PERFORMANCE Flashcards
Cruise ceiling
Altitude at which the max rate of climb capability at max continuous power and best CLB speed is 300ft per min
Service ceiling
Altitude at which max rate of climb capability at max continuous power and best climb speed is 100ft per min
VT/VF
Specific range. Is TAS/Total FF, OR nm per pound of fuel
VT/VF MAX
The max Value of specific range for a given weight & altitude
99% VT/VF MAX
The value of specific range resulting from increasing TAS from the speed at VT/VF MAX, to give a value of specific range which is 1% less than VT/VF max
Long range cruise
Term that identifies flight at the speed of 99% VT/VF MAX
VH
Structurally limited max level flight speed (recommended limit speed)
Normal bleed
When compressor bleed air is used to operate the aircon & pressurisation system
(800”lbs extra TQ)
All bleed
When compressor bleed air is used to operate the engine & wing/tail surface anti ice systems as well as the normal bleed functions
(extra 1200”lbs)
Drag index
that is proportional to drag change asssociated with a change in aircraft configuration
What advantage do props have over jet engines
advantage in power/weight ratio over jet engines at speeds up to about 350 k
What is the general power utilization of a turboprop
Over 90% of the energy is extracted by the turbines to drive the compressor(s) and the propeller; the remaining energy appears in the jet exhaust as thrust
What are the four factors affecting power output AND specific fuel consumption
- Forward speed
- Temperature
- RPM
- altitude
How does temperature affect power output?
An increase in intake temperature = an expansion of air particles. This will reduce power output because the mass flow through the engine will be reduced due to reduced air density.
How does altitude affect power output
At a constant TAS, power output falls with increase in altitude due to the decrease in air density. This is mitigated however by a decrease in air temp = increased air density
How does forward speed affect power output?
As forward speed increases, ram effect increases air pressure at the intake, increasing power output (up to about 400kts)
Define specific fuel consumption
The measurement of fuel used/hr/kW (power)
How does RPM affect SFC
Turboprop engines are designed to operate most efficiently at Max continuous RPM. For the minimum (best) SFC, engines should be operated at this at all times
How does temperature affect SFC
SFC improves in cold air because of the increased thermal efficiency of the engine.
How does altitude affect SFC
No direct effect as fuel control unit will reduce fuel consumption as air density decreases.
How does forward speed affect SFC
Shaft power increases with speed because of the improved mass flow through the engine. The GFC will be higher overall.
Summarise the best configuration for minimum SFC (max efficiency)
a. At MCrpm.
b. At high altitude (better thermal efficiency in colder air).
c. At a TAS between 300 kt and 400 kt, so that advantage may be taken of ram effect while the
propeller efficiency is still high.
define specific air range
defined as air distance travelled per unit quantity of fuel
Power required is a product of?
TAS and drag