I kept a log on one airplane many years ago. I kept the log for about 6 months which is how long I owned the airplane. I bought the airplane second hand and it needed some work to repair mistakes made during its initial assembly. It was a Sterling Cub, a .15 size. Originally the log was intended to help diagnose some of its many problems. But I included the flight time. Long story made short, after selling the airplane I was able to calculate the cost per flight while I owned it. I forget how much it was, its been nearly 30 years. But it was something like 20 cents including fuel costs. It was an interesting expereiment.

I still keep notes on new airplanes that are going through a difficult and involved "debugging" phase. When I get home, I sit down and write down how the plane behaves. I write how the controls feel. How the throttle response is. I generally concentrate on the area giving me difficulty. I write about the effects of changes that I have made concerning the "bug" I am working on. And I write down what I think is the likely cause and the likely solution. This is handy as I might not get around to actually working on the plane again for a week or more. These notes written while the experience is still fresh in my mind are very helpful. But once I have the plane flying the way I like, and all systems are working properly, I generally discontinue any form of note keeping or log.

Everyone's mind works a little differently, I suppose. I for one can rarely imagine the most simple and eloquant solution to a problem at first glance. I prefer to think about things for a while, a day , or even several days, until the best of many possible solutions is chosen. Having some data recorded that can be referenced is priceless.