Atmósfera ISA — Transcript

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1. 0:07Today we are going to talk about ISA atmosphere
2. 0:10Which is commonly used in aviation as a reference to atmospheric changes
3. 0:13And also for aircraft performance calculations
4. 0:17So, First of all, what does "ISA" Mean?
5. 0:19"ISA" is the abbreviation for "International Standard Atmosphere"
6. 0:23Or in spanish "Atmósfera Estándar Internacional"
7. 0:25These are standard atmospheric conditions for Pressure and Temperature
8. 0:29At the mean sea level (0 feet of altitude)
9. 0:33The pressure is 29,92 Inches of Mercury
10. 0:36Or 1013,2 Hectopascals (Milibars)
11. 0:39Whichever, since both units are accepted in aviation
12. 0:43The temperature is 15°C or 59°F
13. 0:48Now, the ISA atmosphere has standard temperature and pressure gradients as the altitude increases
14. 0:54So, let´s review them
15. 0:57Let´s start with the temperature
16. 0:59The temperature chenge rate with altitude in the ISA atmosphere is constant until reaching the tropopause
17. 1:04Which is layer of the atmosphere
18. 1:06The standard altitude of the tropopause is 36089ft
19. 1:10However it depends of our position in the earth
20. 1:14If we are close to the poles, the tropopause is lower
21. 1:17And if we are close to the ecuator, it is higher
22. 1:19But it is assumed that the standard altitude is 36089ft
23. 1:23As you can see in this graphic, the temperature is 15°C at sea level
24. 1:29And starts decreasing
25. 1:31Until reaching the tropopause
26. 1:32It means, until 36089ft
27. 1:34Apart from that point, it remains constant at -56,5°C
28. 1:40This means that the temperature has a constant change rate
29. 1:44Of -1,98°C for every 1000ft altitude increase
30. 1:49For quick calculation purposes
31. 1:51We can assume the rate of 2°C per 1000ft until 36089ft
32. 1:55And then it remains constant
33. 1:58That´s all about the temperature. Let´s see the pressure
34. 2:01The pressure change rate with altitude varies as it increases
35. 2:05So, it has not a constant rate like the temperature
36. 2:08In ISA atmosphere, the air is considered an ideal gas
37. 2:12And as you can see in this graphic, the pressure rate varies
38. 2:15It is 1013,25 Hectopascals at mean sea level
39. 2:20And it starts decreasing
40. 2:21In this graph, it is only shown until 40000ft
41. 2:24However we can say that in the first 10000ft of altitude
42. 2:27The pressure gradient is aproximately 1 Inch of Mercury per 1000ft
43. 2:32So then we can say the pressure reduction rate is 1 Inch of Mercury for every 1000ft altitude increase
44. 2:37But only in the first levels
45. 2:39Since the pressure rate is not constant
46. 2:42We have seen the temperature and pressure gradients characteristics in ISA conditions
47. 2:46Here is a table with all of those values
48. 2:50As you can see, it refers to altitude in feet, the temperature in Celcius
49. 2:54The pressure is shown in different units
50. 2:57The pressure gradient, as you can see it varies
51. 3:00Atmospheric density and also the speed of sound as the temperature decreases
52. 3:05We have to remember that ISA conditions are only a reference datum
53. 3:10Since very few times the atmosphere is under standard temperature and pressure conditions
54. 3:14So again, it is only a reference
55. 3:19In example, there is an airport at the mean sea level
56. 3:22And it´s temperature is 15°C
57. 3:25In this case, this airport is under ISA conditions
58. 3:29However, other airport at mean sea level
59. 3:32With a temperature of 30°C
60. 3:35Would be in ISA+15° Conditions
61. 3:38Since it is 15° above the standard temperature at that altitude (0ft)
62. 3:42And for example, other airport at sea level with 5°C
63. 3:46Would be in ISA-10° Conditions
64. 3:49Since it is 10° below the standard temperature at that altitude (0ft)
65. 3:53Changes in these conditions mean different aircraft performance
66. 3:57So it is really important to know ISA conditions and the deviations from it
67. 4:01In order to precisely calculate the performance of an aircraft
68. 4:06I hope this video was useful to understand the ISA atmosphere concept and it´s gradients
69. 4:11Subscribe for more aeronautical knowledge
70. 4:14And let me know in the comments below, which other topics would you like to see in other videos.