Control Lines For all you fly-by-wire fanatics!

c/g of a control plane

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Old 01-10-2014, 11:09 AM
  #1
jayseas
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Default c/g of a control plane

On a standard stunt model control line plane where should you start at to find the correct c/g?
I have tried to do a search here but have found nothing.

Should c/g be between the leadout wires?

Red And blue bird is a 15 size, 30" wing.
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Old 01-10-2014, 12:26 PM
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mikeainia
 
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(Neat little plane, by the way).

Actually, the leadout wire location is best determined by the CG, not the other way around. A good generalization - starting point - is 15-20 % of the average chord. You would want the leadouts to exit the wing somewhat behind this point (exactly where depends on the line length, diameter and the plane weight and speed). Here is a graphical representation:
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Old 01-10-2014, 12:54 PM
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Quote:
Originally Posted by mikeainia View Post
(Neat little plane, by the way).

Actually, the leadout wire location is best determined by the CG, not the other way around. A good generalization - starting point - is 15-20 % of the average chord. You would want the leadouts to exit the wing somewhat behind this point (exactly where depends on the line length, diameter and the plane weight and speed). Here is a graphical representation:
So with the info you have given i'm coming up with about 1.5" aft of the leading edge.
Wing is 30" long 6" at the tip, 9" at root.I will try this.
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Old 01-10-2014, 01:06 PM
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Note that the 1.5 inches is 1.5 inches HALFWAY OUT ON THE WING ( 7.5 " from the fuselage on your model). If there is any sweep in the leading edge, it will be less than that at the tips and more than that at the fuselage (or wing centerline). If you were to balance at 1.5 inches AT THE TIPS, you may be somewhat tail-heavy if there is sweep in the leading edge.

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Old 01-10-2014, 01:19 PM
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Quote:
Originally Posted by mikeainia View Post
Note that the 1.5 inches is 1.5 inches HALFWAY OUT ON THE WING ( 7.5 " from the fuselage on your model). If there is any sweep in the leading edge, it will be less than that at the tips and more than that at the fuselage (or wing centerline). If you were to balance at 1.5 inches AT THE TIPS, you may be somewhat tail-heavy if there is sweep in the leading edge.
No sweep in the l/e, it is straight.
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Old 01-10-2014, 01:50 PM
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Then, yes - 1.5" would be 20% Mean Chord. Like I said, for the average, stunt-type this will be pretty safe. You will probably never want to go aft of that point. For other types of flying, there may be other optimum spots. Most combat planes that I've measured were more nose-heavy than that - I know, that seems backwards, but it's often true. My carrier planes are balanced as tail-heavy as I dare fly them so maybe 22-25%. I usually add tail weight until they are just a little too squirrely to fly level on high speed and then take the last bit out again. RC planes will generally balance even more tail-heavy.
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Old 01-10-2014, 02:51 PM
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Quote:
Originally Posted by mikeainia View Post
Then, yes - 1.5" would be 20% Mean Chord. Like I said, for the average, stunt-type this will be pretty safe. You will probably never want to go aft of that point. For other types of flying, there may be other optimum spots. Most combat planes that I've measured were more nose-heavy than that - I know, that seems backwards, but it's often true. My carrier planes are balanced as tail-heavy as I dare fly them so maybe 22-25%. I usually add tail weight until they are just a little too squirrely to fly level on high speed and then take the last bit out again. RC planes will generally balance even more tail-heavy.
Thanks Mike for your help.
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Old 01-11-2014, 03:41 PM
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Generally speaking, it's best to start with the plane a little nose heavy, as a failsafe setting.

It's easier to fly a boring tankful with a nose heavy plane than an exciting half a tankful on a tail heavy plane.

Greg
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Old 01-11-2014, 04:03 PM
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"Nose-heavy airplanes fly poorly. Tail-heavy airplanes fly once."
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Old 01-11-2014, 05:03 PM
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Greg and Mike, well both are nose heavy, and look to need about 1.5 - 2 oz's of weight to the tail, now i have to figure what to use.Here's my other nose heavy ship.It's a plane i built over a year ago, had life problems come up,Did some changes to it, shortened the fuselage by 2" and the wing by 4".The smaller red and blue has a foam wing.powered by a magnum 15, the larger has a magnum 36.
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Old 01-11-2014, 07:26 PM
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I recommend you start out with the CG 1/2 to 3/4 in back of the leading edge. If the airplane does not fly to suit, move the CG back about 1/8 in at a time until if flies to suit you.
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Old 01-12-2014, 03:20 AM
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Quote:
Originally Posted by Jim Thomerson View Post
I recommend you start out with the CG 1/2 to 3/4 in back of the leading edge. If the airplane does not fly to suit, move the CG back about 1/8 in at a time until if flies to suit you.
That's how I'd do it as well.
Also roofing washers (the lead ones) come with a convenient hole in the middle, so you can bolt them to the rear fuselage. If you can't get them, just sheet lead drilled so you can bolt it on.

Greg
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Old 01-12-2014, 07:20 AM
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I looked for thin sheet lead here in Austin, and was told none available. A friend told me about lead pipe boots. The are availale at anyplace which sells roofing materials. Lead is 1/16 inch, or a little less, thick.
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Old 01-12-2014, 08:08 AM
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Thanks for the tips on the lead washers, what are lead pipe boots?
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Old 01-12-2014, 10:15 AM
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They are a flat plate with a hollow cylinder sticking up. Go around pipes sticking out the roof, I suppose. They can show them to you anywhere that sells roofing supplies.
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Old 01-12-2014, 03:07 PM
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They sound kind of big.
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Old 01-14-2014, 01:14 AM
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The other handy device is the self adhesive wheel weights. The type used for alloy wheels. I believe they are available in small weight increments (5gms in OZ) Also in bigger sizes.

Or take a walk along any major road and collect discarded wheel weights, and melt them to any convenient shape and attach it however you will.

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Old 01-14-2014, 08:35 AM
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I picked up some pine wood derby weights.
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Old 01-14-2014, 02:09 PM
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Quote:
Originally Posted by jayseas View Post
I picked up some pine wood derby weights.
Jayseas,

Are they Pine wood? sounds light/large to me. Can't you find anything heavier? Steel? Brass? a pound of feathers?

Greg
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Old 01-14-2014, 02:53 PM
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No they are lead weights for "Pine Wood Derby" cars - a Boy Scout program of building and racing
small wooden cars down a ramp.
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Old 01-14-2014, 03:22 PM
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Quote:
Originally Posted by greggles47 View Post
Jayseas,

Are they Pine wood? sounds light/large to me. Can't you find anything heavier? Steel? Brass? a pound of feathers?

Greg
As Mike said, they are lead, flat with sticky tape, come in 2 oz packages,you can separate them and use what you need.
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Old 01-14-2014, 04:48 PM
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They sound just like what you need. And exactly like wheel weights.

Good find.

G
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Old 03-11-2014, 09:23 PM
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On weights,,,, Just thought of this while reading all the ideas,,,,,,,,,,,,,,,,,,,,,motorcycle spoke weights that is if you have 'wire' landing gear, just a thougt
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Old 03-19-2014, 08:01 PM
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Fishing weights can be found in many sizes and styles. You have a hammer you can make them as you like.

Most any family type department store has a fishing/sporting department.

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