on the shell. And such a design avoids any bonding that could reasonably crack. Any presumably lends itself to fast and reliable manufacture. Cost effective. Similar might be possible for the fuselage although you use a somewhat boxy cross section. but let's say you could do the fuselage as a one piece shell or only one bulkhead for a penalty of only 2kg, it might well be very worth it.
Going to need to see the manufacturing video. How are all those pieces connected together? Seems like it would require lots of labor and lots connection points including attachment to the skins. I'm a fan but I'm a bit skeptical on this one until I see more. Former Boeing Manufacturing Engineer here although I left that field in 2000 and never worked with carbon fiber wings.
Odd question 🙋♂️ within the core of the wings could you add carbon fiber rods with tensioners on the end to stiffen and relax the wing. Don’t know if that makes sense. Wondering so I could make a 3d print airplane myself and test different wing designs.
I mean this as a huge compliment. In your next life you would make a fantastic Mechanical Engineering Professor. You have the rare ability to explain complex concepts in an easy to understand presentation. Thank you.
I think it's essentially gravity drain through interconnected compartments and a large reservoir between the wings to collect before sending to the engine fuel lines.
I always look forward to your new releases. These videos are great for educating and building confidence in your design. I’ve always wondered however why are you teaching building classes to people who are not necessarily interested in building your aircraft?
This channel is a Gem for the engineering community, it doesn't has to be applied on building specifically their aircraft in order to be useful for us. Knowledge is always useful
On the manufacturing topic, could you give us some insight into how the hollow grid is bonded to the skin? Specifically how you can count on that in a tank application.. Love these videos, incredible content. Great job guys!!!
Agreed, love the innovative ideas and think this is brilliant for things like control surfaces. But have to admit I am skeptical of that being used as a tank. There is a whole lot of bond area there and if any bit of it fails it will both leak and be inaccessible for repair.
I can’t stop looking at that beautiful carbon fibre 😍 fascinating discussion about why you’ve made the choices you have, and how it benefits the design.
I would love to know if you guys have been surprised by anything you've learned yet while building this very coot plane? Is there anything that you just didn't even think about or is the building and design process calculated to the last detail and you haven't been surprised by anything? Keep up the cool videos, I get excited when I see a new one.
Hi Paul! Thanks for checking out our videos and thanks for the great question. Yes, lots of surprising challenges popped up along the way. A big one was canopy manufacturing, which turned out to be much more involved than expected. We spent too much time on that before we ultimately outsourced the process. We might try to bring it back in-house at some point. Making large honeycomb sandwich panels to meet our own standards turned out to be hard as well. We figured out how to do it at a small scale pretty quickly, but scaling it up was difficult.
Excellent content and presentation, guys! You all have great skill at not only highly technical processes but also the ability to convey it down to our level without coming across as condescending or droll. Congrats! keep them coming!
I started watching these, because I just love fast and efficient aircraft. However, these videos provide such an in-depth insight into composite manufacturing that my engineering interest now benefits more from it than my passion for flight 😄
It's always nice to see machines being built as embedded thought, taking maximum advantage of the properties of the materials. Relates to "Zen and the Art of Motorcycle Maintenance.
Almost certainly easier, assuming You obtain the velocity/pressure distribution over the airfoil at several important angles of attack. It is simpler to integrate loads to multiple shear webs, and wing skin cells, than over an entire wing, flowing to a single spar which is constrained in placement due to thickness, and location of the Aerodynamic center.
I am most interested in actual takeoff and landing distance. Looking at the competition VL3, Blackwing they have very short takeoff and landing distance over a 50' obstacle. I need that for sure.
This was incredibly well explained and you're a very good speaker! I'd heard of the DarkAero but wasn't really following it, I watched this out of pure engineering curiosity. Definitely interested in hearing more.
Nice video. I got interested about your hollow grid concept. Did you analyze the possible failure modes associated to having such a thin sandwich shear webs. I'm particularly worried about debonding in the T joint (between shear web and skin). How did you address this problem.
Based on my knowledge and hands on experience, the honeycomb core will be saturated with fuel after a while. Primarily due to cyclic ambient pressure change (with altitude). It is impossible to make them perfectly sealed, fuel will go through tiny gaps and stay there. It will add extra dead weight, better to use monolitic webs in the fuel tanks.
Hi Kirill! You have highlighted a valid concern! It is definitely possible to create honeycomb sandwich panels that are sealed against liquid/gas leaks. Sealed cells are often the default result for certain panel manufacturing methods, and this can be a problem in certain applications, which is partly why vented honeycombs exist. This is something we were concerned about when we were developing our sandwich panels, and resistance to fuel ingress was a criteria we tested and achieved.
11:24 observations. this design results in a wing whose dom is less-than optimal. a wing is Supposed to have a contiguous*, LOAD-BEARING main spar, located at thirty percent of chord. (* where a wing is swept or has dihedral, the use of a Central main spar (section), that spans the width of the fuselage is normally necessary.) should we assume that air pressure in all those compartments is able to Equalize. this aircraft could be built LIGHER, using Tradition all construction methods.!!! consequently, it is not clear WHATthehel you are trying to prove.
How will your wing handle a bird strike? Will it continue to remain strong enough if say 10% of the cord is damaged? I've seen pictures of airplanes with leading edge damage almost to the spar and the wing remained strong enough to continue to safely get the crew back on the ground. With no main spar how much damage can your wing take from a bird before it's catastrophic?
For these thin walled structures the failure mode would inevitably be local buckling on the compression side but I can't seem to find any robust mathematical framework to predict this buckling. Also what should the spacing and configuration of the ribs be? Can you point me in the right direction? thanks
Love this video and the info you share but I'll join the chorus of others anxiously awaiting info on how the beam structure to skin bond is done. Bonding the core is easy, but mostly useless. How do you get a solid bond between the super thin rib skin to the outer structural skin? Traditional technique would require taping each joint but that would be enormously labor intensive and impractical here.
At 6:38 you show the Hollow Grid wing. It is beautiful. I had read some years ago that the primary wing spar structure should be in the traditional location. Having primary load carrying structure closer to the trailing edge of the wing could cause wing structure issues in flight and lead to possible wing failure. Can you comment on that? Thank you.
Thanks for sharing! Well somethimes the best overal design is not only the 'best' functionally; for example in therms of weight or mechanical strength. Often manufacturability, serviceability, and availability, supply chain (availability of technique) and cost play an important factor too. I wonder how you guys at DarkAero made the full trade off, for example; Is the 5% weight reduction now worth 2x the cost in manufacturing? Lets say one damages its left wing against a hanger door; can this be repaired without bringing the full structure back to DarkAero? Or is there a common understanding if this Honeycomb.
@DarkAeroInc Genuine question: Wouldn't it be better to distribute the spars keeping equal celular volume instead of equal distance in between spars? On your approach, it seems like the denser and stiffer part of the wing is towards the trailing edge. Was it deliberate?
I have a project that I am working on... using a laminate consisting of 2x2 twill, 10oz triaxial and 5 harness. About 10 plys... what is a good feed rate / pass thickness amd plunge for the CNC? Thanks in advance
Me: Doesnt want to learn calculus to be a mechanical engineer.. Also me: gonna build my own airplane.. # F Calculus i found a calculator! Any time you build something new.. You cant just use it.. NO you gotta do destructive testing on it and build it again.. I dont wanna destroy the plane! :( destroys a 4 inch x 6 inch piece of carbon fiber. Kinda like how Million dollar super cars refuse to do any crash test ratings cause its too expensive to rebuild one.. How does carbon fiber do in a impact? does it just crack or snap off? I feel like the epoxy used could make it too brittle for impacts. just dodge them birds sully! Or hope your over the Hutson! 🤣 F that parachute it is..
I've seen other people talking about some peculiar challenges of carbon fiber that makes it not my favorite choice for a plane. With repeated bending it becomes weaker. Resin becomes weaker under VU light. Especially when the parts are not painted. And a third reason is i don't like the way carbon fiber breaks. For a military plane, it could be better for a bullet to pass through a wing and leave a hole-like defect. While with carbon fiber a single bullet could break the whole wing in two. Said all that, i still love composites. I would just not use them for critical parts. Something that my life depends on. Composites are perfect for the body of sports cars that are using a metal pipes frame underneath to hold it all together. Good for fishing rods, because my life does not depend on the fishing rod. Camping tents etc.
Thank you for your detailed explanation! I have one question: how does your wing structure accomodates torsion? I mean, classical wingbox (the front spar, the rear spar, the skin between) is used for torsion stiffness also. Is the same approach in your structure (the front and the rear spars are stronger than other)?
Thoughts about the very linear stress strain curve of carbon fibre? I am a structural engineer - in seismic engineering we use the non linear section of the stress strain curve (from yield to ultimate) to dissipate seismic energy (hysteresis - ie with steel ultimate strain is ~2.5x yield). This allows us to design for lower seismic force level and we intentionally let the building go non linear to dissipate energy - with the primary intent to prevent collapse (and the building is also not likely useable after a design seismic event). In the high performance sailing world, I think this has been one of the fundamental issues with CF. They are hitting yield loads followed quicly by structural failure because of the lack of a yield plateau (there is no ductilty). Do not know how the aeronautical codes are written but IMO, use of carbon fibre probably needs higher factor of safety in comparison to say aluminum. With CF you basically cannot afford to go past yield...
That’s how Lear jet did their wing in the 60’s. They used that on all models but the 40 &70 series. Rather than a main spar and an aft spar, they went with 8 “spars” and the entire wing is one fuel tank.
I'm interested in knowing if having an incompressible fluid filling the wing produces any changes in how the wing performs under the same test loads and flexing. Could the fuel load the internal structures and possibly separate the ribs from the skin?
Kudos. You guys are so professional and so generous with your time in sharing your knowledge and vision. If I was 40 years younger I would beg to work with you.
I'm curious how you are bonding to the wing skins -- are you using a jig to secure the shear webs for bonding? How are you guaranteeing the quality of the bond fillets between webs and upper and lower skins?
Nice presentation, taking advantage of the CNC router to simplify the manufacturing, to iterate faster on the design/product. I can feel this approach is already used and reused on the whole plane.
Great video, and you are selfless in what you share. Another reason we should be moving away from ribs and spars, is that they are an outdated function. They were needed to take mechanical loads when we had cloth wing skins! Now we have wing skins with serious stiffness/weight properties, we really don't need them so much! Yes theres shear to deal with and face collapse, but i love your design. Be really interested to know how you connect the cell spars to the upper wing skin when you close the structure, how do you know the glue is touching? :) Cheers from UK
Hello, very nice design, I deal with carbon strucures as well even thow not in the aero field, and One of the issues I have to face Is brittleness of carbon strucures. How do you deal with that for instance to avoid cracks from impact with birds?
I assume that there will not be a "tank" in the wing or a bladder in the wing for the fuel. As the chambers inside your grid wing are quite small, how are you managing fuel flow and scavenging inside the wing? Are there small holes in the grid to allow flow but limit sloshing of the fuel.
Is this a top skin that is then epoxied to a bottom skin (after adding reinforcement sandwiches)? If so, how where you able to epoxy the front leading edges to one another when the material layed up is so thin? Are you gluing a thin edge to a thin edge?
