manifold pressure and rpms

[save]

Thanks all for an interesting discussion.

What did the Kommandogeräte do to ease out pilot workload regarding the engine management on German 190's and later 109's, and did they differentiate from each other ?

[madrid311]

Just to clarify, are you asking about the theory of it (which has pretty much been discussed         ) or how to operate and manage manifold pressure and RPM in a realistic manner?

         

Both actually.

[morfiend]

If that's German nomenclature, it means atmospheres.

So, 1.42 ATA is 1.42 times atmospheric pressure (at sea level, I believe, but caveat emptor on that).

 Yes I understand that by why ATA and not just TA and I read alot about absolute but for the life of me I cant find out what it actually means.


   

[Scherf]

Yes I understand that by why ATA and not just TA and I read alot about absolute but for the life of me I cant find out what it actually means.


   

Ah, well then you want the German wikipedia:

http://de.wikipedia.org/wiki/Technische_Atmosph%C3%A4re

Definition[Bearbeiten]Die Technische Atmosphäre wurde genormt als die Größe des Drucks, die 10 Meter Wassersäule verursacht.

1 at:= 10 mWS = 1 kp/cm² = 9,80665 N/cm² = 0,980665 bar = 98.066,5 Pa

Abgeleitete Einheiten[Bearbeiten]Je nach Bezugsniveau wurden aus der Technischen Atmosphäre die folgenden Einheiten abgeleitet:

absoluter Druck (Bezugsniveau: 0): ata (pa)
Druck in at über dem Bezugsniveau: atü (pü)
Druck in at unter dem Bezugsniveau: atu (pu)


[google translate]

Definition [edit] Technical atmosphere was standardized as the amount of pressure that caused 10 meters of water.

1 atm = 10 m wg = 1 kgf / cm ² = 9.80665 N / cm ² = 0.980665 bar = 98066.5 Pa

Derived units [edit] Depending on the reference level derived from the Technical atmosphere the following units:

absolute pressure (reference level: 0): ata (pa)
Pressure at above the reference level: atm (pü)
Under pressure at the reference level: atu (pu)

So, ata is absolute since it is not in reference to any other level of pressure. For example:

atü[Bearbeiten]Die alte Einheit atü (für „Technische Atmosphären über Bezugsniveau“) fand sich z. B. auf den Reifendruckfüllgeräten an Tankstellen. Da der PKW-Reifen das Fahrzeug nur tragen kann, wenn der Reifen im Verhältnis zum Umgebungsdruck (etwa 1 bar) einen Überdruck beinhaltet, zeigen die Reifendruckfüllgeräte nur den Überdruck (atü) an. Wird der Reifen mit 2,2 atü befüllt, beträgt der absolute Druck im Reifen 2,2 + 1,0 bar, also somit ca. 3,2 bar.

[google translate]

atü [edit] The old unit atü (for "Technical atmospheres above reference level") was found, for example, on the tyre inflation machines at petrol stations. Since the car tire can only support the vehicle when the tire pressure is higher relative to the ambient pressure (about 1 bar) the tyre inflation machines only show the overpressure (atü). If the tires filled with 2.2 atm, the absolute pressure in the tire is 2.2 + 1.0 bar, so therefore about 3.2 bar.

[colmbo]

Both actually.

General rule when making power changes on an engine with a constant speed prop:

Increase power -- Mixture adjusted as needed, prop RPM increased to desired setting THEN throttle up to desired MP.

Decrease power -- throttle down to desired MP, prop RPM decreased to desired setting, mixture adjusted as needed

For takeoff the prop control will be at the High RPM setting so that you can get maximum HP.  Mixture will be rich.  Throttle up to the Takeoff Power MP setting.  Once in the climb you usually reduce power to a Climb power setting, then when level an additional power reduction.  The operating handbook for the aircraft will have a chart showing usuable MP/RPM/mixture combinations for each mode of flight.

On the B17 (as we fly it present day)takeoff power is 42" MP, 2500 RPM with mixture in Auto Rich.  For climb power MP is reduced to 36" MP, RPM down to 2300, mixture stays at Auto Rich.  Once level we used 30"MP/2000RPM/Auto Lean as our cruise power setting.  For doing our rides we would use 28"/2000RPM/Auto Rich.  If power went above 31" OR 2100 RPM the mixture must be moved to Auto Rich.

For the B-24 it was same procedure but slight different power settings.  We would engage the turbochargers (just ballparked the setting based on experience) then for takeoff would use 42-44" MP/2700 RPM/Auto Rich.  After climb established turbos OFF, MP 36"/RPM 2500/Auto Rich.  For cruise we used the same 30/2000/Auto Lean as the B-17.

R/L you can damage an engine by running to high of MP with lower RPM....pressures inside the cylinders can be high enough to cause the head/cylinder to fail (and it can be quite impressive when they do let go  ).  This is the reason for increasing RPM before MP and decreasing MP before reducing RPM...to avoid overboosting the engine.

In game you don't have to worry about breaking the engine but if the RPM is set to low you won't get the power needed.  Try a takeoff with the RPM set to minimum.

You can reduce fuel consumption by reducing RPM.

On the B-17 my setup for bombing when at altitude is I leave the throttle all the way forward but reduce the RPM to 2300 which reduces the MP to 38"(A realistic effect of the supercharger, B-24 doesn't do this but it should).  A realistic power setting, it stabilizes the speed for an accurate drop and with the throttle forward you don't have to worry about bumping it and changing your power setting on bomb run.

[madrid311]

General rule when making power changes on an engine with a constant speed prop:

Increase power -- Mixture adjusted as needed, prop RPM increased to desired setting THEN throttle up to desired MP.

Decrease power -- throttle down to desired MP, prop RPM decreased to desired setting, mixture adjusted as needed

For takeoff the prop control will be at the High RPM setting so that you can get maximum HP.  Mixture will be rich.  Throttle up to the Takeoff Power MP setting.  Once in the climb you usually reduce power to a Climb power setting, then when level an additional power reduction.  The operating handbook for the aircraft will have a chart showing usuable MP/RPM/mixture combinations for each mode of flight.

On the B17 (as we fly it present day)takeoff power is 42" MP, 2500 RPM with mixture in Auto Rich.  For climb power MP is reduced to 36" MP, RPM down to 2300, mixture stays at Auto Rich.  Once level we used 30"MP/2000RPM/Auto Lean as our cruise power setting.  For doing our rides we would use 28"/2000RPM/Auto Rich.  If power went above 31" OR 2100 RPM the mixture must be moved to Auto Rich.

For the B-24 it was same procedure but slight different power settings.  We would engage the turbochargers (just ballparked the setting based on experience) then for takeoff would use 42-44" MP/2700 RPM/Auto Rich.  After climb established turbos OFF, MP 36"/RPM 2500/Auto Rich.  For cruise we used the same 30/2000/Auto Lean as the B-17.

R/L you can damage an engine by running to high of MP with lower RPM....pressures inside the cylinders can be high enough to cause the head/cylinder to fail (and it can be quite impressive when they do let go  ).  This is the reason for increasing RPM before MP and decreasing MP before reducing RPM...to avoid overboosting the engine.

In game you don't have to worry about breaking the engine but if the RPM is set to low you won't get the power needed.  Try a takeoff with the RPM set to minimum.

You can reduce fuel consumption by reducing RPM.

On the B-17 my setup for bombing when at altitude is I leave the throttle all the way forward but reduce the RPM to 2300 which reduces the MP to 38"(A realistic effect of the supercharger, B-24 doesn't do this but it should).  A realistic power setting, it stabilizes the speed for an accurate drop and with the throttle forward ythrottleou don't have to worry about bumping it and changing your power setting on bomb run.

   

Thanks Columbo, I bow down to your flying real airplanes. great explanation of real world usage of MP and rpm. I'm going to the Pacific air Museum in Hawaii today to see what's up. Thanks for the knowledge sir.