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Some of the difficulties remaining are :
(a) Differentiation between background and flame light.
(b) Obtaining the largest possible image per frame with existing lenses.
(c) The prevention of over or underexposure, usually the former.
(d) Adaptation of the optical system of the camera to that of the optical schlieren system.
(e) Coordinating the optical speeds of the schlieren system with that of the camera and film.
(f) Minimizing vibration and optical misalignment in an area subject to the former.
(g) Protection against corrosive fumes and high temperatures, etc.
Studies were also made of the fluidflow behavior and mixing rates of the spray of the rocket motor injector. In general, it can be said that propellant entry sequences and mixing rates were determined with dyed water (yellow and blue) and elaborate solenoid camera starting devices. These latter were necessary since the fluid was injected into the atmosphere at 1 50 fps.4
Summary
Properly protected, the rota ting-prism type cameras have proved to be excellent recording mediums for short periods during rocket motor testing.
However, it has seemed desirable that cameras of larger film capacity and longer running times be designed for this particular application. For example, it would be more advantageous to have a 20-sec capacity.
It, is felt that only a beginning has been made and that many more applications can be found for the high-speed camera in rocket motor research and development.
The authors acknowledge the assistance of Mr. C. Kurland in some of this work and the cooperation of various members of the Bell Aircraft Corporation Rocket section.
References
1. D. R. Bellman and J. C. Humphrey, "Photographic study of combustion in a rocket engine," NACA Report RM No. E8F01, June 1948.
2. K. Berman and S. E. Logan, "Combustion studies with a rocket motor having a full-length observation window," J. Am. Rocket Soc., 22, No. 2: 78-85, 103, Mar.Apr. 1952.
3. J. H. Altseimer, "Photographic techniques applied to combustion studies — two-dimensional transparent thrust chamber," J. Am. Rocket Soc., 22, No. 2: 86-91,Mar.-Apr. 1952.
4. Kurt R. Stehling, "Injector spray and hydraulic factors in rocket motor analysis," J. Am. Rocket Soc., 22, No. 3: 132-138, MayJune 1952.
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May 1953 Journal of the SMPTE Vol. 60