J2M Raiden

[tomo pauk]

...
Comments and Thoughts?

- Ivan.

Usage of 100 oct and better fuel allows for one big fuel tank instead of the fuselage tank and ADI tank - 500L total in fuselage, 680 L (180 US gals) total per A/C internal. In WAllied use, stick the 165 gal tank under fuselage (make the tail wheel strut longer need be). Fuel consumption a bit higher than the 2-stage Merlin? Not that rangy for ETO LR escort work, but still much rangier than Spitfire or Typhoon/Tempest - 400 to 500 miles, depending on cruise altitude and speed?
Engine power is no worse than of the german fighters before mid 1944. I'd try to switch to the Kinsei 24 model, with slightly improved altitude performance. Compression ratio of 6.5 might allow for 50-55 in Hg of manifold pressure with 100/130 or C3 fuel.
'Butterfly flaps' shuld make it possible to out-turn any Western fighter of the era.

 

[Shortround6]

My own opinion is that it would have done quite well and would not have been out of place but it would also depend on what altitude it had to fight at. At low altitudes, it was pretty hot, but typical combat against bomber escorts was much higher in Europe and although its altitude performance was good by Japanese standards, it wasn't good by European standards.
(1560 HP @ 17,900 feet Military Rating)
Then again, if it was operated in Europe, it probably would have had better than the Japanese Navy 92 octane fuel and would not have needed water-methanol injection most of the time.


As for swapping engines, the whole concept of this aeroplane was to fit a very large diameter high powered bomber engine into a fighter.
The engine was very wide but not very deep, so I am guessing that to convert to a P&W R-2800 would require quite a bit of structural modification.
As for using the additional power, I do not believe this would have been a bit deal..............
..................With better fuel, perhaps the volume taken by this 120 liter tank could be used for additional fuel.

Comments and Thoughts?

Just so we are all on the same page fuel wise.

87 oct.......68.29 PN
91 oct...... 75.68 PN
92 oct...... 77.78 PN
95 oct.......84.85 PN
96 oct.......87.50 PN
100 oct......100 PN

Use of JM2 by Italians is problematic due to the Italian fuel situation.
Use of JM2 by the Germans is also problematic. Results on B4 fuel even with water/alcohol is not going to be good. Results with C3 fuel may be better?
Use of JM2 By Russians is probably still going to call for water/alcohol.
Use of JM2 by British/Americans might be limited by the strength of the engine rather than fuel. Will the Kasei actually stand up to the pressures the allied fuel will allow?
Granted not everybody measured fuel the exact same way. I would also remind people that the Germans, Russians and Japanese never actually measured or rated the fuels for rich response. Japanese, if getting their fuel from the Dutch east indies may have had a bit better than 92 octane for rich response. Depends on aromatic content.
The Wright R-2600 is the closest western equivalent. it was 200-300lbs heavier depending on version which makes one wonder about the life of the Kasei at high power levels. The Wright may not have had a very good supercharger, or they didn't change it much on the 1900hp BB series?

As to propellers, they were sometimes matched to expected altitudes. The prop that works at sea level for take-off or sea level speed runs often doesn't work so well at higher altitudes (over 20,000ft?) depending on the power of the engine. The big props on the R-2800s were to transmit 1800hp at 15,500ft (no water injection and no RAM) or 1650hp at 22,500ft. The air at 22,500ft is roughly 80% as dense as the air at 16,000ft.

The R-2800 "B"s ran 2700rpm max so difference in reduction gear is minor.

Another problem is cooling on these radials, not so much in high speed level flight but when climbing. Please note the "C" series R-2800s required about 10% less cooling air at the same power as the "B" series engines. Also note that the 1900hp Wright R-2600s used a massive increase in cylinder and head fin area compared to the 1700hp versions. You not only have to make the power, you have to survive making the power.
A Kasei given Allied 100/130 fuel might very well be able to make much higher power for a few moments, the question is for how long? And under what flight conditions? Flying straight and level or trying to climb at max climb rate? or running at military power (or WEP) while banked over and doing a hard turn at low speed? How long before temperature needle goes into the red zone?

 

[Ivan1GFP]

As to propellers, they were sometimes matched to expected altitudes. The prop that works at sea level for take-off or sea level speed runs often doesn't work so well at higher altitudes (over 20,000ft?) depending on the power of the engine. The big props on the R-2800s were to transmit 1800hp at 15,500ft (no water injection and no RAM) or 1650hp at 22,500ft. The air at 22,500ft is roughly 80% as dense as the air at 16,000ft.

The R-2800 "B"s ran 2700rpm max so difference in reduction gear is minor.

This is what I meant by Propeller Power Coefficient. Designed operating altitude influences propeller "size" as shown by the P-47 versus Corsair with engines generating approximately the same power but operating at different altitudes.
I was thinking 2500 RPM to 2700 RPM would require some changes in gearing to be optimal, but I also have never really looked at what kinds of advance ratios the Raiden has at various speeds.

Another problem is cooling on these radials, not so much in high speed level flight but when climbing. Please note the "C" series R-2800s required about 10% less cooling air at the same power as the "B" series engines. Also note that the 1900hp Wright R-2600s used a massive increase in cylinder and head fin area compared to the 1700hp versions. You not only have to make the power, you have to survive making the power.
A Kasei given Allied 100/130 fuel might very well be able to make much higher power for a few moments, the question is for how long? And under what flight conditions? Flying straight and level or trying to climb at max climb rate? or running at military power (or WEP) while banked over and doing a hard turn at low speed? How long before temperature needle goes into the red zone?

This aeroplane had an engine driven fan operating through a very small cowl opening. If necessary, the gear ratios could be changed.

- Ivan.

 

[Shortround6]

Most of the time fans were needed for ground running and initial climb out. Any fixed gear ratio fan is only going to optimised for a narrow speed range. This gets a bit of a boost in air flow as the speed of the plane increases.
However I don't believe fans were the magic cure all that some people seem to think. There are a wide variation in both the heat load of the engine in different flight situations and a wide variation in airflow through the cowl at different airspeeds. Very few aircraft had any cooling troubles at high speed in level flight (high speed was always done with radiator/cowl flaps fully closed), the over heating problems came while taking-off, (max power and below stalling speed), initial climb out (trying to gain altitude with undercarriage still hanging down) and climbing with a heavy load and most of the time such flight was done with radiator/cowl flaps fully open. Fans could help at the low speed, needing less exit area (flaps) and smaller inlet openings. I would note that very few post war commercial aircraft used fans on their air cooled engines. While top speed may not have been important to the airlines fuel economy (low drag) and easy of maintenance was.

How many people here have any experience with clutch fans in cars? These provided cooling air flow with the car stopped or moving in traffic but at high speeds 945-60mph) the airflow, even after going through the radiator, was fast enough to drive the fan faster than the engine. The fan went into free wheel and imposed no load on the engine. Of course if the fan clutch crapped out the fan flopped around on the end of the shaft and the imbalance soon took out the water pump.
Now cars use electric fans and some cars only run one fan out of two if one fan will keep the coolant with temperature.

 

[Ivan1GFP]

Hello Shortround6,
I am in pretty good agreement with most of your post, but post war prop liners are not really operating under the same parameters.
As you noted, cost, economy of operation and ease of maintenance are the most important things. A couple hundred Horse Power less for maximum power won't be more important than an economical cruise and time between overhauls.
As such, they are not really comparable.
If engineered properly, a cooling fan (such as on the FW 190A) doesn't cost anything more than a little weight and mechanical complexity.
Obviously the Mitsubishi engineers figured out enough to get things right at least according to the Allied Test Pilot's report.

Now keep in mind we are arguing the fine points of a hypothetical. I never claimed the idea would be easy to implement, but certainly it would be easier than to design a sleek fighter around the Kasei engine.
....and we haven't even mentioned what the additional weight of a heavier R-2800 engine would do to wing loading, maneuverability and climb rates.

I am actually quite familiar with automotive clutch fans and water pumps. I have had to replace each a few times. Once it was due to worn out engine mounts which allowed the fan to contact the fan shroud under hard acceleration. Some were done in the quest for improved performance and some were general maintenance. Water pumps should never be driven by the timing belt, but I have seen it done that way. Do you know what your water pump bearings look like? I do. I found a few of the roller bearings sitting on top of my battery and radiator when a water pump seized and threw the serpentine belt.

- Ivan.

 

[GregP]

What are you using to convert PN to Octane and back, Shortround? Not saying you are incorrect ... am asking.

A reference of some wort would be nice for formula background. I find a lot of stuff on it, but little that explains WWII avgas ratings, other than the numbers themselves.

 

[Shortround6]

I am using a chart in a booklet/book provided by the Ethyl corporation to the USAF and US Navy around 1950. The book was written/prepared by Sam Heron who was one of the leaders in developing the PN scale.
The PN scale may not be exactly linear but it is a lot better than the octane scale.

Airplane Fuels and their Effects on Engine Performance Book, NAVAER, USAF 1951

I am not the seller
I recommend it to anyone really interested in aviation fuel regardless of where you purchase it from or library access.

 

[swampyankee]

If engineered properly, a cooling fan (such as on the FW 190A) doesn't cost anything more than a little weight and mechanical complexity.


- Ivan.

... and power absorption which is greatest in high power, low speed operation. I read somewhere (on this forum) that the FW190 fan used 70 hp in climb; this means that the FW190A's "clever" little fan cooling cost something around 250 fpm in rate of climb. The additional weight is probably on the order of 0.1% to 0.5% of operating empty weight, which is in the noise. Engine cooling fans are a feature (or misfeature) that some designers thought beneficial, probably because they made different decisions to satisfy customers. I don't think any mass-produced US or UK fighter or bomber used cooling fans; this may mean that FW and Mitsubishi engineers were not as good at cooling system design as their American or British counterparts or it may have meant that the German and Japanese engineers didn't have access to the design tools that were available to the English-speaking world: NACA, especially, and ARC devoted quite a lot of effort towards improving the cooling of air-cooled engines, the former largely to improve the performance of commercial aircraft, which are going to spend significant time at high-power settings at low speed for climb and single-engine operations.

 

[Shortround6]

Surprisingly (or not?) the ability to manufacture air cooled engines with huge amounts of finning was not as easy at it seems. The "C" series R-2800 needed 10% less air flowing the cowling/baffles as a "B" series engine due the greater amount of fin area on the heads and cylinder barrels. However to manufacture the heads and barrels with such finning in quantity required new manufacturing techniques. Wright also came up with new methods of enlarging fin area. The technique of machining groves in the cylinder barrels and then rolling/caulking sheet metal fins into the groves also required a fair degree of investment in specialized tooling.

If you don't have the ability to manufacture such heads and cylinders in quantity (hand work is not going to cut it) you are either limited in power or have to resort to extra tricky cooling systems (or both).

 

[tomo pauk]

... and power absorption which is greatest in high power, low speed operation. I read somewhere (on this forum) that the FW190 fan used 70 hp in climb; this means that the FW190A's "clever" little fan cooling cost something around 250 fpm in rate of climb. The additional weight is probably on the order of 0.1% to 0.5% of operating empty weight, which is in the noise. Engine cooling fans are a feature (or misfeature) that some designers thought beneficial, probably because they made different decisions to satisfy customers.
...

The cost was 70 PS on sea level for the BMW 801S engine - 2000 PS at the prop reduction gear, 1930 available for prop after deduction of 70 PS is mande for the prop. Other exmaple is the BMW 801D - around 40 PS at 5.7 km, or 1440 for the prop vs. ~1490 PS after reduction gear. It is a percentage of total power, not a flat value. Bill/drgondog will probably know more about this, but, once we're at 400+ mph speed, a drag reduction (provided by tight cowling that was provided by fan) gives better return than extra 20-40-60 PS on the 801D.
I don't think that extra 2-3% more HP will net you a 7-8% increase in rate of climb.

 

[Ivan1GFP]

... and power absorption which is greatest in high power, low speed operation. I read somewhere (on this forum) that the FW190 fan used 70 hp in climb; this means that the FW190A's "clever" little fan cooling cost something around 250 fpm in rate of climb. The additional weight is probably on the order of 0.1% to 0.5% of operating empty weight, which is in the noise. Engine cooling fans are a feature (or misfeature) that some designers thought beneficial, probably because they made different decisions to satisfy customers. I don't think any mass-produced US or UK fighter or bomber used cooling fans; this may mean that FW and Mitsubishi engineers were not as good at cooling system design as their American or British counterparts or it may have meant that the German and Japanese engineers didn't have access to the design tools that were available to the English-speaking world: NACA, especially, and ARC devoted quite a lot of effort towards improving the cooling of air-cooled engines, the former largely to improve the performance of commercial aircraft, which are going to spend significant time at high-power settings at low speed for climb and single-engine operations.

Hello Swampyankee,
It all comes down to a matter of design choice rather than quality of engineering in my opinion.
The design choices by Japanese and German engineers were not the same as the one by American engineers.
The requirements that resulted in the A6M are a perfect example of compromise using the available technology to meet a requirement.

In my opinion, Mitsubishi did pretty well to fit a medium / high horsepower engine with a very large frontal area to a sleek fighter. Without fan cooling, they never would have achieved this.

American aircraft tried many times to use spinners on radial engines but were never successful because it interfered with cooling. If you consider this to be an indication of superior engineering for cooling a radial engine, I would have to disagree.
As mentioned earlier, the requirements for a prop liner engine are pretty different from that of a combat aircraft, so what was used there isn't really terribly relevant. Do you really think a commercial airliner is designed with the intent of sustained single engine operation in mind? It should be able to stay in the air, but with a lot of other compromises. They certainly won't be running (War) Emergency Power to climb away from someone shooting at them. You would adjust the flight profile to suit what you have for optimum maintenance and overhaul cycles and not eat up the life of your engines trying to impress anyone. Also keep in mind that the prop liners came along quite a few years after their engines had been developed for war time use. The typical R-3350 didn't catch fire all that often by that time.

As for the FW 190A, I thought we had covered this already when discussing the comparison between Corsair, Hellcat, and FW 190:
The 70 HP consumed by the fan was at very low speed. By the time the FW 190 was at best climbing speed, there was already enough airflow to drive the fan and thus it did not absorb any significant power from the engine.

- Ivan.

 

[swampyankee]

Pratt & Whitney, Curtiss-Wright, and their customers went to a great deal of effort to maximize cooling effectiveness without using fans and would likely consider them a crutch. Since, as you say, the FW190 didn't need the fan in normal climb, it seems to be a device of very limited utility. Possibly, the US used lubricants and materials. which could better tolerate short periods of high temperature and so the engines could tolerate temperature excursions better than either German or Japanese ones in those periods when cooling airflow was insufficient. Possibly, they spent more time and effort on cooling system design, or had more experience (my hypothesis) or they were simply better at this aspect of design. I suspect it's a mix of experience and materials, and a customer base that would not tolerate fans.

 

[Ivan1GFP]

Pratt & Whitney, Curtiss-Wright, and their customers went to a great deal of effort to maximize cooling effectiveness without using fans and would likely consider them a crutch. Since, as you say, the FW190 didn't need the fan in normal climb, it seems to be a device of very limited utility. Possibly, the US used lubricants and materials. which could better tolerate short periods of high temperature and so the engines could tolerate temperature excursions better than either German or Japanese ones in those periods when cooling airflow was insufficient. Possibly, they spent more time and effort on cooling system design, or had more experience (my hypothesis) or they were simply better at this aspect of design. I suspect it's a mix of experience and materials, and a customer base that would not tolerate fans.

Hello Swampyankee,
As I commented before, it is really a matter of choices. With a cooling fan, you need it really just for low speed and ground operation.
Without the cooling fan, you end up with a larger cowl opening, no spinner for reduced drag, and perhaps even propeller cuffs.
With one idea, there is a small power penalty at low speed. With the other, you have extra drag at all speeds.

I know what my choice would be.

- Ivan.

 

[swampyankee]

The cost was 70 PS on sea level for the BMW 801S engine - 2000 PS at the prop reduction gear, 1930 available for prop after deduction of 70 PS is mande for the prop. Other exmaple is the BMW 801D - around 40 PS at 5.7 km, or 1440 for the prop vs. ~1490 PS after reduction gear. It is a percentage of total power, not a flat value. Bill/drgondog will probably know more about this, but, once we're at 400+ mph speed, a drag reduction (provided by tight cowling that was provided by fan) gives better return than extra 20-40-60 PS on the 801D.
I don't think that extra 2-3% more HP will net you a 7-8% increase in rate of climb.

An FW190 had an operating weight of about 9,500 lbf. Seventy PS is about 32,500 ft-lbf/min. Multiply 70 PS by 32,500 and divide by the weight, one gets 240 ft/min.

 

[tomo pauk]

An FW190 had an operating weight of about 9,500 lbf. Seventy PS is about 32,500 ft-lbf/min. Multiply 70 PS by 32,500 and divide by the weight, one gets 240 ft/min.

The Fw 190A-8 with 1400-1440 PS climbed at 12 - 12.5 m/s between 2.5 and 5 km. With greater power in overboost, 1600-1650 PS, (a 15% increase), RoC went to 14 -14.5m/s, a 16% increase. Say we delete the fan, and cooling is still okay. We get 1450-1490 PS at that altitude band, +50PS or ~5% increase, that nets us a 5+% increase in RoC, 12.7-13.2 m/s.
0.7 m/s extra = 2.3ft/s = 138 fpm.
Granted, 50 PS != 70 PS.
If cooling is not okay now, and we need to 'widen' the cowling so it is not that tight - how much of extra drag is that worth?

 

[DarrenW]

With one idea, there is a small power penalty at low speed. With the other, you have extra drag at all speeds.

I know what my choice would be.

Hi Ivan,
So basically what you are saying is that without this cooling fan arrangement the FW-190A would have been even more 'draggy', when compared to it's American radial-engined counterparts?

 

[swampyankee]

The Fw 190A-8 with 1400-1440 PS climbed at 12 - 12.5 m/s between 2.5 and 5 km. With greater power in overboost, 1600-1650 PS, (a 15% increase), RoC went to 14 -14.5m/s, a 16% increase. Say we delete the fan, and cooling is still okay. We get 1450-1490 PS at that altitude band, +50PS or ~5% increase, that nets us a 5+% increase in RoC, 12.7-13.2 m/s.
0.7 m/s extra = 2.3ft/s = 138 fpm.
Granted, 50 PS != 70 PS.
If cooling is not okay now, and we need to 'widen' the cowling so it is not that tight - how much of extra drag is that worth?

Probably not enough to notice; nose shape of subsonic aircraft, a category that includes all WW2-era aircraft, is not that important as long as there's no separation. There may be a small increase due to wetted area. Check out the zero-lift drag coefficients of US radial-engined aircraft vs the FW190.

 

[Shortround6]

A lot of US aircraft had spinners on the prototypes. most lost them on the production versions.

Now for a quiz, what was the purpose of the discs behind the props on the Boeing 307.

 

[tomo pauk]

Probably not enough to notice; nose shape of subsonic aircraft, a category that includes all WW2-era aircraft, is not that important as long as there's no separation. There may be a small increase due to wetted area. Check out the zero-lift drag coefficients of US radial-engined aircraft vs the FW190.

Shape of the nose of Fw 190D made it 10% less draggier than the Fw 190A.
US fighters? Seems like Cd with "Cl as required for high speed" was greater than 0.028 for Corsair, greater than 0.029 for Hellcat, service condition. Link, table on pg 75 of report, FWIW.

...
Now for a quiz, what was the purpose of the discs behind the props on the Boeing 307.

To improve cooling? Just a wild guess.

 

[DarrenW]

Hi Tomo the link didn't work for me. Is it perhaps for NACA report L5A30?