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Old Dec 16, 2010, 12:54 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
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Hot Box.

[QUOTE=wyowindworks;16836792]Blue foam can off gas at higher temps and create blisters. I typically don't take my cores above 110-115*F - 43-46*C.
Secondly, I leave the mylars on until the post-cure is complete. This reduces the amount of fabric print-thru.
QUOTE]

Thanks Adam. The temp seems to be ranging between 42 - 45 *C which will be ok then.
I have stipped the mylars off in my enthusiam and eagerness to view the results. However, for just a primed on the mylars job, print through does not matter like it would for finish painted mylars.
When doing any finish painted ones in future, I will try and keep them on for post curing for reasons you explain.

All seems to be on track. Except for one small detail I will attend to today. The hot box extension that I built onto my box means that the temperature is not evenly distrubuted. I will try and obtain an old computer fan and install it inside to provide some air circulation. I will also rotate the wing end for end every 12 hours or so to equalise any difference remaining.

Jim.
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Old Dec 16, 2010, 02:51 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
6,549 Posts
Bubbles!!

I have removed the wings from the hot box after I found that bubbles had already started to form! Only slight, but very dissapointing after all the care to avoid them I have taken and all the preparation that has gone into these wings!
I am beginning to suspect it might be the batch of foam that I have. The only wing cores that I have vacuum bagged and have not subsequently bubbled have been foam cores that came from another source. One set of Jart wings that I did for a flying pal have not shown any bubbling at all. And the very first set that I got from "Off the edge Sailplanes" have not bubbled since vac bagging. I might put them in the sun for a while (they never flew) and see what happens.

And further more, the P63 Kingcobra wings that I recently built also bubbled (fortunately only on the bottom), even though I took lots of trouble to roll any entrapped air out of the mylar/vac bag assembly.

A revealing experiment might be for me to hot box an old damaged wing that I have that were done with the premade skins glued on with PU glue. If the source of my repeating problem with bubbles is the foam, like I am beginning to suspect, then they should also bubble. At least I think so, even though they are glued on post hot box curing of the skins.

Another experiment that I might be able to set up is to effectively "Cryovac" a small piece of the foam and heat it up in the hot box and/or the sun. I can make up a small special vac bag, evacuate it, and then heat seal it with a soldering iron, using the inflation bladder sealing technique. Then put it into the box.
After some time, if the vacuum is partially relieved, this would reveal offgassing of the foam.

Jim.
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Old Dec 16, 2010, 07:49 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
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Foam source and description

I contacted the representative for the company who supplied the foam I am using (DCT Australia). Unfortunately, proper descriptions and specification seem to continue to be difficult to obtain from this company. The best that I can get from them is the suggestion that it is "probably" LB grade high density blue foam.
But what was most revealing is the fact that this foam either comes from Europe or it uses European approved expanding gas, as distinct from that used in the US. This has led us to wonder if it has a different temperature tolerance before it becomes unstable and burst the foam cells.

All the above is speculation only at this stage. However, I will either be avoiding hot box elevated temp curing all together, or I will do so at a lower temperature (lets say 40 deg C ?). This is not a lot, as we have some days each year with atmospheric temps around this figure.

Jim.

Still wondering!
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Old Dec 16, 2010, 09:25 PM
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Quote:
Originally Posted by Jimbello View Post
I contacted the representative for the company who supplied the foam I am using (DCT Australia). Unfortunately, proper descriptions and specification seem to continue to be difficult to obtain from this company. The best that I can get from them is the suggestion that it is "probably" LB grade high density blue foam.
But what was most revealing is the fact that this foam either comes from Europe or it uses European approved expanding gas, as distinct from that used in the US. This has led us to wonder if it has a different temperature tolerance before it becomes unstable and burst the foam cells.

All the above is speculation only at this stage. However, I will either be avoiding hot box elevated temp curing all together, or I will do so at a lower temperature (lets say 40 deg C ?). This is not a lot, as we have some days each year with atmospheric temps around this figure.

Jim.

Still wondering!
Cuuld this be caused by moisture in the foam? or could hotboxing the foam prior to bagging resolve any gassing issues?
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Old Dec 16, 2010, 10:44 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
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Quote:
Originally Posted by AUSELECTRIC View Post
Cuuld this be caused by moisture in the foam? or could hotboxing the foam prior to bagging resolve any gassing issues?
That is just what I have been thinking!
I will give it a go on two samples. One in the box before, and both after.
That should reveal something. It would be nice to know what exactly is causing this.

Jim.
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Old Dec 18, 2010, 02:21 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
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Delay

I am experiencing delays with the gel coat spraying of the plug. I took it up to a fibreglass shop, which is quite a drive from my place, for them to do it for me, and it has been nearly 3 weeks now. Last I called, it was still not done! I am hoping it is done before the xmas break! If not, it will be weeks more before I get it! It makes me consider the wisdom of sending it out to be done and I might look at getting a gel coat gun. One difficulty is the choices involved here, I don't really know what type is needed.

Meanwhile, I have begun some airbrushing experiments for the eventual paint job. I now realise that a low wing plane is not a most suitable platform for a bird look decoration. However, I have not abandoned the idea yet.
This is one of my basic wing feather outline experiments. The concept is for the included colour to be transparent and graded from the green to the azure at the tips. The outline could be cobalt blue or a full green. The background will be the duck egg blue of the head and shoulders of the bird.
I still have to find out how to airbrush the pin feather detail of the body of the bird. Anyone know how to do this?

The feather outline was done very easily using only one cardboard feather template fastened to a stick which functioned as a radius arm on a pivot. It was able to be slid on this pivot to provide the curve required. Some of this can be seen in the picture.

Meanwhile, I do have the control surfaces and servo holes etc. to cut out of the wing. Splooging and hinging etc. I will get on with that today.

Jim.
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Old Dec 18, 2010, 05:00 PM
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Jim

that is really nice! Is the plan to do a couple of colors in each 'feather' ?

My experience has been that computer fans don't move much air in a volume the size of a hotbox (what is your hotbox by the way?). I picked up a little cheapo 6" desk fan from bunnings/bigw etc. for $10 which worked great.

Steve
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Old Dec 18, 2010, 05:12 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
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Hot Box

[QUOTE=flyonline;16859328]Jim

My experience has been that computer fans don't move much air in a volume the size of a hotbox (what is your hotbox by the way?). I picked up a little cheapo 6" desk fan from bunnings/bigw etc. for $10 which worked great.


That is a good tip Steve. I have tentatively decided not to hot box cure my wings, at least untill I have solved my bubbling problems. However, I will continue to extended hot box cure fuselages.

Jim.
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Old Dec 18, 2010, 05:24 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
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Colours

Quote:
Originally Posted by flyonline View Post
Jim

that is really nice! Is the plan to do a couple of colors in each 'feather' ?
Steve
Yes Steve. I am planning to do the inside of the feather depiction profile in a graded green to azure sort of colour mix. Then do the feather outline, similar to the above, in a darker cobalt blue.
The remaining area outside the feather wing painting might be either a duck egg blue or possibly even a yellow! I don't know yet, but will be doing lots of trials on scrap laminated board.
I don't want the too much dark colour on the model though, as I am aware of the thermal properties of have dark colours on epoxy while the model is in the sun. I understand that this is why full size gliders are almost always mostly white.

So some of my plans are in conflict with each other here! I'll see as time goes on and I experiment some more.

Jim.
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Old Dec 18, 2010, 05:57 PM
Twisted and Confused
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Quote:
Originally Posted by Jimbello View Post

So some of my plans are in conflict with each other here! I'll see as time goes on and I experiment some more.

Jim.
He he he
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Old Dec 21, 2010, 04:44 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
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Movement

Quote:
Originally Posted by flyonline View Post
He he he
You see Steve, its not only you TWF types who are "twisted and confused"!

There is some movement with the project again. My helpful fibreglass blokes have finally got around to spraying my plug. I have now sanded it and its about ready for a final check and then polish. So I will be fitting it into the mould in the next couple of days. I am advised that will be sufficient time for the gel coat to cure. Wax with several coats of PLP8 wax and then PVA.

So all this means that I will be starting the mould layup on the first side at the end of the week. It will give me something to do over the xmas break, which is not my favourite time of the year.

Jim.
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Old Dec 21, 2010, 05:40 PM
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Hey Jim... I like that feather look, detail pics of how you do that would be great... I have an airbrush, but dont know much about it yet.

Next time just spray your plug with some 2 part auto primer or something. I'm a complete paint gun newb, but I was able to get quite fine results with a cheapo gun. I just wet sanded after to 2000grit, then polished with 3M swirl remover. I have two molds from said plug, both with mirror finishes, and I'm pulling parts a couple times a wk, no prob, the parts are also mirror, no post mold finishing needed. No need for 'send-out' gel coats. Maybe this has already been addressed in this thread though. Of course, I paint outside with respirator. (And, I did kill my nicer HVLP spray gun by letting the primer set up in the gun)

Happy Holidays... Ben
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Old Dec 21, 2010, 09:04 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
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Plug finish coat

Quote:
Originally Posted by flyonline View Post
Jim

I'd suggest going to a different car place and asking if they'd do it the next time they do a job ..............................Steve
I did get another quote Steve. This time it was $70!
The gel coat spraying only cost me $10. I had to wait, but that was because of the busy time of year.
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Old Dec 21, 2010, 09:06 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
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Originally Posted by skinnydoc View Post
Hey Jim... I like that feather look, detail pics of how you do that would be great... I have an airbrush, but dont know much about it yet.
Ben
Ben,

I will take some pics of the template system that used for the feather pattern. Very easy!

Jim.

Ok. Here they are. The radius arm slides along the pivot at the top right hand corner of the photo.
The template itself is a bit of cardboard cut to shape and pinned onto the back of a strip of timber with drawing pins.
If you look carefully at the bottom of the pic you can see a pencil line curve with intervals marked on it. They were used to position the template for each feather and gave a regular graduated interval between each feather.
I then used a fairing battern to extend the curve of the LE beyond the curve of the template of the outboard wing shadow. This line was taped off and shadowed in (several coats) before removing.

The set up and geometry can be done in pencil untill the arm and position line etc. are set correctly.
Then it is very quick and easy. Just need to watch the usual airbrush variables - several lights coats etc.

I am looking forward to trying it out with colour! After a lot of researching, I have finally decided to go with acrylic lacquers. I will do it outdoors and with a mask etc. The reports say the water based paints are very good, but there are some traps for begginners. Solvent based paints are simple with no compatiblity mysteries etc.

The 2 pack question was discussed in some detail on page 3 (I think) Ben.

Jim.
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Old Dec 22, 2010, 05:26 PM
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Eureka, CA
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Originally Posted by Jimbello View Post
I did get another quote Steve. This time it was $70!
The gel coat spraying only cost me $10. I had to wait, but that was because of the busy time of year.
Nice work Jim! That template tool is a good idea and here I thought you free handed the whole thing.

Just to give you a little bit of my experience I had trying to get someone to 2k clear my plane, it was a hassle. I called every auto body shop in my small town and the first 4 or 5 shops wouldn't touch the job for some reason, I guess it wasn't worth their time. I had two shops that were willing to look at my plane and give me an estimate. The first shop told me that it would cost me 250 dollars to paint becuase of the expensive 2K clear he used ( which was totally untrue since I knew the brand he used and the dealer he bought his paint from prices). So then I tried one last shop which turned out to be a back alley type auto body shop which really didn't do much work but turned out to be a very nice guy. He quoted me 50 bucks and some beer and at this point I thought it was a very good deal and was done with it.

So all in all, I'm saying 50 bucks for painting 2k isn't too bad a price unless you have a hookup. Sure it could be done much cheaper by you, but your liver will thank you for it.
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