the same time that ballast is normally required in flight. This system simulates the effect of rising and falling in the atmosphere and indicates the effectiveness of the controls which have been applied.
In order to simulate flight, it is necessary that three conditions be maintained within the system. The first is that a leak of air into the bell jar is permitted at a rate of pressure increase which has been observed during balloon descent. A large lag chamber is connected into the bell jar to supply the second condition which is a delay similar to that inherent in the control action on an actual balloon flight. It is necessary to properly adjust the volume of such a lag chamber to obtain the desired magnitude of control action.
A third requirement is that the response of the vacuum pump must correspond to that response which has been observed when a balloon system drops ballast. In order to measure this, the control mechanism has been allowed not only to switch the vacuum pump on and off but also to actuate the standard ballast-flow equipment. This system may be adjusted so that the amount of pressure change which a single period of pumping produces accurately represents the amount of ballast thrown off during flight.
The barogram shown in Figure 18 is an example of such a test. On this test the rate-of-ascent ballast switch was added to the displacement switch after the latter had operated for a period of six hours. The combination of the two is seen to have effected a reduction in
Flight Similitude Record Of Pressure
A- Displacement Switch Operating.
B- Displ. & Rate Of Ascent Switches Operating.
Figure 18. Sample barograph record.