M17 M1 7 PROP PROPE ELLER LLER 29.11.2012
DAC
EASA Part-66
CAT A P66 M17 A E
Training Manual For training purposes and internal use only. Copyright by Lufthansa Technical Training (LTT). LTT is the owner of all rights to training documents and training software. Any use outside the training measures, especially reproduction and/or copying of training documents and software − also extracts there of − in any format at all (photocopying, using electronic systems or with the aid of other methods) is prohibited. Passing on training material and training software to third parties for the purpose of reproduction and/or copying is prohibited without the express written consent of LTT. Copyright endorsements, trademarks or brands may not be removed. A tape or video video recording of training courses courses or similar services is only permissible with the written consent of LTT. In other respects, legal requirements, requirements, especially under copyright and criminal law, apply. Lufthansa Technical Training
Dept HAM US Lufthansa Base Hamburg Weg beim Jäger 193 22335 Hamburg Germany Tel el:: +49 +4 9 (0) (0)40 40 507 070 0 252 2520 0 Fax: Fa x: +4 +49 9 (0) (0)40 40 50 5070 70 47 4746 46 E-Mail:
[email protected] www.Lufthansa-Technical-Training.com Revision Identification:
The date given in the column ”Revision” on the face of this cover is binding for the complete Training Manual.
Dates and author’s ID, which may be given at the base of the individual pages, are for information about the latest revision of that page(s) only.
The LTT production process ensures that the Training Manual contains a complete set of all necessary pages in the latest finalized revision.
Training Manual For training purposes and internal use only. Copyright by Lufthansa Technical Training (LTT). LTT is the owner of all rights to training documents and training software. Any use outside the training measures, especially reproduction and/or copying of training documents and software − also extracts there of − in any format at all (photocopying, using electronic systems or with the aid of other methods) is prohibited. Passing on training material and training software to third parties for the purpose of reproduction and/or copying is prohibited without the express written consent of LTT. Copyright endorsements, trademarks or brands may not be removed. A tape or video video recording of training courses courses or similar services is only permissible with the written consent of LTT. In other respects, legal requirements, requirements, especially under copyright and criminal law, apply. Lufthansa Technical Training
Dept HAM US Lufthansa Base Hamburg Weg beim Jäger 193 22335 Hamburg Germany Tel el:: +49 +4 9 (0) (0)40 40 507 070 0 252 2520 0 Fax: Fa x: +4 +49 9 (0) (0)40 40 50 5070 70 47 4746 46 E-Mail:
[email protected] www.Lufthansa-Technical-Training.com Revision Identification:
The date given in the column ”Revision” on the face of this cover is binding for the complete Training Manual.
Dates and author’s ID, which may be given at the base of the individual pages, are for information about the latest revision of that page(s) only.
The LTT production process ensures that the Training Manual contains a complete set of all necessary pages in the latest finalized revision.
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! Y L N O S E S O P R U P G N I N I A R T R O F
PROPELLER
EASA PART 66 M17
M17
PROPELLER
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M 17 PROPELLER M 17.1 FUNDAMENTALS
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M17.1
PROPELLER FUNDAMENTALS
GENERAL The propeller is driven by an engine with a performance measured in shaft horse power or brake horse power). It accelerates a mass of air and the reaction produces thrust. Propellers can also be used as aerodynamic brakes by reversing the direction of air acceleration. The propeller consists of a propeller hub and two or more propeller blades. The propeller is connected to the propeller shaft by the hub. The propeller blades have an aerodynamic profile. When they move through the air (rotation of the propeller), an air mass is accelerated by the difference in pressure on the surfaces of the blades. The following terms apply to the propeller blade: leading edge trailing edge blade root and blade tip. 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.
As the pressure differences on the propeller blade airfoils are small by nature, the acceleration of the air mass is also small. This leads to low downwash speeds with high propulsive efficiency at low to medium airspeeds (mach 0.5 to 0.6).
HOW THE PROPELLER WORKS PRODUCTION OF THRUST ! Y L N O S E S O P R U P G N I N I A R T R O F
The way the propeller works is based on the reactive principle. The air mass flowing through the propeller plane is accelerated by the difference ∆v. The reason for this acceleration of the air mass is the change in pressure in front of and behind the propeller plane, which occurs as a result of the air flowing around the propeller blade airfoil. As a reaction to the accelerating forces, propeller thrust (Fs) is created. As the air mass in the propeller plane also receives an accelerating component in the direction of the circumference, the air mass spirals away from the propeller plane. Because of the higher velocity of the propeller wash behind the propeller plane, its cross −section is reduced there.
propeller plane
Figure 1
Propellerstream
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HUB
LEADING EDGE
BLADE TIP
anti-icing tip
Spinner
BLADE ROOT
AIRFOIL
TRAILING EDGE
BLADE ROOT
reference station
chord length BLADE TIP
! Y L N O S E S O P R U P G N I N I A R T R O F
Figure 2
Propeller Components
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M 17 PROPELLER M 17.1 FUNDAMENTALS
M17 ANGLES OF THE PROPELLER BLADE Blade Angle (ϕ)
The angle between the propeller chord and the rotational plane of the propeller is the blade angle or the angle of incidence. The blade angle is not constant over the whole length of the propeller (see aerodynamic twist). In practice the angle always refers to the pressure side of the blade, even if the profile chord differs from this. As the blade angle is not constant over the whole length of the blade, a particular part of the blade is termed the reference station. This station is generally at 3/4R of the propeller. Angle of Attack (α)
The angle of attack is the angle between the profile chord line and the relative air flow towards it. With the angle of incidence running appropriately the length of the blade, the desired lift distribution is achieved from the resulting angles of attack. As the propeller moves on a plane which is perpendicular to the forward movement of the aircraft, two velocities, perpendicular to each other, are definitive for the angle of attack: the relative air flow velocity, resulting from aircraft airspeed (v) the relative air flow velocity, resulting from propeller peripheral speed (u). Both velocities produce the resultant relative velocity (w) and determine direction and magnitude of the velocity (w). Angle of Advance (β) The angle of advance (β) is the angle between the rotational plane of the propeller
and the relative velocity (w). The angle of advance increases with increasing airspeed (v). ! Y L N O S E S O P R U P G N I N I A R T R O F
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angle of attack α angle of advance β chord
bladeangle resulting velocity w
! Y L N O S E S O P R U P G N I N I A R T R O F
air speed
propeller plane peripheral speed u
Figure 3
Propeller Angles
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M 17 PROPELLER M 17.1 FUNDAMENTALS
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AIRFLOW ONTO THE PROPELLER BLADE Influences on the Angle of Attack
A change in airspeed or a change in peripheral speed (depending on RPM) results immediately in a change of resultant relative air flow direction and velocity. This can even lead to a negative angle of attack, for example during descent with idle power. The propeller would then drive the engine (windmilling). This would mean negative torque for the engine. As a certain angle of attack is optimal for any given propeller, a fixed propeller only works optimally within a given speed range. Thus fixed propellers are good for climbing performance, or optimized for towing or for high cruising speeds.
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Influences on the Angle of Pitch
Change of Peripheral Speed u
Change of Airspeed v
Figure 4
Influences on the Angle of Pitch
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GEOMETRY OF THE PROPELLER BLADE
Tip Section
Blade Shapes and Profiles (Airfoil Sections)
Blade Angle
For every speed range there is an optimal profile shape with regard to lift and drag. Thick profiles are used for low speeds and thin ones (usually laminar profiles) for high speeds. At the same time the profile changes from thick at the root area to thin at the blade tips. This is of advantage regarding static stress. In the root area, where the forces are higher, we find a thicker material cross −section, so that the stresses affecting the material do not exceed the permissible range. The blade shape depends on the purpose of the propeller, whereby performance, airspeed and diameter play a role. The higher the circle load is, the wider the propellers which should be used. For reasons of reducing noise, propeller tips should be elliptical.
s n o i t c e S “ 6
Blade Twist
The further the profile section of the propeller blade is from its rotational axis, the greater will be the peripheral speed at constant rotational speed. If a nearly constant angle of pitch is to be retained, the propeller blade must be twisted. The angle of incidence must become smaller the further it is from the axis in order to keep a nearly constant angle of pitch. In practice the angle of incidence running the length on the blade determines the angle of pitch in such a way that an optimal distribution of lift results. In addition to the angle of incidence, the profile shape also changes for static and aerodynamic reasons.
! Y L N O S E S O P R U P G N I N I A R T R O F
Blade Shank
Center of Hub Blade Butt
Figure 5
Twisted Blade
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Figure 6
Twisted Prop. Blades
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M17 Geometric Pitch
If the propeller were to spiral through the air on a course, where the angle of pitch equalled the blade angle, the propeller would, in one rotation, have moved forward axially by the ”geometric pitch”. If the aircraft moved through the air according to the geometric propeller pitch, the propeller angle of attack would be zero. To calculate the geometric pitch of a propeller based on the blade angle, you use the blade angle at the reference station on the blade. This is normally 3/4 of the propeller radius. Effective Pitch
The actual helical path on which the propeller moves through the air has an angle of pitch which corresponds to the angle of advance. With one rotation of the propeller the aircraft moves forward by the effective pitch. The effective pitch can be calculated by replacing the blade angle by the angle of advance in the above equation. Slip
Slip is geometric pitch minus effective pitch. It is given in percentage of geometric pitch. PROPELLER PITCH AND EFFICIENCY Propeller Efficiency
! Y L N O S E S O P R U P G N I N I A R T R O F
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Propeller efficiency is basically the performance produced by the propeller in relationship to its motive performance. Motive performance is the same as the output power of the engine (brake power). The performance produced is the thrust performance of the propeller. Thrust performance can be calculated from thrust and airspeed. Propeller efficiency can also be calculated by dividing effective pitch by geometric pitch. Propeller efficiency ranges from 0.8 to 0.9 (80% − 90%).
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effective pitch = angle of advance β
geometric pitch = blade angle ϕ
Figure 7
Propeller Pitch
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M17 Aerodynamic Forces on the Propeller Blade
When air flows towards the propeller blade with the resultant (w), resultant air force (FR) is produced. With regard to the propeller element it is termed ∆FR. This can be split into its components ∆FL and ∆FD. The quotient of ∆FD and ∆FL results in the lift/drag ratio. As with air flowing around a wing, here the drag ∆FD is considerably lower than lift ∆FL. The resultant airforce can also be divided in such a way that the component ∆Fs lies in the direction of flight and ∆FT in the propeller rotational plane. The component ∆Fs represents the share of thrust and ∆FT is the tangential force component. If ∆FT is multiplied by the effective lever to the propeller’s axis of rotation, the result is the share of propeller brake moment. The sum of all partial forces ∆Fs over the radial extent of all propeller blades results in the propeller thrust. If the torque of all partial forces ∆FT are added together over the same area, we arrive at the resultant propeller torque or the brake moment of air forces affecting the propeller. At constant rotational speed the sum of propeller brake moment and engine torque is zero.
The reason for the air forces created on the profile is the difference in pressure on the profile, arising from the air flowing around it. As the acceleration of air in the propeller wash is caused by the difference in pressure, the resultant air force ∆FR can be looked upon as being the force which is reactive to the accelerating forces of the air.
! Y L N O S E S O P R U P G N I N I A R T R O F
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turn direction
flight direction
! Y L N O S E S O P R U P G N I N I A R T R O F
Figure 8
Forces on the Blade
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M 17 PROPELLER M 17.1 FUNDAMENTALS
M17 PROPELLER BRAKE MOMENT Brake Moment with Changing Airspeed
The Brake moment is produced by the partial force ∆FT, which affects the propeller blades. As ∆FT is a component of the resultant air force ∆FR, ∆FT is to a great extent directly dependent on the angle of pitch. Thus the propeller blade angle of pitch has a direct influence on the brake moment. With constant rotational speed the angle of pitch can be influenced by changes in airspeed or blade angle (pitch). When the airspeed increases, the partial force ∆FT becomes smaller, as does the brake moment. If the engine continues to supply the same motive power and the propeller is not adjusted, the rotational speed will increase until the moments return to equilibrium. Accelerating to very high airspeeds, an engine with fixed propeller can exceed its maximum permissible rotational speed. In such a case a timely reduction in power is necessary. Brake Moment when Changing the Blade Angle
A reduction in blade angle (pitch) leads to a reduction on the partial force ∆FT and thus to a reduction in the brake moment. With constant motive power the rotational speed will increase. An increase in pitch has the opposite effect. If the pitch is adjusted to a changing airspeed, the magnitude of brake moment can be maintained. This leads to a constant rotational speed without changing engine power and to almost constant propeller thrust FS.
In this way propeller efficiency improves for the whole of the aircraft’s speed range. Thus with the same engine power higher airspeeds can be achieved than in the case of a fixed propeller. ! Y L N O S E S O P R U P G N I N I A R T R O F
EASA PART 66
Brake Moment when Windmilling
If with constant pitch airspeed increases rapidly or rotational speed is greatly reduced, a flow of air to the propeller occurs which causes the propeller to windmill. In this case the partial force ∆FT works in the direction of rotation and drive the propeller. As thrust ∆Fs is relatively large in this situation and directed against the direction of flight, the aircraft drag is considerably increased by a windmilling propeller. The drag caused by the propeller is greatly reduced if it is put in the feathering position.
Brake Moment at Reverse Thrust
If the blade angle is reduced so far that the angle of attack is less than the zero lift angle of attack, thrust acting against the direction of flight results. The partial force ∆FT acts contrary to the direction of rotation, so that the brake moment it causes must be overcome by the drive. The brake moments which occur very quickly become very large when the blade angle is reduced. So corresponding engine power must be available to maintain the rotational speed. As the air mass flowing through the propeller plane is not accelerated but decelerated, maximum achievable brake thrust increases with airspeed and can even exceed take −off thrust.
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Reverse ! Y L N O S E S O P R U P G N I N I A R T R O F
Windmilling
Reverse direction of turn
direction of turn Figure 9
Windmilling and Reverse
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EFFECT ON THE AIRCRAFT Effect of Engine Torque on the Aircraft
The counter moments caused by engine torque tries to turn the aircraft around the longitudinal axis against the propeller’s rotation. Due to this moment the main landing gear on that side is pushed strongly towards the ground when taxiing and especially on take−off. This leads to an asymmetric distribution of roll resistance and produces a yaw moment around the aircraft’s vertical axis, in other words causing a certain run−off tendency at take−off. To compensate for the roll moment during flight, aerodynamic means are normally used. An example of this would be a small trim strip or a trim tab on one of the ailerons. Exact compensation is only possible for one particular speed and engine power. Normally cruising speed is chosen. At greater and lower airspeeds the pilot must make corrections with small deflections of the aileron. The Twist Effect of the Propeller Wash.
! Y L N O S E S O P R U P G N I N I A R T R O F
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 and produces a stabilizer load (FQ) or a yaw moment around the aircraft’s vertical axis. At the same time a roll moment around the aircraft’s longitudinal axis is created. If the propeller is rotating clockwise, as seen by the pilot, these moments will make the aircraft slew to the left. This tendency is heightened by engine torque. To compensate the vertical stabilizer is normally mounted obliquely by 1 ° to 2° to the aircraft’s longitudinal axis. This aerodynamic compensation is only perfect for one operational regime (normally during cruise). In addition, there are other effects of the propeller wash which are of note. If the propeller is mounted in front of a wing and rotates clockwise (as seen from behind), the propeller wash is deflected to the left. Rotating anti-clockwise, the deflection is to the right. The main reason for this is the circulation around the wing, which through the superpositioning with the propeller airstream increases the rate of flow in the upper propeller semi-circle while reducing it in the lower. In a homogenous parallel stream these changes in velocity would lead to a downwards deflection. But as the propeller wash is twisted it causes, in the same way as a gyro, a pitching motion known as precession. The described deflection of the propeller wash to one side can, depending on how the tailplane and fin are arranged, lead to a change in the direction of air flowing to these parts.
Figure 10
Twisted Fin
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twist effect due to propeller wash
twist effect due to engine torque
Figure 11
Effect of Propeller Wash
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PROPELLER NOISE The Components of Propeller Noise
If we analyses propeller noise, we can distinguish between the following components according to their origins. 1. A. 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. B. 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. C. 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. D. Blade Vibration Noise This noise occurs with periodic stalls, for example when the stall limit of the blade is alternately exceeded and fallen below. The rotors of helicopters are a good example of this phenomenon. E. 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. The latter can then work in an undisturbed airflow. This is not the case with variable pitch propellers when the angle of pitch is negative and the propeller has zero thrust. Then the vortices of the preceding blade hit the leading edge of the following blade. This results in noise. A similar occurrence is possible if the airflow on the preceding blade stalls as a result of excessive load.
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db(A)
Brake Power Propeller Diameter
2−Blade 3−Blade 4−Blade
Speed of Sound 330 m/s
! Y L N O S E S O P R U P G N I N I A R T R O F
-1 min RPM Figure 12
Propeller Noise
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G Influence of Propeller Blade Shape
With the same power, blade area, profile type, camber, profile section, ratio and diameter a scimitar −shaped propeller produces the least noise, and one with straight tips the most. This favorable effect of the sabre −shape is due to the increasing outward sweep of the propeller blade as the locally occurring effective mach number is reduced by the factor cos ϕ (ϕ = angle of sweep). The following list shows by about how much propeller noise can be changed according to various influencing factors: blade tip shape: 3 − 6 dB profile type: 2 − 3 dB blade contour: 1 − 2 dB blade twist: 1 − 2 dB profile camber: 1 − 2 dB profile section ratio: 1 − 2 dB G Influence of Material
If the blades are not made of metal but of wood or composite construction, they have a more favourable vibrational behavior due to better self −damping properties. The noise caused by blade vibrations is lower in the case of such blades. Also by using composite construction more aerodynamic and low−noise blade shapes can be realised without problems regarding strength and stiffness occurring. The SAAB 2000 propeller is a good example of this. Its construction was optimized with a view to the influences described above. In order to keep noise development as low as possible, this composite propeller rotates when cruising at only 950 rpm. ! Y L N O S E S O P R U P G N I N I A R T R O F
Figure 13
Different Shapes of Propellers
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a) Scimitar Shape b) Elliptical Shape, with rounded Tips c) Straight Tips
! Y L N O S E S O P R U P G N I N I A R T R O F
swept propeller Figure 14
Propeller Shapes
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PROPELLERBELASTUNGEN
t
BLADE SHAPES AND PROFILES (AIRFOIL SECTIONS)
For every speed range there is an optimal profile shape with regard to lift and drag. Thick profiles are used for low speeds and thin ones (usually laminar profiles) for high speeds. At the same time the profile changes from thick at the root area to thin at the blade tips. This is of advantage regarding static stress. In the root area, where the forces are higher, we find a thicker material cross −section, so that the stresses affecting the material do not exceed the permissible range. The blade shape depends on the purpose of the propeller, whereby performance, airspeed and diameter play a role. The higher the circle load is, the wider the propellers which should be used. For reasons of reducing noise, propeller tips should be elliptical.
Clark Y
d
Clark Y
RAF 6
PROPELLER LOADS
The components of the propeller are subject to very high loads when in operation. We differentiate between static and dynamic loads.
RAF 6
G Static Loads
! Y L N O S E S O P R U P G N I N I A R T R O F
Centrifugal force is the main static load on the propeller. Furthermore the propeller is subject to loads from brake moment and the thrust acting on the blades. Torque loads affect the propeller because of the off −centre shift in the centre of pressure and from the blade’s mass distribution together with the centrifugal force. The static loads are superimposing at the blade root. Thus the greatest stress from static loads occurs in the region of the blade root. Damage and repair work, for example the blending of strike damage, are not permitted in this area. As the blades are attached to the hub, this too is subject to high loads, and thus high stresses also affect its material.
NACA 16
NACA 16
Laminar-Profil
Figure 15
NACA Shapes
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centrifugal force thrust distribution
thrust
Bending by braking moment
FS
Bending by thrust loads
centre of pressure point of rotation
! Y L N O S E S O P R U P G N I N I A R T R O F
M torque loads due to mass distribution and centrifugal force
Figure 16
Static Loads
torque loads by difference of point of rotation and pressure
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F. Dynamic loads Maximum dynamic loads occur in the range of the natural frequency of the propeller. The vibrations are excited by the inconstant drive RPM of piston engines as a result of the operating stroke phases of the individual cylinders or by vibrations of the propeller gearbox. Additionally unfavourable aero dynamic conditions cause vibrations. The natural frequency of the propeller blades depends on blade length, blade shape, blade root and material. The basic frequency ranges from 20 Hz (metal) to 60 Hz (wood). The blade’s natural frequencies also change over the RPM range due to differing centrifugal loads. At a distance of about 20% of the blade radius from the blade tip the highest vibrational loads occur. This region is therefore particularly susceptible. Nicks caused by scratching, corrosion and strikes affect the durability of metal propellers particularly severely. For this reason it is essential to look out for such damage during a blade inspection. Damage is to be rectified in accordance with the manufacturer’s manual.
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unsymetr.
1.Order
symetr.
R= 0,8
Point of max. Vibration Loads (Outer Nodal Point)
! Y L N O S E S O P R U P G N I N I A R T R O F
2.Order
3.Order
Figure 17
Dynamic Loads
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B. Dynamic loads due to Resonance
The exciting frequency for propeller blade vibrations changes with RPM. The combination of engine and propeller is chosen in such a way that the vibrational behaviour of the combination is not critical in the operational range of the engine. With some propellers the frequency excited by a certain RPM range may lie within the natural frequency range of the propeller. With 2 −blade metal propellers used on small aircraft this resonance is found at about 2100 − 2200 propeller RPM range. This range is therefore not suitable for continuous operation and should be avoided. In order to have a picture of the vibrational behaviour of the propeller, a resonance diagram is constructed. The horizontal line shows engine RPM (min−1) and the vertical line the calculated frequencies (min −1). Frequency lines 1 − 4 and the line of the natural frequency of the propeller are drawn on the diagram. The natural frequency line of the propeller must not cut through the lines of exciting frequencies in the operating range.
max. design load
off limit rpm range ! Y L N O S E S O P R U P G N I N I A R T R O F
propeller rpm
Figure 18
Keep ou out Zo Zone
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resonance diagram f
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natural frequency 1 natural frequency 2
engine rpm
Figu Figure re 19
Res Resonan onance ce Dia Diagra gram
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M 17 PROPELLER M 17.2 CONSTRUCTION
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M17.2
PROPELLER CO CONSTRUCTION
GENERAL 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. Variable pitch propellers are further categorized according to the method of pitch changing, for example hydraulic, mechanical or electrical, according to the type of change, e. g. changing to a particular angle or a particular RPM or according to the scope of change. In this respect there are propellers which, in addition to normal change of pitch, can also be feathered and/or put into reverse thrust.
Wooden blades are either made in one piece from laminated wood or as a combination, with kunstharzpressholz (Synthetic Resin Compressed Wood) at the blade root and a light wood (e. g. spruce) for the body of the blade. The certification of these propellers requires a great deal of time −consuming work and a vibration examination. They have not become very popular and are used only in special cases.
FIXED PITCH PROPELLERS
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Fixed pitch propellers are used for up to about 200 kW (250 hp) performance and speeds of up to 250 km/h (160 mph). The blade angle (pitch) cannot be changed and is determined in accordance with the purpose it is to be used for. For steep climbing and towing low (fine) pitch is needed and for more gradual climb and cruising flight a higher (coarse) pitch is preferred. Greater efficiency can only be achieved over a small range of speeds. Fixed propellers are favourable with regard to production and maintenance costs. These propellers are generally manufactured from forged light alloys or layers of bonded wooden strips (typically birch). The fixed pitch propeller has a thick hub to create a smooth transition from the thick airfoil section at the blade root (with its high blade angle) to the hub. In most cases these propellers can be attached directly to the engine with bolts. To maintain a larger distance from the engine flange, which allows for a more favourable engine cowling, spacers are used, which are available in different thicknesses.
ADJUSTABLE PITCH PROPELLERS The blade angle of an adjustable pitch propeller can be changed on the ground when the engine is shut down. The blades are clamped in the hub. When the clamping bolts are loosened, the blades can be turned in the hub. There are generally adjusting marks in the blade and the hub. The hub is usually made of forged light alloy or steel. The blades are manufactured from forged light alloy or wood.
Figu Figure re 20
Adju Adjust stab able le Pit Pitch ch Prop Propel elle lerr
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CRANK SHAFT
Propeller Installation
REAR SPINNER BULKHEAD
PROPELLER DOWEL PIN SPACER
SPINNER DOME
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FORWARD SPINNER BULKHEAD
Figure 21
Fixed Propeller
RING GEAR ASSEMBLY
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VARIABLE PITCH PROPELLERS GENERAL CONSTRUCTION
In the case of a variable pitch propeller the blade angle can be changed during operation. In this way it can be adjusted for different operating conditions. This type of propeller is therefore more efficient over a wider range of speeds. Nowadays hydraulically controlled variable pitch propellers are almost exclusively in use, except for motorized gliders, the propellers of which are often adjusted mechanically (3 position propeller) or electrically. The blades of a variable pitch propeller are mounted on ball, roller or needle bearings in the hub and can be turned to adjust the blade angle. They can be made of forged light alloys, steel, fibre reinforced plastics, or of a wooden composite construction. The components for adjusting the blade angle are normally found on the front of the hub but in some cases they are inside the hub itself. The main parts are the pitch change piston and the pitch change cylinder, whereby either the piston or the cylinder can move axially. The axial movement of the piston or cylinder is converted into a rotational movement of the blade via pins, bevels or linkages. The oil needed for the hydraulic action is taken from the pressurized oil in the engine lubrication system. It is supplied to the pitch change piston and cylinder via a valve on the governor and through the hollow propeller shaft.
PITCH CHANGING MECHANISM (McCauley BLACKMAC)
Figure 22
Pitch changing Propeller
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Figure 23
Pitch changing Propeller
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PITCH CHANGE RANGE
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. In the case of 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 (least drag). With large aircraft the production of reverse thrust is intended to shorten the distance on landing. For this purpose the propellers are turned to reverse pitch, where air is accelerated forwards while the propellers continue to turn in the same direction. Thus reverse thrust is produced. The following types of propeller commonly have hydraulic pitch change mechanisms: Constant speed propellers (pitch change from low (fine) to high (coarse) pitch) Constant speed propellers with feathering position Constant speed propellers with feathering and reverse (for turboprop engines)
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Low Pitch
High Pitch
Pitch Change Range
Reverse ! Y L N O S E S O P R U P G N I N I A R T R O F
Feather Position
Figure 24
Pitch Ranges
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M 17 PROPELLER M 17.2 CONSTRUCTION
M17 SINGLE ACTING PROPELLERS
Some propeller systems operate in such a way that 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. Propellers which have such a pitch change mechanism are called single acting propellers. Single Acting Propellers for Single-Engine Aircraft
With these propellers the oil pressure moves the blades in the direction of high (coarse) pitch and the spring moves it towards low pitch. After engine shut −down the blades are in the lowest (fine) 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.
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Oil Pressure increases Pitch
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Spring Force decreases Pitch
Pitch Changing Mechanism for Single Engine Aircraft Figure 25
Single Acting one mot
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Single Acting Propellers for Multi-Engine Aircraft
If single acting propellers are used on multi-engine aircraft, oil pressure moves the blades in the direction of low (fine) pitch. The springs and torsional moments of the blades move the blades towards high pitch. If 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. PITCH CHANGEMECHANISM
BLADE
FLYWEIGHTS
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HUB
Figure 26
Pitch changing Propeller
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oil pressure decreases pitch
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flyweight increases pitch
Figure 27
Single Acting dual or quat mot
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PITCH CHANGE MOMENTS FROM CENTRIFUGAL FORCE (FLY WEIGHTS)
The centrifugal force of the propeller blade mass produces a pitch change moment which turns the blade in the direction of low (fine) pitch. The creation of this natural pitch change moment (or flymoment) is due to the distribution of the propeller blade mass. The mass elements not lying on the blade axis create a proportion of centrifugal force, the effect of which is at a small angle away from the blade axis. Thus this force has a component in radial direction F ZR and one in tangential direction F ZT. The latter component is at right angles to the blade axis. This tangential force component affects the blade laterally to its axis. This means that the force components work with a lever on the blade axis, on which the blade turns, and therefore produce torque 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. The creation of the pitch change moment from the centrifugal force of the flyweight is based on the same principles as for the propeller blade. The torque in the direction of high (coarse) pitch produced by the flyweight is as a rule twice the amount of the natural torque in the direction of low pitch.
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Figure 28
Flyweight and its Moment
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DOUBLE ACTING PROPELLERS
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. The valve for controlling the flow of oil to the two ends of the piston is mounted either behind the gearbox or in the propeller hub.
If the control valve, as in the Dowdy propeller of the Fokker 50, is mounted behind the gearbox in the PCU, the propeller shaft must have two oil transfer tubes, one for the front and one for the back of the piston. These oil tubes are constructed as coaxial tubes (here beta tube).
COARSE PITCH OIL COARSE PITCH OIL
FINE PITCH OIL FINE PITCH OIL
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COARSE COARSE
Figure 29
Moving Cylinder Propeller Figure 30
Moving Piston Propeller
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BLADE ASSEMBLY
COUNTERWEIGHT
CYLINDER
PROPELLER CYLINDER
PISTON
CROSSHEAD SHAFT
HUB
OPERATING PIN ASSEMBLY
PISTON DOWEL HOLE
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BLADE ROOT
BETA TUBE
CROSSHEAD YOKE
Figure 31
Double Acting Propeller
HUB
CROSSHEAD YOKE
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SPINNER
Spinners are mounted for reasons of better aerodynamics, as a mechanical protection for the hub and for visual reasons. They are usually manufactured in one piece from aluminium alloy or glass fibre composites. They are attached to the spinner backplate (or spinner bulkhead) and there is normally a support at the front end of the propeller hub for centering. 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. Repairs are limited (mostly drilling to stop a crack is allowed). On installation it must be ensured that no noticeable wobble is present. Balanced spinners which are identified as such must be installed in accordance with the identification.
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STARTER RING
SPINNER
O-RING SEAL
GREASE POINT MOUNTING NUT ! Y L N O S E S O P R U P G N I N I A R T R O F
D U T S
Figure 32
Constant Speed Propeller Installation
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PRODUCTION METHODS AND MATERIALS Propellers are categorized according to the material used for their blades. There are: Wood propellers Metal propellers Composite propellers WOODEN PROPELLERS Construction of Wooden Propellers
A wooden propeller consists of several layers of wood bonded together with a watertight resin glue. At least 5 layers are used. Birch is the most commonly used wood. But mahogany, cherry, ash, beech, oak and walnut may also be used. After bonding, the propeller is given its desired shape by planing. If necessary, glass fibre laminations and edgings are applied. A final coating of poly-urethane paint will act as both mechanical and UV protection . Wooden propellers have metal strips on the leading edges and may also have a glass fibre jacket. The outer thin areas of the propeller blade tips are often reinforced by a fabric sheathing. Wooden propellers are lighter than metal ones, more economical and because of the better damping effect are less likely to be cracked by vibrations. They do however have slightly poorer efficiency. Because of damaging UV rays wooden propellers should be protected by a coat of coloured polyurethane paint. No vibration measurements are required for the registration of wood propellers. Special attention must be paid to the torque of the hub bolts, as the wood of the hub can be damaged by bruising if over −tightened. ! Y L N O S E S O P R U P G N I N I A R T R O F
Figure 33
Propeller Manufacture
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BONDED WOOD LAYER
SHAPED PROPELLER
FINISHED PROPELLER
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FABRIC SHEATING HUB ASSEMBLY
LAMINATED WOOD BLADE
Figure 34
METAL TIPPING
Production of a Wood Propeller
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METAL PROPELLERS
Metal propellers are used for greater engine power. Generally propellers forged or milled from aluminium alloy are employed. But there are also propellers made from steel plate. Aluminium Propellers
Aluminium propellers are milled to the desired profile shape after forging. The twisting of the blades is optimized afterwards. When the propeller has been ground to its final shape and balanced, the surfaces are protected. This is done either by painting, coating or anodizing. It is possible to make aluminium propellers thinner than wooden ones. The propeller profiles can be made very efficient without having to worry about structural limitations. Aluminium propellers need a great deal less maintenance than wooden ones and therefore have lower operating costs. Steel Propellers
Steel propellers are not in common use. They are found on some older aircraft or often on transport aircraft. Steel blades are normally hollow, but solid blades are also in use. Solid blades are forged and then worked in the same way as aluminium ones. The twisting of the blades follows to give them the desired aerodynamic twist. Hollow steel propellers have a ribbed structure which is foam filled in the region of the blade tip. In this way the profile shape remains intact and the blade vibrations are dampened. Steel propellers are extremely durable and resistant to damage. ! Y L N O S E S O P R U P G N I N I A R T R O F
Figure 35
Metal Propeller
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Figure 36
Metall Propeller
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COMPOSITE PROPELLERS Construction of Composite Propellers with a Metal Spar
Composite propeller blades can be constructed in the manner shown in the picture below. The spar runs through the centre of the blade, with foam or honeycomb in front and behind as filling material. The fibre −glass shell is constructed around these parts.
The spar absorbs the centrifugal force and the bending load. The shell gives the component the necessary torsional rigidity. There is a heating element on the inner part of the surface of the leading edge and a metal guard on the outer part. The surface is protected by a coat of conducting polyurethane paint. This serves as protection against erosion and as a precaution against the blade becoming statically charged.
SOLID ALUMINIUM ALLOY FIBERGLASS SHELL HONEYCOIMB OR FOAM FILLING MATERIAL BLADE RETENTION
METAL TIPPING
HEAT MAT
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SPAR
Figure 37
Composite Blade with Spar
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Figure 38
Composite Blade with spar
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Construction of Composite Blades without Metal Spar.
The picture below shows a blade without a metal spar. The two carbon fibre components in the blade form the spar and the hollow centre is filled with polyurethane foam. The fibre −glass shell surrounds the spar. At the root of the
blade the spar is attached to the metal blade −root components. The operating pin is inserted in the pitch change mechanism.
Polyurethane foam core
Polyurethane leading edge protection
Aluminium braid lightning conductor
Glas fiber envelope
Glas fiber blade envelope
Carbon fiber spar Outer sleeve
Polyurethane foam core
Carbon fiber blade spars
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Glas fiber wedges
Figure 39
Composite Blade without Spar
Inner sleeve
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POLYURETHANE FOAM
CARBON FIBER CUFF
POLYURETHANE COATING
CARBON FIBER SPARS
POLYURETHANE FOAM CORE GLASS FIBER BLADE ENVELOPE
DE-ICER BOOT LEAD WOOL
RUBBER PLUG
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BALANCE TUBE OUTER SLEEVE
POLYURETHANE SPRAY COAT
METAL BRAID LIGHTNING CONDUCTOR
NICKEL LEADINGEDGE GUARD
Figure 40
Dowdy Blade (F 50)
INNER SLEEVE
OPERATING PIN
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M 17 PROPELLER M 17.3 PITCH CONTROL MM
M17
M17.3
PROPELLER PITCH CONTROL
CONSTANT SPEED PROP. FOR PISTON ENGINES FUNCTIONAL PRINCIPLE OF THE CONSTANT SPEED PROPELLER
With a propeller working on the constant speed principle the RPM selected by the pilot is kept constant by changing the blade angle (pitch). If the propeller RPM changes, for example as a result of changes in flight attitude, the propeller change mechanism reacts by altering the blade angle. This has an effect on the brake moment of the propeller and the RPM returns to the selected value. A reduction in pitch leads to a smaller brake moment and thus higher RPM. Increasing the pitch creates a greater brake moment and revolutions decrease. However this system can only keep RPM constant if the blade is not at either pitch stop. 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. If the propeller control lever in the cockpit is pushed right forward during static ground operation, the propeller moves to the low (fine) pitch stop. In this position RPM is dependent only on the motive power of the engine, i.e. on the position of the thrust lever.
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M17
Airflow RPM = const. if Brake Moment MB = Drive Torque MA Drive Torque MA
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P = MA * n * 2π
Brake Moment MB
Figure 41
Brake Moment
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M 17 PROPELLER M 17.3 PITCH CONTROL MM
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THE 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 propeller governor and an oil supply from the engine hydraulic oil and scavenge oil system. The governor receives its RPM signal either from its installed position on the engine. The governor is set to the selected RPM via rods or a push −pull cable from the cockpit. Inside the governor there is a pilot valve. 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. 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 spring, the tension of which can be adjusted by the propeller control lever in the cockpit. (RPM selection). The governor continuously compares the selected RPM with the actual RPM and adjusts the pilot valve accordingly. The propeller control lever is also called speed lever or condition lever.
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single actingsingle engine propeller governing system
SCAVENGE OIL
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SCAVENGE OIL
SCAVENGE OIL
Figure 42
Constant Speed System
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M17 PROPELLER PITCH CHANGE
Small single engine aircraft usually have propellers without a feathering position. With propellers of this size oil pressure causes a change only in one direction, towards higher (coarser) pitch. This kind of variable pitch propeller is known as a single acting propeller. 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 less drag when starting the engine.
SPEED ADJUSTING CONTROL LEVER HIGH RPM STOP LIFT ROD SAFETY SPRING
ADJUSTING WORM
SPEEDER SPRING FLYWEIGHT DRIVE GEAR SHAFT
TOE FLYWEIGHT HEAD
PILOT VALVE PLUNGER
BYPASS PLUG
BYPASS PLUG
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RELIEF VALVE PROPELLER CONTROL LINE ENGINE OIL INLET
Figure 43
Any Governor
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M17
Shown:
Nact
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ENGINE OIL INLET
Figure 44
Propeller Pitch Control
Nact = Ncmd
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M17 PROPELLERS FOR TURBOPROP ENGINES CHARACTERISTICS OF TURBOPROP ENGINES
RPM Ranges
The efficiency of the compressor and turbine is dependent on RPM. For this reason turboprops can only supply the power needed over a small RPM range. As the maximum output power of the engine at any given RPM is only a little above the brake power of the propeller, an increase in RPM would take place only slowly. Thus the propeller of a turboprop rotates with constant RPM within its operating ranges. Changes in power are achieved by changes in torque. To adjust the brake moment to drive moment over the total range of performance, the propellers of turboprops have a greater range of pitch change than those of piston engines.
FLIGHT IDLE
GROUND IDLE PERCENT
PERCENT
RPM
RPM TURBO PROP
RECIPROCATING
Beta mode
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 beta mode. This can only be selected on the ground. In beta mode the blade angle is changed directly with the power lever, so that any angle between zero thrust and flight idle can be selected. Here the RPM is selected with the condition lever and remains constant. Engine speed (and propeller RPM) in beta mode are generally lower than in alpha mode. When the power lever is moved behind the zero thrust position, the propeller moves into the reverse beta range to the corresponding blade angle.
TAKE OFF
FLIGHT IDLE (GLIDE RPM)
P P RECIP P TPE
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P Prop
RPM Figure 45
Engine Power vs. Propeller Power
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M17
45° MAX BLADE ANGLE
45° MAX BLADE ANGLE
CONSTANT SPEED OPERATING RANGE CONSTANT SPEED 20° MIN BLADE ANGLE
OPERATING RANGE
GROUND IDLE 5° FLIGHT IDLE ZERO THRUST
PLANE OF ROTATION
GROUND IDLE BETA RANGE REVERSE ! Y L N O S E S O P R U P G N I N I A R T R O F
PROPELLER OF A RECIPROCATING ENGINE Figure 46
PROPELLER OF A TURBOPROP ENGINE Comparison of Blade Angles
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M17 The green coloured condition lever or propeller lever (speed lever) controls the propeller rotation speed in alpha mode. The forward stop is the T/O position. When the condition lever is retarded the feather position is selected. In beta mode you take direct influence on the engine power.
PROPELLER CONTROL Prop. Governing Mode
This typical engine control stand shows the control levers of the engines and the propellers. The yellow coloured power lever controls the engine power and the drive moment in alpha mode. The power lever takes direct influence on the blade angle in beta mode.
POWER LEVERS
RPM
FWD P
HI
THRUST
O W E R
FLT IDLE LATCH ARM
FLIGHT
HI
CONDITION LEVERS (SPEED LEVERS)
LO GROUND LO
FLT IDLE GND IDLE
ENGINE STOP REV
AND
THRUST
EMERGENCY FEATHER
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FRICTION LOCKS
FRICTION
engine governor
alpha mode
beta mode
POWER LEVER CONDITION LEVER
CONDITION LEVER POWER LEVER
Figure 47
Control Stand
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Figure 48
Control Stand(1)
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M17 In the system shown here of the TPE 331 engine the underspeed governor is located in the fuel control unit. It regulates the RPM below the range controlled by the prop governor. The propeller is of the single acting type. The RPM range in alpha mode is relatively small, from 95% to 100%. RPM is selected with the condition lever and power is set between flight idle and maximum with the power lever.
Prop. Governing Mode
In the flight range (alpha mode, prop governing mode) the propeller operates as a constant speed propeller. Here the propeller is controlled with the aid of the prop governor in the same way as the constant speed propeller of the piston engine.
Engine and Propeller Control in Propeller Governing Mode (Take Off and Flight Operation) Prop Governor controls RPM
PROP GOVERNOR
Power Lever movement
PROP PITCH CONTROL
has no effect on PPC
FLIGHT IDLE
(BETA VALVE)
and Prop Governor
FUEL FLOW
Pressure
PROP RPM
GROUND IDLE
FLIGHT IDLE
MAX FF MAXIMUM
REVERSE
POWER LEVER
Cond. Lever
Power Lever Condition Lever
controls
sets RPM ! Y L N O S E S O P R U P G N I N I A R T R O F
influence on USPD Gov. inhibited
Fuel Flow
PROP GOVERNING MODE Blade Angle: +14° to +40° Engine RPM:
100%
95% to 100%
FUEL CONTROL UNIT
95% METERING
UNDERSPEED
SECTION
GOVERNOR
CONDITION LEVER
LOW
(SPEED LEVER)
ENGINE STOP
HIGH
CONDITION LEVER
FUEL
ENGINE STOP
FLOW
Figure 49
FEATHER
(SPEED LEVER)
Alpha Mode
CONDITION LEVER
FEATHER
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M17
GUST LOCK LEVER
POWER LEVER CONDITION LEVER ! Y L N O S E S O P R U P G N I N I A R T R O F
FRICTION LOCKS
Figure 50
Control Stand DO 328
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M 17 PROPELLER M 17.3 PITCH CONTROL
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MM
M17 Beta Mode
In beta mode the blade angle is changed directly with the power lever, so that any angle between zero thrust and flight idle (or full reverse) can be selected. Here control of the blade angle works in the form of follow up control. For this purpose the power lever works directly on the beta valve. On reaching the position selected for the propeller blades, resetting of the beta valve takes place through mechanical feedback from the propeller to the beta valve. The RPM is selected for the governor inside the
control unit with the condition lever and then remains constant. In this operational range the prop governor is ineffective. RPM in beta mode is usually smaller than in alpha mode.
Engine and Propeller Control in Beta Mode (Ground Operation)
PROP
PROP PITCH CONTROL
GOVERNOR
(BETA VALVE)
Power lever controls Blade Angle (+14° to -14°) +14° OIL PRESSURE
GROUND IDLE
FLIGHT IDLE
PROP RPM
MAXIMUM
(0−THRUST) POWER LEVER
Cond. Lever influence on PG inhibited ! Y L N O S E S O P R U P G N I N I A R T R O F
-14° REVERSE
Power Lever
Condition Lever
influence on FCU inhibited
controls Engine RPM 65% to 96%
FUEL CONTROL UNIT
BETA MODE OPERATION Blade Angle: +14° to -14°
100% 95%
Engine RPM: 65%
to 96% METERING
UNDERSPEED
SECTION
GOVERNOR
HIGH
CONDITION LEVER (SPEED LEVER) METERING
UNDERSPEED
SECTION
GOVERNOR
Figure 51
FUEL
Beta Mode
LOW
CONDITION LEVER
ENGINE STOP
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M17 Featherlng
If the engine is shut down during flight, the propeller must be moved into the feathering position so that there is as little drag as possible. In the system seen here this is done by reducing the oil pressure in the propeller change mechanism. The propeller is then moved into the feathering position by spring pressure. If the condition lever is pulled from low via engine stop to feather, the following occurs: 2. The engine is shut down by closing the HP fuel shutoff valve. 3. Oil pressure in the pitch change mechanism is reduced by opening the feathering valve.
PROP PITCH CONTROL
FLIGHT IDLE
OIL PRESSURE
Auto Feather System
In order to keep the pilot’s work load low if an engine loses power during take −off, auto feather systems are employed. They are activated for take −off and react to the decreasing torque of an engine in case of its malfunction. When the engine torque has dropped off far enough, the auto feather system switches the feathering valve to the feather position and turns on the feathering pump.
POWER LEVER
HP FUEL SHUTOFF VALVE
FEATHERING VALVE
FUEL CONTROL UNIT
! Y L N O S E S O P R U P G N I N I A R T R O F
OIL BLEED
METERING FUEL SECTION
UNDERSPEED
HIGH
GOVERNOR
FLOW
CONDITION LEVER (SPEED LEVER)
Figure 52
Feathering System
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M 17 PROPELLER M 17.3 PITCH CONTROL
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M17
A /
B
POWER
Engine Power Loss During
LEVER
FROM PROPELLER
NP INDICATOR
ELECTRONIC CONTROL
Take Off
SERVO LO PITCH
VALVE
Loss of Engine Torque below a Certain Value BLADE ANGLE CHANGING MECHANISM
FUEL LEVER
FEATHERING
OVERSPEED
GOVERNOR
VALVE
REDUCTION GEARBOX POWER TURBINE
FLT
GND
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PUMP
FEATHER AUTOFEATHER
UNIT
AUTOFEATHER
HP PUMP
FEATHERING
ON
COMMAND FEATHER PUMP
AUXILIARY OIL TANK
Figure 53
ENGINE OIL
Auto Feathering
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ELECTRONIC PROPELLER CONTROL
In the case of turboprop engines with electronic propeller control the task of the propeller governor is taken over by the propeller electronic control unit (PEC). A mechanical overspeed governor is also installed on the engine and the pitch control unit (PCU) takes over the hydromechanical functions in the control system. Electrical control of the PEC is carried out via the servo valve located in the PCU. With constant speed control (prop governing mode) the flow of oil to the propeller is controlled solely by the PEC via the servo valve.
The PCU contains the feathering valve and the beta valve. The PCU is connected to the propeller via the beta tube. This serves as an oil transfer tube and also transmits the feedback signal in beta mode. The rear end of the beta tube together with the corresponding parts of the PCU forms the beta valve. In prop governing mode the functions of the beta valve and the feathering valve are not required.
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M 17 PROPELLER M 17.5 PROPELLER ICE PROTECTION
M17
M17.5
PROPELLER ICE PROTECTION
GENERAL Icing of the propeller when in operation leads to vibrations and to lower propeller efficiency. When the aircraft is flying under icing conditions, icing protection is necessary to prevent ice from forming on the propeller blades. There are two main methods: Fluid anti−icing system Electrical de−icing system
THE FLUID ANTI −ICING SYSTEM A very simple and problem−free method to prevent ice formation 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. 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.
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Ice Accumulation on a Propeller Figure 54
Iced Propeller
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M 17 PROPELLER M 17.5 PROPELLER ICE PROTECTION
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M 17 PROPELLER M 17.5 PROPELLER ICE PROTECTION
EASA PART 66 M17 SLINGERRING BULKHEAD BOOT WITH GROOVES
VENTLINE
FLUIDTANK
RIVET
CHECK VALVES
BULKHEAD
RHEOSTAT FILTER ! Y L N O S E S O P R U P G N I N I A R T R O F
SLINGERRING RIVET
FLUIDPUMP SLINGERRING FLUIDFEEDSHOE
Figure 55
Fluid Anti-Icing System
ANTI ICE LINE
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ELECTRICAL DE −ICING 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 two heating elements embedded in them. Electrical power is supplied via slip rings from the aircraft electrical system. 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.
SPINNER
EXTENSOIN DOME
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BULKHEAD AND RING ASSY
Figure 56
BLADE
BLADE SWITCH
Anti Icing Ring
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DEICING POWER CIRCUIT BREAKER OR LIMITER
DE-ICING POWER LINES POWER RELAY
NACELLE BUS SHUNT
PROPELLER BLADE
STAINLESS STEEL RIBBON
POWER RELAY LOADMETER
CONTROL PANEL
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TO OTHER PROPELLERS
TIMER OR CYCLING UNIT FUSELAGE BUS
TO OTHER PAIR OF BLADES PROPELLER DEICE ROOT BONDED TO BLADE
INTERNAL OR EXTERNAL HEATING ELEMENTS
PROPELLER HUB
CONTROL SWITCH CONTROL CIRCUIT BREAKER
Figure 57
QUICK DISCONNECT WIRING HARNESS
Electrical De-Icing System
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M 17 PROPELLER M 17.6 PROPELLER MAINTENACE
M17
M17.6
PROPELLER MAINTENANCE
GENERAL The propeller is a component which is subject to high loads. In particular, the influence of stresses at points for which the propeller is not designed are critical. Therefore it is not permissible to push or pull smaller aircraft by the outer parts of the propeller. Influences of the environment, such as corrosion, erosion or stone strikes together with high dynamic loads create points from where cracks can start (stress riser). In the case of variable pitch propellers water produced by condensation in the lubricants can lead to corrosion, with the result that propeller blades may become jammed and that leaks will occur. For these reasons the instructions of the propeller and aircraft manufacturers must be strictly adhered to. The UK Civil Aviation Authority Airworthiness Notice No. 75 is a Mandatory notice detailing the maintenance requirements for variable pitch propellers installed on aircraft holding a UK Certificate of Airworthiness.
TIME BETWEEN OVERHAULS
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The manufacturer determines the times between overhauls. For some types of propellers fitted to commercial aircraft permissible operating periods for the propeller hub, actuator and blades often differ from each other. For operational reasons the propeller blades are combined in such a way that their periods of use on one propeller are not the same. In this way only one blade has to be changed at the end of the respective operating time. Generally the intervals are tied to a particular number of operating hours of the aircraft. In addition to this stipulation many manufacturer also demand a calendar time limit so that propellers which are not used so regularly are included. The reason for this is not the operational but the ageing of lubrications and seals, and the effects of corrosion over time. In this respect the following abbreviations are important: TSN = Time since new (i.e. total operational time since manufacture) TSO = Time since overhaul (i.e. operational time since last overhaul) TBO = Time between overhaul (i.e. permissible operating (sometimes calendar) time between two overhauls) The aircraft operator is required to keep a log of TSN and TSO.
INSPECTION & REPAIR WOODEN PROPELLERS Inspection and repair
When examining the blades the surface protection coating must be inspected. It must be 100% intact so that no moisture can penetrate. Cracks at the beginning of and along the metal tipping are usually insignificant and caused by differing expansion of the material. Cracks in the paint across the blade are signs of flexural vibrations. Cracks through the leading edge tipping are the result. If the tipping is cracked in this way, it must be replaced immediately. In the case of riveted tipping, loose rivets are a sign that the wood beneath it is damaged. The propeller should be taken out of service immediately. Less significant damage on the trailing edge or on the blade can be filled with plastics. Indentations in the metal tipping can be filled by soldering. In this case the use of any significant heat is to be avoided and balance must be taken into consideration. Perforated tipping must be replaced. When checking the surface for damage, attention should be paid to any signs of delamination of the layers of the wood. The following damage cannot be repaired and renders the propeller unusable: Cracks across the grain A splintered blade Delamination Missing material Cracks in the hub Enlargement of the hub shaft bore Elliptical bolt holes After installation of a new fixed pitch wood propeller the attachment bolts must be re−tightened after 25 hours with the torque prescribed. Afterwards the tightness must be checked at least every 50 hours as humidity causes the wood to shrink and expand.
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CRACKS IN LEADINGEDGE
CRACKS
BLADE ROOT LATERAL CRACKS IN THE PAINT DUE TO VIBRATION
TYPICAL EROSION
LAQUER METAL TIPPING
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METAL TIPPING
SOLDER
Figure 58
RESIN
BRONZE MESH
Typical Damages on a Wood Propeller
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M 17 PROPELLER M 17.6 PROPELLER MAINTENACE
M17 METAL PROPELLERS
Metal propellers are particularly prone to metal fatigue. This is caused by the high dynamic loads. Scratches, hairline cracks, impact marks and the effects of corrosion are potential starting points for cracks. As a result of additional bending and centrifugal forces the crack extends, usually over the matt black sprayed back side of the propeller blade. Care of Metal Propellers
In order to avoid a failure of the propeller blades the following measures are recommended: 4. Maintenance instructions and intervals are to be strictly observed. 5. RPM limitations are to be observed. 6. Never taxi at high power if sand, stones or other material can be sucked into the propeller. 7. Clean the propeller regularly (not with alkaline cleaning agents) and rub with an oily cloth or car polish. 8. Do not cover the propeller (moisture forming can cause corrosion). 9. When handling small aircraft do not pull using the outside of the propeller blades but use the propeller root instead. 10.Carry out careful pre − and after −flight inspections for nicks, scratches and other damage. Deep nicks must be repaired immediately according to manufacturer’s instructions. 11.Every 100 hrs or at least at every annual check inspect the propeller thoroughly for damage after cleaning. In case of doubt use a magnifying glass or other methods of checking for cracks (using dye check). ! Y L N O S E S O P R U P G N I N I A R T R O F
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Repair of Damage
Information on permissible repairs can be found in the manufacturer’s manuals. If no information is available, the following source can be used: FAA AC 4313 −1A Aircraft Inspection and Repair Permissible repair on the blade width is normally 1.2mm from the root to 0.6R and from 0.6R to blade tip 2.4mm, however not under the permissible blade width. Permissible repair on the blade thickness is 0.7mm over the whole blade, however not under the minimum blade thickness nor across the whole of the blade. WARNING: NO REPAIR WHATEVER IS PERMISSIBLE ON THE BLADE
ROOT
Nicks must be worked out with a large radius (10 x depth of nick). The profile shape of the leading edge must remain intact. The place repaired must be checked for cracks and the surface smoothed with fine abrasive cloth. This prevents cracks extending from marks left by tools. Working and polishing must always be done in the direction of the blade axis. Repair also includes removing any compressed material beneath the nick. When repairing the blade tips the minimum permissible diameter must be observed. Under no circumstances is it allowed to apply material using heat treatment or to fill nicks with plastics. All types of cold working are also prohibited. On completion of the repair the surface is to be appropriately protected. After material has been removed, a ground run should be conducted to check whether the propeller has become unbalanced. In the case of a two −blade propeller the removal of about 2 − 3 gm is noticeable as a vibration. When in doubt, the propeller must be rebalanced. Lubrication
Many variable pitch propellers have no provision for additional lubrication. In this case filling with lubricant during overhaul will be sufficient. Those propellers which have provision for additional lubrication are treated in accordance with manufacturer’s instructions using the appropriate approved grease. The nipple on the opposite side must be removed on various Hartzell propellers so that the seal is not forced out. Inspection of the hub
During periodic inspections the hub must be checked for cracks and corrosion. The exterior parts of the pitch change mechanism and the hub should be free from corrosion. Grease leaks indicate damage of the blade attachment seals. Oil leaks are a sign of damaged seals in the pitch change cylinder or of damage to the blade attachments (oil−smeared blade bearings). As a protection against corrosion lubricant spray can be applied to the hub after cleaning. If there is excessive play on the blade tips or of the blade angle, the cause may be damage to the blade attachment or the pitch change mechanism. It is equally serious if the blades stick (stiffness can be due to construction).
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MAXIMUM THICKNESS OF BLADE SECTION AT POINT APROX: 0.3 OF LENGTHS SHOWN CORRECT METHOD
CROSS SECTION BEFORE REPAIR
0,3 CHORD LENGTH
CROSS SECTION AFTER REPAIR
ORIGINAL SECTION
REWORKED BLADE
NOTE:
! Y L N O S E S O P R U P G N I N I A R T R O F
A : MAINTAIN ORIGINAL RADIUS B : REWORK CONTOUR TO POINT OF MAX.THICKNESS C :RADIUS IS TO LARGE D : CONTOUR IS TOO BLUNT
DAMAGED PORTION BEFORE REPAIR
INCORRECT METHOD
Figure 59
AFTER REPAIR
Repair of Metal Blades
SURFACE CRACK BEFORE REPAIR
AFTER REPAIR CRACK WORKED OUT
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COMPOSITE-PROPELLER Inspection & Repair
When inspecting a composite blade, this has to be checked in the same way as all other composite structures. Damage is classified as skin perforated damage and skin not perforated damage. Skin not perforated damage: abrasion scratches gouges nicks deboning delamination dents Skin perforated damage: lightning strike holes In addition the condition of the tipping on the leading edge and the heating element (if present) are to be checked. When the propeller remains attached, only minor repairs are possible, such as the recoating of the PU finish, for example. If struck by foreign material the edges can be smoothed and the missing material replaced.
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CHECK BLADE FOR: -ABRASION (WHOLE SURFACE) -SCRATCHES -GOUGES -NICKS -DEBONDING -DELAMINATION -DENTS -LIGHTNING STRIKE -HOLES -CONDITION OF LEADING EDGE
LIGHTNING STRAP
LEADING EDGE SHEATH
EROSION COATING,
BLADE HEATER ALUMINUM SPAR ! Y L N O S E S O P R U P G N I N I A R T R O F
FIBERGLASS SHELL
Figure 60
Inspection of Composite Blades
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BLADE CG
CG
BALANCING STAND ROTATIONAL AXIS OF PROP BLADE C
ROTATIONAL AXIS OF PROP C G
G
BALANCING PLATE
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LOCATION
STATIC IMBALANCE
DYNAMIC IMBALANCE Figure 61
Propeller Balancing
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AERODYNAMIC BALANCING
Propellers can be affected by vibrations because of the differing aerodynamic loads of the blades resulting from the different blade angles. In this case the blades produce individual thrust forces of different values. The sum of the individual thrust forces of the blades (total thrust of the propeller) no longer lies at the propeller’s axis of rotation. Total thrust, being off −centre, rotates with the propeller leading to vibrations. Aerodynamic balancing is only necessary for propellers with high performance. Manufactured blades are compared individually with a master blade and receive, according to deviation from the zero lift angle, an aerodynamic correction factor in the form of a reference to the blade angle difference necessary to the basic setting. Blade angles differing from each other are here intentionally prescribed. The correction factor is usually marked on the blade root. Determining the correction factor is also known as blade indexing.
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RESULTANT THRUST
CL
CL
RESULTANT THRUST
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BLADE THRUST
BLADE THRUST
AERODYNAMIC BALANCED
Figure 62
AERODYNAMIC UNBALANCED
Aerodynamic Balancing
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M17 CHECKING BLADE TRACKING Blade tracking is the ability of one blade to follow the other in the same plane of rotation. Tracking is held to reasonable limits to prevent roughness. To check the tracking, place a smooth board just under the tip of the lower blade. On controllable props, move the tip fore and aft carefully through its small range of motion, making small pencil marks at each position. Center the blade between these marks and draw a line the full width of the blade. Repeat this procedure with another blade tip. The lines should be separated by not more than 3 mm. Differences greater than 3mm may be an indication of bent blades, improper installation or foreign particles between the hub and crankshaft mounting faces.
PROPELLER ENGINE RUNNING PISTON ENGINE PROPELLER RUNNING
A propeller installed on an engine must be checked before, during and after the engine has been ground operated. A propeller whose pitch change mechanism is electrically actuated may be checked prior to the engine being operated. TURBOPROP ENGINE PROPELLER RUNNING
Turboprop engine operation is quite similar to that of a turbojet engine, except for the added features of a propeller. The starting procedure and the various operational features are similar. Engine ground operations should be performed by qualified staff only.
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TRACK ADJUSTING ON A WOOD PROPELLER WITH SHIMS
SHIMS
FACEPLATE STICK ATTACHED TO WING
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BLADE TRACKS
MAXIMUM TRACK VARIATION
Figure 63
Blade Tracking
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M 17 PROPELLER M 17.7 STORAGE AND PRESERVATION
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M17.7
PROPELLER STORAGE & PRESERVATION Oil leakage at seal on pitch change rod plug
INSTALLED PROPELLERS PERIODS UP TO 3 MONTHS
Installed propellers require to be kept in a clean condition and inspected at regular intervals for corrosion. The propeller must be exercised on a weekly basis by carrying out an engine ground run to lubricate the internal components such as the pitch change mechanism and the constant speed governor. In the event that an engine ground run can not be carried out then the pitch change mechanism must be exercised by feathering and unfeathering the propeller.
Oil leakage between pitch change rod and reverse adjustment sleeve
Oil leakage between cylinder base and cylinder-side hub half
PERIODS OVER 3 MONTHS
If the propeller is to be stored ’on the wing’ 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. All external parts should be treated with Lanolin or an approved anti-corrosive treatment and inspected regularly for corrosion. NOTE:
ENSURE THAT LANOLIN DOES NOT COME INTO CONTACT WITH THE DE-ICER BOOTS
Grease leakage at lubrication fitting ! Y L N O S E S O P R U P G N I N I A R T R O F
Oil leakage at seal between engine flange and propeller mounting flange
Grease leakage at bladesocket in hub
Figure 64
Hub Leackages
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M 17 PROPELLER M 17.7 STORAGE AND PRESERVATION
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Figure 65
Ground Engine Run
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M 17 PROPELLER M 17.7 STORAGE AND PRESERVATION
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UNINSTALLED PROPELLERS ASSEMBLED PROPELLERS
Assembled propellers should be stored on racks or stands in a clean, dry and warm environment. The propeller should be kept in the original manufacturers packing but if the original packing is not available it should be wrapped in waxed paper. The pitch change mechanism should be inhibited with an inhibiting oil and all external components should be coated in Lanolin. All loose components - oil tubes, cones etc. should be coated in Lanolin and wrapped in waxed paper. COMPONENTS USED TO RETAIN THE PROPELLER ONTO THE ENGINE ARE CONSIDERED TO BE PROPELLER PARTS. Propeller bearings are required to be exercised after 6 and 9 months. After 12 months the bearings need to be cleaned, checked for ’Brinelling’ and corrosion and then regreased. Brinelling is a material surface failure caused by contact stress that exceeds the material limit. This failure is caused by just one application of a load great enough to exceed the material limit. The result is a permanent dent or ”brinell” mark. It is a common cause of roller bearing failures. It is also caused by vibrations that occur from machines nearby while stored or during transportation. NOTE:
DISASSEMBLED PROPELLERS
! Y L N O S E S O P R U P G N I N I A R T R O F
All parts should be immersed in an inhibiting oil, drained and any bearings coated with a mineral jelly. Clean all electrical equipment and and treat external surfaces with a rust preventer. Electrical connectors should be coated with petroleum jelly and stored in moisture proof bags. all other parts should be wrapped in waxed paper and stored in suitable crates. The maximum storage period is up to 3 years 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.
Brinelling marks
Figure 66
Bearing with Brinelling
g n i n i a r T l a c i n h c e T a s n a h t f u L
M
M 17 PROPELLER M 17.7 STORAGE AND PRESERVATION
M17
Brinelling marks
! Y L N O S E S O P R U P G N I N I A R T R O F
EASA PART 66
Figure 67
Brinelling
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TABLE OF CONTENTS M17 M17.1
M17.2
M17.3
M17.5
M17.6
M17.7
PROPELLER . . . . . . . . . . . . . . . . . . . . . . .
1
PROPELLER FUNDAMENTALS . . . . . . . . . . . . . . . . . . .
2
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . HOW THE PROPELLER WORKS . . . . . . . . . . . . . . . . . . .
2 2
PROPELLER CONSTRUCTION . . . . . . . . . . . . . . . . . . . .
28
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FIXED PITCH PROPELLERS . . . . . . . . . . . . . . . . . . . . . . ADJUSTABLE PITCH PROPELLERS . . . . . . . . . . . . . . . . VARIABLE PITCH PROPELLERS . . . . . . . . . . . . . . . . . . . PRODUCTION METHODS AND MATERIALS . . . . . . . .
28 28 28 30 44
PROPELLER PITCH CONTROL . . . . . . . . . . . . . . . . . . .
52
CONSTANT SPEED PROP. FOR PISTON ENGINES . . PROPELLERS FOR TURBOPROP ENGINES . . . . . . . .
52 58
PROPELLER ICE PROTECTION . . . . . . . . . . . . . . . . . . .
70
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THE FLUID ANTI−ICING SYSTEM . . . . . . . . . . . . . . . . . . ELECTRICAL DE−ICING SYSTEM . . . . . . . . . . . . . . . . . .
70 70 74
PROPELLER MAINTENANCE . . . . . . . . . . . . . . . . . . . . .
76
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TIME BETWEEN OVERHAULS . . . . . . . . . . . . . . . . . . . . . INSPECTION & REPAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . CHECKING BLADE TRACKING . . . . . . . . . . . . . . . . . . . . PROPELLER ENGINE RUNNING . . . . . . . . . . . . . . . . . . .
76 76 76 86 86
PROPELLER STORAGE & PRESERVATION . . . . . . . .
88
INSTALLED PROPELLERS . . . . . . . . . . . . . . . . . . . . . . . . UNINSTALLED PROPELLERS . . . . . . . . . . . . . . . . . . . . .
88 90
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TABLE OF FIGURES Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
Propellerstream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Propeller Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Propeller Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Influences on the Angle of Pitch . . . . . . . . . . . . . . . . . . . . . . . . . Twisted Blade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Twisted Prop. Blades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Propeller Pitch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forces on the Blade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Windmilling and Reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Twisted Fin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effect of Propeller Wash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Propeller Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Different Shapes of Propellers . . . . . . . . . . . . . . . . . . . . . . . . . . Propeller Shapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NACA Shapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Static Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dynamic Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Keep out Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resonance Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Adjustable Pitch Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fixed Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pitch changing Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pitch changing Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pitch Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single Acting one mot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pitch changing Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single Acting dual or quat mot . . . . . . . . . . . . . . . . . . . . . . . . . . Flyweight and its Moment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Moving Cylinder Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Moving Piston Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Double Acting Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Constant Speed Propeller Installation . . . . . . . . . . . . . . . . . . . Propeller Manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Production of a Wood Propeller . . . . . . . . . . . . . . . . . . . . . . . . . Metal Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 3 5 7 8 9 11 13 15 16 17 19 20 21 22 23 25 26 27 28 29 30 31 33 35 36 37 39 40 40 41 43 44 45 46
Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure
36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 75 76 77 78 58 59 60 61 62 63 89 90 91 92
Metall Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Composite Blade with Spar . . . . . . . . . . . . . . . . . . . . . . . . . . . . Composite Blade with spar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Composite Blade without Spar . . . . . . . . . . . . . . . . . . . . . . . . . Dowdy Blade (F 50) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brake Moment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Constant Speed System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Any Governor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Propeller Pitch Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Engine Power vs. Propeller Power . . . . . . . . . . . . . . . . . . . . . . Comparison of Blade Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . Control Stand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control Stand(1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alpha Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Control Stand DO 328 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Beta Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feathering System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Auto Feathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Iced Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fluid Anti-Icing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anti Icing Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrical De-Icing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical Damages on a Wood Propeller . . . . . . . . . . . . . . . . . . Repair of Metal Blades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inspection of Composite Blades . . . . . . . . . . . . . . . . . . . . . . . . Propeller Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aerodynamic Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Blade Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hub Leackages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ground Engine Run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bearing with Brinelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brinelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47 48 49 50 51 53 55 56 57 58 59 60 61 62 63 64 66 67 71 73 74 75 77 79 81 83 85 87 88 89 90 91
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TABLE OF FIGURES
