Climb Speeds
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Join Date: May 2001
Location: Norveg
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Constant IAS means that Mach number, Mno, (and TAS) will increase; you could experience shock stall due to shock wave formations on the wings. Constant TAS will also cause Mno to rise, as the local speed of sound decreases with increasing altitude (up to the Tropopause). They use IAS up to "Changeover- / crossover point", after which Mno is used as reference. Usually around FL280-ish.
Climbing at constant IAS will require you to pitch down in order to increase TAS (to keep IAS constant because of decreasing density). This will give a lower climb gradient and is sometimes referred to as the kinetic energy factor.
Climbing at constant IAS will require you to pitch down in order to increase TAS (to keep IAS constant because of decreasing density). This will give a lower climb gradient and is sometimes referred to as the kinetic energy factor.
Join Date: Jan 2001
Location: Australia
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I think our friend is asking "Why?" one would perhaps elect to climb at a constant TAS or a constant IAS.
For example, does either give an advantage in situations like..
- running late and want to achieve minimum sector time, fuel economy not a consideration?
- want to minimise fuel and time to top of climb?
- etc.
One example - in a Metroliner 23 turboprop, which surprisingly tended to burn the same kg/nm regardless of altitude (F050 to F250), you could drop the standard climb schedule and immediately accelerate to Vmo/Mmo after cleanup and achieve the same rate of climb with a 40kt speed gain that increased up to FL165, at which point the Mmo needle started marching back. This was good for picking up a few minutes on sectors over 200nm.
Another - best L/D ratio occurs at (roughly) the same IAS for a given weight. So if you decide that the best way to climb today is to climb at the IAS that gives you AoA for best L/D, then plug that speed into the panel. Whether you would actually do this or not depends on your powerplant charachteristics, such as fuel flow vs thrust vs altitude.
Oh dear, I shouldn't start these posts when I have had a few quiet ales. Somebody clever jump in and help the poor fellow.
For example, does either give an advantage in situations like..
- running late and want to achieve minimum sector time, fuel economy not a consideration?
- want to minimise fuel and time to top of climb?
- etc.
One example - in a Metroliner 23 turboprop, which surprisingly tended to burn the same kg/nm regardless of altitude (F050 to F250), you could drop the standard climb schedule and immediately accelerate to Vmo/Mmo after cleanup and achieve the same rate of climb with a 40kt speed gain that increased up to FL165, at which point the Mmo needle started marching back. This was good for picking up a few minutes on sectors over 200nm.
Another - best L/D ratio occurs at (roughly) the same IAS for a given weight. So if you decide that the best way to climb today is to climb at the IAS that gives you AoA for best L/D, then plug that speed into the panel. Whether you would actually do this or not depends on your powerplant charachteristics, such as fuel flow vs thrust vs altitude.
Oh dear, I shouldn't start these posts when I have had a few quiet ales. Somebody clever jump in and help the poor fellow.
Last edited by ITCZ; 25th May 2003 at 01:16.
