Cruise settings from P-51D training manual question
Posted: 20 Mar 2015, 12:11
Hi, after several years on "hiatus" I'm coming back around to flight simming and I've reinstalled my old original WOP P-51D/H package and the WWII Fighters CD (the latter into both FS9 and FSX) and installed the 1.2 patches for all of them. After re-reading what documentation I have and what I could find, I followed the "fly it by the book" advice and looked up a P-51D/K pilot's manual for the real life performance and operating tables. I'm hoping some of you also have these charts, as I'm finding something in them a little surprising/confusing.
I won't go into the full procedure of how to read the charts, it seems pretty straightforward. On the "Flight Operation Instruction Chart" for a given weight and external load, the chart is divided into 5 main columns that progressively trade off speed for range. At the bottom of each column are the settings for prop rpm, manifold pressure, mixture setting, gallons per hour, and true airspeed for various altitudes. What I found surprising and perhaps a little confusing are how many of the settings call for the manifold pressure to be set at "F.T.", which the chart legend identifies as full throttle. For example, even in the "maximum air range" column it gives the M.P. Inches setting as "F.T." for everything above 15,000 ft with differing rpm settings for each 5,000 step in altitude.
I'm not sure what "full throttle" means in this context. Engine limit info shows military power as 61", max continuous as 46", and max cruise as 36". So, what is "full throttle"? If the max continuous MP setting for the engine is given as 46", I would think that perhaps would be considered "F.T." for cruise purposes (then why is 36" called "max cruise...) except other columns in the chart actually use 46" as a specific setting with "F.T." listed higher in the same column. Am I missing something? Also, and maybe there's a scientific answer for this, it seems counter intuitive that "full throttle" would be used for an economical cruise setting? This info is coming from the actual P-51D pilot training manual, right on the page it says the data is from flight tests in 1944 so I don't doubt the authenticity - it's just not entirely making sense to me.
I won't go into the full procedure of how to read the charts, it seems pretty straightforward. On the "Flight Operation Instruction Chart" for a given weight and external load, the chart is divided into 5 main columns that progressively trade off speed for range. At the bottom of each column are the settings for prop rpm, manifold pressure, mixture setting, gallons per hour, and true airspeed for various altitudes. What I found surprising and perhaps a little confusing are how many of the settings call for the manifold pressure to be set at "F.T.", which the chart legend identifies as full throttle. For example, even in the "maximum air range" column it gives the M.P. Inches setting as "F.T." for everything above 15,000 ft with differing rpm settings for each 5,000 step in altitude.
I'm not sure what "full throttle" means in this context. Engine limit info shows military power as 61", max continuous as 46", and max cruise as 36". So, what is "full throttle"? If the max continuous MP setting for the engine is given as 46", I would think that perhaps would be considered "F.T." for cruise purposes (then why is 36" called "max cruise...) except other columns in the chart actually use 46" as a specific setting with "F.T." listed higher in the same column. Am I missing something? Also, and maybe there's a scientific answer for this, it seems counter intuitive that "full throttle" would be used for an economical cruise setting? This info is coming from the actual P-51D pilot training manual, right on the page it says the data is from flight tests in 1944 so I don't doubt the authenticity - it's just not entirely making sense to me.