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Architecture options estimate for the near-medium-haul aircraft control system by the reliability, mass and power consumption criteria

  • S. E. PostnikovEmail author
  • A. A. Trofimov
  • S. V. Baikov
Original Paper
  • 83 Downloads

Abstract

Current trends in increasing fuel efficiency and improving aircrafts flight characteristics place engineers before task of reducing the weight of onboard systems and decreasing power consumption with preserving required degree of reliability. In part of aircraft control system, the main stream is the actuators usage with power supply. In this article, three architecture options of the power part of the aircraft control system with different electrification levels are considered. The considered options of the power part of the control system are estimated by three criteria: reliability, mass, power consumption. The selected criteria allow for the preliminary conclusion about the prospects one or another aircraft control system architecture.

Keywords

The control system architecture The control system reliability The control system mass The power consumption of the control system The aircraft actuator Reservation Electro-hydrostatic actuators 

1 Introduction

The development of aircraft airborne systems is on the way to increasing the aircraft fuel efficiency by reducing weight and increasing the level of electrification with the same level of functional and operational characteristics of onboard systems and units [1].

In the part of the aircraft control system, the main stream is the use of surface power supply actuators such as:
  • electro-hydrostatic actuator (EHA);

  • electrical backup hydrostatic actuator (EBHA);

  • electromechanical actuator (EMA).

The use of surface power supply actuators in the control system has impact on system reliability and, as a consequence, its architecture, as well as the parameters of the aircraft’s power systems. The development of the architecture, design and placement of the control system assemblies on the aircraft obliges to take into account the fulfillment of all regulatory documents requirements in terms of ensuring operability, reliability and safety for complex onboard systems. In part of reliability, the control system must comply with the requirements of documents AR-25, FAR-25 and CS-25.

Based on the requirements of aviation regulations and operating experience, it can be seen that the loss of aircraft control over one channel (roll, pitch or yaw) with a high degree of probability leads to a catastrophic situation under adverse flight conditions (adverse weather conditions, critical combination of weight and the center of gravity of the aircraft) and/or erroneous crew actions. Thus, the loss of control of one channel intensity should be an event not more likely than 10−9 and should not be a consequence of a single failure.

The most of near-medium-range aircraft (NMRA) such as the A320, RRJ-95, B737 have two surfaces for pitch control (elevators), one surface for yaw control (rudder) and two to ten surfaces for roll control (ailerons and spoilers) as shown in Fig. 1.
Fig. 1

Aircraft surfaces

In this article, we propose to consider control schemes for the roll by the ailerons and the two end sections pairs of spoilers. The end sections of the spoilers have the maximum efficiency in roll control; however, taking into account the requirements for reducing the loads on the wing of a thin profile and the large elongation characteristic of the aerodynamic configuration of modern aircraft, a limitation is imposed on the number of pairs of interceptors in roll control. Interceptors refer to secondary steering surfaces, the failure of which is not critical; however, with loss of control of the two ailerons, the interceptors retain the possibility of efficient roll control.

Let us consider three options of power part of control system architecture with a high level of electrification.

The first option implies the presence of a local hydraulic system (HS). Implementation of this option leads to the inclusion of an additional pumping station located in the tail fuselage. For conformity of safety requirements, the pumping station must be connected to at least two power supply systems (PSS).

Using EHA will save the control of the main surfaces in case of local HS failure. This option is shown in Fig. 2.
Fig. 2

Control system with local HS

The second option of the power part of the control system with a high level of electrification is the architecture with two HS. Figure 3 shows the architecture of the control system of a typical near-medium-range aircraft with the replacement of all electrohydraulic servo actuator (EHSA) of one HS at the EHA.
Fig. 3

Control system with two HS

The third option of the power part of the control system with a high level of electrification is shown in Fig. 3. This variant includes an EHSA powered by one HS and EHA, operating from two power supply systems to correspond the safety requirements (Fig. 4).
Fig. 4

Control system with one HS

2 Comparative criteria and initial data for the calculation of typical examples of the surface control architecture

In this article, we consider three criteria for evaluating the power part of the control system architecture: reliability, mass, and power consumption.

Based on the analysis of publications and scientific works of domestic and foreign authors over the past 10 years, statistical data on Tu-154, Tu-204, A320, A321 and others [2, 3, 4, 5, 6, 7, 8, 9, 10, 11], as well as expert estimates, averaged data were obtained:
  • in part of the typical components of control systems (CS) failure rate, Electro System (ES) and Hydraulic System;

  • EHA mass and power;

  • required power of the surface actuators.

3 Architecture estimate of a control system based on the safety criterion

The average failure rates are presented in Table 1.
Table 1

Average value of failure rates

Control system components

Failure rate indicators

Average value

Aircraft hydraulic system (HS)

40 × 10−6

1 × 10−4

1.68–2.12 × 10−5

5.3 × 10−5

Aircraft electric system (ES)

10 × 10−6

4 × 10−7

5 × 10−6

Electrohydraulic servovalve actuator (EHSA)

40 × 10−6

25–30 × 10−6

10−7

1.34 × 10−5

Electro hydrostatic actuator (EHA)

115 × 10−6

2.20 × 10−5

1.61∙10−4

9.2 × 10−5

The electronic part of the control system is not considered in this article, since the electronic part can be the same unchanged, regardless of the chosen version of the power part of the control system architecture. Also, there are strict requirements for fail safety to the electronic part of the control system which achieved by the high level of redundancy of computing and functional capacities, the total failure of which is almost an incredible event.

In this article, failures of the “jamming” type are not considered, as the general reason for the loss of control of one surface.

As an example of a typical calculation, the option of the power part of the control system with three HS is presented:
$$\begin{aligned} \lambda_{\text{roll}} &= \lambda_{\text{ailerons}} \cdot \lambda_{\text{spoilers}} \\ & = \left[ {\left\{ {\left( {\lambda_{\text{left ail out}}^{\text{EHSA}} + \lambda_{\text{ail}}^{\text{HS}} } \right) \cdot \left( {\lambda_{\text{left ail in}}^{\text{EHSA}} + \lambda_{\text{ail}}^{\text{HS}} } \right)} \right\} }\right. \\ & \quad \left.{\cdot \left\{ {\left( {\lambda_{\text{right ail out}}^{\text{EHSA}} + \lambda_{\text{ail}}^{\text{HS}} } \right) \cdot \left( {\lambda_{\text{right ail in}}^{\text{EHSA}} + \lambda_{\text{ail}}^{\text{HS}} } \right)} \right\}} \right] \\ & \quad \cdot \left[ {\left( {\lambda^{\text{HS}} + \left( {\lambda_{\text{sp4 left}}^{\text{EHSA}} + \lambda_{\text{sp 4 right}}^{\text{EHSA}} } \right) } \right) }\right. \\ & \quad \left.{+ \left( {\lambda^{\text{HS}} + \left( {\lambda_{\text{sp 3 left}}^{\text{EHSA}} + \lambda_{\text{sp 3 right}}^{\text{EHSA}} } \right)} \right)} \right] \hfill \\ &= \left[ {\left\{ {\left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right) \cdot \left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right)} \right\} } \right. \\ & \quad \left.{\cdot \left\{ {\left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right) \cdot \left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right)} \right\}} \right] \hfill \\ &\cdot \left[ {\left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right)}\right.\\ & \quad \left.{ + \left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right)} \right] \\ & \quad = 2.24 \cdot 10^{ - 13} ; \hfill \\ \end{aligned} $$
$$ \begin{aligned} \lambda_{\text{pitch}} &= \left[ {\left( {\lambda_{\text{left elev out}}^{\text{EHSA}} + \lambda_{\text{left elev out}}^{\text{HS}} } \right)}\right. \\ & \quad \left. { \cdot \left( {\lambda^{\text{HS}} + \left( {\lambda_{\text{left elev in}}^{\text{EHSA}} \cdot \lambda_{\text{right elev in}}^{\text{EHSA}} } \right)} \right) }\right. \\ & \quad \left. {\cdot \left( {\lambda_{\text{right elev out}}^{\text{EHSA}} + \lambda_{\text{right elev out}}^{\text{HS}} } \right)} \right] \hfill \\ &= \left[ {\left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right) }\right. \\ & \quad \left. {\cdot \left( {5.3 \cdot 10^{ - 5} + (1.34 \cdot 10^{ - 5} \cdot 1.34 \cdot 10^{ - 5} )} \right) }\right. \\ & \quad \left. {\cdot \left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right)} \right] = 2.34 \cdot 10^{ - 13} ; \hfill \\ \end{aligned} $$
$$ \begin{aligned} \lambda_{\text{yaw}}& = \left( {\lambda_{\text{upper rud}}^{\text{EHSA}} + \lambda_{\text{upper rud}}^{\text{HS}} } \right) \cdot \left( {\lambda_{\text{midlle rud}}^{\text{EHSA}} + \lambda_{\text{midlle rud}}^{\text{HS}} } \right) \\ & \quad \cdot \left( {\lambda_{\text{lower rud}}^{\text{EHSA}} + \lambda_{\text{lower rud}}^{\text{HS}} } \right) \hfill \\ &= \left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right)\\ & \quad \cdot \left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right) \\ & \quad \cdot \left( {5.3 \cdot 10^{ - 5} + 1.34 \cdot 10^{ - 5} } \right) = 2.93 \cdot 10^{ - 13} ; \hfill \\ \end{aligned} $$
$$ \lambda_{\sum } = \lambda_{roll} + \lambda_{pitch} + \lambda_{yaw} = 7.5 \cdot 10^{ - 13} $$
where λ, failure rate (1/h);
Table 2 presents summary data on the failure rate, each control channel for the three options considered of the power part of the control system with an increased level of electrification, and the typical control system with three HS.
Table 2

Summary of failure rates

Control channel

Typical option

Option 1

Option 2

Option 3

Roll

2.24 × 10−13

2.24 × 10−13

3.41 × 10−13

4.99 × 10−13

Pitch

2.34 × 10−13

4.99 × 10−13

3.41 × 10−13

3.23 × 10−14

Yaw

2.93 × 10−13

6.25 × 10−13

4.28 × 10−13

6.25 × 10−13

7.5 × 10−13

1.36 × 10−12

1.11 × 10−12

1.16 × 10−12

Analyzing Table 2, it can be seen that all variants are close in terms of the total failure rate. The most reliable option for the control system is a option of the architecture of the power section with two HS.

4 Architecture estimate of a control system based on the mass criterion

The averaged values of the mass of the EHA and power are presented in Table 3.
Table 3

The averaged values of the mass and power for EHA

Mass (kg)

Power (kW)

Aircraft model

20

3.18

 

15.5

1.91

Elevator An-148

20

1.75

Rudder Aн-148

41.82

4.8

Rudder F-35

65

13.36

Aileron A380

80

19.51

Elevator A380

19

1.26

Aileron A320

11.5

2

Aileron A321

140

42.5

 

11.6

2.2

 
Based on the data on the required power and the mass of the EHA, a distribution curve is generated that expresses the mass-to-power relationship. The plot of the dependence is shown in Fig. 5. For the EHA, it is worth noting the considerable mass of the electronic control module. For the control system actuators, the ratio of actuator power to power electronics usually has ranges from 1 to 2 kW/kg.
Fig. 5

Dependence of the power on the mass of the EHA

The resulting curve can be described by a polynomial of the second level:
$$ y \, = \, - 0.0335x^{2} + \, 4.4928x \, + \, 8.9805 $$
(1)
where x is the required actuator power; y is the mass of the EHA.
The dependence of power on mass is calculated on the basis of expert analysis of actuators up to 4 kW. The mass ratio of EHSA to power can be represented in the form of the graph shown in Fig. 6:
Fig. 6

Dependence of the power on the mass of the EHSA

For EHSA, for the power up to 4 kW, the mass-to-power relationship can be described by the linear Eq. (2):
$$ y \, = \, 2x \, + \, 9.48 $$
(2)
where x is the required actuator power; y is the mass of the EHSA.
Based on the statistical data of the actuator loads, as well as the expert evaluation, the average required power required to control the various surfaces of the aircraft of the near-medium-range aircraft power consumption is calculated and the data are presented in Table 4.
Table 4

Average power consumption

Surface

Average power consumption (kW)

Aileron actuator

1.7

Elevator actuator

2.24

Rudder actuator

4.09

Spoiler actuator

3.73

On the basis of the obtained dependency data and an estimate of the power requirements of the actuators, we calculate the mass of the power part of the control system of the considered options.

Table 5 summarizes the mass of the power section of the control system for the three options considered as well as for the traditional option with three HS.
Table 5

Summary of mass data

 

Typical option (kg)

Option 1 (kg)

Option 2 (kg)

Option 3 (kg)

Mass

228.1

247.05

254.13

285.08

5 Architecture estimate of a control system based on the power consumption criterion

Architecture estimate of a control system based on the power consumption criterion.

Based on the data on the efficiency and power of the units, we can draw a conclusion about the energy perfection of the system. The power consumption of the control system, each options of the architecture, is estimated by calculating the total consumed power and hydraulic power.

The required power of the power part of the control system is brought to the output shaft of the power unit of the aircraft power units taking into account the losses of energy conversion and power transmission.

NΣ (kW) is the total power consumed by the power system of the system and the energy taken from the main energy sources of the aircraft is calculated by the formula:
$$\begin{aligned} N_{\sum } &= \, (N_{\text{SEHSA}} \cdot \eta_{\text{EHSA}} \cdot \eta_{\text{pump}} \cdot \eta_{\text{hydrotrans}} ) \,\\ & \quad + \, (N_{\text{SEHA}} \cdot \eta_{\text{EHA}} \cdot \eta_{\text{eg}} \cdot \eta_{\text{pt}} ) \end{aligned}$$
where NΣEHSA is the sum power of EHSA in active mode; ηEHSA is the EHSA efficiency—80%; ηpump is the efficiency of the volumetric pump taking into account volumetric (compression of a liquid), hydraulic (leakage) and mechanical (friction) losses—80%; ηhydrotrans is the efficiency of hydrotransmission taking into account the local resistance, friction of liquid against the walls of pipelines, leaks in hydraulic system assemblies—90%.

The overall efficiency for the hydraulic system from the actuator to the primary energy source of the aircraft is 72%;

NΣEHA is the total power of the EHA in the active mode.

ηEHA is the EHA efficiency—80%;

ηe.g. is the efficiency of the generator when working under load—85%.

ηpt is the power transmission efficiency taking into account the resistance of the mains and the presence of protection devices and switchgears—95%;

The total efficiency for the electrical system from the actuator to the primary energy source of the aircraft is 80%.

For a local hydraulic system with the presence of double energy conversion, the overall efficiency from the actuator to the primary source is 57%.

In this research, for hydraulic actuators, we do not consider the power consumption for controlling the servo valves because it is negligible compared to hydraulic energy.

A well-known principle of the configuration of the power part of the control system is considered:
  • ailerons, elevator controls—active/damping;

  • rudder wheel—active/active/damping;

  • spoilers—active.

The distribution between the active/damping actuators between the EHSA/EHA is based on the diversity of the power systems (electro-/hydro-) to eliminate single faults resulting in the loss of two similar control surfaces.

The calculation of the power consumption is presented in Tables 6, 7, 8 and 9.
Table 6

The calculation of the power consumption for option 1

Surface

Type of active actuator

Average power consumption, kW

Sum efficiency

Power consumption, kW

Right aileron

EHSA

1.7

0.58

2.93

Left aileron

EHSA

0.58

2.93

Right elevator

EHSA (local HS)

2.24

0.46

4.86

Left elevator

EHA

0.6

3.73

Rudder

EHA (local HS)

4.09

0.46

8.89

EHA

0.6

6.81

Spoilers right wing

EHSA

3.73

0.58

6.43

EHSA

0.58

6.43

Spoilers left wing

EHSA

0.58

6.43

EHSA

0.58

6.43

   

NΣ, kW

55.89

Table 7

The calculation of the power consumption for option 2

Surface

Type of active actuator

Average power consumption, kW

Sum efficiency

Power consumption, kW

Right aileron

EHA

1.7

0.6

2.83

Left aileron

EHSA

0.58

2.93

Right elevator

EHA

2.24

0.6

3.73

Left elevator

EHSA

0.58

3.86

Rudder

EHA

4.09

0.6

6.82

EHSA

0.58

7.05

Spoilers right wing

EHSA

3.73

0.58

6.43

EHA

0.6

6.22

Spoilers left wing

EHSA

0.58

6.43

EHA

0.6

6.22

   

NΣ, кBт

52.52

Table 8

The calculation of the power consumption for option 3

Surface

Type of active actuator

Average power consumption, kW

Sum efficiency

Power consumption, kW

Right aileron

EHA

1.7

0.6

2.83

Left aileron

EHSA

0.58

2.93

Right elevator

EHA

2.24

0.6

3.73

Left elevator

EHSA

0.58

3.86

Rudder

EHA

4.09

0.6

6.82

EHSA

0.58

7.05

Spoilers right wing

EHSA

3.73

0.58

6.43

EHA

0.6

6.22

Spoilers left wing

EHSA

0.58

6.43

EHA

0.6

6.22

   

NΣ, кBт

52.52

Table 9

The calculation of the power consumption for typical option

Surface

Type of active actuator

Average power consumption, kW

Sum efficiency

Power consumption, kW

Right aileron

EHSA

1.7

0.58

2.93

Left aileron

EHSA

0.58

2.93

Right elevator

EHSA

2.24

0.58

3.86

Left elevator

EHSA

0.58

3.86

Rudder

EHSA

4.09

0.58

7.05

EHSA

0.58

7.05

Spoilers right wing

EHSA

3.73

0.58

6.43

EHSA

0.58

6.43

Spoilers left wing

EHSA

0.58

6.43

EHSA

0.58

6.43

   

NΣ, kW

53.41

Based on the results of the power consumption analysis, it is evident that with the same dimensionality and aerodynamic layout of the aircraft local hydrosystems are introduced, due to the increase in total power consumption.

In the schemes using the EHA, a decrease in energy consumption is observed in comparison with the typical option with three HS.

6 Conclusion

In this article, an analysis of various options for the control system architecture and a comparative evaluation with a typical option of the control system architecture is conducted.

According to the reliability criterion, the considered architectures are close to the typical CS architecture with three HS. That allows to draw a conclusion that all considered options of architectures with an increased level of electrification meet the requirements of regulatory documentation in terms of safety.

According to the mass of the power part of the control system, it can be concluded that the CS mass increases with an increase in the electrification level and a decrease in the number of HS. Reducing the number of HS to two leads to an increase the mass CS by 11% and reducing the number of HS to one leads to an increase the mass CS by 24%. The use of a local HS in the tail of the aircraft will lead to an increase the mass CS by 8%. However, this calculation does not take into account the mass of aggregates of HS and ES. The increase in the mass of the control system without estimating the change in mass of HS and ES should not be considered as a negative result.

By the criterion of power consumption, the introduction of a local hydraulic system entails an increase in the power consumption of the control system by about 5% in comparison with the rest of the schemes. The other options are close to each other by the criterion of power consumption.

Thus, it is established that the scheme with three hydraulic systems and the option with two HS and one power ES have close characteristics for all the parameters considered. This data the possible reduction in operating costs and maintenance time associated with the exclusion of one of the hydraulic systems, as well as the possible reduction in mass due to the exclusion of hydraulic aggregates and pipelines, the power part of the control system architecture, using two central hydraulic systems and EHA, is promising.

The considered options of the control system require an assessment of the impact on the stability and controllability of the aircraft, as well as a comprehensive analysis, taking into account changes in the hydraulic system and the power supply system.

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Copyright information

© Shanghai Jiao Tong University 2018

Authors and Affiliations

  1. 1.Moscow Aviation Institute (National Research University)MoscowRussia

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