Throttle, RPM and the Propellor

Could someone explain how the Throttle RPM and the Propellor work on the Mustang as I am obviously missing something in my understanding. Why doesn't the RPM increase when the throttle is increased? Is prop RPM different from engine RPM? What about Prop pitch or Mixture?

I understand perfectly well how all this work and interact on a car but am mythed by the what's going on with this aircraft engine. :unsure:

Could someone explain how the Throttle RPM and the Propellor work on the Mustang as I am obviously missing something in my understanding. Why doesn't the RPM increase when the throttle is increased? Is prop RPM different from engine RPM? What about Prop pitch or Mixture?

 

I understand perfectly well how all this work and interact on a car but am mythed by the what's going on with this aircraft engine. :unsure:

The throttle is your gas pedal

The prop pitch is your stick.

Someone like Buzz could explain it better.

By Stick you mean gearstick in a manual? (I'm British!) interesting!

If the throttle is the gas pedal why doesn't it increase RPM and if it is just injecting more fuel how does that differ from the Mixture setting?

By Stick you mean gearstick in a manual? (I'm British!) interesting!

If the throttle is the gas pedal why doesn't it increase RPM and if it is just injecting more fuel how does that differ from the Mixture setting?

The throttle just controls the air let into the carb via a butterfly valve. I can't say much on the mixture though. Hitting the maintenance manual PDFs is your best bet for that. At a guess, the mixture of fuel/air is proportional to the amount of air allowed into the carburetor (by the throttle and butterfly valve).

Throttle, RPM and the Propellor

The prop control only controls the pitch of the propeller, the resulting change is an increase or decrease in RPM (biting more or less air). The throttle is power, the higher the throttle the more power output from the engine, this is read by manifold pressure. You have independent control over both the power and the propeller pitch. This allows you to run the engine more efficiently aka ( a constant speed or pitch prop). The normal rule is when increasing power to increase the prop lever (RPM) before increasing the power (manifold pressure). Then when decreasing power do the opposite, decrease the throttle (manifold pressure) then the prop control (RPM). This is how you get a max continuous setting of 46” Manifold and 2700 RPM and a combat setting of 61” manifold and 3000 RPM etc...

Mixture only controls the fuel air mixture to the engine. Even though increasing engine power has a direct increase in the amount of fuel dumping into the engine. The mixture (air to fuel ratio) never changes based upon your setting. In the Mustang it’s automatic so you never need to worry about it. If it was manually controlled then as the air thins with altitude you have to compensate by decreasing the mixture thus reducing the amount of fuel mixing with the air into the engine. If you didn’t do this the engine would be constantly flooding with fuel causing a loss of power and eventual failure.

Eyyyy I guess right haha

The Throttle controls the amount or air going into the carburetor or both Fuel and air? (mixture of fuel/air ratio?) So what does the mixture setting do?

RPM controls the propellor pitch? (DCS P51D in the controls menu lists RPM as Engine RPM!) There is no "Prop pitch control" listed for the P51D like there is in IL2? (I'm confused as IL2 lists both Propellor RPM and Propellor Pitch as different controls).

So RPM doesn't mean 1 single revolution of the propellor then? (as changing the pitch wouldn't change what equates to 1 revolution (1RPM)).

Sorry but I am now horribly lost!

Except that is wrong Campbell, you do NOT control the propeller pitch in the Mustang. The Prop lever controls the RPM. Prop pitch is automatically adjusted to maintain the manifold pressure set by the throttle and the RPM set by the prop lever.

You can have a set MP and RPM, go to F2 view and watch the pitch of the prop change (on the data tape) depending on the aircraft's speed and load on the engine

To back that up, from Page 35 of the P-51 Flight Manual:

The propeller RPM is controlled by the Propeller Control lever on the throttle quadrant in the cockpit. The propeller governor automatically controls propeller pitch to maintain a constant speed between 1800 and 3000 RPM, depending on the Propeller Control setting. The propeller cannot be feathered.

Throttle, RPM and the Propellor

The Throttle controls the amount or air going into the carburetor or both Fuel and air? (mixture of fuel/air ratio?) So what does the mixture setting do?

RPM controls the propellor pitch? (DCS P51D in the controls menu lists RPM as Engine RPM!) There is no "Prop pitch control" listed for the P51D like there is in IL2? (I'm confused as IL2 lists both Propellor RPM and Propellor Pitch as different controls).

So RPM doesn't mean 1 single revolution of the propellor then? (as changing the pitch wouldn't change what equates to 1 revolution (1RPM)).

Sorry but I am now horribly lost!

Well I was trying to keep things simple without going into exhaustive details. In laymen’s terms, think of the throttle as the gas pedal the more you give it the more power you get. The power output is read as Manifold Pressure on the Manifold pressure gauge. Think of the prop lever as a gear shifter. Yes I know I told you it controls prop pitch, because it sets the RPM to whatever you set it to and the governor does the pitch changing for you to hold the set RPM’s. (same damn thing). Move the prop lever to set the RPM’s on the RPM gauge. The mixture control, only controls the fuel to air mixture in the combustion chamber. There’s nothing I can think of similar on a car because the fuel air ratio is not controlled on a car (if it is I’m not familiar). The mustang auto controls mixture in the run position, and you only use full rich for emergencies. (Reference pg 35 & pg82 from the manual),

Don’t get confused between “prop pitch control” and “Engine RPM control”. One uses oil in the prop hub with a spring and piston to change the actual prop pitch thus changing the RPM’s, the other is controlled by a governor so when you set engine RPM the governor actually changes the pitch for you. In laymen’s terms they pretty much do the same thing just mechanically different. Hope that helps some!

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Though, by trying to simplify it and using inaccurate description of what is REALLY going on with the controls, only confused him even more. Stick to the facts and there will be less confusion.

Thanks guys for taking the time to reply

Could someone explain how the Throttle RPM and the Propellor work on the Mustang as I am obviously missing something in my understanding. Why doesn't the RPM increase when the throttle is increased? Is prop RPM different from engine RPM? What about Prop pitch or Mixture?

I understand perfectly well how all this work and interact on a car but am mythed by the what's going on with this aircraft engine. :unsure:

comparing p-51 to any car is huge miss.

throttle is not rpm control

throttle is controling MP Manifold Pressure (p-51 have automatic MP control this mean that system will not allow MP greater then 61" w/o WEP wire broken.)MP is air/fuel mixture pressure entering engine's combustion chambers. higher MP more air and fuel is inducted to the engine = more power, if 30" (is about SL pressure) gives 1000hp for example, 60" will give you 2000hp (this is only example not real data)

Automatic MP system works above 40" of MP

rpm handle is controling rpm of the engine (gavernor is the automatic unit which control blade pitch in propeler dont get confused when you add throttle fast rpm goes up its only lag in gavernor system) if i remember correctly you can set 1600-3000 rpm in p-51. On the ground you may have impresion that throttle is controling rpm no it is not. rpm control kick in whne set rpm is reached by engine.During engien run up you can play with rpm hnadle. so befor engien run up set rpm handle full forward add throttle to reach 2300 rpm than move rpm control full back you will see that gavernor will limit engine rpm you should have 700rpm drop form 2300rpm that is indication that gavernor is working fine.

you can play even more in flight reach 300mph (use continous power setting which is 46"/2700rpm) thant move throttle fully back and you will see that gavernor still is able to keep 2700 rpm(dont be alarmed that rpm drops a little gavernor need some time to change prop blade pitch in this case engine is at idle thorttle but air passing through propeler will allow gavernor to maintain rpm simply at this point propeler act like air brake, seting hig rpm and retracting thorttle to idle gives nice braking effect). when air speed drop air flow is not sufficient and rpm will start droping.

mixture handle is used for starting/ shuting down engine in normal operation mixture should be in auto rich position (p-51 has automatic mixture control. air/fuel ratio will change during fligh at cruise power settings engien can run safly with lean mixture but at high power settings it require rich mixture to run safly all this work in p-51 is done by automatic mixture control)

the power of piston engine is combination of MP and rpm

The mixture control is the same as a mixture control (choke) on a car. If you have driven a car from the 70's or earlier you will remember setting the mixture outside temperature for starting etc. Once the car was warm it went to the"run" position and you didn't worry about moving it.

This control has an automatic setting which is what you normally use "Auto rich", a full rich that can be used for emergencies, i.e. when the auto mixture fails or is damaged and an "Auto lean" position which is used under certain restrictions to conserve fuel when you need to fly long distances, line escorting B-17 to Berlin, something we will sadly never do in DCS.

Forget Il2's abstractions and what the experts there do, it is not realistic, however in the Spitfire Mk IX and the P-47D you can see the mixture lever on the throttle quadrant marked with these positions. The mixture control did not have the ability to incrementally increase or decrease the mixture in % but only the three positions.

The mixture control is the same as a mixture control (choke) on a car. If you have driven a car from the 70's or earlier you will remember setting the mixture outside temperature for starting etc. Once the car was warm it went to the"run" position and you didn't worry about moving it.

 

This control has an automatic setting which is what you normally use "Auto rich", a full rich that can be used for emergencies, i.e. when the auto mixture fails or is damaged and an "Auto lean" position which is used under certain restrictions to conserve fuel when you need to fly long distances, line escorting B-17 to Berlin, something we will sadly never do in DCS.

 

Forget Il2's abstractions and what the experts there do, it is not realistic, however in the Spitfire Mk IX and the P-47D you can see the mixture lever on the throttle quadrant marked with these positions. The mixture control did not have the ability to incrementally increase or decrease the mixture in % but only the three positions.

choke is difrent thing than mixture control in cars(old cars) mixture is set to factory specs and you cant change it unless you will meddle with carb it self.

choke is difrent thing than mixture control in car mixture is set to factory specs and you cant change it unless you will meddle with carb it self.

No, they are exactly the same thing. Both allow the driver to adjust the mixture from the drivers seat. Generally on an American downdraft carburetor it is referred to as a choke and it normally adjusts the mixture by restricting airflow. On side draught carburetors like SU or Bendix like we have on a Merlin engine, it works by directly adjusting the fuel jet. This is how almost all cars worked when I was learning to drive, a few expensive ones had an automatic choke or even more exotic, had fuel injection. Thankfully none of them required advancing or retarding the spark with a little lever on the steering wheel, although it is a great feature and I would love to be able to do it. A computer now makes that decision for me so in a way we have come full circle.

No, they are exactly the same thing. Both allow the driver to adjust the mixture from the drivers seat. Generally on an American downdraft carburetor it is referred to as a choke and it normally adjusts the mixture by restricting airflow. On side draught carburetors like SU or Bendix like we have on a Merlin engine, it works by directly adjusting the fuel jet. This is how almost all cars worked when I was learning to drive, a few expensive ones had an automatic choke or even more exotic, had fuel injection. Thankfully none of them required advancing or retarding the spark with a little lever on the steering wheel, although it is a great feature and I would love to be able to do it. A computer now makes that decision for me so in a way we have come full circle.

maby it works similar but in plane mixture control plays difrent role, compensating for temp changes and altitude changes not realy used for operation while engine is cold

after engine is at operating temps mixture need constant adjustment during flight

and definetly it is not done by restricting airflow

and v-1650 uses updraft injection type carb

Why are you all arguing?

The Throttle controls the amount or air going into the carburetor or both Fuel and air? (mixture of fuel/air ratio?) So what does the mixture setting do?

The throttle (pedal on car, or lever in plane) control carburetor butterfly valve allowing piston suction sucks more or less air, this air draw fuel in atomized form, then more the throttle control is open allow engine sucks of this "mixture" = more power.

The mixture control of some IL-2 planes (in P-51 or Spitfire... mixture control is automated, the lever is used only for cut-of the engine) allow decrease/increase the amount of fuel draw by carburetor suction for compensate air density variation at different altitudes.

At high altitudes the air is less dense, hence is need decrease fuel admission in carburetor for keep the relation air/fuel balanced, what in some planes (e.g. a LaGG-3) is need do manually using the "mixture" lever.

BTW - In a (carburetor) car the mixture adjust is done setting an screw in carburetor once, since cars travel - more or less, with few altitude variation, the driver don't need control mixture. But modern fuel injection systems adjust this dynamically, based on analyze of exhaust gas.

In IL-2 (GB) you can do a "analyze" of mixture, observing exhaust flames color.

The throttle (pedal on car, or lever in plane) control carburetor butterfly valve allowing piston suction sucks more or less air, this air draw fuel in atomized form, then more the throttle control is open allow engine sucks of this "mixture" = more power.

 

The mixture control of some IL-2 planes (in P-51 or Spitfire... mixture control is automated, the lever is used only for cut-of the engine) allow decrease/increase the amount of fuel draw by carburetor suction for compensate air density variation at different altitudes.

 

At high altitudes the air is less dense, hence is need decrease fuel admission in carburetor for keep the relation air/fuel balanced, what in some planes (e.g. a LaGG-3) is need do manually using the "mixture" lever.

 

BTW - In a (carburetor) car the mixture adjust is done setting an screw in carburetor once, since cars travel - more or less, with few altitude variation, the driver don't need control mixture. But modern fuel injection systems adjust this dynamically, based on analyze of exhaust gas.

 

In IL-2 (GB) you can do a "analyze" of mixture, observing exhaust flames color.

 

in p-51 throttle is linked with boost control unit too

oh yeah il2 have nice things which dcs is missing like flame color or smoke which indicate very rich mixture

It has a lot more than that. I've got 10 years flying it and it spoils you. I hope ED gives WW2 more love.