Author Topic: RPM setting (Read 473 times)

KayBar · « **on:** December 15, 2006, 06:03:04 PM »

when I change RPM it slows (or increases) engine speed (rpm) but so does throttle. what the point of RPM setting?

And is there a manual or readme that explains ALL the stuff in AH?

Max · « **Reply #1 on:** December 15, 2006, 06:32:09 PM »

Once you're airborne and pull up the clipboard, you'll see a hot-click for E6B. Click on it and you'll find some valuable info. You can manage your fuel economy by manually adjusting rpm's and manifold pressure/boost. This comes in handy should someone, or an ack gun puncture one of your fuel tanks. Or. simply if you wish to extend your range, given the fuel you took off with.

Throttle adjustment will determine your manifold pressure or boost. The + and - keys adjust rpm's. E6B will show you the various mileage/minutes you can expect by adjusting throttle/rpm's.

Get it?

As for manuals/readme's - use the web related HELP button. You can also find a wealth of "getting started" info at http://www.netaces.org

Good luck and welcome to the game. Shout back if you have further questions.

GunnerCAF · « **Reply #2 on:** December 15, 2006, 06:33:05 PM »

RPM changes the prop pitch, throttle changes the manifold pressure.

You can use your engine RPM to and manifold pressure to increase fuel economy. If you open the E6B tab on the clipboard, you will see four power settings.

Emergency Power - Full power with WEP on - To get you out of trouble

Military Power - Full power with WEP off - Use for air combat, takeoff, etc.

Normal Power - Reduced power setting for normal flight

Max Cruise - Maxium distance at level flight

Each of these setting will have an RPM and Maniflold Pressure. To set your power setting, reduce RPM to the indicated setting, and use your throttle to adjust the manifold pressure. The E6B will calculate the fuel burn rate, and distance with the remaining fuel for your present RPM/Man Pressure setting.

Gunner

Benny Moore · « **Reply #3 on:** December 15, 2006, 07:24:26 PM »

The following is true for United States fighters. It is different for German fighters. At least, it was different in reality. I do not know if it is different in the simulator.

If your engine quits, lowering your R.P.M. will improve your glide slope. The lower, the better. For maximum efficiency, you do not want your R.P.M. to be much greater than your manifold pressure. A good guideline for powered flight is to keep the propeller levers and the throttles at roughly the same position if you are trying to get maximum speed for that throttle setting. If you're trying to slow down, however, raise your R.P.M.

The reason for this is that lowering your R.P.M. tells the propeller governor to maintain low R.P.M. In order to do this, the governor causes the blade angle to turn parallel to the aircraft's direction of travel, but perpendicular to the propeller's direction of rotation. This presents a broad surface to the propeller's direction of rotation, but the propeller cuts through the air in the direction of the aircraft's movement like a knife.

Raising your R.P.M. tells the propeller governor to maintain high R.P.M. It does this by changing the blade angle to be perpendicular to the aircraft's direction of travel, but parallel to the propeller's direction of rotation. This presents a broad surface to the aircraft's airflow, but the propeller cuts through the air in the direction of its rotation like a knife.

I hope I explained this clearly and properly. It took me a great deal of time to figure this out, even with much help. A diagram would, perhaps, be best, but unfortunately I cannot draw a matter of this complexity clearly enough.

An interesting fact which does not apply in simulators is that, at least under certain conditions, raising manifold pressure before raising R.P.M. and lowering R.P.M. before lowering MaP. could cause an engine failure. I believe this was especially true at high altitudes. I'm not certain what all of the conditions were, but American fighters, particuarly the P-38, had to worry about this. In addition, lowering R.P.M. in a dive was sometimes necessary to avoid over-revolving the propeller. The P-38L's maximum R.P.M. was 3200; diving at full power and R.P.M. could add several hundred R.P.M., which is bad for the engine.

tedrbr · « **Reply #4 on:** December 16, 2006, 01:37:25 PM »

I've rarely used the RPM settings in the fighter, unless, like stated, my engine goes out. More often than I like......

I do use RPM settings in high altitude buff runs when I'm looking for pin point accuracy. I'll set my Manifold and RPM's to where the flight of bombers stays level while on my bomb runs. B-17's, Lancs, B-24's, B-26's, JU-88's, and to a small degree, Ki-67's all have a tendancy to gain altitude, even in level flight, when at full throttle, which throws off a long bombsight calibration.

Only a few times I've flow with lower man/rpm settins in a fighter, and that was usually to keep formation with bombers as their escort on a long flight (more often SEA than MA or various WA's). Conserve fuel until close to enemy territory, then speed up and "racetrack" around the buffs to keep my E up.

I've noticed, on large bombing formations, that some people seemed to have managed to tie their RPM and Manifold settings together. Not good when trying to maintains a large buff formation, but I wonder if it does any good in a turnfighter?

Benny Moore · « **Reply #5 on:** December 16, 2006, 03:06:29 PM »

When climbing, you need the most power available. This means full manifold pressure and full R.P.M. When turning at speeds below your corner turning speed, it is the climbing ability of your aircraft that determines how well you turn. Therefore, you again need full MAP. and R.P.M. when maneuvering below corner velocity.

When diving, lowering the power and R.P.M. a little bit can perhaps get you better acceleration. But when turning at high speeds, bleeding off enough speed to get to corner turning speed makes for the tightest and fastest turn. Therefore, lowering the R.P.M. will actually hurt your turn, because you retain energy too well. It's much better to make a high yo-yo to get to corner turning speed, and leave the propeller lever alone.

KayBar · « **Reply #6 on:** December 16, 2006, 10:17:24 PM »

Thanks to all!!! Got it.

Benny Moore · « **Reply #7 on:** December 17, 2006, 12:54:54 PM »

Quote

Originally posted by Benny Moore
When turning at speeds below your corner turning speed, it is the climbing ability of your aircraft that determines how well you turn.

Someone kindly pointed out to me privately that this statement is badly worded. I'll try to reword it. If the following still does not make sense or if I've missed anything, please post.

The things that determine your climbing ability also determine the sustained turning ability of your aircraft. What determines both lifting and climbing ability is the lifting ability of your wing and how much power your engine has. Weight and drag are obviously the opposites of these, but if they cancel turn they will also cancel climb. Generally, if an airplane climbs well, it will turn well, and a good turner will also climb well. Rockets - and other aircraft that rely primarily on thrust - obviously are exceptions to this, as they are exceptions to most of the laws that govern conventional airplanes. That is because they do not rely on wings to fly.

Benny Moore · « **Reply #8 on:** December 17, 2006, 03:06:39 PM »

Hmm! Upon further discussion with my unnamed benefactor, it appears my understanding of the issue is not as clear as I thought. The example of a biplane seems to disprove what I said. Please disregard my explanations involving turning; I can't edit them anymore. I'm still quite confident in the rightness of my explanations of R.P.M., however.