Ki-27 with Retractable Landing Gear — Japan's Mini Zero (Mini Ki-43)

[_PabloSniper_]

What if the Nakajima Ki-27 had been developed with retractable landing gear?

The idea behind this hypothetical version is to turn the already very light and maneuverable Ki-27 into something resembling a miniature Zero — or perhaps more accurately, a mini Ki-43.

The original Ki-27 was designed with fixed landing gear, prioritizing simplicity and low weight. But replacing the fixed undercarriage with a retractable system could have significantly reduced drag and given the aircraft a cleaner aerodynamic profile.

The concept is to keep the basic Ki-27 airframe and philosophy intact:

• very low weight
• excellent maneuverability
• low wing loading
• compact dimensions
• simple radial engine
• retractable landing gear
• improved aerodynamic efficiency

Essentially, a small, lightweight Japanese fighter following the same design philosophy that would later produce the Ki-43 and A6M Zero.

The result could be thought of as a "mini Zero" (mini Ki-43) — a hypothetical intermediate step between the Ki-27 and the later generation of Japanese lightweight fighters.

This is, of course, a purely hypothetical/fake project. I'm interested in how much performance could realistically have been gained by giving the Ki-27 retractable landing gear while keeping the aircraft as light as possible.

Could the Ki-27 have evolved into a Japanese "mini Zero" or "mini Ki-43" if Nakajima had pursued retractable landing gear?

What do you think?

 

[Shortround6]

Japanese figured (unknown how) that retractable landing gear would have gained 3% in top speed for the Ki-27.

 

[Howard Gibson]

What if the Nakajima Ki-27 had been developed with retractable landing gear?

The idea behind this hypothetical version is to turn the already very light and maneuverable Ki-27 into something resembling a miniature Zero — or perhaps more accurately, a mini Ki-43.

The original Ki-27 was designed with fixed landing gear, prioritizing simplicity and low weight. But replacing the fixed undercarriage with a retractable system could have significantly reduced drag and given the aircraft a cleaner aerodynamic profile.

The concept is to keep the basic Ki-27 airframe and philosophy intact:

• very low weight
• excellent maneuverability
• low wing loading
• compact dimensions
• simple radial engine
• retractable landing gear
• improved aerodynamic efficiency

Essentially, a small, lightweight Japanese fighter following the same design philosophy that would later produce the Ki-43 and A6M Zero.

The result could be thought of as a "mini Zero" (mini Ki-43) — a hypothetical intermediate step between the Ki-27 and the later generation of Japanese lightweight fighters.

This is, of course, a purely hypothetical/fake project. I'm interested in how much performance could realistically have been gained by giving the Ki-27 retractable landing gear while keeping the aircraft as light as possible.

Could the Ki-27 have evolved into a Japanese "mini Zero" or "mini Ki-43" if Nakajima had pursued retractable landing gear?

What do you think?

The Ki.43 Oscar was the Japanese army's answer to the Mitsubishi A6M. The Ki.27 had around 800HP, not nearly enough for mid-war. The Ki.27s were vulnerable to good tactics by P40s as recommended by Claire Chennault.

The Mitsubishi A5M "Claude" was the mini-zero, also vulnerable to good tactics.

 

[_PabloSniper_]

The Ki.43 Oscar was the Japanese army's answer to the Mitsubishi A6M. The Ki.27 had around 800HP, not nearly enough for mid-war. The Ki.27s were vulnerable to good tactics by P40s as recommended by Claire Chennault.

The Mitsubishi A5M "Claude" was the mini-zero, also vulnerable to good tactics.

I didn't choose the A5M Claude simply because it had an open cockpit, which doesn't really fit the concept I was proposing.

Also, at no point did I claim that this hypothetical Ki-27 would be a good mid-war fighter, nor did I say that it wouldn't be vulnerable to P-40s. My point was much more modest: with retractable landing gear, it might have been somewhat faster than the original Ki-27, while also giving it a cleaner and, in my opinion, more attractive appearance.

 

[FulmenTheFinn]

Japanese figured (unknown how) that retractable landing gear would have gained 3% in top speed for the Ki-27.

If it's worth any relevance, Finnish tests with a retractable landing gear on the Fokker D.XXI also produced an increase of only a few percent in top speed, and in at least one test with retractable skis the top speed actually decreased.

 

[GTX]

As done by Apophenia here:

Note: Is fictional creation.

 

[Admiral Beez]

If it's worth any relevance, Finnish tests with a retractable landing gear on the Fokker D.XXI also produced an increase of only a few percent in top speed

I wonder why. If you put fixed undercarriage onto a Spitfire or Mustang surely the drag would cause an appreciable reduction in speed. Perhaps the drag of radial engine is the issue? When Argentina ordered fixed wheel Curtiss Hawks were they much slower than the normal type?

 

[FulmenTheFinn]

When Argentina ordered fixed wheel Curtiss Hawks were they much slower than the normal type?

I would expect there was a decrease. China I believe operated fixed-undercarriage Curtiss Hawks as well. If memory serves Finnish experiments with flying Brewster 239s (radial engine) with skis without retracting the landing gear slowed the aircraft down a fair bit. I'm not sure why the increase on the Fokker D.XXI was so marginal. Perhaps modifying the aircraft to fit a retractable landing gear increased its weight so much that it effectively negated the benefits in drag reduction?

 

[Admiral Beez]

Perhaps modifying the aircraft to fit a retractable landing gear increased its weight so much that it effectively negated the benefits in drag reduction?

I'm no aerospace engineer, but my understanding is that weight does not directly change an aircraft's absolute top speed, but it does affect how quickly the aircraft accelerates and the induced drag it experiences at various angles of attack. For example, while the PR Spitfire was up to 400 lb lighter (often less due to greater fuel load) than the usual fighter spec Spitfire, the 10–15 mph faster speed was achieved by reducing drag, mainly through eliminating or reducing the various ports and protrusions associated with the armament.

 

[Shortround6]

A lot depends on what else is going on dragwise.

Also speed is a function of thrust vs the cube of drag. Basically a plane doing 325mph vs 300mph needs 27% more power if the drag stays the same.
You could get some pretty crappy looking airplanes into the 285-300mph range. Many had retracting landing gear, they screwed up a lot of other things.

The Japanese could have put retracting gear on the Ki-27 but the question is at what cost. Ki-43 used a wing about 15% bigger. It used bulges in the wing leading edge to house the wheels where the wing joined the fuselage. They managed to fit the landing gear in front of the forward spar. You can bend the spar or use some sort of box to carry the load through that part of the wing but both solutions are going to be heavier. Ki-27 was to be a light as possible. Speed was not the only goal. Another 5-10mph might not have been judged the higher wing loading/poorer maneuverability.

 

[FulmenTheFinn]

I'm no aerospace engineer, but my understanding is that weight does not directly change an aircraft's absolute top speed, but it does affect how quickly the aircraft accelerates and the induced drag it experiences at various angles of attack. For example, while the PR Spitfire was up to 400 lb lighter (often less due to greater fuel load) than the usual fighter spec Spitfire, the 10–15 mph faster speed was achieved by reducing drag, mainly through eliminating or reducing the various ports and protrusions associated with the armament.

Apparently the modification to the Fokker D.XXI increased its weight by 200-300 kg (EDIT: although, this might be including a bunch of other stuff). According to Finnish aeronautical engineer and aviation historian Jukka Raunio a 300 kg weight increase would result in a loss of 3 kmh at a low altitude and 4 kmh at an altitude of 4 km, at least on the Fokker D.XXI, which, granted, isn't much (Jukka Raunio (2019): SIHL Erikousnumero 4: Fokker D.XXI, p. 38). Before the modifications were made it had been estimated that a retractable landing gear would produce 30-40 kmh of extra speed. However testing revealed the actual increase in most cases to have been around 10-15 kmh.

 

[tomo pauk]

FWIW:
- the PZL P.11 was supposedly loosing (up to?) 25.2 km/h due to the fixed U/C it used; granted, the U/C on the Ki-27 does not have the wires to increase the drag
- Finns have gotten 15 to 37 km/h with the retractable U/C Fokker D.XXI mod (link)


Does the mod for the Ki-27 solves everyting if it was done? Nope. Is a possible 25 km/h gain a good thing? I'd say yes.
Granted, my 'Ki-27 special' would've also have the early Sakae in the nose, as well as some extra firepower Paving the way for a Ha 41/-109 powered something

 

[muskeg13]

A lot depends on what else is going on dragwise.

Also speed is a function of thrust vs the cube of drag. Basically a plane doing 325mph vs 300mph needs 27% more power if the drag stays the same.
You could get some pretty crappy looking airplanes into the 285-300mph range. Many had retracting landing gear, they screwed up a lot of other things.
View attachment 893614

The Japanese could have put retracting gear on the Ki-27 but the question is at what cost. Ki-43 used a wing about 15% bigger. It used bulges in the wing leading edge to house the wheels where the wing joined the fuselage. They managed to fit the landing gear in front of the forward spar. You can bend the spar or use some sort of box to carry the load through that part of the wing but both solutions are going to be heavier. Ki-27 was to be a light as possible. Speed was not the only goal. Another 5-10mph might not have been judged the higher wing loading/poorer maneuverability.

What about to go from 300 to 350? That would put a fighter firmly "in the game" in the first part of the war.

 

[Howard Gibson]

What about to go from 300 to 350? That would put a fighter firmly "in the game" in the first part of the war.

Something like 60% more power. Assume we start at 800HP.

octave:2> 800/300^3*350^3
ans = 1270.4
octave:3> 350^3/300^3*100
ans = 158.80

 

[Admiral Beez]

Why is it that we see so very few single seat monoplane fighters with fixed undercarriages AND liquid cooled V-12 engines? There's the Miles M.20, Kawasaki Ki-5, and Dewoitine D.500, with only the latter being produced beyond a prototype. Should we include the steam-cooled Supermarine Type 224? Perhaps the big gaping radial engine on the likes of the Ki-27, A5M, PZL P.11, and Fokker D.XXI created so much drag that it did not matter if the undercarriage was present or not.