Originally Posted by
disco87
I've been reading about why Jets climb as high as possible, I'm quite comfortable with the changes to SFC and also minimum cruise drag on the airframe. However I'm struggling to get my head around why there is an increase in the TAS.
As far as I'm aware, above a certain altitude the mode of speed management is in relation to the MN. Therefore this would result in a decreasing TAS as you climb at a constant MN, however it seems that the TAS increases from what I've been reading, which has confused me a bit.
I'm just looking for an explanation of why this is the case.
Thanks
Generally correct except for the bit about TAS increasing after climbing at a constant MN. It doesn't. TAS decreases when climbing at a constant MN, due to the fact that the temperature decreases, and therefore the TAS associated with that MN decreases with temperature. Until you reach the tropopause, above which the temperature ceases to decrease and therefore the TAS remains constant with MN no matter how high you climb.
The tropopause will vary considerably due to location, seasons and weather, but is typically around 35000' in a standard atmosphere.