Weather
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Page 54 of the BMS manual says:
Temperature and pressure both have a further impact on air density which affects flight performance.
The higher the pressure the lower the density and the higher the temperature the higher the density.This seems to conflict with:
Then on page 55 of the BMS Manual it says:
Therefore:
Low pressure / high temperature will decrease performance at low level but increase performance at high level
High pressure / low temperature will increase performance at low level but decrease performance at high level.But won’t low pressure/high temperature decrease performance at any level
and won’t high pressure/low temperature increase performance at any level?[edit RD: corrected next version]
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It might have meant “the higher the density altitude” instead of density. Hot air is less dense for the same pressure.
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It might have meant “the higher the density altitude” instead of density. Hot air is less dense for the same pressure.
Yep, p54 and 55 need clarification.
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instead of opening a new thread, I post here.
Regarding the cumulus layer height,Ok, you input the height you want it to begin, but does the height of the cumulus cloud depend on its thickness or coverage, or is it totally random.
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The original subject is a complex one, made even more so when one adds humidity as a factor, at least where takeoff data is concerned.
Though I didn’t calculate takeoff data as a boomer, I was able to educate myself somewhat on the subject because there were descriptions and takeoff data charts in my Dash One.
IIRC, density altitude is what the altimeter will show if it was set to 29.92 on the ground. If set to the local barometric pressure, it will show the airfield’s altitude above sea level.
My greatest exposure to takeoff data occurred when I was on alert. The data was calculated twice a day and posted prominently for all to see. Cold and dry conditions with high barometric pressures made for the best takeoff conditions, and vice-versa.
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Close, pressure altitude is the altitude of the standard atmosphere that has the same pressure as the local conditions. This is often expressed as the barometric altimeter reading when set to 29.92’'Hg/1031.25mb.
Density altitude is the altitude of the standard atmosphere that matches the same density as the local conditions. Since few airplanes carry instruments which can directly sample density, it’s calculated by adjusting for factors that affect density (except for pressure since that is read directly). The first is temperature with hot air being less dense for the same pressure. Humidity is a more minor effect but an H2O weighs 10/14ths as much as an N2 so more water makes for a less dense gas. Engines are doubly influenced by humidity because not only is the mass per volume lower but engines burn oxygen and there half as many O’s in H2O vice O2.
