Baseline HST NASA

The relative economic payoff of technology improvements is dependent upon the requirements and characteristics of the reference HST baseline (e.g. its mission, configuration, design features and technology state-of-the-art).

The fundamental purpose of the module "Baseline HST definition" is to organize the relevant data in a way that is appropriate to be exploited within the remaining phases of the general method such as within the DOC technology modules.

In carrying out this purpose, information from previous studies is used at this stage.

The next process then responds to the basic rules and constraints that are part of the initial input of this phase.

The basic definition method is divided into two main parts:

• Information Processing - with the aim of forming a complete and coherent information package going to acquire and filter data for HST to be used for the preparation of the next documentation useful for the next steps.

• Documentation - or prepare the baseline definitions output. The documentation will contain the data of the aircraft related to mission, operation, performance, design, weights and technological data. These data will be present both in tabulated quantitative form (useful for the successive DOC and Technological parameters equations) that in descriptive form to provide both an adequate understanding of the HST baseline and its technology and to ensure a certain flexibility in the preparation of information content to accommodate special areas of technical interest.

65 P r e s e n t a t i o n o f c o s t e s t i m a t i o n m o d e l

As previously mentioned, the HST baseline definition applies specifically to hypersonic aircraft that use airbreathing engines that can take off and land horizontally.

Within these limits, however, the baseline definition method has the ability to adapt to certain mission and design variables, as summarised in the following table:

• Variations in payload type have minimal effect on baseline development because the density of an airplane passenger compartment is comparable with the density required to accommodate most potential cargos. In the case of a liquid hydrogen-fuelled airplane, where the fuel density is similar to cargo or

• passenger compartment densities, payload weight variations maybe traded for fuel, with subsequent range changes.

• The parameters and relationships in this method are generally applicable to the hypersonic Mach number of 5 to 12. Mach beyond this interval should not be treated without a preliminary assessment of suitability.

• Although the model for the definition of the HST design baseline are highly dependent on the type of fuel, the basic methodology is not. This leads to also consider different types of fuel.

• The definition of structures is expressed in fractions of weight and values of parameters associated with the Technology. (e.g. parameters of housing, method for cooling structures, types of tanks whether integral or not).

• The method is able to adapt to large variations in aerodynamic configuration (L/D ratio)

• Basically, this method is formulated to describe two types of propulsion systems, one accelerator/descent type and the other accelerator/cruise type.

So, it is able to adapt to turbojet engine systems - Ramjet or single Ramjet-scramjet engines.

Variable Category Major Alternatives Accommodated

Payload Cargo, passenger or combination Cruise Mach number 5 - 12

Fuel type Liquid hydrogen, jet fuels, methane, etc., and combinations

Structure Actively cooled, uncooled, or combination;

integral or non-lntegral fuel tanks Aero configuration Blended wing-body, all-body or

conventional

Propulsion

Separate turbojets and ramjets or integrated

propulsion systems; supersonic or subsonic combustion, or dual-mode ramjets

Table 1 – Design variables in NASA methodology [2]

It is therefore necessary to refer to two types of input data, in order to be able to develop this first phase.

The first type of data related to requirements and ground rules with the purpose of:

(1) identify the HST project covered by the baseline definition;

(2) identify the reference documentation from which the required data are to be extracted;

(3) identify descriptive data related to technological particulars.

The other type of data, on the other hand, is related to the actual data of the HST (associated technological parameters and other qualification characteristics).

The types of input data needed for the preparation of the output modules useful for the following phases include data related to mission, performance, operations, aerodynamics, propulsion, design, structures, weights and related technologies.

A demonstrative example of this phase of the method of esteem of the costs used a airplane from cargo with a Mach of cruise pairs to six and with an operating capacity of 7400 km. The profile of the mission for HST sees the cruise to be realized to an altitude between the 27600 m and the 28800 m and a mission duration of about 2 hours.

Aerodynamic performance is reported in terms of aerodynamic efficiency L/D, with a reference value of 4,6 (the most conservative of that obtained in the wind tunnel test). Other operational characteristics required by the method and presented are:

Block time:2.25 hr

Average utilization: 3000 block hr/yr Deplorable life: 10 yr

Hours of use during operational life: 30000 hr No-use hours during operational life: 576000 hr Flight hours over the operational lifecycle:26700 hr Flight cycles during operational life: 13350

The fuel used is liquid hydrogen, with tanks located at the front and rear of the fuselage for considerations related to the weight and centre of gravity of the fuselage,

Figure 46 – NASA HST concept [2]

as well as for reasons of stability and balance control. This includes the positioning of the loading space. The shape of the fuselage blended wing-body with a single vertical rearing that guarantees a reduced aerodynamic resistance and a surface of continuous pre-compression for the engines. The material of the structure is 7075-T6 aluminium alloy cooled to an average temperature of 367k through the use of a water-glycol-based refrigerant fluid and special heat exchangers.

A combo engine, consisting of 4 turbojets for subsonic speeds and a series of dual-combustion Ramjets, is examined as a propulsion system (subsonic dual-combustion during the transition from transonic velocity to supersonic, and supersonic combustion to address hypersonic phases).