Originally Posted by oh58skid

The airplane is flying great and you will not be disappointed in how it performs.

Unless you have thumbs like Terry

Jerry
I have flown a 43%carden with a counter balance and now I fly 124 pros without counter balance . I know I reduced the amount of rudder throw in my pros as it was a lot more sensitive . I may agree it takes more torque to have the no counterbalanced rudder. I think thats why the real ones have them if they didn't you prolly couldn't move the rudder while flying . As far as apperance goes I like the counterbalanced look but I like flying without one . As far as coupling goes I did not find hardley any difference between counter balance and no counter balance .
That's just my opinion
Bryon

Originally Posted by Pistolera

Unless you have thumbs like Terry

Thanks Earle......I can tell by all the dancing bananas that you just complimented me...LOL

I find that the rudder is more sensitive and has more authority without the counter balance. In knife edge the airplane has no coupling...now I don't know if it has anything to do with not having a counter balance on the rudder or not.
Hopefully myself, Jerry and some of the other guys who are flying the 3.1 can get together and compare notes.

Originally Posted by oh58skid

Thanks Earle......I can tell by all the dancing bananas that you just complimented me...LOL

YEP!!!!!! I just sent in my registration for the Nats. I'll have you whipped into shape by then

O.K. guys, I will weigh in on the counterbalance thing.

I agree 100% with Jerry.

And, I will be using counter balances on all my surfaces.

Most of the reasons are just what Jerry said. And, it's not just that I may want to do some 3D with this plane. A snap in the IMAC sequence is a high energy maneuver, and I want to be able to stop on a dime. The ailerons and rudder are big factors in this. Also, I want to use the right (least) number and size of servos for the task (i.e. total torque).

And, as for the rudder, well it just needs it. It's not a wing with a lot of length. You can't project it down, because you need to land the plane and have a tail wheel. And, you don't want to project it too tall, otherwise there is too much eccentricity. However, some height is desirable, since it helps counter the weight of the main landing gear in knife edge flight.

Anyway, it's a wide control surface, and the torque required for it is high, since the torque required is a function of the square of the width of the control surface, not counting counter balancing. What is a typical rudder width? 8" to 12"? Where an aileron or elevator is maybe 4" to 6". That's like comparing 5^2 = 25 vs. say 10^2 = 100. So a rudder has about 4x the torque requirement per length that an aileron or elevator has. I'll take the counter balance to help the servos.

Some of the Krill 3.1m guys (see discussion on "Krill 41% Extra 330 SC Build") were having some problems with aileron servos breaking. And, it has counter balanced ailerons. The ailerons on that plane are huge. Anyway it appears they may not have been using near the total servo torque they needed. Here is part of a post I made there with reference to the AMA Large Model Aircraft requirements and a calc for minimum required torque for the ailerons. You can apply this to all your control surfaces. And, I bet many of you do not have enough servo torque on some of you planes' surfaces.

"
http://www.modelaircraft.org/files/520-a.pdf

"B. LMA Model Requirements:

"13.
"(d) The minimum torque requirement formula a conventional control surface is
calculated as follows.

Minimum torque = A *Chord *Span * Chord/3 * Servo Arm/Control Arm

A = Airspeed factor (see Table 1)
Chord = average control surface chord (root chord + tip chord) / 2
Span = control surface span
Servo Arm: the distance from the center of the servo arm to the control linkage
attachment.

Control Arm: the distance from the hinge line to the control linkage attachment"

and, from Table 1,

Airspeed factor, A = 3.0.

The root and tip dimension of the ailerons was given by "drewbags" back on Page 1 in Post #13 as about 9.5 in. at the root and 6.5 in. at the tip. These are big ailerons if that is a correct interpretation from the scale used.
For comparison my 40% Carden 330 has 6 in. and 4 in. , and my 42% DPA Slick 540 has 7.5 and 4.5 in., respectively.

Just assuming the aileron length is about 54 in., and we take off 2x 4 in. for the counterbalance, for L= 46 in., total torque by the Program, and recommendations for calculating, is,

Total Torque Req'd ~= (3(46)((9.5 + 6.5)/2)^2/3)(1.5/1.5) = 2944 oz-in

(Note: the 3s cancel out for aerobatic aircraft.)

That's 4 x 736 oz-in,
or, 3 x 981 oz-in servos.

Although, I believe it is more correct to calculate it as,

Total Torque Req'd ~= (3(46)((9.5^2 + 6.5^2)/2)/3)(1.5/1.5) = 3047 oz-in,

squaring first before taking the average.

That's 4 x 762 oz-in,
or, 3 x 1015 oz-in servos.

Note: I used the servo arm and control horn arm to be the same at 1.5 inches.
Note also: The requirement goes up by the square of the width ( or chord) of the control surface.
and.... Note also: You can do this for all surfaces, including rudder, which has a large chord."

Kurt Koelling did a nice write up about his observations with not going with a counter balance on the rudder. I wish I could remember where that was but it was most likely in one of Fixed Wings build threads. One of the observations that alot of folks have actually felt flying one with and one without is that rolling turns are easier due to less coupling and the rudder authority is greatly enhanced. Do I like the look of the counter balance better YOU BET! However I do believe that for a precision airframe (whether it's giant scale or F3A) the counter balances are not needed and in fact can cause some undesirable flight charateristics.

Originally Posted by pcastine

How so? I don't understand...

Thanks,
Pete

Hi Pete.


The extra area of the counterbalance hypothetically would be more effective at the same deflection. Therefore you would use less servo travel to achieve the same rudder effect.

Or, the counter balance part is on the opposite side of the hinge line and centerline of rudder from the rest of the rudder, and puts an eccentric force from the wind x arm, or moment, opposite that of the rudder on the other side of the hinge/rudder centerline, which cancels out part of the rudder moment below, effectively reducing the torque required. Not to mention, the counterbalance portion, as an airfoil, is at a much higher angle of attach to the wind than the deflected/curved shape of the remaining rudder, putting more lateral force in the tail than without the counter balance. So, the rudder with counter balance does not need to deflect as much to create the same lateral force on the tail of the plane.

Originally Posted by wingwall

Or, the counter balance part is on the opposite side of the hinge line and centerline of rudder from the rest of the rudder, and puts an eccentric force from the wind x arm, or moment, opposite that of the rudder on the other side of the hinge/rudder centerline, which cancels out part of the rudder moment below, effectively reducing the torque required. Not to mention, the counterbalance portion, as an airfoil, is at a much higher angle of attach to the wind than the deflected/curved shape of the remaining rudder, putting more lateral force in the tail than without the counter balance. So, the rudder with counter balance does not need to deflect as much to create the same lateral force on the tail of the plane.

Makes sense but it seems opposite of what others have said they have experienced. It seems like those with no counter balance require less rudder and actually have to reduce the throw to match the same feeling with a counter balance. This is very interesting. I am in no way qualified to discuss the physics of this situation but just reading and hearing feedback from those who have tried both on the same airframe.

No test flight as yet but here is the finished model except the canopy trim. Anyone in the UK following this thread you will need a long wheel base van or have to cut the bulkhead to get the 9 ft fuss in. Test flight hopefully next weekend
Lee




You can just see the cut that was made in the bulkhead to get the plane in

Just as an FYI, I require significantly less rudder with my 124 pro as I was using with my 118 carden for the same feel.

Now there are many reasons why, but reducing the servo arm length to achieve this does apply more torque to the surface.

Tony

Yes. Or, more control horn arm length.

Great looking plane, Lee. That 3.1m Jtec Extra 300 CS does look large. Is the rudder removable?

Well done Lee, what are your plans for it? You fly IMAC , 3D , sport fly or a lil of everything?