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Old Feb 12, 2002, 10:40 AM
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c.g....how to find it....

I have been reading about the dive test. I am new to this flying thing I have a zagi 3c.......is there an easy way to find the C.G....I am interested in different ways to find it..thanks...
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Old Feb 12, 2002, 11:37 AM
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Zagis are difficult enough to fly without deliberately crashing them!
The c.g. for the Zagi is on the plans. The plane will fly VERY WELL with the c.g. at that point. A slight bit aft of that and it will become VERY UNSTABLE! Flying wings are like that. Small twitchy flying wings.. OI!!!!
There's no need to "dive test" a Zagi.
.
The c.g. is where the plane balances; the nose and tail ends an equal distance from a horizontal surface. There is ALWAYS a point where this happens. Positioning that point properly (per the plans) determines if the plane is flyable. Too far ahead of the plan's position, the plane will be sluggish and slow. Too far aft, it will be too sensitive and difficult to control if it flies at all.
Nose heavy planes fly sluggishly, tail heavy planes fly once.
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Old Feb 12, 2002, 11:52 AM
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The C.G.

If the center of G. is to far foreward you said it would fly slugish...and slow...I like planes that fly slow (cause I suck a flying) but by slugish does that mean it will stall a lot??? I guess what is your Def. of slugish..thanks!!!!
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Old Feb 12, 2002, 11:57 AM
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I think that by sluggish he means that you have to input my control and hold it longer to initiate and complete the maneuver. Nose-heavy aircraft are much more predictable, stable, but you are trading that for ability to thermal, etc...

I typically start with the CG forward just a bit of the CG indicated on the plans just to get comfortable flying the plane, and then gradually move the CG back to where you like to fly.

Personally, I hate twitchy airplanes.

Tail heavy airplanes fly only once...seriously!

Tim
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Old Feb 12, 2002, 12:11 PM
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Re: The C.G.

Quote:
Originally posted by thor4944
If the center of G. is to far foreward you said it would fly slugish...and slow...I like planes that fly slow (cause I suck a flying) but by slugish does that mean it will stall a lot??? I guess what is your Def. of slugish..thanks!!!!
.
Nose heavy.. the plane flies, but it responds slowly to inputs. And tend to stall because the nose has to be held up by the elevator. Because it's near the stall, aileron input tip-stalls it quickly.
Tail heavy, the plane will be twitchy.. very rapid, sometimes way too rapid response to elevator. Lots of zooms and dives. Very fast rolls.
The c.g. on the typical construction plan or ARF will be conservative.. that is, forward of the most aft acceptable point, and the best place to start to fly a new plane. Then if you want more activity it can be moved aft. Depending on the plane's size, small amounts of clay or lead can be used.
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Old Feb 12, 2002, 12:59 PM
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?

What do you mean by fly only once???? And I probably should add weight to my nose...my C.G. is about 8 inches from nose....it weighs about 18 oz......
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Old Feb 12, 2002, 01:14 PM
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what is nose heavy

What would you guys consider nose heavy?? 7 inch...7 1/2 inches?? on a zagi 3c.....
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Old Feb 12, 2002, 01:33 PM
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by flying only once, we mean that the airplane will be so miserably unflyable, that it will ultimately crash.

Usually on a conventionally winged plane, I will go perhaps a quarter of an inch ahead of what is indicated on the plans.

tim
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Old Feb 12, 2002, 02:58 PM
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This is for Zagi's only, alright?

1) put two fingers 1" back from nose/leading edge.

2) trim 1" sections from each wingtip until the Zagi balances, slightly nose down, on your fingers.

This will give you a perfect Zagi.
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Old Feb 12, 2002, 06:49 PM
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IRSUDOG?

Irsudog..I am sorry..this is my first time flying. I have been working hard for the past month trying to fly this Zagi. I am confused about what you mean...I dont know if your trying to make fun of me or what..But I would appreciate some advice. Thanks for your time....If you are serious what do you mean by triming your wing....?
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Old Feb 12, 2002, 10:40 PM
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I don't think irsudog likes Zagi's (unless he's flying one with a three inch wing span).
Eight inches from the nose should be close. But hey, it is a personal thing for the most part. Fuss with it. 1/8 inch at a time if you have the patience. You'll eventually find the sweet spot.
And a tail heavy Zagi is one that you can crash over and over again till you get it right.
You might also try the foamie forum. Lots of Zagi nuts over there.
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Old Feb 13, 2002, 06:38 AM
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thanks gliderguy!!!

thanks
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Old Feb 13, 2002, 09:46 AM
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I read posts about CG on this board all the time. They constantly frustrate me. The best thing, and I do mean the BEST thing you can do is experiment!!!!! Start with where the manufacturer recommends. And then work this forwards and backwards in small increments. See what happens. You can only learn so much about CG from reading posts and articles. They are a great start, but experimentation is the ultimate teacher. Moving it backwards will make it more touchy and harder to fly. But if you move in slow increments (move the CG about a 1/16" to 1/8" at a time) you will start to slowly notice when it gets tricky to fly and stop there before you enter the dangerous realm! Besides its a Zagi a bad landing or two wont kill it!

After rereading these posts mine says essentially the same thing as gliderguy. Finally someone I agree with!

Happy Experimenting!

Nick Wisdom
Orlando, FL
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Old Feb 13, 2002, 10:42 AM
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Best way

What is the best way to move the C.G. back....clay ball nails what do people add for weight on the plane to move the C.G.?
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Old Feb 13, 2002, 11:00 AM
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Whenever possible you would want to change your CG by moving around equipment already on the airplane. On a zagi this may not be possible, so you would do it by adding weight as far back or forward as possible to reach the desired effect. When experimenting I just tape the weight on top of the airplane till I have the CG where I want it. Then I worry about how to install it permanently. I use the stick on lead weight from great planes available at any hobby store. It comes in 1/4oz increments. You can also easily cut it in half to make 1/8oz sizes too. You can also use lead shot, or anything metal and heavy. Lead being the best.
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