We REALLY need a ...

[BBQ]

... guide to engine management for this beast. I've found a few threads -- also been reading the engine manual, but have not come across an official, or un-official for that matter, guide to engine management:

 

1. Typical settings for "cruise"
   
2. Typical settings for "boom and zoom"
   
3. Typical settings for "turn radius fight"
   

 

Or is it one of those things that you just eventually "intuit" after so many hours training?

 

Thanks for any replies --

 

BBQ

[Merlin-27]

rn radius fight"

Or is it one of those things that you just eventually "intuit" after so many hours training?

 

I'd say definitely yes to that. You use the settings you need at the moment. However, you do need to start with the knowledge of what settings stress the engine and what setting will run all day.

 

Cruising all day: 46" & 2700 RPM (Max Cruise - Best continuous operation)

 

The typical operating settings for the P-51D are listed in many places including a placard inside the cockpit.

 

Anything over cruise would be used in situations where you need extra grunt from the engine/prop but comes at a cost (Heat and Wear on the engine) Avoid drastic movements of the RPM lever after the initial push forward for startup. Abuse of this lever tends to put enormous strain on the engine/prop governor/internals and is a good way to kill the Merlin.

 

61" & 3000 RPM (Full Military Power) is the typical way to enter a A2A fight unless you're diving of course. Just keep in mind that if your speed decreases in a climb or turn, the engine will build heat VERY quickly. Try your best to keep your airspeed above 150 at all times. Opening the radiator doors is also helpful to manage heat.

 

Get used to checking the Coolant and Oil temps regularly.

 

That should get you started...then intuition comes later.

[sobek]

Cruising all day: 46" & 2700 RPM (Max Cruise - Best continuous operation)

 

That is maximum continuous. Maximum cruise is 36@2400.

 

Maximum continuous is the absolute maximum that the engine is able to sustain, it won't like it much nonetheless to be driven all day at max cont. Whenever you are just cruising around, it is better to throttle down to max cruise.

[BBQ]

Sobek,

 

Thanks for taking the time to write that up! Should be a sticky:

 

"Engine management for newbies"

 

It's just what I was looking for - something as you say, to get started with. Thanks again.

[sobek]

It's just what I was looking for - something as you say, to get started with. Thanks again.

 

It's all on the placard to your right in the pit, take a look at it. Useful other stuff like min temps for TO on it as well.

[Merlin-27]

That is maximum continuous. Maximum cruise is 36@2400.

 

Maximum continuous is the absolute maximum that the engine is able to sustain, it won't like it much nonetheless to be driven all day at max cont. Whenever you are just cruising around, it is better to throttle down to max cruise.

 

My bad, I wrote that at 5:40am. Max Continuous.

 

For what it's worth, you can run 46"/2700 ALL day with no problems in the sim.

[alfredo_laredo]

First of all, excuse my english...

Im going to cover the very Basics of engines and props. (Im in no way expert on the Merlin Engine)

 

The engine works like any other 4 cycle engine works.

Fuel and O2 enters the cylinder, piston compress it and then it ignites.

 

What is the MP?

Manifold Pressure meassured in Inches of Mercury.. is the amount of Mix of Fuel/o2 that goes into the Cylinders.. and meassure the SUCTION into the cylinders.

 

Logic says that the more suction, the more power.

 

But this power is send to the propeller.

 

The prop in the P-51D is a constant speed propeller.

Lets explain this thinking first in a Fixed Pitch Propeller.. or in this..

 

Notice the Blades of this fan. they are big and they have a certain angle.

 

This is done to produce the most amount of "thrust" at the lowest posible speed. and so it has a low Pitch

 

Now, Imagine mounting this fan on the top of your car and turn it at its maximun speed. Obviously is not going to have enough thrust to move it but it will generate a minumun amount of thrust...

The question here is... if you start the engine of the car.. and accelerate.. at what speed the fan will act more as an Air brake than as a Help in moving it?

The answer.. at a very very low speed... because again, is designed to produce the most thrust at the lowest speed.

 

The same principle goes to a fixed pitch propeller. For example a Cessna 152. have a propeller designed to work better at certain speeds.

If you need to archive the shortest take off distance posible you need a Low Pitch propeller

If you need to archive the fastest cruise speed you need a High Pitch Propeller.

 

The Cessna 152 (and most of other light airplanes) is a balance of this two needs.

 

a High performance aircraft like the P-51 requires both.

and so, it has a Constant Speed Propeller.

 

This means that by moving the RPM lever, you are not instructing the prop at what angle it has to be.. you are instructing the Governor at what pitch it has to be to mantain a certain amount of Revolutions.

 

The Propeller governor will give you between 1800RPM and 3000RPM by constantly adjusting the porp between 23° and 65°, at different speeds and MP setting

Explaining this.. the Prop of a P-51 flying at 30000 RPM at 150 MPH will not have the same pitch angle of a P-51 flying at 3000 RPM but at 250 mph.

 

In take off, to archive maximun thrust at the lowest speed (like the fan) it has to be a very Low Pitch, so moving the RPM lever to the max. will archive this.

 

But once you are in the air and speed starts to build up, and keep the RPM and max.. the prop will start to work as an Air Brake.

 

So its time to change its pitch by reducing the RPM... normally at climb you mantain 46" MP and 2700 RPM... this gives you the best pitch for climbing.

 

Now.. for combat operations, as far as I know most pilots in real life (and in DCS) just keep the RPM High, 2800-3000 this just takes away the worries of having to deal with engine managment while they are being shoot at.

 

But be very careful with diving at high RPM.. because normally, the engine is the one that moves the prop... but in a High speed High RPM dive, the prop will start to act as a brake and also the Wind will start to "windmill" that prop, and causing it to go faster and faster..

At the end.. the PROP is the one that will be driving the engine, and this is very dangerous to the engine. (think of it like going down slope on your car at the First Gear... the tires are the one driving the engine)

 

So at high speed dives, reduce your RPM.

 

this are the recommended settings for different flight situations (MP"@RPM)

Take Off.

61@3000 Max time 5 minutes

 

Emergency

67@3000 Max Time 5 minutes

 

Combat

61@3000 time max 15 min

 

Max (no time limit)

46@27000

 

Max at Cruise

36@2400

 

The Time limit is there for temperature control! and Temperature control deserves a whole new post. :music_whistling:

 

You can exceed this times as long as temperatures are in the limits (still not recommended)

Edited October 20, 2013 by alfredo_laredo

[sobek]

You mixed the pitch angles up.

 

High RPM and low speed means low prop pitch. High RPM and high speed means slightly higher prop pitch. Low RPM means high pitch.

 

What the prop governor does is adjust the angle of attack of the prop blades so that the torque supplied by the engine results in the set RPM. Naturally, the angle of attack of the blades is dependant on airframe speed, so the faster you go, the lower the AoA becomes, so the governor has to increase pitch. The same thing happens when you increase the torque output of the engine. The governor always adjusts for an equlibrium of torque between the engine and the prop at the RPM you have chosen.

[alfredo_laredo]

You mixed the pitch angles up.

 

High RPM and low speed means low prop pitch. High RPM and high speed means slightly higher prop pitch. Low RPM means high pitch.

 

What the prop governor does is adjust the angle of attack of the prop blades so that the torque supplied by the engine results in the set RPM. Naturally, the angle of attack of the blades is dependant on airframe speed, so the faster you go, the lower the AoA becomes, so the governor has to increase pitch. The same thing happens when you increase the torque output of the engine. The governor always adjusts for an equlibrium of torque between the engine and the prop at the RPM you have chosen.

 

fixed, thanks