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PostPosted: Fri Mar 20, 2015 12:11 pm 
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Joined: Fri Mar 20, 2015 10:31 am
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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.


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PostPosted: Sun Mar 22, 2015 8:43 am 
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Joined: Wed Feb 11, 2004 12:55 pm
Posts: 15326
Location: USA
Meta,

One thing to keep in mind is you are flying a product that is almost ten years old. While these planes likely still hold up to competing products on the market today, A2A with Accu-Sim is light years ahead since. If you are looking for the ultimate P-51 Mustang experience, you really need to get the latest Accu-Sim P-51, either the civilian or military variant.

Those military charts, show F.T. any time you use full throttle. Keep in mind, the throttle is basically mapped to a manifold pressure, and the manifold pressure obtained is higher with higher RPM. Higher altitudes where the air is thinner and lower RPM where the supercharger isn't producing as much boost, means the engine will have a harder time reaching the desired manifold pressure. Also, ram air planes a significant roll, so lower power and lower speeds means again, harder for the engine to reach the desired manifold pressures.

I hope this answers your question.

Scott.

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PostPosted: Thu Mar 26, 2015 2:59 pm 
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Airman Basic

Joined: Fri Mar 20, 2015 10:31 am
Posts: 2
Hi Scott,

Thank you for your reply. My question wasn't really about the older products and performance in the simulator(s), just about how to interpret the data in the P-51 training manual as I was trying to fly "by the book". I'd have the same question I think even if I was flying the WOP3 models. I understand what you mean by having to use more throttle to attain a given manifold pressure at higher altitude - that makes sense. I think what is confusing (and to a degree still doesn't seem "right", not with the model in FS but the charts in the P-51 training manual) is that if the "critical altitude" for the Mustang is 32,000 feet (I don't recall exactly where I read that) it just seems odd that the MAX range/most efficient cruise configuration for the real plane, for all altitudes above 15,000 ft, would be "full throttle". I guess I just expected a military document to be "military precise" with all the data, and "full throttle" seems kind of vague where other parts of the chart use precise manifold pressure values. To me, F.T. means just that - max power before going into WEP, 61" M.P. if achievable. Yet the engine limitations describe 46" as "max continuous" and 36" as "max cruise", neither of which should be F.T. for a P-51D cruising several thousand feet below critical altitude with a properly functioning supercharger, or there wouldn't be any power in reserve for max-performance and/or combat maneuvering (excluding WEP). I'm sure they can't be suggesting cruising for over 1,000 miles at military power! Keep in mind this chart, or at least this section of the chart, is supposedly showing the settings for achieving maximum range, not maximum speed, at the specified altitudes for a given weight and fuel load. In the "max range" column it still shows "F.T" as the M.P. setting as low as 15,000 ft. I would expect "full throttle" to be necessary to achieve lower than 61" M.P. at altitudes above 32,000 ft. (assuming that is the correct value for the critical altitude above which the supercharger can no longer produce the maximum rated M.P.), but would think the most efficient cruise setting below that to be a lower throttle (and M.P.) setting, along with the different R.P.M's. Anyway, who am I to question the real test flight data? If that's the data they used to train pilots in the real aircraft, I guess it must be correct - it's just one of those things that didn't look right, even if it is.

About flying the 10 year old FS models... well, take it as a compliment I guess - just like the real aircraft they've aged well! The Accu-Sim Mustang is very much on my upgrade list, along with the B-17 and probably at least a couple other newer A2A products. While I'm craving the "Ultimate Mustang", my computer can't deliver "Ultimate FSX" so I'm considering a new build that should get the most out of it. In the meantime, I'm revisiting FS2004 and the better addons that I've put into it over the years - and the fact that it runs fast and smooth with maximum settings on my current system doesn't hurt either. When I (finally) get FSX running the way it should be, I expect the Accu-Sim Civilian Mustang to be getting the vast majority of my sim flying hours.


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