Three-Line Control Handle
Several construction articles for three-line CL models have featured bellcranks made from two Perfect or Fox bellcranks. None of these articles had much to say about what kind of handle to use with the homemade bellcrank. A commercial handle will work, but if you would like to try threeline flying with a minimum investment, consider the handle presented here. The first time I became aware of the possibility of a homemade three-line unit was years ago in an article by D. Chinery in an old Aeromodeller. The English unit was made of wood, and I felt that the trigger arm was positioned so it would hit your other fingers before much movement was obtained. I did not think this wooden unit would be durable enough to survive the rigors of Carrier flying.
Do We Really Understand Our Propellers
THE TITLE of this article stems from the fact that Eq. 1 is widely used to calculate either required propeller pitch or the speed a model will fly based on the nominal propeller pitch and inflight rpm. As a pitch equation, it identifies the correct nominal pitch for optimum efficiency for propellers with symmetrical airfoil. The airfoil used for the typical model aircraft propeller possesses considerable camber, however, and Eq. 1 does not contain sufficient information to deal with this fact. As a result, it tends to overstate required pitch by 25-35%.
Propeller Power and Efficiency
THE SELECT-A-PROP NOMOGRAPH was constructed using propeller thrust and power coefficients, CT and CP, calculated by Vortex Theory equations. Assumptions were a) 10% thick flat-bottom airfoil, b) constant nominal pitch along the blades, and c) blade chord/radius ratios as measured on a standard 10 × 6 Zinger. HP values assume equilibrium flight at J (V/nD) values equal to pitch/diameter (p/d). This is a viable condition for optimum efficiency for the airfoil camber considered.
Airfoils: Plotting the Four-Digit, Five-Digit, and 6-Series NACA
ALTHOUGH the plotting procedure is somewhat different from the ordinary, you should have no trouble following the instructions. So, a few words will be said about the development of these airfoils and how they relate to model application, bearing in mind that our activities generally go on in the realm of Reynolds numbers (RN) below one million. As seen in using the chart, all these sections are formed by combining thickness distribution ordinates (Yt) with mean line ordinates (Ym). When the mean line is straight, the resulting shape is called symmetrical. When the mean line is curved, or cambered, the resulting shapes are called by a variety of other names depending on the combination of thickness and camber used.
