Landing Gear Layout Design For Unmanned Aerial Vehicle
14th National Conference on Machines and Mechanisms (NaCoMM09),NIT, Durgapur, India, December 17-18, 2009NaCoMM-2009-TKAj2Landing Gear Layout Design for Unmanned Aerial VehicleAkhilesh JhaSDET Division, ADE/DRDO, Bangalore, IndiaCorresponding author (email: akhilsdet@yahoo.com)landing gear system required for those UAVs, which hasconventional take-off and landing.Abstract1.2 Landing GearAircraft landing gear mechanism serves several designpurpose such as supporting the weight of aircraft, providing rolling chassis/taxiing and shock absorption function especially during takeoff and landing etc. The present study carried out to layout design of landing gearsystem for unmanned aerial vehicle (UAV) at conceptual design stage. The nose wheel tricycle landing gearhas been the preferred configuration for UAV. The mostattractive feature of this type of undercarriages is theimproved stability during braking and ground maneuvers. The results of present study indicated that landinggear stability could be improved by longer wheel axle,stiffer damping mechanism and smaller wheel mass andlower aircraft sinking velocity. The present approach hasbeen following the recommendations of the previousdesign of landing gear layout of other aircraft and international standard federal aviation regulations (FAR).More work to be done to prove the viability of this conceptual layout design. Detailed results needed furthersimulation study for validations.Landing gear system is a major component of everyaircraft. The landing gear serves a triple purpose in providing a stable support for aircraft at rest on the ground,forming a suitable shock-absorbing device and acting asa rolling chassis for taxiing during manhandling. It is themechanical system that absorbs landing and taxi loads aswell as transmits part of these loads to the airframe sothat a majority of impact energy is dissipated. The mainfunctions of the landing gear are as follows:1. Energy absorption 2. Braking 3. Taxi controlThe important types [1] of landing gear are as follows:1. Tri-cycle type (nose gear in fuselage andmain gear on wing)2. Bicycle type (with or without outriggers)3. Tail-gear typeIn above-mentioned types of landing gear arrangement,the tricycle type with nose gear in fuselage and maingear on wing also called nose wheel landing gear has aseries of unquestioned advantages over other layout oflanding gear. In a general sense, the analytical solutionof UAVs landing gear layout has received very littleattention. One reason for this neglect is that its verywider classification and applications. The traditionallanding gear design process for transport aircraft hasdescribed in textbooks “[1-4]”. Therefore, in this papernose wheel landing gear layout design for unmannedaerial vehicle has been described on basis of theoreticalkinematics and international standard FAR.Keywords: UAV, Landing gear stability, Shock absorber, Tip back angle, Landing gear load factor.1IntroductionThis section contains the basic definition, classificationand function of unmanned aerial vehicle and landinggear systems.1.1 Unmanned aerial vehicleAn unmanned aerial vehicle (UAV) commonly referredto is a remotely piloted aircraft. UAVs come in twoclass: some are controlled from a remote location andothers fly autonomously based on pre-programmedflight. There is a wide variety of UAV shapes, sizes,configurations, and characteristics.UAVs perform a wide variety of functions. Themajority of these functions are some form of remotesensing this is central to the reconnaissance role mostUAVs fulfill, others functions include transport, research and development, to search for and rescue peoplein perilous locations etc. Nishant, Predator and Globalhawk are importantly placed in the list of UAVs. The2 Landing Gear Layout Design ParametersThis section represents a typical step by step approachthat would be taken by the landing gear layout designerduring conceptual design phase.2.1 Main landing gear locationIn the landing gear layout, the aircraft centre of gravity(c.g) location is needed to position the main landing gearsuch that ground stability, maneuverability and clearance requirements are met. The aerial vehicle has two471
14th National Conference on Machines and Mechanisms (NaCoMM09),NIT, Durgapur, India, December 17-18, 2009c.g positions, forward c.g. corresponding to full fuelmass at the time of take-off and the aft c.g. when fuelhas been used or at the time of landing.NaCoMM-2009-TKAj2gear so that the appropriate level friction forces neededfor steering can be generated.Nose gear loads in the static condition generallyvary about 6-20%, but these should be considered asextremes. A preferable range would be 8% with the c.gaft, increasing to 15% with the c.g. forward has beenconsidering in present design calculations.Max static main gear load (per strut) F-M W (0.42-0.46)W 2F Max static nose gear loadFig. 1: Aerial vehicle with two c.g. positions. F-L W (0.08-0.15)W F The position of aircraft c.g. can be obtained by knowingthe component weight and their positions. Mean aerodynamic chord calculation (MAC) calculation based inFig. (2) and Eqs. (1-2).Fig. 2: Half 2-D plan view of UAV for calculation ofMAC.2MAC length (M) 3 CR CT CR CT C R CT (3)(4)Fig.3: Diagram for Nose landing gear load calculation.Min static nose gear load(1) F-N W (0.08)W F Max breaking nose gear loadS (CR - M)H (2)C R - CTThe following steps are needed to position the mainlanding gear.1a: Determination of mean aerodynamic chord of aircraft by using above Eqs. (1-2).1b: Locate the forward and aft c.g. limit on the meanaerodynamic chord .1c: Lines are drawn vertically from these forward andaft c.g. limits to locate the vertical position of the c.g.along these lines.1d: Involves a recheck of the ensuing location of themain landing gear. It should be between about 50-55%of the MAC “[2]”.(5) W Max static load 10J (6) 32.2F Where W is the Take-off weight of aerial vehicle andother quantities are defined in Fig. (3). The equation (6)determines nose gear dynamic load, this is important fortire selection of landing gear “[4]”.2.3 Shock absorber stroke length calculationThe landing gears in most unmanned aircraft today arethose making use of the solid steel spring or rubber andthose making use of a fluid acting as spring with gas oroil, commonly known as the oleo-pneumatic landinggears. This technical paper has focused for conceptuallayout design of oleo-pneumatic type shock absorberfor both the main landing gears and the nose landinggear. The oleo-pneumatic shock absorber has been selected because it has the highest energy-dissipating efficiency among the various types of shock absorbers currently in use in the UAVs industry. It has efficienciesranging as high as 0.7- 0.9.Based upon the required sink speeds and load factors,the vertical wheel travel must be determined. Normal2.2 Load calculation on nose wheel andmain wheelThe calculation of nose wheel and main wheel load arebased on the diagram shown in Fig.(3) and the following as given relations and their constraints in Eqs. (3-5).The nose gear should be placed as far forward as tominimize its load, maximize flotation and maximizestability. Conversely, to allow for adequate nose wheelsteering, a minimum normal force must act on the nose472
14th National Conference on Machines and Mechanisms (NaCoMM09),NIT, Durgapur, India, December 17-18, 2009design in which the wheel and strut travel the same distance.The first step is to determine the maximumloads accept able in the shock strut. This load comprisesthe static load plus the dynamic reaction load. When thatload divided by the static load, the reaction factor N obtained. This is some time called to landing gear loadfactor or merely landing load factor. Its valued rangesfrom 2.0–3.0 for small utility aircraft or UAVs. Its permissible magnitude is determined by the airframe toaccommodate those factors during landing impact.Initially, the aircraft is assumed a rigid bodywith no relative acceleration between the c.g. and gearattachment point. Thus, the load factor at the c.g. is thesame as the attachment. To understand fully the relationship between the load factor at the center of gravity Nc.gand the landing gear load factor N, consider a free bodybeing acted upon by shock strut forces and lift, asShown in Fig. (4), Where Fs is the shock strut force andL, the lift. ThusSum of all external forces Fs LNc.g (7)MassMNaCoMM-2009-TKAj2Thus, for a given aircraft load factor, N will be higherfor FAR Part23 aircraft than for FAR Part 25 aircraft.When the aircraft comes to rest on the ground, the lift iszero and the shock strut force is equal to the aircraftweight i.e. Fs W ThereforeNc.g 1 N for FAR part 23 AircraftThe shock absorbers and tire act together to deceleratethe UAVs from landing vertical velocity to zero verticalvelocity. Therefore shock absorber and tire must alsoabsorb the sum of the kinetic energy and potential energy of the aircraft; thus,TireStrutKinetic PotentialEnergyEnergyEnergyEnergySt n t N W St n s N W W V2 2g( W-L ) (S St )(9)Where St Tire deflection under N times static load, ftS Vertical wheel travel, ftnt Tire efficiencyns Shock strut efficiencyN ReactionW Aircraft weightL LiftV Sink speed2.4 Lateral location of main gearThe tread and wheel base should to be determined. Therelationship between the tread and wheel base is dictatedby the turnover angle, which is determined as follows(Ref.Fig.5 ).(1) Draw a top view showing the desired nose most forward C.G location(2) Draw a side view showing the landing gear withshock absorbers and tire statically deflected and the C.Gposition.Fig. 4 Shock strut dynamicsWhen lift weight W ( as specified in FAR part25 fortransport- type aircraft*) Fs LF s gWMMgIf, for convenience, the landing gear load factor N isdefined as being equal to Fs/Mass, the gear load factordetermine how much load ,the gear passes to the airframe, which affects the airframe structural weight aswell as strength.ThenNc.g 1 N for FAR part 25 AircraftOn utility and aerobatic aircraft, the rules of FAR part23* apply and lift 0.67w; i.e, W l/0.67, asF 0.67 g Nc.g s L (8) M L Fig. 5 Wheel track calculation based on turn over angle473
14th National Conference on Machines and Mechanisms (NaCoMM09),NIT, Durgapur, India, December 17-18, 2009(3) Establish line A-B Extend the line to a point “C”.(4)Through point, “C” draws a perpendicular to line A-B.(5) Through the c.g. (in the plane view draw a line parallel to A-B and obtain point “D”.(6)From point “D” measure height of the c.g. (H) obtained from the side view and obtain point “E”.Ψ 63deg for aircraft that are restricted to operate onsmooth, hard surfaced runways. This values is based ona side friction coefficient of µ 0.55 and the assumptionthat the aircraft will slide sideways instead of tippingover.NaCoMM-2009-TKAj21112MACFwd C.G position13Load factor0.74 m (7 cm max)4.90 m(Approx)from nose2.53.1 Load calculationNose gear loads calculation based on 8% with the c.g.aft, increasing to 15% with the c.g. forward.Max nose gear load 2000x15/100 300kgMin nose gear load 2000x8 /100 160 kg2.5 Tire selectionMain gear load (per strut) 850kg and 920 kgThe tires are sized to be carried out the weight of theaircraft .Typically the main tires are carry about 90% ofthe total weight of the aircraft weight .Nose tires carryonly about 10 % of the static load but experiencehigher dynamic loads during landing. In conceptualdesign stage we can find a tire size by using a statisticalapproach “[3]”. Given below equations developed fromdata for rapidly estimating main tire size (assuming thatmain tire carry about 90% of aircraft weight). Thesecalculated values for diameter and width should increaseabout 30% if the aircraft is to operate from rough unpaved runways. Nose tires can be assumed to be about60- 100% the size of main tire.Calculation of wheel diameter and width for mainwheel Main wheels diameter or width (inch) A WBWWW weight on wheel. For general aviation aircraft,A 1.51, B 0.349 for calculation of diameterA 0.715, B 0.312 for calculation of width3.2 Shock absorber stoke length calculationFor instance, let N 3, St 0.9 ft and V 15ft/s and assume 1 g wing lift such that L/W 1(at the time of landing ) Then stroke length calculation as given in eq.(9) 3(0.9 x 0.47 S x 0.8) 152 / 2 x 32.2 (1-1) Stroke (S) 11.10 inch(S 0.9)Table -2: Shock absorber stoke length1.2.3.3 Numerical Case StudySink velocity(ft/s)Load factor(g load)15121032.52.0Strokelength(Inch)11.1075.3For an initial layout, assume that a quarter to a third ofthe total stroke is used in moving from static to compressed thus for a 11.10inch stroke,3.7 inch is the distance from static to compressed and 7.4 inch that fromstatic to extended.In this section we will discuss a case study of landinggear layout for following given dimensionsTable -1: Landing gear layout case study parameters3.3 Nose landing gear position1Analysis ParametersAircraft Take offweightValue2000 kg2.Length of UAV10 m (approx)3.Wing location45678910The length of landing gear must be set so that the taildoes not hit the ground on landing. This is measuredfrom the wheel in the static position assuming an aircraft angle of attack (α0 0.9) for landing which gives 90%of the maximum lift this range from about 3-8 deg formost types of aircraft.3.5 m (L.E) fromnose of UAVWing span21 mRoot chord0.975mCalculated DataMAC position4.34 mC.G (vertical)1.5m ( From ground)C.G shift0. 10 times of MAClengthTip chord0.5 mAft C.G location5.0 m from noseAnother hand the “tip back” angle is the maximum aircraft nose up attitude with the tail touching theground and strut fully extended. To prevent the aircraftfrom tipping on its tail, the angle off (θ) the verticalfrom the main wheel position to the c.g. should begreater than the tip back angle or 15 deg whichever islarger. There is a rule-of–thumb which are correlate between alpha (α0 0.9) and theta (θ) as That isθ0 α0 0.9 30474
14th National Conference on Machines and Mechanisms (NaCoMM09),NIT, Durgapur, India, December 17-18, 2009NaCoMM-2009-TKAj2For a given parameters C.G height H 1.5 approx andvalue of D 2.7 m and wheel base 3 mAt conceptual design stage we have taken arange ( 30-80 ) of value alpha (α0 0.9 )which are feasiblefor this solution than corresponding value of thita ( θ)in that range is (60 –110) With known value of verticalc.g. height (H) from the level ground so corresponding(M) distance between Aft c.g. to main wheel positionhorizontallyasshownpreviousFig.6.From given geometry in Fig. 5, we can calculate wheeltrack as givenTan Ψ H / K,Where CD K ,ThenTan50 1.5/K K 1.3There fore sin Φ K / D Φ 28 deg( where D 2.7 m)Now TanΦ Z / F Z tan 28 X F Z 0.53 x3 Z 1.53 m(F 4.115 m)wheel track 2 Z 2x1.53 3.2mFor a given wheel base F 3m, M 2.37m, for differentturnover angle wheel track as belowFig. 6 Tricycle landing gear geometrySuppose as ideal value α0 0.9 is 6 deg than corresponding value of θ is 9 deg an nose wheel carry 10% ofMTOW than wheelbase can be calculated asTable- 3: Wheel track corresponding given wheelbaseSo value of M H tan (θ) 1.5 tan 90 0.237 m(where value of H 1.5m approx) Load on nose wheelis 200 and corresponding load main wheel 900kgTake moment about nose wheelWe have calculated the wheel track for the turnover angle range from 45 deg to 55 degMax static main gear load (per strut) W (F-M)/2F,where F is wheel base in meter3.5 Tire sizing 900 2000 (F-M) /2FCalculation of wheel diameter and width for main wheel.For general aviation aircraft and UAVs, F 10X.0.237 2.4mA 1.51, B 0.349 for calculation of diameter “[4]”.D AWBw for diameter calculation,wheel of main landing gear 1000 kgTable- 2: Wheelbase corresponding given turnoverAnglemax load perUse log both sides logD log A B log WwÖ logD log1.51 0.349 log 920 D 16.40 inTire dia range from (14-16.40 in )Similar way for width (T) calculation of main wheelT AWBw, By using log both sides, log T log A Blog WwLog T log0.7150 0.312 log 1000 kg Tire width (5.0-6.1in)3.4 Lateral location of main landing gearCalculation of tire diameter for nose wheel where nosewheel total (static dynamic) Max load 650 kg (including 7% margin of safety) Nose wheel tire can be assumed to be about 60- 100% the size of the main wheeltires. Nose wheel tire detail tire size 13-16 in and tirewidth is around 4-6 in.Calculation of lateral location of main landing gear,which is, depends upon turnover angle and C.G height.For a given C.G height, we can calculate the lateral location of main landing gear in a given feasible range ofturnover angle. The turn over angle θ must not be more63 deg for typical UAV to operate on smooth, hard surfaced runways. We can calculate the lateral separationof landing gear475
14th National Conference on Machines and Mechanisms (NaCoMM09),NIT, Durgapur, India, December 17-18, 2009quirement. While the shock absorber stroke is not afunction of the aircraft weight, nevertheless it is vital toincrease the size of the stroke to lower the landing loadfactors and thereby minimizing the structure weight dueto landing loads. To accommodate this requirement,larger-section tires can be utilized. However, the penaltyfor this solution is the increase in aircraft weight andtherefore reduced payload that would be too costly forUAVs.4.0 Results and DiscussionThe results of the study also indicated that landing gearstability could be improved by longer wheel axle,smaller wheel mass and lower aircraft velocity. The nosewheel tricycle gear has been the preferred configurationfor UAV. It leads to a nearly level fuselage when theaircraft is on the ground, important for payload safety.The most attractive feature of this type of undercarriagesis the improved stability during braking and ground maneuvers. Under normal landing attitude, the relative location of the main assembly to the aircraft cg produces anose-down pitching moment upon touchdown. Thismoment helps to reduce the angle of attack of the aircraft and thus the lift generated by the wing.4.5Wheel Base5 Concluding RemarkBased on present study of landing gear layout design ofUAVs the following concluding remark are drawn. Nose gear loads in the static position preferable oroptimum range would be 8-12%. The wheel track of landing gear is approximately25-30 % of wing span in UAVs cases. The stroke length of oleo –pneumatic shock absorber is approximately equal to touchdown sink speed. The strut length is about 2.5 to 3.0 times thestroke length. Nose wheel diameter is 60-100 % of main wheeldim in nose wheel landing gear.Many more options could be decided to functionallyand operationally improve the present conceptual design by using various computer simulation programs.These results needed experimental data to validate it.8% MT Ow on Nose wheel9% MT OW on Nose wheel10% MT OW on Nose Wheel11% MT OW on Nose wheel12% MT OW on Nose wheel543.532.521.512.53.54.55.56.57.5CL Max Angle8.5Fig. 7: Nose wheel Vs wheel base at constant angleReferences30L.G.F 2.5gL.G.F 3g[1] Roskam(1986), Airplane design part IV: Layoutdesign of landing gear systems, Roskam aviation andengineering corporationsL.G.F 2g25Stroke LengthNaCoMM-2009-TKAj22015[2]Currey (1988). Aircraft Landing Gear Design: Principles and Practices 1st Edition, American Institute ofAeronautics and Astronautics.10507.51012.5Sinking Velocity15[3]H.G Conway, “Landing gear design,” The RoyalAeronautical Society Chapman and Hall Ltd, 1958.17.5Fig. 8: Sink speed Vs vertical wheel travel[4]Daniel P. Raymer (1992). Aircraft Design: A Conceptual Approach 1st Edition, American Institute ofAeronautics and Astronautics, Inc, p229-256.Sinking velocity 10fps19171513119753Stroke LengthSinking Velocity 11 fps[5] Joseph E. Shigley (1977). Mechanical EngineeringDesign 3rd Edition, McGraw Hill, Inc., p26, 34, 37-40,43-45, 60, 94-120, 295-313.Sinking velocity 9fps11.522.5Landing Gear Load Factor3[6]Department of Transportation, Federal AviationAdministration (1976). Airframe and Power plant Mechanics Airframe Handbook Revised 1st Edition, Aviation Maintenance Publishers, Inc., p341-405.3.5Fig. 9: Vertical wheel travel Vs load factor[7].Young ,D,E., “Aircraft landing gears-The past, present and future,” proceedings of the institute of mechanical engineers,vol 200,noD2,1986,pp. 75-92.In addition, the braking forces, which act behind theaircraft c,g., have a stabilizing effect and thus enable theexternal pilot to make full use of the brakes. These factors all contribute to a shorter landing field length re-[8]S.F.N Jenkins, Landing Gear Design and Development, Proc. Instn. Mech. Engrs. Vol. 203, pp. 67-73.476
search and development, to search for and rescue people in perilous locations etc. Nishant, Predator and Global hawk are importantly placed in the list of UAVs. The landing gear system required for those UAVs, which has . Max static main gear load(per strut) F-M W(0.42-0.46)W (3) 2F .
5.4. Landing gear (Undercarriage): The landing gear is an assembly that supports the aircraft during landing, or whiles it is resting or moving about on the ground. The landing gear has shock struts to absorb the shock of landing and taxiing. By means of a gear-retraction mechanism, the landing gear at
BODY HARDWARE LANDING GEAR Part No. Component Landing Gear 23002220 Landing Gear - Mark V 2SPD "Dumps" LGS-5D-105 23002230 Landing Gear - Mark V MF "LG Handle Leg" LGS-3D-113 23002224 Landing Gear - HD Mark V Reverse LGS-3B-001 - 16.5-in. Travel 23002223 Landing Gear - JOST A401T3-17 Low Profile - Reverse Mount 23002225 Landing Gear - JOST A400T2-19 Dump With Crank Holder
dash8 - q400 - landing gear page 9. figure 12.13-5 landing gear alternate extension door landing gear alternate extension open overhead door first pull ring to open panel to extend and lock main landing gear, operate hand pump until handle is stiff. nose l/g release pull fully up visual check for gear down & locked
landing gear as seen on most commercial aircraft, actively controlled landing gear, and passively controlled landing gear. This paper will focus on the third approach. Examples of existing research within this field include the avian-inspired perching landing gear by Doyle et al. [2013] which through clever mechanical design uses
Abstract: Landing gear strut is a dynamic structural unit element of an aircraft which allow to launch and land safely on the ground. A diversity of landing gear strut design are used depending on the compartment and size of an aircraft. The most frequent type is the oleo strut plan with one nose landing gear unit and two main landing gear units.
Also, nose landing gear carry nearly 12% of aircraft overall weight. So, the load acting on the nose landing gear (113761.2) *(12/100) 13651.344 N Thus, static analysis of the aircraft landing gear can be done by loading the landing gear at the top and as well as at the bottom. If the loading is at top, which
There are many examples of aircraft with tricycle landing gear, including the F-16 and Cessna 172. Bicycle Gear A relatively uncommon landing gear option is the bicycle undercarriage. Bicycle gear . Single main landing gear This design is particularly simple, lightweight, and low drag and may even include skids
Work out the gear ratios of these gears: (numbers inside the circles are the numbers of teeth on each gear) Blue drive gear, green driven gear, pink idler gear, yellow compound gear 1: Simple meshed gear 2: Simple gear train with idler gear 15 3: Compound gear train 4: Choose the correct words to make these statements true for these gear trains.
