3638. Buoyancy Effects on Mass Properties Analysis


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J G Montgomery: 3638. Buoyancy Effects on Mass Properties Analysis. 2015.



This research project is designed to determine the effect of buoyancy on the weight of a specimen during final mass properties testing. The hypothesis is that the mass of the air displaced by the spacecraft is significant enough to warrant consideration during these tests. Also considered were the effects of the air displaced by the material that comprises the object being weighed, and the mass difference between a load cell standardization weight and the specimen under consideration.
To demonstrate these effects a test specimen was weighed in three different configurations. These configurations were open top, closed top and helium filled. It was demonstrated that there is a measurable difference between the first two configurations and the last configuration.
These buoyancy effects are not very relevant to objects that stay in the atmosphere. However, these effects should be considered when testing specimens that are to be used in space or very high altitudes. There will be buoyancy effects everywhere, but in the case of objects that leave the atmosphere, or go where there is a measurable pressure difference, there will be some measurable effect. These effects should be taken into account during mass properties final testing.
The results of the experiment showed a definite weight decrease when taking the buoyancy effects into account. The helium filled configuration weighed less that the open top and closed top configuration. This demonstrates a measurable effect of the displace air from inside the experimental vessel.
The goal of any final test in mass properties is to determine the mass at the highest accuracy possible. Some of the uncertainty can be reduced by taking into account that the propellant system will take up more volume than any other system due to the air displaced by the tanks. We can also reduce some of the uncertainty by factoring in the amount of air displaced by the volume of material in the spacecraft. Load cells are calibrated with this in mind, however they do not consider the material that the spacecraft is made of.


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