CG Question
 

I have a friend that purchased a used senior telemaster ( 95"span). Unfortuantly we have been unable to fing any info for the CG on it. We have just installed the radio gear into it , any help with the location or some suggetions where a safe place to start would be.

thanks

flynte

RE: CG Question
 

somewhere around 30-33 % of the wing chord will get you close

RE: CG Question
 

In my experience the CG doesn't have to be exact. I like flying very slightly nose heavy. An easy way to tell if your CG is right is if you fly it upside-down. Is the nose pulls towards the ground ride-side-up and upside-down you're slightly nose heavy.
G

RE: CG Question
 

I was told (don't know how true) that most high wing trainer type airplanes have the CG at the main wing spar.
That kind of makes sense from a structural point of view. When the airplanes are designed the main spar should be near the CG for strength at that critical area. (stop me I am rambling again :D )

RE: CG Question
 

G'day Mate, I have had 2 senior Telemasters 20 years apart, start with balance point on the centre of the spar, & she will be fine, you can move it back from there if need be, also add a couple of degrees of down thrust to the motor & you will not have to add too much down trim at full throttle.
Good flyin mate.
Allan.

RE: CG Question
 

The CG location isn't a do-or-die deal but you do need to start out in the safe range.

There is an excellent one-page CG computer application on the internet. You strap the wing on your model, whip out a yardstick and measure the sucker. It takes about 2 minutes. Then plug the measurements into the application and TAA DAAAA...... http://www.geistware.com/rcmodeling/cg_super_calc.htm The page is somewhat self explanatory.


Funny, but I've just been posting in a thread on the same subject on this forum. http://www.rcuniverse.com/forum/m_43...tm.htm#4318162 Some good info in that thread about the same issue.

I just used the application. The link is working fine.

I've been flying a H9 Ultra Stick 40. It doesn't seem to want to snap so I've been moving the CG back. When I assembled that ARF, I didn't bother to consult the booklet for it's recommended CG location. I've been doing this stuff since Civil War times and figured to go with what felt right to me. When the plane showed reluctance to snap, I still didn't look at the book. I just started moving the CG back.

Well, your question made me consider using that application to see where my CG was according to the formulas.

Turns out that the H9 UStick booklet suggests the CG be from 3.5" to 4" back from the LE. Turns out that the classical theory puts the CG range from 2.87" to 4.75" which has the suggested range dead in it's center. And turns out that I've got mine back to about the midrange for what H9 suggests.

The formula parameter for the online application suggests MARGIN values of 5%, 10%, 15%, and 20%. Taking H9's UStick as an example, the 10% and 15% margins would be their range and could be considered as the "safe" range.

With my UStick, the range of CGs covers almost two inches. The safe range is under an inch. Since the H9 UStick's wing chord is 12.5", that shows just how wide a range you can have the CG on such a model.