SAR/SGR/SFC Flashcards
SAR
ANM/UNIT of FUEL
x ANM/1000kg
TAS/FF * 1000
Therefor SAR =
TAS/FF *1000
Add weather, get
SGR
SGR =
GS/FF * 1000
Example FF 4506 kg/hr TAS 463 kts
SAR = TAS/FF * 100 ===== 463/4506 * 1000 ===== 102.75 ANM/1000KG
If you want this figure in KG/NM –>
invert the formula - drop the 1000!
FF/TAS
= 4506/463 = 9.73kg/nm
High SGR is GOOD
the > the NM you get /1000kg of fuel, the better!
WAT- Wind affects SGR?
Weight Altitude, Temperature & Wind!
High weight = LOW SGR
Less Nm/1000kg - due increased Drag!
Higher gross weights at a fixed AOA result higher max range speeds (1.32 Vimd)!
Max range is based on fixed…
AOA Increasing weight moves the curve up and right meaning a higher speed is required to achieve the LIFT required by the increased weight!
ALTITUDE –> with fixed weight, increasing altitude increases SGR(good) UNTIL!
Optimum altitude for the weight and speed is achieved!
OPTIMUM ALTITUDE Is where the highest
SGR is achieved & where design RPM produces required thrust corresponding to wing AOA and Speed for the best performance (range)!
above/below OPT ALT SGR
SGR decrease! Due to increased thrust required which is only achievable by increasing engine RPM above design RPM!
TEMPERATURE Has little affect on SGR
Increase OAT = Increase FF BUT Increase OAT also = Increase TAS SO Much the same SGR results
Wind Maximum Range DEPENDS on
Wind
Max Range is determined by the (ratio)
GS/Drag ratio!
Drag being FF
GS/FF
In strong HWC’s fly f…. than nil wind max range speed to
minimise the time the HWC is acting on it.
In strong TWC’s fly s…. than nil wind max range speed to
give the HIGHEST GS/FF ratio!
Specific Fuel Consumption
a measure of engine efficiency!
SFC is the ratio of
kg of fuel/ kg or thrust
LOW SFC is b…..
BEST
Low SFC means that you are consuming less kg of fuel and producing a greater amount of
kg’s of thrust!
SFC - RAT! Factors affecting SFC
RPM Altitude Temperature
RPM (design 92-98% of max)
Increase off RPM above Design RPM Increases SFC (More Kg of fuel/kg of thrust)
Low SFC is b…
BEST
Altitude
With increasing altitude, air density decreases as does both T & FF - yielding lower SFC UNTIL the tro…..
Thrust and Fuel Flow - below the tropopause…..
Decreasing temperatures in the tropopause results in
REDUCTION of SFC!
Above the tropopause SFC
increases back toward S.L. values!
Temperature condition - constant TAS & RPM If OAT increase thrust and FF will….
Decrease! Meaning SFC remains STABLE (very minor, insignificant changes possible!)
DRAG CURVE - moves DOWN and LEFT as f
Fuel is burnt!
DRAG CURVE - moves UP &; and LEFT with Fla…
Flap Selection!
DRAG CURVE - moves UP and DOWN with Al
Altitude!
Maximum endurence speeds are lower at lower gross… w….
at lower gross wieghts!
A low SFCratio means low fuel consumption compared to
Thrust produced
A high SFC is less….
Inefficient!
Regarding best AOC and excess thrust - as fuel is burnt the drag cure moves down and left resulting in a
Lower excess thrust speeds at lower gross weights!
