Hi Guys Some of the stuff I have been reading here is really worrying - particularly after we had some input from Phil (Oz) - with particular reference to weight distribution and G loading requirements.
This may be one good example of leaving well alone unless you know what you are talking about. It is interesting that the pilots that have experienced flutter become very preoccupied with wanting tell everyone that will listen. (at least those that lived to talk about it). Fortunately the irreplaceable Tony Bingelis did both (experience and survive flutter) I wish I could find the URL to the original articles by Mr. Bingelis who (in my opinion) does know what he is talking about. In the interim, this extract from one of two articles (by Tony) that I have on the topic. I do not remember any copyright restrictions - I tend to look for and respect such warnings. I would not be surprised if these (and more) are in the KRnet archives somewhere - failing which, I am happy to email both to anyone interested - let me have your address. MS Word format would mean you get to see his drawings as well (not many). I selected this particular section because of the recent flurry of discussion on G loading of counter-weights. Steve J How to Mass Balance Control Surfaces Sport Aviation- 08/79 By Tony Bingelis (Extract Only - Not the Complete Article) Distribution of Mass Balance Concentrating a single externally mounted mass balance weight in one location to balance the control surface may not be ideal but because of limited space available inside the structure, it is usually more convenient to do so. However, whenever possible, distribute the weight uniformly along the span of the control surface. If the weights must be separate and attached in two or more locations along the span, they should be positioned, if possible, on either side of hinges to reduce flexing and torsional stresses on the structure. A method for obtaining good distribution of balance is through the installation of a solid steel rod along the entire length of the leading edge or perhaps you could install a steel tube instead. Although the steel tube would be lighter than a steel rod, its weight could be increased to exceed that of the solid rod by pouring in molten lead to obtain whatever additional weight is needed. You may have to pre-heat the tube to achieve this objective. (Naturally, you will remember to plug the open end?) Not only must balance weights be attached solidly, they must also be capable of withstanding high G loads. How high's high? Well, in a yesteryear study conducted at the NASA Langley Research Center by Arthur A. Regier (Flutter of Control Surfaces and Tabs), it was determined that the balance weights should be capable of withstanding 36 G's normal to the surface. However, more recently (1979), the FAA, in its AC23.629-1 "Means of Compliance with FAR 23.629, Flutter," states that all balance weight supporting structure should be designed for a limit static load of 24 G's normal to a plane containing the hinge and the weight and 12 G's within that plane parallel with the hinge. FAA also points out that proof of these criteria can be accomplished by simple static tests of the control surface mounted in a jig. That's really not too much as a 2 lb. weight need only be static tested to 48 lbs. to equal the requirement imposed on store bought aircraft. Now that you have all this under control, take care that the weights will not work loose under prolonged use and vibration or all that G load capability will be for naught. A Summary On Balancing Controls Many aircraft currently flying do not have balanced ailerons or elevators or rudders. These designs, however, have proven to be inherently free from flutter problems for the most part. So, I can't say with any conviction that the designer intended for them to be balanced or that they need it. However, and of this you may be sure, regardless of whether your plans require mass balancing of one or more control surfaces, you will never be sure they are flutter-free until they have been tested in flight - for that tendency
