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Old Jul 30, 2012, 08:38 PM
G_T
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Charlie, remind me in about three weeks, and I'll get one to you.

Gerald
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Old Jul 30, 2012, 10:17 PM
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Gerald,

Are you using 1.7 kevlar in the boom or 1 oz?

Thanks,

Gary
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Old Jul 30, 2012, 11:07 PM
G_T
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1.7oz would be too much of a weight penalty so it's 1oz for now. Lighter, of what I have tried, did not give the mechanical properties I was looking for in this version of my fuselage. Though it was a lighter layup that I showed in the picture with the weights hanging off the tailboom.

I will be testing alternative layups, particularly once I get the next ~10 fuselages completed and out the door. I reserve the privilege of refining the layup as I go along.

Knowing the layup I use in my fuselage may be of little use to someone else with a different fuselage design. Results are geometry, materials, and process dependent. My layup would be stupid heavy on a fat fuselage. Stupid stiff too, FWIW. If I used a fat fuselage layup on mine, a strong thrower would break it. If someone with an ovalized boom used my layup, there would be way too great a stiffness difference in the horizontal and vertical flex directions and the tailboom would be unstable in horizontal bends - it would twist but the direction of twist may not be predictable (for the mathematically inclined, see bifurcation theory).

Gerald

PS - I will lay up #14 tomorrow night as I did most of the prep for it earlier this evening.
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Old Jul 31, 2012, 11:04 AM
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just reading along
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Old Aug 01, 2012, 12:22 AM
G_T
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#14 all tied up.

Note the non-ideal right angle terminations on the fabric layers. This is because frankly it saves time and effort. Right now these fuselages take too much time for them to be worth it to me financially, even at their current price. What you can't see well is the staggering of the layers top to bottom, and hidden pieces of fabric like strips of S-glass and strips of HM unicarbon. Orientation doesn't show well in pictures like this either. These things are overbuilt, but not heavy.

I figured you all might want to see this step in the process.

The bottom side fabric all resides just a hair below the mold flange. Some layers, such as Kevlar, are lower than that. You really want to avoid having Kevlar fibers migrate onto the flange... A little is not that much of a big deal, but a lot would be rather annoying. Also, it is for cosmetics. A Kevlar stripe down the tailboom wouldn't look as cool as that all carbon look.

The upper side, except at the tip of the nose, has a lot of fabric over the flange. It is the side with all the extra side reinforcement and most of that is pretty well centered at flange height.

The upper side has its fibric tied down and out of the way, encapsulating the balloon and fill stem. The bottom is carefully laid over the top, and clamped at the rear and temporarily at the front. Then the threads are cut and pulled out. Clamps are applied, and the slack is taken out but they are not tightened except for the back two and the front one. The stem is anchored to the rear clamp with binding wire.

Then the balloon is pressurized up to 45psi for about half an hour, with that small gap along the sides of the mold. The mold oozes epoxy.

Speaking of oozing epoxy - I spent about two hours chipping it off the mold this weekend. That is why the molds look pretty clean. Afterwards, I waxed all the outside surfaces. I don't want to spend two hours doing it again!

After tha half hour is up, I progressively clamp the mold solidly. After that only a little epoxy is going to be able to get out. That's the problem with tight fitting molds! Then the warmth is added. Not much actually, just some heating pads and a tent of sorts. This elevates the temperature enough to improve the cure and cure rate for MGS slow.

The mold stays clamped for at least 18 hours and really it should be 24. Sometimes I'm a bit impatient and don't let it have the full 24. I do keep samples of the epoxy and check it for brittle failure before unclamping. If one bends a sample and it snaps then the epoxy is at least moderately cured. Before that it is definitely NOT ready for demolding.

In the case of this particular fuselage, the balloon developed a micro leak at the back end after epoxy evacuation and full clamping. It would occasionally push a little bubble out the back of the mold. Were this a bladder I'd call it quite a bit better than average. However with a balloon, usually it works or it is shot. This one is unusual.

I gave it a test - close off the valve to the fill stem for a few minutes. When I opened it back, I could not hear any air going in. So I know the leak is very small. The little bubbles are rare and not increasing in rate. I'm thinking it will be ok this time. As the epoxy thickens this one will seal up the rest of the way, just like what always happens with bladders.

Pressure is left at a bit above 40psi for initial cure, which is my usual pressure. This is backed off a few pounds from the evacuation phase. My mold's tooling coat is not as hard as I'd like, so I keep the pressure down to this level. It is enough.

When I made the tooling coat I thought I had enough aluminum in it but it showed evidence of settling during cure. If I do it this way again, I'll add more aluminum and vacuum degas the tooling coat. Then the tool will be harder.

I got some artifacts in the mold surface when I used pressure up towards 70psi once. I figure eventually the mold will need repolishing to remove any accumulated artifacts. But at least so far, the artifacts from the PVA layer greatly exceed the artifacts from the mold surface. This mold has a great many pulls left in it before it warrants a repolish, at least as long as I stay in the current pressure range.

Gerald
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Old Aug 01, 2012, 01:05 AM
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Quote:
Originally Posted by G_T View Post
When I made the tooling coat I thought I had enough aluminum in it but it showed evidence of settling during cure. If I do it this way again, I'll add more aluminum and vacuum degas the tooling coat. Then the tool will be harder.

I got some artifacts in the mold surface when I used pressure up towards 70psi once.
Looking good, Gerald.

The stability of the mold finish under high pressures is controlled by the chosen resin more than the fillers. In fact, resins that are heavily loaded can be more prone to creeping than lightly loaded ones. The hardness of the surface is also less important than materials ability to resist creep under the sustained pressure. The resin behind the surface coat backing also makes a difference. A hard surface coat can still creep if the resin behind it creeps under pressure. I stopped using US Composites in my bladder molds for this reason. I could heavily load it with silicon carbide (harder than aluminum) and still have the problem if the mold was pressurized at elevated temperatures. For me the problem was solved by using resins that have a higher HDT when heat cured. This typically means that the resin has a higher cross-link density which makes them less prone to creep under higher pressures and heat.

The reason that I bring it up is to spare you some labor on your next mold. I've been down this road of trying to eliminate the problem. No filler or loading that I tried would resolve the issue. Only a resin change fixed it. I've been making my surface coats from MGS and backing them with Adtech laminating resins for tooling (301 and 302-PC) with great success.

When it comes to edge durability the granulated fillers don't make a big difference either. It mostly comes down to the tensile strength of the resin.
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Old Aug 01, 2012, 08:18 AM
G_T
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Ok, interesting, and thanks for the information. I used System 2000 for both surface coat and backing on this mold.

Gerald
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Old Aug 01, 2012, 02:04 PM
G_T
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Everyone,

If there are questions you have or pictures that you might want to see, feel free to ask! Admittedly, when I'm working with epoxy the camera gets forgotten or ignored since I have to take off gloves and stop the process to use it. But if you want to see something and have a bit of patience I'll generate some pictures. They won't be great pictures as you can tell from the ones I've posted. I'm using my GoPro Hero2 as a camera. It works, but is not ideal in that role.

If there is interest in fuselages from batch 2 then feel free to let me know. Batch 1 will likely be finished in about a month when I run out of fabric. I think that might get me through the list of everyone who has expressed interest in a fuselage to date.

Those who have received fuselages should feel free to comment or make suggestions! I'd love to get more feedback!

If a fueslage gets broken - crash, midair, sat on, whatever - I'd like to see pictures and a description of the event if possible. It may be that I can do something so that future versions would suffer less damage.

If a hatch suffers damage I can provide a replacement that fits like new. I will have to charge something for hatches though and I haven't decided how much. Hatches should be pretty resistant to damage being S-glass and Kevlar so I doubt I'll get many requests.

Gerald
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Old Aug 01, 2012, 02:27 PM
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Great stuff Gerald. Could you post a pic of the different fabrics cut and ready to be placed in the moulds.
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Old Aug 01, 2012, 03:20 PM
G_T
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I can do that. Tomorrow I'll either be prepping for another fuselage, or laying one up. I might get you a picture then. But realize it is a moving target.

For instance, recently I've gotten the fiber ratio higher. As a consequence the layup is now better compacted; ie, thinner. A thinner layup is not as stiff. I've added some bits of reinforcing fabric to compensate. Also, the lower epoxy content resulted in persistent bubbles appearing in the surface at the front of the wing saddle and at the front of the hatch. Now I have bits of fabric and splooge in these locations as well, to fix the cosmetics.

So what it is, is not what it was, and may not be what it will be.

Gerald
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Old Aug 01, 2012, 03:25 PM
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Too funny Gerald. I've only built 4 wings with the exact same layup. I now have a very good idea what my standard layups will be, but its taken a while to get there, and I've been waiting on special fabric to do it with. So again, the layup may change in the future!
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Old Aug 01, 2012, 08:50 PM
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I have been blessed to see some "How to", professional manufacturer in Europe
does his fuses.Not DLG's ones but lightest /strongest F5X ones I have ever held in my hands.
Controlled amount of resin in lay up and bladder pressure from 0.5 to 1 bar.
If slow curing resin is used in lay up,does not make any sense to go beyond that pressure
torturing Your mold....Just think about that.
Yuri.
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Old Aug 01, 2012, 09:12 PM
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Quote:
I have been blessed to see some "How to", professional manufacturer in Europe
does his fuses.Not DLG's ones but lightest /strongest F5X ones I have ever held in my hands.
Controlled amount of resin in lay up and bladder pressure from 0.5 to 1 bar.
If slow curing resin is used in lay up,does not make any sense to go beyond that pressure
torturing Your mold....Just think about that.
Yuri.
Thought about it.....

I was able to add an additional layer of material for the same weight in my DLG fuse by going from 40 psi to 65 psi. I do use faster setting resins for production reasons that undoubtedly come into play (require higher pressure). I have gotten Vf% over 70% will lower pressure and slow setting resins but the porosity level within the laminate is higher. Most high performance structures that are made in autoclaves are processed at 7 bar (101.5 psi). The pressure not only pushes the fibers closer together but presses any air voids into a smaller state. Both improve the quality of the laminate. The Vf% shows diminishing returns as the pressure goes up but the porosity reduction will continue to improve.

If you are happy with the results of 1 bar then great. Why go any higher?
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Old Aug 01, 2012, 09:17 PM
G_T
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My fuselage will gain a few grams of epoxy, at half the pressure. Controlling the amount and location of resin to a greater extent than I'm doing right now requires disturbing the fabric more, and taking more time. I started there, and my current fuselages are better. But, for $50US more per fuselage, sure. The results won't be any better and could well be worse.

Kevlar yarn soaks epoxy. The excess epoxy can be squished back out for the most part. Kevlar yarn is also rather porous, unlike glass, so if you don't get it wet to start with, you will have a lot of air in there. Air means unsupported fiber, which is a definite no-no with Kevlar. IMHO, with Kevlar in the mix, it definitely makes sense to get it wet and then use a bit of pressure in the bladder. Even unicarbon is a bit of a sponge. I am presuming they are not vacuum infusion impregnating the layup which gets rid of some of these issues as there won't be air that needs to be removed that way.

I appreciate the information, but I do not agree with it for this application. But you are of course welcome to do it that way on your fuselages!

Gerald

PS - Adam, just saw your post. Mine is redundant!

PPS - Fuselage #14 should finish out somewhere around 42g with the current screws. Cosmetics is the best yet. This one is slightly heavier because I added glass compared to previous ones. That is a light glass patch plus splooge to get rid of a bubble at the front of the hatch that was becoming a recurrent cosmetic issue, and two additional small strips of S-glass for additional reinforcement of the canopy opening. That's a precaution to handle the layup being thinner due to better fiber ratio (though honestly I do not know the real fiber ratio - it is harder to figure accurately with the hardpoints, structural and cosmetic splooge [3 types], and I think 8 types of fabric and uni [3 types of Kevlar, 2 of glass, 1 carbon fabric, and 2 types of carbon uni]).
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Old Aug 03, 2012, 11:15 AM
G_T
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Fuselage #12 is 43.6g with screws. Fuselage #14 is 43.8g with screws. Probably these are pretty typical weights now. I was wrong on the weight for #14 and probably for #13. The hatch cutout does not weigh nearly as much now as it used to. I relocated some S-glass to where it would do more good, as in not as much is cut away when I make the hatch cutout, and the fiber ratio is higher. Amazingly the cutout lost well over a gram from early prototypes. Essentially it weighs half as much. So my guesstimates of final weights have been off when they were obtained before I cut the opening.

Alan Anderson gets #12 and Gavin gets #14. #13 has already been shipped and is in Larry's hands.

#14 was the first one with some additional small S-glass strips beside the canopy opening to compensate for the layup getting thinner. It is noticably stiffer there now. All future fuselages will have these little strips.

#15 goes to Brian. That one is a custom layup using a scrap of Oxeon spread tow for the outer layer instead of the carbon I've been using. I got the scrap from Phil - leftover from Fr3aK wing production. I did not like the cosmetics and conformability of this fabric when I tried it on fuselage #2. But my methods are a little different now, so I'm curious. I know the conformability will be an issue, but whether it traps bubbles because of it... That remains to be seen. I'll get this one in the mold either tonight or tomorrow, for shipping on Monday.

#16 will be mine (I still haven't kept one for myself), and should be in the mold somewhere around the middle of the week if not sooner. That one, and all the following ones except for one, will be standard production layups.

The other experiment won't be for a few weeks as I need more 100gsm HM uni, but it is Samurai outer carbon, for Sam (who donated the fabric scrap for a test, left over from his wing production). I'll make that one once I have the rest of the required carbon. I thought I had it, but when I unrolled the rest of my roll, it was a few inches short of being useful for the long pieces.

The list, as it stands now:

Gavin - #14 shipping today.
Alan - #12 giving to him Sunday.
Brian - #15 should be shipping Monday.
Me - #16 finally!
Sam Carter - (1) custom when I get the carbon.
Paul Harvey (1)
Tai (2)
Kevin (1) - on the condition he not use it to pull a fuselage mold!
BavarianCharles (1)
Brian Hummel (1)
Buddy Roos (1)
Todd Long (1)
Killercando (1)

I don't know if I have the carbon to make it through this list before I run out. What doesn't make it into the first production batch will be in the second.

If there are additions/corrections, let me know. The list is not a commitment.

In about two to two and a half weeks I should have the Titanium front screws. From that point it will be standard for the fuselages, for a small weight savings.

Gerald
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