Airline Pilot Central Forums - View Single Post - CRJ -200 N1 question

Cubdriver · 12-27-2007, 07:18 AM

For hi-bypass turbofans thrust available decreases with increase in both altitude and velocity. You are going to have to bump it up as you climb to get the same output. Not a lot- because thrust output has an exponential relationship to N1 speed as the latter increases. A complete analysis can be found in books on jet propulsion or "jetpro" as they say in school. And as Rick says there's a limit imposed by the materials in the engine on internal temps due to wear rate on blades and other parts. Bear in mind TAS increases with altitude, so 250 kts indicated at sea level isn't the same speed at altitude. If you try and hold the TAS the same I doubt you will find as much of a difference in power setting required.

12-27-2007, 07:18 AM	#4 (permalink)
Cubdriver Has A Custom Title Joined APC: May 2006 Position: CFI Posts: 1,318	For hi-bypass turbofans thrust available decreases with increase in both altitude and velocity. You are going to have to bump it up as you climb to get the same output. Not a lot- because thrust output has an exponential relationship to N1 speed as the latter increases. A complete analysis can be found in books on jet propulsion or "jetpro" as they say in school. And as Rick says there's a limit imposed by the materials in the engine on internal temps due to wear rate on blades and other parts. Bear in mind TAS increases with altitude, so 250 kts indicated at sea level isn't the same speed at altitude. If you try and hold the TAS the same I doubt you will find as much of a difference in power setting required. __________________ Turn the heat O-F-F! Last edited by Cubdriver : 12-27-2007 at 07:35 PM.