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Vanessa c.g. Rig: How to.

Old 10-12-2009, 11:23 AM
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Default RE: Vanessa c.g. Rig: How to.

You want to adjust the friction so that you can roll the dowel with your fingers but it will stay where you put it. When you have the plane level, the plumb bob will point to the current CG. If it is not where it should be, add, remove or reposition weight and level it with the dowel again.

I don't quite understand the controversy about this thing. It is just a simple way to hang an airplane up and check the CG. It does nothing magical. But the originator never said that it did.
Old 10-12-2009, 12:47 PM
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Default RE: Vanessa c.g. Rig: How to.

Kitbuilder,
The dowl is not supposed to rotate, it will stay fixed, and the strings which hang off of the dowl will support the model so that gravity will center the weight of the model underneath it naturally. The pointer, or plumb bob (or any other pointer weight you chose) is slung underneath the dowl, naturally gravity will point it straight down through the center of gravity of that model hanging off the device. The dowel should not have to rotate, only thing i would add is just make sure the dowel is perfectly round and fairly strong so that it doesnt bow much when the model is hanging off of it, and when the model is hanging in the rig, orient the plane so its completely level with the floor before you beging checking the c.g. The location of where the strings will sling under the model is not that important just so long that the rear of the model is supported and the front is supported or another way is around the wings where the rear and foreward part of the wings are supported. so that the model can hang level with the ground.

The device doesnt adjust the c.g. it just shows you where the center of gravity is on the model at that particular time. You take it to the next step by moving weight around inside of the model (e.g. batteries, receiver) or adding lead to the nose or tail area and then checking it again. The idea is to get the pointer at the location the kit designer/manufacturer calls for, such as ("5 and 3/4 inch aft of the leading edge" as an example). Once again, hang the model in the vanessa rig, and check where the pointer or plumb bob indicates. You do these 3 steps repeatedly, until the pointer finally lines up with where the C.G is supposed to be. 1.) Hang the plane in it, 2.) read where the pointer is, 3.) move weight around in the model accordingly.

If for example, the instructions/designs of my model suggests that i need the c.g. to be 4 inches aft of the leading edge, i usually stick a piece of masking tape on top of my wing and then use a pen making a small mark on the piece of tape exactly where 4 inches aft is. Then i hang the model in the rig and see where the pointer shows. if its pointing behind the mark then im tailheavy, if its in front, then im nose heavy.,

The Vanessa in itself wont balance a plane, think of it as an instrument which reads out exactly where the center of gravity is at the time, regardless if that spot is where the c.g. must be or not, nothing else.
Hope i helped!

Louie
Old 10-12-2009, 02:56 PM
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Default RE: Vanessa c.g. Rig: How to.

I saw, I built, I used. It's a beautiful thing !

I slotted the wood that has the dowel going thru it and added a thumb screw to adjust the tension on the dowel.
Old 10-12-2009, 05:16 PM
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Default RE: Vanessa c.g. Rig: How to.

here is my camel set up in the vanessa, i have been using this for about 4 years now. love it.
the dowel will rotate in the block, i have a set screw to give it just enough tightness that it wont rotate on its own.
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Old 10-12-2009, 08:02 PM
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Default RE: Vanessa c.g. Rig: How to.

This has to be the greatest model COG device out there. Here is how I made mine. If you have questions, just ask.

Bob
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Old 10-15-2009, 11:28 AM
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Default RE: Vanessa c.g. Rig: How to.

ORIGINAL: Tisoy909

Kitbuilder,
The dowl is not supposed to rotate, it will stay fixed, and the strings which hang off of the dowl will support the model so that gravity will center the weight of the model underneath it naturally. The pointer, or plumb bob (or any other pointer weight you chose) is slung underneath the dowl, naturally gravity will point it straight down through the center of gravity of that model hanging off the device. The dowel should not have to rotate.........


The Vanessa in itself wont balance a plane, think of it as an instrument which reads out exactly where the center of gravity is at the time, regardless if that spot is where the c.g. must be or not, nothing else.
Hope i helped!

Louie
Right... I've always understood it being a tool to identify the CG at that point in time requiring you to make adjustments for that particular aircraft. I just don't see how it works yet. I guess the whole plane will come to rest in the sling the CG being fore, aft or directly under the plumb bob based on its current CG? Seems like it wouildn't be as sensitive to small changes but it obviously works so I'll need to make one and then the lightbulb will go off. Thanks for putting up with me!
Old 10-15-2009, 12:10 PM
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Default RE: Vanessa c.g. Rig: How to.


ORIGINAL: KitBuilder

I just don't see how it works yet. I guess the whole plane will come to rest in the sling the CG being fore, aft or directly under the plumb bob based on its current CG?
KitBuilder,

The principle behind the Vanessa is simple: two superposed plumbs.

One is the plumb bob, the other is the airplane.

The CG of each will take the lowest possible position for a pendulum.

Hence, IF THE PLUMB BOB AND THE AIRPLANE HANG FROM THE SAME POINT (the dowel), both CGs will be in different positions, but ALWAYS on the same perfectly vertical line.
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Old 10-15-2009, 06:00 PM
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Default RE: Vanessa c.g. Rig: How to.

Question,

Does it make a difference if you check the cg on a low wing plane in the upright or inverted position with this device?

Old 10-16-2009, 07:13 AM
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Default RE: Vanessa c.g. Rig: How to.


ORIGINAL: Tisoy909

Kitbuilder,
The dowl is not supposed to rotate, it will stay fixed, and the strings which hang off of the dowl will support the model so that gravity will center the weight of the model underneath it naturally. The pointer, or plumb bob (or any other pointer weight you chose) is slung underneath the dowl, naturally gravity will point it straight down through the center of gravity of that model hanging off the device. The dowel should not have to rotate, only thing i would add is just make sure the dowel is perfectly round and fairly strong so that it doesnt bow much when the model is hanging off of it, and when the model is hanging in the rig, orient the plane so its completely level with the floor before you beging checking the c.g. The location of where the strings will sling under the model is not that important just so long that the rear of the model is supported and the front is supported or another way is around the wings where the rear and foreward part of the wings are supported. so that the model can hang level with the ground.

The device doesnt adjust the c.g. it just shows you where the center of gravity is on the model at that particular time. You take it to the next step by moving weight around inside of the model (e.g. batteries, receiver) or adding lead to the nose or tail area and then checking it again. The idea is to get the pointer at the location the kit designer/manufacturer calls for, such as (''5 and 3/4 inch aft of the leading edge'' as an example). Once again, hang the model in the vanessa rig, and check where the pointer or plumb bob indicates. You do these 3 steps repeatedly, until the pointer finally lines up with where the C.G is supposed to be. 1.) Hang the plane in it, 2.) read where the pointer is, 3.) move weight around in the model accordingly.

If for example, the instructions/designs of my model suggests that i need the c.g. to be 4 inches aft of the leading edge, i usually stick a piece of masking tape on top of my wing and then use a pen making a small mark on the piece of tape exactly where 4 inches aft is. Then i hang the model in the rig and see where the pointer shows. if its pointing behind the mark then im tailheavy, if its in front, then im nose heavy.,

The Vanessa in itself wont balance a plane, think of it as an instrument which reads out exactly where the center of gravity is at the time, regardless if that spot is where the c.g. must be or not, nothing else.
Hope i helped!

Louie
Hi Louie (Tisoy909),

I'm sorry to tell you, but you are wrong when you say the dowel is not supposed to rotate.

The way the vanessa rig works, is as follows:

Mark an "X" on a piece of masking tape, then put the tape on the airplane exactly where the CG is supposed to be.

You then hang the airplane from the dowel. The dowel should be fairly snug in the piece of 2X2.

You then place a level on the airplane and rotate the dowel until the bubble is in the middle of the level.

The plumb bob points to where the CG actually is.

If the plumb bob is ahead of your CG mark either add some weight to the tail or move your battery to the rear of the fuse.

If it is behind the CG mark add some weight to the nose or move your battery forward.

Then rotate the dowel until the level is centered again and the plumb bob should have moved closer to your CG mark.

Continue adding or redistributing weight and rotating the dowel until the plumb bob points directly to the "X" and you're done.

Hopefully that clears it up for you, Kitbuilder.

Regards,

Dennis
Old 10-16-2009, 08:58 AM
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Default RE: Vanessa c.g. Rig: How to.

ORIGINAL: Tx_RcFlyer

Question,

Does it make a difference if you check the cg on a low wing plane in the upright or inverted position with this device?


No it does not. I have a low wing plane that checks out perfectly right side up in the vanessa but if you check it on your fingers you have to flip it. On a low wing plane, the CG is above the wing. So if it tips slighty, it will want to flip over. With the vanessa, the plane is suspended, so there is no tendancy to flip over, so it can be leveled and checked right side up. Because it is not critical how you attach the sling, it also works for bipes and delta wing planes.
Old 10-17-2009, 09:52 AM
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Default RE: Vanessa c.g. Rig: How to.

Youre going to it lock down before you take measurements wont you? So in that sense you dont want the dowl to move. Rotatable for convenience yes, so you may level the plane before using the c.g. reading.
Louie
Old 10-17-2009, 11:32 AM
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Default RE: Vanessa c.g. Rig: How to.


ORIGINAL: Tisoy909

Youre going to it lock down before you take measurements wont you? So in that sense you dont want the dowl to move. Rotatable for convenience yes, so you may level the plane before using the c.g. reading.
Louie
You want the dowel to be snug enough that it does not move on its own, otherwise you would never be able to get the airplane to stay level enough to get a reading from the plumb bob. You are not "locking it down", just making it snug.

Regards,

Dennis
Old 10-24-2009, 09:07 AM
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Default RE: Vanessa c.g. Rig: How to.

I built mine a few months ago and love it! One question, can you use it to balance a Zagi XS 48" flying wing? That is the one plane I own that should fly like it's on rails, but it doesn't.
Old 10-24-2009, 09:19 AM
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Default RE: Vanessa c.g. Rig: How to.

Yes, Vanessa can find the CG of any model that can be hung.

If you don't know it, you can also verify the proper location at:

http://www.geistware.com/rcmodeling/cg_calc.htm#cg
Old 10-24-2009, 11:34 PM
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Default RE: Vanessa c.g. Rig: How to.

That's my issue.. if the dowel does not rotate.. how does the plane achieve the two different attitudes in the pic?
Old 10-25-2009, 01:07 AM
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Default RE: Vanessa c.g. Rig: How to.

the dowel DOES rotate. use the dowel to adjust the attitude of the plane using the level. you want a slight amount of drag on the dowel so it wont rotate on its own just when YOU turn it.
Old 10-25-2009, 09:59 AM
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Default RE: Vanessa c.g. Rig: How to.

Kitbuilder,

The dowel should be able to rotate and pull the cords up in order to place the plane in a horizontal attitude.

The reason for the wrapping of the chords that is shown in Posts #12 and #13 of page 1 is to guaranty that the cord is attached to the dowel by friction.

When the center line of the plane is not perfectly horizontal, which is required to locate the projection of the CG over the wing precisely, a fine rotation of the dowel will bring it to the horizontal attitude.

The pics of Post #82 just show that the tri-dimensional location of the CG is not related to the attitude of the plane.
The real CG is a spatial point, and it will be located over the vertical line that extends from the plumb bob down, regardless of the position of the model.
The model always rotates around its CG, either hanging from the Vanessa rig or flying.

The designer of a model specifies the CG as to be located in a range measured along the wing root and at certain distance from the leading edge, which is the reference line.
For those reasons, the model should be in a level flying attitude while hanging from the rig when locating the projection of the CG over the wing (which is the extension of the vertical line that passes thru the actual CG).
Old 10-25-2009, 06:07 PM
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Default RE: Vanessa c.g. Rig: How to.


ORIGINAL: KitBuilder

That's my issue.. if the dowel does not rotate.. how does the plane achieve the two different attitudes in the pic?

Mike:

Just build one. Once you see it in operation, you'll wonder why you had any questions.

(Think slapping your forehead, saying "Doh, I get it now!!)

Regards,

Dennis
Old 10-25-2009, 08:52 PM
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Default RE: Vanessa c.g. Rig: How to.

Will do.. thanks..
Old 10-25-2009, 09:00 PM
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Default RE: Vanessa c.g. Rig: How to.

post in error
Old 10-26-2009, 09:42 AM
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Default RE: Vanessa c.g. Rig: How to.


ORIGINAL: KitBuilder

That's my issue.. if the dowel does not rotate.. how does the plane achieve the two different attitudes in the pic?
I think you've been a little mis-led by the picture... the plane should always be level (well, at correct flight attitude, ie: stab at zero degrees) when balancing. You mark the desired CG point on the wing and hang the plane as described, rotate the dowel (which is tight enough not to rotate on its own, but still can be rotated by hand) to level the stab (using a line level to check it), then compare the plumb bob's position against the desired CG point. If it's out, out add weight to the nose or tail as required then rotate the dowel to re-level the plane again (checking stab again with line level) before re-checking the plumb bob against the CG point.

I admit I had problems understanding how it worked till I built one... perhaps this is simpler. Forget for a moment that it's a plane you're balancing and imagine a stick with a sliding weight on it and a long string tied to either end, as in the diagrams below. If you place the weight near one end and suspend it by the string so the stick is level, one end of the stick must protrude further past the hanging point than the other. If you then slide the weight to the other end and reset where it hangs from so it's level again the balance point will have moved along with the weight. In this example the stick is our plane and the sliding weight is altering our CURRENT centre of gravity, the stick's CG will always be directly below the hanging point once the stick is level (which is why the plumb bob hangs loosely from the rig's dowel). We add weight to one end or the other of the plane to alter the current cg and re-level the plane so the bob is showing us where our cg has moved to. It works exactly the same way as a lever (with a balance sitting on a pivot point) except the balance is suspended below the pivot instead of sitting on top of it, and just like a lever as the balance shifts so does the pivot point. The vanessa rig won't tell you where the CG should be, it'll only tell you where the CG currently is... finding out where it should be and getting it there is up to you.
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Old 11-27-2009, 09:20 AM
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Default RE: Vanessa c.g. Rig: How to.

It looks like I am going to make this device and use it. Thanks RC Fans for posting the neat photos and explaining how to use such a simple device. Best Regards Capt,n
Old 02-23-2010, 10:44 AM
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Default RE: Vanessa c.g. Rig: How to.

For planes with removeable wings (most jets)Iuse just two cords suspended from my garage cieling through some turnbuckles, the ends protrude through a 1/8" wing gap
created by not fully pushing the wings fully against the fuselage! These are looped through a dowel that is positioned exactly at the desired CG. Then by pulling on the cords, Ican adjust the CG by adding weight or shifting batteries
inside the plane. This is a very quick and easy method and also very reliable
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Old 05-11-2010, 08:30 PM
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Default RE: Vanessa c.g. Rig: How to.

Hi, The pictures of C and D shows the lines different from each other, one side crossed. We would like a little help.


We think this is a great C. G. Rig.


Wayne

303 841 2038
Old 05-12-2010, 11:59 AM
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Default RE: Vanessa c.g. Rig: How to.

The cords should NOT be crossed. Just make a few wraps around the dowel with each one. If they are both crossed, it will still work. You will just have to twist the dowel opposite of the way you want the plane to go (that would just make me think too much). If one is crossed, like the drawing shows, the plane will not move properly when you twist the dowel.


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