Author Topic: cheap balancing fixture (Read 3865 times)

scott matthews · « **on:** February 07, 2012, 07:00:38 PM »

Found a cheap way to make a balancing fixture. This is made by purchasing two door stops from the hardware store for under $4.00. Place a length of wood on the edge of your building table, then screw into the wood two door stops so that they are standing up and spaced to touch a rib on each end of your wing.Then place your plane on the tips of the door stops so that the CG point is where the the tip of the door stops are placed and add weight to the tip or tail till it balances.If your plane is like mine the wheels will extend bellow the edge of the table and keep it from falling off the tips of the stops, if your plane is nose heavy it will dip forward but the wheels will keep it from falling off the tips of the door stops until you add enough weight to balance it. If this does not work, place your airplane up side down to balance it or you may have to add a block of wood at each end where the door stops are to elevate your ship till it will teeter to balance it.

john e. holliday · « **Reply #1 on:** February 08, 2012, 10:22:33 AM »

Even cheaper is the old lead pencil put into a couple of drilled holes in a board.

Glenn (Gravitywell) Reach · « **Reply #2 on:** February 08, 2012, 01:13:26 PM »

That is a neat idea and its great to see all the great ways others do things. I too use the "two pencil in a hole" trick. I also bought a pack of erasers for the pencils from the dollar store that are pointed on the top. Makes it real nice and easy as well.

Tim Wescott · « **Reply #3 on:** February 08, 2012, 02:45:51 PM »

Uh. Fingertips?

Howard Rush · « **Reply #4 on:** February 08, 2012, 03:03:34 PM »

http://home.mindspring.com/~the-plumber/Vanessa%20CG%20Machine.htm

Here is the same idea used to find the CG of an engine-pipe assembly.

Howard Rush · « **Reply #5 on:** February 08, 2012, 03:07:33 PM »

Quote from: john e. holliday on February 08, 2012, 10:22:33 AM

Even cheaper is the old lead pencil put into a couple of drilled holes in a board.

I had consistently bad experiences with this method until somebody told me to do it eraser-side up.

KenP51 · « **Reply #6 on:** February 08, 2012, 04:54:02 PM »

Quote from: Howard Rush on February 08, 2012, 03:07:33 PM

I had consistently bad experiences with this method until somebody told me to do it eraser-side up.

Dang it Howard
That was funny
I had a mouthful of cereal in my mouth. I darn neared spewed it out my computer screen. Held it and choked instead

Were the pencils sharp?

I use the pencil erasers method to balance also

Bootlegger · « **Reply #7 on:** February 09, 2012, 07:59:08 AM »

I'll say it again, Howard you ain't right...

Rafael Gonzalez · « **Reply #8 on:** February 09, 2012, 08:09:49 AM »

Quote from: Howard Rush on February 08, 2012, 03:07:33 PM

I had consistently bad experiences with this method until somebody told me to do it eraser-side up.

Don't do that again!

I splattered coffee all over my computer...

john e. holliday · « **Reply #9 on:** February 09, 2012, 09:56:02 AM »

Bet, that Howard gave his college profs a fit. He was missed when he left the Kansas/Missouri area.

Mike Haverly · « **Reply #10 on:** February 09, 2012, 11:50:07 AM »

I don't think Howard is trying to be funny, that is exactly how I balance my models. Two front support strings on the mains and the rear on the tail wheel. Level the airplane by adjusting the strings and the plum bob will point to the exact cg. Any crane rigger that picks big loads on three points will tell you the same thing. Of course the grimy old engine is a little humorous. Be kinda hard to check an electric motor that way.

Edit: I took some pictures. I don't ever take a new airplane to the field without doing this. I can set the CG to the recommended spot with no guess work. Cheap too. A plumb bob and some string.

Dick Pacini · « **Reply #11 on:** February 09, 2012, 01:07:15 PM »

Quote from: Mike Haverly on February 09, 2012, 11:50:07 AM

I don't think Howard is trying to be funny, that is exactly how I balance my models. Two front support strings on the mains and the rear on the tail wheel. Level the airplane by adjusting the strings and the plum bob will point to the exact cg. Any crane rigger that picks big loads on three points will tell you the same thing. Of course the grimy old engine is a little humorous. Be kinda hard to check an electric motor that way.

Edit: I took some pictures. I don't ever take a new airplane to the field without doing this. I can set the CG to the recommended spot with no guess work. Cheap too. A plumb bob and some string.

Mike, I must be missing something here. Where is the plumb suspended from in relation to the other strings? To me, your method would show where the CG is, but suppose it wasn't where it should be? Is adding nose or tail weight going to make a difference in the way it hangs?

Mike Haverly · « **Reply #12 on:** February 09, 2012, 01:20:26 PM »

The string is suspended from the ceiling. My shop is very small, I can't get picture of the whole thing. If the CG is not right you add tail weight or nose weight and readjust until the airplane is level. If it take three ounces then that is what it takes. No guess work. Saves a lot of work and sometimes some embarrassment at the field. This is just part of bench trimming.
You can adjust your tip weight also. Note the plump bob on mine points near the outside of the fuselage. Just add or remove tip weight and level the wings until you are sure the CG is outside of the middle of the fuselage. I have measure friends model with this system and they were surprised. This is not my idea by the way. I'm sure I saw it in Stunt News a few years ago. Any machinist knows that the easiest way to set up and irregular object is on three points, the milk stool system.

Dick Pacini · « **Reply #13 on:** February 09, 2012, 01:31:46 PM »

Quote from: Mike Haverly on February 09, 2012, 01:20:26 PM

The string is suspended from the ceiling. My shop is very small, I can't get picture of the whole thing. If the CG is not right you add tail weight or nose weight and readjust until the airplane is level. If it take three ounces then that is what it takes. No guess work. Saves a lot of work and sometimes some embarrassment at the field. This is just part of bench trimming.
You can adjust your tip weight also. Note the plump bob on mine points near the outside of the fuselage. Just add or remove tip weight and level the wings until you are sure the CG is outside of the middle of the fuselage. I have measure friends model with this system and they were surprised. This is not my idea by the way. I'm sure I saw it in Stunt News a few years ago. Any machinist knows that the easiest way to set up and irregular object is on three points, the milk stool system.

Sorry, I still am not clear. What point on the ceiling? At the same point as the strings on the gear? If the plane is level hanging by the strings, how is adding tail weight going to change anything?

Mark Scarborough · « **Reply #14 on:** February 09, 2012, 01:52:41 PM »

Dick,
follow the link, it explains it
http://home.mindspring.com/~the-plumber/Vanessa%20CG%20Machine.htm

Mike Haverly · « **Reply #15 on:** February 09, 2012, 02:12:43 PM »

OK, I took some pictures. Notice what happened to the plumb bob when I moved the ten ounce battery around. Obviously, when it was on the tip it move way out off the fuselage. When I placed it on the tail the model was no longer level. When I leveled the model look where the plumb bob went, an ovious tail heavy condition. The first picture just shows how it is hooked to the ceiling. Got it yet? If not we'll try it again.

Dick Pacini · « **Reply #16 on:** February 09, 2012, 04:04:59 PM »

OK, mystery solved! All the strings are hung from the same point. Yes, it is obvious and a good way to balance without risking the plane falling off the rig.

I have a (Great Planes, I think) balancer that has scales to measure how far from the leading edge the support points are. It is a bit tricky to use and very easy to knock the plane off. Your setup looks very safe.

Brett Buck · « **Reply #17 on:** February 09, 2012, 04:54:03 PM »

Quote from: Mike Haverly on February 09, 2012, 02:12:43 PM

OK, I took some pictures. Notice what happened to the plumb bob when I moved the ten ounce battery around.

Plumb bob or Sword of Damocles?

Brett

Mike Haverly · « **Reply #18 on:** February 09, 2012, 05:29:54 PM »

"Plumb bob or Sword of Damocles?

Brett"

Yeah, it's a bad boy. I keep a piece of foam on it until after everything is secure. Also, that's why I use curtain chord, not just kite string.

Joseph Patterson · « **Reply #19 on:** February 13, 2012, 06:15:32 AM »

I believe Noel Drindak had an article in Stunt News several years ago using a similar system.
Doug

Gerald Arana · « **Reply #20 on:** February 14, 2012, 04:00:01 PM »

You could always put the eraser on the plumb bob tip instead of the steel tip.

That way it would only poke...............well maybe a bigger hole

Steve Helmick · « **Reply #21 on:** February 14, 2012, 09:01:22 PM »

If you want cheap, I'll give you cheap. But bear in mind that I'm not that fussy about the initial CG location, because I am pretty sure that I'm going to move it around some anyway. A finishing nail into a rafter will do.

What I would do is make sure the front LO can go forward to the recommended CG location from the plans. Then, I'd hang the plane from the front leadout at the recommended CG location, adjust the nose/tail weight until the hingeline is vertical, and call it good. The next step, of course, is to move the midpoint of the LO's back to the proper location, go fly, and start adjusting from there.

Steve