MAN&RPM

[Dawger]

1. Not everyone takes off from the nearest field to the fight and flies one way 10 miles to die at the bottom of the furball. My long time personal habit is to land every sortie I can and I rarely takeoff at the closest field to the fight. Part of the fun for me and my squad is the formation climb out bull session. Fuel management is a concern on every sortie in my squad because we rarely have sorties under 30 minutes long.

2. Windmilling versus feathered. Most single engine aircraft did not have the ability to align the prop blades with the wind (also known as "feathering") but if they have controllable pitch propeller then choosing maximum pitch to get the blades as close to the wind as possible would reduce the drag produced by the windmilling prop.

Many of the feathering systems on WWII aircraft were one shot deals. You could not get the engine out of feather once it was there. I once had to clamber out of my WWII era twin tail dragger and use the un-feather paddle (a long stick with a prop shaped hole in it) to horse a prop out of feather after I was too slow on the trigger during the pre takeoff feather check. The airliner behind me had to wait and I'm sure he was laughing while cursing my name for causing the delay.

[BoilerDown]

I've never flown an aircraft IRL but...

In AH, if you set RPM to minimum you maximize how far you can glide without engine power.  Conversely, while gliding in for an unpowered landing you may want to put the RPMs back to max to lessen how far you glide if you think you might overshoot the runway, so be aware of that.  It works like a speed brake in that regard.

If you have a radiator hit, you can greatly extend how far you can fly by not letting the engine overheat and blow, by cycling the engine off (not idled, but off) before the temperature goes max red.  When you turn the engine off, also turn the RPMs to minimum so you glide further.  After the engine has cooled down, you can turn the engine back on while simultaneously turning the RPMs back to full.  You may have to cycle every few seconds, it can be a lot of work.  Depending on your aircraft you can actually gain more altitude than you lose while doing this, but in the worst case you can extend how far you glide and maybe make it back to a base for a landing.  Thanks to AH Trainer Rolex for teaching the training squad this technique.

If you have an oil hit, the oil for some reason stops leaking if you have the engine off (not idled, but off).  So my strategy is usually to head back towards base at full WEP in a shallow climb until the oil is almost gone.  Then glide at minimum RPM setting as far as possible.  The last bit of oil will stay in the engine in case I can't glide far enough, or if I'm going to overshoot the base and need some powered flight to make another pass, or if some knit or bish tries to shoot me down and I need powered flight to make an evasive move, etc.  In any case its almost always better to save the last bit of oil than let the engine lock up.

And finally, the engine settings are useful for extending the flight time.  This could be when you want to loiter over an area, you're in a scenario and you know your fuel won't last if you use full settings the entire time, or you're almost out of gas (fuel tank hit or maybe you misjudged how long you could stay at the fight) and you want to make it back to base.  

Of course people use throttle for other things, but usually aren't adjusting the RPMs in a dogfight that I'm aware of.  As a side note, in the scenario I did, we were in A6M2s and we only adjusted the throttle to save fuel, not the RPMs.  I think it would have been better fuel economy to adjust both but I just followed my instructions and it worked out.


Edit:  Two important things I forgot. 

The "E6B" on the clipboard tells you what the max cruise, WEP, and "military" aka full non-wep power settings are, and usually a setting or two in between max cruise and full power.  If you want to maximize your fuel efficiency, set the RPMs and manifold pressure (throttle) to the max cruise settings.  Technically this might not be the absolute best setting, but its close and you won't find better without experimenting on your own.  Obviously the in-between settings sacrifice some fuel efficiency for better performance.

And your manifold pressure (throttle) and RPMs can change from what you set them at when you change altitude, so if you're trying to save some gas while in a climb or dive, keep an eye on them if they're not set to full, and adjust as necessary.  This might not be strictly correct, but unless you're willing to research best fuel settings at every altitude, its the best we've got.  They're also safe to ignore when they're set to full.  Also note that WEP in some aircraft doesn't get you anything at certain altitudes.  You can tell by looking at the aircraft's performance charts, or by looking at the manifold pressure.  If it doesn't move when you turn on WEP, its not doing anything for you and you can leave WEP off at that altitude so you have it when you need it.

[Traveler]

The throttle (MAP) controls the amount of air that can be sucked in by the pistons and thus the amount of air available to the engine. 

 

This statement is just not correct. 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.

[Traveler]

If you have a radiator hit, you can greatly extend how far you can fly by not letting the engine overheat and blow, by cycling the engine off (not idled, but off) before the temperature goes max red. 

This was always good example of the gammy part of Aces High.  Most military aircraft of the 40’s and all of them from the 30’s needed to be either propped or started with an external force.  The Coffmann Stater is a great example.  Used by the Navy and Army air Core.  The Germans used inertia starters on the ME109’s and I think the 190’s as well. 

[TequilaChaser]

This statement is just not correct.

I guess when I started as a "Nose Picker" and went on to working on several varietys of Naval Aircraft,  radial piston , turbojets and jet engines.......I should throw away every damn thing I was taught by the US Navy .including my low & high power turn qualifications...... my Trouble Shooter qualifications on the Launch deck both day & night ops......

because you are the most hotchit knowit all in this whole damned message board......by popping up and telling "EVERYONE" on these boards they are incorrect and you are "THE KNOW IT ALL MAN".......

just wanted to lay that out there......

and hell no..... I do not care to go scan 3 to 4 damn qualification jackets of my qualifications just to prove my squealing point....  ( edit: my navy attitude came out that word starting with Sq actual started with an F )

[dtango]

LOL TC, I was just going to let it rest .

Traveler, sorry - Reading your post I'm not sure I understand what you think I said incorrectly.  Can you clarify?

Tango

[Dawger]

This statement is just not correct. 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.

So what does the throttle control? You don't give us an answer even though you state "This statement is just not correct." What is the throttle doing if it isn't regulating the airflow into the induction system? Why is it called a throttle? I'll give you a hint.

throttle 1 a (1) : to compress the throat of : choke.

Choke being in the definition of throttle leads us to the choke also found on many internal combustion engines. Interesting that two items on an engine are named after words used to describe restricting airflow in a neck.

I wonder why that is?

[Traveler]

LOL TC, I was just going to let it rest .

Traveler, sorry - Reading your post I'm not sure I understand what you think I said incorrectly.  Can you clarify?

Tango

Sure, you worte "The throttle (MAP) controls the amount of air that can be sucked in by the pistons and thus the amount of air available to the engine. "

That's only partly correct.  It's a combination of fuel and air that the throttle controles.  That's why the turbocharger to provide additional air at alt. and the mixture to lean the abount of fuel mixed with the available air.

[Traveler]

So what does the throttle control? You don't give us an answer even though you state "This statement is just not correct." What is the throttle doing if it isn't regulating the airflow into the induction system? Why is it called a throttle? I'll give you a hint.

throttle 1 a (1) : to compress the throat of : choke.

Choke being in the definition of throttle leads us to the choke also found on many internal combustion engines. Interesting that two items on an engine are named after words used to describe restricting airflow in a neck.

I wonder why that is?

As you increase the throttle setting, more fuel and air is flowing to the engine; therefore, MAP increases.

As you climb to altitude moving the throttle forward will not provide more oxygen , which is what is needed for the combustion to take place.   

The throttle controles the combination of fuel and air mixed.  Not just one or the other.  thuss the need for turbo charging and mixture control.  turbocharging ensured a supply of oxygen and the mixture allowed precise fuel control.

[MoJoRiZn]

Sure, you worte "The throttle (MAP) controls the amount of air that can be sucked in by the pistons and thus the amount of air available to the engine. "

That's only partly correct.  It's a combination of fuel and air that the throttle controles.  That's why the turbocharger to provide additional air at alt. and the mixture to lean the abount of fuel mixed with the available air.

wow, now we have all learned that every single piston engine- inline or radial, all actaly had those superchargers, turbochargers

htc better get with the program according to Traveler. guess TC was correct in calling him a quote

you are the most hotchit knowit all in this whole damned message board......by popping up and telling "EVERYONE" on these boards they are incorrect and you are "THE KNOW IT ALL MAN"

please teach me my lil grasshopping self, thy way of the master, please

[Dawger]

Sure, you worte "The throttle (MAP) controls the amount of air that can be sucked in by the pistons and thus the amount of air available to the engine. "

That's only partly correct.  It's a combination of fuel and air that the throttle controles.  That's why the turbocharger to provide additional air at alt. and the mixture to lean the abount of fuel mixed with the available air.

Incorrect but thanks for playing.

The throttle controls air intake and Bernoulli and his principles take care of the fuel flow. (Carburetor)

Early fuel injection still used Bernoulli. Modern Electronic Fuel Injection measure airflow (Mass Air Flow sensor or MAP sensor) in combination with other sensors to determine fuel flow required.

There is no such thing as a throttle that directly controls fuel flow (unless you count the acceleration pump feature on carbs back in the day....this sent a shot of fuel into the carb during rapid throttle advance to keep the mixture from going lean)

If it controls fuel flow directly it is called a power lever, not a throttle. (Jet engines)

[Traveler]

wow, now we have all learned that every single piston engine- inline or radial, all actaly had those superchargers, turbochargers

htc better get with the program according to Traveler. guess TC was correct in calling him a quote

please teach me my lil grasshopping self, thy way of the master, please

I never said all aircraft have turbocharges.  that's why some aircraft were poor performing at alt.  The P40 comes t mind.  All I said was that the throttle did not only control air flow.  if that's an incorrect statement.  Please show me where.

[Traveler]

Incorrect but thanks for playing.

The throttle controls air intake and Bernoulli and his principles take care of the fuel flow.

The throttle controls the amount of fuel and air.  The air via the airintake drawn down into the Venturi wher fuel is mixed with the air.   

Or are you saying that the fuel flow is at a constant rate and only the air flow can be controled?

[Dawger]

The throttle controls the amount of fuel and air.  The air via the airintake drawn down into the Venturi wher fuel is mixed with the air.   

Or are you saying that the fuel flow is at a constant rate and only the air flow can be controled?

I am saying that the throttle only controls the air. The air controls the fuel in a carburetted engine and in period fuel injection system. There is no direct pilot control over fuel flow using the throttle.

The method the pilot uses to control fuel flow is the mixture control.

There are three levers for each engine in an airplane with a variable pitch propeller.

1. Throttle to control air intake
2. Mixture to meter fuel
3. Propeller to control RPM

[Traveler]

I am saying that the throttle only controls the air. The air controls the fuel in a carburetted engine and in period fuel injection system. There is no direct pilot control over fuel flow using the throttle.

The method the pilot uses to control fuel flow is the mixture control.

There are three levers for each engine in an airplane with a variable pitch propeller.

1. Throttle to control air intake
2. Mixture to meter fuel
3. Propeller to control RPM

In real life, you are 100% correct, in this cartoon arcade adventure  the only control we have is the throttle to control a mixture of fuel / air flow to the engine.  For that matter it controls the vacuum created below the throttle valve,  that sucks the  fuel / air mixture into the combustion chamber .  With no mixture control there is only one way in the game to not have a fuel / air mixture controlled by the throttle.  That being to be out of fuel .  The Original OP wanted to know how to control RPM.  I think the subject has been hijacked enough.