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Author Topic: Bugout Bird Dog  (Read 1228 times)
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TimWescott
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« on: September 17, 2020, 04:44:59 PM »

Starting a new thread, because the name has changed.  OCD can be a terrible thing, especially if your hands really are a bit dirty all the time.

The long story is here.  The short story is that I'm building a plane in commemoration of having to evacuate my place.  We weren't gone long, and we're back now, but I'm going to stick with the theme of something simple that can be built with minimal materials in a hotel room or even an evacuation shelter if you're desperate (and polite to your roomies).  Because who knows?  If the wind kicks up from the East or the North, this place may be threatened again.

I'm building a Cessna Bird Dog using the Hales FrogFlite/Yeoman Quick Build all balsa sheet models from Paul and Ralph Bradley's Model Airplane Hangout.  It looks like a pretty cool site.

I will be finishing it out in the color scheme of the South Vietnamese Air Force plane flown by Major Buang-Ly to escape the fall of Saigon, to keep an "evacuation" theme.  Consistent with Major Buang-Ly loading his wife and five children into a two-seater, I'm sure I'll build it over weight.
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TimWescott
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« Reply #1 on: September 17, 2020, 04:46:25 PM »

Thinking way in advance -- the original looks like it was finished in dull aluminum.  I'm thinking of using an airbrush to spray a super-light coat of silver dope on the thing -- is that going to work, or should I just stop now, take a deep breath, and plan on putting markings onto the bare wood with a Sharpie?
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Indoorflyer
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« Reply #2 on: September 17, 2020, 08:22:03 PM »

Here it is, "restored" in Pensacola.  Presumably in accurate colors/markings?  Roll Eyes

https://www.airport-data.com/aircraft/photo/001062632.html

https://www.airport-data.com/aircraft/photo/001393905.html

There's also an O-1 in San Diego at the "Midway Museum," painted up to look like the one in Pensacola.  I guess nobody wants to pay money to see a scruffy, oil-streaked plane with faded, chipped paint...           which would be a more realistic exhibit.


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OZPAF
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« Reply #3 on: September 17, 2020, 08:27:54 PM »

Tim - you are not considering using Paul's printed onto balsa approach? If not - I suspect that any paint would be too heavy nad would prefer to just go the marker route.

That must have been a harrowing experience for the major - overloaded to that extent. He must have been a very good pilot.

John



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TimWescott
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« Reply #4 on: September 18, 2020, 12:52:41 AM »

Tim - you are not considering using Paul's printed onto balsa approach? If not - I suspect that any paint would be too heavy nad would prefer to just go the marker route.

Probably.  I was thinking a really light mist -- but I suppose then it'd just look like sparkly balsa, so what's the point?

And given that the general theme is "I could build this sitting on a cot in a shelter", I'm going with absolutely minimal tools, including not hunting down a printer that I can stuff a sheet of balsa into (but -- definitely maybe later).

That must have been a harrowing experience for the major - overloaded to that extent. He must have been a very good pilot.

It was a pretty good landing.  This video is a bit over-dramatized, but it's good footage of the landing.  It says it was a crosswind landing, but it was a freaking carrier -- they knew how to steer a boat into the wind, and I've read an account from the captain of the carrier saying "we sailed into the wind".

https://youtu.be/IbIXrdciFZQ?t=96
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TimWescott
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« Reply #5 on: September 18, 2020, 09:38:32 PM »

OK, right thread this time, and maybe the attachment will take.

Patterns cut out. I did not stick with the arrangement of the cut sheets because I scaled them down a bit to fit on my printer, and I think I can rearrange things to get more bits out of the wood.

I also think that because I am in my own shop now and I can use Ambroid, that I am going to make up some 1/16 balsa plywood out of a couple of sheets of 1/32 in material. I have done this before, and it works really well, and I absolutely dread cutting out two of each thing and then trying to get them to line up when I glue them. I think it will be much easier to cut one piece each out of super duper light plywood.
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TimWescott
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« Reply #6 on: September 19, 2020, 05:02:34 PM »

If I inventoried my formers correctly, I only need one 3" x 3" sheet of plywood.  So that's what I made -- I can always make more.

Glue is Ambroid and nitrate dope.  As an experiment, instead of double-gluing with just Ambroid, since I've got a painting project all over my bench, I did the priming step with well-thinned nitrate dope.  Once that was dry I thinned some Ambroid in lacquer thinner & brushed it on.  I'm hoping to get a strong, lightweight joint. I'll start to know as soon as I cut it up -- if it delaminates, I'll know I've screwed up!

Any time you glue up large expanses of sheet with solvent-based glue (whether the solvent is stinky or just water) you need to let it dry for a good long time before you can consider it done.  Since this is 1/32" balsa, that good long time is probably a few hours -- but I'm doing work-work this weekend, too, so I may not get back to it until tomorrow anyway!

Here's the plywood all weighted down and drying.  I just glued onto the end of a larger sheet of balsa, mostly out of laziness, but also because if I didn't make enough, I can just append another 3" wide cross-grain sheet on there.
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Indoorflyer
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« Reply #7 on: September 19, 2020, 07:15:35 PM »

Sounds like a plan. This is a cool build. 
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« Reply #8 on: September 20, 2020, 11:10:32 PM »

Tim,

I live in central Washington State.  We don't have any fires close to us, but we've just emerged from a solid week of smoke from California, Oregon, and Washington to the southwest of us that closed us into the house for all but a brief walk to the shop.  Thanks to Covid, I at least had a mask to filter out the ash.  The sun here was literally a bright spot, usually with no form, and there were not any shadows until Thursday.  Prompted me to start a project of my own:  an Earl Stahl,  Howard GH-1, which I'm enlarging to 30" wingspan.

Justin
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TimWescott
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« Reply #9 on: September 21, 2020, 10:59:25 PM »

We got rain Thursday and Friday (we're no longer in an evacuation zone!  Although we're less than a mile from one).  That cleared the air up nice, but there's fires burning within 5 miles of us in a couple of directions, so it's slowly gotten smokier.

I messed up on the plywood -- in part, I think, because I didn't let it dry enough, but definitely because I made the actual glue coat too thin.  I used Ambroid thinned way more than 50%, and it just wasn't enough glue.  I've been discovering my plywood delaminating and teasing more glue into the pockets and weighting it down.

The picture shows one such image, with a weight on a former.  Several formers cut out, a couple to go.

To compensate for too little glue on the plywood, I put too much rubber cement on the stuff I was transferring to balsa, and I stuck it on wet.  This time (with the fuselage side) I painted it with rubber cement and let it dry for half an hour and then stuck it down -- I'm hoping it'll hold on well enough to cut easily, and let go nicely when I ask it to.

The calipers are there because I checked the thickness of the wood -- my "1/32" balsa was nearly .040" on one sheet, and .035" on the other.  I wanted to use the thicker wood for the fuselage sides.  I'm not sure if it shows in the pictures, but it's fairly nice C-grained wood, which seems right for the fuselage.
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TimWescott
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« Reply #10 on: September 22, 2020, 04:58:15 PM »

I think I already knew that rubber cement that has been allowed to dry makes a bond about as good as a post-it.  I just forgot.  At any rate, it's somewhere between really held on and just making a nice high-friction surface that won't squirm around, and that's nice.

I did crack a bit of wood sanding the thing to contour; I glued it up with a bit of CA (the duffer's friend).  But I can say that I'm really attached to this plane now.
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MKelly
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« Reply #11 on: September 22, 2020, 05:23:20 PM »


I messed up on the plywood -- in part, I think, because I didn't let it dry enough, but definitely because I made the actual glue coat too thin.  I used Ambroid thinned way more than 50%, and it just wasn't enough glue.  I've been discovering my plywood delaminating and teasing more glue into the pockets and weighting it down.


The Zaic Utility Special I'm building uses formers and a landing gear platform laminated from multiple layers of 1/64" sheet.  I found (just as you did) that thinned Duco didn't bond the laminations well.  Full-strength Duco worked fine, although even with the stack heavily weighted I got some warping in the cured result.

Mike
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DHnut
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« Reply #12 on: September 22, 2020, 05:34:13 PM »

Would an aliphatic work better in this application. The ability of cellulose based cements to warp are well understood and they dry slowly when not exposed to air. Superphatic is also an option. Just a thought.
Ricky
 
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faif2d
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« Reply #13 on: September 23, 2020, 10:53:07 AM »

I have a block from a 2 x 4 that I use to make simplex airfoil strips.  I have tried Tightbond and my duco ,ambroid,527 mix and they took ages to dry and the middle never did.  The next time I tried I used epoxy and scraped almost all of the glue off.  That worked and it only took a day to cure.
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I used to like painting with dope but now I can't remember why!    Steve Fauble
TimWescott
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« Reply #14 on: September 23, 2020, 11:13:19 AM »

I have a block from a 2 x 4 that I use to make simplex airfoil strips.  I have tried Tightbond and my duco ,ambroid,527 mix and they took ages to dry and the middle never did.  The next time I tried I used epoxy and scraped almost all of the glue off.  That worked and it only took a day to cure.

I was wondering if I should try epoxy.  Foaming urethane glue (i.e. Gorilla glue) may work, too.
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TimWescott
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« Reply #15 on: September 28, 2020, 07:06:18 PM »

I must be the essence of the slow builder -- as I get time, I cut out a piece or two, then get back to work-work (granted, I'm working at a startup and I undertook a vital and much harder than it looked task -- so I have about half a dozen people staring at me -- figuratively at least -- and tapping their watches).

For the things that were done with doubled 1/32, but make sense to do in 1/16, I'm using 1/16.

Fin cut out.  It's kinda crappy balsa (the grain runs about 1/2 inch in a 1/16 inch thick piece).  I'm hoping that it'll do -- if not, I have one nice piece of C-grain around here someplace.  I left a bump on the end of the extension, because I didn't want an infinitely thin cross-grain piece.  I'll glue it together, and hopefully the glue joint will support that bit as I sand it down to fit.
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TimWescott
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« Reply #16 on: October 30, 2020, 06:10:37 PM »

Well, it's a typical build thread -- for me.  Work basically ate my life for most of this month.  Today I got ribs cut out, and glued into the wing.  They're glued in cockeyed, but I'm going to ignore that.  I'm getting ready to glue stuff up.  Then I'll stare at the rain and wish I could fly.

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lincoln
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« Reply #17 on: October 30, 2020, 10:10:54 PM »

If it makes you feel any better, it was snowing while I was picking tomatoes this morning.
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OZPAF
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« Reply #18 on: October 31, 2020, 08:21:41 PM »

Well and truly late - but I second the use of thin epoxy for laminating balsa. No warping and as F2D mentions you do not need much. I am planning to laminate 2 layers of 0.8 with 31/2 glass between them as a substitute(much stronger) for 1.5 light ply. It doesn't appear to be heavier and the only epoxy used is applied to the glass separately over plastic.

John
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TimWescott
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« Reply #19 on: November 02, 2020, 11:18:10 AM »

Well and truly late - but I second the use of thin epoxy for laminating balsa. No warping and as F2D mentions you do not need much. I am planning to laminate 2 layers of 0.8 with 31/2 glass between them as a substitute(much stronger) for 1.5 light ply. It doesn't appear to be heavier and the only epoxy used is applied to the glass separately over plastic.

John

So, squeegee the glass to get almost all the epoxy out, and then laminate it flat with a bit of pressure?  Or am I imagining too much detail?

Is there a web site that shows this technique?  It sounds interesting.
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OZPAF
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« Reply #20 on: November 02, 2020, 08:00:53 PM »

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So, squeegee the glass to get almost all the epoxy out, and then laminate it flat with a bit of pressure?  Or am I imagining too much detail?

That's the basic idea Tim.

I couldn't find a link for you but I used a method used for wetting out glass when moulding.

A layer of plastic sheet(i use domestic freezer wrap) is taped down to the bench.

The glass cloth is placed on this and the resin poured along it and then spread along the cloth.

It helps if you then place another layer of plastic over the wet cloth and then run a squeegee over the plastic - it pushes all the excess out along the edges and helps to avoid capturing air bubbles.

The necessary area/shape of the wet cloth patch required is then marked on the top plastic(or template) and then cut out through all 3 layers -2 plastic and 1 of the cloth.

One layer of plastic is peeled off and the cloth placed in position and then the second layer is peeled off.

It is a good way to handle areas of light cloth as well as helping to reduce the resin content while avoiding air bubbles, and is/was commonly used in moulding layups - particularly for carbon spars.

I have also used it to apply light (3/4 oz) cloth to wing skins wet - although this can require help to hold the other end. The cloth can be rolled down onto the skin through the plastic before it is carefully pulled off the glass. I have also this system to bond a balsa skin onto a foam core. No resin  was placed on the balsa or the foam - the wet glass effectively glued both together and it worked well on a 4m WS UAV prototype.


John
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TimWescott
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« Reply #21 on: November 15, 2020, 09:47:47 PM »

I kinda got stalled, because it wasn't perfect -- which is pretty silly, given that it's an all-sheet project that I started because it'd be quick.

So -- time to apply the FIFI* rule and just go forward until the end of the project is reached.

Fuse built up to the point of needing the landing gear stuck in.

* "F**k it -- fly it"
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TimWescott
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« Reply #22 on: November 21, 2020, 05:36:43 PM »

OK, fuse to the point where I really ought to put the LG on it soon.  But the cowl is on, and mostly looking good.
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TimWescott
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« Reply #23 on: November 23, 2020, 04:57:09 PM »

Over and over I try to hold to the principle that if you're not going to weigh each piece going in, you should refrain from weighing the final product.

Once again I have failed...

This is everything for a basic airframe except for wheels, prop, noseblock and rubber.  I'm going to guess that -- assuming I don't need a brick in the nose -- I should bring it in under 16g, and maybe 14 with luck.  Not too bad for 9 pound balsa and profligate use of medium-thick CA.

Not too bad for something that would have taken me one school night to build when I was 14!
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TimWescott
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« Reply #24 on: November 23, 2020, 06:09:42 PM »

Too small.
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