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Old May 10, 2012, 11:11 AM
Jim C
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Gerald is going to be busy. I have one of his "seconds" as well. Got to get it flying with something soon. I am calling it the GT BB fuse. (bunker buster)
It is very strong yet light. I will try to get some pictures up soon.
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Old May 10, 2012, 03:14 PM
G_T
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Hmmm, I might have to use that name!

Pictures always appreciated! Anything that I have to take a good picture with, is from the film era.

Gerald
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Old May 14, 2012, 04:34 PM
Launchpad McQuack
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/Offtopic

Gerald, can you wipe your PM inbox please?

/Ontopic
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Old May 14, 2012, 04:51 PM
G_T
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Ok, there is a little space now. But it tends to fill up quickly.

Gerald
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Old Jun 06, 2012, 11:03 PM
G_T
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Well, I screwed up another fuselage. That's what happens when one is too tired to be working, and then has some bad luck.

The bladder failed, but progressively. It wouldn't hold much pressure by the time an hour had passed. I had to wait until the epoxy was beginning to gel before swapping it out for a second bladder, a couple hours later. Of course that first bladder tested out perfectly BEFORE using it! Then the second bladder also had a leak - probably scratched it inserting it into the mold, as the edges of this mold are a little sharp and neither the mold nor the inflation stem were designed for a re-insert. The consequence is full pressure couldn't be used and pressure was low early on. So this fuselage is carrying perhaps 7g of extra weight in epoxy. That's bad. Also the seam on one side under the wing saddle did not come out perfectly.

To add to the fun, being tired, I swapped the order of two Kevlar laminates in the top side of the fuselage. In practice that makes no difference, just that the outer layer on the bottom is crowsfoot and the outer layer on top is not. Cosmetics. Heck, I even forgot to put a little cabosil splooge around the perimeter of the hatch opening, so it is rough there rather than smooth.

Even with all this, it is still a usable fuselage. It would be an ok fuselage to put on a beater DLG or perhaps for a light sloper (not v-tail though as boom fabric orientation is not correct for that). It really doesn't look all that bad on the outside but that extra weight is bad news for a DLG. Extra weight is NOT a cosmetic issue.

If someone wants it, warts and all, I'll send it for $80 which includes the $10 shipping. Continental US... I'll take it back if it doesn't pass your inspection; you would just be out the return shipping. If you want to keep it, mail me back a check. But realize what you are getting here. This is usable junk, not a contest grade fuselage. It would ship this Friday - I still need to trim up a canopy blank to fit, clean up the hatch opening a little, and clean out any epoxy that got into the hardpoint threads.

If nobody wants it, that is cool too! I certainly wouldn't put a prime wing on it.

Gerald
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Old Jun 07, 2012, 01:04 AM
One Idiot is plenty...
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What material do You use for the bladder Gerald?
Thanx.
Yuri.
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Old Jun 07, 2012, 01:14 AM
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GT,

If it's still available, I'll take it. I'd have sent a PM, but ....

Gary
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Old Jun 07, 2012, 09:42 AM
G_T
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Gary, it's yours if you want it. My PM box is not full, so just send a PM. Of course, feel free to comment on it, good or bad, when you get it.

Yuri, my bladders are made of various materials... The 1.5 mil drop cloth ones seem to be the best. The first bladder was of something else in this case - a force-flex trash bag. Likely the seam was just a little thin somewhere at the back on the first one, or it had a really small starting leak that I didn't detect. I've had minor leaks before in bladders at the back where they are taped. This is the first one that became anything other than minor. Usually they self-seal, and hold pressure regardless. I've not seen artifacts due to this, except for this fuselage. Here, it is about as one would expect from low pressure, or from not getting adequate pressure before the epoxy had thickened a fair bit. I hit it with 60psi for a few minutes early with the second bladder to try to squish more epoxy out (before backing it off to 40psi to prevent the minor leak from getting worse). I'm sure it helped but I knew it wasn't going to be enough.

Gerald

PS - Final weight of this fuselage, minus hatch and screws, is somewhere around 45g. I don't recall the hatch weight - likely about 3g. In my use normally I'd cut about 1.5" off the back of the boom.
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Old Jun 07, 2012, 11:53 AM
Aurora Builder
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45g is plenty flyable in a DLG, Gary is getting a steal!

I'm currently flying a 45g fuselage under my wing. 35-38g would be nice but I'll take 45g if it is dork proof.
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Old Jul 08, 2012, 07:54 PM
G_T
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Hi everyone,

Just thought I'd post a few pics from parts of the process. I apologize for not having more pics, or better quality. I used my GoPro to snap a few, but once I started with the epoxy I sort of forgot to take pictures... My bad. Perhaps I'll get some more pics next time I lay up a fuselage.

I have switched over to using Qualatex balloons for the inflation bladder. They are working better. The bladders I made tended to have tiny pinhole leaks. These leaks were often not on the seams, just random locations in the bag material. They would be hard to spot, as one can't pressurize the bladder all that much without the mold backing it up.

For balloons, one has to use slightly different techniques. My fill stem has a series of holes down its length. With a balloon, one wants just one hole, out near the end. One also has to be particularly careful that there are no sharp places to scratch or puncture the balloon.

I'm using the 160 balloons. These are roughly 1" in diameter and will stretch out to around 60". I do not pre-stretch these out like most do. I want maximum flexability in the radial direction. If one stretches the material in the lengthwise direction, flexability in the radial direction is likely lost. At least, with most sheet-like cross linked polymers that should be the case and I'm presuming this will hold for latex. So my initial inflation is only enough to get the full length inflated.

I can't blow these up with lung power. They are hard to get started. These things start out small enough one could put one inside a soda straw for storage. What I do is position the opening over the little hole in my fill stem and apply some pressure - perhaps 5PSI. I haven't checked the gauge but it is something in this range. When it inflates to the end I quit. It still has a fair bit of stretch left in it at this point, BTW.

Next I put a drop of liquid hand soap on the end of the inflation stem. I have my little valve set so only a little air will go in. With the soap, I can get the mouth of the balloon over the end of the stem. Once it is over, it will slide down pretty effortlessly. I don't use vaseline for this operation as it is messy and interferes with tape adhesion. The tiny bit of soap cleans up super easily.

I slide the balloon down until it hits the transition in the stem. This is at the base of the stem, where it widens out to just under the diameter of my tailboom. The mouth of the balloon doesn't go over this step easily - and I don't try. Instead, I grab the outside of the balloon and pull it over. This works easily. The balloon gets inverted inside but it doesn't matter. I just drag balloon over the back of the inflation stem until perhaps a quarter inch is left in front of the stem.

Now I disconnect the pressure fitting, and using the hand valve, gradually drop pressure so the balloon collapses in place. I don't let quite all the air out - I leave it a diameter roughly equal to the larger part at the back of the stem. One has to hold the balloon, as now it wants to pull itself forwards.

Next, I take a knife and score around the balloon at the back. It separates, exposing some of the metal at the back of the inflation stem. I use black electric tape to secure the balloon to the stem. In my case, about three layers is what it takes to make the back of the stem a snug fit in the mold. Once this is done then I let the rest of the air out of the balloon. It is now ready to go. Really, it takes less time to do this than I think it took to type it.

I also included some other pictures of my shop setup and steps of the process.

Gerald
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Old Jul 08, 2012, 08:01 PM
G_T
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PS - I pretty sure I've solved the cosmetics issues. However, it still takes way too much time to make a fuselage. I only have the time available on weekends, and not every weekend at that. So production is pretty slow.

Right now, from getting ready to mix epoxy until cleanup and lights out, is somewhere around 2 hours 45 minutes. Add in perhaps an hour or two for fabric prep, mold cleanup and prep, hatch trimming and fuselage cutout, and chasing the threads, and it is getting somewhere around 5 hours total.

I can reduce this by perhaps an hour just by changing fabric selection, but that will have to wait until I order fabric. But the kicker right now is I need that 3 hour window for the wet work. That means weekends.

Gerald
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Old Jul 08, 2012, 10:29 PM
One Idiot is plenty...
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Joined Jun 2005
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Gerald.
You are saying that epoxy won't eat through the balloon while curing?
And You are saying that if balloon survives curing process /would be a miracle,unless You don't use MGS/ it wont stick to the fuse after all?
Thank You for the pictures.
Yuri.
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Old Jul 08, 2012, 11:41 PM
G_T
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Hi Yuri,

The balloon survives fine. Unfortunately this time it broke off at the back when extracting the inflation stem - a tight fit - so I'll have to fish it out when I cut the hatch opening. No big deal. I use MGS slow for the fuselage.

Gerald
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Old Jul 09, 2012, 12:20 AM
G_T
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Here are some more pictures. Impatience won out; I went ahead and demolded.

Initially I unbind the inflation stem. That is, cut the binding wire that prevents it from pulling out. It still cannot be pulled out though, as it is sized for a very snug fit.

Next I progressively release the tension on the clamps, and then remove them when all are loose. Now I go ahead and pull the inflation stem as it is no longer clamped by the mold halves.

My molds have a very slight bow to them, which would yield about 1mm separation at the center when not clamped. These molds are pretty stiff, so when the clamps are removed the two sides automatically begin separation. I have screwdriver slots in each end, and a gentle twist is all that is needed. The bottom side mold (which is on top the way I do the molding) lifts right off. Actually the screwdriver isn't even required. Just lifting the one side of the mold will drop the other due to its weight.

You can see that there is a thin layer of epoxy+PVA which forms the flashing. For scale, it is about the thickness of a piece of paper. I just peel it off while the fuselage is in the mold. Without any fabric on the flange, it just snaps off pretty cleanly. Little additional cleanup of the seam is required. BTW, this is about twice the epoxy usually present. This time I didn't have the mold fully clamped before putting in about 5PSI. I wanted to see if I could get out a little more epoxy that way. My mold closes so tightly otherwise that epoxy has to migrate through the little resin channel out to the front of the mold to get out. Tentatively, this change might have removed a little more epoxy but much less than 1g. It is probably not worth the extra risk of the epoxy flow pushing a fabric fiber out onto the flange which would then prevent the mold from closing fully.

Removal of the fuselage from the upper side mold requires some care. I snapped a fuselage in half a couple days ago. It was an experiment in a little lighter but stiffer layup. It wasn't strong enough to survive extraction - or more likely I wasn't patient enough! In any event, if the fuselage survives extraction it is pretty tough.

The threaded inserts effectively bond themselves to the alignment pins. This joint, for the two pins, must be broken free. Really this is the only thing holding the fuselage into the upper mold with any force. Otherwise it would lift right out with essentially no force being required.

I start the process with a wooden dowel inserted in the tailboom to act as a lever. I gently lift the tailboom from the mold, and insert a playing card. I slide the card along the fuselage towards the front. It gets quite tight as one approaches the wing saddle area. If one is patient and persistent, the fuselage pops out with a "crack" sound. It is alarming the first time or two one hears it, but it is normal.

The PVA needs removing, and the dummy hatch needs to be removed. But I'll throw this fuselage in for post cure first.

The hatch can generally be removed by squeezing the fuselage enough to get part of the hatch to lift. Then an inserted playing card will work it the rest of the way off. Sometimes though one has to resort to a knife. The more knife work required, the less usage I get from the dummy hatch. I suppose I could just use it as the real hatch as the fit is perfect, but that dummy hatch is saturated with wax and PVA to prevent it from being glued into the mold. It would take some work to get it all out. I may try sometime though as it would eliminate the fitting step of a new hatch.

I initially cut the hatch opening with cutoff blades. I have some diamond ones now so I'm curious how they do. Then I grind the opening to shape with drum sanders. Then a touch of wet sanding with 600 grit gives a very smooth clean edge.

I did have one cosmetic defect on this fuselage. I trapped a bubble on the surface. That's what I get for working with a headache and an upset stomach, well after midnight when I should have been sleeping. Also karma, from saying I had the cosmetic issues all solved!

This fuselage is going to get my JJEdge wing which is a perfect fit. I've been waiting for building and flight reports from others but nobody - to my knowledge - has built up one of these fuselages yet. So I'll do it myself.

I'm done with experimenting for now. The next fuselage will go to someone on the list.

Oh, expected weight after cleanup, with hatch - about 43g, or perhaps 42 after trimming to length.

Gerald

PS - They sure don't look as good with PVA on them as they do once cleaned up!
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Old Jul 09, 2012, 01:18 AM
One Idiot is plenty...
Dbox's Avatar
United States, OR, Portland
Joined Jun 2005
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Quote:
Originally Posted by G_T View Post
Hi Yuri,

The balloon survives fine. Unfortunately this time it broke off at the back when extracting the inflation stem - a tight fit - so I'll have to fish it out when I cut the hatch opening. No big deal. I use MGS slow for the fuselage.

Gerald
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.
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