Balancing Question
 

I've built a few planes and assembled a few ARFs, but I've never been sure if I'm balancing a plane properly. I seem to get it right because I've never had a problem in flight. But sometimes I think it's becuase I'm just lucky. As I get further into this hobby, I'm building more expensive planes, so I'm worrying more now than before. Here's the question:

When I set the plane on the balancing machine - I use several different kinds based on the size of the model but the same principle applies - how do I know when the plane is in its straight & level attitude?

I've always set the model so that the horizontal stabilizer is horizontal to the ground but sometimes the angle of attack of the fuselage doesn't look right.

Am I doing this correctly? Any comments or suggestions would be much appreciated.

Thanks

RE: Balancing Question
 

G'day Mate,
That's the way I do it, tailplane level, or horizontal stabiliser in USA.
High wing upright, low wing upside down, mid wing, depends on how it sits on the balance, if it's stable right way up, then ok, if not turn it over.
I always balance my planes at the rearward end of the balance range, because almost all planes have very conservative balance points, in the instructions.
But I always make sure I have conservative elevator throws, on low rate, for the first flight, with about 20 to 25% more on high rate, so I have somewhere to go if it is not enough.

RE: Balancing Question
 

For precise location of the CG for any model try this:

http://home.mindspring.com/~the-plum...%20Machine.htm

http://www.rcuniverse.com/forum/m_708060/tm.htm

RE: Balancing Question
 

Thanks, lnewqban. I've useed the Vanessa Machine for several years to balance my giant scale planes.

I know where the CG is and how to estimate it when there are no specifications. The question was " . . . how do I know when the plane is in its straight & level attitude (while balancing)? . . . I've always set the model so that the horizontal stabilizer is horizontal to the ground but sometimes the angle of attack of the fuselage doesn't look right. . . "

Mike

RE: Balancing Question
 

Thanks, Alan0899. I appreciate the confirmation.

Mike

RE: Balancing Question
 

It depends on the plane, but if you want it to be exact ,use and incidence meter. Just make sure the center of the meter is over your prospective CG. Most of the time I try and use a small bubble level on a surface I know to be flat when the plane is level. Some planes just don't have a good spot.

David

RE: Balancing Question
 

Mike:

I believe that you should do as the airplane designers normally do: to use the center line of the fuselage as your horizontal reference.
They estimate that this is the attitude that achieves the minimum drag for cruising speed at level flight.
Because the wing AOA changes for slower or faster level flight, the center line of the fuselage will deviate from the horizontal for other than the cruising speed, increasing the total drag of the airplane.

However, the angle of the centerline of the horizontal tail not always coincides with the angle of the centerline of the fuselage.
As you know, the function of the stabilizer is to lift down in order to compensate for the total pitch torque or moment produced by the wing, thrust and drag.
A few airplanes require a positive lift at the tail.

Please see the attached schematics.

In order to produce that negative lift, the stabilizer must have an AOA relative to the airstream that hits it.
Because the wing generates a downwash, that airstream hits the stabilizer at several degrees coming from above.
That AOA of the stabilizer relative to the downwash should be the appropriate in order to generate the needed negative lift.

In other words: the apparent or geometric angle of the stabilizer may be misleading.

The good thing about the Vanessa device is that the plumb will always cross the actual CG, regardless of the attitude of the model; hence, extending the plumb line for two or more positions, is a sure method to locate the vertical and horizontal position of the CG.

Regards!

RE: Balancing Question
 

Keep in mind that there is no "exact" CG location. Balance it however you normally do - if it's worked until now, you must be doing something right. But then FLY the model and see if it flies the way YOU want it to.

YOU might like it better with the CG moved slightly forward or aft - This is why there is a CG "Range"

RE: Balancing Question
 

Some say balance it to the rear of a specified CG range. Some say towards the front. Some say in the middle.
Just remember this.... a tail heavy plane will usually fly only once.. an nose heavy plane will fly again. Also the more you shift your CG towards the rear the more sensitive it will be to control inputs. If you are a low time pilot and not real sure of what your model is going to do...then balance towards the forward range of your specified CG range. You can always adjust it back after you have a feel for the thing. But if you are toward the rear of your CG range and it (plane) has some issues then you will more than likley not have to worry about a second flight. That is unless you are a real real good pilot, so why take a chance on the first flight???.

RE: Balancing Question
 

build a vanessa and you'll always be accurate!!!

RE: Balancing Question
 

Hi!
Use you index finger!
25%-30% of the wing cord is the norm! Plane should be slightly nose heavy at this point!

Then fly it and see how it behaves! Do a sharp turn to the left at full power, pylon turn at low level (5-6m)! If the plane noses down in the turn it is nose heavy! Move the battery back. That simple!!!

RE: Balancing Question
 

not all planes like the 2 finger method, i would love to see you do the 2 finger method with this one!!

RE: Balancing Question
 

eagledancer, I've had several planes like that and have always used the two finger method - It works just fine.