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geetarman
11-17-2004, 03:22 PM
I usually use planes in IL-2 that have constant speed propeelers (P-38, F6F, etc).

I've decided to "dig into" proper engine management and have a question some may be able to answer.

What is the relationship between setting and maintaining MP and RPM? My understanding is that the throttle (mapped to my joystick slider) controls the pressure of air entering the engine manifold. More throttle = more air coming into the engine = more power available to the engine. Does an increase then, in throttle settings also effect engine rpm's?

CSP's are designed to adjust the props to maintain the desired revolutions that the engine turns. If a pilot wants to maintain 2500 rpms, he "sets" those rpms and the props will adjust, depending on the the position of the plane, to maintain those rpms. My question then is if the throttle controls MP and is used to "set" MP, what control is used to set desired RPM's?

p1ngu666
11-17-2004, 03:58 PM
prop pitch basicaly sets the engine revs in p38, f6f, spit etc.
the blades figure out the best angle for themselves. somehow. dontaskmetoexplaincosidontknowandmybrainwillturnto gooyness.

manifold pressure u are right, that effects the air, and airfuel mix also in most planes i guess (ull use waaay more fuel for wep use, or should)

on lancaster, for best fuel economy with merlins, a resonably high boost pressure, and low rpm was used
aim was to get 200mph ish at lowest revs possible, that be best air miles speed.

TX-EcoDragon
11-17-2004, 04:41 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by geetarman:
What is the relationship between setting and maintaining MP and RPM? . . . Does an increase then, in throttle settings also effect engine rpm's?

****nope, the prop governor maintains a set RPM regardless of the airspeed and power settings (when within the governing range, ie when above idle power range). The throttle controls the power as indicated on the manifold pressure gauge****

CSP's are designed to adjust the props to maintain the desired revolutions that the engine turns. If a pilot wants to maintain 2500 rpms, he "sets" those rpms and the props will adjust, depending on the the position of the plane, to maintain those rpms. My question then is if the throttle controls MP and is used to "set" MP, what control is used to set desired RPM's? <HR></BLOCKQUOTE>

The prop lever/knob. In the sim it is simply prop pitch setting that you have mapped to your keyboard/stick.


Here are some links that deal with this topic.

http://www.avweb.com/news/columns/182082-1.html

and regarding MP

http://www.avweb.com/news/columns/182081-1.html

geetarman
11-17-2004, 09:02 PM
Thanks for the help

effte
11-18-2004, 09:08 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by geetarman:
Thanks for the help <HR></BLOCKQUOTE>

BTW, the throttle controls the throttle valve and, in the simplest incarnations, does nothing about the mixture.

However, many more powerful aircraft incorporate auto enrichment at high power settings, richening the mixture automatically at high power settings to prevent detonation.

Just learned from SkyChimp the other day that for the F4U, Il-2 does model the throttle correctly as it set the target pressure for an automatic MAP (MAnifold Pressure) regulator rather than the throttle valve position directly. Niceness!

Regards,
Fred

LilHorse
11-18-2004, 02:25 PM
@ TX-EcoDragon:

I understand what is being talked about in the Pelican's Perch article regarding MP. I can understand why one needs to know the state of the MP in a boosted engine (supercharged or turbosupercharged) because of the danger of overboost. But in a normally aspirated engine what is the utility of knowing the MP if it can be at high pressure for either low or high power? Or for that matter, the MP can be set to a nominal level but changes in the RPM create an increase in power. It would seem that RPM is the important indicator for gauging power. Can you explain?

effte
11-18-2004, 03:05 PM
The power output of a reciprocating engine is closey tied to the airflow through the engine. The airflow through the engine depends on MAP and RPM. With a constant speed prop, the RPM stays the same. This means the MAP is the easiest to use measure of power output.

For powerplants without constant speed propellers, the RPM is the best power indication.

For turboprops, you typically measure the torque on the output shaft to get a good power indication.

Clear as mud? If not, ask! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Regards,
Fred

LilHorse
11-19-2004, 08:02 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by effte:
The power output of a reciprocating engine is closey tied to the airflow through the engine. The airflow through the engine depends on MAP and RPM. With a constant speed prop, the RPM stays the same. This means the MAP is the easiest to use measure of power output.

For powerplants without constant speed propellers, the RPM is the best power indication.

For turboprops, you typically measure the torque on the output shaft to get a good power indication.

Clear as mud? If not, ask! http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Regards,
Fred <HR></BLOCKQUOTE>

Actually, that clears things up quite nicely. Thanks.