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Old Jul 09, 2012, 04:51 AM
Now fortified with carbon
DLGjunkyard's Avatar
Canada, ON, Puslinch
Joined Apr 2010
2,732 Posts
Quote:
Originally Posted by Dbox View Post
I mostly work with MGS slow and noticed that is one aggressive resin.
Eats through different ,paints,plastics as well as rubber balloons.
Thing is , one balloon survives molding process and another dont.
It pops during the curing in about one hour from being inflated and when I am taking balloon from the next screwed fuse it looks like it has been eating by
moth.I am using same balloons as You Gerald,just 260 size.
And still Gerald,do You remove the balloons from fuses without any problems
cause You wipe them with mold release or some other stuff before inflating ?
In my case RUBBER BALOON +PRESSURE +MGS makes perfect bond to fuse wall,just perfect.
Sorry to bother Your thread,but I am getting paranoid when it comes to
inflation bladders....too many materials and time have been wasted...
Yuri.
This post kind of finds me confused. I use the same combo [mgs with balloons] and they pull out so well I have used them for two cycles at times. I do use PVP with partall #2 and I also rub Vaseline over the outside of the balloon. I did over 50 pods last winter this way. Perhaps its your mould release.
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Old Jul 09, 2012, 07:55 AM
G_T
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I am not putting anything on the outside of the balloons at all. They release themselves for some parts of the fuselage, when the pressure is released, and for others I just twist them out. I'm using the black balloons. In my experience so far, they do not stick to the inside of the fuselage any worse than some bladders. I have two areas of the fuselage where both tend to stick. One is the internal hard points. The other is the tip of the nose. But so far I've always succeeded in removing either bladders or balloons and I've done no special prep of either.

Seriously, this last fuselage, the balloon released from the tailboom and retracted itself up in the fuselage before I could grab it. It is attached to the tip of the nose and the hardpoint locations, and appears unattached elsewhere. When I cut the hatch opening it should be an easy extraction.

The previous one didn't get away from me. I just twisted it out from the tailboom end.

MGS makes two families of resins. Perhaps you are using the other one? I'm using 285 and 287. Or perhaps you received some knock-off balloons?

Perhaps I have just been lucky. But my experience so far seems to mirror that of others I've talked with. That's why I made the change.

Balloons are one of the standard methods. But they are not the only method. If they don't work for you, don't use them!

Perhaps you are using too much pressure, or too high a temperature in the initial cure?

Gerald
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Old Jul 09, 2012, 08:14 AM
Now fortified with carbon
DLGjunkyard's Avatar
Canada, ON, Puslinch
Joined Apr 2010
2,732 Posts
285 MGS here also and I dont heat in the mold until about 8 hrs has passed.
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Old Jul 09, 2012, 08:29 AM
Aurora Builder
United States, MD, Lusby
Joined Nov 2003
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FWIW I don't think the 285/287 MGS resin/hardener is any worse than other resins I have used (West, Pro-Set, Resin Research, Composite Pro) in eating through materials. I've had no problems with different paints and reactivity. Nor have I had issues with mold sticking on a Corian mold, which is essentially a super hard plastic. I can't speak to the inflation bladder issues.

Gerald, thanks for posting some details of your build process. I have the same issues as you do, time to build these things is hard to come by, I'm pretty much swamped every weekend so weeknights are my build time. If it makes you feel better, it is closer to 4 hours of material prep time per wing, a solid 4 hours of layup time to do the skins, and then another 2 hours to close the molds. Basically a 3 night process. Things get faster during every layup but I doubt I can get much better unless I build everyday.

Will be great to see your fuselage flying!!

-Sam
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Old Jul 09, 2012, 10:27 PM
G_T
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Joined Apr 2009
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Not much progress and no pictures from today.

The PVA has been washed off. Now it is nice and shiny. As usual there is still a bit too much epoxy in this thing. My mold seals a little too well. I may have to do something about that sometime. I'd guess the fuselages could lose 1g epoxy and not miss it. But a little extra epoxy is not a bad plan with Kevlar... Tradeoffs...

The hatch was really attached on this one. I had to use a knife to score around the perimeter and gently lift along an edge. Once it was slightly started, I used a playing card worked under the edge to pop it off. It came off readily enough once the edge bond was broken.

I've drilled through the bottom of the hardpoints where the fabric covers the holes, and chased the threads with a 6-32 tap to remove traces of epoxy and wax.

The hatch opening still needs to be cut, and the balloon removed. It is rattling around loose except for being stuck at the very nose. The tailboom needs trimming to length as well.

I haven't decided whether or not to use the hatch that I made the mold with, or to make a hatch from the blank I just made at the same time as this fuselage. I can shape hatches very accurately but it is probably a bit faster to just use the one molded to fit. The only real minus is the need to get the wax out of the molding hatch or things won't stick well to it. I made a half-@#$@d attempt using denatured alcohol. It will be interesting to see how well tape sticks to it tomorrow. I've used this hatch for a few fuselages now so it has been well saturated with wax and PVA. It would probably be smarter just to keep it for molding purposes.

This fuselage will get my old JJEdge wing (heavy but solid, with top drive Hyperions), one of the Fr3aK vertical tails (WITH rudder), and it should get a full flying horizontal on a Spring-V mount. That will either be an Edge horizontal, or a new foil that I've nearly finished for full flying tails. I'd like to go with the new foil as a test. This will be my new beater moldie. I'll likely stick a 300MAh NiMH battery in the nose, followed by a Futaba 6008 receiver, and then a pair of JR 285 servos. The battery will plug directly into the receiver. I may change the receiver based on what I have on hand; ditto the servo selection. If I still have an SM-22 laying around it may become the rudder servo. Ballast will likely be a lollipop system. Hatch retention is undecided. Structurally this fuselage doesn't require the hatch to be taped, so I have options. I'll clip the servo leads on the wing and put in an autoconnect. Tail pushrods will be internal carbon rods - one of the lightest and stiffest systems.

Gerald
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Old Jul 09, 2012, 10:55 PM
Just fly it!
wyowindworks's Avatar
Cody, WY
Joined Nov 2007
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Quote:
Originally Posted by G_T View Post
My mold seals a little too well. I may have to do something about that sometime.
Just don't clamp it together so tightly. I can change the final Vf by 5% by tightening or loosening the clamps 1/4 of a turn. After the first 20 minutes you can go ahead and tighten everything down tight. I can slip a .003" feeler guage between the mold halves during the evacuation period. The final flashing mics from .0005" to .002".
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Old Jul 09, 2012, 11:17 PM
He bowls overhand
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Falcon, Colorado
Joined Oct 2004
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What Adam said. Leave the moulds a few mills apart when you first inflate the bladder, and also inflate it harder during those few minutes. I was doing 70psi for 15 minutes. Then, release some pressure, (40psi) and close the moulds. It keeps the print through to a minimum but also evacuates a bunch more epoxy then any other way I tried.

If the bladders are sticking at all, just give a quick spray of Frekote and wipe with a rag before use.
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Old Jul 09, 2012, 11:56 PM
G_T
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This time I didn't clamp tightly before pressurizing, but I used much lower pressure until clamping was completed. The flashing showed about twice the epoxy evacuation towards the sides compared to usual. But in the end I don't think it made a noticable difference in the total epoxy content. I'll try a bit more pressure next time. But what I want to avoid is having epoxy flow force fibers out onto the flange.

Gerald
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Old Jul 10, 2012, 12:02 AM
He bowls overhand
threcixty's Avatar
Falcon, Colorado
Joined Oct 2004
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If you are doing a lapseam with carbon or kevlar, the stiffness of the fiber itself should keep it from pushing into the seam under these pressures. We are only talking about a .005-.015 gap here.
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Old Jul 14, 2012, 08:17 PM
G_T
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Joined Apr 2009
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This time I allowed a bit larger gap and used 40psi for a bit before closing the mold solidly. That helped. The fuselage came out perhaps 2-3g lighter. Cosmetics are still good. A few random fibers did migrate onto the flashing region but not enough to cause an issue.

I should be laying up another one tomorrow, the third one this week. We'll see if it also ends up in the <43 gram range.

For those who are waiting for fuselages, I'm trying to get caught up.

As for pictures, once I start mixing epoxy, I forget all about the camera.

I altered my procedures and knocked the wet work time, between sitting to mix and turning off the lights when done, down to 2 hours 15 minutes. The last 15 minutes are mostly waiting for the mold to evacuate extra epoxy before closing it down solidly. That reduces it down to where it is feasible for me to lay up an occasional fuselage after work. There is still probably two hours of mold cleanup and prep, fabric cutting, and hatch work. So this is still a fair bit more total time than I'd hoped.

Gerald
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Old Jul 14, 2012, 09:09 PM
One Idiot is plenty...
Dbox's Avatar
Planet Earth
Joined Jun 2005
5,186 Posts
I just made two fuselages to see the weight difference between fabrics used.

One made with 12K UNI----no clearcoat 33gr. Strong boom.
Another with 1.5K UNI----heavy clearcoat 34gr. Flexing boom
NO DIFFERENCE IN FINISH APPEARANCE
Both weights with -No canopies ,or blind nuts .....
Yuri.
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Old Jul 14, 2012, 09:39 PM
G_T
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Joined Apr 2009
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So you are probably somewhere close to 38g ready to go, assuming no servo tray required for structural purposes. You'll just have to see if they are stiff enough, strong enough, and durable enough for what you want. Light is relatively easy. Light and good enough is much harder. Hopefully you now have what you want!

I'm presuming the unicarbon is in the tailboom or between layers where it cannot be seen. 12K vs 1K for a real unicarbon wouldn't matter to me. What would matter is the thickness and weight of the carbon layer and the modulus and strength of the carbon fibers. For example, consider 100gsm HM unicarbon vs 125gsm unicarbon, from the same manufacturer and available from R&G. The former is quite a bit stiffer for the weight, the latter is a little thicker and not as brittle for the weight. One would use them for different purposes. I neither know nor care how many K the tows contained that were laid down for these unicarbon materials. For unicarbon I fail to see how it matters.

IMHO, clearcoat is a waste of weight on a fuselage. It adds nothing structurally and it doesn't really add all that much to appearance if the layup itself is done fairly well. It looks like you don't have a reason to use clearcoat! It is nice to get rid of steps that are not required. Besides, if one is going to add the weight of clearcoat I'd rather see that weight in fabric and epoxy as that is structural. That's just what you did apparently with the change you tested. It seems like a good change to me.

I'm aiming for something pretty bulletproof compared to most DLG fuselages, so they can take real world abuse even from a pilot like me, without taking damage. I've seen too many fuselages break on strong launches. Or crack when squeezed a bit. I'm not expecting that to happen to one of mine! Also being 2.4 friendly incurs a little bit of a weight penalty as well as adding complexity to the layup. I don't like wiskers out in the airstream as they add a lot of drag plus they are easier to damage on the outside than on the inside.

Gerald
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Old Jul 15, 2012, 02:15 PM
Father of Fr3aK, DLG Pilot
tom43004's Avatar
USA, OH, Worthington
Joined May 2002
6,733 Posts
Quote:
Originally Posted by G_T View Post
I altered my procedures and knocked the wet work time, between sitting to mix and turning off the lights when done, down to 2 hours 15 minutes. The last 15 minutes are mostly waiting for the mold to evacuate extra epoxy before closing it down solidly.
That's usually when I clean the shop and prep for the next part. I like to babysit my molds for at least 20-30 minutes after closure just to make sure I get the parts to the correct pressure / temperature etc.
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Old Jul 15, 2012, 02:46 PM
Make Flying Fun
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United States, MD, Lutherville-Timonium
Joined May 2003
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+ 1000 for babysitting!
Curiosity is very compelling and annoying as well !
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Old Jul 15, 2012, 08:53 PM
G_T
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Joined Apr 2009
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Hello everyone,

I received a request today to possibly cut a hatch opening a particular way... The hatch starts 2.5" back from the nose, and extends for 5". For reference, here is how I normally cut the opening. I start about 3/8" back from the front of the hatch and don't go as close to the rear. There is obviously room to cut larger if one wants. A Dremel with a sanding drum does the job fairly well. A touch of wet sanding afterwards cleans up the remaining fuzz. The width of the opening is right about 3/4".

I can also provide the fuselages without the opening cut. If I do that, then the recipient gets to remove the balloon. It always snaps at the back when I remove the fill stem, and shoots up front. It removes easily. Beware though - these fuselages are pretty tough around the canopy opening so don't expect it to be easy to cut the opening.

If a custom cut for the opening is needed, then I'd need to know that.

The fuselages come with the required 6-32 screws of appropriate lengths.

All this is just FYI.

Gerald
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Last edited by G_T; Jul 16, 2012 at 09:07 AM.
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