Let's Talk About The CG
MOST airplane factories have a huge room full of engineers who sit at big drafting tables designing landing gears, wing ribs, engine mounts, fuselage bulkheads, etc., etc. Periodically, usually every day, each designer is approached by one of many "Weights Engineers" whose job it is to keep track of how much things weigh and where they go. Weights engineers seem to have a built-in resistance to adding anything or making changes which will add weight. They are also sort of sneaky. If a designer wants to add a bracket to support an autopilot, let's say, and estimates it to weigh 1.5 pounds, the Weights Engineer will probably convince him that 2 pounds is a more realistic figure. If the designer later finds that he can do without the item, the Weights Engineer will usually begrudgingly give him back only a pound and a half.
Let's Talk About Airplane Design
AFTER A YEAR OR SO of building and flying models, many modelers begin to develop a healthy curiosity about the principles that underlie successful designs. Unfortunately, clear, accurate, and digestible information about aerodynamics and the many other aspects of airplane design is difficult to find. For example I have several books on the subject, yet only half of them are really useful. The others are written in an esoteric fashion by prima donnas who seem to be more interested in displaying their facility with differential equations than in down-to-earth discussions that might enlighten the reader. I believe that there is no idea in human knowledge that cannot be explained so that a bright 12-year-old can understand it if presented in a simple, forthright manner.
Let's Talk About: Airplane Design
PROLOGUE: In the October issue my article consisted of 20 questions on airplane design. As it turns out, I only got a grade of 90%. I missed the one on P-factor, and as a result, I gave bad advice about propeller swing on twin-engine designs. During and after WW II (1939-1952) I was a preliminary design engineer at Convair. In those days P-factor was unheard of. When, many years later, I read a brief description about it in a flight manual, I simply dismissed it as a simplistic explanation of the effects of torque. It did not appear in any aerodynamic texts that I was aware of, nor had any of my old cohorts heard of it (probably because, in those days, we were designing large jet-powered aircraft where P-factor was not a consideration).
Let's Talk About: Airplane Design
IN THE APRIL 1980 issue of MA, in an article entitled "Let's Talk About the CG," we discussed the subject of Static Longitudinal Stability. Whether one flies models or full-size aircraft, an understanding of this subject is essential for satisfactory performance-and safety, as well. An unstable airplane is difficult, if not impossible, to control. Thus, it poses a threat to bystanders in the case of models and can be life-threatening to the pilot of a full-size plane.
Let's Talk About Airplane Design
IT WAS IN 1978 when I first submitted an article to Model Aviation entitled, "About the Size of It." Presented was an exercise in dimensional analysis that explained how things such as weight, speed, power, etc., vary with size or scale. I tried to make the material understandable to a "bright 12-year-old," and while it was well-received by readers, the letters I received were, for the most part, from modelers in their 50s and 60s, people like myself who had rekindled a youthful interest in modeling. No 12-year-olds, bright or otherwise, seemed to be reading the stuff. At least, they didn't correspond. I think this is too bad because there is something spell-binding about model airplanes that seems to stay with one all his life.
