Author Topic: Grumman-Schweizer Ag Cat  (Read 5002 times)

0 Members and 1 Guest are viewing this topic.

Fingers

  • Moderator
  • Full Member
  • *****
  • Posts: 184
Grumman-Schweizer Ag Cat
« on: December 15, 2011, 11:05:31 AM »
It's been quite some time since I posted anything here, so I'm glad to have something to contribute -- finally.

A while ago I asked for help in locating plans for a Grumman-Schweizer Ag Cat, not because it's by any means a favorite airplane of mine, but because the Empire State Aerosciences Museum where I volunteer had expressed an interest in doing a display on it. The Ag Cat has abundant connections to New York State -- Grumman on Long Island and Schweizer Bros. in Elmira -- and has been exported all over the world to help fight agricultural pests and famine as well as wildfires, so it was deemed an appropriate subject for such a display. I volunteered to build the model, and several SMM members were gracious enough to offer suggestions for an appropriate plan.

Most of the plans out there with sufficient accuracy and detail were of the early, open-cockpit version of the Ag Cat, so I had to make do with the best ones available and make such changes to them as I could. I finally settled on a stick-and-tissue version that came from a 1961 issue of American Modeller magazine, and made templates from that.

Never in my life has a model given me a harder time. The first fuselage I carved was awful, and I ended up throwing it away half-carved and started over again. The second iteration was much better. I got the fuselage, wings and tailplane all carved and decently fitted together and began painting...

Well, at this point, I made a sickening discovery: Somewhere along the way, the makers of automotive enamel spray paint had changed their formulations to eliminate the volatile organic chemicals (VOCs) that traditionally had been used as solvents and propellants in rattle-can spray paints. After applying several coats, which went on fairly well, the can I was using ran dry and I had to switch to a new one -- of the same brand -- and the instant I applied it disaster struck. All the paint previously applied immediately crazed into a gooey, shrivelled mess. Worse, it absolutely refused to dry, so there was no possibility of  stripping it off and repainting. I tried everything I could think of, but it soon became clear that the project was a total loss. Four months' work down the crapper...

I'm just cantankerous enough not to admit defeat, though, so after an appropriate period of denial, mourning and finally anger, I got back at it. I was able to salvage a few parts -- engine, struts and metal fixtures -- which saved me a little work, and this time I tossed out the spray paints and used Floquil bottle paints applied with a brush, oversprayed with Krylon clear. The results, for better or worse appear below.

Never been so glad to finish a model in my life...
« Last Edit: December 15, 2011, 11:09:44 AM by Fingers »

Mark Braunlich

  • Hero Member
  • *****
  • Posts: 536
Re: Grumman-Schweizer Ag Cat
« Reply #1 on: December 15, 2011, 02:43:20 PM »
Glad you were able to finish it Fingers!  Looks fine and thanks for posting.  What scale is it?
I'm glad you overcame all the heartache and achieved such a nice model for the museum.

Mark

lastvautour

  • Administrator
  • Hero Member
  • *****
  • Posts: 6205
Re: Grumman-Schweizer Ag Cat
« Reply #2 on: December 15, 2011, 07:01:08 PM »
Wonderful model. Tell us about the details such as wing alignment and engine build up. Congratulation on such a fine project.

Lou

Fingers

  • Moderator
  • Full Member
  • *****
  • Posts: 184
Re: Grumman-Schweizer Ag Cat
« Reply #3 on: December 15, 2011, 09:40:31 PM »
Thanks, Mark and Lou. Scale? Not being good at math, it's hard to say. I'll try, though:
 
The Ag Cat has a 36-foot wingspan (432 inches), and the plan I used had a 36"-inch wingspan. That means one foot = one inch, making the original plan 1:12 scale (with 12 inches -- one foot -- on the full-size airplane being equal to one inch on the model). I reduced the size of the model to a 15" inch wingspan, so 432 divided by 15 = 28, making the model 1:28 scale, if I figure correctly. And that's positively all the math my poor brain can stand...!

Engine build-up:  The engine crankcase is made from basswood turned on a Dremel, the cylinders are made from poplar dowels, chucked in a drill press and scored with a file. The rocker arms are straight pins, the rocker boxes are made from wooden toothpicks, the variable-pitch control hub on the propeller shaft is made from strips of duct tape, and the prop shaft is made from brass tubing, as are the sprayer pipes under the wings. The exhaust collector ring also is brass tubing, carefully bent into a circle and soldered, and the exhaust pipe was fluted on one end with the tang of a file and soldered to the ring on the other end.

Wing alignment was essentially by the Mark I Eyeball. I have no clue when it comes to building alignment jigs. I just marked the positions of the interplane strut sockets very carefully on the wings from the plan templates, drilled them out with a Dremel and notched the bases of the struts to fit. When the time for assembly came, everything went together fairly well. It might not be absolutely perfectly aligned, but it's certainly close enough that you couldn't tell from the back of a running horse!

The center-section struts were more problematic. I hadn't taken into account that the top-decking in front of the cockpit was slightly taller in this canopied version of the aircraft than the original open-cockpit version, so when I went to fit the cabane struts I discovered they were too tall! I ended up filing and sanding them shorter and shorter until they fitted properly in the requisite space. The top ends were notched into grooves Dremeled into the wing, and the bottoms were first tack-glued in place, then secured with the glued tip of a toothpick inserted through a tiny hole drilled through the base of the strut and into the fuselage.
« Last Edit: December 15, 2011, 09:45:30 PM by Fingers »

Mothman

  • Full Member
  • ***
  • Posts: 112
Re: Grumman-Schweizer Ag Cat
« Reply #4 on: December 16, 2011, 03:25:30 AM »
And there, gentlemen, is the overwhelming problem with acrylic paint.  It is rubbish, muck, filth and it's being foisted upon us by a bunch of fascists in government who couldn't hold a paint brush the right way round never mind use spray paints.  I have a local supplier of cellulose paint and have gone back to that wonderful stuff. It covers itself, it dries in minutes, it polishes in a day or so.  Wonderful, proper paint. I will NOT be told by some clueless, chinless wonder what to do with my hobby and indeed my one time business.  Much less when those directives come from a cess-pit country where the locals ignore every utterance from the EU. I have lived and worked there and know of what I speak!

Any paint which reacts with itself is unforgivable.

But whilst I am a lover of Floquil, they too have changed their formula and it isn't a patch on what it used to be. Plus I couldn't get it sent to me from the one shop in Britain that sold it, because they weren't allowed to post it, so I got ten pots sent from America...by post!! Haha!  You gotta get up early to mess me about!  That shop went broke by the way, serves them right.

Martin (anarchist modelmaker)

Balsabasher

  • Hero Member
  • *****
  • Posts: 1821
Re: Grumman-Schweizer Ag Cat
« Reply #5 on: December 16, 2011, 04:29:27 AM »
What a co-incidence ? I have just been looking at some pictures of older models and this was one of them,a scratch built Grumman Ag Cat,a somewhat younger balsabasher holding the framework of a flying model of this interesting machine,the model was completed and flown successfully and I remember contacting a crop spraying company who owned a fleet of these requesting the upper wing incidence of the real aircraft,the one thing that I have learned over the years is to follow the original designers set up for successful flight and this was no exception.
You can just see in the picture the large built up radial engine where the four stroke motor was buried within,the model would get airborne within a few feet with all of that lift from those wings and the small field from where it was flown was ideal as the Ag Cat would drop its nose as the power was reduced bringing it in for a typical draggy biplane landing,it was exceptional fun to fly.
I will get away with this one here by declaring solid model elements !

Barry.



http://smm.solidmodelmemories.net/Gallery/albums/userpics/10005/Dec16_02.JPG

Ken Pugh

  • Sr. Member
  • ****
  • Posts: 411
Re: Grumman-Schweizer Ag Cat
« Reply #6 on: December 16, 2011, 05:23:25 AM »
Well done Ag Cat.  I have been interested in building the ShowCat modification.

The age old problem of making sure your paints are all of the same exact type.  Really annoying when you keep brands and find the hard way they are no longer the same.  It was good that you stuck with it through this and produced a good looking model.

Ken Pugh

Fingers

  • Moderator
  • Full Member
  • *****
  • Posts: 184
Re: Grumman-Schweizer Ag Cat
« Reply #7 on: December 16, 2011, 09:12:02 AM »
If I'd been half smart I'd have tested the "new" paint before applying it over the "old". It just never occurred to me that it would react the way it did. But it's right there on the cans -- provided you read the small print and catch on to what they're telling you. The old ones say you can re-coat or overpaint "anytime". The new ones say something about doing it "within" 15 minutes or so, or, alternatively, having to wait several days, presumably  until the paint fully cures. The wording is really vague...

I suppose the solution is to learn to use an airbrush -- something I've always shied away from...

lastvautour

  • Administrator
  • Hero Member
  • *****
  • Posts: 6205
Re: Grumman-Schweizer Ag Cat
« Reply #8 on: December 16, 2011, 09:27:56 AM »
Air brushing is no guarantee of making a good paint job. Like all things, trial and error proves out in the end.

Lou

Balsabasher

  • Hero Member
  • *****
  • Posts: 1821
Re: Grumman-Schweizer Ag Cat
« Reply #9 on: December 16, 2011, 09:36:14 AM »
Paint will generally take several weeks to flash off,the effect of re-painting on uncured finish is to just soften the underlying coat,for a gradual heat try sitting the model on top of your computer is best,it all helps to make the paint really hard ready for the next coat and most of all the masking process,but never rush the process.
Airbrushes are the most mis-understood model making tool,they require years of practise to achieve good results and do not suit everyone,keeping them clean is a pain requiring ultrasonic cleaning for best results.

Barry.

Fingers

  • Moderator
  • Full Member
  • *****
  • Posts: 184
Re: Grumman-Schweizer Ag Cat
« Reply #10 on: December 16, 2011, 11:06:25 PM »
Yes, that's about what I figured. It's the main reason I've shied away from it all these years...

Ken Pugh

  • Sr. Member
  • ****
  • Posts: 411
Re: Grumman-Schweizer Ag Cat
« Reply #11 on: December 17, 2011, 08:16:43 AM »
I think we all know we should test all paint before we put it on a model but probably few of us actually do the test and even rarer still do we do it every time.  It bites us all at some time or another.  Paint is chemistry and chemistry is a fickle science.  Unfortunately, many times we learn about chemical reactions by trial and error.

I really try to read all the instructions before I use something because I have seen many cases of people getting poor results, especially with acrylics, where they did not read the instructions.  Chemical engineers are the best initial source of information regarding their products, a lesson I have learned the hard way.  We also see people get poor results with electronic hardware and software because they did not read the instructions.  When I get bit, that is usually why.  I also always read the instructions on glue bottles, no matter how much I think I know about the product.  I spend a lot of time in the store reading all the bottles to make sure I am getting what I want. Even filler paste, read the instructions.  Chemical formulations change in products, so enlist the help of the chemical engineer who knows the product best.

Painting is, by far, the most difficult thing we do.  It not only requires artistic skills, but chemistry comes into play.  Paints and adhesives will get us every time we let our guard down.  You hit problems then overcame them, that's the sign of a good modeler.  Live and learn, sometimes the hard way.  Lessons learned by failure usually serve us best.

Ken  Pugh

Fingers

  • Moderator
  • Full Member
  • *****
  • Posts: 184
Re: Grumman-Schweizer Ag Cat
« Reply #12 on: December 17, 2011, 09:12:13 AM »
I often tell people that one of the things I like most is about model-building is that it incorporates a high degree of problem-solving. There's a special kind of satisfaction derived from butting up against a problem you encounter, thinking it through to a solution, and then overcoming it. It's not the kind of thing you can master by practice or repetition -- like learning to play a musical instrument, for example, or memorizing geometry theorems -- it's something you have to confront, typically in a completely different form, with each new project. Have you noticed that even the best-drawn model plan usually has at least one flaw in it somewhere that must be corrected or compensated for? Something the designer left out, overlooked, expressed or illustrated poorly, and which you often don't notice until you run headlong into it mid-way through tghe project? Or perhaps you find yourself having to improvise or substitute some material or part for something you just can't get your hands on? Or build a tool to take the place of one you might need to perform some task, but which you don't have or can't find? It's part of why we model airplane-builders are such pack rats -- why we have drawers filled with bits of junk we've saved: lengths of wire and tubing, parts from broken clocks, springs from ballpoint pens, old banjo strings and  odds and ends of wood. It might come in handy some day in solving a problem! Now if we could just solve the problem of chemistry!
« Last Edit: December 17, 2011, 09:14:08 AM by Fingers »

Mothman

  • Full Member
  • ***
  • Posts: 112
Re: Grumman-Schweizer Ag Cat
« Reply #13 on: December 17, 2011, 05:39:03 PM »
There is no problem of chemistry here, only a case of being fobbed off with shoddy goods. I repeat...a paint which reacts with itself is unacceptable.
Cellulose doesn't do it and neither does quality enamel.  If they can't satisfactorily test their new products before charging us through the nose to be their guinea pigs it's a damned poor job.

Airbrushes are both misunderstood and over hyped.  I have a couple and use them rarely as they are fragile things, difficult to clean, though not as bad as some. Mine are Paasche with needles blunt by design so that they cannot be damaged easily.  But far more useful and competent in every way are my spotting guns. Little spray guns that cost a fraction of an airbrush and do almost the same job.  They are simplicity itself to clean with a thinners wash-out.  I always leave a little thinners in the cup during storage.
Enamels are a little more fiddly because they take so much longer to dry.  I would always use sign-writing enamels as the pigmentation is denser than most and the coverage is better.

Martin

Balsabasher

  • Hero Member
  • *****
  • Posts: 1821
Re: Grumman-Schweizer Ag Cat
« Reply #14 on: December 18, 2011, 04:34:51 AM »
http://www.narrowboatcolours.co.uk/topcoats.html

Superb paint,expensive but it will last you for a long time,the pigments are very fine and the binders flow beautifully leaving brush free results,ideal for hand painted markings.

Thank you Martin for reminding me of this excellent product.

Barry.