Estimation of Technology Influence

There are several technologies to improve a new SCT. In order to evaluate the importance of a technology, we must be able to estimate its influence on the realisation of an SCT. At present level of knowledge, there is a hierarchy of technologies from fulfillment of constraints over cruise performance to operations. The operations arc still at the last position, because we are on search for a technical solution. When a solution is found, operations will become more important, because they contribute strongly to cost performance

1.3.1 Technologies to fulfill constraints

Here technology estimation is possible by looking for the relevant physical principles. Influence on aircraft cruise performance and cost is indirect, but can be very strong and limiting.

The most important constraints for an SCT are:

Take-off:

• Field length:

The required thrust (i. e. engine si/c) is determined by weight (acceleration) and aerody­namic lift (span, w ing area, rotation angle) at lift-off (i. e. minimum airspeed).

Take-off field length is defined by runway length of the relevant airports to be used by SCT. Today about 11000 ft arc assumed

•Climb rate:

The required thrust is determined by Height and aerodynamic performance UD After take-off. a climb rate with one engine out must be maintained of

0.5% with gear extended and 3% with gear retracted.

Noise:

Noise is determined mainly by exhaust velocity of the jet engines (as long as the turboma – chincry »s well shielded by inlet and nozzle) and mass flow (i. c. thrust) (take-off thrust = mass flow exhaust velocity).

Stage 3 compliant low noise exhaust velocities are between 300 m/s (Airbus A340. well below stage 3 limits) and at most 400 m/s (47); for compliance, bypass ratio* of about 2 or comparable measures are required.

Low speed thrust is determined by field acceleration, by weight and drag during climb, and by drag during approach.

In the rules of ICAO, annex 16. chapter 3 and its derivations FAR 36. stage 3 or JAR etc. maximum noise allowed at take-off and landing is defined. Figure 11 shows the three points, where noise is measured Maximum noise levels allowed for the different points depend on aircraft weight and number of engines. Noise levels are measured in EPNdB. which is a time integral of the EPNL(dB) weighted noise. Additionally, if noise at one point is only a little more elevated (at most 2 dB). it may be compensated by lower noise at the other points, following some complicated weighting.

Figure 11 Noise Measurement Points Transonic acceleration:

The highest wave drag values and the worst engine efficiency at nearly the same low su­personic speed may determine engine size.

Best supersonic cruise performance docs not make any sense, if the supersonic aircraft is not able to reach supersonic speed

Range:

Fuel amounts toa very high portion of gross weight (50% or even more). Therefore cruise efficiency determines range capability.

Airlines indicate, lhal a viable supersonic transport must be able to fly at least about 5 500 nm Many routes include segments over inhabited land, where only subsonic speeds are allowed.

Supersonic cruise:

Reduce aerodynamic drag (here by slenderness), reduce weight and improve super­sonic engine efficiency (here via decreased by pass ratio), to meet range requirements.

Drag at supersonic cruise is dominated by wave drag, but friction drag and induced drag are important as well Drag has to be balanced by thrust

Subsonic cruise:

Improve subsonic engine efficiency (here via increased bypass ratio) and reduce aer – (dynamic drag (here mainly larger span); both reduce supersonic efficiency.

Drag at subsonic cruise is dominated by friction drag and induced drag, possibly vor­tex drag due to separation. Drag has to be balanced by thrust.

Controllability:

Provide control authority for ail disturbances either external (gusts, manocuvcrs) or inter­nal (failure cases like inoperative engines, cabin pressure loss).

Emissions:

It seems that most important will be SOx-generation for us influence on the ozooclaycr.

NO*-gcncration is determined by peak temperatures which occur only at spot points in the burner, where stochiomctric conditions are met Low NO,-bumers reduce peak temperatures, but still maintain high mean temperatures.

Some of those constraining influences work against each other. For estimation of val­ues compare subsonic aircraft of similar weight, c. g. B747. but pay attention to tlsc significant physical parameters.

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