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Old Sep 13, 2012, 05:44 PM
Big gov never Works
St. Martin's Avatar
Skunk Water, Rhode Island
Joined Jul 2002
12,417 Posts
Not sure of your location, Conrad. But, I really like National Balsa. They have a bargain contest grade. Just a little dis-coloring ocassionally. http://www.nationalbalsa.com/Aero_Li...Grade_s/21.htm

Fuzz
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Old Sep 13, 2012, 06:10 PM
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glewis's Avatar
USA, FL, Tampa
Joined Jul 2002
4,860 Posts
Hi Conrad.
A word about your next build, consider the weight of every part as you build.
How can I lighten this part without weakening it too much?
Remember, most of the Guillows models were designed to withstand the compression and torque loads of a fully wound rubber motor. This makes the the fuselage aft of the CG way too heavy.
As you found out at the end of your PBY build the weight sneaks up on you and adds up fast.
Your model will fly fine. Set your CG at 20-25% MAC. My suggestion would be try to take off from wet grass. Let it gain enough speed to lift off on its own, resist the urge to yank it off the ground with the elevator.
Good luck!
Glenn
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Old Sep 14, 2012, 10:22 AM
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conrad907's Avatar
China, Guangdong, Shenzhen
Joined Feb 2012
402 Posts
Fuzz,
I ordered from Specialized Balsa http://www.specializedbalsa.com/index.php. It was a small order to see how the service is and how the wood looks. I saved your link Fuzz, I will send my next order thru them and check out their service. Since I live in Alaska, I always pay out the nose for shipping, but I am accustomed to that.

Glenn, I actually remade many parts out of contest grade sheet, like fuselage formers, and all my wing ribs, as well as the leading edge for the wing. I kept crushing fuselage formers! I'm too clumsy to use it for fuselage formers I decided! As you say though, each part must be made as lite as possible, I am fully onboard with that idea now. The Cessna I just started has typical heavy Guillows wood. I just built the tail feathers, lightened them as much as I though prudent, but now I am considering rebuilding them out of lite balsa when my order arrives. They still seem heavier than they need to be.

I do have a question on servos. I used a 6 gram servo on each aileron, it seemed adequate in my mind for such a small control surface. But I also used the same servos for the rudder, and the elevator. Since these are also attached to about 9-10 inches of Sullivan cable, I am wondering if the proper servo should be like a 9 gram unit with a bit more beef to it. I have some 9 gram servos I bought with metal gears, I got to looking at them and thought maybe these would have been a better choice. Is there a simple rule of thumb to avoid trouble on servo selection?
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Old Sep 14, 2012, 12:15 PM
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glewis's Avatar
USA, FL, Tampa
Joined Jul 2002
4,860 Posts
You're in Alaska? Guess taking off from snow would be more appropriate then!

You might consider laminating the tail surface outlines. This saves a lot of weight.

About the servos, I think the 6 gram ones will be fine for the ailerons.
Since the other servos are driving through Sullivan cables (I hate those things) you might want to consider larger ones. I say this because if the smaller servos are stalled or close to it, they will draw a lot of current causing your BEC to shut down.
We all know what happens when we lose power to the receiver, it ain't pretty...
Glenn
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Old Sep 14, 2012, 12:54 PM
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conrad907's Avatar
China, Guangdong, Shenzhen
Joined Feb 2012
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Glenn,

Yeah, I have about 6 months of snow here each year, so I figured it would be a good time to attempt the PBY maiden. As for my other planes, I will just build ski's for them as I build them for winter use.

I think I will upgrade those tail feather servos before I attempt a flight. I would rather change a few grams for the piece of mind.
John
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