Jan Holnicki-Szulc

Institute of Fundametal Technological Research,Polish Academy of Sciences

Swietokrzyska 21, 00-049 Warsaw, Polande-mail: holnicki@ippt.gov.pl, web page: http://smart.ippt.gov.pl

Smart Technologies

for Adaptive Landing Gears

Presentation outline:

• Adaptive Landing Gears for Improved Impact Absorption• Adaptive pneumatic landing gear for UAV application• Adaptive flow control based airbags

FP6-2002-Aero-1, 2003-2006

Adaptive Landing Gearsfor Improved Impact Absorption

to absorb the kinetic energyassociated with airplane verticalvelocity

to provide elastic suspension anddamping during taxiing and groundmaneouvres

The main functions of the airplane landing gear are:

The typical design of theoleo-pneumatic shock absorber:

Levered trailing armgear

Cantilever gear

Gas

Oil

Dampingelement

Piston

Cylinder

Wheel

Shock absorber

Main fitting

Evolution of total ground load for different landing conditions:

10000

0

5000

1.0 1.1 1.2 1.3 1.4Time [s]

Fz [daN] Angle = 12 deg

Angle = 0 deg

According to the regulations (e.g. FAR25) the landing gear is designed forthe appropriately chosen limit load case (e.g. vertical velocity equal to3,05m/s)

Statistically, the touch-down velocity during most of the typical landingsdoes not approach this limit

Shock absorber’s efficiency E :

max max

WEF L

0

( )L

W F x dx

W – energy dissipationFmax – maximal damping forceLmax – maximal stroke

Adaptive Landing Gear [ALG]

• Magnetorheological Fluid

• Piezo-valve

Real-time adjustment of LG characteristcs:

Sensing and control:• Position and velocity measurement system

• Real-time ALG controller

Ultrasonic distance and velocitymeasurement

Transmitter

Receiver

Generated ultrasonic wave

Reflected wave

Measured distance H

GT RT T

Return-time estimation

Level of discrimination

Other, more advanced methods

Multi-level detection with assumed thresholds

Zero-crossing backbacktracking with time window

Phase angle observation

Matched filters

Adaptive shock absorber

MRF – Magnetorheological Fluid ALG

cylinder

piston

coil

orificeMRFfluid

magnetic head

Gas

Liquid

Dampingelement

Distribution of the magnetic field in the magnetic head:

Gas

Liquid

Dampingelement

PPA 80XL

Adaptive shock absorberPiezo-actuator based ALG

Full scale laboratory tests• Experimental stand for dynamic testing at the Institute of Aviation

Fz(t) - vertical ground loads

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

0 0.05 0.1 0.15 0.2 0.25 0.3

time [s]

Fz [daN]

PZ105

PZ107

PZ155

PZ172

Pz105 – low touch-down kinetic energy, no controlPz155 – low touch-down kinetic energy, optimal controlPz107 – high touch-down kinetic energy, no controlPz172 – high touch-down kinetic energy, optimal control

No control

Optimal control

Evolution of total vertical ground load

time [s]

Fz [daN]

Change of vertical touch-down force in time and corresponding controlsignal governing the dynamics of adaptive landing gear

Fz [daN]

Time [s]

U [V]

Advanced modelling, design, manufacturing and field tests- Instiute of Aviation

Flight tests PZL Mielec – M28 „Skytruck”

Adaptive pneumatic landing gearfor UAV application

(national project: Aeronautica Integra)

Scheme of the proposed active system

Main working principles:

• piezoelectric valve (responsetime: 2 ms) controls flow of thegas between lower and upperchamber of the cylinder

• the measurements from bothpressure sensors are utilized tokeep constant level of pressuregradient between upper andlower chamber

Pressure sensor 2

Controlunit Decompressed

chamber

Compressedchamber

Pressure sensor 1

Piezoelectricvalve

1. Equations of equilibrium

3. Mass flow rate definition

4. Energy balance

2. Ideal gas law

M2p1(t)

p2(t)

M1

u2(t)

V(0)=V0

u1(t)

Passive pneumatic damper

ExperimentNumerical model

Impacting mass

Pneumatic cylinder

Pressure sensor

Displacement sensor

Pressure sensor

Accelerometers

m = 27kg, h = 40 cm p0 = 3 atm; valve fully opened

a2 [ms-2] V2 [ms-1]

p2-p1 [Pa] Fk [N]t [s]

t [s]

t [s]

t [s]

Experimental and numerical results

Comparison of the energy dissipation obtained forvarious initial pressure and valve openings

m = 27kg, h = 40 cm

p0 = 3 atm, s = 0…150 ump0 = 1 atm, s = 0…150 um

u [m] u [m]

p2-p1 [Pa] p2-p1 [Pa]

Active system equipped with adaptive valve

Piezoelectric stacks

Displacementattenuator

valvecompartment

Comparison of forces generated by the absorber insemi-active and active system

p2-p1 [Pa]

p2-p1 [Pa]

u [m]

t [s]

m = 27kg, h = 40 cm, p0 = 3 atm

sensorp2

Objectp1-p2

sensorp1

ControlVelocity

Mass

Disturbances

Final laboratory tests of optimal shock absorber

m = 10kg, h = 65 cm

Semi-active systempmax = 0,85atm

Active systempmax = 0,64atm

p [Pa]p [Pa]

t [s] t [s]

semi-controlled pfully controlled p

Ultrasonic distance and velocitymeasurement

AVI-3

20 40 6030

210

60240

90 270120

300

150

330

180

0Recognition of the landing conditions in the last phasebefore touchdown can be regarded as an important factor ofaircaft’s safety.

AVI-3 provides short-range single-point measurements ofthe sink speed and height of an aircraft by means of set ofultrasonic sensors. This technology can be succesufflyapplied for small aircrafts (including UAV) in applicationsrelated to landing monitoring (e.g. during pilot’s training) orproviding initial data input for systems of adaptive landinggears.

Establishing full 3D position of the aircraft with respect tothe surface of the landing and its vertical kinetic energy ispossible by combinig three AVI-3 units.

Main features:

• microprocessor-based data processing

• low power consumption

• miniature size

• analogue and digital output interface

• water-resistant ultrasonic heads with wide directivity

• high background acoustic noise immunity

Adaptive flow control based airbags(patent pending)

• The system of external airbags allows for significantincrease of the structure crashworthiness and safety of thepassengers

NASA OrionNASA Orion

Motivation for the research:

• Only several airbag systems applied in passengercars are equipped with exhaust valves nowadays

• Additional controllable exhaust valves increasethe airbag effectiveness and allow to adjust theairbag characteristics to the actual impactscenario

• The airbags are rarely used in other applications than automotive

Recent applications of the passive airbags

NASA Mars Pathfinder surroundedby multi-chamber airbag

Polish helicopter Anakonda equippedwith airbags for landing on water

Israelian BELL 216 equipped withairbags for emergency landing

KAFLOAT –system protecting theship against sinking

Flow control based adaptive airbags

• Adaptability:

- airbags inflation adjusted to landing velocity, direction and he licopter mass- substantial gas release by fabric leakage as in typical airbag- additional controlled release of pressure using High Performance Valves (HPV)

• System of sensors:- ultrasound velocity sensor- pressure sensors inside airbags- accelerometers inside helicopter chassis

Control objectives:

• Mitigation of acceleration acting on passengers

• Alleviation of forces acting on helicopter and stresses arising in undercarriage

• Stabilization of the helicopter during touch-down

Estimation of required parameters:

- total dimensions of the airbags: 4 x 1m 2 x 0.5m

- constant pressure in the airbags necessary to avoid direct coll ision with ground

for velocity 10m/s: 1.25 atm overpressure

Simplified modelling of emergency landingNumerical model:

- total mass: 5000 kg; impact velocity: 5m/s to 10m/s (free fall ing from 5,1 m)- 2D model: falling helicopter modelled by beam elements and poin t masses- 3D model: helicopter undercarriage (shell elem.), airbags (memb rane elem.)

p(t) p(t)

M=5000kg

V0=10m/s

Minimisation of falling object acceleration• Measured response: acceleration of the concentrated mass

located in the middle of the falling object

Controlled

gas release

• Simplified simulation of the landing

• Fast release of pressure during first stage

• Mitigation of the following rebounds

Pressure [N/m2]

• Optimal initial pressure in closed airbag: p 0=0.4atm. Max. stress: 397MPa

• Optimal airbag with gas release: p0=0.9atm, discharge coefficient providing

utilisation of whole airbag stroke. Max stress: 290MPa

• Fully adaptive system: constant pressure during impact p=1. 1 atm, Stress: 263MPa

• Measured response: maximal stress in the lower beamof the falling object

Mass of the gas [kg]

Minimisation of stresses in helicopter undercarriage

Stress [Pa]