RE: Vanessa c.g. Rig: How to.
 

I'm in the process of converting a HobbyZone SC to a low-wing trainer. I have a question about locating the CG. I've used my version of the Vanessa rig and am not sure if I'm making a correct application. Take a look at the build thread and help me with the cg, if you will.

[link=http://rnew.lonestarfieros.org/SuperCub/]The build is located here.[/link]

I've only been able to move it about 1/2in. by placing a 7cell battery. I first placed the battery at the rear edge of the original wing location and leveled. The cg moved about 1/2in. to the rear.

I then moved the battery to the front of the original wing, just centered f>r over the lead edge and leveled. The cg then moved to about 1/2in. in front of the first location.

Is this plane properly balanced, or did I miss something.

Unless I misunderstood something, 3in. would be about 43%.

RE: Vanessa c.g. Rig: How to.
 

I just read this and im going to make me one this weekend.Im putting together a 31% staudacher wich this would be perfect since im in the refurbishing stage.(picked it up built for $150.00 built but needed some improvments.)Im going to get some use out of this thread for sure,thanks for sharing!

RE: Vanessa c.g. Rig: How to.
 

Grubbyjeans, I'd have to say the photo showing the plumb bob pointing at 3" back from the wing leading edge is considerably too far back. You need to either get some weight out of the tail or add it to the nose. Lead ballast on the firewall if you must, but first try moving your battery as far forward as you can get it. Since you have a straight (not tapered) wing, you can just take somewhere between 25-30% of the chord back from the leading edge and use that to set up. If you can get 30% just by moving the battery or other components forward, I'd settle for that for test flying. If you're more forward than 25% back from leading edge, that will be pretty noseheavy, and will take a lot of elevator to keep it from diving. There are plenty of CG calculator web pages, just google for them. I'd give you a few good links, but I'm on a new computer, don't have the bookmarks handy.

As far as proper use of the Vanessa method, what your photo shows is just fine. Your rig works, now you just have to shift weight in the model to get the pointer in the 25-30% range back from wing leading edge.

RE: Vanessa c.g. Rig: How to.
 

I've used my Vanessa to balance my planes, but it's caused some damage to the thin trailing edge of the wing. I see in one of the photos in this thread that one user put one sling loop over the fuse in front of the landing gear and one behind the wing, maybe fastened there with tape? I'm curious if where the attachment points are on the plane affect the machine.
My Vanessa was made from thread reposted here. The dowel sits spanwise above the model. So if I did put my slings on the fuse, how are they rigged to the machine?
THanks
sam
AH, never mind. I looked at the first page and figured it out -- The fuselage sling is one continous loop!

RE: Vanessa c.g. Rig: How to.
 

If your model is too big and heavy for ypur fingertips, suggest using a ruler and a weighing scale, then calculate using the 2 equations and 2 variables method, thus:

Lets assume that that Connie weighs 25 pounds and the distance between the main landing gears and nose wheel is 24 inches. Also assume that the weight on the nose wheel is 5 pounds, and the weight on the two main wheels is 20 pounds. Then:

let x = distance from nose wheel to CG
let y = distance from main wheels to CG

equation 1 is x + y = 24 inches
equation 2 is 5x = 20y so we will write this another way x = 20y/5 and x = 4y

substuting eq. 2 into eq.1 we have 4y + y = 24 inches or 5y = 24inches
so y = 24/5 inches which is 4.8 inches forward of the main wheels to the CG
and from eq 1 x = 24 - 4.8 or 19.2 inches aft of the nose wheel to the CG

feihu

RE: Vanessa c.g. Rig: How to.
 

OK, let me see Vannessa rig $5 parts and stores in a small space or, 3 "accurate" scale sets and a calculator, cost how much?:eek:
I guess if you are doing a model that weighs in excess of around 75lbs, that is a better option

RE: Vanessa c.g. Rig: How to.
 

Hello,
i build the Vanessa " machine"
I level my Mig 15 level and the BOB is pointing way tail heavy...I know if I fly with this Cg will be a very hard plane to Handle!?
What I'm doing wrong?
Thanks.
J-C

RE: Vanessa c.g. Rig: How to.
 

How I forget a picture[img][/img]
how you post a pic?

RE: Vanessa c.g. Rig: How to.
 

[img][/img]

RE: Vanessa c.g. Rig: How to.
 

I'm not experienced with swept back wings, nor with jets, but the photos look like the plumb bob is pointing pretty close to 1/3 of the aerodynamic chord, so it doesn't look all that tailheavy to me. Do you have a recommended CG from somewhere? And how does the plumb bob indication relate to that recommendation?

RE: Vanessa c.g. Rig: How to.
 

Thank for this fast reply. Funny is only 4 centimetres off..I flew this model several time last year, rock solid and feel comfortable. I will try to move the CG back a little first.
Amazing gadget.
I build the Vanessa to find the perfect CG on a BMV Electra a 10 pounds jet.
;)

RE: Vanessa c.g. Rig: How to.
 

I am seeking information here, not being critical. The CG equipment described here will determine the CG of the mass of the components of the airframe. This will not determine the aerodynamic requirements of the airplane, such as aerodynamic balance point and/or at the correct decelage angles if any.

Or does it?

Ed S

RE: Vanessa c.g. Rig: How to.
 

You are correct. The rig does not tell you what a good CG should be for a particular model, it only tells you where the actual center of mass is.

RE: Vanessa c.g. Rig: How to.
 

does it matter how far you hang the sling , can you hang in from like the fire wall and the tail ? would this give the same results? and whats the best way to use this way on a bipe?

jason,

RE: Vanessa c.g. Rig: How to.
 

I usually connect just behind the prop and to the prop shaft. On the rear I would connect to the tail wheel allowing the front edge of the horizontal stabilizer to support the sling. The location is relatively unimportant but should be convenient and not damage the airplane.

Bill

RE: Vanessa c.g. Rig: How to.
 

Use the atached diagram to determine the MAC of a swept wing. Looking at the pictures I would agree with Majortom. Project the pointer position out to the MAC and it looks about right.

Ed S

RE: Vanessa c.g. Rig: How to.
 

There's a big difference between the MAC and the CG.

I don't believe I would ever trust that device.

Charles

RE: Vanessa c.g. Rig: How to.
 

been using the vanessa for years now on my giant scale and havnt had a problem yet, lots of bipes........

RE: Vanessa c.g. Rig: How to.
 

hi, I think this CG device is amazing. I cannot wait to make one. It took me a while to understand how it worked. Is there such a device to balance side to side? One question. If the plane is level and the plumb bob is at the planes suggested CG point, then the planes CG has been validated? thanks

RE: Vanessa c.g. Rig: How to.
 

That is correct.

Les

RE: Vanessa c.g. Rig: How to.
 

Hey guys I have a question, I'm trying to be certain that I am properly setting the C.G. on this KMP Corsair that I have just completed, I need opinions please (help!) My concern is that I may be off and wonder if you would suggest a vanessa for this job. The manual calls for C.G. at 130mm aft of the leading edge. I have always balanced my planes with the two dowel method so by going with what i'm used to, I made an amped up version to try and balance this Corsair at the curve of the gull wing. I have it sitting inverted such that when the model is on its called for factory c.g. point, the chord of the horizontal stab will be at 0 degrees to the floor or that is parallel with the floor. What feels disconcerting to me is that when I look at the model balanced on its called for C.G. and the Hori. Stab flat with the floor the fueslage in general appears as if its tail heavy(tail low). Perhaps this is just due to the shape and geometry of the Corsair but its enough to have me concerned. Here are images of how it looks on its factory called for 130mm cg and notice the overall appearance of the fuse relative to the surface of the table (appears tail low). I'm just worried if i'm possibly missing something here and have possibly a tail heavy condition. Any help and input will help me out a lot and I thank you in advance.
Louis

BTW: I measured the Main wing chord length at the root and got roughly 400 MM. So with the factory specified 130 MM c.g. point that I set the balancing line with on the tape, this came out to a 32.5% of max chord length. is this acceptable?

RE: Vanessa c.g. Rig: How to.
 

Louis,

I think you are being deceived by the shape of the fuselage. The Wing, Stab and thrust line of the plane all appear to be level. I would think that plane is about right.

RE: Vanessa c.g. Rig: How to.
 

In post #4, the figures D and F in the drawing showthe string on the right side of the dowel is obviously wound in the opposite direction to the one on the left side. Explanation please, as later in the thread (post #12and #13) they are shown wound in the same direction, or am I missing something?

RE: Vanessa c.g. Rig: How to.
 

I don't want to say that the creator of the device drew it wrong, but, the photos are correct. If the cord is wound as shown in the drawing, they will not wind correctly when you twist the dowel. If they are wrapped as they are in the photo, you will be simply tilting the planes nose up or down as you twist.. The other way it will rotate at an odd angle that will not help the process at all.

RE: Vanessa c.g. Rig: How to.
 

I finally got around to finishing a mustang that I partially built 12 years back.the plans are gone and not available so I dont know where the CG really is. are you saying if I make the vanessa device the plumb bob will give me a accurate point of where the CG actually is? or do I use the complicated math formula?

RE: Vanessa c.g. Rig: How to.
 

It will tell you where the center of balance (aka CG) is, but not where it belongs.

Les

RE: Vanessa c.g. Rig: How to.
 

so it means that I would have to likely take 25 to 30 percent of the CG line ??

RE: Vanessa c.g. Rig: How to.
 

Go here first.<a href="http://www.palosrc.com/instructors/cg.htm">

http://www.palosrc.com/instructors/cg.htm</a>

Les

RE: Vanessa c.g. Rig: How to.
 

I have made and used the Vanessa jig for a few months now and find it works. It also served to get me interested in some kind of jig that I could just set a plane in and check the balance. I am probably being excessive. I first made a 2 "U" shaped pcs. from some 3/8's ply with one leg of the U about a 3rd of the other and then connected the two pcs with dowel and hung it from a string and set my electric model on it after balancing the jig and marking the cg of the jig. It appeared to work. So then I purchase some 3/4" pvc and some fittings and started cutting and glueing etc. etc. until I came up with this jig.
The first pic is of the jig on my mobile bench with the back legs and safety uprights on, the back uprights are removable and are to keep the plane from sliding off, they are removed to place the plane in the jig. I have marked the same point "cg" of suspension on both lower legs and for the purpose of trying it out one inch forward of this to accommodate my old bipe. The next pic is the jig by itself balanced by itself with the lower legs lined up with a level horizontal surface and then the third is with an old Aeromaster bipe with the front edge of the lower wing placed on the one inch mark and a string tied over the aft part of the fuse to hold it in proper flying attitude. The jig flexes, when suspended. as expected in the fourth picture but I think this is of little importance and something I could fix if it is. I originally determined to use larger dia. pvc to avoid this but it was not available. My intention is to put a leveling bubble on the horizontal leg for accuracy.
The whole thing with the plane installed and suspended seems very stable and appears to work although I question whether it is sensitive enough. It doesn't compare to the Vanessa rig for cost and ease of storage but the ability to place a plane in it and hang it and then add weight to see the results is interesting. I can see hanging a plumb bob for more accuracy from the upper support.
I'm really looking for feed back about the design and logic used. It has been fun and interesting so far and accommodates my one giant scale gas as well. The dimensions are approximately: width 15" height 20" without the legs [img][/img]and length 20".

RE: Vanessa c.g. Rig: How to.
 

I think the rig is great.balancing a plane can never be excessive .I have learned after several decades of flying that even the most complex plane flies rather easily if properly balanced .I balance both foward and lateral.my last maiden flight required 2 clicks of up and thats it.I also use the mac formula to find the CG but your jig would be a backsaver especially with big planes.

RE: Vanessa c.g. Rig: How to.
 

I built one of these and it works great for me. The only thing I changed on mine is the plumb bob. Instead of a Nail set, I used an old Dodge van key. Heavey enough to do the job, but won't poke thru the covering if it slips.

RE: Vanessa c.g. Rig: How to.
 

think its time to build one thanks folks

RE: Vanessa c.g. Rig: How to.
 

Hi Guys, Just finished building a vanessa and i don,t really know how i guessed this stuff for so long. i tried it on all of my stuff and found one that i thought was right but never flew right. it was out of cg by 3/4 of an inch aft. like mikey sez " try it, you'll like it"

RE: Vanessa c.g. Rig: How to.
 

I agree. I made one of these several weeks ago after reading this thread. I cannot believe how much some of my planes were off. I am almost done building a Dumas Big Swamp Buggy boat and intend to use the Vanessa rig to set the COG on that also.

Bob

RE: Vanessa c.g. Rig: How to.
 

How does it allow the plane to rotate for or aft? Seems like the rod in the wood block would be to much friction to get an accurate reading? Actually i'm studying the diagrams seeing the dowel is locked in placeand usage of the plumb bob but it's not making sense yet.

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.

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

RE: Vanessa c.g. Rig: How to.
 

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

I slotted the wood that has the dowel going thru it and added a thumb screw to adjust the tension on the dowel.

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.

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