Cruise Flashcards
How is ground specific range determined
ground speed / fuel consumption per hr
what causes specific range to increase
when mach number or lift/drag ratio increases
what causes specific range to decrease
when mass or fuel consumption increases
What is MMR
- maximum range mach number
- it’s the mach number at which specific range is it’s greatest
how does MMR change with constant altitude and constant weight
- at constant altitude, MMR decreases slightly as weight reduces
- at constant weight, MMR increases as pressure altitude increases
What is MLRC
- Maximum long range cruise mach number
- it’s 99% of SRmax due to an INCREASE IN SPEED
- MLRC has 1% HIGHER FUEL BURN than MMR
how doe s MLRC change with constant pressure altitude and weight
- at constant pressure altitude, MLRC decrease as weight decreases
- at constant weight, MLRC increases pressure altitude increases
what is MECON
- economic mach number, the most economical mach number for the flight
how is MECON determined
on a graph of direct operating cost, cost of fuel and cost of time against mach number, it is the lowest direct operating cost that is higher than MMR but lower than MLRC.
how does MECON change with constant pressure altitude and weight
- at constant pressure altitude, MECON increases as weight decreases.
- at constant weight, MECON increases as pressure altitude increases.
What is cost index?
= cost of time / cost of fuel
what’s the relationship between MECON and cost index
as cost index increases, MECON increases and vice versa.
How is the speed of MECON affected by high and low cost indexes
- CI is high when fuel cost is low so the plane will fly faster and MECON will be closer to Mmo.
- CI is low when fuel cost is high so the plane will fly more conservatively and MECON will be closer to Mmr
what happens to M and MLRC when flying at a constant mach number
- the gap between them will increase so fuel consumption increases past optimum
what are the characteristics of optimum altitude
- for each SR there is a optimum altitude
- at optimum altitude, the aircraft is at max lift/drag ratio at selected mach number
- there is an optimum altitude for every mach number (lower at lower mach numbers).
