Japan's top brass obsession with the Homare

[msxyz]

How many airplane designs where ruined, delayed or not brought by their fullest potential by the Japanese's top brass (both IJA and IJN were equally guilty) obsession with the Homare?

I can think of a few of them, but this is not a 'what if post' but rather an attempt to understand why the military leadership clang so hard to this engine when it wasn't delivering, it proved to be a too ambitious design and the deteriorating quality of fuel and materials (not to mention workmanship) would only make things worse.

Overconfidence, delusions of grandeur or collusion with the Nakamura industrial complex?

If we exclude the compact diamter (118cm) of the Homare, the trusty and proven Kasei (132 cm diameter, 750-800kg) engine had the same weight, power output (with 92 octane gasoline plus methanol) and even better performance at altitude. On top of that, the Kasei was easier to service and didn't need complex manufacturing techniques like the cooling fins being machined and welded to the head instead of being cast in a single piece.

Also the Kasei engine's 18 cylinder bigger brother, used operationally only in the Ki-67, would have been a better choice for other bomber designs like the Ginga and the Renzan being able to develop 1900hp with only +175mm of manifold pressure (so fuel quality going down would have had a minor impact in performance) and up to 2400 with methanol injection.

 

[taly01]

One of my pet redesigns is the Kawanishi N1K1-J, as seaplane N1K1 it used the early Kasei motor, if they had stayed with the Kasei and its improved versions I think it would have been better overall than the Homare. AFAIK Kawanishi never even built a test landplane with the original fitted Kasei (which was already smaller diameter than fuselage!) This suggests the promised performance of the Homare was irresistable to designers!

Could be a case where engineering samples were much better built than mass production ones, as well as i'm sure engineering tests had good quality fuel also unlike in the field.

 

[Piper106]

Great minds think alike taly01. About a week earlier over in the engine section, I wrote; .

Then there is the speculation of 'what if' when Kawanishi was reworking the Kasei powered N1K1 float plane into the land based N1K1-J they had stayed with the Kasei instead of switching to the Nakajima Homare. As I recall, later versions of the Kasei were nearly as powerful on paper as the Homare, and if I believe some of my other reading, the Kasei would have been more or less equal to the Homare in the field.

 

[rinkol]

Exotic schemes for minimizing drag were pursued in many countries during the 1940s:
- engines buried in the wings (in the US, the NACA carried out extensive investigations and several engine developments, such as the O-1230 and Tornado, were motivated by this idea)
- ducted spinners or extension shafts to implement tapered cowlings (Germany/Japan)
- 3 or 4 row air cooled radial engines (US/UK/Japan)
- surface evaporation cooling (Germany)
- tandem engine configurations (Italy/Germany)
- coupled V12 engines (Germany and US)
- V16 engines (US/Germany)
- laminar flow wings(US, Japan, and UK)
- remote controlled turrets (US/Germany)

Many of these were outright failures or at best, more trouble than they were worth.

I can see that the idea of trying to achieve a low frontal area radial engine of high power based on the idea of using Sakae sized cylinders configured in two rows with 9 cylinders/row would seem both logical and reasonable. At the same time, the Kasei might have been more widely used as an alternative.

 

[taly01]

The post WW2 US commission reports on Japanese aero engine manufacturers is interesting reading, Nakajima engineers said the JAAF engineers chose to work out the problems on the Homare themselves rather than come back to Nakajima, When asked about how good were the JAAF engineers the Nakajima engineers laughed a bit.....ouch!

 

[rinkol]

The post WW2 US commission reports on Japanese aero engine manufacturers is interesting reading, Nakajima engineers said the JAAF engineers chose to work out the problems on the Homare themselves rather than come back to Nakajima, When asked about how good were the JAAF engineers the Nakajima engineers laughed a bit.....ouch!

Japan's military capabilities were certainly handicapped by organizational rivalries and compartmentalization. In particular, the Army and Navy were bitter rivals who were loath to co-operate. Examples include:

- separate and independent radar development programs
- different families of aircraft weapons without even ammunition compatibility
- separate aircraft development programs, even when the application requirements would have been the same

There also seems to have been many examples of reasonable industry suggestions/requests being turned down by the services. Conversely, the industry had its problems (Nakajima's stubborn persistence with the Mamoru comes to mind).

I'm sure that others can provide further insights.

 

[windswords]

Could it be that the Homare had much more upside potential than the Kasei? There were plans to boost output to 2400 hp or so I thought I read somewhere. What if the Kasei had reached its limit or close to it? Then 1850/1900 hp was all you were going to get.

 

[msxyz]

Could it be that the Homare had much more upside potential than the Kasei? There were plans to boost output to 2400 hp or so I thought I read somewhere. What if the Kasei had reached its limit or close to it? Then 1850/1900 hp was all you were going to get.

Homare started as a 1800HP engine and later examples should have been able to achieve a 2000HP output... in theory. Homare was designed with 100 octane fuel in mind and, using the standard navy fuel of the time (92 octane), it could get past 1500hp only with a low pressure methanol/water injection system which sprayed the additive once a pressure hsensor detected that manifold pressure went above a certain threshold.

The Kasei was not different in this regard... with 92 octane gas it could achieve 1560HP and needed water/metanol injection to gain some 300HP more. One could argue that this is a stop gap solution and also the Kasei had some teething problems when the ADI system was first tried (smoke, irregular combustion, more vibrations)

However the Kasei was a 42L engine that spun at 2500-2600rpm while the Homare reached 3000 rpm. As the war situation deteriorated also the quality of alloys worsened, so an engine running at lower rpm is preferable as it puts lets strains on bearings and all those surfaces subject to friction.

Other critical factors present on the Homare and not on the Kasei:
-The poor cooling of the rear row of cylinders
-The complex manifolds and exhaust arrangement made even worse by the small diameter... I'm sure Homares were a nightmare to service on the field!
-Worse high altitude performance

One thing that leaves me skeptical about the true qualities of the Homare is that Nakajima never delivered a 14 cylinder version to replace the Sakae on the Zero. A reinforced Sakae crankcase and accessory section mated to 14 pots from the Homare should have delivered 1400 HP in a less troublesome engine (at least from the poing of view of cooling and serviceability) and it would have been easy to develop and adapt. Why nobody in Nakajima came up with this plan to revitalize the ailing A6M? Or maybe the truth is that the promised 1800-2000HP couldn't be obtained outside of the lab, in mass produced engines and with the fuel and materials available at the time, and that the Homare was performing more like a 18 cylinders Sakae than like an entirely new and uprated engine?

 

[rinkol]

It is certainly curious that the development of the Sakae didn't get more attention given its use in key aircraft types. The Sakae 31 is supposed to have received some of the features employed in the Homare, but doesn't seem to have been a very successful development. It appears that methanol-water injection was tried, but ultimately abandoned, leaving the modified valve timing as the main improvement. In comparison, Mitsubishi managed to implement much greater improvements in the Kinsei during the same time frame.

Perhaps this was a case of the best being the enemy of the good.

 

[fastmongrel]

Its probably a good example of the Sunk Cost Fallacy which is well known in business

The Sunk Cost Fallacy. The Misconception: You make rational decisions based on the future value of objects, investments and experiences. The Truth: Your decisions are tainted by the emotional investments you accumulate, and the more you invest in something the harder it becomes to abandon it.

So much time and effort had been sunk into the Homare it became difficult to lose face and admit a mistake had been made and it was time to abandon the investment and start again.

It wasnt unique to the Japanese and the Homare, the Napier Sabre, all of the German multi bank engines and the Hyper engines in the US are also examples of projects that should have been killed long before they would have been able to produce workable engines.

At least in Britain and the US telling your boss the last x years and y millions of money have been wasted didnt get you a severe dose of lead poisoning.

 

[Shortround6]

There is not a lot of magic in basic engine calculations.
Since the volume (not weight) of air to gasoline is something like 9000 to 1 an engines power is almost entirely related to the amount of air that goes through it per unit of time.
The Homare was a 2187 cu in engine (35.8 liters) so it needed either a lot of boost (more air per revolution of crankshaft) Like a 2240cu in Griffon and with Japanese gasoline that is not likely or it needs a lot of RPM, like the 2240 cu in Sabre. Likelihood
of a radial pulling much into the low 3000rpm range is?????
2 engines did it but both used a much lower boost than the Homare and both used a much shorter stroke.
A big problem with air cooled engines was the cooling. They were much more limited by cooling than liquid cooled engines.

Making power is one thing, surviving for more than seconds at a high power level is another.

 

[Greyman]

There is not a lot of magic in basic engine calculations.

Try being as dumb as me. It all becomes quite magical.

 

[msxyz]

There is not a lot of magic in basic engine calculations.
Since the volume (not weight) of air to gasoline is something like 9000 to 1 an engines power is almost entirely related to the amount of air that goes through it per unit of time.
The Homare was a 2187 cu in engine (35.8 liters) so it needed either a lot of boost (more air per revolution of crankshaft) Like a 2240cu in Griffon and with Japanese gasoline that is not likely or it needs a lot of RPM, like the 2240 cu in Sabre. Likelihood
of a radial pulling much into the low 3000rpm range is?????
2 engines did it but both used a much lower boost than the Homare and both used a much shorter stroke.
A big problem with air cooled engines was the cooling. They were much more limited by cooling than liquid cooled engines.

Making power is one thing, surviving for more than seconds at a high power level is another.

On the other side, one could argue that the smaller pistons, shorter rods and lighter reciprocating parts made it easier to spin it faster, as the inertia forces are lower. Gasoline engines also favor smaller pots due to the way the combustion starts.

As you say, however, the Homare proved a bit too much for the alloys, oil and gas available to Japan at the time.

Nakajima 130x150 pot design went from 940 HP of the fist Sakae (33HP/L) to 1200 HP of the later variants (42 HP/L). If we consider the Homare pots/heads an evolution of the design employed in the Sakae, it debuted at 1800HP (50HP/L) and reached 2000 HP (55 HP/L) when development ceased.

In contast, the Kasei debuted at 1460HP (34HP/L) in the G4M, the Kyofu floatplane and the earlier models of the Emily. Late war examples topped at 1850 HP with ADI (44HP/L) for the J2M Raiden and the Emily. The Kasei was available with and without a forced cooling fan and extension shaft, to allow a more streamlined installation. The larger 18 cylinder model (Ha-104?) debuted at 1900 HP (35HP/L) but was able to reach 2300 HP (42HP/L) in the later variants with ADI and used forced cooling.
By some accounts, Mitsubishi engineers were progressing fast on the development of a 22 cylinders variant for a transoceaning bomber before the project was shut down.

 

[Shortround6]

On the other side, one could argue that the smaller pistons, shorter rods and lighter reciprocating parts made it easier to spin it faster, as the inertia forces are lower. Gasoline engines also favor smaller pots due to the way the combustion starts.

As you say, however, the Homare proved a bit too much for the alloys, oil and gas available to Japan at the time.

Nakajima 130x150 pot design went from 940 HP of the fist Sakae (33HP/L) to 1200 HP of the later variants (42 HP/L). If we consider the Homare pots/heads an evolution of the design employed in the Sakae, it debuted at 1800HP (50HP/L) and reached 2000 HP (55 HP/L) when development ceased.
.

I was in in error only one high speed radial had much shorter stroke than the Nakajimas.
One of the radials to exceed 3000rpm was the Gnome-Rhone 14M with 122mm x 116mm cylinders. Piston speed 2,258fpm at 3030rpm.
The other was the Bristol Taurus with 127mm X 143 mm cylinders which are close to the Nakajima cylinders. Piston speed was 2,906fpm at 3100rpm.
It had cooling problems at 44.5hp/liter.

The R-2800 used 146mm X 152mm cylinders. heavier pistons but not much difference in piston speed. The fatter cylinders helped the R-2800 flow about 28% more air per revolution and that is a lot to make up with RPM. To flow as much air the Homare (at the same boost pressure ) would have to run 3450rpm ?

An R-2800 making 2400hp is making 52.3 HP/Liter.

I have no idea how much the Japanese were trading engine life for power output.

 

[msxyz]

I have no idea how much the Japanese were trading engine life for power output.

I think engine life must have been quite low. I remember reading that there was a shortage of Baabit metal and of good bearings due to the manufacturing plants being among the favourite targets of the US bombers.

Workmanship in the last yar of the war must also have been quite terrible. You can find pictures of Homare engines in museums with very crudely welded exhaust ducts and other minor details hinting at a step decline of the skills of the people manufacturing the engines.

 

[Kilkenny]

Lots of good points here... Both the IJA and IJN would have been better off if they cooperated on installing and improving Kinsei and Kasei engines (instead of any other 14+ cylinder engines!) and then doing the same in 1942 for the Kinsei and Kasei 18-cylinder derivatives.... In other words, no Zuisei, Sakae, Mamoru, Ha-109, Homare (and especially not the Atsuta!)....

 

[FLYBOYJ]

Lots of good points here... Both the IJA and IJN would have been better off if they cooperated on installing and improving Kinsei and Kasei engines (instead of any other 14+ cylinder engines!) and then doing the same in 1942 for the Kinsei and Kasei 18-cylinder derivatives.... In other words, no Zuisei, Sakae, Mamoru, Ha-109, Homare (and especially not the Atsuta!)....

Just so you know this thread is over 3 1/2 years old - I think a few members are still on here who may give you a response.

 

[msxyz]

Lots of good points here... Both the IJA and IJN would have been better off if they cooperated on installing and improving Kinsei and Kasei engines (instead of any other 14+ cylinder engines!) and then doing the same in 1942 for the Kinsei and Kasei 18-cylinder derivatives.... In other words, no Zuisei, Sakae, Mamoru, Ha-109, Homare (and especially not the Atsuta!)....

On the lack of cooperation: while the diffidence, bordering sometimes animosity, between IJN and IJA is often quoted as one of the factors contributing to the demise of Japan's war effort, it should be noted that, at the time, many nations still tended to give a certain independence to the various military branches because cooperation was seen as undermining the prestige, expertise and tradition of each of them.

Aviation, in particular, the 'new kid on the block' of the 20th century, was often seen as a 'sidekick' of traditional armies and warfare, with the result that many nations failed to use it in the proper way. In Italy, for example, despite the great emphasis on aviation, there was an almost complete lack of cooperation between the navy and the air force, with the result that often the combat ships were left unescorted and oblivious to the enemy movements while the air force was busy bombing small convoys elsewhere in the Mediterranean.

As for Nakajima, I don't think they would have ever given up developing their engines. Japanese conglomerates tended to do vertical integration and diversification, therefore, if they were in the business of aviation, like Mitsubishi, Nakajima or Kawasaki, they had to develop also the engines and push for their adoption. What possibly lacked was somebody like the figure of Albert Speer in Germany who coordinated the industrial effort setting priorities. The Homare pushed so many boundaries (size, specific power, high rpm) at the same time that, even if for some fortuitous coincidence the engineers got it right at the first try, its manufacture still wasn't easy at all... and, of course, there was no 100 octane gasoline available.

 

[tomo pauk]

Japanese top brass was right to focus on the Homare. It was offering a lot of power in a small package, even in a de-rated form. What was wrong was the obsession with small engines, like the Sakae from Nakajima, and Zuisei from Mitsubishi. Another obsession was that with the DB 601A copy, these gave neither power, nor reliability, nor were available in a timely manner.