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Time to get wet.

Old 11-24-2003, 10:13 PM
  #1  
William Robison
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Default Time to get wet.

Back in the '50s I built a lot of sail boats because the engine and fuel cost was zero. It did cost me some effort beyond building and rigging the hulls, though; my mother refused to make the sails after the first two or three, I had to learn how to run the sewing machine. A skill that has served me well in areas other than modelling since.

My first "Fancy" boat was a Sterling (?) model of the Chris-Craft 52' Catalina, LOA was about three feet, with a Pittman "Super Panther" geared motor, a Willard NT-6 wet cell battery, and an exotic (for the time) two channel radio. Flyball actuator for the rudder, proportional steering was controlled by pulse rate, forward speed by pulse on time. Or the other way around, not sure now. Battery life was very short, tube radios in those days. The boat now sits on my son's mantel, it hasn't been in the water for years.

About five years ago I got a wild hair, and decided to build another boat. Something for my grandson and I to play with, without having to go to a flying site. The lake was at the back end of the property. Convenient.

After I moved down here, one of the neighborhood kids knew I did RC, he came to me with a "WalMart" toy boat, wanted me to help him with it. Took my electric runabout off the shelf, and went with him to a local pond. He looked at his boat running less than 1 mph, and looked at mine skimming over the water, planing nicely, and actually bouncing the prop all the way out of the water going over swells, and decided his WalMart toy wasn't worth the time and money. Wanted a fast boat for himself. This finally gets us to airboats.

Made him a deal. Some used surface radio gear, a used Cox engine and prop, and enough wood to build an airboat. Fifty bucks.

I refused to build it for him, but I built one for myself to be a model for him to copy. He finished the hull, mounted the servos, but never went any further, (didn't pay me either) then his family moved away. I still have the one he was working on, still unfinished. But I did complete mine.

Design criteria included having the power loading such that the boat would have good speed, but not so fast as to be hard to control or tend to flip in a turn.

I made the hull more like a punt than a classic airboat, with a sharply raked bow and a shallow semi-Vee bottom. The sides are curved, and the outer hull is made from 0.016" aircraft plywood. The top deck is 1/8" balsa, with a hatch for access to the radio compartment. Except for the radio box, the hull is filled with NHP two-part expandable foam which both reinforces the skin of the hull and makes it impossible to sink the boat. Engine is a CoxTeeDee 05RC.

Small, but the design has worked out nicely.

Bill.
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Old 11-25-2003, 02:24 AM
  #2  
pro27
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Default RE: Time to get wet.

My first airboat was built back in the mid 80's. A Dumas Lil' Swamp Buggy. I had loads of fun with it, also powered with a Cox .049 engine. Not that fast, but very managable. I got into other boats after that. But would still have an AB around to have some fun with

Based on the LSB, I designed several small airboats for the same powerplant. Some worked good, and some s*#%^*. BUt not much money was invested, but it taught me alot of what I now know about airboats.

I revisited my younger years a few years ago and designed some more .049 boats. All four of these hulls are entirely balsa, with a few pieces of ply here and there. Covering is not paint, but iron on plastic covering like you use on airplanes. Great to work with, fast, no odor, fast, lots of bright colors,fast. Did I say fast? I could cover one of these in about 1 1/2 hours and have it running minutes after that.

The engines used on them are as follows........Cox 290 (twin port), Cox Babe Bee (single port), Cox Black Widow (twin port) and a Norvel .049. ALL of these motors do not have throttle control. They run wide open from the first flip to the last drop of fuel. Loads of fun.

I have built other airboats in the past, powered by McCoy Redheads, K&B Greenheads (you older type fly guys should know what these are) Super Tiger G's, OS MAX's. And moving along to a more modern timeline, OS FS, and my favorites, MDS. When I get an itch to try something new, that meant getting rid of one to make room. I lost count of how many I have built over the past 20or so years. My favorite was a canard design w/.049 power. Always did want to scale it up.............

Excuse me, I hear a pencil and paper calling.................
Old 11-25-2003, 02:37 AM
  #3  
pro27
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Default RE: Time to get wet.

I am reposting some of my pics here on this forum so you don't have to jump back and forth.

The #1 boat has a flat bottom, minimal draft and a Cox 290 engine, 18" long, 21.5" OAL.

The #7 boat hsa a semi tunnel, minimal draft, Norvel .049 engine,22" long, 25" OAL.
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Old 11-25-2003, 02:44 AM
  #4  
pro27
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Default RE: Time to get wet.

A couple more 1/2A boats.

#3, Upside down airfoil hull, flat up front transitions to a very shallow vee, Cox Black Widow, 18.5" long, 22.25" OAL.

#5, Flat bottom hull, Cox Babe Bee, 18" long, 21.5" OAL.

Max weight for any of these four hulls is less than 1#.
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Old 11-25-2003, 03:05 AM
  #5  
William Robison
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Default RE: Time to get wet.

Pro:

They look nice, but I have a question.

I have nevr trusted the film coverings to be waterproof at the seams. While I've seen some seaplanes with film covering they never stay in the water very long. And I have seen film covering peel easily from the joints. All I have used in recent years has been polyurethane varnish. It's strong, easy to use, and it's both fuel and water proof.

Have you had any problems with seam opening, water entry, or wood damage from either water or fuel entry?

Bill.
Old 11-25-2003, 10:06 AM
  #6  
pro27
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Default RE: Time to get wet.

By the time I started using it on airboats, I had learned alot of tricks and techniques from covering airplanes and High Power Rockets (I've had numerous sideline hobbies in the past also).
Here are a few tips:

*Balsarite. A brushon liquid that I would not do without.

*a soft rag. I will, for instance, cover a hull side with film, using a sealing iron, and then hit it with a heat gun to warm it again while at the same time using the rag with some pressure to help seal it down. Do a small 5-6" area at a time

*Trim Solvent. A lot of the trim accents are actually not ironed on, but attached using this solvent. A little trick I also do is after all the covering is applied, I'll hit the seam with a q-tip and solvent.

*Stick to one brand of plastic covering. They ARE all compatable, but why push your luck? The two I use most are MonoKote, and UltraCoat. They have a very simular heat range for application.

* Large seams. Airplane guys always seem to want the least amount of overlap. For boat use, the larger the better. I generally use 1/2-3/4" overlaps on my seams.

*Use Pressure. What I mean by this is to slightly pull the material to the edge of the surface you are working. This helps to eliminate bubbles and wrinkles

*Practice. The more you do it the easier it becomes, and the beter the results. It's fast also. I hate having to wait for paint to dry, not to mention multiple coats, the smells. And there is hardly any prepping before applying. The most important tip is to start with a CLEAN surface. No sanding dust.

Take your time, and experiment.

One thing to keep in mind is that plastic film coverings add no strength to the wood like a good epoxy paint or urethane will. It is more suseptable to damage because it is a softer material. It won't hold up to rocks and other large abrasives any better than paint will. But for smaller, lighter weight projects, I myself find it ideal.

In areas such as motor mount bulkheads, fuel tank pods, I still use paint, usually over an epoxy glue sealed wood.



These are my opinions and observations only, I assume no liability what-so-ever!
Old 11-25-2003, 01:22 PM
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William Robison
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Default RE: Time to get wet.

Pro:

When you said Balsarite your success was explained.

You mentioned the strengthening of the polyurethane coatings. And I add my 0.016" aircraft ply hull plamking.

With my electric runabout I hit an almost submerged pipe so hard that the double 1/4" balsa motor mount was broken from the impact, and I have never found a mark on the hull.

Bill.
Old 11-26-2003, 02:57 AM
  #8  
pro27
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Default RE: Time to get wet.

There is always a time to use the right product!

All my small (1/2A) airboats are design/idea test beds. They are cheap and fast to build, cheap to equipt, cheap to run, but are still a lot of fun.

I use the plastic covering on all my small boats for a couple simple reasons.
It's fast . And I consider the boats expendable. They are design tests after all.
Also with the covering, if I want to make a modification, I don't have to sand down paint to get glue to stick, a quick slice through the covering, a little heat and peel it off.

If the small boat makes it through the testing stage, well then, I have another fun boat.
Don't get me wrong, the covering is durable, but not as durable as a good hard coat finish.
If I hit the same pipe you did, I'm sure you would be able to tell.
Old 11-26-2003, 03:29 AM
  #9  
William Robison
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Default RE: Time to get wet.

Pro:

Here's a picture of the motor on its mount. This is as it was, there is now a plywood reinforcement on each side. The mounting is two 1/4" vertical sheets, with the tops rounded for the motor's seat. They both broke just about where the wire for the rubber band hooks goes through.

Bill.
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