Towertalk
[Top] [All Lists]

Effect of Altitude...

 To: Effect of Altitude... crb@nanoteq.co.za (Chris R. Burger) Thu, 26 Sep 1996 09:36:11 +200
 ```As a rule of thumb, the ISA (International Standard Atmophere) looks like this: Pressure: 29.92" Hg at sea level. Lapses at roughly 1" Hg / 1000'. Round figures, at 5000': (30 - 5)" Hg = 25" Hg, or 83% of the sea level value. Temperature: 15 deg C at sea level, lapsing 6.5 deg C per km, or 1.98 deg C / 1000'. At a constant temperature, the density is proportional to pressure. Provided you're close to 15 deg C (59 deg F, if I'm correct), you can accept this proportionality with very little error. A lower temperature leads to higher density, while a higher temperature leads to a lower density. To quantify the effect, convert the temperature to kelvin: deg C + 273 = kelvin Example: 15 deg C = 288 K Then calculate the percentage change from this value. For example, if the lowest expected ambient temperature (worst case) is -10 deg C, the change is 25 K, or almost 10%. This means the dynamic pressure will be 10% more than expected on the basis of the pressure alone. Dynamic pressure (as mentioned before) is 0.5 (density) (velocity) (velocity) Make sure you check the units. I hope this helps. Didn't have time to design a well reasoned treatise, but this should get you started. Chris R. Burger ZS6EZ Hobbyist pilot South African Airline Transport Pilot License, Instructor's Rating US FAA Commercial SEL/MEL, Instrument -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: K7LXC@contesting.com Sponsored by Akorn Access, Inc & KM9P ```
 Current Thread Effect of Altitude..., David & Barbara Leeson Effect of Altitude..., Bill H. Jackson Effect of Altitude..., Chris R. Burger <=