Balancing ailerons
 

Balancing Ailerons...

I have never balanced ailerons before. The faster the plane I fly the higher the torque servo I have used. So why not balance to help prevent the high speed flutter. Anyway, what is the proper way to determine the balance point on your aileron? 25% MAC just like you would a wing?

I plan to add the weight inside the leading edge of the aileron and then proceed to glass over it. The lead wire will be in sections between the point hinges.

Any advice from someone who knows?

Thanks,

Blue Skyy

Balancing ailerons
 

I think you should balance ailerons or any surface exactly to the hinge point. If no servo is connected, the surface should not move at all --> the same way you balance a propeller.

Balancing ailerons
 

The hinge point in this case is just a 3/16" from the leading edge of the aileron. So it's based on the point of hinging and not based on the CG of the entire control surface?

Blue Skyy

Balancing ailerons
 

There's actually two types of control surface balancing.

The first and most usual is the mass balance where weights are placed ahead of the hinge line in some manner to balance the weight of the control surface. This moving of the control surface balance point towards the hinge line is usually related to reducing flutter tendency.

Then there is aerodynamic balancing. This is where there is a large portion of the control surface ahead of the hinge line so that the aerodynamic forces can reduce the loads required to move the surface. This is often seen on full sized aircraft and on some of our modlels. For example lots of fun fly designs have the rudders or elevators "turn the corner" at the tips of the surfaces so they have tip ears that extend to the leading edges. A few years back it was common to see this on model sailplanes.

For the most part our model servos have more than enough power to move the surfaces against the air loads related to the speeds we fly at. And one disadvantage of the balancing ears at the tips is that they stall almost immediatley and actually have LESS control effect than if the stab and elevator just had a simple hinge line so the whole surface could act as a proper variable camber surface.

On a fun fly it's not a big deal as there is MORE than enough power to go around. On the older sailplanes it was often found that modifying the design to eliminate the balance ear by joining it to the fin the rudder response was enhanced and less drag was also noticed.

Balancing ailerons
 

Thank You BMatthews for the input and insight. I am a wiser person now than I was 10 minutes ago!

Blue Skyy

Balancing ailerons
 

I was also wondering about a double beveled control surface versus a non-beveled that has the gap sealed. I have seen both philosophies used. What is your opinion of the two?

Balancing ailerons
 

To add- some counterweight on ailerons on our powered aerobats is always better than no counterweight .

The reason is an obvoius - the power pulses twist the plane and the ailerons always are the last thing to get the message
So they tend to remain still -which makes theSERVOS take upall the shock.
by counterweighting - the load on the servo is lessened.
Personally - I always counterweight ailerons - -my favorite is a tip balance -usually 1/4" wide and aprox 2" long- extending forward into the wing tip.
It is filled with lead.
the differece in balance is easily seen during engine run up - much les "ringing" in the ailerons.
One can argue the other effects - but the NET effect is less damage to the servo .
Response whilst flying is the same -
We really should be running interconnected - balanced ailerons but most of us are far too lazy to do this correctly .
On 40% areobats -I think it is a good idea.
Double bevel/single bevel - same thing - the total gap must be the same -
on our little planes hard to say if it makes any real difference - both are really lousy setups for a ful lscale plane .

Balancing ailerons
 

Both Mr. Hanson and Mr. Mathews gave good advice. I have found, especially on very large ailerons, mass balance is very important to take the strain off the servo gears when you make that inadvertant hard landing. I have stripped servo gears doing just that as the mass of the unbalanced ailerons overcame the strength of the gears.. This can also happen to the elevator servos if the elevator is not mass balanced and is very large.

Balancing ailerons
 

While I was at the Joe Nall Flyin and as I was taking pictures, which can be seen at (not selling anything, I just enjoy photography and airplanes) ......

http://webpages.charter.net/benlanterman/Index.html

and

http://public.fotki.com/benlanterman/

I noticed that the surfaces in the aerobatic airplanes were drooping. I have to admit total ignorance about the modern digital servo, I can't afford them. I asked the second guy I took a photo of if he could move the elevators to align with the horizontal tail, it lookes better on the picture. He said no and demonstrated that the weight of the tail and the low power off friction of the servo would cause them to droop to full deflection in a couple of seconds. I was impressed at the time with the friction free setup and only later remembered what the implications were.

I don't remember any of the pure scale big machines having the problem but then again my memory starts getting faulty with airplanes in the 500 to 1000 range.

As Dick and others mentioned, the very airplanes that could benefit the most seemed to be the worst offenders.

Balancing ailerons
 

OK, I will ask the obvious question. If a control surface weighs 4-6 ozs and with the linkage and control moment, the torque implied to the servo may be 10 ozin of force. Most digitals will put out over 100ozin of torque. Only 10% or less of the total working torque is used to offset the weight of the control surface. The holding torque is 2-3 times the working torque so what is the big need to balance the control surfaces????

...wait...wait...flame suit on.... OK, I am ready! :D

Balancing ailerons
 

No flames -but you missed the point.
the totalweight of the aileron means nothing -- it is the weight on a moment arm that causes the problem - I lighten ailerons as much as I can -- then add back weight -in a balance setup -
This reduces the servo load.
Here is a simple test.
hold a yardstick in you hand - by one end-- add a small lump of clay to the end close to your hand - - feel the weight - now move that lump to the extreme end of the sticjk - obviously the weight feels much heavier.
this is the problem (in example) of the model ailerons .
The weight increased by the moment arm caused some pretty nasty forces - when vibrating or moving quickly.

Balancing ailerons
 

Adding to what Dick said -

If you write out the equations for flutter, and I won't, there are mass terms, and moment arms of those masses that determine when the moment of inertias and when flutter will occur. Of course the speed is a factor as well as the flexibility of the surface and slop in the linkages.

Getting the center of mass over the hinge line removes the weight plus moment arm. The moment of inertia is still there but much reduced in magnitude.

Balancing ailerons
 

It only takes a moment to cause a real problem ---------

Hmm...
 

Interesting information.

I've had good results with balanced and unbalanced surfaces, as I'm sure we all have. Still, when I've done experiments with the "balance tabs" at the ends of the elevator and rudder, those surfaces did seem to be more effective. (I seal all my gaps anyway, so I can't really say if there was a difference in flutter prevention.)

What I'm most curious about at this point is: Why do many modern aircraft tend to use the aerodynamic balance tabs on the tail, but much less often on ailerons?

Balancing ailerons
 

ailerons on full scale TYPICALLY have ailerons interconnected unlike our LOUSY individual servo ailerron setups - so aileron loads are low.
On the elevators - the counterbalance will lessen the stick forces necessary to move them.
You NEVER want stick loads to be less than zero -but the use of spades etc- can bring aileron stick loads to zero -if that is what you want .
The 300 Extra for example is a thumb and finger load type force for ailerons-
On our models each aileron (NOT interconnected is constantly fighting the servo for position.
sometimes the ailerons win--
interconnected ailerons counter each other and a servo moving this setup sees small loads.
models went to individual servos years back - to gain more control and individual control per aileron - frankly most individual setups suck - Done right they require good balance and LOTS of holding power from the servos.

Balancing ailerons
 

Dick, I agree with everything you said except....

The weight of the ailerons are canceled as you said but the stick forces inflight also include an aerodynamic hinge moment about the aileron hinge. Connecting them across with linkage doubles the aerodynamic hinge moments.

Cancel inertial forces, double aerodynamic forces.

Balancing ailerons
 

yes - but as the gravedigger always said - don't forget the spade ---

Control surfaces.....
 

BlueSkyy,Bill,Ben,Dick,Et Al.....Very good commentary on balancing of surfaces.......want to know what weight the servo is holding up on a surface.....put a spring scale @ T/E edge and thats the weight a servo will have to hold up when powered up......thats a "general" method....one must also consider where the surface is driven from(Mechanical Advantage or disadvantage)...while a full scale usually has all linkages hidden our models many times have all linkages exposed which gives a better mech advantage by putting control horns on the bottom (side in case of rudder) to move the surfaces.....I fly all big warbirds and havent balanced any of the surfaces...only reason being is havent a need to do so....no problems have been encountered.....part of the answer might come in the fact as ones plane becomes airborne aerdynamic forces help neutralize some of the weight the surfaces have.....I use lots of washout about 2*-2 1/2* and use a slight droop 1/16" for my ailerons to "load" them up...just as full scale planes........I've found what causes the most trouble is sloppy drive systems.........thats the biggest culprit...... during routine maintenace I will replace any component thats showing signs of wear usually a control horn or servo arm.....Bill......

Balancing ailerons
 

Dick, true, throw on the aero spades and the forces drive to zero. I had neglected that.

Bill, The zero airspeed force that the surface feels is at the center of gravity of the surface. With no mass balance and with normal taper it probably is about 1/3 aft of the leading edge. If that distance corresponds to the length of the control horn located at the leading edge then it is close to the force that the servo sees. In full scale that moment plus the aero moments are totaled to give a "hinge moment" about the surface pivot. Then you can size the actuator. It doesn't matter where the hinge moment comes from, through a rotary actuator or a servo through a control hinge, it is the same magnitude of moment.

The measurement at the trailing edge is closer to 1/2 to 1/3 what the servo sees when sitting on the ground.