16.01.2009, 14:05
Hey guys, I noticed some people pay decent attention to prop pitch. Any advantage to not leaving it on AUTO?
When and What do I use prop pitch for?
16.01.2009, 16:32
Yes, the advantage is being able to sustain a pure vertical climb for slightly longer when increasing prop to 100% from auto.
100% seems to pull the hardest torque and RPM, whilst AUTO works good in a dive.
Turn & burn dogfights = 100%
Catch a bandit in a dive = Auto or 80 - 90% prop.
That's my take - in a nuttshell.
100% seems to pull the hardest torque and RPM, whilst AUTO works good in a dive.
Turn & burn dogfights = 100%
Catch a bandit in a dive = Auto or 80 - 90% prop.
That's my take - in a nuttshell.
16.01.2009, 19:01
the prop pitch has various uses, one of which is for planes with allison engines (example: p40) they will go faster on around 80 prop pitch than 100.
Other planes that i've noted are the Ki27 which seems to be much faster on around 60% prop pitch compared to 100% (it's around 60 u have to fiddle with it)
Other reasons for using it is to cool engines so 90% throttle and 90% pitch seem to work well in F4U and that will stop u from overheating pretty much ever.
Other planes that i've noted are the Ki27 which seems to be much faster on around 60% prop pitch compared to 100% (it's around 60 u have to fiddle with it)
Other reasons for using it is to cool engines so 90% throttle and 90% pitch seem to work well in F4U and that will stop u from overheating pretty much ever.
16.01.2009, 20:02
Hey Man...think of prop pitch as a manual tranny in a car
but first...
What is pitch?
Propeller theory includes a variety of concepts that may at times be called pitch. Pitch can refer to the blade angle with respect to a flat plane, the distance that a propeller will advance through the air for each rotation or the amount of "bite" that the blade has on the air. Essentially these concepts all describe the same thing.
To use automobile analogy,
pitch is like the gear ratio of the gearbox. The important thing to note with pitch, is that it is available in a wide variety of degrees, or 'amounts', much like different gear ratios.
To demonstrate, consider the following examples:
A fine pitch propeller has a low blade angle, will try to move forward a small distance through the air with each rotation, and will take a 'small' bite of the air. It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a low gear in your automobile.
A coarse pitch propeller has a high blade angle, will try to advance a long distance through the air with each rotation, and will take a big 'bite' of the air. It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds. This is like having a high gear in your automobile.
With a variable-pitch propeller, you really have choices.
To use the automobile analogy again,
your car now has a real gearbox that you can change gear with on the go. In addition, rather than being limited to 4 or 5 gears, you can utilise any pitch along the continuum from maximum to minimum. The pitch of the propeller may be controlled in flight to provide improved performance in each phase of flight. Typically you would take-off in a fine pitch (low gear) allowing your engine to develop reasonable revs, before increasing the pitch (change up gears) as you accelerated to your cruising speed. You'll end up with the propeller at a relatively coarse pitch, (high gear) allowing the miles to pass beneath you at a rapid rate, while your engine is gently ticking over at a comfortable RPM.
This feature of a variable-pitch propeller will provide you with performance advantages, including:
Reduced take-off roll and improved climb performance. Fine pitch allows the engine to reach maximum speed and hence maximum power at low airspeeds. Vital for take-off, climb,
and for a go-around on landing.
Improved fuel efficiency and greater range. Coarse pitch allows the desired aircraft speed to be maintained with a lower throttle setting and slower propeller speed, so maintaining efficiency and improving range.
Higher top speed. Coarse pitch will ensure your engine does not overspeed while the propeller absorbs high power, producing a higher top speed.
Steeper descent and shorter landing roll. With a fine pitch and low throttle setting, a slow turning propeller is able to add to the aircraft's drag, so slowing the aircraft quicker on landing.
The inflight-adjustable propeller allows the pilot to directly vary the pitch of the propeller to the desired setting. Combined with the throttle control, this control allows a wide variety of power settings to be achieved. A range of airspeeds can be maintained while keeping the engine speed within limits. While rare in larger aircraft, the inflight-adjustable propeller is the most common type of variable-pitch propeller that is encountered in aviation.
Easy
but first...
What is pitch?
Propeller theory includes a variety of concepts that may at times be called pitch. Pitch can refer to the blade angle with respect to a flat plane, the distance that a propeller will advance through the air for each rotation or the amount of "bite" that the blade has on the air. Essentially these concepts all describe the same thing.
To use automobile analogy,
pitch is like the gear ratio of the gearbox. The important thing to note with pitch, is that it is available in a wide variety of degrees, or 'amounts', much like different gear ratios.
To demonstrate, consider the following examples:
A fine pitch propeller has a low blade angle, will try to move forward a small distance through the air with each rotation, and will take a 'small' bite of the air. It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a low gear in your automobile.
A coarse pitch propeller has a high blade angle, will try to advance a long distance through the air with each rotation, and will take a big 'bite' of the air. It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds. This is like having a high gear in your automobile.
With a variable-pitch propeller, you really have choices.
To use the automobile analogy again,
your car now has a real gearbox that you can change gear with on the go. In addition, rather than being limited to 4 or 5 gears, you can utilise any pitch along the continuum from maximum to minimum. The pitch of the propeller may be controlled in flight to provide improved performance in each phase of flight. Typically you would take-off in a fine pitch (low gear) allowing your engine to develop reasonable revs, before increasing the pitch (change up gears) as you accelerated to your cruising speed. You'll end up with the propeller at a relatively coarse pitch, (high gear) allowing the miles to pass beneath you at a rapid rate, while your engine is gently ticking over at a comfortable RPM.
This feature of a variable-pitch propeller will provide you with performance advantages, including:
Reduced take-off roll and improved climb performance. Fine pitch allows the engine to reach maximum speed and hence maximum power at low airspeeds. Vital for take-off, climb,
and for a go-around on landing.
Improved fuel efficiency and greater range. Coarse pitch allows the desired aircraft speed to be maintained with a lower throttle setting and slower propeller speed, so maintaining efficiency and improving range.
Higher top speed. Coarse pitch will ensure your engine does not overspeed while the propeller absorbs high power, producing a higher top speed.
Steeper descent and shorter landing roll. With a fine pitch and low throttle setting, a slow turning propeller is able to add to the aircraft's drag, so slowing the aircraft quicker on landing.
The inflight-adjustable propeller allows the pilot to directly vary the pitch of the propeller to the desired setting. Combined with the throttle control, this control allows a wide variety of power settings to be achieved. A range of airspeeds can be maintained while keeping the engine speed within limits. While rare in larger aircraft, the inflight-adjustable propeller is the most common type of variable-pitch propeller that is encountered in aviation.
Easy
16.01.2009, 22:37
I mess with prop pitch when im cruising at altitude while flying bombers. A good B-17 cruise setting is 70% throttle, 80% pitch
16.01.2009, 22:55
Wish there was like a pocket guide to what pitch to use in what aircraft etc for newbies like my self :roll:
17.01.2009, 02:27
i have a book that lists a few planes and thier ideal prop pitch , name the plane and i will see if its in there.
here are a couple of examples :-
La-7 :pilot notes.
Combat engine setting: 2,500rpm, best cruise 2,100rpm, economy cruise 2,000rpm.
P-40e:pilot notes.
combat engine setting :3,000rpm, best cruise 2,600rpm , economy cruise 2,500rpm.
Although this doesnt tell you prop pitch , You will have to look at your instruments. Remember reducing prop pitch = reduced RPM. Correct use of throttle and prop pitch will result in better performance.
Of course each different engine has its own power band and best operational rpm, The merlin for spitfire, or hurricane for example is best left at 100%-98% prop pitch as the engine works best at 3,000rpm ( this would be in Mk V mk IX has auto prop pitch) There is a red marker on the spitfires rev counter :wink:
hope this helps S~
here are a couple of examples :-
La-7 :pilot notes.
Combat engine setting: 2,500rpm, best cruise 2,100rpm, economy cruise 2,000rpm.
P-40e:pilot notes.
combat engine setting :3,000rpm, best cruise 2,600rpm , economy cruise 2,500rpm.
Although this doesnt tell you prop pitch , You will have to look at your instruments. Remember reducing prop pitch = reduced RPM. Correct use of throttle and prop pitch will result in better performance.
Of course each different engine has its own power band and best operational rpm, The merlin for spitfire, or hurricane for example is best left at 100%-98% prop pitch as the engine works best at 3,000rpm ( this would be in Mk V mk IX has auto prop pitch) There is a red marker on the spitfires rev counter :wink:
hope this helps S~
17.01.2009, 09:03
On all aircraft with controllable props the prop has to be at low pitch/high rpm to develop its rated takeoff horsepower and rpm.
17.01.2009, 11:32
Congompasse Wrote:On all aircraft with controllable props the prop has to be at low pitch/high rpm to develop its rated takeoff horsepower and rpm.
Not to seem ...picky or whatever,
but the term Low pitch is confusing to someone that does not actual fly aircraft,
as it is actually refered to as "Fine" or "Coarse" pitch in aviation.
Low or High does not really describe anything that the propeller is doing.
Don't mean nothing,just I see the term Low and High refered to quite abit.
Yet you will never see that written in any aviation book you need for a pilots license.
It's always refered to as Fine or Coarse pitch,which actually describes what the prop is doing.
Easy
17.01.2009, 12:56
Low pitch refers to low blade angle. Most tech manuals refer to setting the low pitch and high pich stops when setting up the prop for any particular powerplant installation.
Although some older adjustable-pitch propellers could only be adjusted
on the ground, most modern adjustable-pitch propellers are designed so
that you can change the propeller pitch in flight. The first
adjustable-pitch propeller systems provided only two pitch settings?a
low-pitch setting and a high-pitch setting. Today, however, nearly all
adjustable-pitch propeller systems are capable of a range of pitch
settings.
Aconstant-speed propeller is the most common type of adjustable-pitch
propeller. The main advantage of a constant-speed propeller is that it
converts a high percentage of brake horsepower (BHP) into thrust
horsepower (THP) over a wide range of r.p.m. and airspeed
combinations. A constant-speed propeller is more efficient than other
propellers because it allows selection of the most efficient engine
r.p.m. for the given conditions.
An airplane with a constant-speed propeller has two controls-the
throttle and the propeller control. The throttle controls power
output, and the propeller control regulates engine r.p.m. and, in
turn, propeller r.p.m., which is registered on the tachometer.
Once a specific r.p.m. is selected, a governor automatically adjusts
the propeller blade angle as necessary to maintain the selected r.p.m.
For example, after setting the desired r.p.m. during cruising flight,
an increase in airspeed or decrease in propeller load will cause the
propeller blade angle to increase as necessary to maintain the
selected r.p.m. A reduction in airspeed or increase in propeller load
will cause the propeller blade angle to decrease.
The range of possible blade angles for a constant-speed propeller is
the propeller's constant-speed range and is defined by the high and
low pitch stops. As long as the propeller blade angle is within the
constant-speed range and not against either pitch stop, a constant
engine r.p.m. will be maintained. However, once the propeller blades
contact a pitch stop, the engine r.p.m. will increase or decrease as
appropriate, with changes in airspeed and propeller load. For example,
once a specific r.p.m. has been selected, if aircraft speed decreases
enough to rotate the propeller blades until they contact the low pitch
stop, any further decrease in airspeed will cause engine r.p.m. to
decrease the same way as if a fixed-pitch propeller were installed.
The same holds true when an airplane equipped with a constant-speed
propeller accelerates to a faster airspeed. As the aircraft
accelerates, the propeller blade angle increases to maintain the
selected r.p.m. until the high pitch stop is reached. Once this
occurs, the blade angle cannot increase any further and engine r.p.m.
increases.
On airplanes that are equipped with a constant-speed propeller, power
output is controlled by the throttle and indicated by a manifold
pressure gauge. The gauge measures the absolute pressure of the fuel/
air mixture inside the intake manifold and is more correctly a measure
of manifold absolute pressure (MAP). At a constant r.p.m. and
altitude, the amount of power produced is directly related to the fuel/
air flow being delivered to the combustion chamber. As you increase
the throttle setting, more fuel and air is flowing to the engine;
therefore, MAP increases. When the engine is not running, the manifold
pressure gauge indicates ambient air pressure (i.e., 29.92 in. Hg).
When the engine is started, the manifold pressure indication will
decrease to a value less than ambient pressure (i.e., idle at 12 in.
Hg). Correspondingly, engine failure or power loss is indicated on the
manifold gauge as an increase in manifold pressure to a value
corresponding to the ambient air pressure at the altitude where the
failure occurred.
The manifold pressure gauge is color-coded to indicate the engine's
operating range. The face of the manifold pressure gauge contains a
green arc to show the normal operating range, and a red radial line to
indicate the upper limit of manifold pressure.
For any given r.p.m., there is a manifold pressure that should not be
exceeded. If manifold pressure is excessive for a given r.p.m., the
pressure within the cylinders could be exceeded, thus placing undue
stress on the cylinders. If repeated too frequently, this stress could
weaken the cylinder components, and eventually cause engine failure.
You can avoid conditions that could overstress the cylinders by being
constantly aware of the r.p.m., especially when increasing the
manifold pressure. Conform to the manufacturer's recommendations for
power settings of a particular engine so as to maintain the proper
relationship between manifold pressure and r.p.m.
When both manifold pressure and r.p.m. need to be changed, avoid
engine overstress by making power adjustments in the proper order:
When power settings are being decreased, reduce manifold pressure
before reducing r.p.m. If r.p.m. is reduced before manifold pressure,
manifold pressure will automatically increase and possibly exceed the
manufacturer's tolerances.
When power settings are being increased, reverse the order-increase
r.p.m. first, then manifold pressure.
To prevent damage to radial engines, operating time at maximum r.p.m.
and manifold pressure must be held to a minimum, and operation at
maximum r.p.m. and low manifold pressure must be avoided.
Under normal operating conditions, the most severe wear, fatigue, and
damage to high performance reciprocating engines occurs at high r.p.m.
and low manifold pressure.
In actuality most aircraft throttle quadrants are probably marked increase/decrease RPM which is what it acually does by changing the tension on the speeder spring inside the prop govenor. The speeder holds tension on the flyweights that sense rpm,s by the cent force they feel at any given rpm. This aspect is also adjusted when installing props. Though I have seen some WWII quadrants marked as low pitch high rpm/ high pitch low rpm. Aviation sure is fun.
During run up you normally cycle the prop control several times to check its operation and to get warm oil up into the prop dome. It is left in the high rpm setting for take off. As the throttle is advanced you monitor the manifold pressure so as not to overboost. The operating manual will tell you the maximum allowable manifold pressure . For take off it might say 2250 rpms at 35" . If the manual says 2000 RPM,s and 30" manifold pressure for climbout you adjust prop control and throttle to acheive these settings. When leveling out for cruise the manual might say 1900 rpms at 28" . Inches refers to inches of mercury . This is most WWII aircraft flown by the USA. Most of this information is gleamed from the TO,s or Technical Orders that come with the aircraft. This is a series of tech manuals that cover everything from the erection and maintenance to operations. The erection and maintenance portion will cover things like control surface installation. Control rod settings. Control cable tension settinga at given temps. Covering methods for fabric covered control surfaces etc.
Although some older adjustable-pitch propellers could only be adjusted
on the ground, most modern adjustable-pitch propellers are designed so
that you can change the propeller pitch in flight. The first
adjustable-pitch propeller systems provided only two pitch settings?a
low-pitch setting and a high-pitch setting. Today, however, nearly all
adjustable-pitch propeller systems are capable of a range of pitch
settings.
Aconstant-speed propeller is the most common type of adjustable-pitch
propeller. The main advantage of a constant-speed propeller is that it
converts a high percentage of brake horsepower (BHP) into thrust
horsepower (THP) over a wide range of r.p.m. and airspeed
combinations. A constant-speed propeller is more efficient than other
propellers because it allows selection of the most efficient engine
r.p.m. for the given conditions.
An airplane with a constant-speed propeller has two controls-the
throttle and the propeller control. The throttle controls power
output, and the propeller control regulates engine r.p.m. and, in
turn, propeller r.p.m., which is registered on the tachometer.
Once a specific r.p.m. is selected, a governor automatically adjusts
the propeller blade angle as necessary to maintain the selected r.p.m.
For example, after setting the desired r.p.m. during cruising flight,
an increase in airspeed or decrease in propeller load will cause the
propeller blade angle to increase as necessary to maintain the
selected r.p.m. A reduction in airspeed or increase in propeller load
will cause the propeller blade angle to decrease.
The range of possible blade angles for a constant-speed propeller is
the propeller's constant-speed range and is defined by the high and
low pitch stops. As long as the propeller blade angle is within the
constant-speed range and not against either pitch stop, a constant
engine r.p.m. will be maintained. However, once the propeller blades
contact a pitch stop, the engine r.p.m. will increase or decrease as
appropriate, with changes in airspeed and propeller load. For example,
once a specific r.p.m. has been selected, if aircraft speed decreases
enough to rotate the propeller blades until they contact the low pitch
stop, any further decrease in airspeed will cause engine r.p.m. to
decrease the same way as if a fixed-pitch propeller were installed.
The same holds true when an airplane equipped with a constant-speed
propeller accelerates to a faster airspeed. As the aircraft
accelerates, the propeller blade angle increases to maintain the
selected r.p.m. until the high pitch stop is reached. Once this
occurs, the blade angle cannot increase any further and engine r.p.m.
increases.
On airplanes that are equipped with a constant-speed propeller, power
output is controlled by the throttle and indicated by a manifold
pressure gauge. The gauge measures the absolute pressure of the fuel/
air mixture inside the intake manifold and is more correctly a measure
of manifold absolute pressure (MAP). At a constant r.p.m. and
altitude, the amount of power produced is directly related to the fuel/
air flow being delivered to the combustion chamber. As you increase
the throttle setting, more fuel and air is flowing to the engine;
therefore, MAP increases. When the engine is not running, the manifold
pressure gauge indicates ambient air pressure (i.e., 29.92 in. Hg).
When the engine is started, the manifold pressure indication will
decrease to a value less than ambient pressure (i.e., idle at 12 in.
Hg). Correspondingly, engine failure or power loss is indicated on the
manifold gauge as an increase in manifold pressure to a value
corresponding to the ambient air pressure at the altitude where the
failure occurred.
The manifold pressure gauge is color-coded to indicate the engine's
operating range. The face of the manifold pressure gauge contains a
green arc to show the normal operating range, and a red radial line to
indicate the upper limit of manifold pressure.
For any given r.p.m., there is a manifold pressure that should not be
exceeded. If manifold pressure is excessive for a given r.p.m., the
pressure within the cylinders could be exceeded, thus placing undue
stress on the cylinders. If repeated too frequently, this stress could
weaken the cylinder components, and eventually cause engine failure.
You can avoid conditions that could overstress the cylinders by being
constantly aware of the r.p.m., especially when increasing the
manifold pressure. Conform to the manufacturer's recommendations for
power settings of a particular engine so as to maintain the proper
relationship between manifold pressure and r.p.m.
When both manifold pressure and r.p.m. need to be changed, avoid
engine overstress by making power adjustments in the proper order:
When power settings are being decreased, reduce manifold pressure
before reducing r.p.m. If r.p.m. is reduced before manifold pressure,
manifold pressure will automatically increase and possibly exceed the
manufacturer's tolerances.
When power settings are being increased, reverse the order-increase
r.p.m. first, then manifold pressure.
To prevent damage to radial engines, operating time at maximum r.p.m.
and manifold pressure must be held to a minimum, and operation at
maximum r.p.m. and low manifold pressure must be avoided.
Under normal operating conditions, the most severe wear, fatigue, and
damage to high performance reciprocating engines occurs at high r.p.m.
and low manifold pressure.
In actuality most aircraft throttle quadrants are probably marked increase/decrease RPM which is what it acually does by changing the tension on the speeder spring inside the prop govenor. The speeder holds tension on the flyweights that sense rpm,s by the cent force they feel at any given rpm. This aspect is also adjusted when installing props. Though I have seen some WWII quadrants marked as low pitch high rpm/ high pitch low rpm. Aviation sure is fun.
During run up you normally cycle the prop control several times to check its operation and to get warm oil up into the prop dome. It is left in the high rpm setting for take off. As the throttle is advanced you monitor the manifold pressure so as not to overboost. The operating manual will tell you the maximum allowable manifold pressure . For take off it might say 2250 rpms at 35" . If the manual says 2000 RPM,s and 30" manifold pressure for climbout you adjust prop control and throttle to acheive these settings. When leveling out for cruise the manual might say 1900 rpms at 28" . Inches refers to inches of mercury . This is most WWII aircraft flown by the USA. Most of this information is gleamed from the TO,s or Technical Orders that come with the aircraft. This is a series of tech manuals that cover everything from the erection and maintenance to operations. The erection and maintenance portion will cover things like control surface installation. Control rod settings. Control cable tension settinga at given temps. Covering methods for fabric covered control surfaces etc.
17.01.2009, 20:36
There are four common families of propeller,
They are fixed-pitch, ground-adjustable, inflight-adjustable and constant-speed. The last two are both examples of variable-pitch propellers.
The term Low and High were used in what I wrote above:
A (fine pitch propeller) has a ( low ) blade angle, will try to move forward a small distance through the air with each rotation, and will take a 'small' bite of the air. It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a low gear in your automobile.
A (coarse pitch) propeller has a ( high ) blade angle, will try to advance a long distance through the air with each rotation, and will take a big 'bite' of the air. It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds.
This is new>
The load on the engine is the propeller torque.
When the aircraft is stationary, with the engine throttle wide open, the propeller torque and the static thrust generated,(i.e. the efficiency of the engine and the propeller combination) depend on the propeller pitch.
If the pitch is zero or slightly negative, the static thrust will be zero and the propeller torque will be very low so that the engine will race — overspeed — and lose power because of inefficient cylinder charging, etc.
If the pitch is 'fine' ( low ), the propeller will generate near maximum static thrust and sufficient torque to maintain (high engine rpm), thus delivering ample power to the propeller shaft. This is the ideal situation to get the aircraft rolling for take-off and climb-out.
If the pitch is very 'coarse' ( high ), then static thrust is low but propeller torque is very high,
which will slow the engine. This is the worst situation for take-off ,
the aircraft will move forward sluggishly and, most likely, will never reach take-off speed.
I see how people come to refer to low/high
I still think it is a confusing term compared to fine or coarse, just my opinion though...
I have scoured through some more books at home here ,
in all the books I have the term Fine /Coarse is used ,with some only refering to low/high after the term fine or coarse is used. Most topics only fine or coarse are mentioned when describing pitch.
The automobile analogy>
A (fine pitch) propeller has a (low blade angle), will try to move forward a small distance through the air with each rotation, and will take a ('small' bite of the air). It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a ( low gear ) in your automobile.
Stick it Low and go.....Take-off
A (coarse pitch) propeller has a (high blade angle), will try to advance a long distance through the air with each rotation, and will take a(big 'bite' of the air). It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds.
This is like having a ( high gear ) in your automobile.
Get up there and stick it in High gear and cruise Man...
In escense the term low and high are in referance to a blade angle,
of a fine or a coarse adjustment to the pitch of the prop.
In my mind anyway.....but it went through the 60's and 70's Man..... 8)
Thanks for the read ,it's all been interesting
Everything both of us posted is correct....it's just confusing lol
It's all good Man...
Easy
They are fixed-pitch, ground-adjustable, inflight-adjustable and constant-speed. The last two are both examples of variable-pitch propellers.
The term Low and High were used in what I wrote above:
A (fine pitch propeller) has a ( low ) blade angle, will try to move forward a small distance through the air with each rotation, and will take a 'small' bite of the air. It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a low gear in your automobile.
A (coarse pitch) propeller has a ( high ) blade angle, will try to advance a long distance through the air with each rotation, and will take a big 'bite' of the air. It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds.
This is new>
The load on the engine is the propeller torque.
When the aircraft is stationary, with the engine throttle wide open, the propeller torque and the static thrust generated,(i.e. the efficiency of the engine and the propeller combination) depend on the propeller pitch.
If the pitch is zero or slightly negative, the static thrust will be zero and the propeller torque will be very low so that the engine will race — overspeed — and lose power because of inefficient cylinder charging, etc.
If the pitch is 'fine' ( low ), the propeller will generate near maximum static thrust and sufficient torque to maintain (high engine rpm), thus delivering ample power to the propeller shaft. This is the ideal situation to get the aircraft rolling for take-off and climb-out.
If the pitch is very 'coarse' ( high ), then static thrust is low but propeller torque is very high,
which will slow the engine. This is the worst situation for take-off ,
the aircraft will move forward sluggishly and, most likely, will never reach take-off speed.
I see how people come to refer to low/high
I still think it is a confusing term compared to fine or coarse, just my opinion though...
I have scoured through some more books at home here ,
in all the books I have the term Fine /Coarse is used ,with some only refering to low/high after the term fine or coarse is used. Most topics only fine or coarse are mentioned when describing pitch.
The automobile analogy>
A (fine pitch) propeller has a (low blade angle), will try to move forward a small distance through the air with each rotation, and will take a ('small' bite of the air). It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a ( low gear ) in your automobile.
Stick it Low and go.....Take-off
A (coarse pitch) propeller has a (high blade angle), will try to advance a long distance through the air with each rotation, and will take a(big 'bite' of the air). It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds.
This is like having a ( high gear ) in your automobile.
Get up there and stick it in High gear and cruise Man...
In escense the term low and high are in referance to a blade angle,
of a fine or a coarse adjustment to the pitch of the prop.
In my mind anyway.....but it went through the 60's and 70's Man..... 8)
Thanks for the read ,it's all been interesting
Everything both of us posted is correct....it's just confusing lol
It's all good Man...
Easy
17.01.2009, 21:31
Yes Its pretty ingenius how the prop and prop govenor work together to maintain a constant engine speed, most of my experience is with Hamilton Standard Propellers. some counterweighted and some full hydromatics. Minimum Aeroprop and Dowty Rotol . The really crazy props are the ones that change their pitch mechanically rather than using engine oil hydraulically. This was common in German WWII props and some of the Dowty Rotols. Then of course you have the Curtiss Electrics that have an electric motor mounted in the dome and a brush block to feed it. The motor controls blade angle through a planetary gear train.
18.01.2009, 01:24
o.k you guys know your technical stuff.. but it aint helping the guy who posted :lol: laymen terms please
18.01.2009, 06:28
MWW,
Yea youre right, I guess the answer would be stay in the 8 to 10 range. Personally I mapped the pitch change functions to my left and right mouse buttons. Put it at 10 for takeoff. Pull the prop back to 9 for climbout and back to eight for cruise. I think under combat I would probably just leave it at the high rpm setting. Thats where you are going to pull the most hp out of the power plant and acheive your best rate of climb. The 51 in the game will give a 1500 rpm drop at max manifold pressure which is probably a bit high. Probably should be 600 to 800 rpm. I would need to go look at the TO to see what drop should be at max manifold pressure. You can see by the figures below you are normally working in a 700 RPM range depending on what youre doing with the aircraft.
This is from startup checklist for the 51.
BEFORE TAKE-OFF (Run-Up)
At 2000 RPM, check the following: Suction 3.75 to 4.25 inches HG.
Hydraulic pressure 800-1100 lbs/sq. inch.
Ammeter not to exceed 50 amps.
Check the instruments for the following limitations: Desired Maximum
Oil Pressure 70-80 lbs/sq. in. 90 lbs/sq. in.
Oil Temperature 70 deg C - 80 deg C 90 deg C
Coolant Temperature 100 deg C - 110 deg C 121 deg C
Fuel Pressure 12-16 lbs/sq. in. 19 lbs/sq. in.
Check mags at 2300 RPM. Maximum drop 100 RPM.
At 2300 check propeller - 300 RPM maximum drop - and return to full INCREASE RPM.
Oil and coolant shutters AUTOMATIC.
Wing flaps 20
Yea youre right, I guess the answer would be stay in the 8 to 10 range. Personally I mapped the pitch change functions to my left and right mouse buttons. Put it at 10 for takeoff. Pull the prop back to 9 for climbout and back to eight for cruise. I think under combat I would probably just leave it at the high rpm setting. Thats where you are going to pull the most hp out of the power plant and acheive your best rate of climb. The 51 in the game will give a 1500 rpm drop at max manifold pressure which is probably a bit high. Probably should be 600 to 800 rpm. I would need to go look at the TO to see what drop should be at max manifold pressure. You can see by the figures below you are normally working in a 700 RPM range depending on what youre doing with the aircraft.
This is from startup checklist for the 51.
BEFORE TAKE-OFF (Run-Up)
At 2000 RPM, check the following: Suction 3.75 to 4.25 inches HG.
Hydraulic pressure 800-1100 lbs/sq. inch.
Ammeter not to exceed 50 amps.
Check the instruments for the following limitations: Desired Maximum
Oil Pressure 70-80 lbs/sq. in. 90 lbs/sq. in.
Oil Temperature 70 deg C - 80 deg C 90 deg C
Coolant Temperature 100 deg C - 110 deg C 121 deg C
Fuel Pressure 12-16 lbs/sq. in. 19 lbs/sq. in.
Check mags at 2300 RPM. Maximum drop 100 RPM.
At 2300 check propeller - 300 RPM maximum drop - and return to full INCREASE RPM.
Oil and coolant shutters AUTOMATIC.
Wing flaps 20
18.01.2009, 15:36
That's all good info,
All I think I could add is that I have my Prop on the thumb slider on my throttle.
I have a X-52
All I think I could add is that I have my Prop on the thumb slider on my throttle.
I have a X-52
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