Little boys and men like toys. Especially when they are expensive, luxurious, and unnecessary. Sometimes however such toys may serve as clever tools for applications they’ve never been designed for. Many years ago I bought a VHS video camera and tried to save on tape everything  
    which got in front of my lens. Capturing complete flights may serve as funny memories, and showing the pilots doing their dance in the circle in more or less gracious motion can be pleasant entertainment. Oh, by the way, not having seen and watched Billy Werwage presenting his performance in the center of the circle means not having fully understood one of the essential aspects of Control Line Aerobatics! (sorry, seems I’ve got carried away).
Watching the movies on TV created the idea that I could easily detect all errors on the screen, eliminate them in practice flights, make perfect contest flights - and easily win lots of trophies. Well, as things turned out, it doesn’t work that way. A camera doesn’t see a flight the same way a pilot or a judge does. I quickly became aware that a flight movie cannot serve as a useful tool for training. Judging flights respectively manoeuvres on the TV screen  
in my opinion is impractical, if not impossible ( I’ll not dig any deeper into this topic - this would grossly exceed the scope of this story).
However I found another, quite interesting application for my movies. I had discovered the “single frame advance” function. With this tool we can exactly watch the flight path of the airplane, cut into little pieces. What I did then with the (expensive) VHS camera, can be done today with almost any of these modern compact cameras using video mode. Many of them have this feature ( on my camera I found it just by chance when pushing the wrong button ). With a picture frequency of around 25 to 30 frames per second, they were the perfect tool for my intentions. I wanted to find out how long does it take to fly a manoeuvre, what happens during (for example) a loop, and what time does it take to fly a corner! This is what I did:
At first I shot many sequences of flights of different pilots, just to gain some experience about how to film the manoeuvres; how to follow the airplane and not let it leave the picture frame, how to get a large image of the airplane (using a long lens), and how to get some easily recognizable background on the picture ( more about that later). Please note: I did NOT try to show the quality of a given manoeuvre. If you try to follow the flight path of the
    airplane with your camera, the movie doesn’t show the manoeuvre shape because any background reference is lost. I was not interested in viewing precision of manoeuvre shapes. After several attempts, I decided to shoot flights only which were made with popular line length: close to the maximum FAI number. Shorter lines give different results which have to be considered when doing comparisons. I have used several movies to find out average figures which are reported here.
I started by watching the flights several times, now on the monitor screen. First I tried to find out the exact beginning and end of a manoeuvre, say a Square Loop ( this is one reason I had to have a distinct background in the picture). After having found a distinct point, I timed the duration of this manoeuvre from beginning to end with my stopwatch. The average value for many many movies was 3.5 seconds for an Inside Square Loop. (see Fig. 1)      
For what I wanted to do I needed a video software. A wide choice of such programs is available.Since I was interested in the single frame advance function only, I got “Virtual Dub” which is a very basic software and it’s free. Now this advance tool comes into play. It is necessary when trying to find that exact moment when the airplane leaves its horizontal position and starts to fly the corner. This is also the point where the manoeuvre starts and ends.
Using that single frame advance function I “clicked” each picture, and started counting with number 0 at the beginning of the manoeuvre, which is the last picture with the airplane in horizontal attitude. As soon as the airplane got into vertical position the first time, I wrote down the figure I had counted so far. Then I continued counting the vertical path until the airplane began to turn into horizontal inverted flight ( for the top of the Inside Square Loop). Again I wrote down this number (= last picture with airplane vertical). The same game continues until the first picture with the airplane in horizontal inverted position.
And it is continued until the end of the manoeuvre. It’s exactly the point where the airplane starts its second manoeuvre, or where I started counting for the first time; that’s why we need the background! What we have now is a list of numbers. It helps to have a little sketch prepared. I had made a simple drawing of a Square Loop with all points for beginnings and ends of corners and straights, and the numbers were written down at their respective points. (Fig 2)
After counting all frames, we’ve got some numbers for manoeuvre parts and one final number. These numbers don’t have a meaning in itself, because it depends on the frame-per-second feature of your camera. On my Fuji camera this is 30, so all numbers in this article are based on this. For other cameras these numbers may be different, but that doesn’t matter - the outcome will be the same. Let me call these numbers “time units. Now we can calculate the number of time units for each part of the manoeuvre. (Fig 3)
Since we now know the time needed to do the manoeuvre AND we know the number of time units for each part of the manoeuvre - we can easily calculate the duration in seconds for whatever part of the manoeuvre we want !! We can find out the time for the first corner, the vertical climb, the second corner, inverted top, third corner - etc. etc. We can find out the difference between first and following corners, between climbs and dives, tops and bottoms. This may give an indication about our flying style, flying skills, and maybe engine power. (Fig 4)
As a general note - whatever figures we may arrive at - I think this exercise should give an interesting insight into our activity, what we do, and how we do it. Just imagine: at a certain instant we have to move our wrist for a precise amount of degrees, hold this position for a precise duration of time, at the right moment return to exactly neutral, hold neutral until a certain spot, quickly apply wrist movement for the next corner - - -etc. etc. And all this within FRACTIONS of a second !! To say I was staggered with the results is an understatement. My own findings can give rough information only. If you wish you can find out concrete facts for yourself. I’d like to emphasize such findings when it comes to discussions about what we crazy control line flyers are doing.    
While my pocket calculator was hot, it lead me to another idea. Suppose the airplane in question flies 5,2 lap times on 70 feet lines. That’s 21,33 Meters in metrical terms, very close to the 21,5 m figure given in FAI rules ( handle to thrust line). Let me calculate with this number. At this radius one lap will be 138 meter, and in 1 second the airplane will travel 26,5 meter (that’s about 87 feet for you Imperial guys). Now imagine: after diving down in a Square manoeuvre - especially in the Wingover ! - the pilot has to perform a sharp corner. He has to apply that flash like wrist jerk at exactly the right moment. After that sharp corner he has to pull out at exactly 1,5 meter = 5 feet. Without any whobbles, mind you ! What is the margin of error at this altitude? Easy to calculate:
One second times 1,5 meters divided by 26,5 meters = 0,0566037 second !
To put it quite simply: to twist the wrist five hundredth of a second too late and it’s back to the building board !
Now, of course, not all pilots are flying at this speed. Some experts are able to fly slower lap times. But many pilots tend to fly faster. And in a dive the speed is probably higher anyway. So you can figure out for yourself what chances of surviving you will have. In any case, our sport is fully on par with some of the more popular sports which have the same challenge of exactly meeting a finite limit as closely as possible.
I’m not ready, yet. Watching these videos brought up another idea. This advance frame facility got me thinking about the answer to a question which has bothered stunt flyers for many years. We all know that not so many ! pilots actually fly that mythical five-feet radius corner in Square manoeuvres. Apart from the fact that probably no wing would ever stand the flight loads, I suppose that human reaction wouldn’t allow such tight corners to be flown. Many tests have been made to show what typical - and not so typical - stunt airplanes are capable of, flying by night with light equipped airplanes. Photos were made with the camera in the “time” or “B” mode to show the actual flight path. In all cases the corner radius was much larger than the rule book corner = 5 feet. Since I already had the “pictures”, I tried to find out exact numbers.
Advancing slowly through the video of a model flying a Square Loop, I froze it at the picture showing the airplane in its last moment of vertical dive before the corner, and a second picture showing the moment it achieved horizontal flight. With my VHS system I photographed both pictures from the TV screen and printed them on paper.  
When the film is made with a modern camcorder, the files can be viewed on the computer monitor. With a suitable software it’s easy to select the respective pictures, save them, and use for further applications. The next steps depend on what system is used, but it’s basically the same procedure ( printed photos or software assisted on the monitor).
We need those two pictures: the model in vertical dive, at the moment before beginning the pull out; and the model in the first position of horizontal flight. In both pictures we have the same background. This is where we benefit from some distinct picture background. I just CUT both pictures in half at exactly the same “separation line”; means: a line across the background. Having some distinct details like buildings, trees, or clouds helps to make this cut precisely. It doesn’t matter whether this is done with a picture enhancing software on the computer or with two printed pictures. Basically it’s the same method. Now these two “half pictures” are combined into one picture, showing the airplane twice, in two positions: vertical and horizontal. It goes without saying that this work should be done as precisely as possible.  
Now comes the enlightening moment. On this newly created “double” picture we can draw lines which should run at right angles to the airplane, preferably through the (estimated) point of Center of Gravity. One vertical line (A) and one horizontal line(B). Where both lines cross, this is the center of the corner ! By knowing the length of the airplane (C), we can now easily calculate the corner radius.
Of course I know that this calculation can never be 100% correct. The quality of the “picture” depends strongly on whether the photographer can hold the camera steadily, on lens quality, and on resolution of the camera chip. Also the model is shown very small only. Sometimes there’s only a “blur” which doesn’t help much. A large number of “movies” is required to get some reasonable results. But at least we can get a rough idea about what we do and what our airplane does.
  This combination of two pictures will often show two different corner radii ( the horizontal reference line is usually longer than the vertical one). This is not by accident. Pilots very often fly corners that way. They try to enter the corner softly in order to find the correct pull out level. Once in the corner, they try to adjust for correct height, thereby adjusting the elevator deflection; in most cases tightening the radius. As every pilot will confirm, this job is very difficult to perform in the available time period as explained above. But, well - that’s what we’ve chosen to do ! If it was easy it wasn’t worth doing.
Now all I have to do is to find an experienced photographer to film my flights, evaluate hundreds of corners, and calculate my “personal radius”. This should finally help me to become a good stunt pilot.