[Aerospace] The Standard Atmosphere

When doing calculations in engineering, many of the variables that we deal with are not constants. For example, if we were to calibrate a digital altimeter to collect accurate altitude position, we need the atmospheric pressure at sea level. It would be nice if pressure stay the same, then we could just hard code that number in. Unfortunately, that is not the case. Pressure changes constantly due to a number of factors.

Because of the continuously changing nature of some of the variable we deal with, this present us with a challenge in engineering. How are we supposed to design the aircraft if conditions are keep on changing?

Well, that’s when the Standard Atmosphere come into play. In simplest terms, the Standard Atmosphere is pretty much just a model that engineers and scientists came up with that generally describe what the average conditions are like. 

[Aerospace] Fundamentals of Flight: Part 3

Aerospace Engineering Units
Before we move on any further, it is probably important to talk about some customs of the aerospace world. In the aviation world, travel distance are measured in nautical miles and speed is measured in knots. 1 nautical mile (nm) = 1.15 miles and 1 knot = 1.15 mph.  This system is developed such at 1 degree of Earth’s longitudinal length is equals to 60 nautical miles. For space, we sometime use AU, Astronautical Unit, 149.6E9 m, distance between Earth and Sun. In engineering, we generally use Imperial system for aviation and Metric for space. But both works and I prefer metric. Remember the standard units when calculating: use seconds for time, meter or feet for distance, m/s or fps for speed (60 mph = 88 fps), kg or slugs for mass, Newtons or pounds for force, Kelvins (+273.15 C) or Rankine (+459.67 F) for absolute temperature.