bri6672

My Feedback: (6)

Im interested in this as well!!! Wing incidence seems to vary compared to the water line on some jets! This seems to be an Important factor and no one seems to be addressing it.. Maybe Oliver can chime in on this???

RAPPTOR

My Feedback: (41)

yeee haaa !!! Now were cooking !!!!! Yes yes yes yes
10000000000 percent correct .. Thanks ..
Unit does not "find" c/g

olnico

Well, there are several factors to take into account here.

1. How did the manufacturer establish the CG checking procedure?
Some manufacturers show the plane CG position while sitting on its gear.
Some manufacturers show the plane CG position while the fuselage is level
Some manufacturers show the plane CG position while the wing is level

So my recommendation is to follow the procedure ( levelling ) described by the manufacturer.

Now, if you pickup the wrong levelling. Will it matter?
Not necessarily. It all depends on the angle difference between the several references. Most wing-to-fuselage angles are about 3 degrees.
Most tri-cycle planes sit on the ground with a fuselage angle of 3 to 5 degrees.

2. What's the error like?
Let's take a typical scenario.
The CG is referenced to the wing thickness line.
You are CG checking with the plane sitting on its gear flat.

Wing-to-fuselage difference: 3 degrees.
Fuselage-to-ground difference: 5 degrees.

Reference line to ground difference: 8 degrees.
What's the length difference for a main gear to CG of 100 mm ?
cos (8) = adj/hyp = 0.9902
So you will see a difference of roughly 1% or 1 mm over 100 mm.

In that case the CG position error will be of 1 mm. Does it matter? In most cases, no. However, some will argue that since the machine is able to deliver results to 5 per 1000, why introduce an error of 1 per 100?

So, to summarize, on most cases, the error will be 1% of the measurement dimension. If the dimension is big, the error will be bigger. However, the CG tolerance range will be bigger as well.
If you really want to use the machine to its full precision potential, then level your plane as recommended by the manufacturer.
If you are more kind of a practical person for whom flight characteristics matter the most, then 1% error on the CG shouldn't bother you too much.

Springbok Flyer

It is not worth worrying about - the cg error will be so small that it will never make the plane unflyable. Even if you got the cg 100% spot on as per specification, small changes to that may still be required to bring the flying feel within your personal preference.

Jan

bri6672

My Feedback: (6)

Jan,

Not true... I put a small A6 on the scales just to get used to the system. If it just sat on the gear on a level table it was at 73mm ahead of the mains, if I put an incidence meter on the wing and zeroed it I was at 81mm that's a pretty big swing....

bri6672

My Feedback: (6)

Oli, thank you for the response! The only thing is I have built tons of models and have rarely ever seen the manufacture specify the CG checking procedure. They only give the distance from a reference point ie back from the leading edge at root, and if the gear are up or down....

From your math it seems a non issue and all this is for me is to get a safe starting point in the air so I can find the CG I prefer...

i mentioned in a post to Jan above that I saw an 8mm shift with an A6 from just sitting on the gear to zero wing incidence. I thin that model is a bit of an exception since it sits very nose high AOA on the ground but in the air it flys very tail high and has a large amount of positive wing incidence compared to most models.. Keep in mind this is a little freewing foam airplane that I'm sure is far from scale and has most likely been doctored by the factory to make it easier for some people to fly..

HarryC

My Feedback: (1)

I think we need to keep a bit of perspective.
Without the Xicoy machine, (or your own version of it with scales and a calculator) what did you do? Depending on weight of the model: balance on fingertips; balance on a Great Planes or Multiplex CG machine; or maybe by suspending the model/using a Vanessa balancer. All of those rely on you eyeballing the attitude of the model and deciding when it was right. So with any method there was a considerable level of subjectivity as no two people will use the exact same attitude and call it "level". Many years ago I would balance .20 glow motor size models, i.e. fairly small, on my fingertips (lots of room for error) and decide by squinting from underneath the model if it looked about level. The % "error" was probably quite big yet I never had a CG problem in flight! My point is that whatever method we use there is quite a lot of error due to the subjectivity of the user and it generally is not a problem, for the simple reason that a plane has a CG range, and not the one and only spot CG that almost every model instructions give.

So with the Xicoy machine just chock the model wheels up until the model is in the attitude that you would have called "level" if you were using say, a Great Planes CG machine. To make wheel chocks I got a plank of thick and a plank of thin pine and cut them into 3" long squares and use them to chock up the wheels until the model is in what I call a level attitude. Then you simply put the xicoy sensors between the wheels and the wooden chocks.

Springbok Flyer

...and that will make it unflyable? I don't think so..... unless of course you are already on the edge of your cg range (specially on the tail heavy side).....

Jan

bri6672

My Feedback: (6)

Off by almost 10 mm is pretty significant.... 1-2mm of course not... The reality is we are paying the price for a product that is supposed to provide accurate so we can fine tune the model. If I didn't care about accuracy I would just throw the planes on my Southwest systems easy balancer..

Springbok Flyer

Brian,

I take your point regarding the supposed accuracy of this device ... I own one too. Alas, I have gone back to the way I used to balance by hanging my planes from the rafters of my workshop, having drilled a 3mm hole in the wing seat (on both sides of the fuselage) on the cg position and using a spring steel hook in each.....reason being; if your plane has trailing link oleo's the cg position will move as you have exlained, by simply having the mains either forward or back and changing the indicted cg position (and the horizontal reference) as per this device. So this is a gimmick and merely another toy for us to play with. I now use mine to check how much it can vary theproposed cg, by simply changing the various distances which it uses to calculate the cg, without actually making any changes in the weight distribution of my planes. Hence, how much I can influence this device without actually changing the cg of my plane - bottomline, I would not use it to cg any of my planes.

To my point - an 8mm movement of the balance position (when your plane is within it's cg range) will not make it unflyable - at worst, it will only make it slightly nose or tail heavy. A situation that you can easily correct and fine tune for the feel that you like. So if you know the exact (precise as you put it) cg postion and you end up with that 8 mm cg shift - your plane will still be flyable.

I don't have an argument with the theory of this device, only with the practicality of me trusting it for the maiden flight........

Enjoy playing with your new toy....but rather 'throw' your latest pride and joy back on your trusty Southwest Systems Easy Balancer before you fly it.

Cheers,

Jan

HarryC

My Feedback: (1)

Jan, I disagree, if using trailing links has caused an error in the calculations, it is operator error! You need to determine the cg location w.r.t. the wheels with the model sitting on its wheels, so that the links are in the same position they will be in when on the sensors. If you use the device properly, trailing links have no effect.

olnico

Yep, go give this advice to Airbus, Boeing, Northrop-Grumman, Lockheed-Martin, Dassault Aviation, Gulfstream, Cessna...
Who all use this method to balance all their planes. Including trailing link ones like the B-777, A-380, F-18s and so on.

Springbok Flyer

...you are missing my point.....of course they are using it succesfully.... and they know exactly where the cg should be.....not trying to find it like most on here are trying to do. What is more, on those big birds the cg range is considerable and small movement thereof has little effect on the flying....and easily trimmed out.

Like I said, enjoy playing with your new toy..... I am, but definately don't trust it.... just because the big boys use the same theory. Their instruments are way more accurate than this thing....

Cheers,

Jan

olnico

Actually not.
We calibrate our CG machines to 5 per 1000. This is an extremely high level of accuracy.
The scales we use to balance the B-777 out of the C check are rated at 3 per 1000. So, very close.
1% of CG range is very good. Comparable to full size aviation ranges.

Custmachr

My Feedback: (3)

The trailing links can change your dimensions that you enter into the device for calculations and also effect your leveling. I have solved this by temporary putting a zip tie on each strut to hold it in a fixed position (fully extended) during the balancing. This allows the dimensions and the level to remain constant even as you move weight around to obtain the proper cg per manufacturers design.
Tim

bri6672

My Feedback: (6)

Cool idea Tim! It's all about creating consistancy and that would do it!

mr_matt

My Feedback: (10)

I think part of the issue here is we are measuring the 2D CG location is, and depending where the 3D CG is, it might be more or less sensitive to the incidence when it is sitting on the scales.

skubacb

What does the Xicoy give us that is better than our normal methods of measuring CG, such as hanging, three postal scales, finger tips, seesaw, etc. Convienience All of our other methods of setting the initial CG (iCG) are accurate enough for that first flight. So the calculation of the initial CG is more important than the method we use to set it.The final CG is set from flight results not calculation.

Our seesaw type balancers (I have two high end ones) are cumbersome and take up too much space. Some times I need a large pad between the balancer and the wing to keep from breaking balsa on the wing. Other methods we use are either also cumbersome or inaccurate such as finger tips. The Xicoy removes the need to invert some aircraft during the initial balance (as does three postal scales) and is compact. But since the Xicoy is only used for the initial CG there is little need to bring it to the field every day. What helps to make the Xicoy valuable is the angle measurement which can be bought with it. Without that I would not consider the Xicoy and would continue with our current methods to set the initial CG. Bottom line is the Xicoy does not make the iCG any more accurate or usable just more convenient to set.

All that being said I will highly consider buying a Xicoy but only with the angle measurement attachments.

Edgar Perez

My Feedback: (13)

Agree on the convenience, but if you are handy with excel a simple postal scale will do. No need to pay a high price for that convenience.
(On the other hand, each of us gets to define the value of convenience, so maybe buying the Xicoy balancer is ok to avoid dealing with excel)

mrrandyman

My Feedback: (3)

Any idea when we will see some software updates to fix some of the bugs?

Thanks.

HarryC

My Feedback: (1)

What software bugs?

Damo260

Mine works fine from day I unpack it

Damo

bcovish

My Feedback: (8)

No bugs in mine.

Sekhet

My Feedback: (1)

There be no bugs here!

mrrandyman

My Feedback: (3)

Here is a partial quote that I received from Gasper a while back regarding the Correction point not showing in the right direction on the Tail Dragger Mode.

"Hello Randy,

Yes, we have found that some taildraggers need to enter correction aft of the main wheels, it is needed to enter a negative value for the correction point that current software don’t allow. This will be solved on next software release."

This why I asked about an update on a release.
It doesn't keep a person from using the machine but it's nice to have everything working properly.