da Rock

If you're going to look for a good starting CG (to control the pitch in flight) it's real easy to find that CG based on the things that control pitch. The answer you get matches the measurement usually printed in the model's assembly manual (inches back from LE at the wing root) but is usually more accurate. Which is a lot easier to find than a MAC that has to be plotted on paper and doesn't consider the actual areas of the plane that control pitch. Also, very few model planes today come with any mention of the MAC or how far back on it the CG should be.

http://adamone.rchomepage.com/cg_calc.htm Nine measurements and no plotting on paper. It uses the measurements of YOUR plane and it's pitch stability control, the tail. It also gives you an easy place to find: some inches back from the LE on the root chord.

Run the formula twice, once with 5% and once with 15%, and you will have the safe range for the CG, not just one point. Our models usually perform better and more efficiently aerodynamically with the CG at or behind 10%, and with the info from those two runs, you'll at least have an idea how to do that. or not.... it's up to you.

mikes68charger

My Feedback: (34)

Thanks for the information:

I tried it last night, Thanks for the info, the single bolt worked great, was able to re-level it very easy..

malitape

My Feedback: (213)

Nice Bird. How much does she weigh?


pete

GSXR1000

My Feedback: (7)

Looking at the pics is like reading a manual, can someone make a video of them make the rig step by step with all the parts laid out?

TLH101

My Feedback: (90)

https://www.youtube.com/watch?v=afvfShdOuck
https://www.youtube.com/watch?v=h57T8OXH4qk
https://www.youtube.com/watch?v=AvM03dKWLPk
https://www.youtube.com/watch?v=iCoeaUShWW0

GSXR1000

My Feedback: (7)

thanks,
lol I don't mind looking at picture layouts with the build info like a manual, but I was wanting a video ez mode to build my rig...

Aalaadin

My Feedback: (1)

Good for flat bottomed airfoils. But not on semi or symmetrical one where the CG is forward of the thickest point. That's when the pencil thing AND fingers become useless

ETpilot

After reading in many threads, and now this thread, about the Vanessa Rig, I decided to make one. My dowel rod fit too loose in the Tee assembly so I had to make a small thumb screw to add some friction. I also added a lever arm to the dowel making it into a windlass. Finally, rather than making permanent loops or using slip knots for line adjustments, I am using a Midshipman’s Hitch. This allows me to adjust the size of the loop making it smaller or larger. I even tested the hitch on the thin plumb bob line and it works good. I just added a loop making it easy to untie. You just slide the hitch to make the loop larger or smaller. Looking forward to setting this up. Then I'll cut my permanent lines.

Tom Nied

Very informative illustration how the Vanessa rig works. Thanks, I need one of these for my GSS.

ETpilot

Tom, I believe you will enjoy using the Vanessa Rig. I sure enjoy using mine. I determine the general CG location during the build. It helps in positioning equipment.

Tom Nied

So I'm having some trouble. I'm having a hard time getting the adjustment dowel parallel to the wing spar and the plane sits crooked laterally. Anybody see anything obvious or do I just need to keep tweaking it to get it right?

Tom Nied

I'm wondering if I have the line that holds the airplane (around the fuselage method) too long? I know if the dowel isn't parallel to the wing spar, the plumb is probably off. I might put one on both sides.

ETpilot

Tom, you have to make sure the plane is centered in each loop. If it is centered off the dowel will be off. Also, I can't tell from the picture if you are using 2 lines or one line for the loops. I just use the one line. If using two lines I believe the loops have to be equal in size. Can't really recall on that.

I believe I see a problem in your set up but not too clear from the picture. The loops going around the dowels must be in the same direction on each side. I believe you may have it opposite on each side. I set up my plane with the rear loop first. Then I form my dowel 3-4 loops going in the same direction and then do the front aircraft loop. So the inside of the dowel loops go to the rear and the outside loops go to the front.

See post 12 and 13 and see the loops around the dowel. That is pictured wrong and may be the way you have it. I think. Anyway hope this helps.

Tom Nied

"centered in each loop", good chance I'm not quite right. I'm using the one big loop of line that goes around the fuselage. This was the first hanging and I'm thinking by this time in the day my accuracy is not as good as it could be.

Loop direction, pretty sure I've got this right. Turning the dowel and on both sides either the nose goes up or down. No opposing forces. Although, I do have 7 wraps, maybe I should go down to 5 for easier re-positioning. I will recheck this.

Thanks ET for taking a look at it. I'll recheck my work this weekend. If preliminary indications are even close, my CG is not too bad, which is remarkable. The problem with the Giant Super Sporster is, is that it is so damn big (14.2 lbs) from what I'm use to, it turns into a wrestling match.

Tom Nied

Wait a minute, you're telling me post 12 & 13 are wrong? That is exactly how my line loops around the dowel. When I turn the dowel, both lines on each side move in the same direction moving the nose either up or down.

ETpilot

One more thing I might add. I don't favor the plumb bob being on the side on the dowel. If the dowel alignment is off a bit you will get an incorrect reading. I placed my plumb bob centered on the Tee. So from the ceiling to the tip on the plumb bob is one straight line. I have it where I can easily adjust it for height. For my type of airplanes that has not been a problem. Having a plane like your Super Sportster I will have to take a reading over the canopy. I will come up with something when the time comes.

ETpilot

It seems to me that with that setup you would get a twisting motion. IIRC correctly this was discussed in this thread. I will check that out on my rig tomorrow and let you know what I find. Will see if I find it in the thread. That setup pictured makes no sense to me. It may be part of the problem with the dowel alignment. Having it as I described I get an easy nose up or nose down motion.

ETpilot

My apology Tom. The picture is correct it was the drawing in post 4 that was incorrect. However, I do not like the way the loops were made in the picture. I believe that setup may give you an issue with centering the airplane and maybe with the dowel being out of alignment. I, from the start, wrapped the loops so the inside loops go in the same direction as well as the outside loops. In the picture they are correct but not balanced as I describe. Hope this makes sense.

Anyway, I will play with all this tomorrow and see what I find.

Tom Nied

Yes, I'm thankful for a second pair of eyes looking at this. I think once I get used to it, play around with the tweaking, I'll have a better understanding on how to set this up. The system and its science is sound. But if things like the dowel rod not running parallel to the wing spar, its easy to get a misreading. I love the science how this works, but it's important to get things right in order for correct readings. I bet in the end, I'll pull out the Great Planes CoG machine, just to check my work. The GSS is just a monster to wrestle with. I accept the challenge. Thanks ET.

ETpilot

Good morning Tom. This is what I found:

Looking at my rig I now remember having an issue with the dowel alignment. You can see in the top center of my Tee a vacant hole. That was the original hole I used with a single line going to the ceiling. Working with this rig I decided to go with a 2 line loop so I drilled the horizontal hole. I also add a spreader bar to the loop. I like this setup better. In the first picture you can see the plane is balanced wing tip to wing tip. The dowel is still slightly out of alignment. This has to do with how the plane is hanging in the aircraft loops. I will show this better in my next post. The second picture shows the plane balanced in the longitudinal axis and gives a good view of my rig. The last picture shows how I wrap the loops on the dowel. This is more balanced than as pictured in post 12. Since I have my plumb bob centered on the Tee I don't pay much attention to the dowel alignment.

ETpilot

Now in this set of pictures I have the dowel loops as pictured in post 12. The first picture shows the plane balanced wing tip to wing tip. You can see that the dowel is significantly out of alignment. I attribute this to how the loops are wrapped on the dowel. The second picture shows the plane balanced but the dowel is still way out of alignment. Worse than in previous post. The third picture shows the dowel loops are as pictured in post 12. Not a balanced setup. The fourth picture shows how the plane hanging in the aircraft loops affects the dowel alignment. The plane is not balanced wing tip to wing tip but the dowel is aligned with the spar.

With your GSS hanging in the loops, move a line just a bit to reposition the plane a little and watch how the dowel rotates. This is why I favor the plumb bob in the center of the rig.

Anyway hope all this helps. You just have to use rig and you learn by using it. It is a handy simple device. I have compared results with my PVC balancer and both are right on. I find the rig easier to use.

ETpilot

Here is another thing you can do with this rig. I'm building this plane and wanted an idea of how it would balance with some equipment installed. So I taped the tail section and engine on and positioned the servos. Now I have an idea at to CG. I will do this again when I'm about finished with the build and do the final installation. This helps, IMO, make adjustments as I build. Just something I am trying out.

Tom Nied

OK, those pics help. I can see how the wrap of the lines can make a difference. Looks like there are eight ways the wrap can go, but ultimately its better either from in out, or out in. Mine go from the left to the right, but is unbalanced. You know what I mean. In to out or out to in makes for a more balanced hang. Also I have 7 wraps on each side, makes it harder to tweak the lines to get them to match. Yeah, tomorrow I don't have to work and I can get to it to play around with it, Think I have an even better idea how to use it correctly. Thanks ET.

That looks like a SPAD Debonair? I had one that I built the wing with no dihedral (flat. it was easier to build). I flew the heck out of it. Didn't have to be careful with that plane, was fun too. Wish I still had it, but eventually had to retire it to the landfill and the Thunder Tiger Pro .46 ended up in a Tower Razor. The engine was such a trooper that I wanted its next home to be something more than a SPAD. But SPADS can be a lot of fun

Thanks again.

johnMADRAMS

HI ETpilot and Tom Nied, just my 2 bits- 1 of the last photos clearly show the rope is laid(sprialed) this will not allow the plane to sit easily in the loop- will keep pulling to the favoured side by the lay of the rope. I have used plaited rope (non-laid) and found no problems, I set the plane level by the horizontal stab both ways then see where the plumb bob sits(hangs off the cinch bolt in the centre) adding the weight then relevel the plane and recheck the p/bob. the stearman in my post 05-13-16 has had its 3rd flight today the last one by my hands(shaking) and went well till I touched the grass short of the runway(rudder to repair) but the plane sits in the air nice as does my hustler I just made a new fuselage for. found this the easiest CG check of the systems I had tried. works well so far, all the best for your checks and flights.

ETpilot

Glad the pictures helped. As you work with this rig you will learn more. I've only had mine a few months and have used it on 3 different airplanes. BTW, 7 loops on the dowel is too much. I use 3 or 4 loops. The loops are just there to keep rope slip from happening. The weight of the plane will keep them tight allowing for rotation by the dowel. When you first set up, rotate the dowel aggressively and look at the loops. Make sure they remain flat on the dowel. I had an occasion where one loop started riding on top of another loop. So I now check for this. Also look at my dowel picture. You will see a small dowel on the end of the main dowel. This allows me to make small adjustments without creating much movement on the airplane. Just gently touch and rotate. I believe it is much better than grabbing the dowel and rotating. Movement of the plane with each adjustment is the only minor drawback to this rig. Very minor problem.

When i got back into RC I decide a SPAD Debonair would be my trainer. It has been a good airplane and has had its mishaps. It is the only airplane I have flown since my return. With my current build I will have 5 planes with 4 ready for maiden flights. Problem is I have taken a year off to do home projects. Now I am all caught up and ready to fly again. March 16 will mark the year off. I need to start from the beginning again. I've been training on a few iPad apps I have. Will see how my first flight goes.

John, thanks for the info on the rope. Never gave a thought to the type of rope to use. I just used what I had on hand. Will look into other type ropes and see how they work. Since, like you, I have the plumb bob in the center I don't concern myself with the dowel alignment much. I just level the plane laterally then balance longitudinally. I'm still learning this rig as I use it.