Yokosuka 12-Shi Special Flying Boat (H7Y)

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.

interesting : an other project !

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.

windswords said:

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

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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,

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

Click to expand...

that's just playing at it, what youwant is one of these....

http://en.wikipedia.org/wiki/Napier_Deltic

http://www.ptfnasty.com/ptfDeltic.html

http://www.wis.co.uk/justin/deltic-engine.html

and a wiki page about the Jumo engines,

http://en.wikipedia.org/wiki/Junkers_Jumo_204


cheers,
Robin.

robunos said:

that's just playing at it, what youwant is one of these....

Click to expand...

Gasp ???

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,
Robin.

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?

In the designation index of "Japanese Aircraft of the Pacific War" René Francillon
says "project only". :-\

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?

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!

windswords said:

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?

Click to expand...

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.

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.

windswords said:

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.

Click to expand...

...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.

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

Interesting that you bring up Hiro. In my original psoting to start this topic I mentioned the website Dave's Warbirds. Their page about "Tillie" is actually entitled:

Yokosuka H7Y1 12-Shi ("Tillie")
Hiro H7Y1 12-Shi ("Tillie")

So could it be that on this site that the H7Y1 (similar to the Do 26) and H-97 (similar to the LeO H-246) projects were combined by mistake?

Also based on the information Lark posted it seems to indicate that the H7Y1 was built and not just a paper project. But if it was built wouldn't there be a picture of it, at least a mock-up if not an actual flying model?

The Mikesh and Abe book states clearly that no information was saved and is a later source (1990) than the Bueschel and Abe
article (1959) quoted by lark. Evidently Shorzoe Abe discovered information that led to the changed H7Y1 description in
the Putnam volume.

Jon

from :The Grub Street Dictionary of International Aircraft Nicknames
Variants and Colloquial Terms by John Horton
Tillie :Kusho H7Y Navy special flying boat.Twin engined,gull-wing flying boat
designed pre-war for long range recce over the U.S.
territory.Only one completed.

There should be a drawing of this aircraft in 'Japanese Aircraft codenames&designations'
written by Robert C.Mikesh as far as I remember.(I have the book not at hand for the moment)

If the H7Y was two engined,what is the four engined design in the start of this thread.

As far as I found ,there was no licence for the LeO 246 production in Japan.
(6 ordered by AirFrance for use in the Mediterranean)

"If the H7Y was two engined,what is the four engined design in the start of this thread."

Good question. I thought it was because the Yokosuka and Hiro projects were incorrectly combined but maybe it was Bueschel because the drawing he used in his book was based off the Leo H-246 and not the Do 26. ???

The picture in Mikesh's book is that of the Do 26A V1 (D-AGNT) "Seeadler" in flight.

lark said:

There should be a drawing of this aircraft in 'Japanese Aircraft codenames&designations'
written by Robert C.Mikesh as far as I remember.(I have the book not at hand for the moment)

Click to expand...

Indeed ,a vague pic.of the Seeadler..

The riddle of te H7Y stays unsolved (for the moment)

I can't find any other information in Japanese books and Japanese site.
No drawings and no pictures are available. I can't believe this fact.
It was a top secret project for Japan and failed.

http://www.geocities.co.jp/Bookend-Ohgai/3853/jnrs/jnrsC236c.htm

1937, the Navy landing boats without a round trip flight from Hawaii to the mainland and Japan
Planning, "二試特殊飛行艇 " ( i don't know the meaning)10 (H7Y1) while secretly ordered to trial in the name of an empty Tech Depot
Ta. The Navy issued the request, the range 5,000 nm (9,260 km) long-haul flight
Was that something as simple as possible, a number of commercial plane that was
As were phenomenal.
Plant availability is based on management skills kept secret, as a competent Commander Naval Jun Okamura
Begin to design plans to solve the most crucial thing to challenge long-haul flight
Went. Outline a plan is 4 crew, 18 tons gross weight aircraft, motor fuel is
Dezeruenjin and things to consider adopting the rate of consumption, and ultimately extraordinarily
Ta cruising capacity to produce a weight reduction as well as strength, stability and a minimum value
Beating, and was taken to sacrifice any other policy. The high-wing monoplane with wing
Junkers Jumo Dezeruenjin imported from Germany based on the four wings
As two pairs of twin format Motoe Hazime. Also, in our country is to reduce parasite drag
浮舟 other end of the retractable wings in the first method, a sophisticated and aerodynamic body
Was to have made as much as possible.
The prototype was designed with a range of exclusive devotion, as a commercial plane is about unprecedented
Had a delicate appearance, had just completed trial flights. Nowadays
This machine was planned under tight secrecy has finally become the person we mercenaries
That will come out, the controversy over the presence of mercenaries in this unit a poor value of the speed blunt Armament
The began. In addition, the results of the trial flight was impossible clearly represent design, practical 到底
In what is far, gotten better at trying to repair the aircraft in each departments
Unable to see, and the unwelcome use of this machine is also confident in our value-parties, after all
This plan only one prototype aircraft trial flight was canceled.
Among the top-secret plan, ultra long-range vision of the flying boat prototype.

ps: i have used google translator

Although it was said that all plans/pics/drawings etc. for this aircraft were destroyed I find it hard to believe that nothing official, not even a photo survives. After all this was not the only secret project the Japanese ever did before and during the war. The Ki-94-I and II, the J7W Shinden, and the Ki-87, even the H11K flying boat, among others, were all projects that resulted in prototypes, and we have plenty of pics, drawings, etc. of those, yet nothing for the H7Y? Thoughts?

airman said:

"二試特殊飛行艇 " ( i don't know the meaning)

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Remove the first kana (which is not part of the rest) and you get "Special flying boat trial", in other words "special experimental flying boat".

H7Y1 was ordered to develop in 1937(the 12Th year of Showa(昭和） era).
(Showa era was emperor HIROHITO' s era.)
H7Y1 was called ”十二試特殊飛行艇”. "十二" means ordered to develop in the 12Th year of Showa era(1937). "十二" means twelve. "十"　means ten and "二" means 2. "試” means experimental. "特殊” means special. "飛行艇” means flying boat.
("一" is 1, "二" is 2, "三" is 3, "四" is 4, "五" is 5, "六" is 6, "七" is 7, "八" is 8, "九" is 9, "十" is 10. "百" is 100, "千" is 1000,　"万" is 10000.)
H7Y1 was completed in 1939 and tested, but hard to take off from water because of it's low power.(MTOW was 18ton, engine power was 1,500 HP in take off(2 Jumo 205 engines)). And very hard to control on the water.
It's shape was similar to Do26.

"主翼は高翼単葉とし翼上にドイツから輸入したユンカース・ユモ・デーゼルエンジン４基を２基一組として双発形式とした。" "Was in the form as a set of two twin-engined Junkers-4 group Yumo-Dezeru engine imported from Germany on the wing and wing high-wing monoplane."


Just on this Google translation, is it saying four engines? The attached image pro ports to be the H7Y1 and shows no gull wing and two engines per wing. I don't know the name of the source, however. It was sent to me via email some years ago.


So, if the scan is true, well, seems Bueschel was right after all.

Keep in mind the time. Here was a project designed to reach Hawaii at a time where there wasn't a declaration of war but both sides knew it was coming. The U.S. was already imposing sanctions on Japan at this time. If it was learned the Japanese were designing a plane that could touch U.S. territory, well, that might have provoked war. Hence, the high level of secrecy and apparently absolute destruction of any evidence of the H7Y.

windswords said:

Although it was said that all plans/pics/drawings etc. for this aircraft were destroyed I find it hard to believe that nothing official, not even a photo survives.

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Hikoki1946 said:

"主翼は高翼単葉とし翼上にドイツから輸入したユンカース・ユモ・デーゼルエンジン４基を２基一組として双発形式とした。" "Was in the form as a set of two twin-engined Junkers-4 group Yumo-Dezeru engine imported from Germany on the wing and wing high-wing monoplane."


Just on this Google translation, is it saying four engines? The attached image pro ports to be the H7Y1 and shows no gull wing and two engines per wing. I don't know the name of the source, however. It was sent to me via email some years ago.


So, if the scan is true, well, seems Bueschel was right after all.

Click to expand...

Wow amazing drawing.
Source ; 日本航空学術史(Japanese aeronautical academicscientific history)
Japanese text says that H7Y1 had four engines, two engines were marged into one set of engine.(Or two engines were installed in one engine nacelle same as Do26) So H7Y1's shape was two engine aircraft.
But this drawing has four engines. :-[

Yet another drawing of the Kugisho H7Y1.

According to Encyclopedia of Japanese Aircraft 1900-1945, Vol. II Aichi/Kugisho aircraft:

"The construction of the prototype and experiments were conducted under the highest secrecy, and almost no one outside the project knew about it. No photographs, blueprints, data or other information is left, and this aircraft is considered one of the phantom aircraft. It should be noted that the engines were directly imported by the IJN, and although there are some rumors that it had four engines, it actually had two engines in parallel."


Regards,

LAW

So, in essence, the IJN coupled two Jumo 205C engines together in one nacelle. The drawing doesn't show a push-pull configuration like the Do 26, so, seems the reasonable assumption?

LAW said:

Yet another drawing of the Kugisho H7Y1.

According to Encyclopedia of Japanese Aircraft 1900-1945, Vol. II Aichi/Kugisho aircraft:

"The construction of the prototype and experiments were conducted under the highest secrecy, and almost no one outside the project knew about it. No photographs, blueprints, data or other information is left, and this aircraft is considered one of the phantom aircraft. It should be noted that the engines were directly imported by the IJN, and although there are some rumors that it had four engines, it actually had two engines in parallel."


Regards,

LAW

Click to expand...

In another place the Encyclopedia states:

"Power was supplied by two German Junkers diesel engines used in tandem for their low fuel consumption."

The drawing (from another, unknown source) not correspond with this description. It appears that the aircraft on drawing has two (?) nacelles on wings, not one nacelle in the fuselage centerline.

The more I think about it, I'm thinking that the illustration showing two nacelles on each wing is the correct one. Clearly neither of the two drawings show the push-pull configuration of the Do 26 and there is no solid evidence to suggest that the H7Y used coupled 205C engines in each wing (as I've not found any information that 205C engines were mated together through a common gearbox). I don't think that a twin engine design would come close to the range requirement the Navy was asking for.


Perhaps mounting four engines separate was easier to construct than copying the Do 26 arrangement?

LAW said:

In another place the Encyclopedia states:

"Power was supplied by two German Junkers diesel engines used in tandem for their low fuel consumption."

The drawing (from another, unknown source) not correspond with this description. It appears that the aircraft on drawing has two (?) nacelles on wings, not one nacelle in the fuselage centerline.

Click to expand...

Indeed, both drawings aren't so accurate. But... One source state that H7Y1 had "two engines in tandem", another that "four engines in two pairs"... Where did it come from? If really H7Y1 had four engines, each in its nacelle (i.e. standard, ordinary configuration), why this confusion with number of engines?

I think this drawing is very good, 2×Jumo 205 engines for her extream long range go and return from Japan to Hawaii.
The IJN's request for range was 5,000 nm (9,260 km).This shape is aerodynamically clean and wing area was large, because of parasol wing.
I want to see front view, especially parasol wing support structure.
H7Y1 was completed in 1939 and tested, but hard to take off from water because of it's low power.(MTOW was 18ton, engine power was 1,500 HP in take off(2 Jumo 205 engines)). And very hard to control on the water.
H7Y1 was designed based on Do26. Almost twin engine Do26?

"想像図" means imaginary drawing.

Do26A
Gross Weight ; 20ton, Engine ; Jumo 205C diesel engine, 600hp×4, Range ; 9000km
Do26V1
Gross Weight ; 22.5ton, Engine ; Jumo205D, 850hp×4, Range ; 7100km
H7Y1
Gross weight ; 18ton, Range ; 9260km(5000n.m.)

So the opinion that "the H7Y1 had two Jumo205 engines" is little strange. :-[
Or Kugisho tried to design low cost two engines flying boat with high aspect ratio wing?

Japanese very famous aeronautical historian Tadashi Nozawa (野沢正) said that "H7Y1 was a twin engine flying boat, the opinion that H7Y1 had four engines is mistake".
I think the best way to get long range reconnaissance flying boat which could reach Hawaii at the day was to order Do26 or Do26 drawings, but perhaps the IJN strictly wanted to keep secret of hoping such a long range flying boat which meant the intension to attack Pearl Harbor, and made a mistake to develop such a low powered twin engine flying boat. All informations for H7Y1 indicate apparently low power. If H7Y1 had four engines, structural accidents and difficulty to take off did not occur. Perhaps the IJN forced Kugisho to design twin engine aircraft same as Mitsubishi G4M's case.
Nevertheless I feel gross weight 18ton is too heavy for twin Jumo205 engines. :-[

in 2° volume of " Secret Japanese Aircraft " i have seen that all records about this plane was destroyed. :'(

PUTNAM Japanese Aircraft 1910-1941 page 282 said that "Power was to be provided by two Junkers diesel engines because of their low fuel consumption". This opinion is same as ED's latest work JAPANESE SECRET PROJECTS Volume 2. H7Y1 two side view drawing of this book is very very impressive. I want to see a plan view of H7Y1.