# The Future of Fluid Power for Aerospace Applications

Jean-Charles Maré

► To cite this version:

Jean-Charles Maré. The Future of Fluid Power for Aerospace Applications. The 19th Scandinavian International Conference on Fluid Power, June 2-4, Linköping, Sweden, University of Linköping, Sweden, Jun 2025, Linköping University, Sweden. hal-05110028

HAL Id: hal-05110028

https://hal.science/hal-05110028v1

Submitted on 12 Jun 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

Public Domain
SAAB factory, 1942

# The Future of Fluid Power for Aerospace Applications

© Internet

INSA
TOULOUSE

Pr Jean-Charles MARE

Institut National des Sciences Appliquées de Toulouse - Institut Clément Ader, France

jean-charles.mare@insa-toulouse.fr

<figure><img src="image_1.png" /></figure>
## Emeritus Professor

Courses in Hydraulic systems, modelling and simulation, actuation for aerospace

Research at Institut Clément Ader, Toulouse, on Embedded actuation systems and components

## Building bridges between public labs and industry (better capture needs, shorten time to market for solutions)

* Training (aircraft makers, systems/components suppliers, engineering companies)

* Lab/industry contracting

**Airbus A380:** pressure relief and priority valves, smart brake servovalve, tripod jacks (production line)

**NH90, M51, A340, A380:** EHSA for ground testbenches (primary flight controls, thrust reversers)

More electric actuation since 2001: primary flight controls, landing gears, engines

* Disseminating knowledge

International standardization for aerospace: SAE A-6 (Aerospace Actuation, control and fluid power systems)

Books and international conferences (e.g. SICFP since 1993!)
**FLUID POWER = using a fluid for power/energy conversion, transmission and control**

## Gaz

<figure><img src="image_2.png" /></figure>

## Liquid
# TRANSPORTING ENERGY WITH A FLUID (e.g. liquid)

## Energy carried by kg of liquid:

* Hydrostatic $P/ρ$ at 200 bar and 850 kg/m³: **23.5 kJ/kg**

<figure><img src="image_3.png" /></figure>

Mechanical end-users

* Hydrokinetic $C^2/2$ at 100 m/s: **5 kJ/kg**

<figure><img src="image_4.png" /></figure>

Very little use

* Gravity $gh$ for 1000 m: **9.8 kJ/kg**

<figure><img src="image_5.png" /></figure>

Not an option for aerospace

* Thermal $C_pΔT$ for 60°C and 1900 J/kg/°: **114 kJ/kg**

<figure><img src="image_6.png" /></figure>

Heat transfer

* Combustion e.g. kerosene @ 25°C: **46 MJ/kg**

<figure><img src="image_7.png" /></figure>

Engines

## Transformations of energy

* Bad efficiency from hydrokinetic to hydrostatic, from heat to mechanical work

* Excellent efficiency from hydrostatic to hydrokinetic

* Good efficiency from mechanical work to heat
1. The context of aerospace applications

2. An example: the status for safety-critical actuation

3. The future of fluid power: needs and opportunities

* A more Systems Engineering view

* Materials and manufacturing processes

* Aerodynamics/fluidics

* Engines

* Health Monitoring

4. Summary
# 1. THE AEROSPACE CONTEXT
TIME SCALE (TYPICAL)

**15 years** from **demonstration** to entry into service
(for an innovative technology)

**30 years** of **production** for a given aircraft model

**30 years** of **service** for the last aircraft produced

<figure><img src="image_8.png" /><figcaption>Airbus A320 First flight (1987)</figcaption></figure>

© Internet

Solutions investigated at lab will still be flying in 70 years!
# MATURITY LEVEL

**Technology Readiness Level (TRL)** measures time to entry into service (comes from NASA)
Fundamental research TRL 1-3. Applied research TRL 4-6. Industrialization TRL 7-9

Industrialization
(not funded for research)

Demonstration
(public funding)

<figure><img src="image_9.png" /></figure>

Actual system “flight proven” through successful mission operations

Actual system completed and “flight qualified” through test and demonstration (Ground or Flight)

System prototype demonstration in a space environment

System/subsystem model or prototype demonstration in a relevant environment (Ground or Space)

Component and/or breadboard validation in relevant environment

Component and/or breadboard validation in laboratory environment

Analytical and experimental critical function and/or characteristic proof-of-concept

Technology concept and/or application formulated

Basic principles observed and reported

<figure><img src="image_10.png" /></figure>

5 to 20 years

© Internet
# VERTICAL DECOMPOSITION (COMMERCIAL AIRCRAFT)

## Air Transport Association (ATA) chapters

<figure><img src="image_11.png" /></figure>

© Internet

Does not facilitate adopting a system/transversal view!
POWER NETWORKS AND USERS

<figure><img src="image_12.png" /></figure>

from S. Hanke PhD Dissertation

<figure><img src="image_13.png" /></figure>
GENERAL NEEDS AND CONSTRAINTS (TYPICAL)

**Oversizing** Sized for worst case (e.g. failure), operated in normal case!

**Harsh environment**
Temperature/pressure, humidity, icing, saline fog
Fire, lightning, vibrations, high-intensity radiated field

**Service life (A/C)**
e.g. 5 000 FH (helicopters of fighters)
e.g. 150000 FH (commercial aircraft)
30-year service

**Reliability (A/C)**
Failure rate leading to catastrophic event <10⁻⁹/FH
Fail safe response to failure → passive or freeze or neutral

**Maturity** >98% availability

**Maintainability** Maintenance support available worldwide

**Production rate** Up to 2 aircraft/day, up to 50 flight control actuators/aircraft

**Certification** International standards/regulations to be met (e.g. SAE, FAA, EASA)
COMPLEXITY

<figure><img src="image_14.png" /></figure>

**Decentralization**
of contracting, design, production, integration,
sales, maintenance (but changing?)

**Cost, delays or performance**
time to market in a competitive environment

**System (of systems)**
air transport/aircraft, design/manufacturing/testing

**Need to consider the whole life**
from needs to withdrawal and recycling
human/social/cultural dimension

**Multidisciplinary dimension**
systems engineering, standards, solid/fluid mechanics, heat transfer,
materials, dynamics and control, power/signal electronics, etc.

e.g. Airbus 380:
* 400 top level requirements (10000 low level), 500 km electric wires
* more than 50 flight control actuators, more than 30000 components to make a wing
* 3 types of data networks (Arinc 429, AFDX, ethernet)
* 4 power networks (1.5 MW installed) for non-propulsive functions
KEY DESIGN DRIVERS

Weight

e.g. hydraulic system 1% of maximum total

Envelope

especially in thin wings

Output power capability

e.g. force/strength

Peak power drawn

Natural dynamics

/closed-loop

Embedded power systems
→ Needs, constraints and design drivers not too different (except level)
from those of earth-moving/forest/off-road applications
Common target: Greener, safer, cheaper
/robustness
Energy consumed during the mission
noise, NOX, CO2, chemicals (REACH)
2. AN EXAMPLE

THE STATUS OF SAFETY-CRITICAL ACTUATION
# ACTUATION: Today's applications (high power/safety critical)

<caption>Engines</caption>

<figure><img src="image_15.png" /><figcaption>Engine guide vanes</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>Vector control</figcaption></figure>

<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /><figcaption>Flight controls</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>Primary</figcaption></figure>

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /><figcaption>Mode conversion</figcaption></figure>

<figure><img src="image_22.png" /><figcaption>Secondary</figcaption></figure>

© Images from Internet

<figure><img src="image_23.png" /><figcaption>Braking</figcaption></figure>

<figure><img src="image_24.png" /><figcaption>Extention/retraction</figcaption></figure>

<figure><img src="image_25.png" /><figcaption>Steering</figcaption></figure>
## Power by pipe

<figure><img src="image_26.png" /></figure>

© JC Maré

## Power-by-wire

<figure><img src="image_27.png" /></figure>

Abandoned
# COMPLEXITY, e.g. B-777 RUDDER

## Main functions

Meter, transform ☐

## Power management functions

Mode selection (active, damped, free)

## Protections

Force (pressure) limit, no regeneration

## (Hydraulic) Technology-induced functions

Anti cavitation, filtration, thermal expansion

Pressure maintaining/isolation

## Complexity comes from additional functions

Not main functions

INSA
TOULOUSE

<figure><img src="image_28.png" /></figure>

Jean-Charles MARE, The Future of Fluid Power for Aerospace Applications, 19th Scandino

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>
## Conventional Electro-Hydraulic ServoActuators (EHSA)

Service up to 350 bar, conventional 2-stage servovalve

Still the only acceptable solution for helicopters primary flight controls

Still used for Ariane 6 thrust vector control (Vulcain 2.1 engine)

<figure><img src="image_31.png" /></figure>

© Internet

Mature, established for decades, little margin of progress:

* Overcenter displacement control for flaps and slats (introduced on A380)

* Zonal hydraulics to remove one over 3 hydraulic power network (introduced on A380)

* Better thermal management through SMA bypass valve (introduced A350)

<figure><img src="image_32.png" /></figure>

© R3ASC

Fly-by-Wire generalized, embedded electronics more common (introduced A350)

<figure><img src="image_33.png" /></figure>

© JC More

<figure><img src="image_34.png" /></figure>

© R3ASC

Very little use of direct-drive servovalves, while introduced late 80's
## ElectroHydrostatic Actuators (EHA)

1st demonstrator early 90's, entry into service 2006 (Airbus A380) 350 bar, up to 22500 daN

Power-by-wire, fixed-displacement pump, variable speed/torque electric drive

Commercial aircraft: removes 1 centralized hydraulic power network

EHA = **backup** channel (A380, A350, A400M, KC390, G650)

Used in **front line** for F-35A fighter (no EHSA for flight controls)

First use for launcher thrust vector control Feb 2025

### Remaining challenge:

* Extend pump life for use in front line in commercial aircrafts

* Avoid periodic refill

<figure><img src="image_35.png" /><figcaption>Airbus A400M (EBHA)</figcaption></figure>

© JC Maré

<figure><img src="image_36.png" /></figure>

© JC Maré

<figure><img src="image_37.png" /><figcaption>F-35A Duplex EHA</figcaption></figure>

© Internet

<caption>Long March 8A
first EHA for TVC</caption>
## ElectroMechanical Actuators (EMA)

- Power-by-wire, hydraulic-less

- Well established for secondary flight controls (jamming accepted)

- Flaps /slats (A380 and later), spoilers (4 over 14, B-787), braking (787, A220) and engine reversers (A380, C919)

- Becoming established for launchers TVC (initiated Vega 2012)

### Challenges:

- Power management functions heavy/bulky

- Thermal management

- Lubrication over 30 years service

- Develop geared rotary actuators and associated A/C integration

<figure><img src="image_38.png" /><figcaption>Starship electric TVC</figcaption></figure>

<figure><img src="image_39.png" /><figcaption>O-duct thrust reverser (C919)</figcaption></figure>

<figure><img src="image_40.png" /><figcaption>B787 Spoiler EMA</figcaption></figure>

<figure><img src="image_41.png" /></figure>
# THE FUTURE OF SAFETY-CRITICAL HIGH-POWER ACTUATION

## Aircraft makers view in 2025

EHSA, EHA, EMA = 3 viable options, sufficiently mature for given applications

## Institutional funding view in 2025

Demonstration (up to TRL6) funded during 30 years

Industry must take over development and maturation towards TRL9

Increasing offer of actuators (3 types) from suppliers, including off-the-shelf and new comers

No more (or almost none) institutional funding except for very specific needs

<figure><img src="image_42.png" /><figcaption>Moog common EHA for launchers</figcaption></figure>

<figure><img src="image_43.png" /><figcaption>Ultra Motion EMA for drones</figcaption></figure>
3. THE FUTURE OF FLUID POWER
- NEEDS AND OPPORTUNITIES -
## 3.1 MORE EFFICIENT TIME-TO-MARKET

<figure><img src="image_44.png" /></figure>

### Engineering systems with models (and their simulation)

Now well established in industry for global/local multidomain approaches (wide commercial SW offer)

Digital twin considered from early phases

But **not a** Model-Based Systems Engineering approach

**MBSE = implementation of the Systems Engineering process, with extensive and continuous use of models**

Needs and requirements engineering well established

Still missing continuity of models between needs, architectures, design, integration and V&V tests
and little acceptance of virtual validation by regulatory agencies (safety-critical applications)

Life-cycle will be run more virtually → Need to improve continuity between models

Applies in particular to Fluid Power technology (multiphysics, multiscale)
## 3.2 OPPORTUNITIES OFFERED BY NEW MATERIALS (1/2)

### Lighter fluid power with fibre-reinforced components

Research presented 2010's IFK. Still **to be matured** for extensive use in aerospace

<figure><img src="image_45.png" /><figcaption>Albany hyd. accumulator</figcaption></figure>

### Additive manufacturing of fluid power components

Application to aerospace investigated since 2018

Main barrier to adoption: **traceability of sourcing and process, fluid pollution**

<figure><img src="image_46.png" /><figcaption>ALM body spoiler actuator
Flight tested 2018 (Liebherr)</figcaption></figure>

### Shape Memory Alloy

Attractive for low-dynamic applications

In use on A350 (2013) for thermal control of hydraulic system

Main barrier to adoption: **low speed and hysteresis effect**

<figure><img src="image_47.png" /><figcaption>N2 flow control for inerting
Tested 2025 (Equipaero)</figcaption></figure>
## 3.2 OPPORTUNITIES OFFERED BY NEW MATERIALS (2/2)

### Piezo actuation

- Studied for driving the pilot stage of servovalves (started mid 80's)

- Availability of new ceramics (greater stroke, lower voltage)

- Main barrier to adoption: **stroke too low for power stage** or **still requires a hydraulic first stage**

<figure><img src="image_48.png" /><figcaption>Fuel metering for hydrogen-powered aircraft, A. Plummer, D. Adeyemi, D. Burden, 10th R3ASC (2025)</figcaption></figure>

### Challenges to meet the REACH European regulation* (risks posed by PFAS chemicals)

- Aerospace hydraulic fluid: **no alternative yet** to anti-erosion/anti-corrosion additives

- Coating/surface treatment, seals (fluoropolymers): **no alternative available yet**

→ **restrictions: delayed application of regulation**

<figure><img src="image_49.png" /></figure>

### High demand for new solutions for aerospace products

### Leading to a full re-qualification/re-certification
## 3.3 MORE EFFICIENT AERODYNAMICS AND PNEUMATICS

### New wing movables call for new actuators

#### Folding wingtip (B777X, hydraulic)

#### Adaptive dropped hinge flaps (A350, hydraulic)

#### Morphing winglet (CleanSky, Leonardo 2017, electric)

<figure><img src="image_50.png" /><figcaption>#### ADHF A350 (hydraulic)</figcaption></figure>

<figure><img src="image_51.png" /><figcaption>#### Morphing winglet (electric)</figcaption></figure>

<figure><img src="image_52.png" /></figure>
e.g. Pulsed Jet Actuators (passive fluidic oscillator)

Active flow control to avoid boundary layer detachment (mini scale fluidics)

<figure><img src="image_53.png" /></figure>

Design and evaluation of pulsed jet actuators network for active flow control on NACA-4412 profile, G..L. Quesada, Lucien Baldas, S. Orieux, A. Batikh, N. Mazellier, 3AF conference 2022

Cooling of electronic/electric devices (micro scale fluidics)

<figure><img src="image_54.png" /></figure>

Fabrication of high-frequency microfluidic oscillators with integrated thermal instrumentation, G. Saliba, T. Camps, V. Raimbault, L. Baldas, Sensors and Actuators, 2024

<figure><img src="image_55.png" /></figure>
## 3.4 ENGINES

**Fuel:** from tank to combustion chamber, a **fluid power system** with reservoir, distribution lines, flow control, limiters, heat exchangers, etc.

**Oxidant (e.g. turbines):** flow control (e.g. inlet guide vane actuator)

**Cannot be avoided in combustion engines**

### Conventional gas turbines

well established and mature for turbines (kerosene, natural gas, etc.)
e.g. to reduce combustion residues and emissions

### Hydrogen power systems

at a low level (production, distribution, etc.)
pressure, sealing, risks, etc.

Another essential fluid power system of aeroturbines. Not just an enabling system!

### Fuel system of aeroturbine

<figure><img src="image_56.png" /></figure>

A lot of research work needed
Hard to take it over without close collaboration with industry

<figure><img src="image_57.png" /></figure>

### Aeroturbine lubrication system

<figure><img src="image_58.png" /></figure>
## 3.5 HEALTH MONITORING

### Health monitoring

* **Usage monitoring**

Provides accurate information on effective service

→ better utilization (improved procedures) and more efficient sizing

* **Diagnostic**

Facilitates troubleshooting, reduces mean time to repair

* **Prognostic**

Predicts Remaining Useful Life

<figure><img src="image_59.png" /></figure>

<figure><img src="image_60.png" /></figure>

### Maintenance

On-time

Product life, reduced costs, better availability

Science provides models for HM of fluid power systems
Still a lack of a priori knowledge for modelling fault-to-failure mechanisms

### Prediction

Predicted at nangar/onboard, onboard at parking/in-flight continuous

Distributed (equipment level)/centralized (aircraft level)
<figure><img src="image_61.png" /></figure>

## The future of Fluid Power in Aerospace

**Hydraulically powered actuators will still be flying in 70 years, with partial elimination of power networks**
need increased service life, cheaper and lighter, maintenance and training
... but EMAs use spreads and extends

**New engines still need fuel and oxidant supply and metering**
challenging, little background except for space applications → a lot of research opportunities

**Efficient aerodynamics, mini/micro pneumatics**
promising concepts, e.g. active control of boundary layer & cooling of electric equipment (passive pneumatics)

## Needs to

* Improve the design **process** with a SE view (automated architectures generation, sizing, virtual verification, etc.) and: develop gateways for models and simulation between life phases

* Increase **scientific** knowledge in materials, tribology/lubrication, heat transfer, mini/micro fluidics

* Increase **technical** knowledge and know-how to move new concepts towards aerospace market
<figure><img src="image_62.png" /></figure>

Well established attitude:

- dreaming of the advantages of a new solution...

but ignoring (or having not yet discovered) its drawbacks

- no longer accept the drawbacks of the current solution...

but not remembering (or putting aside) its natural advantages

**Applies very well to electrics vs. hydraulics!**

<figure><img src="image_63.png" /></figure>

At a given time (maturity) and in a given application context, better **to combine the best of each**

**Research and development in Fluid Power:**

- consider **science and technology to feed each other** (fluid power needs both!)

- not to forget the aerospace **context** (safety critical, certification, time scale)

- enable **real validation** with close collaboration with industry
  (cost of demonstrators manufacturing and test environment)

**No clear view on the contribution of Artificial Intelligence to innovation**
<figure><img src="image_64.png" /></figure>

THANKS FOR LISTENING!

Any question?

<figure><img src="image_65.png" /><figcaption>SAAB Gripen (1988), first fighter with DDV for primary flight control actuators</figcaption></figure>