AN ELECTROMAGNETIC LAUNCH SYSTEM FOR UAVs

Transcription

1 Tehnial Sienes and Applied athematis AN ELECTROAGNETIC LAUNCH SYSTE FOR UAVs Lauian GHERAN Depatment of Eletonis and Infomatis, Faulty of Aeonautial anagement, Heni Coandă Ai Foe Aademy, Basov, Romania Abstat: This pape pesents a new design of a launh atapult based on eletomagneti enegy fo tatial UAVs. This tehnology is unde development to launh pojetiles with high veloity but it has theoetially poved the possibility to launh also UAVs. The seond pat pesents a theoetial appoah neessay to find the expession of foe unde etain appoximation fo E-shaped eletomagneti launh system design. Based on the theoetial esults, I have built a physial model in ode to examine the behavio of this design unde laboatoy onditions. Afte that, I have eated a ompute model alibated to epodue the behavio of the physial model with eos below 1%. I have used an inteative softwae pakage based on the finite element method (FE) to analyze, solve theedimensional eletomagneti field poblems and simulate the E-shaped design s behavios. The last pat of the pape pesent the esults of simulation whih pove the possibility of using the E-shape design to launh diffeent masses with a desied speed. Keywods: UAV, oilgun, indution, Loentz foe, eletomagneti launh system). 1. INTRODUCTION Nowadays UAVs have eoded an ineased ate of development and so they an now its ove a lage spetum of missions. If we ompae UAVs based on dimensions we an see that thee ae big UAVs used to opeate at global level though mini UAVs used inside buildings. The big UAVs ae opeated almost like a manned aiaft, fat whih implies the existene of an aipot infastutue and a unway fo take-off and landing. The mini UAVs an be launhed by hand. Between these two extemes, thee is a ategoy of UAVs used at tatial level whih annot be launhed by hand and the ost to build a unway is vey high. These UAVs ae launhed using RATO (oket assisted takeoff) o atapults. These installations ae a good solution beause: - the UAVs an be launhed without any infastutue; - beause the fuel is not used fo launhing the payload weight o the mission time an be ineased; - this appoah is envionmentally fiendly. The atapult installations use diffeent kinds of enegy to aeleate the UAVs like: - mehanial enegy stoed in spings o ubbe bungee; - pneumati/hydauli enegy podued by ylindes and pistons; - eletomehanial enegy podued by eletial motos. All these installations ae made by using many pats whih inease the omplexity and equie a lot of maintenane in ode to be funtional. Also these installations ae not pat of the automati loop used to ontol the UAVs. In ode to impove the launh system this should have few moving pats to edue maintenane osts and should be poweed by eleti enegy in ode to be easily integated into the automati ontol loop. A possible solution an be an eletomagneti launh system like, the ailgun o oilgun. These systems wee initially developed to aeleate pojetiles at vey high speeds. Beause the guns based on hemial 5

2 An eletomagneti launh system fo UAVs enegy ahieved thei maximum possibilities the eseahes found a new way to inease the pojetile speed fom 1.5 km/s to 8 km/s. The fist dietion of eseah and the most developed is the ailgun design. This design onsists of two paallel DC poweed ails, and a sliding amatue between them. This amatue is igidly oupled with the pojetile. The Loentz foe is used to launh pojetiles. A good appoximation of the foe podued by this design is given by the expession (Railgun, 11): (1) whee: - magneti onstant ; I - the uent though system (A); d - the distane between ails; - the adius of the ails. to launh UAVs but it an do it. So in ode to use an eletomagneti launh system to launh UAVs anothe appoah should be taken into onsideation. This new appoah should eliminate the sliding ontats and use less enegy. To do this, suh a system should be based on indution and magneti flux density B should be eated by a oil. Based on this obsevation I have developed a new oilgun. This design is an impovement of an olde, well known design like Thomson Jumping Ring adapted to launh pojetiles. This appoah solves most of issues elated with the ailgun system pesented above: 1) The magneti flux densities B is eated by a oil and a magneti iuit made by soft magneti mateials; ) The uent neessay to podue desiable magneti flux densities B is less than in the ase of the ailgun design; 3) The amatue is a ing made of aluminum and the UAVs an be attahed by ing. 4) The uent is indued into the ing so thee ae not ontats between the amatue and oil o magneti iuits; 5) The Loentz foe podued is only in axial dietion and it is possible to use all the available enegy to aeleate the ing. Fig.1 Rail gun design (Railgun, 11) Beause this system is in an advaned stage of development and the esults obtained ae good, it was used like a possible solution to eplae the steam atapults on US aies. This tehnology poved that it is apable to aeleate an F18 aiplane to the takeoff speed on the same length like the steam atapult. Despite these ahievements the ailgun tehnology has a few dawbaks. The main dawbak is the sliding ontat between amatue and ails. Beause of this the ails must be eplaed afte a etain numbe of launhes. Also beause the ail is like a staight onduto a vey high uent is neessay to podue the desiable magneti flux density B. As a esult the powe soue should be able to povide a lage amount of enegy. Taking into onsideation these dawbaks this tehnology is not suitable yet 6 Fig. E-shaped oilgun design In Gheman et al. (11:75-79) I have demonstated the supeioity of E-shaped design ompaed with Thomson Jumping

3 Tehnial Sienes and Applied athematis Ring design. Despite the fat that this design is still unde development, it has demonstated the possibility to podue enough foe to launh an UAV. This pape pesents this design and the esults obtained unde laboatoy onditions.. THE E-SHAPED DESIGN THEORY This devie is based on two fundamental laws: the Faaday law (indution) and Loentz law (foe). ε = () If thee is N numbe of tuns in the oil with the same amount of flux flowing though it, hene: d ε = N ϕ (3) whee: N numbe of tuns of wie in oil. Loentz s foe is podued by a uent aying onduto (in this ase the ing) pesent in a unifom magneti field of flux density B (in this ase into the aigap between olumns). Dependent upon the dietion of the suounding magneti field, the foe indued is given by (in this ase in axial dietion epulsive sense): F = i( lx B) (4) whee: i epesents the uent flow in the onduto; l length of wie, with dietion of l defined to be in the dietion of uent flow; B magneti field density The goal is to eate an eletomagneti launh system based on the E-shaped design whih podues a Loentz foe at a maximum possible value unde etain ondition in ode to ahieve a speifi muzzle veloity neessay to launh diffeent UAVs with diffeent masses. Fist, I hose the shape of amatue iula beause l is maximum in the ase of a iumsibed ile of a squae. Compaed with a squae it an be witten: π > (5) whee: - the adius of the ile. I alulated the dimensions of the magneti iuits in ode to allow the satuation only inside the oil (the satuation annot be avoided). I alulated the ai gap at a minimum possible to allow the movement of the ing without any fition. The dimensions of the E-shaped launhe ae: 1) oil height H =58 mm; inne diamete d =4 mm; oute diamete D =6 mm; numbe of tuns N=3; winding made of oope wie. ) ing height H =5 mm; inne diamete d =4 mm; oute diamete D =5 mm; made 3 of aluminum; mass m = 1 1 kg. 3) the oil is poweed by a voltage soue of 4 V/ 5 Hz. Beause magneti flux density B is a funtion of linkage flux Φ l and the indued uent inside the ing is a funtion of speed vaiation of a fation of linkage flux, mutual dφ oupled flux, Φ a maximum linkage flux must be eated in ode to ahieve a maximum foe. Fist, let us onside the devie without the ing. The oil is poweed by a sinusoidal voltage. U sin( t ) R i N ω + α = + (6) Whee: U maximum value of soue voltage; α phase angle; R eletial esistane of oil wie; i intensity of uent in oil wie; N numbe of tuns in oil; ϕ magneti flux eated by oil. Fo the limit ase when R = it an be witten: U sin( t ) N ω + α = (7) The solution of (7) is: U ϕ = os( ωt + α ) + C (8) Nω If onsideed at t= ϕ = then: C = Φm osα (9) So, the expession of magneti flux an be witten: ϕ = Φ os( ωt + α ) + Φ osα (1) m Whee the fist tem fom the ight side is the a omponent and the seond tem is the d omponent. Fo us the most favoable m 7

4 An eletomagneti launh system fo UAVs situation is at α = o α = 18 degees when: Φ = Φ m (11) Fo a given voltage, the maximum magneti flux is eated in tansient egime if the eletial esistane of the oil is zeo and the oil is fied at o 18 degees. Unde these onditions, the tansient egime beomes steady state. Now let us onside the devie with the ing in a stati position. The oil is poweed by the same sinusoidal voltage at degee phase. The following system of equation an be witten: R i u L 1 = + (1) R i L + = + (13) whee: L oil indutane; L ing indutane; mutual indutane. In ode to find out the expession of ing uent, let us assume R = and R =. The system of equation beomes: u L 1 = (14) L = (15) and di = u 1 LL (16) The indued uent in the ing is: i = di = U sin ωt (17) LL U π i = sin ωt LL ω (18) U i = os ωt L L ω (19) The indutane of the oil ( L ) and the indutane of the ing ( L ) wee assumed as onstant. In fat, afte the oil is fied, the oe inside the oil is satuated and both indutanes dop apidly to a onstant value. In ode to find out the magneti flux density inside the ai gap ( B g ), the following assumption should be made: 8 1) The magneti flux density inside the ai gap is unifomly distibuted; ) No finge flux at the end of the ai gap. R i u L 1 = + () Beause the assumption it is still valid: d u N ϕ N 1 = (1) d ϕ d ϕ u = N 1 () = l (3) d ϕ u 1 = N l (4) U ϕ = = l l sin ωt N (5) U π ϕ = l sin ωt Nω (6) U ϕ l = osωt (7) Nω All the magneti flux lines ae split into two by the olumns, and the magneti flux density inside one ai gap beomes: ϕl gag = B (8) ϕl ϕl Bg = = (9) A π g he U Bg = osωt (3) Nωπ he Fom equations 4, 19, 3 and beause the ing has two pats inside ai gaps, the total Loentz foe ating on ing is: F = F g (31) π F = LL U os ωt N ωπ he U ω os ωt (3) U F = os ωt LL N he ω (33) N F = Φ os ωt L L h (34) E

5 Tehnial Sienes and Applied athematis But the mutual indutane depends on the distane between the oil and the ing, and the dimensions of the oil and ing. By hanging these dimensions, the mutual indutane will hange. As a esult, mutual indutane an be expessed as a funtion of oupling oeffiient k whee k < 1. = k L L (35) The equation of Loentz foe ating on ing beomes: k LL N F = Φ os ωt (36) LL k LL he k N F = Φ os ωt (37) 1 k 1 he LL This expession of foe is a good appoximation when based on assumptions made. 3. SIULATION In ode to test the theoetial esults, I have used an inteative softwae pakage based on the finite element method (FE) to analyze, solve thee-dimensional eletomagneti field poblems and simulate E- shaped design s behavios. Fist, I built a physial model with the same dimensions aleady pesented. I onduted a lot of expeiments in ode to detemine the behavio of this devie. Afte that, I eated a ompute model alibated to epodue the behavio of the physial model with eos below 1%. In this setion only the esults of the simulation will be pesented. The main objetive of all simulation was to establish how the maximum speed of ing vaies based on the ing s mass and the soue voltage. The mass of the ing was onsideed the mass of the entie ensemble of ing-uav and the dag foes aused by ai fition wee not taken into onsideation. In ode to obtain the maximum foe, the oil is fied in all the simulations at 18 degees. The esults of these simulations ae pesented in the following gaphs. Fist the behavio of the Eshaped devie was simulated unde laboatoy onditions like the physial model. 1) The flux linkage and foe ae simulated unde the same onditions like the physial model in laboatoy. Fig.3 Foe and flux linkage unde laboatoy onditions The foe ahieves the maximum value F=1.86 N at 3.8 ms beause the ing stats to move and, as a esult, the oupling oeffiient is deeases in value. Linkage flux lags behind the voltage with 8.8 degees. The minimum value of the flux is Φl =.766 Wb but the foe ahieves its maximum at Φl =.59 Wb. Not all the enegy is used to eate foe. If the ing is kept in plae fo.8 moe ms, the entie available enegy will be used. These data will be used fo ompaison puposes with futhe simulation data. By ineasing the mass of the ing the foe ating on the ing will inease but the speed of ing will deease. ) The vaiation of the Loentz foe when the mass of the ing vaies with values fom 5 to 1 with step 5 gams and fom 1 to 4 with step 1 gams. Fig.4 The vaiation of the maximum value of the Loentz foe [N] fo diffeent values of the ing mass 9

6 An eletomagneti launh system fo UAVs Beause the mass of the ing is ineased the time when the ing emains into the most favoable position (lose to oil) is also ineased and as a esult the foe is ineased up to the point whee the flux linkage ahieves its minimum in ou ase. The vaiation of the ing speed when the mass of the ing vaies with values fom 5 to 1 with step 5 gams and fom 1to 4 with step 1 gams. Aoding to Fig. 5 gaph, even if the foe is ineased, the muzzle speed of the ing deeases. In ode to inease the speed of ing, the mass of the ing is kept onstant (1 gams) and the RS value of soue voltage is ineased with values fom 1 to 1 V with step 1 V. Fig.5 The vaiation of the maximum value of ing speed [m/s] fo diffeent values of ing mass 3) The vaiation of the ing speed fo a vaiation of soue voltage. 4) The time vaiation of foe fo diffeent RS values of voltage. Fig.7 Foe ating on the ing funtion of time When the voltage value is ineased 1 times, the foe value is ineased 7.63 times. The moment of time when the foe ahieves its maximum deease, fom 5 ms to ms, and this means that not all the available enegy is used. If the powe voltage ineases moe and moe, the devie will be less effiient despite the fat that the foe will inease. In ode to find out the maximum value of the foe fo a etain available enegy, we should keep the ing stati. 5) The foe vaiation fo diffeent RS values of voltage when the ing is kept stati. Fig.8 The maximum foe ating on the ing Fig.6 Ring speed vaiation [m/s] fo diffeent RS values voltage [V] When the voltage is ineased 1 times the speed of the ing is ineased only 3.66 times. The eason fo this behavio will be lea if we study the vaiation in time of foe with powe voltage. The next gaph displays this vaiation. If we manage to keep the ing in initial position until the linkage flux ahieves its minimum, then the foe ating on the ing will be a maximum value and, as a esult, the speed will be at maximum value. Fig. 8 displays a ompaison between the maximum foe ating on the ing when the ing an move feely (gay hat) and the maximum 1

7 Tehnial Sienes and Applied athematis foe ating on the ing, when the ing is stati (blak hat). The vetial axis is logaithmi base 1. But maybe even unde these onditions the foe is not stong enough to launh an UAV. The foe value an be ineased by eduing the eletial esistane of the oil and ing. In the theoy setion of this pape the equation of foe was alulated when R = and R =. The next gaph displays the esults of a simulation with R = and R = when the ing is kept stati in ode to find the maximum value of foe fo a etain value of powe voltage (in this ase RS 4V). The vaiation of foe with R and R = fo U 1 =4V. = Fig.9 Foe and flux linkage when R = R = and A temendous inease in the foe value is obtained unde these onditions. Also, the flux lags behind the voltage with appoximately adians aoding to theoy. If the eletial esistane of the oil and ing is edued to zeo, whih is tehnially possible, the maximum foe geneated an be F= kn. So, instead of ineasing the voltage, a moe effiient way is to edue the eletial esistane of the oil and ing. 3. CONCLUSIONS The E-shaped design is apable to geneate a foe stong enough to launh a UAV. Also, the foe an be adapted based on the UAV mass and launh speed, and as a esult one atapult an be used fo diffeent UAVs. An eletial soue of powe is aleady available to powe othe equipment fo ommuniation and ontol link and an be used to powe this atapult. This kind of atapult an be integated into automati ontol loop. The dimensions of this atapult ae less than those of the atapult uently used. Futhe eseah should be made although the eletomagneti launh systems have poved thei apability to aeleate pojetiles at high speeds. BIBLIOGRAPHY 1. Baliki, A., Zaba, Z., Bienbaum, L & Czakowski, D. (7). On the design of oilguns fo supe-veloity launhes. IEEE Tans. on agnetis, vol. 43, no Fai, H.D. (7). Pogess in eletomagneti launh siene and tehnology. IEEE Tans. on agnetis, vol. 43, no Ghassemi,., olayi Basi, Y., Hamedi,.H. (7). Analysis of foe distibution ating upon the ails and the amatue and pedition of veloity with time in an eletomagneti launhe with new method. IEEE Tans. on agnetis, vol. 43, no Gheman, L., Peasiă,., Stîmbu, C. & Constantinesu, C.-G. (11). Indution oilgun based on E-shaped design. IEEE Tans. on Plasma Siene, vol.39, no Nab, I.R. & Beah, F.C. (7). Naval ailguns. IEEE Tans. on agnetis, vol. 43, no ***. (11). Railgun [online]. Wikipedia. URL: [onsulted on Septembe, 11). 11