westerman

The Ultra Stick line has a balanced rudder with a non-balanced elevator. Most all of the 3D aircraft have a balanced elevator.





For high speed aerobatics is a balanced elevator too much drag?

hugger-4641

My Feedback: (6)

Not sure what you consider  "high speed" aerobatics, but  most 3d planes are not designed for "high speed" performance. For that you want a turbine or a pattern plane.  Balanced elevators are  about increasing control surface area to give more authority at lower speeds, thus they are not really needed on a pattern plane or jet that has plenty of air moving over the control surfaces to induce any desired maneuver.

hugger-4641

My Feedback: (6)

Another advantage of a balanced elevator is it provides a little assistance to the servo.  Since the elevators are very large on 3d planes compared to a similar sized sport plane, the servos are under more load, so a little assistance from a balanced elevator can help reduce the load on the servo. Again, this is not usually an issue on a pattern plane since the control surfaces are smaller.

westerman

Hi Jerry

This is what I call "high speed" aerobatics.

[youtube]http://www.youtube.com/watch?v=25GK6s91pzI[/youtube]

[youtube]http://www.youtube.com/watch?v=xHXBho2L1yo[/youtube]

[youtube]http://www.youtube.com/watch?v=_C3Rgk7zeuM[/youtube]

hugger-4641

My Feedback: (6)

Ok, LOL. Yeah I've watched some of Don's videos and a few of his protege's as well. Those are great skills to aspire to, I'm not anywhere near them myself. But as you can see, the Flying Machine also does not have a balanced elevator. The vertical stab and rudder have less surface area than the horizontal stabs and elevators, so a balanced rudder helps give more control surface area and rudder authority that is not really needed by the elvators. Also, when the rudder acts on the plane, the force is on plane with the wings. This is why the plane can "slip" sideways and still fly straight and level with out tearing the rudder off. However, the elevator's induced force is perpendicular to the plane of the wings. For lack of a better analogy on my part, the elevator is "fighting" the wing. Consequently, if you were to put counter balanced elevators on the Flying Machine, Don would probably have them snapped off in the first loop unless the whole business was really beefed up. I'm no aerospace engineer, so somebody may chime in and give a better explaination, but I hope this helps.

Rodney

There are two types of balance, aerodynamic and static. What you seem to be discussing is aerodynamic balance although it is easy to also have a good static balance by weighting the portion forward of the hinge line enough to balance out the weight aft of the hinge line. The static balance helps to negate the effect of G forces while the aerodynamic balance allows a servo to have more effect for each unit of force it applies to the moveable surface. Just be careful that the area ahead of the hinge line does not exceed about 20% of the area aft of the hinge line else the surface will tend to hunt (swing or oscillate about the neutral position) to the point where it can actually become uncontrollable. Properly set up, you can reliably use very weak servos on a fairly large model when required.

karolh

Swing or oscillate around the neutral point = Flutter, which can eat a model quite quickly.

MTK

Rodney, I don't think you meant it to sound the way it came across......

Please be careful about advice regarding servo power. Any control surface requires adequate power (capacity) for the largest aerodynamic load it is bound to see in normal flying. It doesn't matter if the surface is perfectly balanced, both statically and aerodynamically....when it's deflected during normal flight speed, it sees load and the servo has to be strong enough to overcome that and hold it. The larger the model the larger the load, the larger the servo capacity needed......

Certainly servo power must be much higher if the surfaces are not balanced.

Weak servos should be reserved forback yard foamies

Rodney

In response to MTK, no I am not wrong on that you can use smaller servos. Years back (in the late 50's and 60's) you did not have the higher powered servos as you do today and we flew 1/4 scale by making sure we could handle the large surfaces. Both static and aerodynamic design allowed this with no problems. We also occasionally used boost tabs to do the same thing. I still use boost tabs where lots of aerodynamic force is required, especially on the rudder.
And, in response to karolh, hunting is NOT the same as flutter. It is where just a slight movement away from neutral will let the surface ahead of the hinge line try to overpower the servo and, if on the elevator, causes the plane to gallop through the air, not with the surface in sustained self oscillation of flutter and occurs only when the surfaces are in the neutral position. The same problem with hunting can happen with boost tabs if the boost tab area gets much more than 20% of the moveable surface.

da Rock

Keep in mind that the aerodynamic properties of the balance part of a surface is significantly different from the rest of that surface.

What we might consider the normal part of a rudder acts in conjunction with the vertical stabilizer forward of it. In combination the two make up a changeable airfoil that has quite different properties than something like a stabilator would have. Consider that the balance part of that rudder acts exactly like a stabilator does. And how do stabilators differ from the way normal horizontal tails do?

Stabilators provide their most efficient work at much less AOA than the usual horizontal tail does. The usual hinged surfaces create cambered airfoils as they work. Their resultant shape is a airfoil with much more AOA to work with before stalling. The normal elev/stab tail has a lot more fuselage pitch to play in before it stalls. Stick a stabilator on the outside of the elevator of that pair, and what does that stabilator experience? Yup, that tail winds up with two entirely different shapes tied to each other, and one of them is being driven through a range of angles it's not comfortable with.

Keep in mind that the aero-balance section of a rudder is going to see a lot of AOAs that are beyond it's stall angle. Just having that over-driven part of the rudder being driven into a stall is going to mean there are times when the plane is dragging around a force that's not there with the usual, cleaner stab/rudder. (pun intended)

The aero-balanced rudder probably has more applications than the aero-balanced elevator. It's probable the aero-balanced elevator and the aero-balanced ailerons suit the same applications. But it's probable the proper use of aero-balanced surfaces has to consider the design envelope of the airplane.

Do you know of any WWII fighters that had aero-balanced surfaces?

pimmnz

Spitfire, for one...the initial flights showed that the rudder was overbalanced, and the area was reduced on production versions...109, like the Spit has rudder and elevator balances...both for static and aerodynamic...190, has rudder and elevator aero and static balances...You are likely to find that many of the WW2 airplanes used some sort of aero balance to reduce pilot loads.
Evan, WB #12.

pimmnz

The caution is, of course, to separate what the balance is for...reducing the aerodynamic load...or for statically balancing the surface about the hinge line for flutter reduction. Models don't really need the load balance, but some do suffer the flutter thing.
Evan, WB #12.

da Rock

I was hoping someone would mention a fighter like the Spit. It also had obvious tabs on the elevators as well.

It's interesting to see how those tabs evolved as newer designs came out and as speeds went up. There are fewer tabs that reach the leading edge of the fin. Full scale design seems to have appreciated the value of putting the balance weight farther forward and used the structure to give that weight more moment.

Notice the rudder's tab on the P51 for example.

And notice what the Corsair had on all it's tail surfaces 'cutting the air' for the tabs.

rmh

balancing for flutter problems -done right works very well.
now i am working on several models using "gyros" (accelerometers) and high gain causes some rapid responses which I feel can be resolved with a change in surface balance - so -I am changing th setup on two ofth models - these are aerobatic types with very large surfaces .

A shift in gain wil also change thins BUT i will see if relative balance also works as a fix.

Flypaper 2

I like to use the booster tabs on some of my planes, especially the aerobatic, 3D if you will. Why not make use of them.for models. Also playing with flying stabs. The smaller foamy are good to experiment with but I do have booster tabs on the ailerons and rudder on a 1/4 scale Corby Starlett. The wing shown below. This Zoombi has a booster tab on the oversized rudder where, before I had a hard time getting around the bottom of a knifedge loop. Now it's no problem at all. Flying stab shown is on a Flash 3D. Will do snaprolls in its own length. I just slow down first The Corsair had booster tabs on the right side elevator and aileron. One reason it was fairly agile for its size.