Does any one balance there stabs or is it a was of time . I check mine out with weight and the would take 97.5 grams of weight as im building a skymaster f18f with out instruction why dont the manufactors write them or if they do they are so so old

If SM thought it would be important to counter-balance with nearly 3.5 oz they would do it at the factory, or instruct customers to add it on via an airworthiness directive.
Just use the servo size other SM F-18 builders use.

BTW, a search showed nothing of elevator counter-balancing.

Yeah Scott Im pretty sure they are balanced for in flight loads.

Scott, the problem with balancing them is that whatever weight you add to them you have to add the same amount up front to balance the cg.
Load is only on the stabs at standstill, at flying speeds aerodynamic pressure relieves the inbalance and therefore the loads on the servo's.
Gary.

No it doesn't. For a symmetrical section pivoted at its aerodynamic centre, the moment coefficient of pitching is zero so there is no aerodynamic force making the stabs go level into the airflow.
Harry

taxi on hard asphalt or hard landings will hit big time your servo gears

my 2c

WHAT WILL HIT??????????ARE YOU SAYING BY ADDING WEIGHT ON THE STABS THEY WILL HIT THE GROUND ON A HARD LANDING AT SLOW AIR SPEED

i say that when stabs are not mass balanced ( T.E. heavy)

during hard landings or taxi over holes on the runway

create force that will stress servo gears case and servo mount.

..sorry for the poor english

Full scale aircraft balance all their flying surfaces to mimimize control input, improve control response and to avoid flutter. We usually get away with not balancing our surfaces because of the tremendous torque of our servos and the relatively slower speeds we fly.

But, we have all seen/heard flutter on high speed passes which in many cases may have been prevented if the offending control surface had been balanced. Most manufactures take this into account, either by calculation or trial and error, and will adjust their designs accordingly. I know BV adds lead to the leading edge of the stabs on their F-4 and the Cook Firebird balances all the flying surfaces. If you follow the manufactures recommendations and stay within the design speed envelope, you should be OK.

Craig

Hi,

I know we've been here before (many times), and I don't mean to argue, but I'm not aware of any fullsize production aircraft that have full-flying stabs that are balanced on the pivot. Conversely, I can think of many (every) full-size aircraft with full-flying stabs that are tail-heavy and droop to the rear when powered down. In fact, most full-size aircraft with full-flying stabs do just what the gentleman stated above; that is having stabs that aerodynamically balance at a certain airspeed.

I think people are talking cross purposes here. Aerodynamic balance and Mass balance are there for different reasons and are achieved by different methods. Aerodynamic balancing is there to ease control loading and mass balancing is to reduce flutter. Altering one doesn't necessarily affect the other.

When talking about balance, you have to be specific about what type of balance you mean.

I didn't say they were balanced "on the pivot", just that they were balanced. The aerodynamics of stabilator control is complex and changes significantly as you progress from light aircraft with mechanical antiservo tabs and balance weights to supersonic jets with computer "fly-by-wire" and "irreversible" hydraulic power cylinder control. I can assure you "every" full-size aircraft has taken stab balance into account.

I'll stand by my comment that for our jets, following the manufacturers guidelines is the best course of action.

I think that leads nicely back to the original question. What is Skymaster's recommendation?

Slick,

Understood. Usually, when talking about balancing, most people seem to be referring to the pivot point. I'm sure if you polled the average RC guy on here and asked, "What's mass-balancing a stab?", they'd probably answer "On the pivot." If you read the volumes of 'discussion' on this topic on RCU over the years, you'll understand how I arrived at that assumption. However, I stand corrected, thanks.

One thing, though; I doubt very seriously that many of the ARF manufacturers have taken a moment's consideration of the types of design variables you're talking about. I doubt very highly that there's an aeronautical engineer giving input on stab airfoil vs balance point vs pivot point, etc.

Agreed. Most rely on the "trial and error" method I mentioned above. They start with a reasonable design based upon experience and past success and then if something has a problem or fails during intitial fight testing, it's changed/fixed. Hopefully, but not always, this occurs before retail distribution.

Take to jeff at skymaster and he said to balance them he also balances his on is f16

Two words : Static balance and dynamic balance ! I read many interesting comments around the subject but no one did mentioned that static balance obtained with some lead in the stab will bring some benefit to the dynamic balance : it will dampen the risk of flutter at any speed... this is my personal experience but I hate lead .

All I would like to know is... Does anyone here have a problem or reason not to balance the stabs???? ( Except having to add some nose weight ). I personally have balanced all my Flying Stabs from my first byron F-16, to all three Yellow F-18's that we built side by side.. Most of the Models in question have a very long nose, a little weight will go a long way... in MHO, Balance the damn stabs and be done with it... No more would of, could of, should of .. !!!


My .2 cent's.....

Danno

Ah, I think just leave 'em alone.

I've flown HUNDREDS of flights on jets without balanced stabs and YES on the SM f-18F as well.

What's the enemy of good? Better.

Raf

Hi,

Other than the designer/manufacturer (who happens to hold a Ph.D. in aeronautical engineering) recommending it not be done? Since the advent of way-overkill servos, it's not such a big deal anymore. So, if it gives you peace-of-mind, then do it. Again, I can only point out that you'd have a very hard time finding any full-size aircraft in production that have full-flying stabs balanced on the pivot. Is that just coincidental?

I agree it is the norm to ignore balancing control surfaces on models due to the ability to overpower the surface with today’s servos however, every control surface on every military and commercial aircraft is weightedbalanced. The balance point may not be as clearly defined however static and dynamic loads are calculated and accounted for; even the weight of paint is accounted for. When looking at a control surface sitting static it is easy to assume that it is not balanced however things are not always as they appear.
I am NOT telling you what to do with your model as I will not be accountable for the results however the only effects of flying a model with a balanced control surface (less than Mach) is lighter load on the servo.
Now can anyone point out a time they incurred flutter with a properly installed, rigged, and balanced control surface?


(http://www.allstar.fiu.edu/aerojava/axes32.htm)

BALANCED CONTROLS - Level 3



Controls are sometimes dynamically balanced to assist the pilot to move them. By having some of the control surface in front of the hinge, the air striking the forward portion helps to move the control surface in the required direction. The design also helps to counteract adverse yaw when used in aileron design.

Control surfaces are sometimes balanced by fitting a mass (usually of lead) of streamline shape in front of the hinge of the control surface. This is called mass balance and is incorporated to prevent flutter of the control surface, which is liable to occur at high speeds.

The exact distribution of weight on a control surface is very important. For this reason, when a control surface is repainted, repaired or component parts replaced, it is essential to check for proper balance and have it rebalanced if necessary. To do this, the control surface is removed, placed in a jig and the position of the center of gravity checked against the manufacturer's specifications. Without any airflow over the control surface, it must balance about its specified C.G. This is known as static balance. For example, the aileron of the Bonanza is designed for a static nose heavy balance of 0.2 inch pounds. The C.G. of the aileron is forward of the hinge centerline causing the control surface to be nose heavy.

Many lines to explain the same things I did in very few words ....

Thank you

Bill,

I think we're only talking about balancing on the pivot. I doubt anyone who's discussing balancing their stabs is thinking anything other than on the pivot. Those military planes you mentioned are a good example of what I'm talking about. Of course they're balanced, but it's not as simplistic as we think (as you have pointed out). They're usually aerodynamicly balanced for average flight loads. Whether it be a jet or a prop job, I'm still not aware of any production aircraft equipped with full-flying stabs that are balanced on the pivot...

The pivot location is considered in the design along with airfoil shape and intended flight envelope. The balance has to be capable of resisting flutter at low speeds as well as high subsonic and supersonic. It is necessary to start with the balance on the pivot and adjust as necessary to compensate for shock waves, airstream disruption from the wing/ fuselage and max intended deflections. If you moved the flight control of one of those jets sitting on the flight ramp (with no hydraulic preload) it would surprise you how little force is necessary to move them. An unbalanced surface only adds to the necessary force to operate it and “G” loads only exaggerate the condition.