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Author Topic: Yokosuka 12-Shi Special Flying Boat (H7Y)  (Read 28651 times)

Offline windswords

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Yokosuka 12-Shi Special Flying Boat (H7Y)
« on: November 21, 2009, 09:31:19 pm »
Does anyone have any info or pics or drawings of this airplane?

I just discovered the existence of this plane while visiting Dave's Warbirds - http://www.daveswarbirds.com/Nippon/aircraft/Tillie.htm

I did a google search and found no other info on this project except for a Czech site - http://forum.valka.cz/viewtopic.php/t/31668

I ran their text thru Google Translate and then "polished" up the translation as best as I could. I think Google and I got it right but don't take it as gospel. If I got any of it wrong please correct it:

"Yokosuka H7Y1

History:

Technical specifications issued by the 12-Shi Naval air force in 1937, called for a three-engine or four-engined flying boat with a requirement for a very long-range - 9,250 km while carrying 1,600 kg in bombs. Such a range should allow it to carry out patrol flights over the anchorage at Pearl Harbor without having to refuel at sea.

At that time there was a long-range flying boat, the German Dornier Do 26. It was a four-engined aircraft, whose engines, Junkers Jumo-205cm, were mounted in tandem which was Dornier specialty. Some of these long range diesel engines were ordered from Germany for use on the prototype. The resulting aircraft was designated as "Special flying boat, 12-Shi" H7Y1. Great emphasis was placed decreasing aerodynamic drag and the lowest possible aircraft weight, resulting in a decrease in strength of the airframe, and speed and defensive weaponry were also sacrificed to increase range. The whole project was kept strictly secret.

The first prototype flew in 1939 and during the first few flights fears were confirmed that in striving for a lightweight design, the wings appeared to warp, the airplane suffered strong vibrations of the hull and wings, and various other problems including engines not powerful enough for an aircraft weighing 18,000 kg. Thanks to lightweight design, the Navy had also come to terms with the fact that the airplane was incapable of carrying out a torpedo attack. The design team tried to correct what they could, but the airplane remained too fragile and the Navy eventually decided on 6th June, 1940 to terminate the entire program. Japan was unable to attack Pearl Harbor without carrier based aircraft, even the long range H8K2 "Emily" flying boats had to refuel from submarines, otherwise they did not have the range to fly to Pearl Harbor."




As for the engines (again my rough translation):

"Japan got a few six-cylinder engine Junkers Jumo 205cm engines from Germany. This aircraft engine was interesting in terms of ignition fuel - it was a two-stroke diesel engine. Overall, it was an interesting engine design, if not quite a successful one. This mechanical compressor engine and its extreme height is given by its more interesting design - it was a rotating engine with pistons! This means that one cylinder is moving two pistons. The German planes are used height Junkers Ju-86."

From the diagram the site posted below, it looks like a an opposed cylinder design, where one cylinder houses two pistons.

« Last Edit: July 06, 2016, 03:21:24 am by Skyblazer »
Frank

Offline airman

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #1 on: November 22, 2009, 01:48:13 am »
interesting : an other project ! :D
writers , bloggers , content-curators ,  music composer and passionate of militaria and uchronia

Offline sagallacci

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #2 on: November 23, 2009, 09:13:42 am »
A little clarification.
The Jumo aero-diesel engines were widely produced in several sizes to great success. Though a bit heavy, had great fuel efficency.

Offline Retrofit

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #3 on: November 23, 2009, 10:25:17 am »
From the diagram the site posted below, it looks like a an opposed cylinder design, where one cylinder houses two pistons.

Interesting. Engines using a similar principle are still designed in UK by the company "Power Plant developments" with its "Gemini" series.

http://ppdgemini.com/_PDF/Principles_of_Operation_B&W_8-08.pdf

All the best,
« Last Edit: November 23, 2009, 10:27:13 am by Retrofit »

Offline robunos

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Offline Retrofit

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #5 on: November 23, 2009, 01:39:34 pm »
that's just playing at it, what youwant is one of these....

Gasp  :o  ??? :D

Offline robunos

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #6 on: November 23, 2009, 02:54:22 pm »
I know we've drifted of-topic here, but just a few final points about the Jumo engines...

From Gunston's 'World Encyclopaedia of Aero Engines' :-

"The final wartime engines [developed from the Jumo opposed engines] were staggering
in concept, the Jumo 223 being a family of related 'box' engines comprising four
opposed piston diesels in one unot with a crankshaft at each corner; weighing 2,370kg,
it gave 2,500hp at up to 6,000 m [altitude]. In 1942, it was dropped in favour of the Jumo 224,
which was even bigger and designed for 4,500 hp."
For comparison, the Deltic is rated at  1875 hp.


cheers,
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Where ARE the Daleks when you need them......

Offline windswords

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #7 on: November 24, 2009, 10:21:35 am »
To get us back on topic, does anyone have any further info or drawings of the H7Y1? The site I referenced said one prototype was built. Shouldn't there be a photograph of the aircraft? What does Francillion say about this bird?
Frank

Offline Jemiba

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #8 on: November 24, 2009, 11:00:01 am »
In the designation index of "Japanese Aircraft of the Pacific War" René Francillon
says "project only".   :-\
It takes a long time, before all mistakes are made ...

Offline windswords

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #9 on: November 24, 2009, 12:06:09 pm »
Thanks Jemiba! Now, if the Francillion book is correct, I wonder where the illustration posted on the Dave's Warbirds and the Czech site came from? Further, is it an official illustration from Yokosuka or just someone's conjecture?
Frank

Offline Hikoki1946

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #10 on: November 25, 2009, 07:06:04 am »
The conjecture drawing comes from Richard Bueschel's 1966 book Japanese Code Names. Interestingly, his book says that Tillie was based off the French "Leo H-24-6" transport flying boat. But the rest of the sources I checked (which did not have any images) all say it was based on the Do 26.

Cheers!


Thanks Jemiba! Now, if the Francillion book is correct, I wonder where the illustration posted on the Dave's Warbirds and the Czech site came from? Further, is it an official illustration from Yokosuka or just someone's conjecture?
« Last Edit: November 25, 2009, 07:27:19 am by Pelzig »

Offline windswords

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #11 on: November 25, 2009, 09:11:04 am »
If you look at the pic from http://www.1000aircraftphotos.com/Contributions/Braas/7410.htm of the LeO H-246,
it looks very similar to the image in my first post.

Frank

Offline Hikoki1946

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #12 on: November 30, 2009, 06:46:01 am »
It does...but if the author (Bueschel) believed that Tillie was based off the French flying boat, it stands to reason that the art commissioned for the book would reflect that belief. Given the many Dornier-Nippon projects, the consensus is that Tillie was based off the Do 26, not the LeO H-246.


If you look at the pic from http://www.1000aircraftphotos.com/Contributions/Braas/7410.htm of the LeO H-246,
it looks very similar to the image in my first post.



Offline lark

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #13 on: November 30, 2009, 01:33:21 pm »
...The highly secret 12-shi H7Y1 Special Reconnaissance Flying boat
was designed at Yokosuka in 1937 to meet a specified range requirement of 5000miles
for possible use against Hawai.Power was four imported Junkers Jumo 205c diesels
of 600hp chosen for their low fuel consumption.
Loaded weight of the four seat prototype was 39.700lb.
The H7Y1 suffered from extreme vibrations in the wing and the rear hull section
due to its light construction.The vertical tail was enlarged to aid in stability
but the sole prototype was unacceptable due to the poor performance and armament...

So far: Richard M.Bueschel and Shorzoe Abe in Japanese Navy Aircraft 1940-1945 part II
published in Air Pictorial January 1959.

p.s. The illustration of the aircraft in this article is the same as the one  in this thread.
« Last Edit: November 30, 2009, 01:34:55 pm by lark »

joncarrfarrelly

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Re: Yokosuka 12-Shi Special Flying Boat (H7Y)
« Reply #14 on: November 30, 2009, 02:32:55 pm »
Japanese Aircraft 1910 - 1941, Robert C Mikesh & Shorzoe Abe, Putnam 1990.
Pages 281 - 282, Experimental Kusho 12-Shi Special Flying Boat (H7Y1), Chief designer Lieut-Cdr (Engineering)
Jun Okamura of the Kusho (Kaigun Koko-Shu/Naval Air Arsenal) Yokosuka.
Mikesh and Abe state that the range requirements led to a specification being issued for an aircraft similar to 
the Do-26, not that the aircraft was based on the Do 26. They also state that the aircraft was powered by two
Jumo 205 rather than four, mounted on a high-aspect ratio wing with retractable floats. No photos,
drawings or other data were saved when the project was canceled due to the structural and performance
problems.

Back to the Leo 24-6 conundrum, the 1943 Aeronautics Aircraft Spotters' Handbook, National Aeronautics Council, Inc.,
New York has an entry for a four-engined flying boat with the designation Hiro H-97, said to be similar to the LeO 246.
Of course on the next page the Kawanishi H-97(H6K) is said to be a development of the Potez CAMS 141.

Jon