Propell eksamen 2 Flashcards
It accelerates a mass of air and the reaction produces
thrust
Propellers can also be used as aerodynamic
brakes
As the geometry of the blade changes from the root to the tip, details on chord length, chord thickness and blade angle refer to a particular reference station. This reference station is normally located from
0,7R - 0,75R
The way the propeller works is based on the
reactive principle
Blade Angle / Angle of incidence
The angle between the propeller chord and the rotational plane
Angle of Attack
the angle between the profile chord line and the relative air flow towards it.
The angle of advance
is the angle between the rotational plane of the propeller and the relative velocity (w
Angle of advance increases with
increasing airspeed
Thick profiles are used for
low speeds
Thin (usually laminar) profiles are used for
high speed
For reasons of reducing noise, propeller tips should be
elliptical
In addition to the angle of incidence, the profile shape also changes because of
material stress and for aerodynamic reasons
Slip is
geometric pitch minus effective pitch
Propeller efficiency ranges from
0.8 to 0.9 (80% − 90%).
At constant rotational speed the sum of propeller brake moment and engine torque is
zero
If the blade angle is reduced so far that the angle of attack is less than the zero lift angle of attack
Vil du få Reverse Thrust
The counter moments caused by engine torque tries to turn the aircraft against
the propellers rotation
Due to this moment the main landing gear on that side is pushed strongly towards the ground when taxiing and especially on
(Engine torque) Take off
To compensate for Engine Torque effect
trim on one of the Ailerons
To compensate for Twist effect propeller wash
the vertical stabilizer is normally mounted obliquely by 1* to 2*
The Twist Effect of the Propeller Wash:
The propeller does not only accelerate the air backwards but also causes a twist in the propeller wash. Due to this twist the flow of air to the
vertical stabilizer is asymmetric
In climbing attitude the direction of airflow is obliquely from below. Thus the downward moving blade has a greater
Angle of Attack
Small twin−engined aircraft the flight performance is usually too low if the
critical engine fails
Rotation Noise *
The rotating pressure field of the propeller produces rotation noise. At mach numbers of the blade tips between M = 0.5 and M = 0.85 and an undisturbed flow of air to the blade this noise exceeds all other noise components.
Vortex Noise *
This noise is caused by the vortices leaving the blade tip and blade trailing edge. Its maximum value is found in the plane of rotation of the propeller.
Displacement Noise *
The origin of this noise is the displacement of the air by the propeller blades as they have a finite thickness. It first becomes critical at higher mach numbers at the propeller tips. At blade tip mach numbers above 0.9 this noise source equals that of rotation noise.
Blade Vibration Noise *
This noise occurs with periodic stalls, for example when the stall limit of the blade is alternately exceeded and fallen below.
Noise caused by inconsistent Airflow
Normally the vortices leave the trailing edge and blade tips in such a way that they do not affect the following propeller blade. This is not the case with variable pitch propellers when the angle of pitch is negative and the propeller has zero thrust.
blade tip shape profile type blade contour blade twist profile camber profile section ratio
propeller noise can be changed according to various influencing factors
If the blades are not made of metal but of wood or composite construction, they have a more favourable
vibrational behaviour due to better self−damping properties
What is the main static load on the propeller?
Centrifugal force
The greatest stress from static loads occurs in the region of the
blade root
As the blades are attached to the hub, this too is subject to __________ and thus high stresses also affect its material.
high loads
At a distance of about _____ of the blade radius from the blade tip the highest vibrational loads occur. This region is therefore particularly susceptible.
20%
Nicks caused by scratching, ________ and strikes affect the durability of ________ propellers particularly severely.
corrosion, metall
Propellers are designed as either pusher or puller (tractor) propellers, which are then subdivided into fixed pitch propellers, ____________, ___________
adjustable pitch propellers and variable pitch propellers.
The blade angle of an adjustable pitch propeller can be changed
on the ground when the engine is shut down
Variable pitch propeller the blade angle can be changed
during operation
Nowadays hydraulically controlled variable pitch propellers
are almost exclusively in use
The oil needed for the hydraulic action is taken from the pressurized oil in the
the engine lubrication system
In the range between the low (fine) pitch stop (for low airspeeds) and the high (coarse) pitch stop (for high airspeeds) the propeller can be adjusted to
any angle
Multiple engine aircraft and motorized gliders an engine should produce as little drag as possible when it is shut down. Therefore their blades can also be moved into the
feathering position
With large aircraft the production of reverse thrust is intended to shorten the distance on landing. For this purpose the propellers are turned to ________, where air is accelerated forwards while the propellers continue to turn in the same direction. Thus reverse thrust is produced.
reverse pitch
oil pressure changes the pitch in one direction only. Movement in the opposite direction is the result of spring force and the torsion moments of the blades themselves
Single acting propellers
Single Acting Propellers for Single-Engine Aircraft
With these propellers the oil pressure moves the blades in the direction of ________ pitch and the spring moves it towards
high (coarse) and the spring moves it towards low pitch
Single Acting Propellers for Single-Engine Aircraft
After engine shut−down the blades are in the _______ pitch stop position, which is optimal for restarting the engine. Should the engine fail during flight, this blade position is favourable for windmilling, which makes it easier to restart the engine.
lowest (fine) pitch
If single acting propellers are used on multi-engine aircraft, oil pressure moves the blades in the direction of
low (fine) pitch
If single acting propellers are used on multi-engine aircraft, the springs and torsional moments of the flyweights move the blades towards
high (grov) pitch
If single acting propellers are used on multi-engine aircraft, and engine failure occurs during flight with decreasing oil pressure the blades move in the high (coarse) pitch direction. In this way they have already covered part of the transition to the
feather position
The centrifugal force of the propeller blade mass produces a pitch change moment which turns the blade in the direction of
low (fine) pitch
If the propeller blade is to turn towards high (coarse) pitch as a result of centrifugal force (for propellers with feathering position) then a flyweight must be attached to the
blade root.
Large propellers are generally constructed with pitch change mechanisms where oil pressure leads to pitch change in both directions. These are called
double acting propellers
Spinners are mounted for reasons of better aerodynamics, as a ________ for the hub and for visual reasons
mechanical protection
The dynamic load on the spinner is extremely high. If there are cracks on the blade recesses or in the spinner mounting the parts are to be _______.
replaced.
Propellers are categorized according to the material used for their blades. There are:
Wood propellers Metal propellers Composite propellers
A wooden propeller consists of several layers of wood bonded together with a watertight resin glue. At least __ layers are used.
5
Wooden propellers have ________ on the leading edges and may also have a glass fibre jacket
metal strips
With a propeller working on the constant speed principle the RPM selected by the pilot is kept constant by
changing the blade angle (pitch).
A reduction in pitch leads to a ______ brake moment and thus ______ RPM.
SMALLER brake moment and thus HIGHER RPM.
If for example engine power is greatly reduced by operating the thrust lever, higher RPM cannot be achieved, even if the propeller is at its
lowest (finest) pitch.
RPM = constant if :
Drive Torque = _____
Brake Moment
CONSTANT SPEED PROPELLER SYSTEM
Apart from the variable pitch propeller the components which belong to the system are the propeller control lever in the cockpit, the _________ and an oil supply from the engine hydraulic oil and scavenge oil system.
propeller governor
Inside the governor there is a __________. This valve either supplies hydraulic oil to the change mechanism, allows the oil to flow back into the scavenge oil system, or locks the system hydraulically to keep the selected blade pitch constant.
pilot valve
The governor is set to the selected RPM via ______________________ from the cockpit.
via rods or a push−pull cable
The pilot valve is controlled by a centrifugal regulator (flyweights), which is also located in the governor and is sensitive to engine rpm. This regulator works against a __________, the tension of which can be adjusted by the propeller control lever in the cockpit. (RPM selection).
spring
____________ continuously compares the selected RPM with the actual RPM and adjusts the pilot valve accordingly.
The governor
The propeller control lever is also called speed lever or ____________
condition lever
Small single engine aircraft usually have propellers _________ a feathering position
without
(Single Acting Propeller, single engine aircraft)
The effect in the other direction is from the force of the built−in spring and from the centrifugal force of the propeller blades itself. Additional flyweights may also be attached. When stationary the blades are at low (fine) pitch because of spring pressure and there is ____ drag when starting the engine.
less
In the case of propellers with a feathering position, oil pressure works in the direction of ________
low (fine) pitch
Flyweights produce about double the pitch changing force in the direction of high pitch than ________ _________ _____ does in the direction of low (fine) pitch.
natural centrifugal force
A spring, or in some systems __________, then moves the blades into the feathering position.
pneumatic pressure
So that the blades do not automatically move into the feathering position when the engine is shut down normally, a high pitch stop (______) is installed, which in almost all cases work by centrifugal force.
or centrifugal latch
On starting, the propeller lever is at high RPM. Increasing ________ forces the blades in the direction of the low (fine) pitch stop
oil pressure
If the propeller is driven by a multiple shaft engine (turboprop) the high pitch stop is ________
not necessary
In order to move the propeller into the feathering position the control lever in the cockpit is pulled ___________ .The propeller now moves with spring pressure and centrifugal force into the feathering position and also stops rotating
fully back
To move the propeller out of the ________ again during flight (e. g. to restart by windmilling), a separate connection to a hydraulic actuator or an electrical auxiliary oil pump may be present.
feathering position
At the smallest available power in constant speed mode (alpha mode) and with the propeller in flight idle position thrust would be relatively high when stationary. This would make it difficult to taxi slowly. To enable thrust to be reduced on the ground even further, turboprop engines have a second control mode, the _____. This can only be selected on the ground.
beta mode
In beta mode the blade angle is changed directly with __________, so that any angle between zero thrust and flight idle (or full reverse) can be selected
power lever
In beta mode the RPM is selected with the __________ and remains constant.
condition lever
When the power lever is moved behind the ______ thrust position, the propeller moves into the reverse beta range to the corresponding blade angle.
zero
To enable blade pitch change in beta mode, it is necessary to have a ___________ for the blade angle from the propeller to the pitch change valve. This is mechanical.
feedback signal
To prevent a large blade angle change in the direction of low pitch on loss of oil pressure (and thus excess RPM), double acting propellers on turboprop engines are provided with a
pitch lock mechanism
The underspeed governor is located in __________. It regulates the RPM below the range controlled by the prop governor.
the fuel control unit
On reaching the position selected for the propeller blades, resetting of the beta valve takes place through _______ feedback from the propeller to the beta valve
mechanical
RPM in beta mode is usually _______ than in alpha mode.
smaller
If the engine is shut down during flight, the propeller must be moved into __________ so that there is as little drag as possible.
feathering position
In order to keep the pilot’s work load low if an engine loses power during _______, auto feather systems are employed. They are activated for _______ and react to the decreasing torque of an engine in case of its malfunction.
take−off
When the engine torque has dropped off far enough, the auto feather system switches the __________ valve to the feather position and turns on the feathering pump.
feathering
To move the propeller out of the feathering position (e. g. for restarting during flight) it is necessary to produce oil pressure for the pitch change mechanism. In the system shown here this is achieved with an ________ unfeathering pump.
electrically driven
Before the feathering pump is switched on in the cockpit, the condition lever must be moved out of the ________ in order to close the feathering valve
feathering position
In the case of engines with more than one shaft and auto feather system there is _____ for an unfeathering pump
no need
Negative torque is the operating condition where the
engine is not driving the propeller as is normal, but conversely the propeller drives the engine.
The torque sensor on the engine picks up the negative torque of the propeller shaft and opens the
feathering valve
The propeller moves to ______ and windmilling is reduced. However, the propeller is now working in an underspeed condition.
higher pitch
PTL engines can also be controlled _______. In this case the PEC (Propeller Electronic Control) controls the propeller
electronically.
(Propeller Electronic Control)
A _______ takes over the respective engine controls (for example fuel flow).
FADEC (Full Authority Digital Engine Control)
A mechanical OSG (Overspeed Governor) is integrated into the control system in order to protect the propeller from _______ in case of an incorrect control.
______________ can prevent overspeed by a reduction of fuel flow
overspeed, FADEC
If the RPMs of the propellers of multiple engine aircraft deviate even only slightly from each other, this results in vibrations in the aircraft structure which reduce the life span of the structure and additionally produce
loud noise.
Operating synchronizing systems automatically matches the revolutions of one or several propellers to the ___ of the master engine. This type of system is known as a synchronizer.
RPM
The synchronizer calculates the propeller revolutions with the aid of inductive RPM sensors on the propeller shafts or with pickups on the governors. The computer compares the revolutions constantly, whereby the _______, the master, sets the standard.
left engine
. If there are ________, it sends a signal to an electric actuator on the governor of the slave engine. The tension on the governor spring is changed until the propellers are again synchronized. When the system is switched off, the actuator of the slave engine is automatically set to the central position.
deviations / forskjeller i RPM
Through a _____________ the system receives a phase signal from the propellers in addition to the RPM signal through the RPM pickup or additional pickups. The system then sets the slave propeller to the determined phase position. The phase position of the slave propeller is some degrees off that of the master propeller.
synchrophaser
The synchrophasing function is automatically activated if the power lever is at _____ or _____
CLIMB or CRUISE
There are two main methods:
____ anti−icing system
_____ de−icing system
Fluid anti−icing system
Electrical de−icing system
A very simple and problem−free method to prevent __________ is the fluid anti-icing system using an alcohol based liquid. A pump injects the fluid into a slinger ring on the propeller. From there it runs by centrifugal force onto the grooved anti−icing rubber. The amount supplied by the pump can be varied to suit the intensity of icing.
ice formation
The disadvantage of this system is that the amount of anti−icing fluid on board the aircraft must be constantly monitored. The system works only as a precaution and must therefore be activated before icing begins. It is not able to remove ice once it has formed.
What system?
Fluid Anti Ice system
There is a greater number of electrical de−icing systems in use. They are employed in larger aircraft as these can provide the necessary electrical power. The blade has de−icing rubbers which are heated by _______ embedded in them.
two heating elements
Electrical power is supplied via ________ from the aircraft electrical system
slip rings
Control components in the system switch the heating element segments alternately on and off. In this way the current used is kept to a _______.
minimum
TSN
Time Since New
TSO
Time Since Overhaul
TBO
Time Between Overhaul
The aircraft operator is required to keep a log of TSN and ___.
TSO
WARNING: NO REPAIR WHATEVER IS PERMISSIBLE ON THE
BLADE ROOT
Metal propellers are particularly prone to
metal fatigue
Do not destroy maximum _______ if possible
thickness
Bent ____ propellers or blades can be realigned if the permissible bending is not exceeded
metal
Propeller must not be bent back to their
original position
During periodic inspections the hub must be checked for _____ and corrosion. The exterior parts of the pitch change mechanism and the hub should be free from corrosion
cracks
Damage is classified as skin perforated damage and skin not perforated damage on _______ propellers
Composite
If struck by foreign material the edges can be smoothed and the missing material replaced on _______ propellers
Composite
The blades of variable pitch propellers are pre−balanced using a ______. Packing lead wool into the hollow blade root to compensate for any missing mass
master blade
Dynamic balancing must be done
on the running engine
Vibrations during ____ should be reduced to a minimum as this is the usual operational condition.
flight
The ability of one blade to follow the other in the same plane of rotation. The lines should be separated by not more than 3 mm.
Blade tracking
DO NOT TRY TO START THE ENGINE IF THE TEMPERATURE OF THE OIL IS BELOW
-40C (-40F)
IF THE ENGINE DOES NOT LIGHT WITHIN 16 SECONDS OR IF NH DOES NOT GO TO 64.2% WITHIN __ SECONDS MOVE THE ENGINE START SELECT SWITCH TO OFF.
70
Les side 108 og utover
Bra jobbet, fortsett sånn<3
Nicks on metal propellers must be worked out with a large radius (10 x depth of nick). The profile shape of the _______ must remain intact
leading edge
Skin perforated damage:
________
holes
lightning strike
If the propeller is to be stored ’______’ for periods in excess of 3 months then the pitch change mechanism should be flushed out with an inhibiting oil and then covered with waxed paper.
on the wing
_________ propellers require to be kept in a clean condition and inspected at regular intervals for corrosion.
Installed
Propeller bearings are required to be exercised after 6 and 9 months. After 12 months the bearings need to be _______, checked for ’Brinelling’ and corrosion and then regreased
cleaned
The maximum storage period is up to_______ with inhibiting checks every 12 months.
All propellers and components should be labelled stating:
Part number.
Modification state.
Serial Number.
Date of storage with a record of inspections since that date.
3 years
PILOT VALVE IS CONTROLLED BY FLYWEIGHTS
Pilot Valve is normally controlled by flyweights, in low or high rpm on Propeller lever it is ______ or _______. Se side 71.
lifted or pulled
The propellers used for turboprop engines are _____speed fully ______ propellers with reverse thrust
CONSTANT speed fully FEATHER propellers with reverse thrust
Turboprop propellers in high performance classes are constructed as double acting propellers. If it is driven by a single shaft engine, the propellers will also have a ________
high pitch stop.
