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Old Oct 19, 2012, 10:31 PM
AvB
Wind, hill, ... I'm keen ...
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Looks nice and under control when the paint's drying and things are in the vac bags. A picture a few hours earlier would have looked a bit different.
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Old Oct 20, 2012, 01:07 AM
ETS....Energy retention system
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gold coast australia
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Sound amazing Andrew.. Under 900g will fly awsome in light air , and would be cool f3f at shorn cliff .
The last few pics do look very relaxed..

Tim
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Old Oct 21, 2012, 12:34 AM
AvB
Wind, hill, ... I'm keen ...
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Really bummed ... The stab and fin that I laid up yesterday and PU filled this morning ... The paint stuck badly and the parts are stuffed. My own fault probably. I gave the mould a bit of a rub with the Farecla G3 polish then 4 wipes with Frekote. But I guess I should have gone.back to sealing with Frekote sealer. Whatever.
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Old Oct 21, 2012, 03:14 AM
AvB
Wind, hill, ... I'm keen ...
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I maidened the very light PU wing'ed Scratcho at Shorncliffe just now. Very nice. No dramas. In some ways it felt no different, but in other ways it was quite different. It carved loops with less speed. No bad habits. No trim changes required except I moved the CG forward a bit. The only issues are 1) I need more down elevator authority. Can't get enough compensation for full crow. Just enough for level flight but can't push the nose down. Also the boom that I partially creased removing from the mould is weak, so I'll have to put some patches inside there.

The most impressive thing was flicking really tight turns, barely levelling out and flicking back the other way. The other light Scratcho would have lost height in that light lift but this thing just hung there and even gained height! Really nice. The wind was from the E, so it was off angle the opposite way to usual.
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Old Oct 21, 2012, 03:18 AM
Where is the inspiration
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Moira
Joined Feb 2006
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I know that feeling. Sorry to hear it.
Someone once posted "too much wax is as bad as too little wax.
this was one of my faults. I have had many good pulls since. Sometimes its good to clean the mould down and way again.
saying that I don't have any experience with free coat. The other point is resin release compatibility. Some will stick. I don't know why but I have been warned always test before using in your moulds.
Will
sorry if I am trying to teach you how to suck eggs.
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Old Oct 21, 2012, 04:56 AM
AvB
Wind, hill, ... I'm keen ...
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P.S. - about the paint stuck in the moulds ... I am feeling rather chuffed ... I have worked out a quick fix! I thought darn, I'm not gonna spend many hours chipping away and damaging the moulds like last time. I got some paint thinners and put it on, but it didn't really help much. Still very very stuck paint. But I flooded the mould surface with thinners, laid a patch of paper towel over it, then laid some plastic over that and put the other half of the mould on top, to keep it all shut tight. Ten minutes later, I was able to shave the paint off quite easily with a paint scraper knife, without damaging the mould. So good! I'm so proud I'm going to post it on the composites forum!

Although this was rather a disaster, on the positive side, it doesn't take long to make the tails. Quick and easy paint with the airbrush ... simple and not messy, no overspray and it's amazing how little paint it uses. Probably takes 20 minutes to cut the cloths using templates. Probably 45 minutes to wet it out in the moulds, put the layers of teflon coated glass and paper towel on, and into vac bag. Then 4- 6 hours later probably 20 minutes to trim the edges. Half a day later, it's about a 20 minute job to mix and smear the PU and clamp the moulds. So it's annoying, but not such a big deal. I'll clean it all up and do the process using the mould release first. If it stuffs up again, I'll give up on that Frekote!
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Old Oct 21, 2012, 06:00 AM
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Keep it up Andrew! I always watch with interest! (RT42 molds are almost done =) )
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Old Nov 08, 2012, 06:07 PM
AvB
Wind, hill, ... I'm keen ...
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More updates:

OLD FIN AND STAB MOULDS:
As reported in the thread about the stickups, http://www.rcgroups.com/forums/showt...1726730&page=2 ... once I’d removed the stuck paint there were a few minor scratches to be polished back, so I decided I may as well fix the moulds up properly. So I cleaned them up and repaired various old chips and blemishes. Carefully wet sanded them flush with 800, 1200, 2000 grit (using shaped blocks) and then with G3 and then finish polish. I had some other stuff to polish (post-painted wings) so I borrowed Al’s electric panelbeaters’ foam pad polisher and used it to buff out the polish pastes. They turned out excellent, so in a way I was glad that the stickup had got me to fix up the moulds properly.

Then I did the FMS sealer and Frekote routine. Two-pack painted, laid up the skins, and was this time more careful to splooge the edges to avoid my regular bubbles-on-the-edge problems. Vac cured the skins, trimmed, then laid partial blue foam cores inside, and a little Sicomin PB170 foaming epoxy to fill the gaps. I'm playing with the PB170 because it's less dense and foams up more than the Ampreg F230, and so far I'm really happy with it.

When I popped out the parts, they were my best result yet. A few paint masking blems (the mould release was so good I couldn't even get my good masking tape to stick!) but the edges are all solid, and best finish yet thanks to the mould polishing.

BUT … The trailing edges of both fin and stab looked weird. Instead of tapering to a nice fine point as before, they were really thick. So thick that the skins weren't touching and you can see an epoxy foam sandwich between them.

At first I thought darn, I've trapped something in the moulds and they didn't close properly. I sandwiched blobs of putty in there and shut the mould, and the thickness of the blobs showed that it wasn't a closure problem ... basically too much material has been removed from the moulds. I measured the thickness of the finished parts ... they are 0.4 to 0.8mm thicker than the previous ones! So it's not just the TE area that’s affected … it’s the whole surface. I thought the polishing would take back a microscopic amount of the surface but in fact been cut back a lot. Disaster! I suspect that the polisher was the issue … it’s very heavy and powerful and perhaps the foam tore into the TE taper next to the TE trench.

So basically those moulds are stuffed.

NEW MOULDS
I’ve been trying to get CNC moulds cut. I hired Will from the UK to draw the wing, stab and fin up professionally ready for cutting. But I can’t justify the cost of the cutting! I’ve been trying to find a back door option or hobbyist who’d help, and despite lots of legwork I’ve not gone ahead with it. The problem is that I’m not planning to go into production – it’s just for fun so I don’t want to spend a lot. I’m a mental cot case, ruminating over it, on one hand thinking I’ll give up and stop any further work on the Scratcho, and on the other hand spending hundreds of bucks on expanding epoxies and composites! But I am hoping at least to get new fin and stab moulds done by CNC. My wing mould though crappy actually makes good wings.

POLYURETHANE
I am definitely pretty excited about the results from using polyurethane, expanded in the closed mould. There’s a thread about it: http://www.rcgroups.com/forums/showthread.php?t=1721451

The PU wing is so light and so stiff, it’s amazing. And the foam inside is really nice and solid and consistent. But it was obvious that the weak link in the construction was that the edges are not locked together. The PU is not a strong bond. This was proven when I had a lockout and crashed it and the skin really opened up and peeled off like a banana skin from the wingtip. I have plans to modify the method so the wing can be opened after expanding the PU, and then bond the edges. The idea would be … lay up and cure skins. Trim and put mixed PU in both sides (this step needs a few guys on hand to get coverage within 40 seconds or so from mix) then put a mylar splitter plate over one half, put the other half on top, and clamp together. Unclamp in an hour or 2, and you'll have 2 flush fitting sides fully solidly filled with PU foam (you get the best foam structure if it expands with some back pressure). Then scrape the foam back a few mm from the edges all around. Dribble a bead of Sicomin 170 around the edges, and in trenches. Join the mould again and I’m sure the final result will be one of the strongest light wings ever made.

I thought the busted wing was a throwaway, but Rhys said “so why don’t you just cut both wingtips shorter ?” So I did, very roughly and quickly, using an old Caracho tip as a template for tapered tips, hacking and gouging and just taping the skins together. The damn thing flew brilliantly! People have been telling me I should do elliptical tips and I’ve rejected it because I like the look of the Scratcho and the straight sections are easy to work with. But … of course, I’m now dreaming of a major Scratcho redesign with tapered tips!

BUILDING
These are the 2 Scratchos I’ve been working on. The wings were the first 2 experimental ones for the foam core plus Ampreg method. The cores were loose-laid in these but they weren’t great and needed some fixing to make them good. They were post-painted.They’re really nice stiff, very strong medium-weight wings and are gonna be great for slope and DS. I can’t put the white one together because I’m not happy using the fin and stab with the thick edges!!

Anyway, enough of this … gotta do some work!!
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Old Nov 08, 2012, 08:35 PM
Don't grow up, it's a TRAP !!!
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Australia, QLD, Elimbah
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Andrew, your enthusiasm is inspirational. Being a "cot case" is how most of the greatest things ever invented came to being. Don't judge yourself for that.
In fact, you're the bench mark in how much can be achieved when the mission is there.
I recall a great quote by some person of notoriety when asked by an interviewer, "How do you achieve so much?". They replied, "I dont wish to be rude, but how do you achieve so little".

Keep doing what your're doing. I'm sure I'm not alone when I say we all enjoy following your process.
David
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Old Nov 08, 2012, 08:57 PM
ETS....Energy retention system
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gold coast australia
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"DITTO" on that...

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Old Nov 08, 2012, 09:09 PM
AvB
Wind, hill, ... I'm keen ...
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You guys are too nice. Thanks. You guys are all doing your best too, and most of you have "normal" jobs. Because my kids are well out of nappies now and I work from home and have a very accepting wife, it's too easy for me to skive off and play gliders. So I get a lot of time doing that ... and I do tend to pfaff around and make a lot of dumb mistakes/ decisions. What I'm saying is that I'm sure that given the amount of time I get in the shed I'm sure most of you guys would achieve a lot lot more.

And spending all that time is not good for my real job! I have to reform!
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Old Nov 08, 2012, 09:36 PM
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Avb have you thought about making your own CNC machine?

Mick
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Old Nov 08, 2012, 11:12 PM
AvB
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Mick that's a bad idea!!! Learning CNC is probably even more challenging than learning composites! I already spend too much time in the shed. And if we're honest, the main aim of all this is to be out flying!!!

But I have thought about it. My mate Alan has built one and it's almost RTF, but he has totally stalled on the project. I've offered to buy it but he's refused!
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Old Nov 09, 2012, 12:44 AM
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Quote:
Originally Posted by AvB View Post
Mick that's a bad idea!!! Learning CNC is probably even more challenging than learning composites! I already spend too much time in the shed. And if we're honest, the main aim of all this is to be out flying!!!

But I have thought about it. My mate Alan has built one and it's almost RTF, but he has totally stalled on the project. I've offered to buy it but he's refused!
I know what that's like I have the controller and steppers ready to go. Started a frame just over 12 months ago but then moved house and the project lost legs with it all still packed away.
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Old Nov 09, 2012, 01:58 AM
Where is the inspiration
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Moira
Joined Feb 2006
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Quote:
Originally Posted by AvB View Post
Learning CNC is probably even more challenging than learning composites!
Hello Andrew

Not sure if I agree with your quote above.
Composites is more like whitch craft, where as the CNC stuff is more mecanics with some electronics.

And as normal I am sure there are loads of people here that would support you.

I would live to have my own cnc machine. and in time (Whe the babies are bigger) It may come.

Keep going.

Re the damaged moulds, why not build up the trailing edge and sand it back in? Make it level to the parting surface?
Or put a thick layer of gell coat on and cut the new fin into that. will be with in 1mm or so.
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