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  1. #1
    Aussie Damo's Avatar
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    Lightbulb Special Fail, simple lesson learned

    Well it seems I just couldn't win today. Especially after my first flight in 2 years yesterday was so amazing

    Windy all day long and then when it finally calms down the rain starts
    Finally late afternoon and some reasonable conditions and before I even make it off the balcony (live on 10 acres, fly out of my front yard) I do this to my LST

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    Normally I run 7.4v or 11.1v and a 9x4.7 Slow fly prop (APC)
    Today I thought I would test the 9x6E (APC) for a little bit more airspeed without much loss in thrust/slow fly capability compared to the 9x4.7. For those that dont know the 9*6 is somewhat bulkier and heavier than the SF prop.
    So walking along the balcony I give a flick of the throttle to full power to see how much pull ill have on takeoff and...... BAAM, the prop flies into my chest and the motor/firewall disappears 8 meters off the balcony.

    Turns out the 9x6 has a LOT of pulling power (and rotational momentum with that extra weight) on 11.1v and I learnt a special lesson, ALWAYS ADD REINFORCEMENT to the firewall mount, dont rely on butt joined balsa and ply.

    Oh well, the glue is drying as we speak and hopefully tomorrow will be a better day (the blink should get a fly as well if the weather is good and im confident in the thumbs)

    Damo
    Dead stick landings are the easiest. Doesn't matter your attitude, elevation or airspeed - it's all down hill from there.

  2. #2

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    Quote Originally Posted by Aussie Damo View Post

    So walking along the balcony I give a flick of the throttle to full power to see how much pull ill have on takeoff and...... BAAM, the prop flies into my chest and the motor/firewall disappears 8 meters off the balcony.
    Certainly easily repairable, but you really dodged a bullet with the prop loss. I've seen a number of props shed blades or disintegrate and I always make a conscious effort to try to stay out of the prop disk plane when the engine is running and generally turn my head away if I walk by a running engine. Like most of us here, I've got several prop scars, but luckily, have never been hit in the face.
    the "other" andrew
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  3. #3
    Aussie Damo's Avatar
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    Its funny, I was out of the prop disk plane, I was holding the aircraft out in front of me pointing forwards but when the firewall came out it must of let go on the left side first, shooting the prop back and the motor forward.

    It was a nice reminder how dangerous these can be that turned out okay

    happy flying
    Damo
    Dead stick landings are the easiest. Doesn't matter your attitude, elevation or airspeed - it's all down hill from there.

  4. #4

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    OK, I kind of hate to say this, but that firewall was wrong all along. You should always have something in those corners no matter how little power you think you have. Even some 1/8" square stock would have been good. I'd put some 1/4" triangle in place with epoxy. Be sure to sand the contact areas as best you can to get to clean wood for a good glue joint. An emery board or sandpaper on a stick will work pretty well.

    Glad the spinning prop didn't cut any arteries. That tends to make a person's day a little less sunshiney.
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  5. #5

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    A little fiberglass cloth and epoxy adds massive strength to firewalls and is dead simple to add as you build your plane or during a repair. A little sanding and you can hardly tell it's there.
    I fly aircraft at the leading edge of trailing edge technology!

  6. #6
    Aussie Damo's Avatar
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    Hey guys, thanks for the comments, this is exactly what i went and did (1/8 square balsa to be exact on the sides and bottom).

    Ive never done anything related to fiberglass which is a shock horror considering my old man works for boeing making components for the 787, and always brings home off cuts and stuff that didnt past testing, the stuff is bloody strong. it is definitely something i want to give a try (I am looking into making airboats) but really dont know where to start, what exact materials i need and at the moment money is a bit tight so cant afford to buy larger/in bulk orders

    Damo
    Dead stick landings are the easiest. Doesn't matter your attitude, elevation or airspeed - it's all down hill from there.

  7. #7

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    If you jump over to Curtis Suter's place http://www.tailwindgliders.com there are two excellent videos for sale. They are both of very good quality as well as very informative.

    One of the videos cover the construction of pods and booms for gliders, but I think that at least some of the building techniques for pods are applicable to 1/2A fuselages. On the site is a sample from the pod-video showing how to reinforce the pod with fibre glass and Polycrylic (transparent floor paint). Very easy to do, very lightweight, and very strong. Up til now I've only made tests on testpieces with this building method and it turns out that HK's thinnest fibre glass cloth is too thin for my needs (unless I use two layers), but nevertheless I've got a very noticable enhancement in strength.

    In the wing DVD Mr Suter shows how to cut foam cores, as well as how to sheet them or vacuum bag them. All is done in a way that makes even a noob like me feel I might eventually manage to produce a decent wing.

    I have watched both DVDs several times and I still find them excellent and can honestly recommend them.

    /Stefan


    P.S. Did I say I really like the videos?

  8. #8
    Aussie Damo's Avatar
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    Hey, thanks Stefan. I will look into them

    Damo
    Dead stick landings are the easiest. Doesn't matter your attitude, elevation or airspeed - it's all down hill from there.

  9. #9

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    Aussie - Glassing is incredibly easy. Growing up all I could afford is planes the Airtronics Q-Tee but back then the coolest planes going other than scale were what are now known as Classic Pattern. You know... Dirty Birdies, UFOs, etc.

    Anyway, those guys all glassed their planes and they looked awesome. Of course they could all fly circles around me so I thought they were masters of everything and that fiberglassing was a black art.

    First time I ever tried it the glass came out great. Once you start with it you'll see how very simple it is.

    The best thing to use for reinforcing is a low viscosity epoxy - usually called "finishing resin" or "laminating resin" (may also use the word epoxy instead of resin.) Just be sure you don't get polyester resin. It's more brittle, weaker and the fumes are really horrible. Not to mention it can give you chemical burns if you get it on your skin.

    You'll know if it's polyester resin because it will come with a little bottle or catalyst which I think is peroxide based. You add a couple drops and mix it in. The other problem with it is that measuring the drops in small quantities of resin is hit and miss. If you add too much it will sudeenly set off and if you're half-way through the job you're screwed.

    Now only for small reinforcements like your firewall, you can use regular epoxy instead. It's harder to work through the cloth but will work.

    Best thing to do is brush a little in the joint before you add the glass. Put the glass in place and use your brush to push it down by stippling.

    DO NOT thin the epoxy for any reason.

    You can use a hair dryer to warm the epoxy a little to make it thinner and easier to work with. You can also put the cup your mixed epoxy is in into a larger container with warm water.

    Or you can brush on the epoxy carefully not to move the cloth out of place and then warm the joint with a hair dryer to make the epoxy thinner so you can brush it through the cloth. Don't use too much. Epoxy on top of the cloth doesn't add strength, looks sloppy and is dead weight.

    Just let it cure and you're good to go.

    Oh yeah... if you don't have fiberglass then don't use the stuff they sell in auto parts stores. It's way too heavy and you'll never get it to stay in a corner. 2 oz cloth is the heaviest you should use for your firewall but 0.75 or 1 ounce cloth should be fine.

    Now that I've typed all that I would bother with the glass at all. You'll get more rigidity from square or triangle stock in the corner. it's easier, cheaper and faster.
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  10. #10

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    Triangle stock on the aft side of the firewall and fiberglass on the forward side wrapped around on to the fuselage sides would be SUPER strong!
    I fly aircraft at the leading edge of trailing edge technology!

  11. #11

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    Quote Originally Posted by 049flyer View Post
    Triangle stock on the aft side of the firewall and fiberglass on the forward side wrapped around on to the fuselage sides would be SUPER strong!
    I started glassing my latest Stik last night and that's exactly what I'm doing except four times. Each piece of glass (bottom, sides and top) will wrap around the firewall. Super strong and super fuel-proof. Way more than necessary but as long as I'm putting the glass on anyway it's not any extra work.
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  12. #12
    Aussie Damo's Avatar
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    Hey CafeenMan, thanks for all the tips. It boosted my confidence and ive ordered some glass, now i just need to get some resin and I will have a play,

    I can see this becoming my go to for wing centers etc which im always worried about catastrophically failing

    Ive also been on airfiledmodels page and just put together it is your site, what a fantastic resource

    Thanks
    Damo
    Dead stick landings are the easiest. Doesn't matter your attitude, elevation or airspeed - it's all down hill from there.

  13. #13

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    Hi Damo,

    I'll take some photos of the fuselage I'm glassing so you can see how it goes. It's very simple. Seriously took me less than 5 minutes to lay down the first piece of glass and wet it out. Then I just let it cure. I could have sanded it about 6 hours later, but I work three 12's and on those days I don't get much done. So it's still waiting for me to sand off the excess, feather the edges and move to the next piece. I'll even show you what a mess I made and then you'll see how it looks after I clean it up. I was kind of rushing and the glass came out well where it's supposed to be but some drips stuck the glass down on the side where I don't want it and I have to sand it all off back to bare wood in those areas.

    It sands well and easily so other than looking like I'm a slob, it's really not a problem. I just could have saved some time by blotting some of that up before I left it but I wasn't looking at anything but where the glass was supposed to be and didn't even notice that I'd dripped resin in other places until I looked at it again hours later.
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  14. #14
    Aussie Damo's Avatar
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    Quote Originally Posted by CafeenMan View Post
    Hi Damo,

    I'll take some photos of the fuselage I'm glassing so you can see how it goes..
    Some photos would be excellent.
    I failed again today . Your advice about not getting polyester resin stuck, at the local hardware shop they had a tin clearly labelled polyester resin and the other fibreglass resin. bingo i thought, the second one must be the other type you talked about. The lovely lady behind the counter gave me the catalyst (you see where I'm going now dont you) to it and I was on my way home happy.

    When i got home i checked this forum to see if any pics had been put up and read your post again and "little bottle"..... ahhhh, so it turns out i bought 500 grams of polyester resin.

    To me, after some reading tonight, the easy way to tell them apart is that epoxy type resin is generally mixed in ratios from 1:1 to 1:4 with its agent while polyester is like 1:200 etc.

    Ah well, live and let learn, ill probably keep it and use it on my first airboat I plan on building.

    Just to confirm, I want stuff like this right?
    http://ausrocketry.com.au/accessorie...-369grams.html

    Damo
    Dead stick landings are the easiest. Doesn't matter your attitude, elevation or airspeed - it's all down hill from there.

  15. #15

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    I just finished my work week - got home five minutes ago so the next four days I'm off and if it's not too cold will be working on the fiberglass. No photos yet but haven't touched it since putting on the first piece.

    That resin you linked should be fine but before using it on anything important, glass a small piece of balsa about 3" x 6" and see how long you can work with the resin before it starts setting up. If you really get a good 20 minutes of working time it's fine.

    The stuff I use is 30 minute but it can really be worked for well over an hour. I like it but it is slow to set up. I originally bought the 60 minute but it took WAY long to set up and most of it soaked into the wood which is bad. So I got the 30 minute and like it. But I'd like it better if it were a little bit faster. All of their resins work way longer than stated so I'd get 15 minute if they had it and if it were consistent with their other resins I'd probably have over 45 minutes working time. Only need realistically 15 minutes tops for anything I've ever done. After that you just wait for it to cure.

    http://www.acpsales.com/EZ-Lam-Epoxy.html

    Don't sand too soon. If they excess resin on the cloth is rubbery then it is too soon. If you bend it and it breaks clean then it's ready. You want the resin hard for it to sand well.

    You can use polyester that you have if you want. I just think it's really nasty to work with but it's been used to apply glass for decades so it works.
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  16. #16

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    Hi Damo,

    As promised here are photos of the glassing process and some other stuff.

    It doesn't usually matter what order you put the glass on. it gets feathered together and unlike plastic coverings, it's not going to get fuel under it at the seams. I still use that order though. Bottom to Top, Rear to Front.

    Photo 1) First piece on the bottom. I wasn't being very careful and got lots of resin on the sides. Took less than 10 minutes to sand it off after the resin cured so not a big deal.

    Photo 2) The piece overlaps the firewall onto the front upper deck. In fact all pieces overlap the firewall which give four layers of glass over the firewall. It didn't need any of it and is now massively strong and very fuel-proof as long as the holes are fuel-proofed. I did it just because but none of the glass on the firewall was necessary.

    Photo 3) When the resin is cured, use fine sandpaper to remove the excess. The only thing to watch for here is that you don't get hard glass between the sanding block and the wood and make deep gouges.

    Photo 4) You can see where the glass is attached to a side due to the excess resin. Not a big deal but best to avoid.

    Photo 5) All the excess glass is removed and the edges of the cloth are feathered. Doesn't take long so don't rush and do not sand through the glass in other areas.

    Photo 6) Opposite fuselage side with excess removed and glass feathered.

    Photo 7) Ditto for the top deck. That whit you can see on the corners is glass where the resin soaked completely into the wood. More resin is needed to fill before any more sanding. I'm going to put on the rest of the glass and then see what I need to do so I'm not filling these areas now. Most of it will get filled as new pieces are attached.

    Photo 8) Next piece goes on either side. Two layers of glass on the firewall.

    Photo 9) I was a lot neater this time.

    Photo 10) After resin cures, excess is removed and glass is feathered.

    Photo 11) Close-up of twice-glassed firewall.

    Photo 12) Fiberglass is feathered on all edges.

    Photo 13) Fiberglass over openings will be cut away with a sharp razor and then sanded.

    Photo 14) I didn't weigh the fuselage but it now weighs 165 grams (5.8 ounces).

    Photo 15) I made a test piece about 3" x 6" that is finished exactly as any piece on this plane that are glassed. It is glassed on both sides. I can cut it into four pieces which gives me eight test pieces to see if the rest of the finish will do what I want it too.

    Extra stuff

    Photos 16-18) The interior was coated with resin three years ago when I last worked on the project. I used self-adhesive foam to cushion the fuel tank.

    Photos 19 & 20) Hard Maple exit fairings. I've made them from balsa in the past but didn't turn out to be very durable.

    Photos 21 & 22) Antenna exit fairing. I built this plane before I had a 2.4 system. I don't know if I'll use my old Super 8 or my 12fg but the fairing is going on regardless.

    Photos 23 & 24) Tail wheel cable exits and fairings. Two more exits and fairings are on top of the fuselage for the rudder cables. None of the fairings will be fiberglassed but they will receive a coat or two of resin.

    Photo 25) Miscellaneous parts including the glassed tail feathers, hardwood tailwheel mounting, stabilizer fillets and plywood elevator control horn.

    Photo 26) Fiberglassed fin and rudder.

    Photo 27) Fiberglassed stabilizer and elevator.

    When all the pieces are sanded and feathered I will glue the tail on but none of the fairings. The stabilizer fillets will be sanded and then glassed. The glass will overlap onto the fuselage and stabilizer. When that is cured and the glass is feathered I will brush on another coat of resin to ensure the glass is fully sealed.

    After that it the entire fuselage and tail will be sanded only to remove hard dust specks in the resin and strings.

    The finish is supposed to be a candy red. I want the red to be transparent so the wood grain is visible, but I also want it to match the wing which is covered with red silk. That's why all the test pieces. I'm not sure it will work the way I want it to and I have three ways of getting clear red:

    1) Mix red with a lot of clear.

    2) Put Red powder dye in the resin. I've done this and can testify that it works.

    3) Add red tint to the resin.

    Anyway, this is all well beyond what we were suggesting to you. You only need a small piece of glass on the firewall and overlapped onto the fuselage about 1/2".
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  17. #17
    Aussie Damo's Avatar
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    wow, thanks cafeen man. way more than i expected. I ended up getting finishing epoxy from the LHS and returned the polyester resin to the hardware store. glass should be here tomorrow and i should be able to give it ago.

    thanks for everyones help
    Dead stick landings are the easiest. Doesn't matter your attitude, elevation or airspeed - it's all down hill from there.

  18. #18

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    That's good. I hate it when I buy the wrong thing and then can't return it.

    Something I forgot to mention in the fiberglassing bit.

    A lot of times when glass goes around a fairly sharp corner to a surface that has little contact area, there are problems. The firewall was no problem because it has a large enough radius round over.

    But on the fin and stabilizer, overlapping on to the trailing edge can be a problem. The cloth lifts on the upper surface right at the corner and there isn't enough surface area on the trailing edge to hold the cloth in place.

    Some people use spray glue (just a little bit). I don't. I just go back and squeegee the cloth down several times. That doesn't fully resolve the problem. But it's easy to fix.

    When the resin is cured, wrap a piece of cling wrap around your finger and put a bit of CA in the area. Rub it down and it will stick in a few seconds. Problem solved. You should do that before removing the excess cloth.
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