m.b.H                 München
Increase of speed and climb performance of the Fw 190
through boost increase on the BMW 801 D.
 VB Nr. 126
lfd.Nr. 1213/43

Task: At the instigation of the EZA it was to investigate, which speed increase and which time to climb decrease for emergency power can be obtained by the means of an increase in boost on the BMW 801 D in the Fw 190 A 8 (fighter). The boost was to be adjusted to 1.65 ata for the second supercharger gear by the means of blinds in the air lines on the mixture and boost regulator in the same way it is done with the C 3-injection for fighter bombers (see report Nr. 640/43). As a testbed, a Fw 190 A-5 of the test commando 28 - white 35 - was provided.
Results: 1.) The speed increase was Δvw = 36 km/h  in 3 km altitude and  Δvw = 42 km/h in 5 km altitude. For this, the boost had been increased at n = 2700 rpm from pL = 1.42 ata to pL = 1.65 ata. The cylinder head and oil temperatures remained within the permissible limits. With the same settings a boost of pL = 1.58 ata and a Δvw = 22 km/h were achieved in the first charger gear.

  2.) The time to climb reduction in a climb from 0,0 km to 8,0 with n = 2700 rpm, pL = 1.65 ata compared to n = 2400 rpm, pL = 1.32 ata was 3'39". With a total climbing time of 12'17" at n = 2400 rpm this equals 30%. The cylinder head temperatures were alright, the oil inlet temperature was after reaching 8,0 km 88°C with n = 2700 rpm compared to 73° with n = 2400 rpm.
Faults on aircraft or engine did not occur during testing.

The increased emergency power is to be cleared for the time being with a time limit of max. 10 min per usage for the test commando 28. The test results are to be delivered to BMW.

Detailed results and testing procedures:

At first flights for tuning the blinds in the intake air lines at the mixture regulator and at the boost regulator were done.  A boost of 1.65 ata was to be reached after switching to second charger gear, which was accomplished by a blind of 1.5 x 2.0 Ø at the mixture regulator and 1,5 x 1,8 Ø at the boost regulator.
Both power levels (normal power and increased power) were flown in immediate succession. 4 cylinder head temperatures, outside air temperature and flight time were recorded by the means of a four channel recorder, while boost and speed were read from the boost gauge and the speed indicator by the pilot at predetermined altitudes. The accuracy of the measurements, including the values read from the gauges, was very good, all values could be exactly reproduced in repeated flights.
I.) Speed increase (annex 1)
1.) Level speeds:
The test aircraft had to be designated a fast machine, which obtained already at sea level at normal emergency power 550 km/h and at 5.2 km altitude with increased emergency power vw = 680 km/h. Annex 1 shows the speed plot.
2.) Power:

The related power are also plotted and were calculated from altitude test bench under consideration of ram pressure on the intake air temperature and full throttle altitude, the outside air temperature difference to INA and engine power loss. A follow up check of the speed change with
v2 / v1 = N2 / N1 accounting for exhaust thrust with the power, the speed variances were below 0,5%.
3.) Fuel consumption:
The given fuel consumption was calculated from the measured boost, the aneroid temperature, calculated from the measured outside air temperature, and the adjustment chart. The shallow return curve shape at high boosts resulted in full flow rate in first charger gear up to 0.9 km and in second charger gear from switching altitude to 5.5 km at the increased boost setting. As can be seen in the annex, the specific fuel consumption in second supercharger gear at increased boost at higher than normal temperatures is higher than normal, while it is lower than normal in first supercharger gear. But no thermal overload is to be feared in case of lower than normal temperatures, since the set up of the blinds for the second charger gear only allows up to 1.58 ata boost in first charger gear and enough cooling is guaranteed in fast flight.
4.) Cylinder head temperatures:

Head temperatures were measured at the cylinders 8, 9, 11 and 12, where temperatures on cylinder 8 were lowest and on cylinder 9 were highest. In full throttle altitude second supercharger gear the highest temperatures result, which on the hottest cylinder for summer would be 216°C and for the tropics would be 226°C and would pose no threat for the short flight duration.
II.) Time to climb reduction (annex 2)
1.) Time to climb
The time to climb is plotted over altitude, where the normal climb performance n = 2400 rpm, pL = 1.32 ata was compared to the increased climb performance n = 2700 rpm, pL= 1.65 ata. The climb times were 12'17" and 8'38" respectively. While the time to climb reduction in a climb from 0,0 km to 8,0 km of 3'39" is small as an absolute figure, this is a decrease of 30% because of the generally low time to climb of 12'17".
2.) Power and fuel consumption:
Power and fuel consumption were determined in the same way as described under I. Also for specific fuel consumption the conditions as under I apply.

3.) Cylinder head temperatures:
The cylinder head temperature was increased by 13°C on the hottest cylinder compared to normal combat power and was 211°C in 6 km altitude, where outside air temperature was equal to summer conditions, so that for tropical conditions 221°C result. The flight speed was Va = 265-270 km/h and the cooling flaps were opened to "position 3".
4.) Oil temperatures:
The oil inlet temperature was increased from 73°C to 88°C (permissible for 15 min 80°C) by the increased climb power when reaching 8 km altitude. Since the outside air temperature was equal to highest summer temperature, this value is permissible for a short time. But the oil temperature has to be regarded as a criterion and only a larger test basis can make a final decision possible.


Speed increase through boost pressure increase on BMW 801 D in Fw 190 A-5
Climb time reduction through boost pressure increase on BMW 801 D in Fw 190 A-5

Versuchsbericht BMW 126 (pdf)

Translation by Jörn Dietrich and Mike Williams

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