Start Up, Taxiing and Takeoff
During start up, takeoff and landing the left side fuel tank had to be used. The mixture lever was set to full rich and the hand pump was used to get approximately 0.2 kg/cm^2 of pressure. Five primer pushes were given to a cold engine. Pumping with the throttle was forbidden by the manual. The throttle was set to correspond to 800-1000 RPM. Making sure that the prop pitch control knob was fully forward, the blower at small gear, the ignition was switched to both magnetos. The pilot maintained the fuel pressure with the hand pump, as the mechanic turned the starter crank (in the forward fuselage on the right side). When the starter had accelerated enough, the pilot engaged it to the engine, which also switched on the starting ignition. For the warm up the prop control knob was pulled back. Before the engine test run, the oil had to heat up to approximately 30 degrees. The oil heated quickly, because the oil tank thermostat routed the cold oil past the oil cooler. During the test run the brakes kept the plane in place, and the tail didn't try to rise. The BW taxied at 700 RPM on a level air field. With the tail wheel unlocked, the turning radius was only approximately 12 meters. Using the brakes the plane could be turned on the spot.
The pre flight check was simple and quick: tailwheel locked, prop pitch small angles, blower at small gear, mixture rich, fuel tank switch on left tank, air intake cold, trims set, controls unobstructed and flaps retracted. The throttle was opened fully. The propeller screamed exceptionally nasty at low pitch angles. The takeoff itself was a quick event. The tail lifted after approximately 30 meters, swaying was minimal and the direction was easily kept. The BW lifted off at a speed of 120 km/h. The length of the takeoff run on a calm day was 140-160 meters, taking 8-9 seconds. Total distance to 15 meters altitude was approximately 350 meters. Using the flaps wasn't necessary during takeoff. British tests with a Brewster model 339B showed that 26 degrees of flap reduced the takeoff run by approximately 10 %, but reduced the initial climb rate. After liftoff, the gear was retracted, manifold pressure was set to the continuous range (93 cmHg or below) and the RPMs below 2100. Retracting the landing gear created a noticeable nose-up moment. The best climb speed was approximately 220 km/h. Rolls and slips were levelled with the trims. During summer, the cylinder head heat came close to the maximum values (briefly 260, continuous 235 degrees Celcius).
Performance in Level Flight and Climb
The Brewster was one of only a few of our fighters that which performed according to the manufacturer specifications. The promised climb time to 15000 feet, 4572 meters, on nominal power was exactly 6 minutes with 2275 kg and 6.7 minutes with 2387 kg takeoff weight. A Finnish Brewster, equipped with a seat armor and other modifications, weighed 2020 kg with all accessories, weapons loaded and with the oil tank full. With the pilot and 300 kg's of fuel, the typical take off weight was 2415 kg. Figure 1 shows the climb times and the calculated climb rates at different altitudes, from the test flight with BW-366. The take off weight is not known, but had to have been somewhere between 2300-2400 kg. The manifold pressure was 93 cmHg at takeoff and RPMs at 2100. The climb performance corresponds fully to the manufacturer specifications. Climb speed was 220 km/h IAS at low altitudes, reducing to 180 km/h at 5 kilometers.
To achieve best climb performance, the blower was switched to high gear when the manifold pressure dropped to 75 cmHg on full throttle (this happened at approximately 3 km altitude). When changing the gear, the throttle was reduced to soften the change. The blower gear could not be changed again in 5 minutes. The clutch had to be allowed to cool off. The automatic mixture control of the carburator functioned when using the low gear of the blower. If the engine ran roughly on high gear, the mixture had to be manually adjusted. On high power settings, the mixture lever had to be fully forward, corresponging to full rich. Below 550 HP (low gear) and 450 HP (high gear) then mixture had to be in the cruise setting. Flying with the high gear during cruise was not recommended due to the knocking risk.
Figure 2 shows the flight speed test flown with BW-366. This particular plane was one of the best front line planes during the Continuation War. Top speed at sea level was 428 km/h and the top speed of 480 km/h was achieved at the blower operational altitude (4750 meters on nominal power in static conditions. In practise, due to the intake ram effect, a little higher). The correlation to the manufacturer specifications is, again, excellent. According to those, the top speed at altitude is 484 km/h and 427 km/h at sea level. The Brewster was clearly faster than any other main fighter type we had during the beginning of the Continuation War. The Cyclone-Curtiss, which we had in small numbers, was about as fast even though it had 200 HP more engine power.
On the maximum continuous power, nominal power, fuel consumption was approximately 370 liters/hour at low altitudes. The full 600 liters was good for approximately 1.5 hours of flight. The range was 600-700 km, depending on flight altitude. A normal cruise power setting at 2000 meters altitude was 1850 RPM / 65 cmHg (65% power). The corresponding indicated air speed reading was 330 km/h and true air speed 390 km/h (the air speed gauge showed approximately 25 km/h too slow at cruise speeds). Fuel consumption at lean mixture was 170 liters/hour, corresponding flight time without reserves was 3h30min and range 1350 km. By flying with lower speeds, flight times of well over four hours could be achieved. BW was well suited for patrol and escort missions otherwise, but the oxygen lasted for only 30-40 minutes.
