International Journal of Innovative and Emerging Research in Engineering
Volume 2, Issue 11, 2015
Available online at www.ijiere.com
International Journal of Innovative and Emerging
Research in Engineering
e-ISSN: 2394 – 3343
p-ISSN: 2394 – 5494
Design of Hydraulic Circuit and Hydraulic Loss Calculation
for Pre-Installation Check of Landing Gear Jack Accessories
Narendra Rathore
National Institute of Technology Surathkal, NH 66, Srinivasa Nagar, Mangalore, India 575025.
ABSTRACT:
Universal test rig is the testing bay unit where we can test pressure and flow proof for line replacement units.
This paper is about the design of test hydraulic circuit for the various pre-installation checks. Here the first
challenge is to design hydraulic circuit for pre installation check of the different landing gear jack accessories.
Here we have discussed about how the pre-installation check is work for landing gear accessories. Hydraulic
circuit is the important part to test it. An effective design of hydraulic circuit is important to minimize the head
losses. Based on different design parameter hydraulic circuit are designed and simulated over the automation
studio. During the pre-installation check there is significant head loss occurs. In this research there is calculation
of head loss by analytical method as well as by automation studio. Both results have been compared here and the
variations in the pressure loss results are less than 8%.
Keywords: Automation studio, analytical method, landing gear jack accessories, hydraulic circuit, preinstallation check, head loss
I. INTRODUCTION
In the servicing of aircraft in hangars or on flight decks extreme difficulty has attended the replacement of wheels or
tires due to the compact construction of wheel hubs and axles used with retractable landing gear. The hubs and axles are
necessarily set close to the rim of the wheels and with the large size tires now in use on aircraft it has been found difficult
to locate a vertically lifting device beneath the axle stub. The large size tires when partially or totally deflated spread out
beneath the wheel to a degree which prohibits the use of a hydraulic jack beneath the jacking point on the hub or axle.
Its object to provide a hydraulic lifting device which permits vertical lift of an aircraft wheel despite the collapsed and
spread out tire carcass, hydraulic jack having an extremely low compressed height and a high-extended height, hydraulic
jack that is readily portable and has wheels which without adjusting or latching to inoperative position do not bear any of
the lift load while the jack is in position.
A further object of the invention is to provide a hydraulic jack (Fig 1) [1] of inexpensive construction and one capable
of lifting large loads as found aboard aircraft carriers.
Figure 1 Main undercarriage door jack assembly
A. Nose Under carriage retraction jack
Nose gear jacks (Fig 2) [1] pull the nose gear down to the extended position. One end of the jack is attached to the
structural wall of the nose wheel well. The other end is attached to the hinged nose gear that pivots into the extended
position. Nose gear down lock engagement is provided by the over center position of the hinged two part truss brace with
integrated down lock actuator and spring. The forward sections of the truss brace unfold as the nose gear extends. As the
truss brace unfolds, it forces open the “C” shaped suitcase springs. When the nose gear is fully extended, a hydraulic down
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International Journal of Innovative and Emerging Research in Engineering
Volume 2, Issue 11, 2015
lock actuator and linkage pulls the truss brace slightly over center at the hinge point. The truss brace hinge is also held in
the over center position by the energy of the “C” shaped suitcase springs that close slightly in the over center position.
The springs are necessary to maintain the nose gear in the down locked position without hydraulic pressure. Once
locked into the over center position, hydraulic pressure on the retract side of the down lock actuator is required to push the
truss brace past the over center position and overcome spring pressure. The truss brace hinge has a provision for inserting
a down lock pin to secure the nose gear in the extended position. Nose gear down lock engagement is provided by the over
center position of the hinged two part truss brace with integrated down lock actuator and spring. The forward and aft
sections of the truss brace unfold as the nose gear extends. As the truss brace unfolds, it forces open the “C” shaped suitcase
springs. When the nose gear is fully extended, a hydraulic down lock actuator and linkage pulls the truss brace slightly
over center at the hinge point. The truss brace hinge is also held in the over center position by the energy of the “C” shaped
suitcase springs that close slightly in the over center position. The springs are necessary to maintain the nose gear in the
down locked position without hydraulic pressure. Once locked into the over center position, hydraulic pressure on the
retract side of the down lock actuator is required to push the truss brace past the over center position and overcome spring
pressure. The truss brace hinge has a provision for inserting a down lock pin to secure the nose gear in the extended
position.
Figure 2 Nose under carriage jack assembly
B. Under carriage door jacks
Undercarriage door jacks are fitted in to the doors of aircraft along with the shuttle valve higher issue assembled with
it. All the jacks extend to open the under carriage doors. The extension ports are fitted with shuttle valve higher issues
having fittings as per ISO 7321 to suit 6 dia pipes. The retraction ports have MJ 12 x 1.25 ports to suit fitting as per ISO
7321 for 6 dia pipe. Main u/c fwd. door jacks and nose u/c door jack are fitted with micro switch with three independent
signals to sense the extended position of the jacks. The end fittings are eye ends on cylinder side and fork ends on piston
side to suit pin diameters of 15 mm for main u/c door jacks and 12 mm for nose u/c door jack. Each unit shall be subjected
to the PI checks before installation on the aircraft. The PI checks shall be carried out with a test set up using a hydraulic
power source with the specified fluid (MIL-H-5606H or equivalent) and pressure (280 bars). Cleanliness of fluid in the
test rig shall be equal to that specified for the aircraft [1].
It is to be ensured that the items received for PI checks are already tagged after production acceptance test.
Door jacks are of three types:
 Main under carriage door jack aft
 Main under carriage door jack fwd
 Nose under carriage door jack
C. Door jacks and main under carriage jack Hydraulic circuit
The following is the design parameters for the under-carriage and door jacks;
Table 1 Design parameters of door jacks [1]
Si
no
Part
description
Closed
length(mm)
Extended
length(mm)
Stroke(mm)
Cylinder
area(cm2)
Annulus
area(cm2)
1
Main u/c door
jack aft
256±5
356±5
100±1
44.25
22.16
12
2
Main u/c door
jack fwd
3
Nose u/c door
jack
4
Main u/c jack
assembly (LH)
Main u/c jack
assembly (LH)
Nose u/c jack
retraction
assembly
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International Journal of Innovative and Emerging Research in Engineering
Volume 2, Issue 11, 2015
276±5
400±5
124±1
44.25
22.16
290±5
431±5
141±1440 ±
0.7
37.89
18.99
375.15±0.7
514.2
139.05±7
31.67
26.6
1156.8
440 ± 0.7
34.73
21.38
716.8
II. PRE INSTALLATION TEST
For modelling and simulating the current circuit in hand, we use automation studio version 5.6. The circuit in hand is a
simple one with jacks connected to it. It is important to check the behaviour of the jacks. The behaviour of the jacks
includes the piston pressure, stroke, the time taken for the stroke, rod position, velocity and acceleration. This helps to get
the idea of the behaviour of the jacks and take up any corrections if necessary [1].
Figure 3 Simulated circuit of door jacks
Given below graph (Fig 4) is the variation of the pressure in the pressure during the movement of the piston in the jack.
During the end condition of the extension and retraction of the jack the pressure will be high but during movement in
between the pressure will be remain same so in graph (Fig 5) there is pressure on the rod side and piston side during the
movement of the piston.
Similarly in second graph we can see that there will be pressure difference during movement of the jacks. That pressure
difference can be treated as the head loss in that particular test case and hence during the test we got a graph which shows
the head loss or pressure loss in the hydraulic circuit.
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Figure 4 Plotter for pressure on piston and rod side for main u/c door Aft
Figure 5 Main u/c door Aft head loss
After simulation we got following graphs. Given below graph is the variation of the pressure in the pressure during the
movement of the piston in the jack. During the end condition of the extension and retraction of the jack the pressure will
be high but during movement in between the pressure will be remain same so in graph (Fig 6) there is pressure on the rod
side and piston side during the movement of the piston.
After calculating the pressure difference we got following graphs. In graph (Fig 7) we can see that there will be pressure
difference during movement of the jacks. That pressure difference can be treated as the head loss in that particular test case
and hence during the test we got a graph which shows the head loss or pressure loss in the hydraulic circuit.
Figure 6 Plotter for pressure on piston side and rod side for u/c door jack Fwd
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International Journal of Innovative and Emerging Research in Engineering
Volume 2, Issue 11, 2015
Figure 7 Under carriage door jack Fwd head loss
Given below graph is the variation of the pressure in the pressure during the movement of the piston in the jack. During
the end condition of the extension and retraction of the jack the pressure will be high but during movement in between the
pressure will be remain same so in graph (Fig 8) there is pressure on the rod side and piston side during the movement of
the piston.
Similarly in graph (Fig 9) we can see that there will be pressure difference during movement of the jacks. That pressure
difference can be treated as the head loss in that particular test case and hence during the test we got a graph which shows
the head loss or pressure loss in the hydraulic circuit.
Figure 8 Pressure plotter for rod and piston side for nose u/c door jack
Figure 9 Nose under carriage door jack head loss
As per the design parameters of the different jacks we have simulated the hydraulic circuit and we got following graphs.
Given below graph is the variation of the pressure in the pressure during the movement of the piston in the jack. During
the end condition of the extension and retraction of the jack the pressure will be high but during movement in between the
pressure will be remain same so in graph (Fig 10) there is pressure on the rod side and piston side during the movement of
the piston.
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International Journal of Innovative and Emerging Research in Engineering
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Similarly in graph (Fig 11) we can see that there will be pressure difference during movement of the jacks. That pressure
difference can be treated as the head loss in that particular test case and hence during the test we got a graph which shows
the head loss or pressure loss in the hydraulic circuit.
Figure 10 Pressure at piston and rod side for main u/c retraction jack
Figure 11 Main under carriage retraction jack head loss
The behavior of the jacks and valves can be mapped on to the plots. Many properties like linear position, velocity,
acceleration, pressure and flow properties on either side of the piston. Below circuit is for simulation of the Nose gear
Jack for pre installation check [1].
Figure 12 Simulated hydraulic PI test circuit for nose under carriage jack assembly
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International Journal of Innovative and Emerging Research in Engineering
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Given below graph is the variation of the pressure in the pressure during the movement of the piston in the jack. During
the end condition of the extension and retraction of the jack the pressure will be high but during movement in between the
pressure will be remain same so in graph (Fig 13) there is pressure on the rod side and piston side during the movement of
the piston.
In second graph (Fig 14) we can see that there will be pressure difference during movement of the jacks. That pressure
difference can be treated as the head loss in that particular test case and hence during the test we got a graph which shows
the head loss or pressure loss in the hydraulic circuit.
Figure 13 Pressure head loss for nose under carriage main jack
Figure 14 Pressure at piston and rod side for nose under carriage main jack
III. PLC CIRCUIT FOR 4/2 WAY DIRECTION CONTROL VALVE
This below given circuit (figure 15) is the PLC circuit on time based movement of the jack assembly; this will control
the movement of direction of the direction control valve which will direct the flow of fluid into the jack assembly. We
used here delay on timer for the halting of the piston movement at one complete cycle. So we are using the given below
PLC circuit.
Figure 15 PLC circuit for controlling jack movement
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The PLC cards are connected to the proximity switches which are normally open. When simulation started the proximity
switches close momentarily which activates the coils. The proximity switches are linked to the proximity sensors which
are placed on the actuators. When the coils are activated, the solenoids are activated. These solenoids are linked to the
solenoid of the directional valve. The activation of solenoids causes the directional valve to switch to the first position
which causes the flow and hence the actuation. When the actuator extends to 100% position, the second proximity sensor
is activated. This causes the second proximity switch to momentarily close. At the 100% extension we wish to hold the
actuator for 3 seconds. For this we need to employ the time delay in the circuit. The time delay is set to 3 seconds. After
delay the control is transferred to the next set where the second set of the solenoids are activated. This causes the directional
valve to shift to the third position and causes the actuation to be reversed. The flow is reversed and the actuator comes
back to zero position. At zero position, the first proximity sensor is activated again. This leads to the continuation of the
cycle.
IV. ANALYTICAL HEAD LOSS CALCULATION
Head loss due to the frictional resistance of fluid flow within a hydraulic pipeline system is represented by any
decrease in pressure. The pressure loss is determined according to the well-known Darcy Weisbach equation [1] [5],
[10]:
HL =
f
2Dg
𝐿V2
f = friction factor (dimensionless),
L = length of pipe,
D = pipe inside diameter,
v = avg. fluid velocity,
g = Acceleration due to gravity.
The fluid flow through a pipe can be either smooth or rough, depending on flow conditions. Various factors determine
the nature of flow. In principle, the flow can be stated as either laminar flow, i.e. steady, smooth flow, or turbulent flow,
i.e. the flow is disturbed [6]. From a practical point of view, the Reynolds number indicates if a flow is laminar or
turbulent.
In the case of turbulent flow, the friction factor depends on the Reynolds number, as in the case of laminar flow as well
as on the coefficient of the relative roughness – the relationship between the absolute roughness of the pipe’s inner wall
surface in contact with the fluid, and the diameter of the pipe (∈/𝐷), bearing in mind that the pipe can be either perform
as a smooth, rough or somewhere in-between – liminal (transitional) [5].
Several types of empirical equations that can help to determine the friction factor can be found in literature. Some
fairly useful ones are given below [1], [5], [10], [3].
a) Laminar flow area at Re < 2000:
f = 64 / Re
b) Turbulent flow area within the smooth pipe of a hydraulic system (according to [5],[10] ) at Re > 4000:
f =0.3164 / Re0.25
c) Transitional flow type area within range 2000 < Re < 4000:
f = 3.9×10-6 ×Re + 0.0242
And if the flow in the circuit is turbulent that means Reynolds Number (Re)>4000 it means the fluid flow is turbulent
flow, so to find the friction factor of the pipe we have to follow the Moody chart [5], [10] according to that we have to plot
Re and relative roughness (∈/𝐷), and after plotting their values we will get following friction factor f (table 2) [1],[4] .
Where ∈ absolute roughness and D is internal diameter of pipe.
Table 2 Resistance factor 'k' for various fittings [1], [4], [2]
Circuit element
T Joint
ball Valve (wide open)
K factor
1.8
0.19
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3/4 open
0.90
1/2 open
4.50
1/4 open
24.0
90˚ Elbow
0.75
45˚ Elbow
0.42
Check valve
4.0
Inline filter
10.0
Manifold
1.80
Direction valve
5.0
Entrance losses – inward projection
1.0
Square edge inlet
0.50
Chamfered inlet
0.25
Rounded inlet
0.04 - 0.50
A. RESULTS AND DISCUSSION
Here we are comparing the pressure loss calculated manually by above given formulae and the pressure loss measured
by the Automation studio. This is particularly used for the circuit simulation and analysis. The differential pressure
appeared during the various hydraulic circuit simulations. We have calculated the pressure loss in the circuit at different
flow condition for different test of the line replacement units.
B. HEAD LOSS CALCULATION
Based on the type of line replacement units we setup the experimental analysis in the automation studio as well as
analytically calculation [1]. The results are quite impressive that validate the methods of analysis used. The following head
losses (Refer table 3) are results of different test hydraulic circuits for the test of particular LRU during pre-installation
checkup.
Table 3 Comparison of hydraulic loss in different pre installation test [1]
Line replacement Unit
Nose u/c jack retraction assembly
Main u/c jack retraction assembly
Main under carriage door jack Aft
Main under carriage door jack fwd
Nose under carriage door jack
Pressure loss (bar)
analytically
calculated
13.6
8.5
2.1
2.2
2.1
Pressure loss (bar)
automation studio
Flow
(LPM)
12
8
1.89
2.1
1.9
148.2
48.9
11.7
14.4
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V. CONCLUSIONS
This test rig is proposed for the testing of line replacement units. Based on the requirement of the pre installation check
of test element we have designed test rig stand and power pack. Also designed mountings and fixtures for holding the test
elements ie LRUs. The test rig equipped with hydraulic pipes and hoses, flow meter, shut off valve as well as quick
disconnect couplers. For jack assemblies we have designed LM guide ways, slider and fixture and test block. The preinstallation test procedure for line replacement units also require a power pack that is capable of supplying fluid
continuously with required pressure and flow rate. The power pack requires a set of motors and pumps and several other
components that effectively deliver the fluid. The components must be selected based on the power and flow rate. All the
components are selected based on the suitable calculations and the power pack is built. In designed test rig we are
successfully capable of test for all line replacement units.
Using both analytical and virtual methods the head loss in every case has been calculated and being compared. The
variation in both analytically and virtual experimental results are upto 5-10% only. Head loss in the hydraulic circuit will
guide us to compensate the head loss during the pre-installation check. Automation studio does not consider the fitting
losses and initial head.
ACKNOWLEDGMENT
I am very thankful to my project guide who supported me throughout that period. I acknowledge that the work I have
done during my post-graduation. This will definitely going to help me for my career. During the project I have learnt
immense of practical and theoretical things which are really important to me. Once again I am very thankful to those who
guided me during writing thesis and research paper on my work.
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REFERENCES
[1] Narendra Rathore and M R Ramesh, “Design of universal test rig and virtual experimentation of hydraulic circuit for
testing of line replacement units” IJSER, Vol 6, pp 1326-1321, 2015.
[2] Taher Salah and Saad Kassem, “Development and manufacture of a universal hydraulic test rig for proportional, servo
valves and cylinders”, IEEE explore, 2012.
[3] Machine tool design hand book, Central Manufacturing Technology Institute, Bengaluru, Edition 2001.
[4] Robert W Fox, Alan T Mcdonald and Philip J Pritchart, Introduction to fluid mechanics, John Wiley & Sons, Inc. 8th
edition.
[5] IE Idel’ Chik, Handbook of Hydraulic Resistance, 2nd edition Springer, Washington, 1986.
[6] Herbert E. Merritt, hydraulic control systems, John Wiley & Sons, Jan-1967.
[7] Vladimir Savic, “Determination of pressure losses in hydraulic pipeline systems by considering temperature and
pressure”, Journal of Mechanical Engineering, 2009.
[8] Military specification, “Test rig hydraulic system components”, USA Defence department, June1985.
[9] Hafeezur Rahman.A, SantoshP Sugate and S. Ganesan, ”Evolution of an Overhaul Methodology for a High Speed
Combat Aircraft Gearbox”, IOSR-JMCE, 2015.
[10] Tudorica Daniela, “Pressure drop in the flow of oil products through pipelines – application for hydraulic calculation”,
World appl. programming, Vol (4), No (5), May, 2014. pp. 140-145.
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