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[pic]

Figure 5.2 Noise limits imposed by ICAO Annex 16 for certification of aircraft.

On take-off, however, aircraft with fewer engines climb out faster, so they are higher above the measuring point. Here the “reasonable and economically practicable” principle comes into dictate that three-engine and two-engine aircraft have lower noise levels at the take-off noise station than four- engine aircraft.

There is some flexibility in the rule, in that the noise levels can be exceeded by up to 2 EPNdB at any station provided the sum of the exceedances is not over 3 ENPdB and that the exceedances are completely offset by reductions at other measuring stations.

6 Noise Level Calculations

17 Tupolev 154M Description

For most airlines in the CIS, the Tupolev Tu-154 is nowadays the workhorse on domestic and international routes.

[pic]

Figure 6.1 Tupolev 154M main look

It was produced in two main vesions: The earlier production models have been designated Tupolev -154, Tupolev -154A, Tupolev -154B, Tupolev
-154B-1 and Tupolev -154B-2, while the later version has been called
Tupolev -154M. Overall, close to 1'000 Tupolev -154s were built up to day, of which a large portion is still operated.

Table 6.1 Tupolev 154M main characteristics

|Role | |Medium range passenger aircraft |
|Status | |Produced until circa 1996, in wide |
| | |spread service |
|NATO Codename | |Careless |
|First Flight | |October 3, 1968 |
|First Service | |1984 |
|Engines | |3 Soloviev D-30KU (104 kN each) |
|Length | |47.9 m |
|Wingspan | |37.5 m |
|Range | |3'900 km |
|Cruising Speed | |900 km/h |
|Payload Capacity | |156-180 passengers (5450 kg) |
|Maximum Take-off | |100'000 kg |
|Weight | | |

The Tu-154 was developed to replace the turbojet powered Tupolev Tu-
104, plus the Antonov - 10 and Ilyushin - 18 turboprops. Design criteria in replacing these three relatively diverse aircraft included the ability to operate from gravel or packed earth airfields, the need to fly at high altitudes 'above most Soviet Union air traffic, and good field performance.
In meeting these aims the initial Tupolev -154 design featured three
Kuznetsov (now KKBM) NK-8 turbofans, triple bogey main undercarriage units which retract into wing pods and a rear engine T-tail configuration.

The Tupolev -154's first flight occurred on October 4 1968. Regular commercial service began in February 1972. Three Kuznetsov powered variants of the Tupolev -154 were built, the initial Tupolev -154, the improved
Tupolev -154A with more powerful engines and a higher max take-off weight and the Tupolev -154B with a further increased max take-off weight. Tupolev
-154S is a freighter version of the Tupolev -154B.

Current production is of the Tupolev -154M, which first flew in 1982.
The major change introduced on the M was the far more economical, quieter and reliable Solovyev (now Aviadvigatel) turbofans. The Tupolev - 154M2 is a proposed twin variant powered by two Perm PS90A turbofans.

6.2 Noise Calculaions

Noise level at control points is calculated using the Noise-Power-
Distance (NPD) relationship. In practice NPD-relationship is used in the parabolic shape:

[pic], where coefficients А, В, С are different for different aircraft types and engine modes. For Tupolev-154M the coefficients А, В, С are shown in the table 6.2 in respect to Tupolev-154.

Table 6.2 Noise-Power-Distance coefficients of similar aircraft.

| |Tupolev-154 |Tupolev-154M |
|Weight, kg |80000 |76000 |72000 |68000 |68000 |
|Vapp, m/s |74,8 |72,91 |70,964 |68,965 |66,91 |
|Thrust, kg |8445,63 |8024,67 |7601,88 |7179,66 |6758,58 |
|LA, dBA |96,74 |96,05 |95,35 |94,66 |93,97 |
|EPNL, EPNdB |112,17 |111,32 |110,48 |109,64 |108,79 |
|?LA, dBA |0 |0,69 |0,7 |0,69 |0,69 |
|?EPNL, EPNdB |0 |0,85 |0,84 |0,84 |0,85 |
|SQRT (Wing |21,082 |20,548 |20 |19,437 |18,856 |
|Load) | | | | | |
|Thrust To |0,10557 |0,105588 |0,105582 |0,105583 |0,105603 |
|Weight rt. | | | | | |

Tupolev 154M has the same aerodynamics as Tupolev 154, thus the necessary thrust for both of them during approach is almost the same.
Tupolev 154M has more powerful engines and it can carry more payload. Its maximum landing weight is 2 tons greater than that one of 154. Noise parameters are different for these aircraft (table 6.2), and the calculated noise levels slightly differ as well.

7 Noise Suppression

7.1 Suppression of Jet Noise

Methods for suppressing jet noise have exploited the characteristics of the jet itself and those of the human observer. For a given total noise power, the human impact is less if the frequency is very high, as the ear is less sensitive at high frequencies. A shift to high frequency can be achieved by replacing one large nozzle with many small ones. This was one basis for the early turbojet engine suppressors. Reduction of the jet velocity can have a powerful effect since P is proportional to the jet velocity raised to a power varying from 8 to 3, depending on the magnitude of uc. The multiple small nozzles reduced the mean jet velocity somewhat by promoting entrainment of the surrounding air into the jet. Some attempts have been made to augment this effect by enclosing the multinozzle in a shroud, so that the ambient air is drawn into the shroud.

Certainly the most effective of jet noise suppressors has been the turbofan engine, which in effect distributes the power of the exhaust jet over a larger airflow, thus reducing the mean jet velocity.

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