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Author Topic: Peanut Andreasson BA-4B  (Read 1035 times)
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Prosper
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« on: July 28, 2012, 05:51:40 AM »

Well, I'm playing with this 'fully-sheeted' style of construction and the fact is, I find it needs lots and lots of practice, and I reckon I'm still at the bottom of the learning curve, as people say. I wanted a direct comparison, and I had made a Walt Mooney Andreasson BA-4B a year or two back, so there it was. I judged that this would be a very quick build for a sheet model, and so it has proved. Each wing panel is made from a single sheet, simply folded round at the L.E. and with several 0.3mm ribs to give the correct section (root ribs are 0.8mm). The wing tips are made the same way. The wing section is a pretty accurate copy of NACA 2412, which I think was what Mr. Andreasson used (not certain because the webpage I got the info from is in Swedish!). The fuselage is just panels with 1/16 longerons (tapered towards the tail) and 0.8mm formers for the decking. The original had fabric covered stringers for the rear decking, and I have made a right mess of emulating this, but I'll know how to do it better next time. Some 1.6mm cross-pieces and some 0.8mm doublers for strength where necessary.

The model has nearly twice the wing area of the 12" span Mew Gull I'm working on, and won't weigh much more I guess. The BA-4B I made to Walt Mooney's plan weighed about 10g with a fairly opaque paint job, that's without rubber, prop and noseweight. It was only my second or third flying scale model so no doubt most folks could get it much lighter, but it gives me some comparison anyway. At a very rough guess this fully-sheeted job will end up a gram or two heavier. It depends a lot on how much paint I ladle onto it.

It's advancing quickly so I should soon find out. . . The thing is, 2g heavier and it'll still have a respectably low wing loading.

All in the pictures weighs 7.8g.

More soon I hope,
Stephen.
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Peanut Andreasson BA-4B
Peanut Andreasson BA-4B
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tross
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« Reply #1 on: July 28, 2012, 07:11:15 AM »

Hi Stephen,
The model is looking great.
I really like it.
Mine weighs 35 grams AUW (say what?) and still flies ( not a floater). Shocked
I ended up hacking it up a bit to change the DH and top wing incidence.
Flew it for a while, but now it's just hangin out. Undecided
So what you're doing should work out just fine.
Cool stuff. Grin

Tony
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Instructions: Step One...Assemble the pile of sticks shown in pic "A" to look like the model airplane shown in pic "B"........
Crabby
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« Reply #2 on: July 28, 2012, 08:15:33 AM »

I have built several of these things, none were floaters, but man what flyers! And they can take a beating. I take mine out every now and then and fly it till its too dark to see.
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Prosper
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« Reply #3 on: July 28, 2012, 10:30:34 AM »


. . .but man what flyers! And they can take a beating.

Yes indeed, Crabby. I was very impressed by the way mine would bounce off tree trunks. It flew so slowly, that if it hit foliage it would stop before getting tangled in it, so it was easy to rescue. It did get punctured a lot by dead weed and grass stalks. Eventually I re-covered it, and took the chance to lower the rear decking and add a headrest (Walt Mooney's 'High Deck' did exist, going by a photo on the internet, but very early in the aircraft's life, possibly before it got that sunburst colourscheme). I reduced the dihedral and gave it a scale tailplane too. Whadyaknow, it never flew as well after that.

I've no idea whether this thing I'm making will be as strong. I doubt it though. The likely weakpoint will be the cabane struts - if the top wing hits something hard it could shear them off at the longerons, and that'll be really hard to fix. At least it should be puncture-proof!

Hey Tony, did you reach any conclusions about dihedral and wing incidences? I plan to give the top wing about a degree more incidence than the bottom, in the hope that that'll pitch it nose down when it stalls.

Stephen.
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Prosper
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« Reply #4 on: July 30, 2012, 09:58:16 AM »

This model approaches completion now. I haven't quite decided how to paint it yet. Yesterday I covered a sheet of polythene with red permanent marker, to weigh it. It took a good while, scribbling furiously like a small child, but it was worth it, since I measured a weight of 2.3g/m2. This seems so light to me that I think I'll use permanent markers first, then mask and spray either acrylics or enamel, hoping to get away with lighter coats, because the markers will have given a good bit of opacity already.

The weight as in the pics is now 9.6g. It always seems to me that at this stage, a model's weight starts to zoom up - wheels, struts, detailing, paint, ballast. . .

Stephen.
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Re: Peanut Andreasson BA-4B
Re: Peanut Andreasson BA-4B
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wordguy
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« Reply #5 on: July 30, 2012, 10:35:21 AM »

Fascinating build, please keep us all informed as this moves fwd.

The landing gear looks especially "trick."  May I ask what you used?
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As it is not at all likely that any means of suspending the effect of air-resistance can ever be devised, a flying-machine must always be slow and cumbersome. . . . But as a means of amusement, the idea of aerial travel has great promise.

— T. Baron Russell, 'A hundred Years Hence,' 1905
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« Reply #6 on: July 31, 2012, 09:59:17 AM »

Hullo wordguy, the gear legs are carbon tow. I can go through it step by step if anyone's interested but essentially it's just carbon tow stroked into shape then wetted out with thin CA over a simple form to get the curvature and the bends, then it's sanded under water (don't breathe that carbon dust!) to finish. You get a very light spring leaf, good for all Cessnas or whatever uses spring steel legs. For my Walt Mooney BA-4B I made the legs thin enough that they assumed the right load and no-load states when the model was grounded or flying. The trouble was that getting the right degree of spring is a bit hit-and-miss, and anyway the gear was too frail then.

Regards,
Stephen.
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gloster
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« Reply #7 on: August 01, 2012, 10:58:21 AM »

Hi Stephen

A job as I like to see, the quality of this cigarette paper assembly seems very good, give me the mark please  Cheesy
Seriously, really impressive.

Cheers
JM


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Prosper
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« Reply #8 on: August 04, 2012, 02:47:53 PM »

I'm assembling this model now. The painting was a shock - it added over a gram of weight, and this has the extra penalty of needing extra noseweight, since most of the painted area is behind the c.g. of course. The problem is that the light colours don't have the opacity to cover the dark grain of the wood, so they need really thick coats.

So, the weight has now jumped to nearly 12g and there's still more to be added. This should still give a decently low wingloading, but I'm wondering if I can find some ways to lighten this building technique generally, otherwise it may hit the buffers.

It should be ready for flight tests soon.

Stephen.
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wordguy
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« Reply #9 on: August 04, 2012, 03:19:23 PM »

Nutty idea, but have you considered the possibility of dying the wood?   Something like Sharpie ink dissolved in alcohol and fogged on with an airbrush for base colors, tissue on top for the accents?  Yes, the wood would show through, but that level of craftsmanship OUGHT to show through!
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As it is not at all likely that any means of suspending the effect of air-resistance can ever be devised, a flying-machine must always be slow and cumbersome. . . . But as a means of amusement, the idea of aerial travel has great promise.

— T. Baron Russell, 'A hundred Years Hence,' 1905
Prosper
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« Reply #10 on: August 05, 2012, 06:52:48 AM »

Far from a nutty idea, wordguy.  In fact, on one or two areas I did indeed colour the wood with Sharpie pens hoping that this would reduce the amount of paint needed. It did make a difference, but not a huge amount. The trouble is, I can't go the whole way and dye the wood because the CA surface is impervious. I guess I could dye it before surfacing even - I'll add that to my list of trials I have to carry out to get the best out of this CA-surfaced balsa business. I've just ordered some titanium pigment. This is very opaque. I wonder if I can add it to the CA before spreading the CA over the surface of the balsa sheet. Of course it may cause the CA to do its stuff and cure to a hot white lump in a split second (gulp) but you have to try these things I suppose.

I'm hoping to avoid tissue, because one of the good things about this method (I'm not saying I've achieved it, but the possibility is there) is that you can get a good, hard, high gloss, which I'm not sure can be done with tissue, well, at least on this scale.

As for the level of craftsmanship - thanks for the kind words, but don't be fooled! The camera is VERY flattering here, and this little ship really doesn't withstand scrutiny. "The camera always lies", I like to say. I've got a long way to go before getting on top of all the various skills required to make a model of the quality I see on so many different HPA threads.

gloster, the cigarette paper I use is Gauloise - or is it Disque Bleu? I can't remember ;-)

Stephen.
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wordguy
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« Reply #11 on: August 05, 2012, 08:38:02 AM »

Don't know if it's available in the UK (or even if its available at all these days) but I used to use "Dr. P. H. Martin's Radiant Transparent Concentrated Water Colors" (can't make that up, can you?) for dying - the good doctor also offers "Translucent" and "Opaque" product lines, as I recall.  They come as a liquid, in an eyedropper-style bottle, and can be diluted, airbrushed, brushed, or even used in a technical pen, I suppose.  Note that I did not say that they were cheap...  Any imaginable color, including "impossible" ones like "transparent gray."  P'haps spray on, then do the CA trick?

My days of using cigarette papers ended (ahem...) with the start of the 1970s.  Still have the hair and beard, though. 
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As it is not at all likely that any means of suspending the effect of air-resistance can ever be devised, a flying-machine must always be slow and cumbersome. . . . But as a means of amusement, the idea of aerial travel has great promise.

— T. Baron Russell, 'A hundred Years Hence,' 1905
Prosper
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« Reply #12 on: August 06, 2012, 04:30:21 AM »

"Dr. P. H. Martin's Radiant Transparent Concentrated Water Colors"

Blimey, what d'you do - drink it, or rub it in??

Actually, I reckon the thing with all these different paints (watercolours, oil paints, acrylics etc) is that the pigments are the same. In fact I know they are. There's a number code (dunno if it's European or worldwide). Thus PW6 is 'Pigment White titanium dioxide' and PY35 is 'Pigment Yellow cadmium sulphide'. I guess the main things of interest to the modeller are the weight of the medium which carries the pigment, and how that medium reacts to water, fuel, dope, glues etc. Watercolours are the lightest because the medium is water - it's a great way of delivering pure pigment to an absorbent surface, as you found out, wordguy. BTW I'm really glad to have learned about Dr. P. H. Martin, and I'm looking for his patent snake oil laquer, to use instead of dope. . :-)

As for the BA-4B, after hiring a crane in order to lower 6 tons of lead into the nose cowling, I deemed it ready for some test hops. You really pay a penalty for scale-sized tailplanes in terms of the more forward c.g. required. My Walt Mooney BA-4B had me trying to make the nose lighter by hollowing out the soft-block cowlings. And that was with a very aft peg position. Anyway, I managed to knock a wing off almost straight away. Wasn't expecting that. It's funny how what seems very strong and light early in the build, suddenly seems frail when you have the weight of the whole model in your hand! So, I've broken it before even finishing the details. . .Luckily no damage, just needs re-cementing. Just a "quality control issue" I guess. Better wait for the wind to die off anyway.

Re. carbon tow spring-leaf gear struts, I forgot to mention that they're very susceptible (at this scale at least) to motor vibration, to the point of shaking into a blur when the motor vibrates as much as mine often do. I've never yet learned to make a reliably smooth motor - it's just a matter of luck with me. The other drawback of these legs is that if the model is left on them for a long time (weeks or months) they slowly sag or twist. I'll be storing this model on a block under its belly (if it survives so long).

Stephen.
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Prosper
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« Reply #13 on: August 08, 2012, 02:46:09 PM »

I managed some short flights today after refixing the wing, and re-braiding and relubricating the motor to stop it vibrating. Maybe I'll get around to detailing it when it next needs significant repairs.

I also made the prop pitch much finer. It's interesting that the BA-4B needs fine pitch and 1/8" rubber whereas the 12" span Mew Gull #1 I made, needs just 3/32" rubber and scoots off despite a very coarse pitch prop, and twice the wing loading. However, something tells me that this bus will stay aloft a little longer than the Mew.

I nudged the c.g. back a couple of times to save noseweight, but it must be getting close to tail stalling. It's flying at 17.3g, that's a good 2g more than I'd hoped, but I just hadn't anticipated how much noseweight it'd need, nor how heavy the paintwork would be.

Just like the Walt Mooney -4B I made, it looks very light and slow in flight; a very benign nodding stall and some slight wing rocking at times.

Anyway the rudder came adrift, and since the sun chose that moment to put in a guest appearance, I thought I'd better photograph it before I smash it or lose it in a tree.

Next, to finish Mew Gull #2.

Stephen.
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Re: Peanut Andreasson BA-4B
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Re: Peanut Andreasson BA-4B
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