The Humu – literally “Reckless” – was produced by Valtion Lentokonetehdas. It was not that the Humu was unconventional in any respect. It was a copy of a seven-year-old American design adapted to make use of locally-available materials and captured equipment, and built without benefit of licence or assistance from the parent manufacturer. The Finnish air arm, Ilmavoimat, had acquired 43 Brewster B-239 shipboard fighters that had been declared surplus to US Navy requirements. These had proved singularly successful in Ilmavoimien service, and, in 1942, it was proposed that an attempt be made by the VL to remedy a shortfall of fighters of this type by producing a copy. Because of shortages of metal, this was to make as much use as possible of wood and to embody so-called “war booty” instrumentation and power plant – equipment captured from the Soviet forces by the Finns themselves and similar equipment captured by the Wehrmacht and sold to the Finns. The task of designing an entirely new wooden wing was assigned to M T Vainio, who was also responsible for the overall project, and, in October 1942, an order was placed with the VL for four prototypes, the intention at that time being to build a series of 90 aircraft. The chosen engine was the 930hp Shvetsov M-63, which was flown on 5 June 1943 in a B-239. Static testing of the wooden wing was not entirely satisfactory. Nevertheless, in September 1943, orders were confirmed for five prototypes of the Humu and 55 production aircraft. The wooden wing was found to add 250kg to air-frame weight, however, and the transfer of the fuel tanks from the wing to the fuselage shifted the CG aft, adversely affecting manoeuvrability. Initiation of series production was, therefore, delayed pending results of prototype tests, and in the summer of 1944 the programme was terminated as it was concluded that the Humu would have inadequate combat capability by the time it achieved service. Only one prototype Humu was completed, and this, having an armament of three 12.7mm guns and a mix of Finnish and Soviet instrumentation, flew on 8 August 1944. The M-63 engine failed to give its full power during subsequent flight testing, but 19 hrs 50 min were flown before, in 1945, the sole example of this aircraft was placed in storage.

The performance of VL Humu was not measured. The information of maximum speed is based on tests of wooden wing and M-63 motor in Brester 239 (BW-392) October 1942. BW-392 was 350 kg heavier than VL Humu and those days the Finns did not adjust the M-63 correctly due to lack of the instruction manual. The Finns got the instruction manual from Germany in 1943.

The prototype of VL Humu (HM-671) is in The Aviation Museum of Central Finland in Tikkakoski, Finland.

Max take-off weight: 2895 kg / 6382 lb
Empty weight: 2050 kg / 4520 lb
Length: 8.03 m / 26 ft 4 in
Max. speed: 430 km/h / 267 mph

On 8 June 1939, the VL (Valtion Lentokonetehdas) received a contract from the Ministry of Defence to design a new single-seat fighter. Chief designer was Dipl Ing A Ylinen, who was assisted by T Verkkola and M Vainio, and, within nine months of receiving the definitive prototype contract on 20 December 1940, the prototype of the Myrsky (Storm) was in final assembly. A conventional low-wing cantilever monoplane, the Myrsky had a plywood-skinned two-spar wooden wing and a welded steel-tube fuselage covered by dural panels forward and fabric aft. Power was provided by a Pratt & Whitney R-1830-SC3-G Twin Wasp 14-cylinder radial rated at 1115hp for take-off. The prototype was flown on 23 December 1941, but immediately encountered the first of what were to be many teething troubles.
On 30 May 1942, the VL received a contract for three development aircraft which were to embody numerous detail structural and other changes, these including an increase in wing area of 1.3sq.m and a change in armament from two 12.7mm and four 7.7mm guns to three (in first and second) or four (in third aircraft) of the larger-calibre weapons. The first of these was completed on 30 April 1943, but crashed a week later, and the second suffered a wheels-up landing three months later, and broke up in the air shortly after resuming flight test. The third was evaluated in service, and, on 17 March 1944, lost both wings in a dive.
In the meantime, VL had initiated production of the first series model which was referred to as the Myrsky II Series. All the progressive changes that had been introduced in the pre-series aircraft were incorporated, armament was standardised on four 12.7mm LKK/42 guns, and by the end of July 1944 the VL had completed 14 of the II Series aircraft, a further 16 having been delivered by the truce of 4 September. Production continued after the truce and the last five of the 47 built were delivered straight to the Air Force Depot on 30 December 1944 without flight testing. The Myrsky II series was assigned to a tactical reconnaissance squadron (TLeLv 12) which received its first aircraft on 23 July 1944, 20 being delivered to the squadron before the Armistice, and a second squadron (TLeLv 16) initiating conversion to the Myrsky meanwhile. The Myrsky was flown operationally over Lapland against the Wehrmacht under the terms of the Finnish-Soviet agreement, but Ilmavoimat flew this fighter only to a limited extent, and the service’s doubts as to its durability and sturdiness, despite continuous reinforcement of various components, finally came to a head on 9 May 1947 when a Myrsky broke up in a dive, all aircraft of this type then being grounded.

Max take-off weight: 3213 kg / 7083 lb
Empty weight: 2337 kg / 5152 lb
Wingspan: 11.00 m / 36 ft 1 in
Length: 8.35 m / 27 ft 5 in
Height: 3.00 m / 10 ft 10 in
Wing area: 18.00 sq.m / 193.75 sq ft
Max. speed: 535 km/h / 332 mph
Range: 500 km / 311 miles