There is a theory that there was a concept to equip the Shinden with a jet engine and call it "Shinden Kai" (J7W2). The basis for this theory is an contribution written by Kunitake Kiyohara, former deputy chief of the 1st Design Division of the Kyushu Airplane Design Department, in an aviation magazine.

In his contribution, Kiyohara wrote, "On June 5, 1944, at the 'Shinden' Project Request Study Group held at the Kugisho, or as an instruction afterwards, a member of the Kugisho's engine staff said as indication to me, "Proceed with the design of modified Shinden using a jet engine. The jet engine to be installed in the modified Shinden will have a ground static thrust of 900 kg, which is equivalent to almost 3,000 HP, and the expected speed will be about 420 kt (780 km/h). However, this modified Shinden requires a take-off auxiliary rocket, which we want to treat as an overload condition."

In his contribution, Kiyohara also wrote, "I thought that the jet engine to be installed in the improved Shinden model would be a Ne-130 jet engine that was being prototyped at the Ishikawajima Shibaura turbine, and I thought that the dogfight era was finally over. Considering the layout of the Shinden's engine, I thought it would not be so difficult to replace it with a jet engine. I was excited by this plan and I wanted to realize as soon as possible. In the end, this plan did not come to fruition, but the twin-engine jet attack aircraft "Kikka" designed by Nakajima Aircraft was prototyped by Kyushu Aircraft, and the war ended when the first aircraft was almost completed.

However, no other specific records have been found of jet engine installed modified Shinden In addition, Mitsuo Nishimura, who served as the chief of Shinden's power outfitting team, also admitted that there was a plan for jet Shinden, but also testified that "no concrete progress had been made" toward its realization. The progress of the development of the Ne-130, a prototype jet engine that was scheduled to be installed at the time, was only at the stage of full-scale testing near the end of the war, and it was not in a situation where it could actually be operated.

The predecessor of the Ne-130, the Ne-20, had a variety of fatal flaws, which shortened its endurance life to only 15 hours at full power. This defect was exposed even during the test flight of Kikka, which was being developed in parallel with Shinden, and it is said that it was not going to be solved. This defect occurred not only in the Ne-20 but also in the Ne-130 under development, and of course it was not in a situation where it could be installed on the Shinden.

Furthermore, at the end of the war, Japan was almost depleted of rare metals (nickel, chromium, etc.) for making heat-resistant metals that were indispensable for jet engines, and the development of alternative metals with high heat resistance due to a lack of resources for exhaust turbines was a major problem. Therefore, even if a prototype jet engine was completed, mass production would have been almost impossible.
 
It's correct that "jet Shinden" existed only as an idea among the design team. Furthermore Ne-130 did not exist even as an idea in June 1944. The work on Ne-130 would not begin until the basic plan meeting on 13 December 1944. Ne-20 started development shortly after on 25 December 1944.

In June 1944, Shinden team was probably instructed to consider the possibility of using a jet engine of generic specifications, when one would come to fruition. That is, no specific work was actually done to this end. It makes some sense because this is roughly the time period where the Navy Aviation staff became interested in the jet engine, because it was reported that it was effective in Germany.
 
If the P-39 could rear-mount a front propeller then it surprises me the reverse was not tried in something like this. It was well known that rotaries overheated in a rear mount.
 
If the P-39 could rear-mount a front propeller then it surprises me the reverse was not tried in something like this. It was well known that rotaries overheated in a rear mount.

I may misunderstand the question. Mounting the engine up front would defeat the purpose of this design. Rear mount allows significant reduction of drag by streamlining the fuselage, and the installation of extremely heavy armament to easily shoot down strategic bombers. But it is correct that there were unresolved difficulties in achieving adequate cooling.
 
If the P-39 could rear-mount a front propeller then it surprises me the reverse was not tried in something like this. It was well known that rotaries overheated in a rear mount.
Dear Madrat,
I get the impression that English is not your first language.

Long drive shafts suffered torsional vibration problems especially when driven by jerky piston engines. Long drive-shafts remained problematic until smooth-turbo-shaft jets were introduced during the 1950s. Hence the only successful WW2 airplanes were Bell’s P-39 Airacobra and P-63 Kingcobra. They mounted engines behind the pilot to make room for 37mm auto-cannons firing through the tractor propeller.
Shinden and most twin-boom pushers needed drive-shafts in order to mount the heavy engine near the center-of-gravity, but still mount the prop far enough aft to streamline the rear end of the engine nacelle/fuselage.

Both Shinden and Curtiss’ Ascender would have enjoyed better stability and control with C.ofG.s even farther forward than OTL.

To be more precise: air-cooled RADIAL engines suffered cooling problems when buried deep in fuselages. All air-cooled engines suffer cooling problems when buried too deep hence the extra cooling fan on the rear engine of Cessna’s 337 Skymaster.

OTOH air-cooled rotary engines were limited to WW1. Since the entire crankcase and all the cylinders rotated around the fixed crankshaft, they cooled great at the low air speeds (e.g. 100 knots) or WW1. Rotary engines were only successful when installed without cowlings (Airco pusher) and or 3/4 cowlings (e.g. Nieuport 17).
 
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If the P-39 could rear-mount a front propeller then it surprises me the reverse was not tried in something like this. It was well known that rotaries overheated in a rear mount.
There's a drawing of the engine layout for the Shinden, it has a driveshaft to the prop at the rear. But the Shinden would have been much better served with a liquid cooled V engine, which would have required a shorter driveshaft to the prop.
 
Dear riggerrob,

You realized right away I meant radial. Clearly, I am not ESL. Radials, like rotaries, were poor for rear mounts for the same reason. Getting clean air evenly across hot spots on the circular layout of pistons was not possible. Liquid cooled V engine was the obvious solution.
 
I assume that the fan was spinning much faster than the prop RPM?
I only found following Raiden data.
14shi interceptor (J2M1)
Engine:Kasei Type 13
Maximum speed 574km/h
Engine revolution: 2,350rpm
Reduction ratio (Propeller) 0.684
Speed increase ratio (cooling fan) 1.000
Peripheral speed at propeller tip: 269 m/sec (969 km/h)
Peripheral speed at the tip of the cooling fan: 62 m/sec (227 km/h)

Raiden Type 11 (J2M2)
Engine:Kasei Type 23
Maximum speed 596km/h
Engine revolution: 2,500rpm
Reduction ratio (propeller) 0.500
Speed Increase Ratio (Cooling Fan) 3.180
Peripheral speed at propeller tip: 216 m/sec (777 km/h)
Peripheral speed at the tip of the cooling fan: 156 m/sec (562 km/h)
 
The main body of the engine and the reduction housing located at the rear end of the fuselage are connected by an extension shaft with a length of 900 mm.
In order to prevent vibration caused by the extension shaft, the three girders of the main wing were installed on the pillars that support the engine, the extension shaft support cylinder, and the reduction housing.
It is a unique support structure for the engine and related parts in which the main wing supports these weights.
This support structure was designed to prevent vibration and seizure due to deflection of the extension shaft.
 

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Presumably, the thrust of the propeller is not applied to the extension shaft to prevent vibration and seizure, but to the extension shaft support cylinder, and then to the engine body and finally to the main wing.
If so, how about Senden?
XP-55 did not use extension shaft.
 

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Presumably, the thrust of the propeller is not applied to the extension shaft to prevent vibration and seizure, but to the extension shaft support cylinder, and then to the engine body and finally to the main wing.
If so, how about Senden?
XP-55 did not use extension shaft.
Yes, Curtiss Ascender did not use an extension shaft, but it also suffered handlingproblems because the center-of-gravity being too far aft.
 

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