The carbon fiber detail no one talks about. 

Composite construction lecture and that airplane construction thingy as a bonus.

Being in composites for more than 15 years getting within 1 percent of the weight is pretty good, this can drop with larger parts. The usage of prepregs and higher end core materials, glue films + autoclave cure will improve those tolerances A sacrificial non structural area can be left in your parts if design allows it, to be cut / drilled to match weight exactly, however very time consuming. Thanks for sharing your processes, nice to follow along.

Hello. I discovered your project today and already went through most of the videos you published 😅 Regarding disparity of weight : - practice more. You will notice that skill is improved by practice and regularity comes along. - regarding disparity in the bond’s quantities , determine the needed quantity and use exactly the same quantity every time (using a seringue for ex) - use a ruler as a guide for straight lines bonds - you don’t use masking tapes properly when you apply the bond : you can define the precise width of the bond you need, use a wedge having the adequate thickness at each side, and scrape any excess of bond. The masking tape will remove the remaining excess. This will ultimately save weight as glue is always over used since lack of it may cause structural weaknesses. - same remark regarding the quantity of epoxy you are using - note that ambient temperature but also air moisture alters the quantity of epoxy you will use. Moisture alters the mechanical characteristics too but i have no idea to what extent. I used to stock my raw materials in a dark warm and dry environment btw. Finally, I noticed in one of your videos that you were using a mix of glass micro ballons and epoxy for bonds. The mechanical figures of such bonds is poor. Test silicium or a mix of these charges and your bonds will be much better. You will also need much less bond. That’s for today 😁. I also have some tips regarding the use of core foam and your fuselage ribs … next time. Good luck and continue to do such a great job !

Found out your project recently so binge watch some of the episodes in a short time. As a glider pilot for years, and also doing maintenance on the gliders, we have to deliver a weight report of each glider every year. So weighing the wings, horizontal stabilizer and the whole glider itself. The gliders we have at our club are mainly constructed out of different weaves and types of fiberglass. We see that over the years the weight of the gliders changes due to moisture, and some minor repairs. I am not an expert on the area of CF constructions, but can the weight difference between the parts be made due to their difference in age and the ongoing moisture absorbtion over time? Or do CF parts have less tendency to absorb some moisture? Keep up the cool video's:)

We used to build helicopter blades at my previous job, single curing step, glass fiber prepreg made in house by hand and rohacell IGF foam core. Up to 10-15 g difference on a ~7kg parts. Pretty good, I think. What I found in practice is that resin content which my suppliers normally declare with some tolerance, is usually much closer to the nominal. Say 35% +/-3 % is in the datasheet, but in practice it is almost always 35+/-0.5%. Same regarding volatile content, if paper says up to 3%, then in reality it is almost always < 1%. After all, that are compliments to the suppliers. My experience is based on measurements of Hexcel, Solvay, Deltapreg, Microtex and Hankuk carbon prepregs.

Guys, you are ABSOLUTELY FANTASTIC, astonishingly professional, every time I dee your (and shortly mine) Dark Aero, it sounds in my brain the word..........CLEAN. All you make is exceptionally clean, perfect, unique, and I would be super happy , not only to buy three units for me and my guys, but also becoming a shareholder and a financier of your beautifull company. I like you guys SO SO MUCH !!!!

I didn't read all the comments below, but have you considered sealing the core prior to infusion? Depending on the amount of absorption, sealing the core would give you a measured amount of sealant per core. This would give you the ability to measure the resin amount for curing with more accuracy, right? The work is amazing, that you fellas have achieved!

Great job!

Brilliant thinking and problem anticipation.

Very interesting explanation of the process and results. Thanks

Just waiting to get it airbrone You are doing a great job dude

I'm part of a team which designs RC cargo airplanes for SAE competitions, we use fiberglass for leading edges mainly as other manufacturing techniques don't reproduce so greatly the geometry as a proper mold. Our RC planes are in comparison very small however. 3.3 mts wingspan. Our parts were around 4-6% in weight difference however our process is wet lay up and our molds don't have CNC precision. The technique we use for mold making is called stereotomy, it consists of assembling laser cutted parts which orthogonally interlock together.

In the high end infusion moulded model aeroplanes I sell the weight variation between the left and the right wing is usually between 0.5% and 1.5%

helpful information! :)

Temperature control in the workspace. Materials will expand and contract appreciably for something the size of and airplane, so a wing layup on a cold day vs a hot day could vary because the material wasn't the same length. It also matters during assembly, metal aircraft that have parts joined at various temperatures will get wrinkled and wavy skin because the metal was slightly longer or shorter depending on what the temperature was. Metal aircraft assembled in a climate controlled shop are very smooth and uniform. Even one degree makes a difference.

Very informative brother 👍

Great topic! Repeatability is a big deal in precision manufacturing. It can drive cost if scrap rate is high due to tolerance requirements.

I am just interested in your project, but really appreciate you asking these questions, because I was wondering about it as well. Thanks!

Very impressive. The fact that you are measuring weight in grams tells it all! You guys are going to go far.

As Tristan say you are doing a pretty good job with tolerances, as he said, in our course of aerospace material at university (Polimi) to reduce these problems the pre impregnated fiber is the leading edge, yes with the cost to have expiring date and “fridge” to store the material before use, also foam has been overlook and the suggestion is to use honeycomb stiffer, lighter... but with the cost of joining and manufacturing particular shapes (in a lecture from Aermacchi about M-346, the boss says that one of the smart solution was to forget symmetry in the building ailerons and flaps but catch the shape in different way). One solution I suppose you have already embedded in the design is mass damper, it’s an elegant solution to make symmetry in mass. For the foam I just realised a possible solution, used in food, and garment production, prepare sub-parts in foam and keep in storage, weight all and join those give the best result/uniformity (ribs). I was forgetting environment: check the humidity day-by-day, hour-by-hour because composite are very sensible to it...maybe there are moments where in average is inside limits, but peaks can make differences (morning, too many people inside...) Also consider this in early ‘90 only the 40% of the composite golf club shaft was inside the tolerance the rest was garbage

Interesting discussion, and the comments are thought provoking. It’s good to hear from actual professionals with experience too. I’m a layman with no experience in carbon fiber. However intuition leads me to the same conclusions as you reached. Variation in the core material under the cf, along with application of adhesive to bond the parts. Then, as the professionals point out, the difference in resin viscosity and atmospheric variations. I know that you are working for maximum precision and consistency, but I can’t imagine that the tiny variation in weights will make any difference in flying qualities of the actual aircraft. You are right to be concerned, and thank you for the video. I’d say that all things told, it won’t matter for a one-off aircraft. Good work!

I used to build fuel cells for race cars. There was a check valve that I assembled in the shop. Some of the bodies would be turned by hand and sometimes they would use cnc to make them. The hand made bodies always had a fail rate of around 10 in 100. The cnc around 2 or 3 in 100. I'm not a big fan of handmade stuff. It can't touch what machines can do.

Excellent points made. Considering the different materials and complexities your numbers are phenomenal, even the cozy parts are likely better than average. You could take and cut multiple cores and match them by weight and do the same for your fabrics to get even closer. The adhesive will get better in time as the process becomes muscle memory. Even with a robot system there will be variation as wear occurs. Pumps, motors, and diaphragms tolerances change with wear. Your design is incredible, however Drago getting dusted of a runway made me think of something. I would tell people to maintain higher speeds above stall in gusty conditions. This is to maintain solid control authority in a super light aircraft. This is not your father's Oldsmobile (Cessna) comes to mind lol.

I suspect that once you make a lot of different parts that have small variations it averages out, for the wings I suspect it matters a lot but gets progressively less important with how close to the middle of the fuselage it is

Have you weighted them out of the mold (or oven) before applying the glue? Glue repeatability: you could use a CNC to dispense it from a syringe (seriously)

Those numbers look very good - especially given all the variables you mention. I'd be impressed with a sub 2% variation even in flat panels - let alone assemblies. Your composites work is really nice! Do you use perforated release film for the infusions (over the peel ply and below the flow mesh) ? With very light reinforcements it seems to help.

very interesting project you are undertaking. Will you add a single piece of ballast once complete?

Great work 👍 i used to work with the fiber for an airline and i had to use a book 3 times thicker than the bible for one part. QC. For every step. Great job guys

PrePeg in an Autoclave if you want consistent professional results. Weigh the foam cores before hand to make matched pairs. Your supposed to micro balloon the foam before hand so it does not absorb excess resin.

Automobile engine builders have this problem with engine internals. Rather than trying to match all the pistons, rods, etc. you just make a lot and pick and choose the ones you want that are within whatever tolerances you have set up.

Love how informative this channel is. Is there a carbon fiber/resin supplier you guys would recommend buying from for small projects ?

Awesome

I have built an electric bike with plastic casings for the removable batteries. As far as I know, a variation of 1-2% for panels of both sides does not affect the performance or stability. We had a tolerance for 4% and the bike steers accurately. However, the Dark Aero One is an aerial vehicle, so those numbers might be reduced. Still, I think less than 1% won't affect the performance much.

Could also be the weight of the hinges. Did you put them on a scale before the installation? An A/C engine maker is putting all the valves, from a large batch, on a scale to be able to find a set with the almost exact weight. You bros are great!

Great job guys, i would like to know about other factor that is over time wear of joints made with loctite glue, the airplane will fly fast and this micro air sheet wiil shock the glue between parts and it will start to wear out thought time, what are you guys making to protect or no, or ou guys are certain that it will not unstick. Other factor, in a long term will the buyer need to re glue the airplane?

Where do you get that cloth and what resin system are you using?

Interesting. You can do a 30x30cm flat piece to test base repeatability. Then test variation in a basic mold. You can also test impact of how stretched the fiber is laid out vs casual. You can also weigh the raw fiber cloth

Would it be possible to take the tare weights of the adhesive and the resin (per part) before assembly to reduce variances? Cheers.

Knowing very little about this, would there be any difference between your current process, and pre-preg fibre?

How would you ensure the adhesive bonding quality inside the parts? Or the other way to ask, how would you detect bonding defects?

I agree that adhesive application is most likely to be the largest source of weight variation in these parts, given that you are using hand application. Do you think you might move to a CNC adhesive application system (or perhaps adapt your own to your existing CNC platform)? Fascinating stuff, I'll be following along.

curious why there is a left and right rudder, on a single vertical stabilizer. are they halfs of the single rudder that you need to glue together?

Safety first: you want to repeat a part's resistance, its weight comes afterwards. If you measure the same weight of carbon for two flaps (or whatever) and impregnate them uniformly, weight differences due to excess resin or greater foam density will have minimal effect on strength because the quantity of carbon at work is equal in both pieces. And since excess adhesive is safer than lack of it, a few extra grams of adhesive are also acceptable. Resistance first, weight second, repeatability third.

What is the spacial volume difference between your right and left flap molds?

What kind of bonding glue you guys use

Repeatability is very important. I use to work in the pizza biz, and having the exact same product every time is essential. The last thing we wanted is a customer to say, "That doesn't taste like it use to."

Supercub elevator both sides hand laid and painted tube and fabric. 6 lbs 2 oz

Your work is fantastic. How do you address erosion due to abrasive sand and other particles since wind turbines that were planned for 20 years have the blades torn down in 3 to 5 years due to abrasive elements on the air?

I would obsess much more on having a true symmetrical finished shape than inherent static balance.

weight variation for the rudders shouldn't matter all that much, as they are co-located essentially. The fact the other parts are so light, I'd think just adjusting the balance of the plane left-to-right at the end of the build would be easy enough, given how little these things weigh, or you might be able to ignore it. If you want to ensure parts match in weight though, could you perhaps add a feature for adding weight to the lighter of a set of parts? After a pair of parts is made, you weigh them, see which is lighter and by how much, and add that little bit of weight to the other one? Since we're talking grams, I don't think this should be detrimental in any way, particularly if you had a preplanned location and method for permanently adding that weight to any given part to prevent any issues with things such as balance and flutter.

Hi, what is the type of the Carbon fiber n it's weight i.e 6k spread Tow Plain weave 400g

Nice work. Interesting to know the weight difference of the whole plane that you are building compared to one that is made out of Aluminium?

Do you use unidirectional carbon in the flap?

At cruise, how much actual wing surface is needed to maintain level cruise on your DA1. F14 tomcat wings swing back to decrease excess lift and induced drag. You guys seem to have the engineering capability to design a wing that decreases in size for increased cruise speeds. I have imagined that the wing could be made to telescope inward. I know that you have fuel in those wings but I think that some would be willing to trade some of the range for speed. Im not the first person to think of a telescoping wing, This was proposed back in the 1940s with the X planes as a way to reduce induced drag for speeds beyond mach 1.5. Wings that rotate back inside the fuselage and others that simply retract strait into the fuselage. The less unnecessary exposed wing, the less induced drag for increased speed. Show those skunk works guys what your made of and come up with something innovative for DA2. I built a GP4 back in the 1990s. The DA1 build tech is much more precise but the airframe shape isnt much different. Not much is new shape wise for 30 years into the future. George Pereira would have been very proud of you following in his footsteps with the DA1.

Every aerospace manufacturer has extensive documentation and methodology to ensure repeatability.

I have a question though. Do any of you brothers hold a pilots license though. Just ask out of curiosity is all. Great video.

Don't worry that's why balance weights were invented. Repeatability and interoperability really are theoretical terms, the difficulties are much less with alloy, but even those parts machined and jig drilled don't match perfectly.

My question is: why do you need to worry about a couple of grams here and there? Repeatability is nice but you don't have to become obsessive about it. When people start painting their airplane the weight will be all over the place.

How did you figure out if carbon fiber fabricated parts can withstand ALL of the dynamic stresses of an aircraft. I mean when you see how soft and flexible CF is prior to resin marry-up it just seems like a whole lot is riding on the resin to keep things in shape given the myriad of forces distributed to the parts. Also, what about deterioration?

At the end of the day, will that variation affect the performance of the airplane? Is your foam approved by the F.A.A.? For more consistency airplane manufacturers use prepreg fibers and Nomex or aluminum honeycomb.

2:23 You are forgetting the mold, are you 100% sure molds are identical, also finishing parts if you are doing it by hand there is no way you can sad same amount on 2 parts, also did you check the weight of all additional hardware I see you have some hinges and screws or rivets, also did you clearcoat the parts by hand..... ...... ...... ?

Pretty surprised that infusion could produce a more repeatable part than prepreg.

Keep up the g8 work...U will eventually get Elon Musk's support

you weigh them all out and then pair them.

Keep in mind that the lighter you make 2 identical parts, the more likely that those parts are going to have a bigger percentage of weight variance compared to a similar part made from heavier materials. 10 grams difference in a 1500g steel part isn't as noticeable as 5 grams difference in a 500g carbon fiber part.

The worst difference I saw was 14 g which is less than a half ounce. It's not going to matter at all in the finished product. The application of paint will probably result in a greater weight difference between symmetrical parts. Even if not, it's such a small amount that it's essentially nothing and not even worth the brain power to consider. If the difference gets bigger then you might have something to worry about.

A few grams difference? Now your just showing off. lol

The only way to get repeatability is simply don't make more than one part. In other words....its not happening

Well the length of a 747 can very by a couple of feet right? ... Of course that's accumulated on a gigantic structure ... Not really apples