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How sensitive?

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Old 10-17-2006, 03:08 PM
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cjposada
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Default How sensitive?

How sensitive is the elevator to changes in CG? Will just a 1/2 inch in AF CG change 4 clicks in up elevator? Thanks
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Old 10-17-2006, 03:18 PM
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RCKen
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Default RE: How sensitive?

Depending on the plane, yes it's absolutely possible for a change like that.

Ken
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Old 10-17-2006, 03:21 PM
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carrellh
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Default RE: How sensitive?

It would not surprise me if a half inch made a big difference.

If the plane is a beginner type plane, the recommended CG range from one extreme to the other may only be a half inch. My PT-60 had a recommended point, and said it could be adjusted 1/4" forward or back. More advanced models, and larger models, may have a wider acceptable range.
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Old 10-17-2006, 03:26 PM
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Default RE: How sensitive?

1/2" shift is actually quite alot on many airplanes.
My latest addition, Seagull Spacewalker II, has a window of 7.5cm to 8cm. that is way less than 1/2"
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Old 10-17-2006, 04:18 PM
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Default RE: How sensitive?

The model is a Phoenix models SeaBee, looks a lot like a .40 sized pattern plane. How would this affect inverted flight?
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Old 10-17-2006, 05:38 PM
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Default RE: How sensitive?

cjposada,

When you do a CG adjustment rearward, you want to do it in very small increments. I work at 1/16" at a time until I find the sweet spot, then back a bit more until I don't like it. Then I'll shift forward until I hit that sweet spot again and I know its dialed in. You'll know real quick if you go too far back. A 1/4" jump could end up getting you into real trouble as some planes are very sensitive to CG changes.

As far as elevator sensitivity, it depends on your individual plane. I've flown two different planes of the same make and model, and they both handled differently. The only way to know is to follow what I said above and slowly move the CG back until you don't like it, then forward a bit.

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Old 10-17-2006, 06:20 PM
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Default RE: How sensitive?

I'll try that and please let me ask something: what are the simpthoms of nose heavy and tail heavy? how to diagnose? Thanks again!
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Old 10-17-2006, 06:36 PM
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Default RE: How sensitive?

Hi,

Symptoms of nose heavy models. They fly. They don't knife edge well. They drop the nose in rolls and they land hot.

Symptoms of too tail heavy. The model flys, but not for long.

Symptoms of slight tail bias model it comes alive but will snap easily.


Cheers,

Colin
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Old 10-17-2006, 06:43 PM
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Default RE: How sensitive?

Cip,
The easiest way to change your CG is take a stick of lead, cut it into the little 1/4oz pieces and stick one on the back and fly, stick another on and fly, so on and so forth. Eventually you will find what you need. Just remember to keep the fuel the same and above all, don't get the plane on the CG edge with a full tank cause about 3/4 of the way through your flight your not gonna be happy... Good Luck!
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Old 10-17-2006, 08:48 PM
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Default RE: How sensitive?

G'day Mate,
Symptoms of Nose heavy = In no special order, nose drops a lot when throttle reduced for landing, & elevators are rather sluggish, when plane rolled inverted large amounts of down elevator are required to maintain level flight, nose drops a lot in fairly gentle turns, right or left. There are more but that will do to be going on with.
Symptoms of tail heavy = In no special order, elevators are super sensitive, plane is hard to land because of elevator sensitivity, & tends to come in to land with tail low, when rolled inverted, plane climbs with no elevator input, & so on, you get the idea. Not the ideal setup, but as was stated earlier, when the sweet spot is found, most planes are improved dramatically.
So don't be afraid to move your balance point, to find the sweet spot, just do it small amounts at a time.
The CG location shown on most plans & ARF instruction sheets, are only a starting point, for the first few flights, it is up to you to adjust or trim the plane , until you are happy with the way it flys.
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Old 10-17-2006, 09:42 PM
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Default RE: How sensitive?

Thanks for all the input, most certain that it will be very helpfull to everybody. As allways you guys are the best!
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