Military Aircraft, UAV’s and Missiles
Simulating the operational envelope of a combat aircraft and the deployment of a missile requires the development of a comprehensive range of wind tunnel test techniques. Here the accurate simulation of the air vehicle’s aerodynamic performance can be the critical difference between its mission’s success and failure.
ARA has worked on some of the World’s most demanding military aircraft and weapons programs and received awards from our customers in recognition for the notable contributions we have made to the success of these projects. The aircraft that ARA has worked on include Tornado, Harrier, T-50, Typhoon and F-35. We have worked closely with the World’s leading aircraft and weapon manufacturers on the development and integration of stores such as Brimstone, Amraam and Meteor.
As the operational envelope of unmanned and remotely piloted air vehicles expands into the high subsonic and transonic speed range, ARA is playing an increased role in the research and development programs of these aircraft types. Stability and control, Pressure Sensitive Paint, weapon bay aero-acoustic and store separation tests have all been undertaken in the ARA Transonic Wind Tunnel.
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 that provides excellent value. The security of the model and all data is assured for every customer.
Store Separation
Store separation testing is vital before a new store (such as a missile or a fuel tank) can be used in service on an aircraft. These tests are used to ensure that a store, on release, is able to clear the parent aircraft safely without endangering the aircraft or pilot.
ARA has developed the Two Sting Rig (TSR) system which we believe to be the most accurate system to meet this requirement in the world with its’ unique store release simulation capability. Using this, positional accuracies can be measured to within 0.05 inches, or 1.25mm. The TSR system achieves this level of accuracy through monitoring the relative positions of lights mounted in known positions on the store and aircraft, using a calibrated camera system. Using this system allows ARA to add value in the area of store release testing (due to efficient and accurate testing) especially when compared with the expensive alternative of flight testing.
The TSR has been used at ARA since 1979 and has been used to support store integration programs in a wide variety of production and developmental aircraft including Stormshadow, Raptor and Brimstone integration on Tornado and Harrier in the UK. International customers include Saab Scania with Gripen, KAI with the T-50 and Lockheed Martin with the F-16.
Why ARA?
If a customer works with ARA they can take advantage of:
- Stores positioned in location and attitude with superb accuracy levels: Pitch, Yaw = ± 0.15°; Y,Z = ± 0.15mm.
- Store movement is continuous allowing for excellent productivity, for example up to 15 trajectories, up to 30 grids (grid survey test technique) and up to 20 traverses (freestream traversing technique) per hour is possible.
- Decades of experience testing a wide range of stores and aircraft.
- Efficient test campaigns: all set up data validated before entry into the wind tunnel reducing costs for the customer.
- Advanced release techniques including extremely high incidence tests.
- A comprehensive range of trajectory simulation parameters.
- A comprehensive range of internal balances for measuring store loads.
Why the Two Sting Rig system?
The TSR is used for the following store release testing techniques:
1. Captive Trajectory Simulation (CTS)
By using a combination of measured and simulated loads the TSR accurately predicts a highly dynamic store release. A full range of release conditions can be simulated including:
- Ejector forces
- Rocket forces
- Control forces
- G-forces due to pull-up or push-down manoeuvres
- Fin deployment
- Pivot Hook release
- Rail constraint
- Autopilots
2. Grid Survey
Store aerodynamic loads are measured at a predetermined array of positions and attitudes to create a database of the spatial variation of the loads in the proximity of the aircraft. These loads can then be used in off-line six-degree of freedom computer trajectory programs.
3. Freestream Traversing
The TSR is used for freestream traversing without the presence of the parent aircraft to measure the aerodynamics of the isolated store.
4. Flow Survey
In addition to the freestream traversing technique, flow angularity and pressures are measured around the parent aircraft model using flow angularity meters and pitot rakes fitted to the TSR.
5. Free Drop Tests
These tests are conducted using mass and inertia scaled stores. Free drop tests can be useful to predict release trajectories involving extreme store attitudes and tumbling stores. The releases are recorded using high-speed digital cameras and the recordings are analysed post-test to determine the trajectory.
Stability and Control
Fighter aircraft are designed with some degree of inherent aerodynamic instability, requiring close control by fly-by-wire computers. Therefore it is vitally important that the stability and control aerodynamics of the aircraft are fully understood throughout the flight envelope at all speeds, attitudes and payload combinations as these data form the basis of the flight control software systems. It is important to acquire stability and control data for a large number of store payloads to provide sufficient data for aircraft flight control systems. The safety of the aircraft and crew are therefore dependent on the fidelity of the aerodynamic database.
For military aircraft, control panel loads determination is also important since control panel loadings are affected by the payload carried on the aircraft, more especially by external stores. Loads on various control panels may be derived either directly, by use of panel balances, or by measuring pressures using Pressure-Sensitive Paint on the upper and lower surfaces of the panel and integrating these data.
Why ARA?
ARA has many years of experience in the measurement of stability and control aerodynamic data for a wide variety of military aircraft throughout the global market, including Tornado, Typhoon and JSF (F35). This has enabled highly accurate stability and control data acquisition methods to be developed coupled with excellent productivity.
Individual control panel loads may also be measured simultaneously with the overall stability and control loads. ARA has extensive experience in the measurement of payload forces and moments for both individual stores and multiple stores on racks/launchers etc. This experience has enabled ARA to couple stability and control data acquisition together with store loads measurements simultaneously during a wind tunnel entry to maximise data acquisition whilst keeping tunnel entry time to a minimum.
Alternatively, ARA’s use of Pressure-Sensitive Paint with a standard forces model provides the customer with component load data from the first test of a new aircraft programme.
Typical Tests
During the wind tunnel test, a sequence of different control panel settings together with various store configurations are tested. Some of the typical measurements made during such a test are listed below:
- Change in aircraft handling characteristics due to the presence of stores before and after release.
- Control panel loads due to the presence of stores before and after release, using either panel balances or by the integration of measured pressures.
Technical Information
Model Attitude:
- Incidence range: -40° to +40° (dependent on model scale, model tested upright and inverted to accommodate full range)
- Sideslip range: ±25° (model tested at appropriate pitch and roll angles to cover required incidence and sideslip ranges)
- Roll range: ±180°
Model Loads:
- Overall model loads
- Control panel load measurements
- Individual store/multiple store assembly loads
Flow Investigation:
- Use of oilflow visualisation to investigate surface flow phenomena such as separation bubbles and trailing edge separations
Data Acquisition:
- Up to 220 channels measured at up to 10 data points per second
- Measurement of up to 1000 steady-state pressures recorded at up to 10 data points per second
- Use of Pressure-Sensitive Paint to provide whole surface pressure data and component loads
Intake Performance
The intakes of the vehicle (i.e. aircraft, cruise missile etc) deliver the air to the engines. It is important that the air flowing into any engine is well behaved so that the engines operate efficiently and reliably with minimal maintenance. The intakes must retain optimal functionality throughout the operational envelope whatever the speed or attitude of the vehicle.
Why ARA?
ARA has extensive experience in the design and manufacture of bespoke ejectors and engine face rakes together with appropriate intake models and support structures. We also have an on-site intake/duct calibration facility: the Mach Simulation Tank. It can be used to calibrate model engine nacelle/duct/intake thrust and discharge coefficients over the range of pressure ratios experienced in both the Transonic Wind Tunnel and a quiescent environment. This facility may also be used to check the operation of engine face rakes.
Due to the dynamic nature of airflow, a high-speed data acquisition system is also vital. ARA has a bespoke system for the acquisition of high-speed steady-state and dynamic data in real-time during testing. Coupled with real-time data reduction techniques this system provides immediate access to the results of pressure recovery and distortion using the ARA data monitoring system.
A Typical Test
An intake test involves the design and manufacture of a model of an appropriate section of the vehicle to be tested (for an aircraft this might be the forward fuselage only, whilst for a missile it may consist of most of the fuselage and the wings in the appropriate deployed position). Integrated into this model is an ejector – powered by a supply of high-pressure air – which induces the required airflow through the intake. An array of measurement probes, usually in the form of an engine face rake, is used to record the pressures of the airflow as it approaches the position of the engine. Temperatures are also commonly recorded.
Tests are usually undertaken over a range of Mach numbers, mass flows, model attitudes and configurations to provide sufficient information for the determination of total pressure recovery and distortion at the engine face and evaluate an intake or engine compatibility envelope over an appropriate full flight spectrum. The effects of mass flow restrictors positioned within the inlet can also be investigated.
Prior to testing in the wind tunnel, it may be necessary to calibrate the mass flow control system being used. These calibrations are performed in the ARA Mach Simulation Tank.
Technical Information
Data Acquisition
- 64 channel dynamic data acquisition which can record up to 20,000 data points per second
- Measurement of several hundred steady state pressures recorded at up to 10 data points per second
- Real time acquisition of steady state and dynamic data, coupled with real time data reduction techniques
Flow Investigation
- Use of oilflow visualisation to investigate surface flow phenomena such as separation bubbles and trailing edge separations
- Use of high speed pressure transducers to measure unsteady pressures to investigate regions of separated flow
Design and Manufacture
- Design and manufacture of bespoke engines
- Design and manufacture of engine face rake assemblies
- Design and manufacture of intake models, both aircraft and missiles
Installed Store Loads
Installed stores are items like fuel tanks and weapons which are carried by aircraft externally on pylons or in internal weapon bays. The very complicated nature of the airflow around an aircraft and the stores that are attached to it means that wind tunnel tests remain an important part of most store integration programs. Wind tunnel tests provide the large quantities of high-quality data needed to provide store loads throughout the aircraft’s operational envelope with speed and reliability.
For some full models, the use of an internally mounted balance is not possible, i.e. models with full ducted airflow (where there is insufficient room remaining within the model to house a suitable balance). In these cases, the pressure measuring method is utilised to acquire sufficient data to enable loads to be obtained by integrating pressures over the whole model or indeed for individual portions of the model.
Wind tunnel tests provide the high-quality balance or pressure data, depending on the methodology used, needed to determine the loads on the overall model or control panels.
Why ARA?
We have a world-leading capability in the manufacture of stores, support mechanisms and balances completed to the very highest standards including bespoke stores with free-floating seeker heads and with spring-loaded free-floating canards or fins.
ARA is also a world leader in the provision of small panel balances together with many years of experience in the use of pressure measurement techniques for overall models and control panel loads.
Typical Tests
During the wind tunnel test, a sequence of different store configurations together with various control panel settings are tested. Some of the typical measurements made during such a test are listed below:
- Aerodynamic loads on stores, store and launcher assemblies and store and pylon assemblies
- Carriage behaviour of stores mounted in tandem, side-by-side or in configurations
- Effect on adjacent stores due to store release
The measurement of aerodynamic loads on stores and store assemblies is obtained using purpose-built force and moment balances installed inside each store. In addition, the overall loads on the parent aircraft may be measured with a main model balance installed inside the parent aircraft. If this is not possible then extensive pressure plotting measurement techniques are utilised and the resultant data integrated to provide overall loads.
Technical Information
Model Attitude:
- Incidence range: -10° to +40°
- Sideslip range: ±40°
- Roll range: ±180°
Model Loads:
- Overall model loads
- Individual store/multiple store assembly loads
- Control panel load measurements
Flow Investigation:
- Use of oilflow visualisation to investigate surface flow phenomena such as separation bubbles and trailing edge separations
Data Acquisition:
- Up to 220 channels measured at up to 10 data points per second
- Measurement of several hundred steady state pressures recorded at up to 10 data points per second
Isolated Store Loads
Isolated stores are items that are separated from a parent aircraft, they range from fuel tanks and missiles to ejector seats, deployed parachutes and flight refuelling probes. Understanding of the aerodynamic loads on these stores is required for many purposes which depend on the nature of the store; examples include the development of flight control systems for a missile or to ensure the safety of an ejector seat.
Wind tunnels can be used for full scale and near full-scale testing of isolated stores in a controlled environment prior to flight tests. For stores with complicated airflows wind tunnels can provide large quantities of high-quality data to validate numerical simulations.
Why ARA?
ARA offers a one-stop service for customers starting with the design and manufacture of stores 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 stores, support mechanisms and balances completed to the very highest standards including the installation and use of remote control systems that reconfigure stores live during a test. We also have a wide range of supports and balances which are available to our customers.
Technical Information
Model Attitude:
- Extended ranges of incidence and sideslip
- Roll range: ±180°
Load Measurement:
- Overall loads
- Control surface loads using customised panel balances
Data Acquisition:
- Up to 220 channels measured at up to 10 data points per second
- Measurement of several hundred steady state pressures recorded at up to 10 data points per second
