Mixture, Prop, Boost....???

[Mad Dog 7.62]

K, I am pretty much a jet guy. I am confused by the mixture, prop, and boost controls, manifold pressures, etc. Is there a rundown for lame brains somewhere on this stuff?? :helpsmilie:

[Enduro14]

Manual is a good place to start

[TacticalOni]

K, I am pretty much a jet guy. I am confused by the mixture, prop, and boost controls, manifold pressures, etc. Is there a rundown for lame brains somewhere on this stuff?? :helpsmilie:

 

Mixture: how much fuel is going into the fuel injectors, in the P-47 Auto Rich will automatically pull the mixture back for optimum power at any altitude. Auto Lean does the opposite, decreases consumption for higher economy in exchange for higher engine temperatures because fuel does have some sway in the cooling of an engine

 

Propeller: The RPM of the propeller is controlled here, this changes the pitch of the blades so you can go faster and move more efficiently through the air at any altitude compared to a single pitch fixed blade prop. (think those wooden jobs on the old Fokkers and Sopwiths)

 

Manifold pressure: This is how hard you are running the engine above everything else. Mp is in Inches Mercury so you can also use a cold, dead engine to set QNH on your altimiter roughly.

 

Boost: The P-47 is fitted with a turbosupercharger, the boost lever controls a waste gate coming out of the exhaust down on the bottom of the fuselage behind the engine. The farther you push the boost lever, the more the waste gate closes, the more exhaust gas is fed into the turbine, which compresses air and feeds it to the engine which gives you the same manifold pressure at any altitude until you reach your max service ceiling. This is automatic in the P-51, the Supercharger switches into high blower around 14,000 feet, while in the P-47 you have finer control over it and therefore have more control over the power you make. You can leave the throttle and boost levers interconnected for most of your flying. I latch mine together once I reach the end of the runway, just before I throttle up for takeoff.

 

I hope that helps, although RTFM is definitely advised here because I'm not the last word on how to make WWII warbirds do the flying thingy.

[gdotts]

Linking button for throttle prop and boost

 

Read the manual and the button location and procedure is not clear. Ive zoomed in real close and individually throttle prop and boost can be moved but LINKED??? Tried the Adjusting map bind link but nothing. Please advise

[VH-Rock]

Read the manual and the button location and procedure is not clear. Ive zoomed in real close and individually throttle prop and boost can be moved but LINKED??? Tried the Adjusting map bind link but nothing. Please advise

 

Roughly align the Boost & throttle levers and then click on the little latch on the boost lever. It latches to the throttle and moves together with it.

[diogofalcao]

Check out this youtube channel. It has some good tutorials.

 

https://www.youtube.com/user/RequiemBoS/playlists?view=50&sort=dd&shelf_id=10

[Sydy]

K, I am pretty much a jet guy. I am confused by the mixture, prop, and boost controls, manifold pressures, etc. Is there a rundown for lame brains somewhere on this stuff?? :helpsmilie:

 

Yep, use my Quick Checklist here:

https://www.digitalcombatsimulator.com/en/files/3310190/

 

 

Looks like this:

 

 

Pretty simple.

[Nealius]

Roughly align the Boost & throttle levers and then click on the little latch on the boost lever. It latches to the throttle and moves together with it.

 

Aha! The manual is absolutely terrible about that point. It just says they're interconnected, but in the sim they aren't by default. I was worried I would have to sacrifice my pitch or mixture axis to deal with the boost axis. We've got four throttle levers but the Warthog throttle only has three axes.

[Mud]

Linking them however can result in a loss of performance. I don't know if that is modelled in DCS however.

 

See

 

I have the Warthog also, and felt I don't need an axis for the mixture settings. So 3 is enough. I have bound mixture back and forward to the china hat.

[=475FG= Dawger]

K, I am pretty much a jet guy. I am confused by the mixture, prop, and boost controls, manifold pressures, etc. Is there a rundown for lame brains somewhere on this stuff?? :helpsmilie:

 

Here is a brief introduction.

 

Reciprocating piston internal combustion engines convert the potential chemical energy present in gasoline into rotary motion.

 

This is done by drawing a mixture of fuel (gasoline) and air into a cylinder containing a piston and then igniting it when the piston is at the top of its stroke (very nearly but that isn't important now).

 

The resulting explosion drives the piston down. This creates linear motion which is converted to rotary motion by the mechanical linkage of the piston rod to the crankshaft.

 

 

This rotary motion drives the propeller or airscrew, which literally screws its way through the air dragging the airplane behind it.

 

 

The pitch of this airscrew determines how much force the engine is resisting while the screwing the aircraft forward. A large blade angle or coarse pitch takes a big bite of the air and the resistance the engine much overcome is greater. The aircraft moves further forward with each revolution at coarse pitch. A small blade angle or fine pitch is the opposite. The aircraft doesn't go quite as far forward for each revolution but the engine has less resistance against it.

 

 

 

The propeller blade angle or pitch is controlled with the propeller RPM control

 

 

More RPM means less resistance to the engine at the expense of less forward movement per revolution. You are not directly controlling the blade angle in normal operation in the P-47. You are selecting the desired RPM and the propeller governor varies blade angle to maintain the selected RPM. Why not just let it go as fast as possible? Because the propeller blade tips go supersonic at remarkably low RPM and the propeller efficiency plummets plus the prop is then subject to remarkable stresses that may result in a failure.

 

The power to turn the propeller comes is indicated on the manifold pressure gauge and is controlled with the throttle and boost levers, for the most part (more on that later). Manifold pressure and propeller RPM are how you manage the total power output of the engine.

 

High manifold pressure and low propeller RPM, in theory, will produce the fastest speeds. The prop is taking a huge bite out of the air and the engine is straining its hardest to spin the propeller. However, in practice it doesn't quite work out like that.

 

First, too much manifold pressure and not enough RPM and the engine just breaks, usually a piston rod or detonation occurs due to over pressure inside the cylinder, seriously damaging the piston and cylinder. Radials tend to pop cylinder heads off when you do this.

 

Secondly, there is a narrow band of efficiency for power/RPM combinations and straying outside that band produces inefficiency and slower speeds.

 

The throttle controls the amount of the air allowed into the engine. More going in means more power produced.

 

Without supercharging the air (compressing it) the air is at atmospheric pressure (~30"hg)before it reaches the throttle butterfly. The restricting of the air flow or "throttling" causes the pressure of that airflow to decrease. Once past the throttling device the fuel is added to the air (carburetor engine) creating the fuel/air mixture "charge". This charge is distributed via the intake manifold (This is where manifold pressure is measured, hence the name) to the cylinders, where it is drawn in, compressed and ignited.

 

Supercharging or compressing the air prior to induction increases the potential chemical energy available, thus increasing the power available.

 

Supercharging in the P-47 is dual. There is an internal geared supercharger driven by the crankshaft that the pilot cannot directly control. It is always working, compressing the intake air. Additional supercharger is available via a turbine spun by exhaust gas. This turbine is connected by a shaft to an impeller which compresses the intake air. The pilot can control this turbine driven supercharger or turbocharger via the "Boost" lever. The boost lever positions the waste gates to allow more or less exhaust gas to hit the turbine.

 

There are three reasons the boost lever exists in the P-47

1. In training, lower octane gasoline was used and lower manifold pressures were required to avoid detonation. The boost lever was how this was achieved.

2. Engine start required throttle movement and it was desired that the waste gates be wide open for start.

3. At high altitude or very high power settings the turbine may reach its RPM limits. The boost lever is used to alleviate that circumstance

 

Not the ideal engineering solution.

 

The final control is the Mixture control. It controls the ratio or mixture of fuel to air in the "charge" by metering fuel at the carburetor.

 

There is an ideal mixture, referred to as the "stoichiometric mixture" of approximately 14.7 to 1. This ideal mixture burns very hot and can easily damage an engine. A mixture containing a higher proportion of fuel is used and the excess fuel acts as a cooling agent. This is referred to as a "Rich" mixture. Under steady state, lower power situations a "Lean" mixture can be used to increase fuel economy (Under most aviation cases, even this lean mixture is "richer" than stoichiometric)

 

So a lot of words to get to some basic engine management.

 

For all phases of flight except cruise, the propeller lever should be full forward. You might be able to eke out a few more MPH by reducing the propeller RPM slightly from the maximum while at maximum manifold pressure but fiddling with the prop controls in combat should probably be discouraged.

 

Mixture should be in Auto Rich except cruise

 

The boost lever should be linked to the throttle lever except during engine start or if you are at high altitude and the turbine RPM is exceeding the limit.

 

 

If the propeller is not full forward and you want to add power, prop goes forward first, then throttle/boost. The manifold pressure will drop as you move the prop forward as the prop takes a smaller bite.

 

The opposite applies for reducing prop rpm. Throttle back first then prop. Moving the prop control back will increase manifold pressure as the propeller takes a bigger bite.

 

[Mogster]

Roughly align the Boost & throttle levers and then click on the little latch on the boost lever. It latches to the throttle and moves together with it.

 

Thanks, I hadn’t realised you could do that as with the real thing. Neat.

[SmirkingGerbil]

Here is a brief introduction.

 

 

Errata and Data

 

 

 

 

Thank you pmiceli - a great read and summary! Much appreciated!

[=475FG= Dawger]

Thank you pmiceli - a great read and summary! Much appreciated!

 

I am glad someone actually read it and got something out of it. You are most welcome and I am glad to be of help.

[diogofalcao]

I am glad someone actually read it and got something out of it. You are most welcome and I am glad to be of help.

 

Thanks for the information. I love ww2 birds and learning everything about prop aircrafts.

If possible, please share more (don't need to be a fully written post, I know it takes time) so a good youtube channel or manuals are much appreciated.