The Kawasaki Ki-100 with an air-cooled inverted V-12 engine.

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Hardrada55

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Feb 5, 2006
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Would there have been any advantage if the Kawasaki Ki-100 had been able to use the Shoda Hikoku Shoda Ken No. 1 air cooled inverted V engine. Shoda-Hikoki Shoda-Ken No. 1, Inverted V-12 Engine. Basically, I think you would have been trading a couple of hundred horsepower (at war emergency power, about the same horsepower at military rating) for a pointed nose and a two-stage supercharger. Would the installation of the Shoda Ken No. 1 (if they could have manufactured the thing in sufficient quantities in a timely fashion) have resulted in a better Ki-100 fighter?

The Kawasaki Ki-100 Type 5 fighter was a remarkably successful aircraft considering that it was an extemporaneous combination of the engineless airframe of the Ki-61-II with the Mitsubishi Ha-112-62 1971ci, 14 cylinder Kinsei radial engine. It had an estimated war emergency power of 1475hp at 16,400. Top speed at military power was 360 mph at 19,685ft and as much as 380mph at war emergency power.

The Shoda Hikoku Company was primarily a subcontractor for the Nakajima Company making "hot fused" cylinder head fins for the Nakajima Homare 18-cylinder radial engine. In 1940 though, the Shoda Hikoku company began developing an experimental air-cooled inverted V-12 engine, the Shoda Ken No. 1. Of 24-liter displacement (1,464 ci) each cylinder had a bore of 120mm and a stroke of 177mm. The Shoda Ken No. 1 was fuel injected (like both other engines) and had a fluid (Vulkan) supercharger drive like the DB-601. Unlike the DB-601 and the Mitsubishi Kinsei, the Shoda Ken No. 1 engine had a two-stage supercharger. It was a little longer and wider than the DB-601 at 208 cm (81.88in) long and 89.6cm wide which was understandable with the big two stage supercharger hanging off the back of the engine. Weight was similar to the DB-601 and the Mitsubishi Kinsei, but it was a little heavier at 650kg. 1200 hp was available at 3200 rpm. With the two-stage supercharger power could have been maintained to a respectable height. Testing of this engine began in 1943.
 
Nose shape -- as long as there's no separation-- is not a major influence on the drag of aircraft until they start operating at transonic speeds. Cooling drag is, and an air-cooled V-12 would have at least as much of that as a radial.
 
swampyankee said:
Nose shape -- as long as there's no separation-- is not a major influence on the drag of aircraft until they start operating at transonic speeds. Cooling drag is, and an air-cooled V-12 would have at least as much of that as a radial.
Click to expand...

Yes and no.

You are assuming the nose shape (cowl) is pretty decent to being with.

Many late 1930s radial installations and some very early 1940s installations were pretty terrible.

The US tried two different airframes with long pointy noses on radial engines and didn't get the improvement they thought they did get a lot of cooling problems. But then the US radial engine fighters (P-35/P-36/P-43/F4F) had pretty decent cowls to begin with. Some other countries did a pretty good job also. Some other countries had a bit sharper radius on the front corner. Some cowls and cowl to fuselage transitions were terrible. See Gloster Gladiator and Macchi MC 200.

Trying to air cooled V-12 can be done but it is not easy, An incomplete museum example is hard to judge but there needs to be an awful lot of good baffling to direct the airflow for it to have a chance of success.


Issota-Fraschini Delta engine showing the baffles to help force the airflow into and over the fins rather than passing between the cylinders doing little to nothing. These may or may not be the only baffles. There may have been enough that you couldn't see much of the engine (at least the cylinders and heads) making for a boring museum display.
 
Shortround, I think we can both agree that a heavier, less powerful engine is not going to improve performance, especially since making the nose a bit pointier isn't likely reduce drag very much unless the nose design was really horrible to begin with.

Not many combat and aircraft had air-cooled V-12s, probably because their long crankshafts and blocks were heavy and cooling them required a lot of very complex, hard to design baffling. An air-cooled V-12 wouldn't be able to get more power per unit displacement or piston area than an air-cooler radial of the same technical level. For high powered inlines, air cooling is probably not the way to go.
 
agreed.

The Issota-Fraschini Delta was about as good as it got for a service air cooled V-12. Granted the Italians were handicapped by 87 octane fuel.

  • Bore: 132 mm (5.197 in)
  • Stroke: 160/165 mm (6.299/6.496 in), with main and articulated rod
  • Displacement: 26.685 Litres (1,628.44 in³)
  • Length: 2000 mm (78.8 in.)
  • Width: 840 mm (33.07 in.)
  • Height: 883 mm (34.76 in.)
  • Dry weight: 510 kg (1,111 lb)
  • Power output: 770hp/2600rpm take off, 750hp/2600rpm/4000meters.
Issota was working a X-24 engine using the parts from the smaller gamma engine, think aircooled Vulture
They thought that was their best bet for a high power air cooled engine.

  • Type: 24-cylinder, twelve row, four bank, air cooled X engine
  • Bore: 125 mm (4.9 in)
  • Stroke: 130 mm (5.1 in)
  • Displacement: 38.3 l (2,337 in3)
  • Length: 1,730 mm (68 in)
  • Width: 1,000 mm (39 in)
  • Height: 1,000 mm (39 in)
  • Dry weight: 760 kg (1,680 lb)
  • 919 kW (1,232 hp) at 2700 rpm
 
One wonders how good would've been a V12 by Wright that used R-1820 as parts donor, or a V12 by Bramo that uses the 323 as a parts donor.

Hardrada55 said:
...
Unlike the DB-601 and the Mitsubishi Kinsei, the Shoda Ken No. 1 engine had a two-stage supercharger.
...
Click to expand...

Care to share a few details about the 2-stage supercharger on the engine?
 
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Dry weight/power similar to Kestrel (early Deltas) and Peregrine (later Deltas)?
 
Hardrada55 said:
I wish I knew more about the Shoda Ken No. 1 engine. It is a topic of future investigation.
Click to expand...

Me too.

I hope the NASM have the induction trunk that has been removed and will one day soon put the engine together and on display with a stand that allows the induction trunk to be fitted. Once the cosmoline has been removed it should look much better.

If we are very lucky Shinpachi or another Japanese member will now find some manuals or other details on this project.

EDIT JohnBR and Member Bill Pearce of Old Machine Press may find something also - both being heavily into engine history and development.
 
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Hardrada55 said:
I wonder if Smithsonian would have any original documentation?
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You could try them on their web page at Archives Research Request .

You are limited to one question per month from memory but I find they are very helpful. The question can be quite wide as in do you have any documentation and photographs, Japanese or American, for the engine and what is the cost to reproduce.

They may well have Japanese material on microfilm tho the quality can be "variable"
 

Hello Hardrada55,

If I were looking at the possible performance of this configuration, I would do a comparison not against the Ki-100 but against the Ki-61-II-KAI.
My own feeling is that with a power output of only 1200 HP, it would need a MUCH higher critical altitude to get any significant performance increase over what was achieved with Ki-61-II which was making 1250 HP @ 5700 meters in Military Power but still wasn't quite at 400 MPH.

- Ivan.
 


Shortround6,
can you tell more about nose/spinner/cowling shapes and their aerodynamics?
Each country or manufacturer came to certain shapes. The later Mitsubishi plane cowlings were supposed to be very good. The cowling of the J2M Raiden was less draggy than the Zero's even with a 20 cm wider fuselage. The Ki-46 and Ki-83 were also high-performing.
And about the annular and drum radiator cowlings of the German planes? The Ju 88's doesn't have any front cowling curve at all.
Shouldn't be too good?
And the spinners, the German ones seems less pointy. I assume that this was more advantageous for cooling airflow.
 
Leaving others to point out the deadendedness of the air-cooled V12, I'd like to say the Ki100 was a good fighter. For 1941. Very much the equal of a Spit V, and inferior to the Fw190A. Quite close to a P-40N up to medium altitudes.
 
A word on cooling. It's how you deal with the outflow. On a V-12 fighter with a narrow fuselage the obvious option for a designer fitting a big radial is to use the fuselage sides as a place to dump the outflow. It is far easier than fairing the sides and using all-round gills, for example. It just so happens that it is the best option for aerodynamic reasons too. And of course you wouldn't do it at all unless the radial had an extra 300HP or your source of inlines had dried up. I is a speculation of mine, unconfirmed by anything I could find, the the FW190 was conceived to take either a radial or an inline. Tank would then be able to fit a DB or Jumo in the event of no radial being available.
 

Google Curtiss XP-42 and Vultee Vanguard. Both started with a special R-1830 with an extended propshaft. You probably won't find all the photos but the XP-42 went through 14 different cowl configurations. At least one of them may have used a fan in a narrow slot (big spinner).

The early J2m was also supposed to use an extended shaft and a very pointy nose. In addition to cooling problems both the Americans and Japanese ran into prop vibration problems with the extended shafts.
 
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