So I have taken my time building my new Seagull models Extra 260 ARF kit. I went ahead and outfitted it with a new EVO 1.00. I want to balance it but the directions say that the CG is 7-8CM from the leading edge of the wing, MEASURED from the wing tip. Since this is measured at the wing tip does this mean that I cannot use my CG machine and have to use a helper to balance the model? I am just used to the smaller sized models I use my CG machine on. I also usually balance my low wings inverted. The Extra's manual does not specify if it should be balanced inverted or right side up.

I have a seagull yak I just finished and it said the same from wing tip thing. I just got my dad to help me. It didnt take long or anything.

Did you do it right side up or inverted?

Balance heavy side down.

So inverted?

Hi,
Have figured out your balancing problem, the solution to your question is simple math. Here is a simple explanation. The CG of a model plane is calculated using a percentage of the cord lengths, located at the root…large end of the wing and wing tip. On most planes it's about 25 to 30%, depending on the style of plane. The formula is A x B = C were A = root, B = % and C = the length from the leading edge.
Here is an example…lets say you measure the root and its 12 inches which is A.
The % in this case let’s say it’s 30% or .30…B
Multiply 12 x .30 = 3.6…(3.6 is about 3 5/8ths inch)…C
Now do the same calculation using the cord length at the wind tip.
Let’s say you measure it at 5 inch.
5 x .30 = 1.5 inch
Measure the 3 5/8 from the leading edge at the root and mark it. Measure the 1.5 from the leading edge at the wing tip and mark it. Now draw a line between the 2 points. Any were on that line is the CG of the plane.
But wait we already have the measurement (C) for the CG but it’s at the wing tip. We need the line between the 2 points.
So what do we need to solve the problem, we need B the % used to calculate lengths from the leading edge.
I’ll make it simple for you. A x B = C. To solve for B we use a little algebra magic.
The formula now C Ă· A = B. C is the given measurement for the Seagull Extra 260 is 7 to 8 cm at the wing tip. (get out your metric scale or conversion chart)
So measure the cord length at the wing tip, that is A. So now we have the A and the C… use the formula and find the % or B.
Measure the cord length at the root and multiply that length times the %. That will give you the C value or length from the leading edge at the root. Draw a line between the 2 point as I explained before. Any were on that line is the CG. Simple huh!
If you still don’t get it there is a book... Acrobatics for Everyone by Dave Patrick, he explains it. In fact if your going to be flying the Extra 260 it would be a good book to read.
Good Luck and Happy Flying
Aerosman[8D]

Oops, one more thing. If you don't already know it, it is recommended to balance a low wing plane upside down, heavy side down.
Aerosman[8D]

Some more?...[sm=regular_smile.gif]
Oh did I say I just bought this plane, Seagull Extra 260. I have had my eye on this one for a while. Looks like a well built plane but the instructions are the pits. If you have any recommendations on putting it together let me know.
A friend of mine recommends using a SPE 26 gas engine for this plane, it cost is about $260.00. It weights 32 ozs. about the same as an OS 120 4 stroke. This will be my first experience using gas. I expect an adventure!
Aerosman

I too have an extra 260 .90 and plan on putting my saito 100 in it. I'm not too sure about the saito providing enough power for the plane. I crashed my edge 540 .60 and hoped to just use all the stuff from that (including the saito 100). Does anyone have any experience with this set up? The two planes seem close in weight. The extra seems to have move wing area.

i have the 206 with a 120 two stroke on it th plane flies great bit if you plan on doing any 3d with it i would recomend gitting a carbon fiber wing tube i flew mine today and i did a wall into a waterfall and then i landed the plane it had about 3 inches of dihederial in it not good but other than that the plane flies great good luck to yall here were you can git a wind tube from for $30 pluss shipping http://www.troybuiltmodels.com/

You've got a 120 2-stroke in it. That thing must scoot! The question I still have is, will the saito 100 4-stroke be enough for this plane? Anyone? I'm in the process of building it, but I'll hold off on mounting the engine till I get this figured out.

The recommended range is 91 to 1.25, 2 or 4 stroke. I would do a comparison between them and your 100 4 stroke. Just of hand I would think it would okay for sports flying. So I guess it depends on how you plan to fly it. Also consider the prop size, a lager prop with less pitch will allow you engine to run at higher speed. I had an Extra 300 the same size with an OS 91 4 stroke in it and that was more then adequate for me. As I stated before I’m going to put a SPE 26 in mine for the simple reason that I would like the power to do any type of flying. Plus gas is cheaper in the long run.
Other recommendation…you must be in a R/C club, ask one of the members that has the experience and you trust…look in the discussion board for threads that deals with engine sizes or start one in a different category other then this one.
The bottom line the decision is yours and that should be based on all the information you collect and the type of flying you want to do.
Good Luck and Happy Flying!
Aerosman

a sato 100 would be alright if you keep the plane lite mine came in at 9 lbs