Yak-3 VK-107 and VK-108

Yak-3 VK-107A (Factory Production Quality)

• General Data
Loaded Weight: 2935kg
Wing Area: 14.85m2
Engine: VK-107A
WEP: 1650hp at Sea Level
Normal Power: 1550hp at 1200m / 1450hp at 3800m

• Max Speed:
- Normal Power:
600km/h at Sea Level - (1500hp)
697km/h at 5000m

The super clean, high quality prototype achieved 611km/h at Sea Level with 1500hp and 720km/h at 5800m at Normal Power.

- War Emergency Power:
619km/h at Sea Level - (1650hp)
719km/h at 5000m

Optimal altitude at WEP power is known to be at 5600m for the VK-107A so you can be looking at ~ 724km/h

• Rate of Climb: (Normal Power)
Time to 5000m: 4:00 (20.83m/s)

• Sustained Turn Time
At Normal Power - 19 seconds
At War Emergency Power - 18 seconds

• Firepower
2x 20mm B-20 (120 rounds per gun)

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Yak-3 VK-108

General Data
Loaded Weight: 2830kg
Wing Area: 14.85m2
Engine: VK-108
WEP: 1850hp at Sea Level
Normal Power: 1650hp at 1500m / 1500hp at 4500m

Max Speed:
- Normal Power:
???km/h at Sea Level - (???hp)
745km/h at 6300m

- War Emergency Power:
~ 642km/h at Sea Level - (1850hp)
???km/h at 5000m

• Rate of Climb: (Normal Power)
Time to 5000m: 3:30 (23.8m/s)

• Sustained Turn Time
At Normal Power - 18 seconds
At War Emergency Power ~ 17-18 seconds

• Firepower
2x 20mm B-20 (120 rounds per gun)

Note:
Sustained Turn Time is at 1000m, 360 horizontal turn, No Flaps

Hello All,

According to "Yakovlev's Piston-Engined Fighters", the Yak-3 VK-107A project was essentially a failure.
The actual performance of the several test aircraft reached the specified 600 KPH at Sea Level as expected but speed at altitude (5400-5900 meters) actually fell slightly short of expectations at 695-697 KPH instead of the expected 700 KPH.
Climb to 5000 meters was also slower than expected at 4.2-4.5 minutes instead of the requirement for 3.9 minutes.

In addition, handling was not so good:
"However, high stick forces from the ailerons and elevator made the VK-107A-powered Yak-3's handling unpleasant. This shortcoming fully came to the fore during mock combat sessions with a Spitfire Mk IX, especially when performing violent maneuvers in the vertical plane."
The final test report came back in June 1946 that the Yak-3 VK-107A had failed to pass State trials. Only the three prototypes were produced. The remaining airframes were scrapped and the larger Yak-9 airframe was selected for further work with the VK-107A.

Note that these aircraft could mount either just the two B-20 synchronized cannon or have an additional B-20 motor cannon.

Note also that the VK-108 aircraft were armed only with a single NS-23 motor cannon "Owing to the special features of the engine design". (The VK-108 engine has multiple rows of exhausts. Some of them are where the cowl guns would normally go.)

- Ivan.

Here are a couple photographs to show the unusual exhaust system of the VK-108 engine.
Note the light coloured heat shields behind each row of exhausts.