Optimization of Turn Around SortieTime of aTypical Fighter Aircraft by Enhancement of Brake System Heat Dissipation through Forced Convection

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The brake unit generates heat energy through frictional force between the brake discs, which then needs to be dissipated quickly to the brake system components and the surrounding environment. The heat energy from the brake discs is dissipated through various modes of heat transfer, including conduction, convection, and radiation. A faster heat dissipation rate to the environment helps to reduce the disc temperature, ensuring that the aircraft is available for the next activity. Multiple authors have conducted research to improve heat dissipation from aircraft brake units through various methodologies. This paper outlines an approach that has been explored to optimize the Turn Around Sortie (TRS) time of a typical fighter aircraft. The paper evaluates the pros and cons of all modes of heat transfer and provides details of the work carried out to improve heat dissipation through forced convection. Brakes Systems TRS Fighter Aircraft Heat Transfer and RTO Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. INTRODUCTION Landing gear system of an aircraft is one of the important safety critical systems which support the entire aircraft on ground, reduce the impact load on aircraft during landing and help in ground manoeuvring of aircraft. Wheel & brake system is one of the subsystems of landing gear system which decelerate the aircraft during taxiing, landing and in Rejected Take Off (RTO) condition. Kinetic energy of the moving aircraft is converted into heat energy during brake application. Quantum of kinetic energy handled by an aircraft brake system is tremendously high due to the heavy weight of the aircraft and higher take-off and landing speeds. Heat energy generated in the brake discs has to be dissipated to the ambient at the earliest since the residual heat energy in the brake discs causes certain operational restrictions. One such critical operational requirement is Turn Around Sortie (TRS) time of the aircraft. This is the time available to prepare the aircraft for the next mission subsequent to a normal landing. Any aircraft, either commercial or military aircraft, always should have a short TRS time for enhanced flight operations. However, one of the constraints to achievingthis is the time required to cool the brake discs to acceptable levels. Brake disc temperature before take-off has to be maintained at an acceptable level to absorb sufficient brake energy in case of an RTO and bring the aircraft to full stop satisfactorily. This is considering the possibility of every take-off leading to an RTO. This paper initially outlines the brake system and the TRS time requirement of a typical fighter aircraft. Subsequently, it discusses in detail the methodology of reducing the brake disc temperature through various modes of heat transfer to cater for the TRS time. The data from the flight and brake dynamometer trial has been presented. 2. AIRCRAFT BRAKE SYSTEM Brakes are typically positioned within the wheel assembly of the Main Landing Gear (MLG) to generate maximum drag force, especially since the majority of the aircraft’s static load is concentrated in the MLG assembly. Large aircraft commonly utilize multiple disc brakes, which can handle the high brake torque and energy requirements.The arrangement and nomenclature of a typical multiple disc brake with in the wheel assembly are depicted in Fig. 1 . Main wheel assembly (10) is usually a bowl-type, split flange arrangement positioned on the MLG axle (18) which rotates over the axle and is supported on two taper-rollerbearings. Multiple disc brakes consist of stators (15) and rotors (16) sandwiched alternatively inside the wheel assembly. The torquetube (17) of the brake unit is a stationary platform over which the stators and rotors are stacked. The stator discs are slotted or keyed on their inner diameter such that they may slide, but not rotate on the torque tube of the brake assembly. The rotors are slotted or keyed on their outer diameter to interface with drive keys in the wheel and rotate together with the wheel assembly with forward velocity of the aircraft. The torquetube is further connected with tie bolts to the piston housing (7) of the brake unit at the front end and the other end is connected to the thrust cone via another tie bolt. Brake torque generated between brake discs is taken out to the landing gear structure via torque tube flange. In conventional brake system design, braking force is generated when hydraulic fluid pressure is supplied to the brake pistons (20) housed inside the brake cylinders. Forward movement of brake piston under fluid pressure applies the braking force on the brake discs normal to the disc surface. Thus, a compressive load is generated over the stators & rotors supported between brake pistons (20) and thrust cones (19) at both ends. During the rotation of rotors together with wheel assembly, this compressive load generates frictional force at the disc interface tangential to the disc surface. The friction force between the brake and the wheel generates brake torque around the wheel axis and this brake torque is then transferred to the MLGtyre (6) through the wheel assembly. On the other end, the torque tube flange interfaced with the landing gear structure, reacts to the brake torque. 3. BRAKE ENERGY ESTIMATION During landing phase, after the main wheel touchdown and nose de-rotation, the longitudinal kinetic energy of the aircraft has to be brought to zero by the deceleration devices. Following are the main deceleration features of an aircraft which develop the drag and retard its forward motion. Drag parachute (F C ) Brake Drag(F B1 ) Aircraft aerodynamic drag (F D ) Nose wheel tyre rolling drag (F N ) Main wheel tyre slip drag (F B2 ) \(\:{\text{E}}_{\text{N}\text{o}\text{s}\text{e}}+{\text{E}}_{\text{S}\text{l}\text{i}\text{p}\:}+{\text{E}}_{\text{C}\text{h}\text{u}\text{t}\text{e}}+{\text{E}}_{\text{B}\text{r}\text{a}\text{k}\text{e}}+{\text{E}}_{\text{D}\text{r}\text{a}\text{g}}={\text{E}}_{\text{A}\text{i}\text{r}\text{c}\text{r}\text{a}\text{f}\text{t}}+{\text{E}}_{\text{T}\text{h}\text{r}\text{u}\text{s}\text{t}}\) [1] \(\:{\text{E}}_{\text{B}\text{r}\text{a}\text{k}\text{e}}={\text{E}}_{\text{A}\text{i}\text{r}\text{c}\text{r}\text{a}\text{f}\text{t}}+{\text{E}}_{\text{T}\text{h}\text{r}\text{u}\text{s}\text{t}}-{\text{E}}_{\text{N}\text{o}\text{s}\text{e}\:\:}-{\text{E}}_{\text{S}\text{l}\text{i}\text{p}\:}-{\text{E}}_{\text{C}\text{h}\text{u}\text{t}\text{e}}-{E}_{Drag}\) [2] In the landing phase of a typical fighter aircraft, the drag components are shown in Fig. 2 . As the aircraft brakes, the friction between the brake discs generates heat energy, converting a portion of the aircraft's kinetic energy into heat energy in the brake discs. The energy absorbed by the brake disc can be calculated by subtracting the energy absorbed by other drag-producing components from the total aircraft energy. As per Military specification, brake energy absorbed by an aircraft can be categorized as below Normal Landing Energy – Energy absorbed by brake discs during landing phase when the aircraft has landed after completion of its mission i.e the aircraft has utilized its stores such as bombs, missiles, additional fuel etc. and mass is reduced. Aircraft has to be brought to full stop without usage of drag parachute. Overload Landing Energy - Energy absorbed by brake discs during landing phase when the aircraft has landed before completion of its mission with higher mass.Aircraft has to be brought to full stop with/without usage of drag parachute. Rejected Take-Off Energy – Energy absorbed by brake discs, when take-off is aborted close to the nose rotation speed with maximum aircraft mass due to some emergency. Aircraft has to be brought to full stop with/without usage of drag parachute. The evaluation methodology for the above is defined by MIL-8860 and SAE ARP 1493 standards. The maximum heat energy to be absorbed by brakes during its service is the energy absorbed by the brake discs during the RTO condition. Therefore, brake discs are designed for RTO brake energy. 4. LIMITING FACTORS FOR MAXIMUM BRAKE ENERGY 4.1 Brake disc material Steel, copper, beryllium and carbon-carbon composites are some common materials used for aircraft brakes. A good brake disc material should have high specific heat capacity, high density, and high strength at higher temperaturesalong with low wear rate and high coefficient of friction. Carbon-carbon composite has the advantage of withstanding high temperatures during RTO conditions for less brake mass as compared to other materials. Based on the above, C-C composite is a good brake disc material compared to others. However, the following are the disadvantagesof carbon-carbon composites Volume occupied by carbon-carbon brake disc will be more due its low density as compared to other brake material. As carbon-carbon brake disc has tendency for oxidation at higher temperature, disc temperature during normal landing conditions are limited to have better service life. Despite the limitations as brought above, almost all latest commercial and military aircrafts use Carbon-Carbon brake material. Properties of common brake material is tabulated in Table 1 . Table 1 Properties of common brake material Material Specific Heat (J/g-°K) Density (g/cm³) Melting Point (°C) Thermal conductivity (W/m-°K) Tensile strength (MPa) Steel 0.49 8.05 1370–1540 35–60 410 Copper 0.385 8.96 1083 350–385 240 Beryllium 1.82 1.85 1283 218 255 Carbon-Carbon 1.42 1.6-2 3000–3700 (Sublimation) 20–160 66 Based on flight trials, it has been observed that when carbon-carbon brake discs temperature increases beyond 800–900°C, there has been a gradual degradation in the friction coefficient of disc material. This result in reduced aircraft deceleration and thereby increase the stopping distance. This fading effect at higher temperaturesposes a limitation in maximum brake energy which can be absorbed by the brake disc. 4.2 Wheel Envelope Wheel size is selected based on the maximum static and dynamic load experienced by the landing gear during operation. Wheel size determines the available brake volume which can be accommodated in the wheel well. At times, wheel size will be limited by the available space inside the landing gear bay which limits the accommodable brake mass. This brake mass limitation restricts the maximum brake energy which can be pumped into the brake discs during landing and RTO conditions. 4.3 Wheel Temperature During RTO and landing events with high brake energy absorption, the heat from the brake disc is transferred to the wheel, tyre and associated brake system components. Modern aircraft wheels are made up of aluminium alloy which loses its strength when the temperature exceeds 200°C. Along with the wheel temperature rise the nitrogen temperature inside the wheel and tyre envelope also rises. The result is an increase in the tyre pressure which may result in the explosive rupture of the wheel if not addressed suitably such as the usage of a “Fusible Plug” in the wheel assembly which containsan eutectic mixture of metals designed to melt at a precise temperature. Hence, maximum brake energy absorption is limited to maintain the optimum operating temperature in the wheel assembly. 4.4 Turn Around Sortie (TRS) Time As per the Standard Operating Procedure, the fighter aircraft completes its mission and lands back (Normal landing) at the base and is brought to a full stop using wheel brakes by absorbing the kinetic energy. Further, it is taxied back to hangar and powered OFF. Thetime from theaircraft is powered OFFin hangar to the subsequent power ON for next sortie is called Turn Around Sortie (TRS) Time. This time is provided to refuel and reload the aircraft for the next mission and typically, 30 minutes is the maximum TRS time allocated for military aircraft operations. Heat energy absorbed by brake disc during the landing & taxi back phase of previous sortie has to be dissipated to associated brake system components and then to the ambient sufficiently before the next sortie. TRS time is critical for the brake system because the brake disc temperature has to reduceto satisfactory levels before the aircraft power ON for the next sortie. If an aircraft is taxied out with a higher temperature than the limit value and it encounters an RTO, then the residual brake energy associated with the brake disc can causeoverheating of the brakes and may blow off the fusible plug before the aircraft comes to full stop. This may result in catastrophe including lossof aircraft and causality to the crew. 5. TURN AROUND SORTIE PROFILE It is mandatory that brake discs have to be sufficiently cooled and brake disc temperature has to be less than or equal to the limit value before the aircraft is cleared for the next sortie. This paper outlines the studies carried out on a 13.5-ton typical fighter aircraft (Referred as Tester 1 subsequently) brake system with respect to TRS time. Tester 1 brake system specification is tabulated in Table 2. Table 2: Brake system specification – Tester 1 Sl. No. Parameters Values Units 1 Maximum aircraft take off mass 13500 Kg 2 Normal Landing mass 8600 Kg 3 Brake unit type Hydraulically operated multiple disc brake 4 Normal Landing Brake energy 21 MJ 5 Rejected Take off Energy 45 MJ Based on the inputs from Tester 1 flight test data and as per guidelines of SAE ARP 1493C, the TRS profile has been generated. TRS profile consistsof two segments namely Landing and taxi back segments as indicated in Figure 3. Each of the LH and RH brakeunits are instrumented with 4nos of K-type thermocouple which measures the brake internal temperatures. Out of four thermocouples, two are installed in pressure & thrust stator which has one friction surface. Other two thermocouples are installed in 2 double stators which have two friction surfaces. Generally, the temperature measured by double stators will be more than the pressure and thrust stator. By analysis and lab level activity, 150°C at double stator/100°C at Pressure stator external surface is arrived as the safe temperature level to be used as the clearance criteria for the next mission/sortie. Once the aircraft comes to a full stop at Stage C of TRS profile, the time required for brake internal temperature (Double Stator) to come less than 150°C has to be evaluated. Brake disc external temperatures are measured using a Non-contact laser gun. The brakeinternal temperature (Double Stator) of 150°C is equivalent to pressure stator external temperature of 100°C. 6. FLIGHT TRIALS FOR TRS TIME ESTIMATION Aircraft has been tested as per the TRS profile indicated in Fig. 3 and the time required for the brake disc to cool to respective temperature has to be measured and tabulated in Table 3 . Table 3 Turn Around Sortie Time estimation from Flight data of Tester 1 Aircraft Flight Brake Energy (MJ) Aircraft Ground Roll (m) Internal Brake Temp (°C) Taxi Back Time (Mins) Tc (Mins) Landing Taxi Back Landing Taxi Back Peak @ stage B After full stop @ stage C Tester 1 A 18.5 1.0 1753 1625 830/633 519/475 4 64 Tester 2 B 17.6 0.7 2074 1439 656/513 465/404 5 66 Tester 3 C 18.0 2.8 1798 4042 756/556 463/436 9 69 Note: Tc - Time for External Temperature to come less than 100 Deg C after full stop @ stage C Based on the flight data from Table 3 , it is observed that the time required for brake disc external temperature to reduce less than or equal to 100°C externally is found to be 64 to 69 minutes. Higher cooling time observed in Flight C might be due to high taxi back brake energy input and prevailed ambient temperature &wind patterns during the test. Brake energies during landing and taxi back was estimated as described earlier in this paper. Ground roll distance was estimated from the aircraft velocity and brake disc temperature values are measured from thermocouplesinstalled in the brake discs. The aircraftwheel speed and brake temperature cooling curve plot are indicated in Fig. 4 . Fromthe flight test data, it is evident that the TRS timing with natural cooling of brakes will be more than 60 minutes which is more than the target TRS time of 30 minutes. Hence, the thermal behaviour of brake discs and the mechanism of heat distribution and dissipation in aircraft brake unitshave been explored. 7. Thermal behaviour of wheel and brake unit of aircraft During the braking phase, heat flux is generated between the interface of stators and rotors. The heatgenerated at the friction radius of the carbon-carbon brake disc is distributed via conduction in radial and axial (z-direction) direction. During taxi back and cooling phase, the heat energy is evacuated away to the torque tube, wheel, piston housing and tyre. Heat dissipation through various modes are indicated in Fig. 5 [ 7 ]. 7.1 Heat transfer through conduction Heat transfer rate through conduction is directly proportional to cross-section area, temperature gradient and thermal conductivity of the material. As the disc size is optimised to the available wheel well volume, the cross-sectional area cannot be increased further. The thermal conductivity of carbon-carbon disc, wheel and torque tube assembly cannot be improved as it is fixed by its material property. However, the temperature gradient can be increased by reducing the outer surface temperature by forced convection. Due to coupling between rotors and wheel, heat is transferred throughconduction in radial outward direction. Due to coupling between stators and torque tube, heat is transferred through conduction in radial inward direction. Further heat energy from the torque tube is transferred via conduction to the piston housing, axle and thrust cone. Heat energy from the wheel is transferred to the tyre via conduction at the bead seating area. 7.2 Heat transfer through convection Three potential air passages are available in the wheel and brake assembly. Primary passage is between the surface formed by brake discs outer diameter and wheel internal surface and another passage is between the inner surface of the torque tube assembly and outer surface of the wheel bearing housing. Both these passages meet behind the thrust cone and communicate with the ambient via vent holes in the wheel assembly. Heat dissipation due to natural convection current formed by buoyancy drive airflow takes place between the following components Between surface formed by brake disc outer diameter and wheel inner surface Between surface formed by brake disc inner diameter and torque tube Pressure stator (PS) and the piston housing Thrust Stator (TS) and the thrust cone Torque tube to axle Wheel to tyre Heat dissipation through convection can be improved by increasing the heat transfer co-efficient by accelerating the mass flow rate of air over the convection interfaces. 7.3 Heat Transferthrough Radiation Heat dissipation due to radiation takes place between components is the same as listed for convection. This exchange depends strongly on the surface geometries and orientations, as well as on their radiative properties and temperatures. The viewfactor for radiation cannot altered as component orientation are finalised based on the functional requirements. Hence, the scope for improving upon heat dissipation through radiation is minimal. Based on the above discussion, it is concluded that heat dissipation from brake discs shall be greatly improved by forced convection which shall achieved by forced air circulation by a cooling fan. 8. Brake Cooling fan Forced cooling of brakediscs will ensure better heat dissipation and brake disc temperature can be reduced to acceptable limits at the earliest. The coolingfan shall be positioned externally or integral to the wheel axle. When a brake coolingfan is used externally as ground support equipment, brakes haveto be cooled post-taxi back of the aircraft to hanger. As military operations do not support the usage of external cooling fan at forward air bases and since the associated mass flow rate is less resulting in less efficiency, a brake cooling fan integral to the main wheel axle has been explored. The brakeCooling Fan layout is indicated in Fig. 6 . As indicated in Fig. 6 , the Brake Cooling Fan motor is mounted inside the Main Landing gear axle and the impeller is mounted in the hollow shaft of the BCF motor. BCF is an axial flow fan which sucks the air from the inboard side of the wheel/brake assembly and pushesover the shroud assembly. The WheelSpeed Transducer (WST) shaft runs coaxially over the hollow impeller shaft and couples with the shroud assembly of the wheel. A briefspecification of the Brake Cooling Fan is indicated in Table 4 . Table 4 Brief Specification of Brake Cooling fan Sl. No. Parameters Values Units 1 Power supply 28 V DC 2 Typical airflow rate 90 Lit/sec 3 Motor power consumption < 335 Watts 4 Maximum Operating Temperature 180 °C 5 Full load current of the motor @ 28VDC 12 A 9. Brake Dynamometer Rig Ground level validation of the performance of BCF is carried out on the brake dynamometer facility. A brakedynamometer is a ground test rig used for qualification testing of aircraft wheelsand brake assembly. Brake energy absorption and stopping time capability of wheel and brake assembly during Normal, overload and RTO conditions are evaluated in the brake dynamometer test rig. It is a dynamic test facility that can simulate the brake energy and the braking application speed of the aircraft. The brakeenergy of the aircraft is simulated by the inertia of the drum and its rotating speed. When the rotating drum attains the required speed, the specimen (Wheel, Tyre& brake assembly) is lowered over the drum to simulate the required static load and brake pressure is applied till the drum attains zero speed. The entire drum'skinetic energy will be absorbed by the wheel and tyre assembly. The dynamometer test facility is completely instrumented to measure the drum speed, wheel static load on the drum, brake torque, brake pressures and disc temperatures. The brakedynamometer facility with the test specimen is indicated in Fig. 7 . 10. Dynamometer Trial with BCF The test specimen is prepared by integrating the BCF with Wheel and brake assembly of Tester 1 aircraft and the same has been tested in the brake dynamometer test facility to estimate the TRS time with forced cooling of brake discs. The dynamometer test parameters are indicated in Table 5 . Table 5 Brake dynamometer Test Parameter with Brake Cooling Fan Sl. No. Parameters Values Units 1 Drum diameter 1.83 m 2 Inertia of dynamometer 3563 Kg-m² 3 Load on the wheel 5900 Kg 4 Drum Speed 823 RPM 5 Brake Pressure 53 bar 6 Stop Time 26.8 seconds 7 Peak torque 440 Kgm 8 Simulated energy of the dynamometer 26 MJ 9 Double Stator temperature at which BCF switched ON 550 °C 10 Cooling Time 26.17 minutes Cooling time is the time required for the brake disc (double Stator) temperature to reduce to less than or equal to 100°C from a full stop of the dynamometer drum. 10.1 Procedure Adopted for Dynamometer Trial: The brake dynamometer drum is gradually accelerated from static condition to slightly above the Brake Application Speed. The loading arm together with the wheel & brake assembly is loaded over the drum to simulate the required static load. Brakes are applied once the drum speed reaches the required brake application speed and retained till the drum speed dropsdown to zero. Brake Disc internal and external temperatures are monitored continuously and BCF is switched ON when each of the brake disc internal temperature is dropped less than or equal to 550°C which is the limiting temperature to avoid oxidation of carbon disc [ 5 ]. BCF is switched OFF when brake disc internal temperature reduces less than or equal to 100°C. Though the normal brake energy of tester 1 aircraft is 21MJ, dynamometer energy was simulated to 26 MJ to cater for energy loss through dynamotor bearings (< 1MJ), tyre slip(≈ 3MJ) and cater for taxi back energy input(= 1MJ). Separate taxi braking runs were not carried out as the energy input is envisaged in the simulated energy of the dynamometer. Cooling curve for the dynamometer run is indicated in Fig. 8 . 10.2 Observation & Inference: From Fig. 8 , it is observed that after full stop of the dynamometer drum, peak temperatures are observed in Double Stator 1 & Double Stator 2(DS1 & DS2). However, at the end of the cooling period, the Thrust Stator (TS) temperature is higherthan the other temperatures. This is because the cooling air pulled by the BCF initially passes over the Pressure Stator (PS), Double Stator 1(DS1), Double Stator 2(DS2), wheel assembly and finally reachesthe Thrust Stator (TS). Therefore, the cooling air temperature moving over the TS will be higher resulting in a lower thermal gradient and this makes its cooling curve shallower. This also resultsin both internal and external temperaturesof TS to read almost equal. Hence, the cooling time is estimated from the full stop of the dynamometer drum to till the thrust stator internal temperature reaches less than or equal to 100°C. Nine dynamometer runs were conducted, and the corresponding brake disc peak temperature and cooling time to reach 100°C are depicted in Figs. 9 and 10 , respectively. 11. Results and Discussions Based on the flight trials carried out on Tester 1 it is observed that the TRS time with natural cooling is of the order of 64 to 69 minutes. However, based on the dynamometer trials carried out on Tester 1 aircraft’s wheel & brake assembly with BCF, it has been identified that TRS time is improved to the order of less than 30 minutes. This indicate that, with incorporation of BCF in brake system, TRS time of 30 minutes can be achieved for Tester 1 aircraft. Following proposals are to be exploredin future work to reduce the brake cooling time (TRS) less than or equal to 30 minutes without using a BCF. Improving the natural convective heat transfer by increasing the size of ventilation hole in the wheel assembly. Increasing the brake disc’s external clearance temperature for next sortie from 100°C to 150°C and validating the RTO brake energy dynamometer trials with initial brake external temperature up to 150°C Better insulation of air gap between the stator outer surface diameter and wheel inner surface. With cumulative improvements from above three proposals, possibility of reducing Brake Cooling Timeless than 30 minutes with natural cooling will be explored. Declarations ACKNOWLEDGEMENTS The authors wish to extend their sincere gratitude to HAL – ARDC for their support and encouragement, which enabled us to present this paper. Funding – No funding was received for conducting this study. However, testing was conducted in the facilities available in Aircraft Research and Design Centre- HAL-Bangalore. Ethics Declaration – Not applicable Consent to publish declaration – Not applicable Consent to participate declaration – Not applicable Author Contribution 1) Prem R, Prasobh J Mechery – Both the authors were involved in activities like preparation of flight plan and co-ordination for flight testing & hangar activities, flight data analysis, preparation of TRS duty cycle, 3D modeling of brake cooling fan layout and finalisation of interface, Dynamo-meter trails set up and co-ordination for test runs and manuscript generation.2) Sudeep KB and Suresh MT – Both played key role in decision making at every stage of flight/dynamometer testing. And they contributed for review and finalization of manuscript. References Norman S. Curry, Aircraft Landing Gear Design: Principles and Practices, AIAA, Washington, 1988. H G Conway, Landing Gear Design,Chapman and Hall, 1958. Military Specification, “Wheel and Brake Assemblies,” Aircraft General Specification for, MIL-W-5013L, October 1991. Aerospace Recommended Practice, “Wheel and Hydraulically Actuated Brake Design and Test Requirements for Military Aircraft,” ARP1493, Revision C, SAE International, November 2013. Use of structural carbon heat sink brakes on aircraft, SAE AIR 1934 Rev A. M.P.Dyko and K.Vafai, Fundamental issues and Recent Advancements in Analysis of Aircraft Brake Natural Convective Cooling, Journal of Heat Transfer, November 1998, Vol 120/840, Transactions of the ASME. Cedric MEUNIER, Jean-Gabriel BAUZIN, Najib LARAQI, Arnaud GAPIN, Jean-Frederic DIEBOLD, Thermal characterization of the braking and cooling stages of an aircraft brake using identification techniques and a life-size experiment test bench, by Elsevier 2022. Additional Declarations No competing interests reported. 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Bangalore","correspondingAuthor":false,"prefix":"","firstName":"Prasobh","middleName":"J","lastName":"Mechery","suffix":""},{"id":440581336,"identity":"d2342800-74f0-46f2-88d4-aa832b4adae5","order_by":2,"name":"Sudeep KB","email":"","orcid":"","institution":"HAL Bangalore","correspondingAuthor":false,"prefix":"","firstName":"Sudeep","middleName":"","lastName":"KB","suffix":""},{"id":440581337,"identity":"ced4660c-d00f-4203-a304-2543a16ebc9d","order_by":3,"name":"Suresh MT","email":"","orcid":"","institution":"HAL Bangalore","correspondingAuthor":false,"prefix":"","firstName":"Suresh","middleName":"","lastName":"MT","suffix":""}],"badges":[],"createdAt":"2025-03-09 03:08:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6186480/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6186480/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":80526342,"identity":"6b1334c4-68f6-4162-9505-31204455c725","added_by":"auto","created_at":"2025-04-14 10:04:06","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":258943,"visible":true,"origin":"","legend":"\u003cp\u003eArrangement and nomenclature of a typical multiple disc brake\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/1e64f894d43055e39eed5a3c.png"},{"id":80526341,"identity":"0703b472-e6eb-42f3-bbae-39350d17db9a","added_by":"auto","created_at":"2025-04-14 10:04:06","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":37116,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of drag components during landing phase of a typical fighter aircraft\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/fffd2bdeace8f6d81a39cae6.png"},{"id":80526347,"identity":"27905b6b-ebd1-43fe-bf41-1db6f34adcbe","added_by":"auto","created_at":"2025-04-14 10:04:06","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":413336,"visible":true,"origin":"","legend":"\u003cp\u003eTurn Around Sortie Profile of Tester 1 aircraft\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/e494cf81b4af59c77c5f44fd.png"},{"id":80526346,"identity":"07795e46-2507-46b1-9446-e3b1732ab667","added_by":"auto","created_at":"2025-04-14 10:04:06","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":425718,"visible":true,"origin":"","legend":"\u003cp\u003eWheel speed and brake temperature plot of Flight B of Tester 1\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/b511f40f7c2a70ea841e5ace.png"},{"id":80526348,"identity":"2255f27a-f097-4772-9259-53310ae8bc35","added_by":"auto","created_at":"2025-04-14 10:04:06","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":662419,"visible":true,"origin":"","legend":"\u003cp\u003eHeat dissipation through various modes in aircraft wheel and brake assembly\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/05bbabdc9560d79dfaff1666.png"},{"id":80527782,"identity":"216ee8ed-a081-4984-a349-8e0abc5464c0","added_by":"auto","created_at":"2025-04-14 10:12:06","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":106008,"visible":true,"origin":"","legend":"\u003cp\u003eBrake Cooling Fan layout of Tester 1 aircraft\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/bdda45ffd6d120543676dce6.png"},{"id":80527784,"identity":"f7c3344a-d753-4cf8-a6a2-c3eff2d819d3","added_by":"auto","created_at":"2025-04-14 10:12:07","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":106940,"visible":true,"origin":"","legend":"\u003cp\u003eBrake Dynamometer facility with wheel and brake specimen\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/c402b5db5ae38f6465bfd7a7.png"},{"id":80526357,"identity":"8c8ff6c1-1e35-4c6f-9d55-d5d3b49c33f4","added_by":"auto","created_at":"2025-04-14 10:04:07","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":248515,"visible":true,"origin":"","legend":"\u003cp\u003eCooling curve of brake dynamometer run-with BCF\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/3ebfae118f6dde46146127c2.png"},{"id":80526351,"identity":"5a6303fe-31ca-410d-9e47-26c807de5b03","added_by":"auto","created_at":"2025-04-14 10:04:07","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":37137,"visible":true,"origin":"","legend":"\u003cp\u003eBrake disc temperature during brake dynamometer run-with BCF\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/3c6a9e59b1b9e95f16cadd7c.png"},{"id":80528052,"identity":"39b70ed3-bc73-4c2b-bd87-ae863321751f","added_by":"auto","created_at":"2025-04-14 10:20:07","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":231028,"visible":true,"origin":"","legend":"\u003cp\u003eBrake disc cooling time during brake dynamometer run-with BCF\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/f1e7dde58afbb1e28066568c.png"},{"id":83329923,"identity":"df2cad73-3cc0-4ad9-a57c-220cd72feb5d","added_by":"auto","created_at":"2025-05-23 07:31:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3339554,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6186480/v1/4d6e3f9b-7825-4890-9e2c-b3e2cfa17537.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Optimization of Turn Around SortieTime of aTypical Fighter Aircraft by Enhancement of Brake System Heat Dissipation through Forced Convection","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eLanding gear system of an aircraft is one of the important safety critical systems which support the entire aircraft on ground, reduce the impact load on aircraft during landing and help in ground manoeuvring of aircraft. Wheel \u0026amp; brake system is one of the subsystems of landing gear system which decelerate the aircraft during taxiing, landing and in Rejected Take Off (RTO) condition. Kinetic energy of the moving aircraft is converted into heat energy during brake application. Quantum of kinetic energy handled by an aircraft brake system is tremendously high due to the heavy weight of the aircraft and higher take-off and landing speeds. Heat energy generated in the brake discs has to be dissipated to the ambient at the earliest since the residual heat energy in the brake discs causes certain operational restrictions.\u003c/p\u003e \u003cp\u003eOne such critical operational requirement is Turn Around Sortie (TRS) time of the aircraft. This is the time available to prepare the aircraft for the next mission subsequent to a normal landing. Any aircraft, either commercial or military aircraft, always should have a short TRS time for enhanced flight operations. However, one of the constraints to achievingthis is the time required to cool the brake discs to acceptable levels. Brake disc temperature before take-off has to be maintained at an acceptable level to absorb sufficient brake energy in case of an RTO and bring the aircraft to full stop satisfactorily. This is considering the possibility of every take-off leading to an RTO. This paper initially outlines the brake system and the TRS time requirement of a typical fighter aircraft. Subsequently, it discusses in detail the methodology of reducing the brake disc temperature through various modes of heat transfer to cater for the TRS time. The data from the flight and brake dynamometer trial has been presented.\u003c/p\u003e"},{"header":"2. AIRCRAFT BRAKE SYSTEM","content":"\u003cp\u003eBrakes are typically positioned within the wheel assembly of the Main Landing Gear (MLG) to generate maximum drag force, especially since the majority of the aircraft\u0026rsquo;s static load is concentrated in the MLG assembly. Large aircraft commonly utilize multiple disc brakes, which can handle the high brake torque and energy requirements.The arrangement and nomenclature of a typical multiple disc brake with in the wheel assembly are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Main wheel assembly (10) is usually a bowl-type, split flange arrangement positioned on the MLG axle (18) which rotates over the axle and is supported on two taper-rollerbearings. Multiple disc brakes consist of stators (15) and rotors (16) sandwiched alternatively inside the wheel assembly. The torquetube (17) of the brake unit is a stationary platform over which the stators and rotors are stacked. The stator discs are slotted or keyed on their inner diameter such that they may slide, but not rotate on the torque tube of the brake assembly. The rotors are slotted or keyed on their outer diameter to interface with drive keys in the wheel and rotate together with the wheel assembly with forward velocity of the aircraft. The torquetube is further connected with tie bolts to the piston housing (7) of the brake unit at the front end and the other end is connected to the thrust cone via another tie bolt. Brake torque generated between brake discs is taken out to the landing gear structure via torque tube flange. In conventional brake system design, braking force is generated when hydraulic fluid pressure is supplied to the brake pistons (20) housed inside the brake cylinders. Forward movement of brake piston under fluid pressure applies the braking force on the brake discs normal to the disc surface. Thus, a compressive load is generated over the stators \u0026amp; rotors supported between brake pistons (20) and thrust cones (19) at both ends. During the rotation of rotors together with wheel assembly, this compressive load generates frictional force at the disc interface tangential to the disc surface. The friction force between the brake and the wheel generates brake torque around the wheel axis and this brake torque is then transferred to the MLGtyre (6) through the wheel assembly. On the other end, the torque tube flange interfaced with the landing gear structure, reacts to the brake torque.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3. BRAKE ENERGY ESTIMATION","content":"\u003cp\u003eDuring landing phase, after the main wheel touchdown and nose de-rotation, the longitudinal kinetic energy of the aircraft has to be brought to zero by the deceleration devices. Following are the main deceleration features of an aircraft which develop the drag and retard its forward motion.\u003c/p\u003e \u003cp\u003e \u003col style=\"list-style-type:lower-alpha;\"\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eDrag parachute (F\u003csub\u003eC\u003c/sub\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eBrake Drag(F\u003csub\u003eB1\u003c/sub\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAircraft aerodynamic drag (F\u003csub\u003eD\u003c/sub\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eNose wheel tyre rolling drag (F\u003csub\u003eN\u003c/sub\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eMain wheel tyre slip drag (F\u003csub\u003eB2\u003c/sub\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{E}}_{\\text{N}\\text{o}\\text{s}\\text{e}}+{\\text{E}}_{\\text{S}\\text{l}\\text{i}\\text{p}\\:}+{\\text{E}}_{\\text{C}\\text{h}\\text{u}\\text{t}\\text{e}}+{\\text{E}}_{\\text{B}\\text{r}\\text{a}\\text{k}\\text{e}}+{\\text{E}}_{\\text{D}\\text{r}\\text{a}\\text{g}}={\\text{E}}_{\\text{A}\\text{i}\\text{r}\\text{c}\\text{r}\\text{a}\\text{f}\\text{t}}+{\\text{E}}_{\\text{T}\\text{h}\\text{r}\\text{u}\\text{s}\\text{t}}\\)\u003c/span\u003e \u003c/span\u003e[1]\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{E}}_{\\text{B}\\text{r}\\text{a}\\text{k}\\text{e}}={\\text{E}}_{\\text{A}\\text{i}\\text{r}\\text{c}\\text{r}\\text{a}\\text{f}\\text{t}}+{\\text{E}}_{\\text{T}\\text{h}\\text{r}\\text{u}\\text{s}\\text{t}}-{\\text{E}}_{\\text{N}\\text{o}\\text{s}\\text{e}\\:\\:}-{\\text{E}}_{\\text{S}\\text{l}\\text{i}\\text{p}\\:}-{\\text{E}}_{\\text{C}\\text{h}\\text{u}\\text{t}\\text{e}}-{E}_{Drag}\\)\u003c/span\u003e \u003c/span\u003e[2]\u003c/p\u003e \u003cp\u003eIn the landing phase of a typical fighter aircraft, the drag components are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. As the aircraft brakes, the friction between the brake discs generates heat energy, converting a portion of the aircraft's kinetic energy into heat energy in the brake discs. The energy absorbed by the brake disc can be calculated by subtracting the energy absorbed by other drag-producing components from the total aircraft energy.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs per Military specification, brake energy absorbed by an aircraft can be categorized as below\u003c/p\u003e \u003cp\u003e \u003cem\u003eNormal Landing Energy\u003c/em\u003e \u0026ndash; Energy absorbed by brake discs during landing phase when the aircraft has landed after completion of its mission i.e the aircraft has utilized its stores such as bombs, missiles, additional fuel etc. and mass is reduced. Aircraft has to be brought to full stop without usage of drag parachute.\u003c/p\u003e \u003cp\u003e \u003cem\u003eOverload Landing Energy\u003c/em\u003e - Energy absorbed by brake discs during landing phase when the aircraft has landed before completion of its mission with higher mass.Aircraft has to be brought to full stop with/without usage of drag parachute.\u003c/p\u003e \u003cp\u003e \u003cem\u003eRejected Take-Off Energy\u003c/em\u003e \u0026ndash; Energy absorbed by brake discs, when take-off is aborted close to the nose rotation speed with maximum aircraft mass due to some emergency. Aircraft has to be brought to full stop with/without usage of drag parachute.\u003c/p\u003e \u003cp\u003eThe evaluation methodology for the above is defined by MIL-8860 and SAE ARP 1493 standards. The maximum heat energy to be absorbed by brakes during its service is the energy absorbed by the brake discs during the RTO condition. Therefore, brake discs are designed for RTO brake energy.\u003c/p\u003e"},{"header":"4. LIMITING FACTORS FOR MAXIMUM BRAKE ENERGY","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Brake disc material\u003c/h2\u003e \u003cp\u003eSteel, copper, beryllium and carbon-carbon composites are some common materials used for aircraft brakes. A good brake disc material should have high specific heat capacity, high density, and high strength at higher temperaturesalong with low wear rate and high coefficient of friction. Carbon-carbon composite has the advantage of withstanding high temperatures during RTO conditions for less brake mass as compared to other materials. Based on the above, C-C composite is a good brake disc material compared to others. However, the following are the disadvantagesof carbon-carbon composites\u003c/p\u003e \u003cp\u003e \u003col style=\"list-style-type:lower-alpha;\"\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eVolume occupied by carbon-carbon brake disc will be more due its low density as compared to other brake material.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAs carbon-carbon brake disc has tendency for oxidation at higher temperature, disc temperature during normal landing conditions are limited to have better service life.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eDespite the limitations as brought above, almost all latest commercial and military aircrafts use Carbon-Carbon brake material. Properties of common brake material is tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eProperties of common brake material\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecific Heat (J/g-\u0026deg;K)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDensity (g/cm\u0026sup3;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMelting Point (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eThermal conductivity (W/m-\u0026deg;K)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTensile strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSteel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1370\u0026ndash;1540\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e35\u0026ndash;60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e410\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCopper\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.385\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1083\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e350\u0026ndash;385\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e240\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBeryllium\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1283\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e218\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e255\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbon-Carbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.6-2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3000\u0026ndash;3700 (Sublimation)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20\u0026ndash;160\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eBased on flight trials, it has been observed that when carbon-carbon brake discs temperature increases beyond 800\u0026ndash;900\u0026deg;C, there has been a gradual degradation in the friction coefficient of disc material. This result in reduced aircraft deceleration and thereby increase the stopping distance. This fading effect at higher temperaturesposes a limitation in maximum brake energy which can be absorbed by the brake disc.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Wheel Envelope\u003c/h2\u003e \u003cp\u003eWheel size is selected based on the maximum static and dynamic load experienced by the landing gear during operation. Wheel size determines the available brake volume which can be accommodated in the wheel well. At times, wheel size will be limited by the available space inside the landing gear bay which limits the accommodable brake mass. This brake mass limitation restricts the maximum brake energy which can be pumped into the brake discs during landing and RTO conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Wheel Temperature\u003c/h2\u003e \u003cp\u003eDuring RTO and landing events with high brake energy absorption, the heat from the brake disc is transferred to the wheel, tyre and associated brake system components. Modern aircraft wheels are made up of aluminium alloy which loses its strength when the temperature exceeds 200\u0026deg;C. Along with the wheel temperature rise the nitrogen temperature inside the wheel and tyre envelope also rises. The result is an increase in the tyre pressure which may result in the explosive rupture of the wheel if not addressed suitably such as the usage of a \u0026ldquo;Fusible Plug\u0026rdquo; in the wheel assembly which containsan eutectic mixture of metals designed to melt at a precise temperature. Hence, maximum brake energy absorption is limited to maintain the optimum operating temperature in the wheel assembly.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Turn Around Sortie (TRS) Time\u003c/h2\u003e \u003cp\u003eAs per the Standard Operating Procedure, the fighter aircraft completes its mission and lands back (Normal landing) at the base and is brought to a full stop using wheel brakes by absorbing the kinetic energy. Further, it is taxied back to hangar and powered OFF. Thetime from theaircraft is powered OFFin hangar to the subsequent power ON for next sortie is called Turn Around Sortie (TRS) Time. This time is provided to refuel and reload the aircraft for the next mission and typically, 30 minutes is the maximum TRS time allocated for military aircraft operations. Heat energy absorbed by brake disc during the landing \u0026amp; taxi back phase of previous sortie has to be dissipated to associated brake system components and then to the ambient sufficiently before the next sortie. TRS time is critical for the brake system because the brake disc temperature has to reduceto satisfactory levels before the aircraft power ON for the next sortie. If an aircraft is taxied out with a higher temperature than the limit value and it encounters an RTO, then the residual brake energy associated with the brake disc can causeoverheating of the brakes and may blow off the fusible plug before the aircraft comes to full stop. This may result in catastrophe including lossof aircraft and causality to the crew.\u003c/p\u003e \u003c/div\u003e"},{"header":"5.\tTURN AROUND SORTIE PROFILE","content":"\u003cp\u003eIt is mandatory that brake discs have to be sufficiently cooled and brake disc temperature has to be less than or equal to the limit value before the aircraft is cleared for the next sortie. This paper outlines the studies carried out on a 13.5-ton typical fighter aircraft (Referred as Tester 1 subsequently) brake system with respect to TRS time. Tester 1 brake system specification is tabulated in Table 2.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 2: Brake system specification \u0026ndash; Tester 1\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003eSl. No.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 227px;\"\u003e\n \u003cp\u003eParameters\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003eValues\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\"\u003e\n \u003cp\u003eUnits\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 227px;\"\u003e\n \u003cp\u003eMaximum aircraft take off mass\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003e13500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\"\u003e\n \u003cp\u003eKg\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 227px;\"\u003e\n \u003cp\u003eNormal Landing mass\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003e8600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\"\u003e\n \u003cp\u003eKg\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 227px;\"\u003e\n \u003cp\u003eBrake unit type\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003eHydraulically operated multiple disc brake\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 227px;\"\u003e\n \u003cp\u003eNormal Landing Brake energy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\"\u003e\n \u003cp\u003eMJ\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 227px;\"\u003e\n \u003cp\u003eRejected Take off Energy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003e45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\"\u003e\n \u003cp\u003eMJ\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eBased on the inputs from Tester 1 flight test data and as per guidelines of SAE ARP 1493C, the TRS profile has been generated. TRS profile consistsof two segments namely Landing and taxi back segments as indicated in Figure 3. Each of the LH and RH brakeunits are instrumented with 4nos of K-type thermocouple which measures the brake internal temperatures. Out of four thermocouples, two are installed in pressure \u0026amp; thrust stator which has one friction surface. Other two thermocouples are installed in 2 double stators which have two friction surfaces. Generally, the temperature measured by double stators will be more than the pressure and thrust stator. By analysis and lab level activity, 150\u0026deg;C at double stator/100\u0026deg;C at Pressure stator external surface is arrived as the safe temperature level to be used as the clearance criteria for the next mission/sortie. Once the aircraft comes to a full stop at Stage C of TRS profile, the time required for brake internal temperature (Double Stator) to come less than 150\u0026deg;C has to be evaluated. Brake disc external temperatures are measured using a Non-contact laser gun. The brakeinternal temperature (Double Stator) of 150\u0026deg;C is equivalent to pressure stator external temperature of 100\u0026deg;C.\u003c/p\u003e"},{"header":"6. FLIGHT TRIALS FOR TRS TIME ESTIMATION","content":"\u003cp\u003eAircraft has been tested as per the TRS profile indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and the time required for the brake disc to cool to respective temperature has to be measured and tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTurn Around Sortie Time estimation from Flight data of Tester 1\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eAircraft\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eFlight\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eBrake Energy\u003c/p\u003e \u003cp\u003e(MJ)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eAircraft Ground Roll (m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eInternal Brake Temp\u003c/p\u003e \u003cp\u003e(\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTaxi Back Time (Mins)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTc\u003c/p\u003e \u003cp\u003e(Mins)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLanding\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTaxi Back\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLanding\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTaxi Back\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003ePeak @ stage B\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAfter full stop @ stage C\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTester 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1753\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1625\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e830/633\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e519/475\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTester 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2074\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1439\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e656/513\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e465/404\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTester 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1798\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4042\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e756/556\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e463/436\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e69\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"10\"\u003eNote: Tc - Time for External Temperature to come less than 100 Deg C after full stop @ stage C\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eBased on the flight data from Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, it is observed that the time required for brake disc external temperature to reduce less than or equal to 100\u0026deg;C externally is found to be 64 to 69 minutes. Higher cooling time observed in Flight C might be due to high taxi back brake energy input and prevailed ambient temperature \u0026amp;wind patterns during the test. Brake energies during landing and taxi back was estimated as described earlier in this paper. Ground roll distance was estimated from the aircraft velocity and brake disc temperature values are measured from thermocouplesinstalled in the brake discs. The aircraftwheel speed and brake temperature cooling curve plot are indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFromthe flight test data, it is evident that the TRS timing with natural cooling of brakes will be more than 60 minutes which is more than the target TRS time of 30 minutes. Hence, the thermal behaviour of brake discs and the mechanism of heat distribution and dissipation in aircraft brake unitshave been explored.\u003c/p\u003e"},{"header":"7. Thermal behaviour of wheel and brake unit of aircraft","content":"\u003cp\u003eDuring the braking phase, heat flux is generated between the interface of stators and rotors. The heatgenerated at the friction radius of the carbon-carbon brake disc is distributed via conduction in radial and axial (z-direction) direction. During taxi back and cooling phase, the heat energy is evacuated away to the torque tube, wheel, piston housing and tyre. Heat dissipation through various modes are indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e7.1 Heat transfer through conduction\u003c/h2\u003e \u003cp\u003eHeat transfer rate through conduction is directly proportional to cross-section area, temperature gradient and thermal conductivity of the material. As the disc size is optimised to the available wheel well volume, the cross-sectional area cannot be increased further. The thermal conductivity of carbon-carbon disc, wheel and torque tube assembly cannot be improved as it is fixed by its material property. However, the temperature gradient can be increased by reducing the outer surface temperature by forced convection.\u003c/p\u003e \u003cp\u003e \u003col style=\"list-style-type:lower-alpha;\"\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eDue to coupling between rotors and wheel, heat is transferred throughconduction in radial outward direction.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eDue to coupling between stators and torque tube, heat is transferred through conduction in radial inward direction.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eFurther heat energy from the torque tube is transferred via conduction to the piston housing, axle and thrust cone.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eHeat energy from the wheel is transferred to the tyre via conduction at the bead seating area.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e7.2 Heat transfer through convection\u003c/h2\u003e \u003cp\u003eThree potential air passages are available in the wheel and brake assembly. Primary passage is between the surface formed by brake discs outer diameter and wheel internal surface and another passage is between the inner surface of the torque tube assembly and outer surface of the wheel bearing housing. Both these passages meet behind the thrust cone and communicate with the ambient via vent holes in the wheel assembly.\u003c/p\u003e \u003cp\u003eHeat dissipation due to natural convection current formed by buoyancy drive airflow takes place between the following components\u003c/p\u003e \u003cp\u003e \u003col style=\"list-style-type:lower-alpha;\"\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eBetween surface formed by brake disc outer diameter and wheel inner surface\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eBetween surface formed by brake disc inner diameter and torque tube\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003ePressure stator (PS) and the piston housing\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThrust Stator (TS) and the thrust cone\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eTorque tube to axle\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eWheel to tyre\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eHeat dissipation through convection can be improved by increasing the heat transfer co-efficient by accelerating the mass flow rate of air over the convection interfaces.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e7.3 Heat Transferthrough Radiation\u003c/h2\u003e \u003cp\u003eHeat dissipation due to radiation takes place between components is the same as listed for convection. This exchange depends strongly on the surface geometries and orientations, as well as on their radiative properties and temperatures. The viewfactor for radiation cannot altered as component orientation are finalised based on the functional requirements. Hence, the scope for improving upon heat dissipation through radiation is minimal.\u003c/p\u003e \u003cp\u003eBased on the above discussion, it is concluded that heat dissipation from brake discs shall be greatly improved by forced convection which shall achieved by forced air circulation by a cooling fan.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"8. Brake Cooling fan","content":"\u003cp\u003eForced cooling of brakediscs will ensure better heat dissipation and brake disc temperature can be reduced to acceptable limits at the earliest. The coolingfan shall be positioned externally or integral to the wheel axle. When a brake coolingfan is used externally as ground support equipment, brakes haveto be cooled post-taxi back of the aircraft to hanger. As military operations do not support the usage of external cooling fan at forward air bases and since the associated mass flow rate is less resulting in less efficiency, a brake cooling fan integral to the main wheel axle has been explored. The brakeCooling Fan layout is indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the Brake Cooling Fan motor is mounted inside the Main Landing gear axle and the impeller is mounted in the hollow shaft of the BCF motor. BCF is an axial flow fan which sucks the air from the inboard side of the wheel/brake assembly and pushesover the shroud assembly. The WheelSpeed Transducer (WST) shaft runs coaxially over the hollow impeller shaft and couples with the shroud assembly of the wheel. A briefspecification of the Brake Cooling Fan is indicated in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBrief Specification of Brake Cooling fan\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSl. No.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eValues\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eUnits\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePower supply\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eV DC\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTypical airflow rate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLit/sec\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMotor power consumption\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;335\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eWatts\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaximum Operating Temperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFull load current of the motor @ 28VDC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"9. Brake Dynamometer Rig","content":"\u003cp\u003eGround level validation of the performance of BCF is carried out on the brake dynamometer facility. A brakedynamometer is a ground test rig used for qualification testing of aircraft wheelsand brake assembly. Brake energy absorption and stopping time capability of wheel and brake assembly during Normal, overload and RTO conditions are evaluated in the brake dynamometer test rig. It is a dynamic test facility that can simulate the brake energy and the braking application speed of the aircraft.\u003c/p\u003e \u003cp\u003eThe brakeenergy of the aircraft is simulated by the inertia of the drum and its rotating speed. When the rotating drum attains the required speed, the specimen (Wheel, Tyre\u0026amp; brake assembly) is lowered over the drum to simulate the required static load and brake pressure is applied till the drum attains zero speed. The entire drum'skinetic energy will be absorbed by the wheel and tyre assembly. The dynamometer test facility is completely instrumented to measure the drum speed, wheel static load on the drum, brake torque, brake pressures and disc temperatures. The brakedynamometer facility with the test specimen is indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"10. Dynamometer Trial with BCF","content":"\u003cp\u003eThe test specimen is prepared by integrating the BCF with Wheel and brake assembly of Tester 1 aircraft and the same has been tested in the brake dynamometer test facility to estimate the TRS time with forced cooling of brake discs. The dynamometer test parameters are indicated in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBrake dynamometer Test Parameter with Brake Cooling Fan\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSl. No.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eValues\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eUnits\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDrum diameter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003em\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInertia of dynamometer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3563\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eKg-m\u0026sup2;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLoad on the wheel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eKg\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDrum Speed\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e823\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRPM\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBrake Pressure\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ebar\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStop Time\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eseconds\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePeak torque\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e440\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eKgm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSimulated energy of the dynamometer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMJ\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDouble Stator temperature at which BCF switched ON\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e550\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCooling Time\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eminutes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eCooling time is the time required for the brake disc (double Stator) temperature to reduce to less than or equal to 100\u0026deg;C from a full stop of the dynamometer drum.\u003c/p\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e10.1 Procedure Adopted for Dynamometer Trial:\u003c/h2\u003e \u003cp\u003e \u003col style=\"list-style-type:lower-alpha;\"\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe brake dynamometer drum is gradually accelerated from static condition to slightly above the Brake Application Speed.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe loading arm together with the wheel \u0026amp; brake assembly is loaded over the drum to simulate the required static load.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eBrakes are applied once the drum speed reaches the required brake application speed and retained till the drum speed dropsdown to zero.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eBrake Disc internal and external temperatures are monitored continuously and BCF is switched ON when each of the brake disc internal temperature is dropped less than or equal to 550\u0026deg;C which is the limiting temperature to avoid oxidation of carbon disc [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eBCF is switched OFF when brake disc internal temperature reduces less than or equal to 100\u0026deg;C.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eThough the normal brake energy of tester 1 aircraft is 21MJ, dynamometer energy was simulated to 26 MJ to cater for energy loss through dynamotor bearings (\u0026lt;\u0026thinsp;1MJ), tyre slip(\u0026asymp;\u0026thinsp;3MJ) and cater for taxi back energy input(=\u0026thinsp;1MJ). Separate taxi braking runs were not carried out as the energy input is envisaged in the simulated energy of the dynamometer. Cooling curve for the dynamometer run is indicated in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e10.2 Observation \u0026amp; Inference:\u003c/h2\u003e \u003cp\u003e \u003col style=\"list-style-type:lower-alpha;\"\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eFrom Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, it is observed that after full stop of the dynamometer drum, peak temperatures are observed in Double Stator 1 \u0026amp; Double Stator 2(DS1 \u0026amp; DS2). However, at the end of the cooling period, the Thrust Stator (TS) temperature is higherthan the other temperatures. This is because the cooling air pulled by the BCF initially passes over the Pressure Stator (PS), Double Stator 1(DS1), Double Stator 2(DS2), wheel assembly and finally reachesthe Thrust Stator (TS).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eTherefore, the cooling air temperature moving over the TS will be higher resulting in a lower thermal gradient and this makes its cooling curve shallower. This also resultsin both internal and external temperaturesof TS to read almost equal. Hence, the cooling time is estimated from the full stop of the dynamometer drum to till the thrust stator internal temperature reaches less than or equal to 100\u0026deg;C.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eNine dynamometer runs were conducted, and the corresponding brake disc peak temperature and cooling time to reach 100\u0026deg;C are depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e and \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, respectively.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"11. Results and Discussions","content":"\u003cp\u003eBased on the flight trials carried out on Tester 1 it is observed that the TRS time with natural cooling is of the order of 64 to 69 minutes. However, based on the dynamometer trials carried out on Tester 1 aircraft\u0026rsquo;s wheel \u0026amp; brake assembly with BCF, it has been identified that TRS time is improved to the order of less than 30 minutes.\u003c/p\u003e \u003cp\u003eThis indicate that, with incorporation of BCF in brake system, TRS time of 30 minutes can be achieved for Tester 1 aircraft.\u003c/p\u003e \u003cp\u003eFollowing proposals are to be exploredin future work to reduce the brake cooling time (TRS) less than or equal to 30 minutes without using a BCF.\u003c/p\u003e \u003cp\u003e \u003col style=\"list-style-type:lower-roman;\"\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eImproving the natural convective heat transfer by increasing the size of ventilation hole in the wheel assembly.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eIncreasing the brake disc\u0026rsquo;s external clearance temperature for next sortie from 100\u0026deg;C to 150\u0026deg;C and validating the RTO brake energy dynamometer trials with initial brake external temperature up to 150\u0026deg;C\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eBetter insulation of air gap between the stator outer surface diameter and wheel inner surface.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eWith cumulative improvements from above three proposals, possibility of reducing Brake Cooling Timeless than 30 minutes with natural cooling will be explored.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eACKNOWLEDGEMENTS\u003c/p\u003e\n\u003cp\u003eThe authors wish to extend their sincere gratitude to HAL \u0026ndash; ARDC for their support and encouragement, which enabled us to present this paper.\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eFunding \u0026ndash; No funding was received for conducting this study. However, testing was conducted in the facilities available in Aircraft Research and Design Centre- HAL-Bangalore.\u003c/li\u003e\n \u003cli\u003eEthics Declaration \u0026ndash; Not applicable\u003c/li\u003e\n \u003cli\u003eConsent to publish declaration \u0026ndash; Not applicable\u003c/li\u003e\n \u003cli\u003eConsent to participate declaration \u0026ndash; Not applicable \u0026nbsp;\u003c/li\u003e\n\u003c/ol\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003e1) Prem R, Prasobh J Mechery \u0026ndash; Both the authors were involved in activities like preparation of flight plan and co-ordination for flight testing \u0026amp; hangar activities, flight data analysis, preparation of TRS duty cycle, 3D modeling of brake cooling fan layout and finalisation of interface, Dynamo-meter trails set up and co-ordination for test runs and manuscript generation.2) Sudeep KB and Suresh MT \u0026ndash; Both played key role in decision making at every stage of flight/dynamometer testing. And they contributed for review and finalization of manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eNorman S. Curry, Aircraft Landing Gear Design: Principles and Practices, AIAA, Washington, 1988.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eH G Conway, Landing Gear Design,Chapman and Hall, 1958.\u003c/li\u003e\n \u003cli\u003eMilitary Specification, \u0026ldquo;Wheel and Brake Assemblies,\u0026rdquo; Aircraft General Specification for, MIL-W-5013L, October 1991.\u003c/li\u003e\n \u003cli\u003eAerospace Recommended Practice, \u0026ldquo;Wheel and Hydraulically Actuated Brake Design and Test Requirements for Military Aircraft,\u0026rdquo; ARP1493, Revision C, SAE International, November 2013.\u003c/li\u003e\n \u003cli\u003eUse of structural carbon heat sink brakes on aircraft, SAE AIR 1934 Rev A.\u003c/li\u003e\n \u003cli\u003eM.P.Dyko and K.Vafai, Fundamental issues and Recent Advancements in Analysis of Aircraft Brake Natural Convective Cooling, Journal of Heat Transfer, November 1998, Vol 120/840, Transactions of the ASME.\u003c/li\u003e\n \u003cli\u003eCedric MEUNIER, Jean-Gabriel BAUZIN, Najib LARAQI, Arnaud GAPIN, Jean-Frederic DIEBOLD, Thermal characterization of the braking and cooling stages of an aircraft brake using identification techniques and a life-size experiment test bench, by Elsevier 2022.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Brakes Systems, TRS, Fighter Aircraft, Heat Transfer and RTO","lastPublishedDoi":"10.21203/rs.3.rs-6186480/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6186480/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDuring the landing phase of a fighter aircraft, the brake system is responsible for absorbing almost 70\u0026ndash;80% of the aircraft's forward kinetic energy, especially in the absence of a brake parachute. The brake unit generates heat energy through frictional force between the brake discs, which then needs to be dissipated quickly to the brake system components and the surrounding environment. The heat energy from the brake discs is dissipated through various modes of heat transfer, including conduction, convection, and radiation. A faster heat dissipation rate to the environment helps to reduce the disc temperature, ensuring that the aircraft is available for the next activity. Multiple authors have conducted research to improve heat dissipation from aircraft brake units through various methodologies. This paper outlines an approach that has been explored to optimize the Turn Around Sortie (TRS) time of a typical fighter aircraft. The paper evaluates the pros and cons of all modes of heat transfer and provides details of the work carried out to improve heat dissipation through forced convection.\u003c/p\u003e","manuscriptTitle":"Optimization of Turn Around SortieTime of aTypical Fighter Aircraft by Enhancement of Brake System Heat Dissipation through Forced Convection","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-14 10:04:02","doi":"10.21203/rs.3.rs-6186480/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5f88a0c5-aa9a-4b8e-a46e-d6a794aaa875","owner":[],"postedDate":"April 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-06-25T12:23:30+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-14 10:04:02","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6186480","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6186480","identity":"rs-6186480","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}