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Old Feb 10, 2013, 09:28 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
6,637 Posts
Good results!

I've just done the re-application of wax, dusted talc, and then PVA applied by spraying.
The results are excellent, without any surface tension induced streaking or fisheyeing etc.
I use a two application method following what WWW Adam uses, and has used, presumably, for along time:
One mist coat, then allow to dry.
Then a moderately heavy coat carefully applied. I did it with my neat little .5mm nozzle detail gun from ebay.

The result when still wet is a glossy, homogenous finish. This dulls off, needless to say, when it dries.

I'm happy that I've sorted this out after a long time with less than satisfactory results.

It doesn't come out in the pics, so I won't post them.
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Old Feb 10, 2013, 10:34 PM
Arrarrar!
josh18's Avatar
Australia, NSW, Wagga Wagga
Joined Jan 2010
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nice one Jim. do you have any issues with dust in the surface? Ive had lots of trouble when sparaying PVA.
Cheers
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Old Feb 10, 2013, 10:46 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
6,637 Posts
Quote:
Originally Posted by josh18 View Post
nice one Jim. do you have any issues with dust in the surface? Ive had lots of trouble when sparaying PVA.
Cheers
Not this time Josh. It dried very quickly due to the high ambient temperature.
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Old Feb 11, 2013, 01:29 AM
Arrarrar!
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Australia, NSW, Wagga Wagga
Joined Jan 2010
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good one! Cant wait to see more
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Old Feb 12, 2013, 07:24 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
6,637 Posts
Second side of tail moulds done.

Sand fill and 5 layers of 185 gsm glass cloth backing added.

Green trim tonight.

One more milestone completed. I will split them in 2 or 3 days.
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Last edited by Jim.Thompson; Feb 12, 2013 at 07:28 PM. Reason: spelling correction
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Old Feb 13, 2013, 03:31 AM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
6,637 Posts
Wing plugs set in parting boards.

The tail surface moulds are complete and sitting on the shelf. I'll split them in a couple of days.
I've now set the two wing plugs in their respective parting boards using "Rainbow Clay" to fill the gaps. They have one coat of wax in the picture.
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Old Feb 13, 2013, 02:48 PM
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killercando's Avatar
United States, WA, North Bend
Joined Mar 2011
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Those look great Jim. You are really cruising.
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Old Feb 13, 2013, 04:04 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
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Too wet for PVA

Quote:
Originally Posted by killercando View Post
Those look great Jim. You are really cruising.
Thanks Lee.
I have to keep myself moving on a project or otherwise I loose my momentum and it doesn't flow. I am appreciating the value of this build thread more and more as I go. It sort of keeps me reminded of my duty to it, as well as forging connections with other builders like you. Also, it's an excellent journal for later reference. I can forget how I did something a year later otherwise!

Today is a rainy day here, so I won't be spraying the PVA. It takes too long to dry in these condtions which means it has a long time to accumulate dust. I found that when spraying the PVA on the tail surfaces in dryer conditions it dried very quickly. Very little dust stuck to it accordingly.

I'm still haunted by the blistering problem of a batch of foam I have been using for years. I thought I had the problem solved, but it seems not. I simply cannot expose these black wing plugs to any heat at all without fear of blisters forming. I did get one very late in the preparation. All I have done to deal with it is to prick it with a pin, sand and then plug with a tiny piece of Rainbow Clay.
This blistering was despite the fact that I coated the foam cores with epoxy before sandwiching them with the wet out skins. Perhaps I should have prepared them by first diluting some epoxy and applying this to the raw cores allowing to tack off (at least) before proceeding with the usual vac bag sequence. I don't know.
I'm hoping to get onto a different source of foam for future projects. I'll be dependant on this being more successfull as I am unable to get access to CNC cutting services anywhere near me. So, any more moulded project will also be hot wire cut, vacuum bagged cores.
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Old Feb 13, 2013, 04:17 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
6,637 Posts
Tail surface construction advice needed!

The tails on this model are swept slightly, as can be seen in the early pics. Sorry, I am unable to provide drawings as I have yet to master one of the drawing programs.
I am uncertain of how to construct these. Do I fit a cap spar and shear web similar to a wing? The incidence pins are at right angle to the root, so will not follow the same angle of a swept spar. Also, they will be ahead and behind the thickest part of the symmetrical section.

Questions:

1. How do I distribute the stress's between the pin receiver tubes and the spar? If I use a spar.

2. One possibility is to use some UniCarbon in the skin layup wide enough to extend past both tubes front and rear, with part shear webs above and below both tubes and at right angles to the root. Is this the way to go?

3. If one of you readers can link me to a thread or post where this has been done before please do so.
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Last edited by Jim.Thompson; Feb 13, 2013 at 04:19 PM. Reason: spelling
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Old Feb 13, 2013, 05:14 PM
Arrarrar!
josh18's Avatar
Australia, NSW, Wagga Wagga
Joined Jan 2010
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Hey jim Dont worry about it too much as the wont see gigantic loads. My scorcher tail has a similar setup, with a swept back shear web and 90* incidence pins. If you are worried your solution sounds great, and just add a blob of splooge in the layup where the pins go- this supports the pins and gives them a nice big contact patch with the skin, spreading the load. I also use about ten tows pressed into the inside corner of the base of the fin. This fills the gap like splooge would but has heaps of strength and resists the pins pulling out the side of the wing. Another couple of things you could do, make mini spar caps to to about half span where the pins go (90* to wing root) or just make your pins stick into the wing further.
Ill see if I can find a scorcher tail pic. - looks like I didnt put tows at the base of that one
Cheers, dont sweat it too much.
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Old Feb 13, 2013, 06:40 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
6,637 Posts
Quote:
Originally Posted by josh18 View Post
.............. I also use about ten tows pressed into the inside corner of the base of the fin. This fills the gap like splooge would but has heaps of strength ................
What size carbon tow Josh/
I have 50k in stock and usually use one or two rows in such places. Two or three in the wing roots and one in the LE.

The skewed sub-spars (in line with the joiners) might be the method I end up using. After all, they will have a drag spar and LE control surface spar.

I looked at the weather forecast - rain for the next week. So I decided to go ahead and spray my wing plugs and parting boards with PVA. I have the heater on in the shed and it is drying nicely.
I expect to be applying the tooling coat this afternoon. Then it will be full on moulding time!

Progress happens.

Thanks Josh.
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Old Feb 13, 2013, 07:40 PM
Arrarrar!
josh18's Avatar
Australia, NSW, Wagga Wagga
Joined Jan 2010
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Good one Jim. I dont know what size my tow is, pretty standatd though- not massive.
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Old Feb 13, 2013, 10:48 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
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Quote:
Originally Posted by josh18 View Post
......... I dont know what size my tow is, pretty standatd though...................
Is there such a thing as "standard" when it comes to carbon tow???
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Old Feb 14, 2013, 12:29 AM
Arrarrar!
josh18's Avatar
Australia, NSW, Wagga Wagga
Joined Jan 2010
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Its about as long as a piece of string...
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Old Feb 14, 2013, 12:39 AM
ETS....Energy retention system
timbuck's Avatar
gold coast australia
Joined Aug 2008
5,330 Posts
Quote:
Originally Posted by josh18 View Post
Its about as long as a piece of string...
Exactly.... Double half it's length....
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