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Models & Hydraulics


RUAG Aviation's aerodynamics department is synonymous for wind tunnel Research, Innovation, Performance and testing.

Wind Tunnel Models

With decades of experience in wind tunnel testing, RUAG Aviation is a perfect partner for the development and manufacture of wind tunnel models. By using a well elaborated wind tunnel model concept, a high level of testing efficiency can be achieved.

Modern development tools and manufacturing machines guarantee highest precision. RUAG Aviation will build your wind tunnel model – with or without engine simulation for subsonic or transonic investigations.

Hydraulic Engines


RUAG has a long history of design and operation of hydraulic systems in its wind tunnels. Hydraulics is used for actuators and to simulate the propulsion for powered wind tunnel models. In this context a number of technologies were developed such as finely controllable hydraulic power stations, balance crossings, and compact high-power, high-rpm hydraulic motors. If handled and operated professionally, hydraulics is a very clean technology with a number of advantages over electric or pneumatic alternatives:

  • Intrinsic heat removal, thus unlimited run times
  • High power density
  • No low temperatures due to gas expansion
  • Inexpensive technology

Although developed for use in wind tunnels, these motors and associated systems are suitable for a wide range of applications, where high power densities, high Speed and accurate control are required.

Hydraulic Motors

The motors are based on piston or in-house gear motor technology, readily scalable to the needed power levels and dimensions. The designs are unique compared to competitor designs with respect to power density (rpm and torque) and diverse options: hollow shaft, specific inlet/outlet topologies (lateral or coaxial), instrumentation, locking mechanism, selectable direction of rotation etc.. The designs allow the simple setup of counter-rotating configurations, by two back-to-back mounted hydraulic motors. Although developed to power wind tunnel models, these motors are suitable for other applications with similar requirements:

  • Restricted volume (high power density)
  • high rpm levels
  • high torque levels
  • stable temperatures
  • coaxial drive system
  • forces and moments to be measured

RUAG Aviation combines these motors with in-house developed rotating six component balances, telemetry and instrumented  carbon model propellers  which need to run within ±10 rpm of the customer required speed over the full rpm envelope and changing torque levels, e.g during pitch and yaw wind tunnel test runs.

Current Engine Portfolio

  • MP10: 37.5 kW, 12‘000 rpm 82 x 110 x 153 mm (w x h x l)
  • MG20: 75 kW, 10‘000 rpm, diameter: 140 mm (optional hollow shaft)
  • MR07: 30‘000 rpm, 18Nm, diameter: 88 mm (optional hollow shaft)
  • MR16: 12'000 rpm, 60Nm

The current portfolio is constantly growing driven by specific model requirements.

M: Hydraulic motor
P: Piston type
G: Conventional gear motor
R: Gear motor, new generation
Number: nominal oil volume displaced per revolution

Hydraulic Balance Crossings

Operating a hydraulic motor on the metric side of a high-precision balance (with the hydraulic power supply on the non-metric side) requires the routing of high-pressure oil at large flow rates and specific temperature over the sensitive balance in a usually very constrained space inside the model. Interference effects on the balance must be kept minimal and correctable by the balance crossing systems.


  • BC42-480-167: e.g. used for powered tests with 1 to 4 MP10 motors
  • BC42-480-777: e.g. used for powered tests with 1 to 4 MP10 motors
  • BC44-800-167: e.g. used for powered tests with 1 to 4 MP20 motors
  • BC22-12-788: e.g. used  for non-stationary automotive “Shaker” tests with 2 hydraulic mini-actuators
  • BC11-1400-300: e.g. used for propeller tests with a 800kW industrial motor
  • BC22-400-767: e.g. used for powered tests with 1 to 2 MP20 motors

BC: Balance crossing

First number:
First digit: Number of independent pressure lines over balance
Second digit: Number of independent return lines over balance

Second number:
Nominal overall volume flow over balance (liters per minute)

Third number:
Nominal balance to be used with this balance crossing

Hydraulic Power Supply

In the RUAG wind tunnel facility four 420 bar/360 litres per minute hydraulic pumps allow the precise rpm control of the motors within the models. The control system is an in-house developed LabView application and allows multiple precise rpm  control by use of motor mounted encoders. The rpm command values can be coupled with wind tunnel speed to prevent overloading of the propeller blades. Safety features, such as rpm and pressure plausibility checks, protect personnel and equipment. Oil temperatures are finely controlled by a massive heat exchanger and heaters to minimize interference effects on nearby instrumentation. A network of pressure, return, and tank lines allow the flexible and safe distribution of high-pressure oil to the wind tunnels and test benches.

A similar hydraulic power supply has recently been delivered by RUAG for use in a high speed wind tunnel.