Stability and Control

Introduction

A typical military aircraft is kept stable by a horizontal tail and a vertical fin which act in a similar fashion to a weather vane – more radical configurations such as flying wings operate quite differently. The typical aircraft is controlled in roll by ailerons on the wings, in pitch by an elevator on the horizontal tail plane and in yaw by a rudder on the vertical fin – one alternative configuration is a V-tail which combines the function of the horizontal and vertical tail assemblies.

Validation of stability and control forms one of the most important parts of any aircraft development program. It is critical to the safety of the aircraft and crew that the control surfaces perform their function throughout the operational envelope at all speeds and attitudes.

The Role of Wind Tunnels

Wind tunnel tests enable aircraft designers to check how an aircraft model performs both within and beyond its operation envelope in a safe and controlled environment. Computers play a rapidly increasing role in the design of aircraft but the complex nature of the airflow around items such as control surfaces and spoilers and around the aircraft post-stall remains a very challenging area for numerical simulation.

Wind tunnels can provide the large quantities of high-fidelity data with the speed and reliability needed to give the highest levels of confidence in the aircraft design and the flight control system before flight test.

A typical test may involve the design and manufacture of control surfaces such as spoilers or ailerons, larger items such as engine nacelles and external fuel tanks, or the complete aircraft model followed by a wind tunnel test. The aerodynamic loads on individual components can be measured by attaching each component to the parent aircraft with a purpose built balance which measures the loads on that component.

World Class Capability

ARA offers a one-stop service for customers starting with the design and manufacture of model components and balances followed by gauging and calibration of balances and finishing with a test program in our Transonic Wind Tunnel. We have a world leading capability in the manufacture of all model components, support mechanisms and balances completed to the very highest standards.

Part of the range of measured components we manufacture is listed below. We are experienced in providing solutions for novel and highly experimental aircraft configurations.

• Control surfaces - Ailerons, Spoilers, Elevators, Rudders
• Horizontal Tail Plane, Vertical Tail Plane and V-Tail assemblies
• Store Pylons and Engine Nacelles
  

A Wealth of Experience

We have decades of experience testing a wide variety of military aircraft for European and US aircraft manufacturers. Recent programs have included the F-35 joint strike fighter including all the contender aircraft.

Excellent Value and Productivity

Our highly experienced test teams deliver excellent test program management combined with rapid model reconfiguration to a superb standard to provide our customers with an efficient and productive service which provides excellent value. Models may incorporate remotely controlled panels such as canards and fins to further improve productivity.

Advanced Materials

We have considerable experience in integrating and testing resin components manufactured using Stereo Lithography; the main advantage of this technique is the significant reduction in time and cost of component manufacture which improves value to our customers. We also test model components made from composite materials.

Data Acquisition and Processing

Customers who test with us can take advantage of our proven and flexible data acquisition and processing capability. We offer seamless integration of customer supplied code and programs into our in-house data processing suite. We provide full visibility and traceability of our data processing steps giving our customers the highest level of confidence in the data we deliver.

Real-time processing and display of data allows our customers to make quick decisions based on a reliable data set and adapt their test program as required. This enables a more efficient use of tunnel time creating better value for our customers.

Fully corrected and validated data is transferred to customers within minutes of completion of each test run. This allows our customers to analyse their data from the beginning of a test program.

Assured Security of Model and Data

When testing with us, the security of the model and data is assured; we tailor our security measures to suit our customers’ needs. Upon prior request, our highly experienced IT support team can set up Virtual Private Networks (VPN) to permit remote monitoring of test data by customer teams from within and outside the UK.

Flexibility

We operate a flexible service throughout the year to suit the requirements of our customers; we have considerable experience in delivering test programs with 24-hour running.

Technical Information

Model Attitude:

• Incidence range: -40˚ to +40˚
• Sideslip range: ±40˚
• Roll range: ±180˚

Model Loads:

• Test into positive and negative buffet onset
• High speed failure cases including spoilers and undercarriage

Flow Investigation:

• Use oilflow visualisation to investigate surface flow phenomena such as separation bubbles and trailing edge separations
• Use high speed pressure transducers to measure unsteady pressures to investigate regions of separated flow

Data Acquisition:

• Up to 220 channels measured at up to 10 data points per second
• Up to 19 balanced components in addition to the main balance can be installed on the parent aircraft
• Measurement of up to 1000 steady-state pressures recorded at up to 10 data points per second