Cruise Flashcards
jet engines designed to be most efficient at …% thrust
90
best SAR is obtained when …
the most air miles are travelled for every kg of fuel burnt
SAR improves as the SFC … and is also dependent on …
reduces
the best ratio of TAS to drag
the best TAS to drag ratio occurs at the tangent to the …
which can be calculated as …Vmd
drag curve
1.32 Vmd
what is the optimum altitude?
At low altitude the aircraft will not be able to fly at 1.32Vmd and maintain 90% thrust (it would be flying faster) and consequently best SFC. Only at altitude will it be able to fly as slow at 1.32 Vmd and also be at the correct thrust for best SFC
This is the optimum altitude and will give the aircraft best range
The optimum altitude increases as mass decreases
why does the optimum altitude increase as weight decreases?
As the weight decreases (as fuel is burnt) both Vmd and induced drag decrease and means that at 90% thrust you will accelerate beyond 1.32Vmd, in effect the optimum altitude has increased
A steady continuous climb called a cruise climb, will ensure the aircraft is always at optimum altitude
SAR takes no account of wind, GFF does
GFF = …
GFF also known as …, the units of which can be given as … or …
fuel flow/groundspeed
fuel mileage
kg/nm or nm/kg
Endurance is …
This depends entirely on …, which is a product of … and …
Therefore best endurance for an aircraft is using best … and flying at …
the time the aircraft can remain airborne
fuel flow
SFC and drag
SFC, Vmd
What is higher, optimum altitude for range or optimum altitude for endurance?
Why?
optimum altitude for endurance because the speed should be Vmd (rather than 1.32 Vmd as for range) and the altitude at which Vmd will be able to be maintained at 90% thrust will be higher
when flying for endurance, what is the best speed even if optimum altitude cannot be realised?
Vmd
Best … speed in the flight manual may be above … as the advantage of speed stability is often considered to outweigh the reduction in endurance by flying faster
endurance
Vmd
prop aircraft SFC is …
fuel flow / power
for prop aircraft the best SAR will be found at the best ratio of …
This speed lies at the tangent to the … curve
TAS over power required
power required
the tangent of the power required curve for a prop represents …
therefore, best range speed for a prop aircraft is …
minimum drag (Vmd)
Vmd
Best endurance speed for a propeller aircraft is …
This is the min power required to maintain level flight and is the point where the product of … are at a minimum
the minimum power speed, Vmp
speed and drag
