Nakajima ki43 Army Type 1 Fighter Hayabusa drawings

Nakajima Ki43 Army Type 1 Fighter Hayabusa drawings

Introduction
Prior to the model construction, I made drawings in a familiar manner. At any rate, I had thought that there was no accurate existing drawings of Ki43 Hayabusa. So I tried to make Hayabusa drawing as accurate as possible.

This is typical mistake of existing drawings.

Ki43-2 (Hayabusa II) can be classified in five subtypes by its production period. And there are different naming of five sub-types. One example of naming is ; Kou early, Kou late, Otsu early, Otsu late, Kai (Kai means "mod"). Another naming is ; early-former, late-former, early-latter, late-latter, kai. These naming are not official but expediency for future generations. Official name of these five subtypes is only "Hayabusa II model". So, I'd simply call them ; initial (squarish cowl, ring oil cooler), early (squarish cowl chin oil cooler), mid (roundish cowl), late (concentrate thrust exhaust), very late (separate thrust exhaust). Anyway, this is only expedient naming.
Photos of actual aircraft
First of all, I'd show some photos. I need "far distance, right beside and sharp" photos for making drawings. Fortunately, barely it exist as for Hayabusa. The following first photo is such good condition. Regrettably, the distance is not so far. This photo taken by Shunkichi Kikuchi was published in "Koku-fun Illustrated (reference -4)". This photo had not been published for a long time, so mosts of existing drawings don't reflect this photo. But I used this photo as the most reliable information. My side view drawings is a trace of this photo.

The first photo is from "Koku-fun illustrated no 79". It is mirror-reversed image. Perspective error is corrected by a free image manipulation program software "Gimp-2". As you see the wing tip, the distance is not so far.

The second photo is Ki43-I of the 50 Sentai. It is far enough but not right beside not so sharp. Perspective error is corrected.

The third is Ki43-I of the Akeno Gakko. This photo is not just fit to the first photo. I think that this original print maybe distorted a little. Moreover, the distance is not far.

The fourth is Ki43-III Kou of the 48 Sentai. This is the best photo of II and III model for drawings. Sheet on the cowl is obstacle. So the next photo is used complementary.

The fifth is Ki43-II very late production. This photo is rather near, but right beside at the cowl and sharp.

Total length
The total length is very much perplexed. There are some official data. BUT, from my past experience, these data are unreliable. Anyway, I show these data.

Total length : 8,832mm (-I), 8,920mm (-II), 8,950mm (-III Kou)
Firewall to #9 frame (fuselage divided line) : 2,583.5mm, #9 frame to rudder hinge : 3,800mm, sub total : 6,383.5mm
Fin height : 1,480mm from fuselage ref.line
Wing chord : 2,660mm (root)

* 1. is from IJA official manual, 2. to 4. is from drawings of official manual.

The total length of 1. is not reliable from my experience of Ki84 (see my article). Tentatively, I presupposed that 2. and 3. are correct. Then I traced the above firs photo. As the result, a ratio of 2. was correct. And I adjusted the total length with the length of 2. Then the total length of Ki43-I became about 8,860 to 8,880mm. Oops, it was differ from 1. data.

How about II/III model? I traced above fourth photo. After some (or vast?) trial and error, I found that II/III is longer by 60mm. The total length of -II was much to above manual data. Mmm... what can I explain...?
Hypothesis as for the fuselage transition
I thought a following hypothesis which was consistent above facts.

The prototype of Ki43-I doesn't have a rudder tub (or different rudder shape or different spinner). So its total length is 8,832mm. This value was written in the manual as -I.
The production model have rudder tub (of modified rudder or spinner). Then its total length is about 8,860mm.
Ki43-II (initial to early) is applied following modifications. The engine mount is extended by 40mm. The spinner is extended by 20mm. Then the total length is 8,920mm. The cowl flap is widened by 15mm. As the result, the trailing edge of the cowl flap moves forward 25mm. The thrust line maybe moved downward by 10 or 20mm (the reason will be described later). The length of the cowl (without cowl frap) is the same as -I model.
After -II mid, the cowl lip is moved forward 15mm. Then the clearance of the propeller is shortened by 15mm. The cowl side becomes roundish and the total width of the cowl is increased. The cowl flap shape is basically the same as initial model (cut-away is modified with exhausts).
As for Ki43-III Kou, the modification is only the cowl upper intake. It is extended upward. Some -III model looks like their spinner are enlarged. Is it the reason of official manual data? But I don't know the truth.
Complement: The reason of -II's enlarged spinner maybe the increase of propeller blades (2 to 3). Some -I's spinner looks enlarged (for example FAOTW no.65 p.77). Is it retrofit?

This is -I model.

This is -II model. See the distance form cowl flap to wing bulge. It looks longer than I model. But it doesn't look more than 45mm extended, does it?

Ki43-I side view drawings
I show -I model side view. Numerical values are rounded off to 5mm except for the length from firewall to #9 frame - it is from official manual. Actual length of 5mm becomes 0.1mm in 1/48 scale. So I think rounding off is not matter too much for modeling.

Rivet lines are written in photos of actual (mostly restored) aircraft.
The wing chord is 2,660mm (C.L. of fuselage, excluding wheel bulge). The wing incidence is 2 deg. The airfoil is not clearly specified. So I use the same airfoil as Ki84 Hayate drawings. The leading edge is located 230mm forward from firewall.
The horizontal fin incidence is 0 deg. according to a reference.
After finishing drawings, when I measured the height of the rudder, it is just 1,700mm and the firewall is just 1,300mm. I think these values are engineer's common maneuver.
Also, the exhaust stack and center stringer are just located on the fuselage reference line.

Ki43-II/III side view
Next, the upper is -II initial/early model. The center is -II mid/late model, and the lower is III . Note the different image of nose cowl between initial and mid.

The separate exhaust stack of II very late and III model are different. The top stack of the early production of III is single like II very late.
Details of II very late exhaust are unknown. The position of the upper stack is different from III.

Comparison for photo
I show my drawings overlaying on the photo.

The perspective error is corrected. Upper portion of the fuselage is looked upward. So some lines of drawing are not fit to the photo.

Common and different portion between I and II
There is a theorem in design of military aircraft that the portion which don't need to change isn't changed rigidly. So, as for making drawings, it is important that how to figure out them. See the figure below, blue lines are -I model, red lines are -II (mid) and black lines are common.

The fuselage after the firewall is common. The engine mount is extended 40mm in II.
The lower frame of the wind screen is common. The front half of the lower frame of sliding hood is common as well.
I think the nose gun mount of II model is lowered a little (10 or 20mm?). Thus the gun blister is removed. Basic position of gun blast tube is common. But the outline shape of the cowl is different. So the vision is different.

The position of the nose gun
The position of the nose gun is the key point for consideration of fuselage cross sectional shape. The gun position (center of fire line) of -I model is described in the official manual ; height : 507.6mm from fuselage ref. line, width : 220mm from center line incidence : 1 degree. But when I drew the gun and engine the fire line was in the circle of 1,150mm diameter of Ha45 engine. Why gun shoots engine cylinder? So I drew each engine cylinder, the fire line avoided the engine.

This cross section shows -I model. Red is front row and blue is rear row. + is fire line at engine position with consideration of 1 degree incidence.

The next step is deciding the fuselage cross sectional shape by the gun position. -I model has gun blister avoiding the gun main unit and feed chute. On the other hand, -II doesn't have gun blister. I think the gun access panel of II is not so plump out but the gun position is lowered. If the engine position isn't changed, the fire line incidence is increased. So I think the engine position is lowered as well. In fact, when I compared the photo of actual aircraft, the thrust line looks reduced a little (I assume 10mm in my drawing).

This section is the front edge of cowl flap. Both I and II (mid) are shown in this figure. Two and ten o'clock are not so plumped out because of forward and downward visibility.

This is the firewall. I and II are the same shape at this section. The top is flat. The fire line at this section (+) is 507.6mm from ref.line.

This is #2 frame. Note the gun main unit and feed chute. I think II is slightly plumped out at this section.

#3 frame. the cross section of the wind screen is common in this section.

The cross section of firewall
One more important point is actual width of the firewall. I decided it from the photo below. The fuselage gun ammunition box access panel can be clearly seen. Its width can be compared with engine cowl width.

The cross section shape of #9 frame and wind screen can be seen clearly as well.

There is a word of caution. This photo is taken from near. So the perspective error should be considered. I corrected this error mathematically and graphically. The result is that the max width of the firewall is assumed 1,050mm and the cowl is 1,200mm (Ha45 is 1,150mm dia.).

This is the correct shape.

Typical mistake.

The cross section drawings
Existing model kits maybe differ from my drawings in the cross section. The fuselage of the actual aircraft is lean and firm. The firewall cross section shape of actual aircraft is not ellipse but close to triangle ( or trapezoidal, or like a guitar pic, or...).

Other frames are traced from photos of actual aircraft under restoration of FAOTW. The fuselage of restrating rear fuselage in Gakken is not correct.
The cockpit shoulder is rather narrow like FW190. Some kits look like F4F Wildcat. The lower side of #7 and #8 frame is not straight but droop down.
#4(green) shows the rear end of the wind screen. The small "L" at #4 and #6 is the slide rail.

The wing
The wing is mysterious as the fuselage. First of all, dimensional data from manual are listed. The semi-span along wing ref. line is 5,750mm (I), 5,450mm (II). The root chord is 2,660mm. The tip chord at tip (sta 5750 virtual) is 1,239.24mm (I). The dihedral is 6.0 degrees. The incidence is 2 deg.(root), 0 deg.(tip). The airfoil is NN2 (root), NN21 (tip).

The wing thick ratio is unknown. Different values are described depending on the literature. I assumed it between 16% and 16.5% by analysis of the photo (I used 16.3% in my drawing).

The wing position (height) is decided from the side view photo. When the root airfoil is put on the photo, the trailing edge is not match to the lower outline of the side view. Thus, this portion of the lower wing surface should droop down. If you have Tamiya's Zero fighter, see this portion. The cylindrical form of the rear fuselage runs into the wing under surface. But most of Hayabusa kits don't represent this droop, and as the result, the wing position of most of Hayabusa kits are too low.

At the same time, the lower surface of the wing front spar at #2 frame droops down slightly. The middle and rear spar are connected to #4 and #6 frame. The lower surface of the middle and rear spar don't droop down.
The top and bottom view drawings of I model

Rivet lines and access panels are assumed from figures of official manual and actual aircraft.
Station diagram of the wing is assumed as following. #1 : 115, #4 : 725, #5 to #7 : 195@3, up to #9 : 215@2, up to #10 : 270, #11(inner end of the aileron) : sta 2295, #12 to #15 : 360@4, up to #17 325@2, up to #19 275@2 (#19 : sta 4935), outer edge of aileron : sta 5215.
The wing span, stab span, wing chord, gun width, aileron span and flap chord are described in the manual. Other values than above are my estimations.
I assumed that the rear spar of horizontal stab and fuselage #19 frame are connected. The length from the leading edge of stab to the rear spar is 775mm. The rear spar to elevator hinge is 75mm. The hinge to trailing edge of elevator (fuselage center virtual) is 500mm. These values are described in the manual.
The gear shaft has sweep back at retracted position.
The leading edge of the wheel bulge extremely droops down. Most of existing kits don't represent this droop.
Station numbers of the horizontal stab are ; 138, 357, 557, 757, 1041, 1325, 1640, 1778, 1980, 2150. Station numbers of the elevator are ; 124 (inner edge), 325, 534, 754, 975, 1195, 1415, 1645, 1838, 1958.
The landing gear connected at 180mm rearward wing LE and 1650mm outward CL.
Existing drawings made following mistakes; the wing panel line at #2 firewall, the position of gear indicator, panel edge of the tip, the number of aileron ribs. .
The upper surface of the flap may be covered with fabric as Ki44 Shoki. This is described in the official manual. The lower side is unknown. I assume it covered with metal.

Top and bottom view of II model

The aileron span is assumed 150mm shorter than I model. The elevator span is assumed 120mm shorter than I. These are estimated by analysis of photos of actual aircraft.
The planer shape of the wing tip is traced from the famous top view air to air photo taken by US.
Some rivet lines of existing aircraft of I and II are different each other. I drew them as each aircraft but I don't know the truth.

The front view drawings

The tread is 3,400mm, width of the gear shaft is 3,300mm (center to center).
The ring type oil cooler of I and II initial are different.

Illustrations

The first one is Hayabusa I Hei of the 3rd Chutai 50th Sentai. Documentary photos were taken at Tokorozawa Base in Japan before going out to the front. The Lightning flash is painted in squadron color : red (1st), yellow (2nd) and third (3rd). The size and position of the fuselage Hinomaru is different for each squadron. Dark green is not painted on the top cowl lip where the gun adjustment scale is painted.

I assumed the color of the spinner is dark green. Because, the spinner of early production -I is unpainted at the factory finish. This is judged from photos of the early -I of Akeno Gakkou. The late production -I and II/III are painted in red brown in the factory. The back face of the blade is red brown. Many modeler (even misunderstand it as black. Small quadrilaterals on the tail are unpainted areas where the serial number is painted. Unfortunately, the number is unknown.

The next two tone camouflage is Hayabusa I Hei of the 2nd Chutai 64th Sentai, Malay Peninsula, March 1942. The photo was taken from the starboard side and the camouflage pattern is a supposition. Some existing color profiles are illustrated without fuselage insignia. I assume Red and Green are invisible in a monochrome photo. I assume the color of the latter half of spinner is white. But it cannot be decided which white or silver.

This natural metal finished one is Hayabusa I Hei of the IJA Akeno Hiko-Gakko (Akeno Flying School), serial 388, Aikoku-Go (patriotism dedication aircraft) no 1028, in spring 1942. I don't have a confirmation of the color of the spinner. The last two digit of serial (88) is painted on the rudder. It has a possibility of black. The front of the fuselage rearward cowl is painted Aotake (clear greenish blue).

The next is Hayabusa II early production flown by Captain Nakakazu Ozaki CO of the 2nd Chutai (squadron) 25th Sentai, Nanjing China, in summer 1943. The upper surface is painted over dark green monotone. So it has a possibility that the under surface is painted in light green gray.

The next one is Hayabusa II mid production of the 25th Sentai, Nanjing China, 1943. Many of the 25th Sentai's aircraft don't have latter half spinner panel. The landing light on the port wing leading edge was introduced sometime around -II late production. So this aircraft don't have the landing light. Note the difference of outline image of the cowl between -II early and -II mid. Also, note the clearance between spinner and cowl.

Kit review

Fujimi 1/72 -I
Fujimi 1/72 is a good kit which well represent rugged outline shape of actual -I model. When its fuselage part is joined together with Hasegawa 1/72, the outline is not much each other. They have good and bad points and the correct outline is different from each one. The cross section shape of firewall is not a trapezoid but an ellipse. The height of the canopy is low, and as the result, the fuselage is high at this rate. The cowl side is roundish as like as -II's cowl. Hasegawa 1/72 -II
Hasegawa 1/72 is a good kit as well. The outline shape of its roundish cowl is well represented. The total length of the fuselage is a little long. The cross section shape of the firewall is the same as Fujimi. The canopy and propeller are poor as like as Hasegawa Ki84 Hayate. The vertical position of the wing is a little low. Hasegawa 1/48 -I
The outline shape of the cowl, fuselage and canopy are good. Hasegawa is the best of all 1/48 kits as for these points. Regrettably, the vertical position of the wing is rather low. So the lower wing droops down in the side view profile like a pregnant woman. The trapezoid shape of the firewall is not represented. Hasegawa 1/48 -II/III
I don't have this kit. But I heard that the rear fuselage is inexplicably deeper than Hasegawa -I. Finemolds 1/48 -II/III
The outline shape of the cowl and fuselage are not so good. The cowl side is not roundish but like a cylinder. The trapezoid shape of the firewall is not reprexented. The firewall is too wide and roundish. Nichimo 1/48 -I
Some old modelers highly recommend this kit. But I don't think so. The outline shape is not good. The value of this kit is a nostalgia. Hasegawa 1/32 -II
The outline shape of the cowl and fuselage is not good. The expressive transformation of the cross section shape of actual fuselage is not represented. The kit' fuselage is like a baseball bat. I want a new tool 1/32 kit! LS (Arii) 1/75 -II
This kit is a nostalgia as like as Nichimo. The fuselage is 1/75 scale, but the wing is 1/72. Sweet 1/144 -I
Sweet is developing a new tool 1/144 kit. I gave all-out cooperation for them. So, I am very much looking forward to it. I highly recommend it.

References

1	The World Famous Airplane of the World No.65 Army Type I fighter Hayabusa (New Eddition)	4-893-19062-8	Bunrindo
2	The World Famous Airplane of the World No.13 Army Type I fighter Hayabusa (New Eddition)	-	Bunrindo
3	The World Famous Airplane of the World vol.1 Army Type I fighter Hayabusa (Old Eddition) July 1972	-	Bunrindo
4	Koku-fun Illustrated No.79 A Record of The Army Airfoece vol.1	-	Bunrindo
5	Koku-fun Illustrated No.80 A Record of The Army Airfoece vol.2	-	Bunrindo
6	History of Pacific Warfare Series 52 Army Type I fighter Hayabusa	4-05-604181-4	Gakken
7	Aero Detail No.29 Nakajima Army Type I fighter Hayabusa	4-499-22735-6	Dainippon-Kaiga
8	Military Aircraft Mechanical Series No.12 Hayabusa / Shoki / Kyunana-Sen	4-7698-0921-2	Kojinsha
9	Airworld Special Number J&P No.1 - 3	-	Airworld

-I modeling article

-II modeling article

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