Principles of flight Flashcards
Formula % power efficiency of an engine
(Power output divide power input) x 100
How can the power output of a turbo prop engine be expressed?
Propeller thrust x TAS
How can the power input of a turbo-prop engine be expressed?
Torque x propeller RPM
How does the efficiency of a turbo-prop vary with speed?
Increases rapidly at low speed, falls to zero at high speeds
How do you increase the solidity of a propeller?
Increase the number of prop blades
What does increasing the solidity of a prop achieve?
Absorbs extra torque available from a more powerful engine and converts it to extra thrust
What design features of a prop blade mitigate against the adverse effects of compressibility due to high speeds at the prop tips
Broader chord to reduce blade aspect ratio and curved blades increasing sweep at the trips
What is the benefit of counter-rotating props?
It mitigates any swing caused by asymmetric blade effect
Formula tubo-jet thrust
M x (Ve - Vi)
Mass x (Velocity Exhaust - Velocity Intake)
Formula turbo-jet power
M x (Ve - Vi) x TAS
Mass x (Velocity Exhaust - Velocity Intake) x TAS
How does the efficiency of a turbo-jet vary with speed?
Increases slowly at low speed but the efficiency continues to increase into the supersonic speed range
How much fuel energyis water producing heat rather than thrust in a turbo-jet engine?
75%
How can a turbo-jet enhance its thrust without overheating the turbine stages?
Using afterburner/reheat increase exhaust velocity
How does a turbo-fan produce more thrust without increasing combustion temperature?
Uses mechanical energy from an additional turbine stage to drive fan stage, increasing by-pass mass flow to produce more thrust
How does efficiency of a turbo-fan engine vary with speed?
Increased by-pass thrust means efficiency increases quickly even at low speed. Efficiency will decrease at supersonic due to drag from fan
Immediate and secondary effects of asymmetric thrust?
Which way will the sideslip indicator move?
I - Yaw towards dead engine
S - Roll towards dead engine
SSI - Towards the live engine
Would X make asymmetric control more or less difficult
Higher speed
Max thrust
Loss of a critical engine
Higher speed - Less difficult
Max thrust - More difficult
Loss of a critical engine - More difficult
Method of regaining control in the event of an asymmetric engine failure…
Below V1
After T/O
Below V1 - Reduce all thrust to idle
After T/O - Maintain wings level and stop yaw with rudder
At or near VMCA, how do you prevent yaw if full rudder already applied?
Up to 5 degrees of bank towards live engine
V? - Min speed maintain directional control on runway, by rudder alone.
VMCG
CIC, TDT, RAF
Control - Identify - Confirm
Thrust - Drag - Trim
MIs
Radio - ATO Cx - FRCs
Phenom VMCA
Minimum control speed - 97kts IAS
Below what speed does air behave like an incompressible fluid
250-300kts
How is mach number calculated?
Ratio of TAS over local speed of sound
MFS
Mach free stream - Mach no. of airflow past aircraft unaffected by its passage
ML
Local mach number- Mach no. of airflow over the a/c measured at a localised point
MCRIT
Critical mach no. - Speed at which first area of aircraft hits mach 1
What happens at MCRIT
Shockwaves begin to form
MDET
Mach detachment no. End of transonic flight and beginning of true supersonic
When a/c approaches mach 1, centre of pressure moves rearwards causing an increasing nose down pitch force, this is known as?
Mach tuck
On large multi engine a/c what is the solution to mach tuck
All flying tail plane
How do we delay formation of shockwaves?
Thin wings, swept wings, area ruling, supercritical wings
Disadvantageous of thin wings
Poor lift at low speed, difficult to incorporate ancillaries, structural integrity
In a/c design, what ensures a smooth change in cross-sectional area from nose to tail?
Area ruling
Name of altitude where MMO and aerodynamic stalling speed converge called?
The buffet boundary
Dutch roll occurs when
Strong lateral stability, weak directional stability
