DarrenW
Staff Sergeant
Are there any trustworthy drag calculations out there for the Zero? I'm interested in all models.
Aerodynamic Drag Properties of the A6M
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DarrenW,
I am not sure exactly what these numbers mean, as I am not an aeronautical engineer, but have been collecting them. The spreadsheet has drag in pounds for a few aircraft (including the A6M3) at a speed of 100 ft/sec.
Any aero engineer, please educate me on what these numbers measure.
Eagledad
I am not sure exactly what these numbers mean, as I am not an aeronautical engineer, but have been collecting them. The spreadsheet has drag in pounds for a few aircraft (including the A6M3) at a speed of 100 ft/sec.
Any aero engineer, please educate me on what these numbers measure.
Eagledad
Hello Eagledad,
I haven't looked at your spreadsheet yet, but if the number is good then it is enough to calculate a Coefficient of Drag which is what I believe DarrenW is looking for. It would only depend on which model of A6M3 because the Wing Area of the Model 22 was a bit more than that for the Model 32.
Edit: I opened your spreadsheet and saw that the source was the RAAF evaluation of the "Hap" at Eagle Farm.
This would make the critter a A6M3 Model 32 and inside the report it mentions that the Wing Area is 232 feet^2.
Haven't finished reading the report. I need to go cook some Dinner now.
If anyone is truly interested in the aerodynamic qualities of the A6M, I believe Koga's A6M2 was put through a wind tunnel test and perhaps something is listed in "The Eagles of Mitsubishi" book or in the book by Robert Mikesh on A6M.
Thanks.
- Ivan.
I haven't looked at your spreadsheet yet, but if the number is good then it is enough to calculate a Coefficient of Drag which is what I believe DarrenW is looking for. It would only depend on which model of A6M3 because the Wing Area of the Model 22 was a bit more than that for the Model 32.
Edit: I opened your spreadsheet and saw that the source was the RAAF evaluation of the "Hap" at Eagle Farm.
This would make the critter a A6M3 Model 32 and inside the report it mentions that the Wing Area is 232 feet^2.
Haven't finished reading the report. I need to go cook some Dinner now.
If anyone is truly interested in the aerodynamic qualities of the A6M, I believe Koga's A6M2 was put through a wind tunnel test and perhaps something is listed in "The Eagles of Mitsubishi" book or in the book by Robert Mikesh on A6M.
Thanks.
- Ivan.
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- Thread starter
- #5
DarrenW
Staff Sergeant
Thanks for your input Eagledad. I will need to read the report on the Spitfire more closely. It looks very interesting indeed....
You are welcome DarrenW.!
Don't forget to check the links in the spreadsheet for the other aircraft, especially the report on the A6M3-32, over at Mike Williams and Neil Stirlings site.
( the drag data for the A6M is at the end of the report)
Eagledad
If you wish to understand a bit more about drag I suggest you get "Aerodynamics For Naval Aviators". Fortunately this excellent work is now available as a free PDF.
100 fps velocity is equivalent to 59.29 knots. Not knowing your source, but this would probably be measured in a wind tunnel at a zero lift AOA to measure relative parasite drag. Induced drag which is a byproduct of creation of lift can be quite high at AOA values where a lot of lift is produced.
Generally speaking at high speed and low AOA parasite drag predominates. At Low speed or high AOA maneuvering the Induced drag will be a very high proportion of the total. As such slowing the plane from high speed will reduce the overall drag till the induced drag contribution overcomes the reduction in parasitic drag. Further slowing will increase the overall drag and actually require an increase in thrust to maintain a steady speed in level flight.
100 fps velocity is equivalent to 59.29 knots. Not knowing your source, but this would probably be measured in a wind tunnel at a zero lift AOA to measure relative parasite drag. Induced drag which is a byproduct of creation of lift can be quite high at AOA values where a lot of lift is produced.
Generally speaking at high speed and low AOA parasite drag predominates. At Low speed or high AOA maneuvering the Induced drag will be a very high proportion of the total. As such slowing the plane from high speed will reduce the overall drag till the induced drag contribution overcomes the reduction in parasitic drag. Further slowing will increase the overall drag and actually require an increase in thrust to maintain a steady speed in level flight.
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- #8
DarrenW
Staff Sergeant
I most certainly will. Judging by it's "drag in pounds" rating (similar to early mark Spitfires), the A6M looks to have a relatively small equivalent flat plate area. But I'm still trying to figure out how to convert "drag in pounds" into the standard Zero-Lift Drag Coefficient (CD0), which would allow for more comparisons to be made concerning parasitic drag as well.
If you have already calculated the equivalent flat plate area, then just divide it by the wing area and you will have your CD value.
The basic equations can be found either on Wikipedia or on NASA sites.
It is
Dynamic Pressure (1/2 Rho * Velocity^2)
Multiplied by Wing Area 232 Square feet according to the report.
Multiplied by Coefficient of Drag
Equals Force.
The Unit conversions will be the fun part.
I started on a spreadsheet to do this last night but realised that I wasn't really that interested in the result.
- Ivan.
- Thread starter
- #10
DarrenW
Staff Sergeant
My main goal in all of this is to determine if the A6M5 was indeed a more aerodynamicly "clean" machine than the earlier A6M2. I'm wonder if the actual increase in speed of the latter model had more to do with the added horsepower and shortened wingspan than anything else.
Hello DarrenW,
I still haven't had a chance to go through the entire report though this is not the first time I have seen it.
I tend to go for specific information when I look at these reports.
There are a couple things I stated in the other thread that the report confirms: the shape of the cowl, reduction gear, and engine power differences.
What do you believe the maximum level speeds of the A6M2, A6M3-22/32 and A6M5 to be?
That would be a pretty good indication of relative drag, especially as the engine power of the A6M3 and A6M5 are given in this report on Hamp. The A6M5 would gain a bit from exhaust thrust which would make the drag seem to be a bit less though.
- Ivan.
I still haven't had a chance to go through the entire report though this is not the first time I have seen it.
I tend to go for specific information when I look at these reports.
There are a couple things I stated in the other thread that the report confirms: the shape of the cowl, reduction gear, and engine power differences.
What do you believe the maximum level speeds of the A6M2, A6M3-22/32 and A6M5 to be?
That would be a pretty good indication of relative drag, especially as the engine power of the A6M3 and A6M5 are given in this report on Hamp. The A6M5 would gain a bit from exhaust thrust which would make the drag seem to be a bit less though.
- Ivan.
- Thread starter
- #12
DarrenW
Staff Sergeant
In my view it's very hard to nail down the performance of Japanese fighters because of the wide range of data we see for any particular model or version. Looking solely at published reference material, I have seen speeds vary by as much as 20 mph depending on source. I have no way of telling exactly where these authors obtained their performance figures for each type, so I'm not sure how accurate they are. That said, my sources have maximum level speeds for each Zero model as follows:
model: various figures given
A6M2: 316/332 mph
A6M3: 339 mph
A6M5: 346/351 mph
Looking at actual test reports on each model (found on the Williams/Stirling website), we get a different take on maximum speeds obtainable:
model: various figures given
A6M2: 289/326/335 mph
A6M3: 310/328/346 mph
A6M5: 327/335/358 mph
The highest speed figures for the A6M3 and A6M5 are found in TAIC bulletins, which are rumored to be based more on calculated performance than actual real-world flight testing. The bulletin for the A6M5 for example has figures for the type with the improved Sakae 31a engine using water-methanol engine boost, but from what I've read this engine was extremely rare to find in this model.
Keep in mind, it is openly admitted in TAIC report No. 38 that due to various structural and mechanical issues the A6M5 under test wasn't performing properly and caused a "pessimistic picture" of maximum speeds obtainable (327 mph). The same however was not said of another A6M5 during testing with the US Navy. According to the report this machine was equipped with the Sakae 31a engine, but for some reason did not have the water-methanol system installed. A maximum level speed of 335 mph was obtained during these tests.
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Hello DarrenW,
Things always get interesting when discussing maximum speeds of Japanese fighters.
Let's just take the case of the A6M2 for discussion purposes.
The AVG captured one that was eventually sent back to Curtiss for testing in the USA.
Maximum speed achieved was extremely low. I believe it was under 300 MPH but it was known that the propeller was out of adjustment.
A crashed A6M2 was captured in the Aleutians and repaired and tested extensively.
When asked about its condition, one of its test pilots commented that it wasn't quite 100%.
This aircraft achieved 335 MPH corrected down to 332 MPH for reports.
Saburo Sakai who flew the A6M2 extensively recalled that it was capable of 345 MPH on overboost or the equivalent of War Emergency Power.
So what was the maximum speed of A6M2?
Was it 335 MPH?
I believe this is unlikely if a crashed and restored example that was in less than perfect shape could achieve 335 MPH while NOT running on its emergency setting.
Was it 345 MPH?
Maybe.
The problem with relying on actual flight test data is that we only have data for captured examples in unknown condition.
The A6M3 tested at Eagle Farm were pieced together from unserviceable / damaged aircraft.
The problem with performance figures with Japanese aircraft is that often the listings are for Normal Rated power instead of War Emergency Power and thus are not directly equivalent to numbers listed for Allied (US) aircraft.
The maximum speed listed in the manual for A6M2 is 316 MPH and for A6M5 it is 338 MPH but these are obviously not at maximum power. That is why I do not believe the 335 MPH maximum for a captured A6M5 is representative.
I commented earlier that although the typically listed power for Sakae 12 is 950 HP and for the Sakae 21 is 1130 HP, the actual power output is much closer
Take Off Power (1 Minute limit)
Sakae 12 - 940 HP @ 2550 RPM
Sakae 21 - 1130 HP @ 2750 RPM
(Note that although their manuals don't list these engine settings for anything other than Take-Off, TAIC reports often list these as WEP ratings for Sea Level performance.)
Sea Level Rated (Military?) Power
Sakae 12 - 830 HP @ 2500 RPM
Sakae 21 - 1100 HP @ 2700 RPM
(Pretty distinct advantage for Sakae 21)
Rated (Military?) Power at Altitude
Sakae 12 - 950 HP @ 2500 RPM @ 4200 Meters
Sakae 21 - 980 HP @ 2700 RPM @ 6000 Meters
(This is where maximum speed is achieved and although the altitude is a bit higher, the actual power difference is not great.)
- Ivan.
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- #15
DarrenW
Staff Sergeant
Yes, the figures have been corrected for altitude and any instrument error.
I'll have to look at my notes when I'm back home. I'm currently out of town on business and have limited access to information.
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- #16
DarrenW
Staff Sergeant
While I respect the opinion of Sakai immensely, front-line pilot reported speeds can sometimes be misleading because instrument errors, altitude variances, and temperature fluctuations that are normally figured in during controlled testing can obviously be ignored during the heat of combat. I personally use caution when quoting these types of figures.
Hmmmm, wouldn't the power difference of 30 horsepower be far more effective than at first glance, due to the reduced air resistance of the thinner air found at the much higher elevation?
In this case, I am much more inclined to believe him.... except that his data doesn't quite fit with other data but more on that later.
His recollection of the maximum speed under normal rated power is a direct match to what is found in the manual and the number he gives is not unreasonable given actual test data on captured aircraft. Keep in mind also that he flew the A6M2 early in the war when there were fewer supply and maintenance problems.
Well, maybe and maybe not. I personally haven't done any great analysis here because at first glance, nothing really fits together all that well.
The maximum speeds given at the "normal rating" are very close in manifold pressure settings +50 mm for Sakae 12 and +75 mm for Sakae 21, but they aren't maximum continuous and aren't military ratings either.
I also have not found a source that lists the actual power output at these engine settings.
One might think that the thrust should be pretty similar except that the propellers are different enough in geometry to make this a guess.
Still, 22 MPH difference at nearly the same engine settings does suggest lower drag for A6M5 even though altitude is higher.
Speeds:
A6M2 ------- 275 kts
A6M3-22 --- 292 kts
A6M3-32 --- 290 kts
A6M5-------- 294 kts
Why is A6M3-22 faster than A6M3-32?
The Model 22 has longer (A6M2 type) Wings and even carries more fuel and sometimes heavier cannon and more ammunition as well.
The Model 52 advantage over Model 32 can be explained by rounded wing tips and an ejector exhaust so that is no surprise.
Still, if the A6M5 has a maximum speed of 351 MPH and A6M3 has a maximum speed between 345 MPH and 348 MPH, then it seems quite strange that the A6M2 is almost as fast at maximum speed when its speed at normal power is so much less.
- Ivan.
Hello Tyrotom,
The Airspeed Indicator on the A6M actually was calibrated in Knots and the listings in the manuals were also in Knots.
This was typical of Japanese Navy aircraft. The Japanese Army used Kilometers per Hour.
The ASI on the A6M rotated twice to indicate the full speed range and had an inner scale and outer scale for numbers.
You can easily confirm this with an image search on the Internet.
Of course Manual is in TAS and the gauge reads in IAS, but if Sakai was an experienced aviator as he certainly was, this would be pretty obvious. Also, considering he was dead-on with his note on the maximum speed under normal power, then he clearly knew enough to make conversions.
- Ivan.
