Prop Pitch question...

[comswim]

I can sorta see what your getting at there Rama, but I too would have to agree with Vidar and Sniper on this too. My question is will it be different when BoB comes out.

S!

Comswim

[BSS_Sniper]

Rama, I apologize. I just tend to get excited when I know I'm right about something, especially if someone blatantly says I'm wrong about something that is my profession. I doubt you tell your professional pilot friends "You are wrong" when they correct you on something. No harm intended though. Vidar stated things more clear than I was able to.

I did talk to our company A&P. (airframe and powerplant mechanic) The one time the pitch changes without input of the prop levers is if you go into a dive. The change is, however, so brief that it is not something noticed and only a technical note. It would have to be something extreme so that the relative wind is driving the prop and not the engine. The RPM's will speed up a bit and only VERY briefly. That will change the prop pitch, but the governor will bring them back to what the pilot set them at. It's just a brief second or two of change, nothing that would be noticed normally by the pilot.

So in the end, the throttle (Manifold Pressure) will not change Prop Pitch.

[BSS_Sniper]

Originally Posted by comswim

I can sorta see what your getting at there Rama, but I too would have to agree with Vidar and Sniper on this too. My question is will it be different when BoB comes out.

S!

Comswim

We can only hope and pray.

[Rama]

Actually... nothing Vidar said actually contradict what I said, except the last sentence.

He even sais in another form what I said:

The reason for Constant Speed/Variable Pitch propellors is to Optimize the pitch of the propellor in conjuction with power -i.e.throttle- settings at various stages of flight.

CSP do control pitch and do it constantly to adjust for RPM... I said nothing different.
So for a fixed position of the RPM Lever, then, inside the CS Propellor limits:
- if you increase boost (admission pressure): CSP will adjust pitch and blade angle will increase to keep RPM constant.
- if you decrease boost (admission pressure): CSP will adjust pitch and blade angle will decrease to keep RPM constant.
- If you pull the stick, speed will go down: CSP will adjust pitch and blade angle will increase to keep RPM constant (up you reach the limit of the CSP, then RPM will decrease, and you will risk overtorque if you did set RPM too low)
- If you push the stick, speed will increase: CSP will adjust pitch and blade angle will decrease to keep RPM constant (until you reach the limit of the CSP, then RPM will increase and you'll risk overreving if you did set the RPM lever too high)

I did try to stay as simple as possible to be sure to be understood (since I begin to think my English is so bad that Sniper and Vidar don't understand it.... then I should go to take some English lessons...)

[BSS_Sniper]

Correct me if I'm wrong, but I believe you are saying that if you increase boost (manifold pressure) the prop governor will adjust the prop pitch to keep a particular RPM. Is that correct?
If so, I have to disagree still. lol

[Flyby]

This is an interesting topic, and I'm trying to learn something about about real life prop pitch control. But I see that since IL2's complex engine management is not the most accurate representation for a few planes (P51 as an example?) this topic has turned a bit arcane for me. In other words I've missed how I can use this discussion to improve my engine managment in the game itself. I'll go back and re-read this thread, and maybe I'll get the gist of it. Getting a bit dim in my old age, I guess.
Flyby out

[Rama]

Originally Posted by BSS_Sniper

Correct me if I'm wrong, but I believe you are saying that if you increase boost (manifold pressure) the prop governor will adjust the prop pitch to keep a particular RPM. Is that correct?

Absolutly correct, and that's what CSP is designed for.
In order to absorb the increased torque (power is equal to torque times RPM) the CSP will adjust the propellor pitch.

If so, I have to disagree still. lol

As you want.... but better then get some documentation about CSP... (The link I provided could be a first step...)
Just a simple question: How do you think the CSP maintains constant RPM?
Once you will have answered this one, there will be no more missunderstanding between you and me.

[BSS_Sniper]

Originally Posted by Rama

Absolutly correct, and that's what CSP is designed for.
In order to absorb the increased torque (power is equal to torque times RPM) the CSP will adjust the propellor pitch.


As you want.... but better then get some documentation about CSP... (The link I provided could be a first step...)
Just a simple question: How do you think the CSP maintains constant RPM?
Once you will have answered this one, there will be no more missunderstanding between you and me.

Take a look at what Vidar said. He also stated that input from the throttle does NOT change prop pitch. I also spoke with our company A&P mechanic as I stated earlier, he said the samething. The prop lever sets the prop pitch AND RPM. Each RPM has a specific prop pitch setting. Thats why in the case of a dive, when the reletive wind drives the prop to a faster RPM, the pitch changes until the prop governor brings it back to the pilot's setting. What I'm trying to convey is that the throttle does not change the pitch of the prop.

You may be saying that introducing more throttle (power) will cause the governor change the prop pitch to take a bigger bite of air to hold the RPM's the pilot set. Am I getting close to what you mean?

[Loco-S]

http://www.faa.gov/pilots/training/handbook/

ADJUSTABLE-PITCH PROPELLER
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. [Figure 5-6]
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.
Manifold Absolute Pressure (MAP)—The absolute pressure of the
fuel/air mixture within the intake manifold, usually indicated in inches
of mercury.
ch 05.qxd 10/24/03 6:50 AM Page 5-4
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.

[BSS_Sniper]

Could of done without the huge copy and paste, thanks all the same though. lol I've got the books and the FAA certificate.

I'm just trying to clarify what Rama is saying so we can get on the same page.