I have a soft spot for “hack job” WW2 fighters. Usually it involved replacing a problematic inline engine with a radial (eg La-5 and Ki-100), although in some cases it went the other way(Fw-190 D); resulting in a plane that had a fat nose, or an elongated one. Sometimes as in the Nakajima K-44, it was the result of an unusual requirement leading to an unusual design. Sometimes they just hacked up a plane designed for one role and got a better one for an entirely different niche (eg. Kawanishi Shiden).
Originally it was the LaGG-3, which had been designed for a powerful inline engine. The LaGG-3 was supposed to address an aluminium shortage by building large parts with phenol-impregnated wood, which also made it heavy. However that engine was found to be unreliable, so they substituted it with a weaker inline, and got an underpowered overweight fighter that moved like a slug. Even Stalin started to notice how awful it was and started breathing down Lavochkin’s collective necks.
Nervously (who wouldn’t be nervous with Stalin watching?) Lavochkin fitted a rather large radial engine, and got a surprisingly decent fighter with a wide cowl for the radial and narrow body originally designed for the inline, which was renamed the La-5 (no G because Godunov was kicked out). When aluminium became more available they replaced the wooden parts with metal and cleaned up the aerodynamics a bit and got the even better La-7.
It started as the Ki-61 Hien, Japan’s one and only inline-powered fighter. The engine was a copy of the German Daimler-Benz that powered the Bf-109, making the plane look like an Italian design (eg. Macchi C.202 Folgore), thus the Allied codename “Tony”.
High powered liquid-cooled inlines were harder to mass-produce. Kawasaki never really solved the problem of quality control. Ki-61 fighters spent a lot of time grounded at their bases due to engine problems, while in Japan there were many more airframes gathering dust in warehouses due to bad engines being rejected.
Then Kawasaki’s engine factory was bombed in 1945, halting all production of that problematic inline. They fitted a Mitsubishi Kinsei radial on the airframes and found a surprisingly good fighter, one that Japanese Army aces said outperformed their Nakajima Hayate. They called it the Type 5 Fighter (Go-Shiki-Sen). Like the La-5, it had a large radial-engine cowl and narrow inline-engine body. It appeared so late that the Japanese and the Allies never gave it a proper codename.
Why didn’t they do this sooner like Lavochkin? Maybe if the Emperor ordered them to or else commit seppuku…
Focke-Wulf Fw-190 D
The highly successful Fw-190 A was a radial engined fighter with one problem: poor high altitude performance. Its powerful BMW engine had been intended for transports and airliners! No one had expected it to power a fighter at high altitude. The engine had been chosen because the more obvious high-altitude inline engines had been snapped up by Messerschmitt, Heinkel, Henschel and Junkers. Even the radial originally picked by Focke-Wulf had been snatched. Only the airliner engine was left.
That made the Fw-190A a sort of hack job already, but at least the plane was designed to accommodate a radial engine of that size. It was a tough bird that shrugged off ground fire and absorb much damage because there were no leaky radiators to worry about.
But high-altitude work was left to the Bf-109, which by 1944 needed a bit more help.
So Kurt Tank of Focke-Wulf put a huge Jumo inline bomber engine on the Fw-190, and stretched the fighter’s body a little for balance, resulting in the gangly and awkward-looking long-nosed Fw-190 D, the “Dora”. It was supposed to be a stopgap until he finished testing the more advanced Ta-152, but the Luftwaffe pilots couldn’t get enough of it, they loved it! A remarkably successful hack-job.
The Ta-152 looked very similar to the Fw-190D, using the same engine and similar fuselage. The difference was in the internal structure which was strengthened to accommodate the increased weight and power and to rebalance the fighter. The Dora was pretty much a fast and high climbing straight-line fighter, the Ta-152 was supposed to be more balanced and able to manoeuvre better. Only a few got into the air before the war ended.
Nakajima Ki-44 Shoki
This is not quite a hack-job: the fighter was designed that way from the beginning. But it deserves a mention anyway. When Nakajima was told to design a bomber-interceptor with a furious rate of climb and speed, the only way they could do it at the time was to fit the biggest radial engine they had on as small a body that could still hold it.
I think it made the designers at Nakajima wince. Their other designs were beautiful.
But it was a reasonably successful design, having a performance remarkable for 1941-42 in climb and top speed that matched the later J2M Raiden (1945).
Nakajima had to stop building them because they had to retool their factories to produce their new fighter, the Ki-84 Hayate. There simply weren’t enough factories to produce all the types of Nakajima planes, although they kept cranking out Zeros until the end.
Yes, Nakajima built Zeros under licence and eventually built more than Mitsubishi did.
Why not stop Zero production and keep building Shokis and Hayates?
Stop Zero production? Kinjiru! (Forbidden!)
Kawanishi N1K1-J Shiden
This is probably the most remarkable hack-job of them all. It was originally the N1K1 Kyofu, a sea-plane with floats under the fuselage and wings. When the Navy decided not to buy any more than a dozen, Kawanishi modified the plane into a land-based fighter by removing the floats, and installing retractable landing gear.
They replaced the engine: the large Mitsubishi Kasei was replaced with the more powerful Nakajima Homare. Now there was no more room for the cowl-mounted machine guns but the holes were left there anyway, it was welcome ventilation in the tropics. The original round cowl now sprouted oil-cooler intakes above and below the nose.
They put on extra large propellers to take advantage of the more powerful engine, but that meant they had to make the landing gear taller by telescoping it out for landing.
Oh, and high velocity cannons. There was already room for a pair in the wings in the Kyofu, so they added another pair in pods under the wings. They called the new plane the Shiden “Purple Lightning”, and added “J” at the end of N1K1 to signify the change from seaplane to land-based fighter.
It was an awful looking plane.
The Navy was lukewarm about it, they were waiting for Mitsubishi to finish the Reppu fighter which was supposed to succeed the Zero. Meanwhile the Zero had its wings shortened for speed and roll and had installed high velocity cannons to shoot at longer range instead of knife-fighting distance of the earlier models.
Mitsubishi never finished the Reppu, and the Zero was hacked out of the sky by newer Allied planes and tactics. Suddenly the Shiden was in demand. It was a fast and nimble flying tank. Japanese planes were notoriously fragile, but the Shiden could take hits and still fly; it turned like it had a turret; and with four high velocity cannons it could shoot like a tank. It was also fast and did not suffer the lousy high-speed handling of other Japanese planes.
The 1945 model N1K2 Shiden-Kai (Improved Purple Lightning) reduced the number of parts, improved the aerodynamics and put the extra cannon in the wings. I suspect they also wanted it to look prettier; the mongrel N1K1 model must have made Kawanishi’s designers cringe, it was an effective but awkward-looking plane.
Remarkably, Kawanishi was and still is a company absolutely specializing in seaplanes, not fighters. Everything else it ever built for the Japanese Navy were seaplanes, seaplanes, seaplanes, flying boats, amphibious planes, flying boats and more seaplanes. A land fighter by Kawanishi? Unglaublich! as the Germans say.