120 psi launch, calculations on some screenshots are compared with simulator data



Some screen shots of a 120 pso launch from the 10L rocket. Video is made with a type CCD photo-camera, that also can record short video's with a frame rate of 10/sec. The screen shots shown here are consecutive frames, so they are taken with a 0.1 second time interval.

before release just released almost end of tube phase water thrust phase with laminar flow and gone!!, look for the little cloud at the end of water thrust phase
The idea is that with the known size of the rocket and the known time interval between the frames, it must be possible to calculate the height, speed and acceleration of the rocket. Then these figures are compared with the results from rocketsim. If you look closely to the last frame, then you see a cloud of expelled water, this cloud is formed at the end of the water thrust phase when almost no water is left in the rocket and the pressurized air breaks through the layer of the remaining water. The laminar flow that formed the pillar of water (below the cloud) changes into a turbulent flow with a mixture of water and air.



The results of the calculations on screen shots are shown in this table
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The height on screen value, is the measured distance bottom screen to bottom rocket.
The multiplier column, is calculated out of the known size of the rocket (190 cm) divided by the top to bottom distance from the rocket on the screen. In the top part of the picture the rocket is further away from the camera, looks smaller so for a height calculation a larger multiplier must be used.
Keep in mind that the frames from the camera are not synchronized with the actual moment of launch.
The calculated values from rocketsim are shown in the graph:
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The calculated acceleration during tube phase compares quite nice with the simulated one. Within tolerances that must be expected doing measurements and calculations in this non exact way.

Then on the transition from water thrust to air blow down phase, rocketsim predicts this on 6.2 meter. The simulator calculates with a clean transition from water- to air-exhaust. In practice this will not be the case, the last part of water thrust will be a mixture of air and water that is expelled. So the cloud of water-air must be below the simulated water thrust and air blown down transition.
Screen height measurements on the cloud gives a height of 5.7 meter for the bottom of the cloud.
This also seems to compare reasonably with rocketsim data.