Ki-84/Homare in the U.S.

[Sgt. Pappy]

I think it's been brought up before but I was thinking this section may provide better results.

The Ki-84 was tested in the U.S. and there are random figures floating around which stated figures of 427 mph in level flight. This is likely calculated data since it happened before the end of the war.

I'd like to know if the U.S. changed the engine in any way, manner or form in order to test it. After all, the Homare's were unreliable during the war. Perhaps they could not run the U.S. 100/130 octane grade without some modification.

[wells]

In the original TAIC manual from Dec.44, the performance was estimated at 422 mph. This was based on the assumption that the lines were similar to OSCAR. Then, in the March 1945 TAIC supplement, the performance was updated to the 427 mph figure. By that time, they had found some aircraft along with some documentation. The aircraft were not flown in the Philippines until the summer, however, so these performance figures are NOT based on any flight test that the US made, but most likely originated from captured japanese documents. To quote Richard Dunn,

I have a copy of a translation of a captured document (hand written notes) of unknown reliability which indicates two maximum speeds for the Ki 84-1 (Light) and Ki 84-1 (Improved). The two speeds apparently relate to the Ha 45 rating of 2000 hp at 1500 meters and 1800hp at 6000 meters.

Ki 84-1 (Light) 664 kph (=412 mph) and 693 kph (=430 mph)

Ki 84-1 (Improved) 658 kph (=409 mph) and 688 kph (=427 mph).

Fully equiped wgt of Light = 3576 kg; Improved = 3858 kg

There was a trial against a Seafire III in which stated,

It's top speed would be about 330 Mph at sea level, 400 Mph at 20000 feet and 380 Mph at 30000 feet when fitted with the Ha.45, Model 21 engine. All figures should be reduced slightly when the Model 12 engine is installed.

In that trial, power was limited to +250mm boost and 2900 RPM, because the engine had only been run for 8 hours.

Note, that is the rated power for the Model 12 engine. The Model 21 engine was rated at +350 mm and 3000 RPM ( +500 mm with methanol injection ).

In that trial, the constant speed unit failed at airspeeds of 230 kias at 5000 ft, 205 kias at 15000 ft, 218 kias at 20000 ft. So, maximum speeds were not reached.

After the war, at least 2 examples were restored in the USA ( T2-301 and T2-302 ) at the Middletown Air Depot ( where it was repainted ). At least one of those was test flown at Wright Field. An article in the January, 1976 issue of Air International gives some details of these tests.

The evaluation at Wright Field comprised a total of 11.5 hours but the test programme was frequently interrupted by failure of exhaust stacks as a result of the poor materials used in their manufacture coupled with inefficient welding. Problems were also experienced with the hydraulics.

According to Richard Dunn ( j-aircraft.com )

According to Wright Field Interim Report No. F-1IM-1119B-ND released January 1947 of a Ha.45 Model 21 engine equipped Frank 1, Serial No. 302:

Speed

Normal fighter Military Power

At sea level 350 mph ( 563 km/h )
At 10,000 ft 389 mph ( 626 km/h )
At 20,000 ft 412 mph ( 663 km/h )
At 23,000 ft 426 mph ( 686 km/h )
At 30,000 ft 400 mph ( 644 km/h )
At 35,000 ft 370 mph ( 596 km/h )

Climb Normal fighter

Time to 10,000 ft 2.6 min
Time to 20,000 ft 5.8 min
Time to 30,000 ft 10.0 min

at S.L. Military Power 3790 ft/min
at Military Power 20,900 ft 3195 ft/min
at 17,900 ft W.E.P. 3615ft/min

Service Ceiling 38,800 ft

These are the exact same figures that appear in the TAIC documents, before any examples had been flown, so it is unlikely that any performance testing was done at Wright Field. Further evidence is given in the Air International Article where the evaluation states,

...it was immediately obvious that initial climb rate was extremely good, although no performance climbs could be attempted owing to flying time restrictions.

Finally, another quote from Richard Dunn,

A technical notebook captured at Clark Field (ADVATIS No. 92) has rather complete data on the Ki 84, however, it is undated and its source uncertain. Max speed is given as 624 kph (=387.5 mph). This is at 6550 meters altitude, 2900 rpm and +250 boost

That's the extent of my research so far. Some conclusions can be drawn however

With the Homare 21 engine, maximum speed is higher than 624 kph, but only estimates of the extent of such performance has so far been found.