Mitsubishi A6M2 Model 21 - Revisited

[Ivan]

The initial version of my A6M2 Type 0 Fighter was first released back in early 2013.
It came with a custom panel derived from a screenshot of a modified virtual cockpit for the aircraft. The virtual cockpit wasn't too bad but was a little too heavy to include as part of the model because of lack of resources but it made a good basis for a panel image.
This was back in 2013 and although I knew what gauges should be on the panel and what they looked like, I did not have the ability to create my own gauges and had to use the closest matching stock gauges.

There were a few other minor problems.

The actual A6M2 Model 21 of the time (1942) could only carry a couple tiny bombs barely worthy of the name. I reflected that in the DP file but of course CFS doesn't really care how big bombs are. They all have the same effect.
After the initial release, I had a few discussions with other CFS people and thought maybe equipping the early A6M2 with a single 250 Kg bomb like the Sen Baku fighter bomber variants from early 1944 wasn't such a bad idea.
The 250 Kg bomb would be an anachronism, but from a load standpoint, it weighed just a few kilograms more than the very common 330 Liter drop tank that the A6M seemed to always carry.
In other words, although I could not simulate the extra fuel capacity or drag of a drop tank, I could simulate the weight of the tank to make carrier and short field take-offs a bit more fun.

Another nagging little problem was the vertical CoG of the model. Like most people, when I built the first version of the A6M series (A6M5) back in 2002 or so, I started at the easiest place, the propeller spinner. It became the vertical centerline of the model. The problem is that with CFS, the Center of Gravity of the model is the center (0,0,0) of the model itself. There are no offsets in Aircraft.CFG.
On real aircraft, a lot of the heavy items are located below the propeller centerline. Think of Wing Structure, Landing Gear, Wing Guns, Wing Fuel Tanks (even empty), Radiators, etc. That means that the actual CoG of the aircraft probably isn't lined up with the Propeller but considerably below it.
A fair number of things in the model (Parts and Textures) had to be relocated to make this happen. I figured it was good prep for any follow-on versions of the A6M.

Attached is an image of the Wireframe of the A6M2 clearly showing the CoG line below the propeller spinner.
Also shown is the 250 Kg bomb in the DP file.

- Ivan.

 

[Ivan]

When the CoG of the model was moved, there were a couple small updates as well.
One was an inconspicuous little addition, one was a small SCASM adjustment, and one was a small texture correction because I had gotten a couple comments from people who actually knew quite a bit more than I did about the Type Zero Fighter.
One might have expected that the topside outline of the flap well was a complete box, but it was not. The outboard edge of the Red outline was not present.

I had mentioned a few times that the markings on my A6M2 were typical of the Tainan Kokutai but never said anything about where I had gotten that idea. Attached is a profile image of "V-172", the A6M2 recovered by the AVG in China in its original markings. This is the aircraft that was test flown in China and then flown to India to be shipped by freighter back to the United States. It was restored by Curtiss and eventually test flown again at Wright Field.

- Ivan.

 

[Ivan]

One of the other major updates as mentioned earlier was the Control Panel.
The initial release had all stock gauges. The current version has about half or perhaps more of the gauges replaced with custom programmed gauges.

Attached is a in-flight screenshot of the control panel. I found out rather fortuitously that selecting 90% power takes the Manifold Pressure down from the Take-Off Rating of +250 mm to the Military or Normal Maximum rating of +150 mm. Actually it is +151 mm but I will accept that. Consider that reading the actual gauge faces if one were the pilot would not be anywhere near that precise.

The Gauges that are replaced are the following:
1. Manifold Pressure
2. Fuel Selector
3. Fuel Quantity
4. Magneto Switch
5. Starter Button - Lifted from the stock Hurricane
6. Air Speed Indicator
7. Trim indicator Gauge
8. Cylinder Head Temperature

Note that some of the gauges don't really look much like the real thing. The Fuel Quantity Gauge indicates the amount in the selected tank. The actual gauge in the aircraft would only show about the last 20 Gallons of fuel
The ASI is not a double rotation type. I thought that was something that was potentially confusing on a desktop flight simulator with no other visual cues other than a computer screen. In an actual aircraft, peripheral vision will tell you pretty quickly whether you are going 120 Knots or 250 Knots.
The Tachometer is still the one from the stock Messerschmitt 109.
The Cylinder Head Temperature Gauge was almost a waste of time. The only real difference between this and what I did earlier for the P-47 is that the markings are arranged differently.

- Ivan.

 

[Ivan]

Did a bit of engine tuning last night. Almost all of the testing has been done at +150 mm boost and 2505 RPM. I actually want 2500 RPM, but it is pretty difficult to get it exact and it is a choice between 2498 RPM and 2506 RPM or so.
Power is a touch high down low (about 30 HP too high) but Speed is just about an exact match.
Further engine tuning is going to depend on how well the performance curves match up to that for the actual aircraft.
I have not yet figured out whether or not to implement an Overboost setting or how to go about doing it.
I don't believe it is a simple Take-Off power setting.

Attached is an excerpt from a report on the Aleutian A6M2. It describes combat reports of some kind of "Additional Speed" capability in combat that was observed. The Overboost control is a knob that is just below the Magneto Switches on the A6M panel in all versions.

 

[Ivan]

There are of course the obligatory screenshots.
First is of a low altitude speed run.
Second is the first landing I have tried in the simulator in years. It might have been easier if I had the aeroplane trimmed properly because it tends to get nose heavy as it gets slow. That is why the approach speed is so high.
No, I actually didn't crash but it wasn't the most graceful landing. The A6M series is quite forgiving of mishandling.

- Ivan.

 

[Ivan]

I found one error in the last release: The maximum manifold pressure was limited to +200 mm. I am wondering where that came from. It should be +250 mm. The other thing that is taking some time is that Ivan's Propeller Shop has not constructed an entirely new propeller in quite some time and this project really calls for one.
The characteristics which determine this are the following: The engine is fairly low power, only about 830 HP at Sea Level at non Take-Off power (+150 mm or 90% in the simulator). Even with this power level, it is pretty fast for the time and climbs quite well.
The minimum pitch setting is fairly coarse and yet the engine can hit full RPM quickly. There is the possibility this is done with Take-Off settings, but that would probably not be used in a sustained climb.
So.... It is a cute little balancing act as usual, and my Propeller Shop technicians are just learning to walk.

- Ivan.

 

[Ivan]

The technicians at Ivan's Propeller Shop had loads of fun with this project.
The first pass at engine tuning was to get an idea of what the actual Propeller Power Coefficients at the important altitudes would be.
It wasn't really necessary to test all altitudes, just the ones of particular interest: Sea Level (really 500 Feet) and 15,000 Feet (really 14,900-something Feet) where the A6M2 reaches its maximum speed. This is actually a bit over 1000 Feet over the engine's critical altitude.
The first pass with the new propeller was fairly close but needed just a little tuning. I then took it back to the spreadsheet to smooth out the curves and fix some of the transition areas. One of the difficulties is that the A6M2 is such a low powered aircraft and the propeller isn't particular small or fine pitched.

I keep mentioning interpolations and how they are never good. In the attached screenshot, the Dashed Red Line represents 32.5 Degrees pitch. Not that it isn't too bad until it gets to Advance Ratio 1.4 after which the curve starts to look really ugly. This isn't of just academic interest. Sea Level maximum speed is very near Advance Ratio (J = 1.5). The engine doesn't have enough power according to the Power Coefficient curves to get to 35 Degrees, so it stays at 32 Degrees. I can adjust the Power Coefficient graph but then I get some really strange looking curves there.
The Propeller Efficiency graph still needs to be tested to make sure I didn't mess anything else up.

- Ivan.