2slow2matter

My Feedback: (1)

I've built many planes both kit and arf. I've always used the fingertip on the wing method of finding CG. However, I remember someone having a rig where they hang the plane and use a plumb-bob to find the exact CG of an airplane. I'm interested in knowing how to set this up for the kit I'm currently finishing up. It has CG located on the fuse (by plans) and wingtips. Sure, I could superimpose that to the root of the wing, but I think I might rather just use the plumb bob method and mark the cg on the fuse as shown in the plans.
I did a search but couldn't find anything. Could someone who has used this approach help me out?
Thanks

bingo field

Look for " Vanessa CG Rig" . Think that's what you're looking for.


http://www.rcuniverse.com/forum/m_70..._1/key_/tm.htm

Found it!

2slow2matter

My Feedback: (1)

Bingo!! (PUN)
That's it, thanks!

jollycub

My Feedback: (5)

Would it work if you were to drill a hole down the center of the plumb bob and mount a cheap laser pointing device. This would point to the center on the wing. I didn't try it, but it should work.

2slow2matter

My Feedback: (1)

Absolutely. I think that would work great. In fact, then the "plum-bob" could be a cylindrical piece of wood drilled out in the center to accept a laser pointer. I'm seeing a hole saw (like for doorknobs) in the 1.5 or 1 inch range for this task.
Maybe I'll do that!

jollycub

My Feedback: (5)

How about a plum bob on a pull chain from a lamp...such as Home Depot or Menards. It would have the center hole already, just begging to be drilled out.

2slow2matter

My Feedback: (1)

Yea, you can buy those pull chains separately for cheap. One of the bigger ones might work good.
What about just hanging the laser pointer as the plumbbob?

jollycub

My Feedback: (5)

Why not?[sm=thumbs_up.gif]

jollycub

My Feedback: (5)

I have a couple of questions about thew Venessa CG machine. First off, how do I know the when the plane is level or in zero incedence. Do I just put the level on top of the fuse and when the bubble is level, then the plane is level? Also, the plumb bob will show where the current CG is. Do I go by the manufactures instructions and put weight fore or aft until the plumb bob is at the CG point that the instructions
indicate? Ans should I put the plane in the Venessa upside down if it is a low wing airplane? Thanks for your guidance.

CJ

Jetdesign

My Feedback: (8)

I read in another plane's manual that to laterally balance the plane, you can balance it on the vertical fin and hold the front by the prop, then see which way the plane wants to tip.

Is this recommended? I don't know another way to laterally balance plane.

Thanks.

RCKen

My Feedback: (9)

No, this isn't recommended. This puts a lot of weight on the vertical stabilizer, and it's not designed to support that weight. You could easily break the vertical stab doing it his way.

What I recommend is to use string of fishing line to laterally balance a plane. Put a loop at one end and loop around the shaft of the engine. On the other end loop it around the tail. Now simply pick up the plane by the string. This will easily give you the lateral balance without damaging the plane. See the pictures below.

Here is a link to the section where I did the lateral balance on my LT-40 build thread.
[link]http://www.rcuniverse.com/forum/fb.asp?m=4397991[/link]

Ken

Jetdesign

My Feedback: (8)

Thanks Ken, that's what I was thinking.

2slow2matter

My Feedback: (1)

With the Venessa machine, and on my plane, I will level the horizontal stab with a level. But that is because my plane is set up for 0-0 incidence, meaning when the horizontal stab is level, so is the wing. However, the wing is curved, so it is much harder to find level for it.
Then, the laser or plumbbob will point at the current cg. One would add weight fore or aft to move the cg into the recommended range.
I will balance my low wing killer bee upright using this machine.