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| | Reason: | Daimler-Benz stated the reason for the low full throttle height of the DB 605 A engine was that the intake scoop was 150 mm diameter, while the supercharger inlet was 155 mm in diameter. On this occasion other airframe related reasons were examined which could cause a bad VDH.
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Test
Procedure: | Full throttle steps (Vollgasstufen) at climb and combat power (n = 2600 rpm; p = 1.30 kg/cm2) were flown with 150 and 155 Ø scoop from 19,685 to 29,528 ft.(6000 to 9000 m) altitude.
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| | The air speed at the intake entrance as well as the temperature of the supercharger air at the scoop entrance and in the supercharger duct was measured. In addition, for comparison, another flight with an early intake with 150 Ø was conducted.
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| Results: | 1.) | Full throttle height in high speed with combat power corrected to normal temperature.
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| | Intake 150 Ø | 20,997 ft. (6400 m)) | Desired value
| | Intake 155 Ø | 20,997 ft. (6400 m)) | n Intake = 0,9
| | Early intake | 20,505 ft. (6250 m)) | 22,966 ft. (7000 m)
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| 2.) | The total pressure at the intake entrance, ~ 50 kg/m2 higher than in the free flow, is due to prop wash.
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| | 3.) | The air temperature in the intake lies 2° above the ambient temperature. The heating thus lies within the measuring accuracy.
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| | 4.) | The supercharger air temperature at 8 km is 92°, the desired value is 107°. (after engine manual with consideration of the ambient temperature, lay 7° over CINA, and Stauauf heating.)
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| Aircraft: | Me 109 G | Werk Nr. 14001 | BD + GU
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| | Engine: | DB 605 A | Werk Nr. 76 233 |
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| Propeller: | 3-flg. VDM-Adjustable propeller
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| Condition
of the machine: | Conforming to provisional production condition with adjustable oil cooler intake (fixed to non-adjustable condition) without wheel covers. In order to be on the unfavorable side, the entrance was widened to the supercharger not as production taper in diameter from 150 to 155 mm, but went without transition in a break from 150 to 155 mm Ø.
A grill with horizontal bars was attached at the supercharger entrance. During flight 3 the intake hood was moved/extended forward 520 mm compared to the standard counterpart of the intake . Rep.Nr.109 24 L 41.
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| | Pilot: | Gutsche
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| | Day of the flights: | 3.6.: 4.6.: 6.6.42.
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| Conduction of
the Measurements: | The measurement was accomplished with altitude, airspeed, supercharger and manifold pressure recorder.
To measure the vacuum in the cockpit, the static pressure was connected to the pitot tube of the registering airspeed indicator.
The charge temperature was measured at the duct intended for this purpose (at the elbow of the supercharger duct) using a resistance thermometer; the air temperature in the intake hood 20 mm behind the intake entrance likewise by means of a resistance thermometer.
A simple NW4 tube was used as pitot tube at the intake hood, while the corresponding static pressure was tapped from the production pitot tube at the edge cap.
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| | Results: | Currently, the known possible airframe-related reasons for the bad FTH have been examined and found to be in order, consisting of: 1.) Heating from exhaust gases, 2.) too narrow plenum chamber, 3.) insufficient ram in front of the intake.
Apparently, however, the supercharger air temperature, ~15° too low, can be attributed to the poor static head of the supercharger.
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Augsburg, den 16.6.42
FEV/EK/Go.
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