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Old Nov 13, 2009, 02:08 AM
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tzyoung's Avatar
United States, VA, Alexandria
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Build Log
Scratch built Super Bandit

This build log will cover a project danstrider and I are working on collaboratively to build a composite fuselage based on jetset44's BVM Super Bandit EDF (http://www.rcgroups.com/forums/showt...t=super+bandit). I built this airplane over the last summer from Bluecore. I was using a super cheap GWS 64 fan with a small inrunner at about 200-250 watts. D an decided that he wanted one as well so we decided to make molds of the fuselage and work out the layup details as we go. This version will fit a 70 mm fan and should have much better performance than the prototype.

The first round of pictures shows the plane as I was flying it and the teardown process to turn it into a plug.
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Old Nov 13, 2009, 02:29 AM
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After creating a plug the next step is fitting it to a parting plane.

I will say a few words about the type of molds that we decided to use. Both of us have had our fair share of working with molds made of composites and we decided to do the molds for this plane from Hydrocal which is a reinforced gypsum plaster. Hydrocal makes for less expensive molds and we will assess their durability as we begin pulling parts from the molds.

A foam dam was built around the part using 3m 77 to stick the wall down to the parting board. All of the seams were sealed with Kleen-Klay to reduce the leakage as the Hydrocal is poured. The attached pictures show the dams for one plug half.
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Old Nov 13, 2009, 02:57 AM
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if you get it to CG with a 4S 3200 in the nose, i'd like to buy one
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Old Nov 13, 2009, 10:31 AM
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We used all of the 50 lb bag of Hydrocal to pour the canopy mold and one half of the fuselage. The fuselage was big enough that it took three batches to fill up the mold half. Our mixing method for hydrocal is the "dry lake bed" approach where the powder is sifted into the water until there is a solid layer at the surface with mud cracks in it. After letting the mixture rest 5 minutes the plaster is mixed to break up and clumps and poured in the mold. This seems to give the best working time and no bubbles in the mold surface.

There is plenty of room in the nose for batteries so I think a 3200 mAh 4s pack would be a good match for this airframe.
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Old Nov 13, 2009, 10:55 AM
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The dams were then torn off after the plaster hardened. A note about this is that this stuff gets super hot and starts melting anything that it can. For that reason I do not advise water based products as a sealer for your plug. The pictures will illustrate why. But we did get away with it and will be able to use the plug to finish the other mold half. We will seal out the mold flange with epoxy and do another pour similar to the way that composite molds are built.
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Old Nov 13, 2009, 11:39 AM
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What will you use for mold release when laying up the parts in the plaster molds? I've made a few plaster molds for smaller parts but haven't layed much glass in them, only once.
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Old Nov 13, 2009, 12:02 PM
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I gotta be honest, we're trying out verbatim the method in the DVD Composite Molding Made Easy. We did change out Hydrocal mixing method from the video to a method suggested here:
Mold Making and Casting Tip: Mixing Hydrocal Plaster (6 min 28 sec)
As for mold prep & release, the DVD suggests to bake out the plaster mold for a few days then to warm the mold and seal it with several layers of epoxy until it stops soaking up into the plaster (wiping it out between coats so it's not a layer of epoxy). I think this is just to harden the surface and seal all the pores. Next is several layers of Partall #2 mold release wax, then spray in PVA when we're ready for making parts.

For layup schedule, the first part we pull will be 2 layers of 6oz s-glass and we'll evaluate how sturdy that is. I did a cowl out of 3 layers of 6oz s-glass recently and it is rather overkill sturdy. There are some flat sides on this fuse that I think we'll add a layer of 6oz and/or a a 1mm layer of foam core. Just a guess at this point; after the first one comes out and gets flown, we'll know much better what to change.

Dan
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Old Nov 13, 2009, 12:50 PM
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My buddy made a mold of a sloper out of Hydrocal. He made a lot of them, so I will ask what he used.

Brian

Quote:
Originally Posted by Ed Waldrep View Post
What will you use for mold release when laying up the parts in the plaster molds? I've made a few plaster molds for smaller parts but haven't layed much glass in them, only once.
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Old Nov 13, 2009, 01:52 PM
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United States, MO, St Charles
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Hi Dan,
Nice build, thanks for sharing. You might try to layers of 4 oz cloth. Check out this http://www.rcgroups.com/forums/showp...&postcount=231 from Steve Niell. He played around with different weights of cloth and settled on the 4oz layers.

Dan Eaton
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Old Nov 13, 2009, 02:48 PM
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Subscribing - I recently put together this exact jet (109%) of Steve's original plans. I'm very interested to see how that mold works out.
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Old Nov 13, 2009, 02:54 PM
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After seeing how much easier this is than a fiberglass mold, I think I am going to go home, break down my design, and mold it with Hydrocal. Every time I fly it I worry about all the time it took to carve it and how long it would take to make again. It sucks to ruin it, but sometimes 1 has to be sacrified for the greater good.

Thanks for starting this thread!

Here is mine.



Brian
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Old Nov 13, 2009, 05:06 PM
2014 EDF JET JAM We be Jamming
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Nice.....
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Old Nov 16, 2009, 01:17 PM
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Hey,

CAn you tell me how you made the parting board? What is it made of and how did you get to fit so perfectly around the perimetr of the plug? I shaped my plug my hand a little at a time without a plan to go off of, so I don't have a template can use to cut the parting board, so just wondering how you did yours?

Thanks,

Brian


Quote:
Originally Posted by tzyoung View Post
After creating a plug the next step is fitting it to a parting plane.

I will say a few words about the type of molds that we decided to use. Both of us have had our fair share of working with molds made of composites and we decided to do the molds for this plane from Hydrocal which is a reinforced gypsum plaster. Hydrocal makes for less expensive molds and we will assess their durability as we begin pulling parts from the molds.

A foam dam was built around the part using 3m 77 to stick the wall down to the parting board. All of the seams were sealed with Kleen-Klay to reduce the leakage as the Hydrocal is poured. The attached pictures show the dams for one plug half.
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Old Nov 16, 2009, 01:25 PM
Who needs a pilot??
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Alexandria, VA
Joined Jul 2002
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Hi Brian,

The parting plane is white-board material, some scrap we had laying around. To make the cutout, I held the plane in the approximate orientation above the board and used a right-edge tool similar to this: http://astro.umsystem.edu/mmrca/lance/sled24.htm (see pic about half-way down. I used a band-saw to cut out just to the line. After I had the hole, I put the plug into the hole as far as it would go and checked with the tool again. A gap of below ~1/16" is what I was aiming for. Simple sanding and trimming to fit after that gets it to fit in the hole until the 1/2 way point. I added a few foam stop-blocks to keep it from falling through the hole. Last, we used some Kleen Klay (plastasine) to fill any remaining gaps and smoothed it out with a screwdriver. If you have any gaps larger that about 1/8", a foam backer block glued to the backside of the parting plane can give some backing for the clay.

Feel free to ask if I wasn't clear... I'm half-watching the shuttle about to launch, so I'm slightly distracted ;-)

Dan
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Old Nov 16, 2009, 01:48 PM
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Dan,

I just watched the shuttle as well.

Thanks for the detailed info!! Wow, that Blackbird is HUUUGGE! That is awesome!

I have wanted to do a mold for a while. I have built quote a few Bandit clones but never knew how to build one. A fiberglass mold would be too expensive, but after seeing your Hydrocal mold, I can deal with that.

One other questions I had was....what keeps the parting board attached to the fuse other than the clay sealing the gaps?

Thanks,

Brian



Quote:
Originally Posted by danstrider View Post
Hi Brian,

The parting plane is white-board material, some scrap we had laying around. To make the cutout, I held the plane in the approximate orientation above the board and used a right-edge tool similar to this: http://astro.umsystem.edu/mmrca/lance/sled24.htm (see pic about half-way down. I used a band-saw to cut out just to the line. After I had the hole, I put the plug into the hole as far as it would go and checked with the tool again. A gap of below ~1/16" is what I was aiming for. Simple sanding and trimming to fit after that gets it to fit in the hole until the 1/2 way point. I added a few foam stop-blocks to keep it from falling through the hole. Last, we used some Kleen Klay (plastasine) to fill any remaining gaps and smoothed it out with a screwdriver. If you have any gaps larger that about 1/8", a foam backer block glued to the backside of the parting plane can give some backing for the clay.

Feel free to ask if I wasn't clear... I'm half-watching the shuttle about to launch, so I'm slightly distracted ;-)

Dan
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