Homare radial confusion? - Aircraft of World War II

Piper106 · 11-21-2008, 05:53 PM

I am dazed and confused about the late WWII Japanese Homare radial engine.

The Homare 21 is listed as having a take off power of 1990 HP.

This is comparable to the Pratt and Whitney R-2800 engine which without water injection had a similar 2000 HP take-off rating.

My confusion comes from that fact that all the texts I can find indicate that the late WWII Japanese Homare radial engine was "an 18 cylinder version of the Nakajima Sakae engine" with a similar 130 mm (5.12 inch) x 150 mm (5.90 inch) stroke. That bore and stroke works out to 35.8 liters or 2186 cubic inches for the Homare.

Considering that P&W, considered to be one of the best engine companies in the world, needed 46 liters (2804 cubic inches) for similar rated power, how did the Nakajima achieve 1990 HP from an engine that was 22% smaller than the R-2800??

I was under the impression that Japanese fuel was inferior to American 100/130 fuel, so higher boost does not seem to be the answer.

I wonder if the cylinder size was mis-translated / mis-quoted at the end of the war and this wrong information has just been repeated since then. Maybe the Homare had larger cylinders, and therefore a larger displacement than nearly every text indicates.

Does anyone have any documents that would shed light on how the engineers at Nakajima trumped the engineers at P&W??

Piper106

HoHun · 11-21-2008, 06:16 PM

Hi Piper,

>The Homare 21 is listed as having a take off power of 1990 HP.

>This is comparable to the Pratt and Whitney R-2800 engine which without water injection had a similar 2000 HP take-off rating.

The TAIC data on the Homare 21 shows that it used ADI (anti-detonant injection, meaning methanol/water) for everything from military power upward, so it would be rather comparable to a R-2800 with water injection.

The TAIC data also has a speed of 3000 rpm for the Homare 21 at take-off power, compared to the 2700 rpm of the R-2800-8 at 2000 HP. Power output increases approximately linearly with rpm ...

Regards,

Henning (HoHun)

Piper106 · 11-21-2008, 06:47 PM

I had seen references to the 3000 rpm operating speed for the Homare.
Intersting that Nakajima was able to operate their engine at that speed, no other large radial that I am aware of operated at such a high rpm.

Question. Was water injection used for take-off power or just combat emergencies??

Piper106

kool kitty89 · 11-22-2008, 04:39 AM

Except for sleeve types of course.

Another thing to note on this engine was the very small diameter, smaller than the compact R-1830 twin-wasp. (the Homare was just over 46" in diameter) As well as being light weight. (well under 2,000 lbs)

It should also be noted that the R-2800 got a hell of alot more power than 2000 hp out of it, especially with water injection. With the P-47M/N's -57C model it had a WEP (with water injection) of 2,800 hp at 2,800 rpm. The previous engines of the P-47D started at 2,300 WEP (with water injection) later increasing to ~2,520 hp and 2,600 hp with 100/150 grade fuel. (2,800 rpm 70" HG manifold pressure) These are in conjunction with turbochargers of course.
The F4U-4's engine got 2,450 hp with water injection and the previous F4U-1D got ~2,250 with water injection. (these with mechanical superchargers)

They could produce more than 2,000 hp without water injection as well. (2,100 hp for the F4U4's engine)

I believe some versions of the Homare also had direct fuel injection.

This thread may be of interest: http://www.ww2aircraft.net/forum/eng...ines-8450.html (Japanese Piston Engines)

as well as this: Translated version of http://www.warbirds.jp/kakuki/sanko/en_japan.htm

Piper106 · 11-22-2008, 08:36 PM

I have new respect for the Nakajima engineers.

I now see that the Homare had exceptionally good power for its size, and power for the weight. As far as I know it had no ground breaking features, just an exceptional well integrated and developed design. This might have been one of the best radials engines in the world, just that its development was cut short because of being on the losing side of the war.

Piper106

kool kitty89 · 11-22-2008, 10:29 PM

I believe there were some reliability problems as well as manufacturing ones. (many of which were related) I think this was mostly due to limitations of the Japanese industry, not to mention the effects of Allied bombing.

Aurum · 06-15-2009, 07:16 AM

Quote:

Originally Posted by Piper106

I have new respect for the Nakajima engineers.

Piper106

By the way, Homare 4x series had 2 stage 3(!!!) speed supercharger. That should be prominent design in fact. That could be the meter of it`s high specific power too.

Does anybody have drawings of this device, and Homare itself?

Shinpachi · 06-21-2009, 01:00 PM

I have 3-view drawings of Homare 21 but can't find them out even after searching for a few days.
I used them for my cg modelling.
My work here may contiribute any to your purposes.
Picasa ??? ???? - Shinpachi - Shinpachi 3D ...

Homare 21
Dimension: Length 1690mm x Diameter 1180mm

Aaron Brooks Wolters · 06-21-2009, 01:18 PM

Very interesting material guys. Great explanations, and Shinpachi, great three dimensional diagrams.

hrandy · 06-21-2009, 04:06 PM

Waht a shame that there isn't a good English laguage book on the Japanese aircraft engines of WWII. I wonder if there are any comprehensive books in Japanese. If not the history of Japanese engine development will be lost forever.

Shinpachi · 06-22-2009, 01:56 AM

Hi, Aaron and hrandy!
I'm glad you are interested in Japanese aircraft engines.

Here are some history books -

"The History of Mitsubishi Aero-engines"
Amazon.co.jp： 三菱航空エン&# x30B8;ン史―大正&#x5 16D;年より終戦&#x307 E;で 1915‐1945: 松岡 久光, 中&#x897F

"Engine of Tragedy, Homare"
Amazon.co.jp： 悲劇の発動機&# x300C;誉」―天才&#x8 A2D;計者中川良&#x4E0 0;の苦闘: 前間 孝則: 本

"Engine History of Nakajima Aircraft"
’†“‡”òs‹@ƒGƒ“ƒWƒ“Žj - Google ‰æ‘œŒŸõ

hrandy · 06-22-2009, 06:49 PM

Shinpaci these are interesting looking books. I really wish I could read Japanese. I used the "look inside" feature that Amazon has on "Engine of tragedy, Homare" and it looks great. I believe there would be a lot of interest in good english translations of books on Japanese WWII aircraft engines. As least the history is not lost.

Shinpachi · 06-23-2009, 05:24 AM

Here are more testimonies about aircraft development by the former engineers.
I cannot promise but will try to introduce them in the future.

In my old memory of reading one of them, main wing design of Kawanishi aircrafts were referred to the wing catalogue of Vickers, U.K.

Aurum · 06-25-2009, 06:38 PM

Ok, figures 2000 h.p. in 35.8 liters and 3000 r.p.m look rater questionable, but so they are in TAIC reports too.

But what can be said about Homare 31 & Homare 42 (Ha-45-42) models that were even more powerful.
Specs data is: 2200 h.p. (in the same 35.8 l), 3100 r.p.m.!
Could that be got in reality?

Shinpachi · 06-26-2009, 11:02 AM

Quote:

Originally Posted by Aurum

Ok, figures 2000 h.p. in 35.8 liters and 3000 r.p.m look rater questionable, but so they are in TAIC reports too.

But what can be said about Homare 31 & Homare 42 (Ha-45-42) models that were even more powerful.
Specs data is: 2200 h.p. (in the same 35.8 l), 3100 r.p.m.!
Could that be got in reality?

Hi, Aurum. That was the question.
Sorry.

Homare 31: plan only.
Homare 42: prototype only.

Also,
Homare 24, 25, 26 and 41: prototype only

Reference site: wiki

11-21-2008, 05:53 PM	#1
Piper106 Junior Member Join Date: Nov 2008 Posts: 7	Homare radial confusion? I am dazed and confused about the late WWII Japanese Homare radial engine. The Homare 21 is listed as having a take off power of 1990 HP. This is comparable to the Pratt and Whitney R-2800 engine which without water injection had a similar 2000 HP take-off rating. My confusion comes from that fact that all the texts I can find indicate that the late WWII Japanese Homare radial engine was "an 18 cylinder version of the Nakajima Sakae engine" with a similar 130 mm (5.12 inch) x 150 mm (5.90 inch) stroke. That bore and stroke works out to 35.8 liters or 2186 cubic inches for the Homare. Considering that P&W, considered to be one of the best engine companies in the world, needed 46 liters (2804 cubic inches) for similar rated power, how did the Nakajima achieve 1990 HP from an engine that was 22% smaller than the R-2800?? I was under the impression that Japanese fuel was inferior to American 100/130 fuel, so higher boost does not seem to be the answer. I wonder if the cylinder size was mis-translated / mis-quoted at the end of the war and this wrong information has just been repeated since then. Maybe the Homare had larger cylinders, and therefore a larger displacement than nearly every text indicates. Does anyone have any documents that would shed light on how the engineers at Nakajima trumped the engineers at P&W?? Piper106

11-22-2008, 04:39 AM	#4
kool kitty89 Senior Member Join Date: Aug 2007 Location: San Jose, CA Posts: 2,412	Except for sleeve types of course. Another thing to note on this engine was the very small diameter, smaller than the compact R-1830 twin-wasp. (the Homare was just over 46" in diameter) As well as being light weight. (well under 2,000 lbs) It should also be noted that the R-2800 got a hell of alot more power than 2000 hp out of it, especially with water injection. With the P-47M/N's -57C model it had a WEP (with water injection) of 2,800 hp at 2,800 rpm. The previous engines of the P-47D started at 2,300 WEP (with water injection) later increasing to ~2,520 hp and 2,600 hp with 100/150 grade fuel. (2,800 rpm 70" HG manifold pressure) These are in conjunction with turbochargers of course. The F4U-4's engine got 2,450 hp with water injection and the previous F4U-1D got ~2,250 with water injection. (these with mechanical superchargers) They could produce more than 2,000 hp without water injection as well. (2,100 hp for the F4U4's engine) I believe some versions of the Homare also had direct fuel injection. This thread may be of interest: http://www.ww2aircraft.net/forum/eng...ines-8450.html (Japanese Piston Engines) as well as this: Translated version of http://www.warbirds.jp/kakuki/sanko/en_japan.htm Last edited by kool kitty89; 11-22-2008 at 04:43 AM.

06-22-2009, 06:49 PM	#12
hrandy Junior Member Join Date: Feb 2008 Posts: 20	Interesting Shinpaci these are interesting looking books. I really wish I could read Japanese. I used the "look inside" feature that Amazon has on "Engine of tragedy, Homare" and it looks great. I believe there would be a lot of interest in good english translations of books on Japanese WWII aircraft engines. As least the history is not lost.

06-23-2009, 05:24 AM	#13
Shinpachi Senior Member Join Date: Feb 2008 Location: Osaka Posts: 783	Here are more testimonies about aircraft development by the former engineers. I cannot promise but will try to introduce them in the future. In my old memory of reading one of them, main wing design of Kawanishi aircrafts were referred to the wing catalogue of Vickers, U.K. __________________

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

11-21-2008, 06:16 PM	#2
HoHun Senior Member Join Date: Oct 2006 Posts: 1,765	Hi Piper, >The Homare 21 is listed as having a take off power of 1990 HP. >This is comparable to the Pratt and Whitney R-2800 engine which without water injection had a similar 2000 HP take-off rating. The TAIC data on the Homare 21 shows that it used ADI (anti-detonant injection, meaning methanol/water) for everything from military power upward, so it would be rather comparable to a R-2800 with water injection. The TAIC data also has a speed of 3000 rpm for the Homare 21 at take-off power, compared to the 2700 rpm of the R-2800-8 at 2000 HP. Power output increases approximately linearly with rpm ... Regards, Henning (HoHun)

11-21-2008, 06:47 PM	#3
Piper106 Junior Member Join Date: Nov 2008 Posts: 7	I had seen references to the 3000 rpm operating speed for the Homare. Intersting that Nakajima was able to operate their engine at that speed, no other large radial that I am aware of operated at such a high rpm. Question. Was water injection used for take-off power or just combat emergencies?? Piper106

11-22-2008, 08:36 PM	#5
Piper106 Junior Member Join Date: Nov 2008 Posts: 7	I have new respect for the Nakajima engineers. I now see that the Homare had exceptionally good power for its size, and power for the weight. As far as I know it had no ground breaking features, just an exceptional well integrated and developed design. This might have been one of the best radials engines in the world, just that its development was cut short because of being on the losing side of the war. Piper106

11-22-2008, 10:29 PM	#6
kool kitty89 Senior Member Join Date: Aug 2007 Location: San Jose, CA Posts: 2,412	I believe there were some reliability problems as well as manufacturing ones. (many of which were related) I think this was mostly due to limitations of the Japanese industry, not to mention the effects of Allied bombing.

06-21-2009, 01:18 PM	#9
Aaron Brooks Wolters Senior Member Join Date: Jul 2007 Location: Abingdon, VA. Posts: 2,300	Very interesting material guys. Great explanations, and Shinpachi, great three dimensional diagrams.

06-21-2009, 04:06 PM	#10
hrandy Junior Member Join Date: Feb 2008 Posts: 20	Waht a shame that there isn't a good English laguage book on the Japanese aircraft engines of WWII. I wonder if there are any comprehensive books in Japanese. If not the history of Japanese engine development will be lost forever.

06-25-2009, 06:38 PM	#14
Aurum Junior Member Join Date: Jan 2009 Posts: 21	Ok, figures 2000 h.p. in 35.8 liters and 3000 r.p.m look rater questionable, but so they are in TAIC reports too. But what can be said about Homare 31 & Homare 42 (Ha-45-42) models that were even more powerful. Specs data is: 2200 h.p. (in the same 35.8 l), 3100 r.p.m.! Could that be got in reality?